Buzz/Vibration during TC Lockup 50MPH/1700RPM?

[SDWA]

My 2002 2500HD/LB/DA has about 135,000 miles. Other than a new tranny at 250 miles and 8 new injectors, everything still works great!


HOWEVER... there is a "buzzing" / vibration I've noticed in the last 10K miles or so that is starting to worry me. It occurs between 45-50mph, on level to slight incline roads, with light to medium throttle. Somewhere around the 50mph point, with the RPM at about 1700, I'm assuming the torque converter locks up, and the RPM drops to about 1500. The buzzing occurs for about 1-2 seconds right before/during the RPM drop. It's easily and predictable and repeatable. You can feel it and hear it. Definitely coming from the front half of the truck.

I've babied the truck since new, no real heavy towing or payloads, the transmission fluid was changed out at 6K miles with Transynd, the filter replaced every 25K and the fluid itself was changed again at 50K and 100K. It's mostly a highway truck, my average MPH via the hourmeter is around 40MPH.

Any ideas??? I'm afraid the thing is going to grenade on me when I least expect it...

Thanks!

Scott

[DmaxMaverick]

A couple simple things to check....

If you have a 2 piece drive shaft (you should), the carrier bearing and/or the isolator (rubber).

Downpipe for a cracked mounting tab. You can check it through the passenger side fender liner (rear of tire) with a flashlight. Easy fix. Just weld it. It may not be the cause of the issue, but it's probably cracked anyway.

Exhaust pipe hangers. There is a bracket that mounts to the transfer case with 2 bolts that can loosen. Worn/weathered hanger rubbers can allow the pipe to contact other metal parts (like cross members) under certain load conditions.

U-joints. Could be an early sign.

[SDWA]

Results of investigation:

1) Center bearing isolator: Practically disintegrated, inner piece is no longer supported by outer piece, it's almost resting on the bottom of the mount!

2) Exhaust downpipe mounting tab: Welds intact.

3) Exahust hangers: Forward hanger above transmission support crossmember - rubber isolator out of support frame.

Does anyone make an aftermarket urethane replacement isolator?

Won't get to drive it until tomorrow, we'll see what just the exhaust hanger back in the right place does...


Thanks DMav!

Scott

[DmaxMaverick]

I don't think I'd want a urethane isolator. That would transmit a lot of harmonics to the crossmember---the reason for your post in the first place. They aren't too costly and easy to replace, so rubber is the best option. If you get 100K out of each one, that's not too bad, in my book. I can remember when motor/tranny mounts were a 50K item. Urethane lasts longer, but transmits a lot of annoying vibrations and harmonics to the chassis (and to your hands/feet/butt/ears).

The exhaust hanger may have been a part of it, but I'd suspect the majority was the carrier isolater's condition. Either way, they need to be remedied.

[SDWA]

Yeah, that makes sense, I'd probably feel the exact same vibration, but at less intensity...

Anyone got a P/N for the rubber isolator?

[SDWA]

Anyone ever replaced the isolator? Dealer says you can only get the entire assembly - bearing, isolator & bracket as P/N 12472456... does that sound right?

Thanks!

[jharden1]

Anyone ever replaced the isolator? Dealer says you can only get the entire assembly - bearing, isolator & bracket as P/N 12472456... does that sound right?

Thanks!

I had this happen on my '93 TD. It was one assembly then, too. As I recall the isolator is molded on to the bearing and into the bracket.

[SDWA]

(while I'm trying to salvage the rest of my truck's issues...)

I need to replace the center driveshaft bearing. Actually, I only need to replace the rubber insulator, but apparently it's only available as an entire unit.

One dealer says P/N is 12472456 @ $99.18, list, and another dealer says that it's P/N 88934865 @ $127.58, list. Watched them both select the bearing from the parts screen.

They are both listed as bearings, but why the price and P/N difference? Can someone with access to a parts computer see what the difference is, and/or tell me which one is correct? If you need my VIN, just PM me.

Thanks!

[DmaxMaverick]

www.gmpartsdirect.com shows the parts for $58 and $75, respectively. You should contact (their email works well) them with your VIN to ensure you get the right part. They usually send me a diagram showing the part to confirm. Cross your fingers, it may be the cheaper one.

Rockauto (the other GM wholesaler) doesn't show either part.

[SDWA]

I watched both parts people use my VIN number to select the same entire assembly (I even verified it on the screen...) but with two different P/N results...

Scott

[DmaxMaverick]

I watched both parts people use my VIN number to select the same entire assembly (I even verified it on the screen...) but with two different P/N results...

Scott

I don't know. Both parts share the same description and application. The part number and price difference does indicate a significant part difference. Perhaps manual/auto? Try contacting gmpartsdirect. It's free to ask.

[SDWA]

It was the driveshaft center bearing... or more precisely, the lack of isolation of the bearing from the support assembly.

The rubber was so deteriorated that it wasn't too much longer until the entire bearing assembly would have started spinning inside the rubber. As it was, the cup that the boot clamps onto was almost resting on the lower half of the assembly. Replaced the entire bearing assembly with P/N 88934865 and the buzz is gone! :)

Scott

[NutNbutGMC]

Anyone ever replaced the isolator? Dealer says you can only get the entire assembly - bearing, isolator & bracket as P/N 12472456... does that sound right?

Thanks!Dang... memory lane. Bear with me. From memory recall and many lost (or archived) threads from here in 2002 and 2003, there is a TSB that will replace the two-piece shaft when a low-end shudder is detected. I'd chalk this up to ....you guessed it, ..... a low-end shudder while under load.

Maybe Dmax will elaborate or refresh my memory on this issue. I had a 2001, model that I had serviced under said TSB. Full warranty claimed under the TSB service allotment.


Just remember this if you get that far.... DO NOT allow a service tech to cut the cross-member that is adjacent to this 2-piece setup. They cut mine and that is how I arrived at the 2002. GM replaced the truck due to potential structural degradation. I had to force the issue. The TSB was eventually revised to stated, "Do not cut cross-member during replacement service...etc."

Just a thought.......

[DmaxMaverick]

Yes. The TSB does allow for a 2 piece to 1 piece replacement on some truck models. The crew cab long bed is not one of them. It needs to have the 2 piece (waaay too long single shaft), and they don't have the shudder problem. Extended cab short bed and regular cab long bed (and some other 4x4 requirements) were the models addressed by the bulletin. Others simply didn't have the issue. A worn out carrier bearing or isolator will shudder, regardless of cab/bed config.

[NutNbutGMC]

Yes. The TSB does allow for a 2 piece to 1 piece replacement on some truck models. The crew cab long bed is not one of them. It needs to have the 2 piece (waaay too long single shaft), and they don't have the shudder problem. Extended cab short bed and regular cab long bed (and some other 4x4 requirements) were the models addressed by the bulletin. Others simply didn't have the issue. A worn out carrier bearing or isolator will shudder, regardless of cab/bed config.
Not to dispute your knowledge, but I ..................ahhhhhhhh...never mind. It just dawned on me ....... I forgot that the one I had replaced was a standard cab truck (2001 model). Oops! My bad error. I have had a CC for so long, I forgot the standards were out there. :D

Thanks Dmax.....

:tiphat:

[Ryan03]

had a similar problem on my 03 reg cab duramax allison 4x4, around 40,000mi, the u joint at the rear axle was beginning to wear irregularly at the cross shaft that mates with the diff yoke, upon pulling the drive shaft, it was tough to tell anything was wrong until I removed the bearing cups and noticed that the cross shaft bearing surface was severely worn on each outside edge, although the wear was on the top side of one, and the bottom of the other, kind of like the torque from the driveshaft was trying to twist the cross right out of the bearing cups. I replaced the joint and the problem went away, however, not before I pulled the diff cover to inspect bearings and change oil, changed trans fluid and t case fluid, checed for exhaust clearence issues or broken hangers, and checked all the engine and trans mounts. that was 2 years ago, and truck has been fine ever since, I have also seen this problem on two other 2500hd 4x4s since mine, however both were 6.0s. hope this helps, good luck:)