Disturbing Clunk

[goodmonkey]

I'm having a problem that I'm hoping that some of you more experienced people might be able to help me with. I have a 95 C2500 with the L65, and last March while home on leave the vacuum pump locked up on me. After replacing it there is a very disturbing and loud "clunk" coming from the front end that often gets me "hey, what's wrong with your truck?" The only time I can really hear it is at idle, but it is more or less hit or miss, unless I put more of a load on the s-belt, either by turning the ac on, or turning the wheel hard left or right, at which time it is very constant. I can take the belt off, and the noise disappears. Fearing that I had received a bad pump, I installed another one with a new pully, but the problem persists. I've seen a few mentions of vacuum pumps causing this noise, and of the crankshaft pully being damaged. I was wondering if there was a way to drive all the accessories with a differnt belt, leaving out the vacuum pump to possibly rule it out. Any thoughts?

[GARY PAGE]

Check the tensioner gauge on the take up pulley. You may have the wrong belt for the tuck if it indicates belt out of service range, it could be slapping. I a previous post I made the late model 95 used a shorter belt than AutoZone offered for the 95, the 96 was the correct belt for the late model 95 from AutoZone. This may account for you noise when the AIR or PS is pulling.

[goodmonkey]

Thanks. I had completely forgotten that those marks were there. Think that my dad showed them to me back when he bought his '95 when it was new. But thinking about it when I replaced the pump I replaced the belt too, because the original had received some damage from the locked up pully. It was indeed out of range, so I put the original back on, but still out of range. Now though the noise is more noticable with no accessories running, but with the ac running it almost totally disappears. Too late for autozone tonight, but I did look up the part numbers for the 95 vs the 96. The belt for the smaller alternator on the 96 is the same as the one for the one without the vacuum pump for the 95. Hopefully I can go during lunch tomorrow. Thanks for your help. smile.gif

[whatnot]

That is exactly what mine did when the rubber let go in the crankshaft pulley. It happened from the extra load right after I got the A/C fixed

[StephenA]

I had chatter from the A/C (belt slipping on A/C pulley) and 1" of belt vibration when A/C was on. Replaced Tensioner- same thing. Came to find out the spare belt from Auto Quest sold with the truck was wrong size- 1/2" too long.
I checked out the GM stock part from the dealer & it was 67 bucks. Come to find out it is manufactured by Goodyear who wanted 48 bucks, lifetime warranty. Found it for $18.57 from Pickproparts. Evreything's smooth now, the gauge is dead on.

4061010 Poly-V, w/AC 6PK2565 GM Part#12555009

http://www.pickproparts.com/PartsList.aspx?AAIASubCategoryID=8905 $18.57

[cruzer]

Mine was making this noise. The rubber in the crank pulley let go. The cross spokes of the pulley was hitting the 4 bolts that retain the pulley to the harmonic balancer. I checked mine by
moving the belt back and fourth and watching the crank pulley move while the center hub stayed still. It moved about a 1/2-3/4" each way with the crank staying still. If this is the case, I'd look closely at the rubber in the balancer too.

[goodmonkey]

Well I did get the shorter belt as suggested. It is 101 inch vs the 102 inch that was on it. It sounds a little different, but still the clunk remains. As in cruzer's case, I've found the same thing, the spokes of the pully are hitting the bolts. Surprized I hadn't seen that before, but I'm still learning. Now is that a difficult piece to replace, and what would I need to look for on the balancer? And can anyone tell me what exactly all the marks on the tensioner mean as far as wear?

[turbovair]

Take your belt off and the crank pulley comes off after removing 4 each 15 mm bolts.You might find it easier to do from the bottom.I paid about $125 at the local dealer for a new pulley.Mine knocked and rattled for a week before I figures out what it was. Check the balancer to be sure the rubber is intact and not dry rooted or swollen by oil, and that the inner and outer rings are rotating in the same plane.As far as the tensioner marks,you basically have a mark for a "new" belt, a square "serviceable" area and a "replace" mark.Good Luck.

[cruzer]

4 bolts and tap off pulley removes it. You may just be able to pull off pulley by hand. I cant remember, so it must be easy. After the pulley
is off look at balancer and you will see a black line(rubber) about a 1/2"-1" from outer edge. Look for cracks,dryrot, or seperation from outer and inner parts. If you can try to look on back side too. Rotate motor by hand to see all. On mine I saw chunks of rubber missing on the back side. With the amount of miles you have on the truck I'd probably replace it too. You will need a Harmonic balancer puller. It will pull the balancer off by the bolt holes the pulley was held on with. Don't forget to replace the front seal while your at it. Balancers & pulley fail quite often on these engines.

[goodmonkey]

Went by the dealer today and picked up the pulley. $206. Ouch. I could have got it a little cheaper online, but I've put up with this for over six months, and couldn't wait any longer. I got it on tonight, and man, what a world of difference. I will no longer be afraid of driving up somewhere and having someone say "sounds like you need a new truck" or "sounds broken." The dampener looked okay, but I can see that the front seal needs replacing. Hopefully someone will buy my Duramax and then I can start the process of doing all that is needed to the ChuckWagon. Thanks again guys. :D