v belt tension?

[chtucker]

For those of us who grew up in the age of the serpentine belt systems...

I replace the belts on my 77' Bronco 302. How do you know when tight is tight enough? I can't seem to get the alternator belt to stop squealing no matter how tight it is...

Howard

[festerw]

From what I remember my grandpa telling me (LOL I grew up with serpentine belts too, auto tensioner's rule!) You should lay a ruler/yard stick/something flat from one pulley to the other and then adjust the belt so there is about a 1/2 inch of deflection. But you know this is all theoretical to me :grinz

[bud16415]

Howard

There are gages out there that do kind of what Will’s grandpa told him. They clamp on to the straight section of the belt on 3 points and with a controlled force measure how far the belt moves.
I have never really seen anyone ever use one on a car or truck it’s mostly done by feel and experience.

Things to keep in mind. When the belt is running it tensions itself on one side while the other side is looser. Just like the chain on a bike. The force that drives the belt is caused by what they call the wrap (the amount of the pulley the belt grabs on). If you want to get an idea of how tight one has to be think of things like a mower deck that has a belt tension idler and a spring. That’s really all the tighter they have to be. Too much tension just puts extra side load on the bearing and that pressure will cause loss of power. The idea is the “V” in the pulley is a slight angle and it should grab the sides of the belt and the harder it pulls the tighter it should grab. Worn pulley will not have the same angle as the belt and will require extra tension. Watch also that nothing has built up in the base of the groove and is lifting the belt. Belt dressings sometimes help but if everything is right they shouldn’t be needed.

Bud

[Pickering Snow]

Howard

Like Bud said theres a belt tenn gage but most of us do it by feel one thing you might want to check is make sure the belt width is right and its not riding low in the groove low groove ride will cause belts to squeal even when tight.

Suggestion use a gates premium belt or Goodyear Dayco belts are really hard to keep from sretching and to keep tight.

[Newtownsnowplower]

You may also have a bad alternator bearing causing the belt to slip. Does the alternator charge? Try spinning the pulley by hand to feel for resistance.

[bud16415]

Below is a page from the gates home page that shows some common V belt failures.
Like Fred said if the belt is riding to low or the sides of the belt are glazed (common in old belts) they will slip and chirp. Even though the alternator turns freely keep in mind that under load it takes something like 5 HP to turn it.

http://www.gates.com/brochure.cfm?brochure=2691&location_id=1244

[Robh]

How old are the belts???

[chtucker]

Brand new...