99 Tahoe grinding noise when let off gas HELP!

[Schrade]

Originally Posted by wafrederick

Pulll the rear driveshaft and the tailshaft cover off the transfer case.Look for a broken snap ring,in 2 or 3 pieces and this is a common problem.

If this is the case, it wouldn't make a difference Drive or Neutral, would it?

With his, it is making a difference...

???

[wafrederick]

I have seen this happen in a 1998 GMC truck.Thought it was in the transmission and it was not finding broken parts inside.Pulled the cover off the tailhousing of the transfer case finding a broken snap ring.

[yungsurge]

Originally Posted by wafrederick

Pulll the rear driveshaft and the tailshaft cover off the transfer case.Look for a broken snap ring,in 2 or 3 pieces and this is a common problem.

I was just reading up on this snap ring too.I'm gonna pull that apart tonight or tomarrow and let you know what I see.Thanks for the help

[YenkoZL1]

I bet it could be your transfer case. The transfer case halves are magnesium on the NP246 model. The gear that pumps the fluid inside wears a "pin size hole" through the outer case half. This causes your fluid to leak slowly and if not kept up, will cause the transfer case to burn up completely. These case halves are very hard to find. Tranny shops will not be able to rebuild your transfer case w/out another case half. Plus, GM has not fixed this issue with the oil pump wearing holes into the transfer case. Tranny shops do offer an elimenator kit that prevents this from happening in the future after a rebuilt. Your looking at anywhere from $800 to $1200 if this is the case. If your transfer case looks like it has a leak look for a pin sized hole on the bottom of the case on the back half of the trasfer case where the rear drive shaft connects. Good luck. If this vibration is from the transfer case this can cause the tranny to go bad if not taken care of in a timely fashion.

P.S. This has happened to me.

[yungsurge]

Well good thing I just picked up a whole transfer case from my buddy for $200 on Friday.(He really needed money)But I'm gonna have him drop the transfer case and look inside and if it's too bad I just swap it.Or if its fixable I'll just fix and keep the other one on the side

[Schrade]

Originally Posted by YenkoZL1

I bet it could be your transfer case. The transfer case halves are magnesium on the NP246 model. The gear that pumps the fluid inside wears a "pin size hole" through the outer case half.

The gear inside wears a hole in the transfer case???

[YenkoZL1]

Originally Posted by cbec1999

The gear inside wears a hole in the transfer case???

Yeah I guess it constantly rubs or vibrates against the case eventually wearing a hole in it. I went to three different tranny shops none of which had a case half to use for the rebuild & said it could be a while before they find a used one without a hole in it. When I asked if the hole could be welded they looked at me funny. I dont know if magnesium cant be welded? Anyways they put a steel plate inside to prevent this from happening. Transfercase models NP246 Autotrac have these issues. The outer casing is magnesium.

[YenkoZL1]

Originally Posted by yungsurge

Well good thing I just picked up a whole transfer case from my buddy for $200 on Friday.(He really needed money)But I'm gonna have him drop the transfer case and look inside and if it's too bad I just swap it.Or if its fixable I'll just fix and keep the other one on the side

Hey does your tahoe have the Autotrac in it? If so, the transfer case needs a special fluid called "SYNCROMESH". Its blue in color. You can get it at your local chevy dealer. It's about $14 a quart. Or you can use Royal Purples version called "SYNCROMAX". Same stuff but its only $10 a quart. Dont use normal tranny fluid in these transfer cases(np246).

[j cAT]

Originally Posted by YenkoZL1

Hey does your tahoe have the Autotrac in it? If so, the transfer case needs a special fluid called "SYNCROMESH". Its blue in color. You can get it at your local chevy dealer. It's about $14 a quart. Or you can use Royal Purples version called "SYNCROMAX". Same stuff but its only $10 a quart. Dont use normal tranny fluid in these transfer cases(np246).

I believe the transfercase fluid is called trac II transfer case fluid made only by GM...only available at dealer...last purchased for 6.oo /qt.. will need 3quarts...actually 2.5qts the fluid is blue when new the fluid needs replacing when it turns gray ...If the fluid is black get your wallet ready..

[yungsurge]

Yes my Tahoe does have the auto trac(good looking on the fluid info).I still havent got around to dropping the t case yet I had a busy weekend.I'm gonna try to start on it tomarrow I really wanna find out what it is.Once again thanks for all the help and as soon as I drop it I'll let you guys know what happend.

[jdmccright]

It is called GM Autotrak II fluid, P/N 12378508, and I was quoted $7.69/qt back in the summer.

[yungsurge]

Quick ? I just dropped the transfer case and does anyone know what size the allen wrench is for the fill plug and how the hell do you fill it once you put the transfer case in?

[j cAT]

Originally Posted by yungsurge

Quick ? I just dropped the transfer case and does anyone know what size the allen wrench is for the fill plug and how the hell do you fill it once you put the transfer case in?

i used a metric allen wrench set ....forgot what size..but you can use the head of a bolt ....

to fill you use a qt bottle hand pumper ....this pumper is very handy to fill the other under vehicle componets..


I use mineral spirits to flush out and clean after use...

[yungsurge]

if it's not one thing it's another. ok I just finished putting the transfer case in took it for a test drive and no noise when I was driving but when I put it 4hi it stays there and wont come out and my service 4wheel light came on. any ideas?

[yungsurge]

Well I just turned the truck off and then I can switch back to 2wd.If im in neutral not movind I can put in 4hi,4lo and auto but if I leave in 4hi and start driving thats when my service 4wd light comes on and won't shift back 2wd.I' disconnected the battery and I tryed pulling the fuse.