Transmissions, Rear ends, Gears, Oh My!

[MrGoodwrench]

Ok, first let me give you my truck specs. Its a 1981, 2WD GMC Serria. C10 I believe. My VIN is 16TCCI4H6BF7II468, if that helps any. Anyway, It has a '76 2 bolt main 350 out of a Caprice. The Tranny is a sm478 4 speed. The rear end is, I think, I think, a 2:56 differential, based on what the Chev delearship told me.

Now, what I want is more highway gear. It's not that bad in 4th @ about 60 or 65, I turn about 2000 - 2200 RPM, but I would like to see that at about 1500 - 1700, or less if I can. Now, everyone I have talked to says 'dont change the transmission, change the rear end', thing is I think I have the highest (lowest, whatever) highyway gear I can in the rear end. Next I'll say I dont need that granny gear, I dont haul, pull, push, or otherwish tax the suspension. I simply drive. It is just a passenger truck. I know the transmission is 'heavy duty' but I dont need that. What I want is better that 8 mi to the gallon. like I said I dont really know what the gear ratio in the rear end is, but i would like a posi-traction. Recently someone told me that a posi-traction wasnt availible in a 81 GMC, but what about 4WD???? I know for a fact that they offered a limited slip (dealership told me).

What I want to know is, what is a good posi-traction, or limited slip rear end that has a good highway gear. And do you think I might just solve this problem, by installing a saginaw transmission? Cause I'm not attached to that sm478, and I have had an offer to swap my trans, for a new (rebuilt) saginaw, plus $200. BTW I have a two piece driveshaft. I know there might be length differences, but the two piece might compensate for it.

Info, suggestions, corrections, please!

[Big Nate's Plowing]

well assuming you have 235/75-15 on your truck with a 1:1 trans, 65 mph would make for 1846 rpm from the sounds of it you have 3.00:1 r/p gears

anything below 1800 on the freeway with a smallblock is lugging it most smallblocks like 2400-2600 for freeway

[MrGoodwrench]

Yeah, I should have posted my tire size. I use 275/60R 15. I know eventually I am going to have to crack the rear end case, and count teeth. No big deal, but what is a good posi-traction, or limited slip with a highway gear? 4:1? I dont even know what was offered in 81.

I found this place through Chucks chevy truck pages, he says he has the most comprehensive page on package options on the web; however he listed NO rear ends for 'C' series trucks. Thanks for the reply!

[ratlover]

There gets a point were droping gear ratio will actually hurt your milage, especially in town and with a lrge heavy unaerodynamic vehicle. Easy way to figure out your rear ratio and play with them is to go to richmond gears website. You might actually pick up milage by going to a lower(higher numericly) gear ratio.

You can drop your effective ratio a bit with bigger tires but going to a non stock ratio will be expensive. Or you could lower it by going with smaller tires. This way you can play with things a bit.

How is it for a general tune up? And the rest of the truck like tire pressures and such.

Unless you get an overdrive transmission it will still be 1.1 final drive. Although having more gears might help in town milage a bit.

What are the rest of the specs on the motor? or is it just a stocker outa a caprice?

[MrGoodwrench]

It might could stand for some plugs and wires, but filters and fluids are ok. I check tire pressure about once a week.

The truck is in really great shape. I dropped about 3k into it about 2 years ago. And no its not shiney, and chrome, my truck is flat olive drab (Camo).

I bought the 350 from a guy who told me the guy he bought it from got it out of a '76 caprice. Reading full (stock) compression, I decided to leave the heads and rings alone. I dropped in a low milage comp cam, honestly I dont know what the specs on it are, I didnt even mic it, but I think its on the order of a 1/4 race, just a small preformance cam. Anyway, the rest of the rotating assembly is stock. I do use cheap 4-1 holly headers. A stock cast iron dual plane intake off a factory 305 H.O., and a holly 600 cfm, I think the model no. is 1850-5 or is that the part no.?. A few chrome dress-up parts (whoopdi-do). Flex fan, has power steering, power brakes. wheel hubs are stock, as are springs, brakes, and shocks. The trans, was changed by one owner to a sm478, I figure either the trans went bad, or it might have been lucky enough to have had a muncie in it that someone wanted. In any case the trans is like a freakin tank, I have R&R'd it 3 times by myself (no shop) thats a real fun job.

I have replaced the center bearing for the two piece driveshaft, u-jonts, wheel hubs all the way around, brakes all the way around, brake lines, fuel lines, e-cable, exaust (which are straight dual, no cats, w/cherry bombs mufflers), suspension bushings, radiator (3 core), master cylinder (brakes have been rebuilt from pedal to pad), bucket seats, carpet, all lenses, all body work done, and about a gazillion other small things I wont mention.

All and all I have probably spent 10 times what the truck will ever be worth, its just been my hobby for awhile. I plan on putting in a new steering coulmn, front grille, mabey a new trans (or rebuilt whatever), and or rear end, and rebuild the motor one more time (fully this time), and swap the block with a 4 bolt main. And I'll be done with it forever.

Lastly, let me tell you. I bought the truck for $5.00. The guy even went and got a new title cause he had lost his. Had a strong 305 H.O, which ran perfectly after I readjusted the distributer that had spun, and a brand new set of (4) Firestone Firehawk 275/R60 15's. I'd say I got a deal, considering the guy thought the motor was bad.

Anyway, enough rambling. thanks for listening, and thanks for the input. Any more suggestions would be great

[EZSnow]

Well, I'd start with looking at that flex fan. If you have it direct-driven, it's eating up a fair share of power (fuel) at highway speeds. If it's clutched, don't worry about it.

I'd have to say you have a pretty darn good setup for mileage as far as your drivetrain goes. If you really have a 2.56:1 gear... you NEED that granny low! (your clutch will thank you for it) As was said before, an overdrive would drop the rpms a little, but 2000rpm is about as low as you would probably prefer. Any lower and you'll find yourself wide-open or downshifting to climb hills on the highway- negating any difference the lower rpms made in the first place. I think you might see greater gains by looking to increase the efficiency of the engine itself. Get a good tune-up on it, and make sure the carb is jetted correctly for your engine. If you are running too rich, you are wasting fuel. Heck- with the amount of dough you could spend on a rear-gear and locker swap, you might be able to afford one of those new bolt-on EFI setups, and realize a greater benefit. You could also probably gain a couple MPG just by putting regular mufflers on... I don't know why, but every time I put pipes on something, the mileage goes in the tank...:burnout :D

As for a posi/limited-slip, they are more or less the same deal. If you want to stay on the cheap, you can get what some people call a "lunchbox locker" -it makes your open diff function as a limited-slip. BTW 4.1:1 is NOT a highway gear... it would cause you to turn very high rpms at similar speeds. And I'm just guessing that you cant go numerically lower that 2.56

Good Luck- EZ

[ratlover]

What is the idel speed and does it have any lope to the idel? If you have a cam that is designed to move the power band up in the rpm(and more than likely it will be designed for higher compression) your motor wont be very effiecent with its low compression and all in the lower rpm range. Depending on what you have a general tune up and maybe a cam swap would help and boost low end a bit. Your dynamic compression might be way low. Have you dont a test to see what your cranking compression is? It will tell you real quick if you have a cam that is a little on the large side. A cheaper way than swapping cams would be to get a bit of low end back with your cam would be to change the cam timing(not the dist) but to actually degreee the cam.

[John DiMartino]

I agree that you will not see enough MPG gains to offset the costs of the gear swap.Also carbs do not run very cleanly under load below 2000RPM,like EFI does.so to run the engine slow to pick up MPG you would need EFI to take full advantage of it.

[MrGoodwrench]

Well, I appreciate the input, but I really hate fuel injection. I wouldn't fuel inject any car. In fact i am known to revert a car to carb upon buying. I have done this to three camaro's, and a few others. I am very happy with carburation. Fuel injection is complicated, expensive, and unreliable. IMO. Furthermore, I use all mechanical features, no solenoid, or vacuum stuff. Yes it's primative, but when everything else is burning out mech is still working. It's just more reliable. IMO

As far as the cam goes. its not that big. it really is a small preformance cam, I have had much bigger in a 350. If I wanted I could measure the lift, and duration without pulling the cam. Anyway that doesnt matter because its not the significant source of my fuel cost.

The whole thing is just geared too high (low, whatever), I dont shift gears until about 4k < that is where my fuel is going, turning high rpm. In town I cruise in third (my primary drive gear) between 15-50MPH, and most of the time I'm above 3k=fuel. I know that a 350 with a 4 speed can do better than that. Hell, I guess I could just do a bunch of modding, and put in a late model 5 speed w/OD, but I'm not really looking forward to that. What will probably happen is a trans, and rear end change. I am sick of the granny gear, I know 4th will still be 1:1, but at least with a saginaw I will have normal gear ratios, not something designed for towing (which I never do). What is the point in having a heavy duty transmission in a truck thats only rated @ 1000lbs??? If I wanted to tow I would buy a 1 ton (or better) 4x4 with a big block.

Thanks for the help guys.

Does anyone know the gear ratios of a posi-traction, or limited slip, that will fit a 81 C10 (seirra). Hell, test your knowledge, list all that you know of I'll take my pick and find one. Thanks.

[ratlover]

Why are you saying you have to wind out the motor? When shifting and while cruising around town.

You can get deccent milage with a carb.

You have just mechanical advance? How did you accomplish this?

What kinda carb do you have?

[wyldman]

It sounds as if your shifting a little late.If the motor needs to be run at a higher RPM,then your SOL when it comes to mileage,and a trans\gear change won't really help.

Try cruising around in 4th,instead of third.

It sounds like this motor may really need to be set up properly.Adding vacuum advance,and setting up the mechanical advance will be a big benefit,in both driveablity,power,and mileage.Advancing the cam will help bring the power range down some too.

The Holley is no good for mileage,unless you really get serious with it,and even then it's not the best.You'd be better off with just a plain old Quadrajet,in good working order.Have you jetted the Holley yet ? They come REAL rich right from the factory,and need some good tuning to work right.

The headers may be the wrong size too,and designed more for high RPM horsepower,and not bottom end torque.Small primary tubes,and long collectors will help build more bottom end power.

You could have anything under there for gears.Most common were 3.23,and 3.42's,which is a decent all around gear.You can get a posi\LS for pretty much any gear ratio.

So the first thing to do is get the motor set up right,just the way you want it.Then once it's well tuned,you'll be able to find the best RPM for cruise,and fuel economy.Once that RPM is determined,then you can decide on what trans\gear combo to go with.

[MrGoodwrench]

Originally posted by ratlover
Why are you saying you have to wind out the motor? When shifting and while cruising around town.

You can get deccent milage with a carb.

You have just mechanical advance? How did you accomplish this?

What kinda carb do you have?

You have to wind the gear out to get a proper synch ratio before shifting, in other words you wont be going fast enough to to shift up. I have good torque. I can spin the tires indefinatley. You cannot shift into 4th comfortably unless you are doing 50+MPH, so up to 50 you cruise in 3rd, a very wide gear, but @ 40MPH I am turning around 3k, if I want to turn only around 2k, then I am creeping at about 30MPH. These are rough figures, I havent accually taken a notepad and recorded this.

As far as the distributor, way, way before HEI, there was something called 'points'. They work just as good as anything else, except they need proper setup, and regular maintenance, which I do. I have the proper advance curve for my advance. my cam is not that big. you can use all the electronic equipment you want, but I tune an engine by ear. I must toot my own horn here by saying I am an 'engine man'. anyway enough of that. I have a holly 1850-5 I think is the part #, the accuall model # is a 4150 I think. By the way the carb was bought new 2 years ago this july. It has the proper power valve (was metered), and the smallest jets available.

[MrGoodwrench]

Originally posted by wyldman
It sounds as if your shifting a little late.If the motor needs to be run at a higher RPM,then your SOL when it comes to mileage,and a trans\gear change won't really help.

Try cruising around in 4th,instead of third.

It sounds like this motor may really need to be set up properly.Adding vacuum advance,and setting up the mechanical advance will be a big benefit,in both driveablity,power,and mileage.Advancing the cam will help bring the power range down some too.

The Holley is no good for mileage,unless you really get serious with it,and even then it's not the best.You'd be better off with just a plain old Quadrajet,in good working order.Have you jetted the Holley yet ? They come REAL rich right from the factory,and need some good tuning to work right.

The headers may be the wrong size too,and designed more for high RPM horsepower,and not bottom end torque.Small primary tubes,and long collectors will help build more bottom end power.

You could have anything under there for gears.Most common were 3.23,and 3.42's,which is a decent all around gear.You can get a posi\LS for pretty much any gear ratio.

So the first thing to do is get the motor set up right,just the way you want it.Then once it's well tuned,you'll be able to find the best RPM for cruise,and fuel economy.Once that RPM is determined,then you can decide on what trans\gear combo to go with.

Adv/ret the cam is not something I am intimately familier with. Dont get me wrong I understand the priciples. This is a performace issue that I was not trained on. I learned to rebuild stock motors only. which I have done on about every common car, and light passenger truck (not desiel). So really when I put on a performance part I am out of my league, as to how dynamic engine performance will be modified.

I undestand that a higher/longer lift/duration on the cam will increase fuel consumption, and such, but I have never heard that back pressure will increase low end torque on a SB V8.

As for the holly, I love 'em. I have had two engine fires from a quadrajunk, and would sooner use an Edelbrock. The holly has been tweaked for the 350. The vacuume was metered, and the correct power valve installed. I put in the smallest jets available. accelerator pump gagued properly, yada, yada, yada. I have the holly factory handbook. It shows you how to setup everything on the carb for any engine.

Anyway enough of that crap. I happen to know that if I dont exceed 2k I get 15MPG which is acceptable. I also happen to know (while I cant quote gear ratios) that the saginaw was a passeger car transmission, geared for passenger car driving, which is what I do with my truck.

Anyway, thanks for all the help. I will be calling a chevy dealership this afterneoon to find out what the RPO's were for rear ends that fit my truck. thats all I need, then this weekend I will be counting teeth on my rear end, then finding out if I can get a posi-traction, or limited slip with a better ratio. and this summer I will probably still put in a saginaw.

[ratlover]

Dont take this as busting your balls.....

4150's are a good hp carb and very tunable but by design not the best in the way of economy. What size is it? Carb dosnt sound like your big problem though.

I know what points are.....I remember adjusting them with a matchbook(who needs feeler guages) and rebuilding my 1 barel carb in the parking lot of a golf range. Points are alright but a HEI(you can set one up to be completely mechanical) will have more zapping power plain and simple. A HEI is still very mechanical. Mechanical advance(that may or may not be complimented by a vaccume advance) The way it sends spark and the way it knows when to send spark are all very "mechanical". A properly set up vaccume advance is very easy to work on and adjust. It will give you lots more advance under low load situations were your motor can handle it without detonating and thus giving you better drivability.

What do you mean the proper sync ratio? I remeber having a k5 with a 456 and simmilar tall gears and each shift would drop the rpm by a bit over 1k rpm. If you were to shift to 4th at 40 mph and it droped your rpm even by 1500rpm you would be in the 1500-1700 rpm range that you wanted to cruise at on the highway.

You know what your cranking compression is?

Your truck might have enough balls and torque but it might not really make it were it should for the rest of your combo and driving style. It just sounds like your motor is a bit mismatched for the rest. A trany with closer ratios would make it seem less so though. But I dont think its worth the cost or the best way to "fix" things

[ratlover]

by advancing or retarding your cam you change how the engin behaves it makes the valve event happen sooner or latter in the pistons cycle.

Check out compcams.com website and go to thier catalogue. Find the how to degree a cam shaft.

Backpressure wont help anything. People say you should have backpressure to help low end torque yada yada yada......ITS WRONG! The thought is almost right. Big pipes hurt low speed velocity. The smaller the diameter(of intake runner or exhaust pipe or a garden hose) the faster the volicity will be. Think of a river, a wide river moves slow but when it necks down what happens to that same river? The speed will pick up at that point. This speed or velocity helps either move things in or move things out of the combustion chamber by way of inertia. Once something gets going it trys to stay going. If you have air/fuel moving fast into the combustion chamber as the piston goes down when it stops going down the air is still moving and it can pack more air in the cylinder like a mini supercharger even though the piston isnt moving down anymore sucking it in and it may actually be moving up. Same happens on the exhaust......hot gas going out and it will help draw more with it, out of that chamber but it will also craet a suction and start drawing from the other tube when it goes buy in a proper header set up down at the collector(full lenght headers are more efficient than shorties). There gets a point though were you start to need to move larger volumes and need bigger "pipes" This is why a big single plane manifold and big tube headers work fine on a car thats runing at high rpm but they hurt low end performance. Enough of the sience class. All of this make sense?

[wyldman]

Excellent explanation,saves me from typing it. :D

The problem with the Holley is mostly low speed atomization and sensitivity.You can tune it all you want,but unless you get into different venturi's and boosters,it's not that great.They are designed to be simple,and flow well at WOT.

An Edelbrock is more along the lines of the Quadrajet,for driveability and mileage.

If you have to wind it out that high before shifting,then you may have a real high rear gear.Even with a 2 series gear though,the shift spacing from 3rd to 4th shouldn't be that severe.It still sounds like it's not very efficient at low RPM's.Just because you can spin the tires doesn't mean you have lots of torque.

If you drop it into 4th at 40 MPH,what do the RPM's drop to ?

[ratlover]

Well you have saved my fingers on quite a few occasions so I figured I'd return the favor:)

[MrGoodwrench]

Originally posted by wyldman


If you drop it into 4th at 40 MPH,what do the RPM's drop to ?

1k

[John DiMartino]

If RPMS drop to 1000 in 4th at 40mph, then 60 mph should be 1500RPM,and 80mph should equal 2000RPM,and you shouldnt need to regear at all.

[MrGoodwrench]

I have found Edelbrock to be more for show than a well designed part. I wish Carter still made carbs. Those are some good carbs.

The main reason I'm dissatisfied with the GMC is that I have 5 other cars setup similar, and it gets the worst gas milage of them all. Accually, its about the same as my Chevelle with a 454. I call that poor. Now out on the highway @ 55 I will get about 15 MPG. However I rarely drive that slow, speed limit here is 70. In town which is most of where I drive the truck, 8-10MPG - sorry. I have 3 camaros, and a nova. The camaros are all setup the same 350 4bbl, 4 speed (manual), my nova has a 305 4bbl, 4 speed (manual), with the exception of the nova (which gets marginally better gas milage) I get 16-20 MPG (highway) and about 12-14 MPG (town). I have absolutely no idea what ratio the rear end is on any of them. I rebuilt the engines and transmissions, and left the rear ends stock (or whatever someone else may have put in them). I just would like to see my truck geared like one of my passenger cars. I am already planning to get something for towing (the wife wants a boat). I'm not into boating that much, but will give me an excuse to buy a 4x4 with a big block :) So mabey I will just sell it altogether. Thing is, I'm sure you understand, after you do so much work on a car you kind of get attached. Someone said something about the cost of a trans, and rear end ha! I've pissed away more money on old cars that I'll never get back. It's a hobby, and like most hobbies it cost money. I like old primative cars heh, now the wife has a 2000 Honda, I wont ride in it :) But I still have to work on it heh. But enough of that, I'm not changing anything on the engine until I rebuild it this late summer, or fall. I am going to do a full rebuild, though 65% of the parts are less than 2 years old. I might think about HEI as a guinnea pig. It's been around for what 25 years, they should have the bugs worked out by now. Anyway thanks guys.

Here is a pic I took last summer of my baby.

[MrGoodwrench]

Originally posted by John DiMartino
If RPMS drop to 1000 in 4th at 40mph, then 60 mph should be 1500RPM,and 80mph should equal 2000RPM,and you shouldnt need to regear at all.

I cant explain why, but your wrong. Furthermore I intend to put a posi-traction or limited slip in regardless. The help I have really ask for no one wants to provide: A list of axle gear ratios (posi or limited slip) that fit a 81 GMC or similar model. Thats all I need. Thanks.

[John DiMartino]

Mr Goodwrench..I am not wrong if your info is correct.If 1000RPM=40mph like you claimed.If your car is at 40mph at 1000RPM,then unless there is slippage .or excess tire growth it must be correct.If your going to accuse me of being wrong,you should be able to back up your claim.I await for your explanation.
BTW my truck in OD with 4.10 ratio and a 33" tall tire is exactly 33.5 mph per 1000RPM. I have verified this on the dynojet.My truck goes 67 MPH at 2000RPM,33.5 at 1000RPM,and 100.5 mph at 3000RPM. top speed is 117 on the dynojet at 3500RPM.

[MrGoodwrench]

Originally posted by John DiMartino
Mr Goodwrench..I am not wrong if your info is correct.If 1000RPM=40mph like you claimed.If your car is at 40mph at 1000RPM,then unless there is slippage .or excess tire growth it must be correct.If your going to accuse me of being wrong,you should be able to back up your claim.I await for your explanation.
BTW my truck in OD with 4.10 ratio and a 33" tall tire is exactly 33.5 mph per 1000RPM. I have verified this on the dynojet.My truck goes 67 MPH at 2000RPM,33.5 at 1000RPM,and 100.5 mph at 3000RPM. top speed is 117 on the dynojet at 3500RPM.

Well since you dont even know what the gear ratio is on the transmission or rear end I dont see how you can profess to know what my truck is turning at a give RPM.

A bit touchy about being wrong huh? Mabey a little ego problem there. Wether your wrong or not I certainly touched a nerve.

I mis-quoted in a previous post so here the trans specs:

Transmission Muncie SM465
1st:6.55 2nd:3.58 3rd:1.7 4th:1.00

Tires Firestone Firehawk
P275 / R60 15"


You want to? You figure it out. No one ask you to. If you had READ my post. I have ask over, and over for axle ratios. You and some other peope took it upon yourself to determine things like. 'your engine isnt turning enough torque', or 'go to a larger tire size', or 'you dont need to change the axle'. Well the axle is getting changed because I want a posi, or limited slip. period. no discussion.

All I wanted was a list of AXLE RATIOS. So I can choose a low numerical ratio. If you know some axle ratios I would be happy to see your post, but I am not into this arguing about my axle speed. The figures I have posted for RPM are GUESSTIMATES, I havent taken a notepad around with me and recorded. Furthermore, it wouldnt matter because my speedometer is off by about 5-20 MPH DYNAMICALLY, so I have to guess at the speed I'm going. I went to calibrate it but the diffrence changes dynamically, so its impossible. so until I have $130 to pony up for an aftermarket speedo. thats the way it is. So thank you for all you time/attention, but if your not going to post axle ratios, I dont need it. Thank you. Goodbye.

[wyldman]

No need to get upset.

John is one of the best guys on this board for advice and information,and he is correct.If your figures are off,don't jump on him for it.His post was correct in stating if your turning 1000 RPM at 40 MPH,then you would be turning 2000 RPM at 80 MPH.It's simple math,and it's linear,as long as your in 4th,with a 1:1 ratio.

IF the figure of 1000 RPM at 40 MPH is correct,then you don't need a higher gear (lower number),as your already to high.1250 RPM's at a cruise speed of 50 MPH is too low for your truck,even with a stock motor.The motor needs more gear,to bring the RPM's up to where the motor becomes efficient,and gets better mileage.IF your figures are wrong,then that goes out the window.

In your original post,you asked for information regarding what posi's,or LS diff's would have a good highway gear,and if changing the trans would help your problem.Lots of good info has been posted,and people are trying to help you out.If you don't want the help,you can go somewhere else to find it.

To answer your question about YOUR gear ratio,you need to get under the truck and find out what it is.RPO codes,internet info,etc are no good if someone changed the diff before you got it.As far as what was available in C series truck of that era,it could be anything from a 2.73 up to a 4.56.

Based on the info you provided (1000 RPM @ 40),with the trans ratio (1:1),and the tire sizes,you have about a 2.08 gear,which would not really be correct.Your RPM figure must be off.

Based on the previous figures of 2000 @ 60,then you would have a 2.77 rear,or close to it.That would make more sense.You don't want any less gear than that,or it would spread out the shifts even more,and your cruise RPM would be too low.

If you want more mileage,and better driveability,and power,then you need to change the trans,to something with better gear spacing,not change the rear gear.The granny low makes that trans basically a three speed.Dropping in a 5 speed with an OD would give you what you want.You would now have many more gears available to keep the engine in it's efficiency range,and the OD will lower cruise RPM even more,if the engine will pull it without lugging.

[MrGoodwrench]

Thanks for the advice. I'm still putting a posi or limited slip in regardless, so it really doesnt matter. the differential is going. period. There is no question to as wether or not I should change it. It will be changed. Furthermore, I was told by the chevy dealership that a 2.56 was availible for that model.

I have done some checking and I think I have decided to go with a 3.42 or 3.73 posi axle, and an external overdrive. they are a bit pricey but I'd prefer that to a late model 5 speed.

If your interested this is what I'm going to buy.

http://www.drivetrain.com/new_overdrive/GM4speedmanal/overdrivegm4spdmanual.html

[John DiMartino]

Thank you Wyldman, I appreciate the help. Mr Goodwrench,ive kept my mouth shut while you've posted incorrect info time and time again. Just your info on the holley carb shows you are clueless as to what to use for economy.I knew your car couldnt do 40mph at 1000RPM. I was seeing if you were man enough to admit the mistake and correct yourself,instead you chose to take a stab at my credibility,and insist im wrong with no proof whatso ever.Thats your choice,and now I know not to waste my time reading your posts,or replying to you since you know it all anyway. :)

[Pelican]

Well this is pretty entertaining!

I'd flip the switch to the barn cleaner, but I'm going to need my fishing boots to make my way over to it!:confused: :headwall

[Alan]

Goodwrench,

I find it amazing that somebody who claims to be so much into engines and cars is asking us for help on a simple thing like axle ratios. I don't think any of us have a spec sheet any more handy than you do. If you found listings for 4wd ratios you already have the most common ones.

It's obvious you have no clue about how axle ratios affect driveability or what works and what doesn't. You're tossing around speeds and RPM numbers that it turns out you are guessing at.

That cheap shot you threw at John about ego was so far off as to be ridiculous. John knows more about drivetrain variations than anybody I know. If you want to tell somebody they are wrong it would be nice if you could back it up with fact instead of quesses.

I would have to guess that maybe you aren't as sharp as you think you are.

[MrGoodwrench]

Oh boo hoo you are right, I am such a moron, and you guys know it all you master mechanics, you master techs, you are gods. Thats why you cant produce a short list of axle ratios? heheh You are right about one thing I am a 'engine man' when it comes to other things I let other people handle it, such as gearing. So gearing is not my forte'. boohooI feel so inadequate.

"Just your info on the holley carb shows you are clueless as to what to use for economy."

Really? I'll admit that Holly isn't the MOST fuel efficient, but when you compare with a quadrajunk the differences in MPG are very very little. If you are getting different readings YOU probably have the carb setup wrong. Furthermore anything under 20 MPG is not considered 'economy' anyway so that is moot anyway. If I wanted the greatist 'economy', I would go with direct port injection. oops, I forgot to tell you I get 16-18 MPG with several Holly's w/4 speeds. Thank You.

"I knew your car couldnt do 40mph at 1000RPM."

It's a truck not a car.

'do'? dunno what you mean. The question was:

quote:
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Originally posted by wyldman


If you drop it into 4th at 40 MPH,what do the RPM's drop to ?

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The answer is 1k, I dont care if you like it or believe it, the answer is 1000 RPM. write it down, and take a picture for refrence.

"I was seeing if you were man enough to admit the mistake and correct yourself"

sure. hindsight is 20/20

"insist im wrong with no proof whatso ever"

I never 'insisted' anything, I simply made ONE simple statement. You have made it out to be more than is was, hence my statement about your ego. And I guess here I could say something like you would say 'well, I was just testing you to see if you knew what you were talking about', but I'm not egotistical.

"I don't think any of us have a spec sheet any more handy than you do."

Well, I could recite mechanical specs for about half a dozen chevy engines. ooooo whoop-di-do. I have rebuilt all types of gasoline engines for passenger cars and light trucks for 14 years. Is that supposed to make me an expert on transmissions, axles, brakes, whatever? Uh, the short answer is no. Your funny, if you think attacking my credentials will accomplish anything. :) I'm not offended in any way. My credentials, and experience with engines speak for themselves.

"It's obvious you have no clue about how axle ratios affect driveability or what works and what doesn't."

Gee, where did you get that idea? Could it be I came here to ask a bunch of morons questions about axle ratios? Did that tip you off bright boy? hmm

"That cheap shot you threw at John about ego was so far off as to be ridiculous"

Really? The posts are there, they speak for themselves. Someone said he was wrong (true or not) he got his little panties in a wad. Be a man dont go off and cry just because someone says something you dont like. And I'm not saying right or wrong, but dont be a little girl. cheap shot ha! read the post.

Well I am through with this forum, I'm probably banned anyway after this post. Surely if a mod got so uptite about being called wrong :) he will surely bann me for this post. It's just as well. A bunch of so called master mechanics, A.S.E. techs, and experts can't answer a few questions about axle ratios that by your own admission are 'simple' yet you STILL cant speak about them, And call me stupid. Funny thing in the few short days it took you guys to ramble about my engine, and everything else, and avoid the REAL question (college is not for you guys) I found all the answers to every question I had, RPO packages, axle ratios, transmissions & ratios, tire sizes, dynamic performance, formulas, and much, much more. So you have done nothing but WASTE MY TIME. Goodbye.

[wyldman]

I won't even bother responding to this,as I have no need to back up my "credentials",or any of the others who have replied to this post.If I offended you,I'm sorry,I was just trying to help.

No need to ban anyone if it ends here.If you want to participate in this forum,that's fine,if not,then leave.

I'm going to close this thread down,as it's going nowhere but downhill.

[Chuck Smith]

I am posting this reply, for one reason, and one reason only, to help anyone that does a search in the future. and has this thread turn up in the results.

For the simple question asked about what axle ratios were available.... (It doesn't really matter)

FIRST find out what axle you have, which is most likely a GM 10 or GM 12 bolt. (Original in 81 should have been a GM 10 bolt.)

SECOND, look at the ads in magazines, or on the internet for available gear sets for that axle, from the various suppliers. It is that simple.

PERIOD. What does the original ratios GM offered have to do with anything????

Again, this is for anyone doing a search... look in your glove box for the RPO decal to find out what axle ratio your truck was equipped with from the factory.... if it matters. All you really need to know is what ratio you need for the desired RPM range.

The calculators on the manufacturer's web site will help you.

~Chuck