How tight is the drivebelt supposed to be?

bowtie_pasta · July 23, 2002

I just replaced the drivebelt on my truck and the new one was waaaaay tighter than the old one. I started it and everything sounds fine. Actually one of the reasons that got me thinking to replace it was a squeaking sound I was hearing. Then I checked the last time it was replaced which looks to be some 60,000mi ago.

Anyway, I just want to make sure this is normal. The new belt is slightly thicker too. What concerns me is the belt tensioner is cranked in a lot more than it used to be.

Sorry for the long post. :sideways:

SilveradoWV · July 23, 2002

It will probably be tighter, the belt manufacturer might even effect the size of the belt!

Tucson_02Silverado · July 23, 2002

The squeaking probably wasn't the belt but the belt tensioner. For some reason the manufacturers (of all makes) are not telling people that the belt tensioner is an expected replacement item at 50K miles. Common problem is the bearings start seizing, second is with all the josling (watch the tensioner as you rev up the engine and then the rpms drop back) the spring weakens, thus you have a loose belt. To replace is usually 1 no more than two bolts. Replace with an entire tensioner/pulley assembly. They do sell it pieces, NOT worth the time and effort to just replace one of the two pieces. There are (in most cases) markings cast into the tensioner and when it reaches the last mark it is suppose to be changed. 50K is a benchmark not the hard fast rule. If you have an intermittent "snag" while steering or doesn't quite cool right anymore (engine and/or AC), voltage drops as you go through puddles in the rain.....check the tensioner.

bowtie_pasta · July 23, 2002

You are probably right about the tensioner. I'm going to replace it. I was reading some documention that showed how to tell when they are worn. The gap will be larger at one side than the other. Plus you will be able to rock back and forth from side to side.

Funny the Haynes guide mentions nothing about this item. No maintenance intervals or anything.

Thanks for the help though. If anyone else has any more info to share that would be great too! :sideways:

Tucson_02Silverado · July 23, 2002

Correction on my comment on the cast marks on the tensioner...they are suppose to be the belts normal range and when the marks reach the designated end the belt is too loose and should be changed.

I've heard a lot of stories of how people change their belts. Common one is they say that they sure are glad it's only belt and you can change it without any tools....that's when I say hold on there...and start describing the tensioner...and they say yea that's it, '...I just lifted it up by hand and put the belt on...'. You definitely need a 1/2" drive socket handle or bar to lift the tensioner off the belt to move the belt. If indeed it's a perfectly good tensioner and you can lift it off the belt by hand, all's I ask is you don't squeeze too hard when I shake your hand.

I don't know why the literary conspiracy exists about the tensioner. I'm still waiting for Helm to get out of backorder so I can get my hardcopy service manual set on my 2002 Silverado and see if it's mentioned yet.

I didn't answer your query about tightness of the belt. Yes the new belt should be tighter, but if you had to lift the tensioner to it's full travel and then released the tensioner and it barely moves, the belt is the wrong size. With Goodyear anyways, the last digits are the actual size of the belt in inches. When comparing serpentine belts old to new with one end flush with each other and the other end measured, the old belt should be around a width a thumb nail gap or a little more with the new belt.

bowtie_pasta · July 23, 2002

That makes me feel better. Because before I probably could have moved it with my hand, but not now with this tighter belt.

I'm sure it was too loose before, sometimes when I got on the gas hard w/ the AC on it would slip. Not all the time but occasionally.

CMNTMXR81 · July 24, 2002

I've never replaced a tensioner unless it made noise. I don't know what you mean about the 50k rule. I've replaced 100's of them, especially on GM trucks.

Normally about 1/4" deflection is sufficient.

Tucson_02Silverado · July 24, 2002

50K miles is the life expectancy of the tensioner/pulley assembly, of course there is the +/- of total engine run hours.

There are two schools of thought on parts replacement, one which seems to be the most common; is to only replace a part when known bad. The other is; if MTBF (mean time before failure) of a part is known, to be preventative and replace the part prior to it's failure. A lot of people are first type and are completely comfortable with replacement at failure or they're trying to be frugal (of course there is a mix of the two), which more than fine. I just happen to be the latter type and expect it to go bad and it isn't an unexpected expense; do things prematurely fail, yes they do, do things last a person's lifetime +, yes they do. That's the nature of the mechanical beast.

I commented that it wasn't a hard fast rule, but if you will, not a rule at all. Fore I have said no one seems to publish the life of the tensioner in service manuals.

'...replaced 100's of them....' when do they fail?

It's somewhat different on any vehicle and even then the engine type. If for example on GM trucks with a 5.7L if they fail consistently around 40K, I myself would probably replace it at 35K. If the failures were around 60K instead, then I would replace at 55K. Others will wait for a noise and replace it then and never care when it'll happen again. It'll either never fail, fail early, or fail at the same time period. NO RULE, just do what you are comfortable with.