Bad crunchy chain slapping sound on occasion

[Nicolai8775]

Ok apologies in advance, this is technically regarding my 2001 Sierra 2500hd, which I own currently, but I found the knowledge and advice I got on some of my previous Chevys was the best around.

Anyways my Sierra, it's my first 8.1/Allison combo.

Occasionally, not always, but consistently only when I accelerate from a dead stop it sounds and feels like the transfer case is about to explode. It sounds familiar to the chain sound I had on my 2500 suburban and that one blew cause of pump rub.

This transfer case on my Sierra was replaced with what looks like a remanufactured unit. And it's been making this sound occasionally for like the last 8 months of daily driving. So I kinda don't know why it hasn't exploded yet. Which is making me wonder if it's the Allison, or something else. I drained the fluid in the transfer case once 4 months ago and it was still red, nothing chunky or gray. Replaced with whatever ATF or whatever Dexron formula was recommended, don't remember what I bought. Still doing it

 

[rockola1971]

Have you checked the fluid level in the Tcase recently? Chain could also be stretched and smacking the inside of the case. If thats what is making the noise then it will be peeking out of the case soon enough.

 

[OR VietVet]

Was it making the noise 4 months ago or just started? Like @rockola1971 said, fluid level now and condition of fluid?

 

[nonickatall]

I would check the wheel bearing hubs. When my died i had also sometimes a horrible noise, but mostly not. Reason was that the debris of a damaged role sometimes get in a position where it makes noise.

 

[NickTransmissions]

Put the vehicle up on all fours and spin the the main drive shaft. Watch how long it takes before the other one starts to move. If you get a quarter turn or more before the other shaft moves, chances are the chain is stretched. Drain fluid (see how much comes out) and inspect fluid and drain plug for metal or aluminum shavings. If present, it’s likely from the case due to the worn chain smacking against it.

Those two procedures should let you rule in or out the T-case as the problem.

 

[Nicolai8775]

I bought the truck last summer and it's been doing the occasional grinding sound since i got it. This truck, is an absolute pile. The bed is shot, the cab corners haven't existed in years, rockers Swiss cheese and it even has 392,000 miles. It's bad everywhere you look.

But then I saw the shiny fresh painted transfer case up in there. Like it looks brand new. It stands out on such a rusty used beat up looking thing.

So after a couple weeks of driving this thing I had the first chain grinding sound. I drained the fluid. I had my light on it, it was all red slightly used looking fluid. No metal on the plug, no chunks came out, I didn't measure it but it seemed the proper 2ish quarts came out.

I refilled it and the problem never went away. Been driving it since.

My guts telling me the t-case despite no metal to be found, but what a bunch of bull if a brand new remanufactured unit crapped out right away like that.



It only grinds when I start going from a complete stop, but not every time. If I let off the gas for a sec and then resume accelerating the grinding stops.

 

[nonickatall]

Check you wheel bearing hub. That was in my truck the same..

 

[Nicolai8775]

Put the vehicle up on all fours and spin the the main drive shaft. Watch how long it takes before the other one starts to move. If you get a quarter turn or more before the other shaft moves, chances are the chain is stretched. Drain fluid (see how much comes out) and inspect fluid and drain plug for metal or aluminum shavings. If present, it’s likely from the case due to the worn chain smacking against it.

Those two procedures should let you rule in or out the T-case as the problem.

I will try that, good tip, didn't know that one.

 

[Nicolai8775]

Check you wheel bearing hub. That was in my truck the same..

I haven't checked hubs yet, but I gotta say I've never had a hub failure sound so violent before lol

It also doesn't sound like it grinds when I turn the wheel a certain direction when turning like other bearing failures.

So I guess that's why I haven't looked at that yet. And last time I had the front lifted I didn't feel any play in the wheel

 

[Nicolai8775]

I would check the wheel bearing hubs. When my died i had also sometimes a horrible noise, but mostly not. Reason was that the debris of a damaged role sometimes get in a position where it makes noise.

Oh ok I didn't see this part. That makes sense!

now I'm also wondering.. if my parking brake disintegrated cause I had to replace rear calipers when I bought this thing. It sounds more like it's in front of me or beneath me however