I think the vents of my vacuum pump are squeaking. It seems to depend a bit on the temperature, but MOTT the squeaking is quite loud. It has become almost the major sound the engine makes.

It can be something else that makes the squeaking. But when turning the pulley on the vac pump slowly by hand, the pump silently squeaks. The squeaking coming from the engine sounds similar to that.

Can I let the pump suck in some engine oil or WD40 or the like without taking the risk of damaging it? I want to get rid of that terrible squeaking ... It sounds as if the truck is befallen by a swarm of giant crickets.

That's the shaft bearings - time for replacement.
The valves are simple plastic flappers.

Check the idler pulley bearings and brackets while you're at it............

a mechanics stethescope will isolate the noise for you. We use them a lot, mostly for supercharged cars to identify noise complaints. Idler arms are often the culprit, mine siezed up on me about a year ago.

Lee could also be alternator bearings

gmctd, do you mean the camshaft bearings? Which one is the idler pulley and the brackets? Is it the assembly with the pulley that keeps the accessory belt tightened?

TDG, using a stethoscope is a good idea :) The sound can very well be a bearing, and it would make even sense because it seems a bit temperature related. If it is, I should find out early enough to get needed parts in advance and to prevent further damage.

TDoc, the alternator has been replaced in October 2003, so it shouldn't already be worn out again. But I'll check it out, too.

I'll make a sound recording with my camera so that you can hear the squeeking. I wanted to do that earlier, but I either forgot the camera or forgot to make the recording ...


PS:
It can also have to do with the accessory belt. Squeaking started about two weeks after I put on a new belt, went away after some time and came back with the new vacuum pump. The pump has eaten up some on the side of the new belt, but after aligning the pump it's running fine now. Only the squeaking has increased since.

Hm, maybe I should put the old belt back on. If the squeaking goes away, I'd wonder what that should tell me.

Has anyone replaced the bearings in the alt? I have a squeeker right now that I have to deal with.

The sound quality is very poor so that the recording isn't particularly helpful. Your can hear a rattle, but that is actually the squeaking. I've taken that standing in front of the truck, engine warm, then moving over to the drivers side to turn the engine off. It didn't squeak that loud today, either.

See here for the soundfile. (http://dieselfuel.de//naphiegeeC6hovieseev/)

quantum, I've never replaced the bearings in the alternator in one of these trucks, but a few years back when I worked as a professional technician I replaced lots of squeaky alternators on both gas and diesel engines in these year vehicles. One had actually caught on fire and burned alot of the wiring, hoses, etc., on top of the engine. So I'd suggest not waiting too long before taking care of the problem.:)

Racer31x,

I took it off. I just didn't care to spend $150 or so on a new one for lack of bearings.
P.S. My other name on the gm-diesel site is Threadweaver.

Kinda thought that's who you were, quantum:)

For what it's worth, I seem to remember seeing a bearing kit called ice-something, intended to cure the problem of bad bearings in these alternators. It was available from that same "top of the mountian" catalog that had those MAP sensors we talked about on the other forum.

Has anyone replaced the bearings in the alt? I have a squeeker right now that I have to deal with.Hey QM.... Me too! Isn't that a co-winky-dink? I'm just gonne throw a new AC Delco from the dealer in ($120) and keep the noisey one as a spare.

It seems that I've solved my squeaking :)

The accessory belt had lengthened enough for the tightener pulley to go down nearly all the way it can, so there was not enough tension on the belt any more. The belt must have been a bit long from the beginning, and the vacuum pump eating at it must have weakened it so much that it became ever more longer over the time.

I'm glad if it's really the belt only and not a bearing ...