imflyn

iTrader: (2)

I found this answer on gm-trucks dot com.

Subject: Information on 2-3 Upshift or 3-2 Downshift Clunk Noise #01-07-30-042D - (05/16/2006)



Models: 2007 and Prior Passenger Cars and Light Duty Trucks

2003-2007 HUMMER H2

2006-2007 HUMMER H3

2005-2007 Saab 9-7X

with 4L60-E or 4L65-E Automatic Transmission (RPOs M30, M32)




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This bulletin is being revised to add the 2007 model years and include passenger cars. Please discard Corporate Bulletin Number 01-07-30-042C (Section 07 - Transmission/Transaxle).


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Important: For 2005 model year fullsize utilities and pickups, refer to Corporate Bulletin 05-07-30-012.

Some vehicles may exhibit a clunk noise that can be heard on a 2-3 upshift or a 3-2 downshift.

During a 2-3 upshift, the 2-4 band is released and the 3-4 clutch is applied. The timing of this shift can cause a momentary torque reversal of the output shaft that results in a clunk noise. This same torque reversal can also occur on a 3-2 downshift when the 3-4 clutch is released and the 2-4 band applied. This condition may be worse on a 4-wheel drive vehicle due to the additional tolerances in the transfer case.

This is a normal condition. No repairs should be attempted.

Ralls

iTrader: (32)

Normal my ***. It's so annoying.

imflyn

iTrader: (2)

Well, at least now you know what is causing it. I always thought that was what it felt like when I was driving, just a brief torque reversal. I guess if any of the tranny guys know how to prevent the overlap you could get rid of it, but maybe at the expense of slower shifts, thus reducing performance at WOT?

BlackHawk T/A

iTrader: (3)

That is a good term for it...pretty much what it feels like. The thing is, my stock transmission didn't do it at all at 76k (trans was actually perfect), and neither did the new one until it had a few miles on it.

I'm starting to think it comes down to tolerances. But why it took a few miles to develop on the built transmission I don't know.

performabuilt

iTrader: (25)

Built transmissions like the stock unit clearances change in the first while , I have had the opuritunity to actually measure the clearance on the 3-4 clutch pack of a unit that has been driven 1000 miles and was returned to be checked out due to a tail housing that had broken as a result of a bad mount , The unit was perfect but I built the unit myself originally and when assembled it has a clutch clearance of .020 that was after being appied at 250 ps1 3 times which is how we set clearance, We do that to get a truer clearance. But after the 1000 miles with no sign of burning or slipping the clearance had increased to .040 so the frictions do compress with time. Which is the reason we use such a low clearance to begin with . I know that you can actually go from .010 to .020 simply by applying the set at 250 three times in some cases reguardless of clutch type when new and dry. The clunk actually happens because the band may release just a tiny amount before the 3-4 clutch can get on , this as the bulletin states can cause a momentary reversal or slack in the internal gear train which will cause the clunk .The clunk dosent hurt anything but agreed can be anoying. Now in exstreme cases of excessive clearance 3-4 or to large a release feed to the servo you can get and actual rev bump during the shift. I will say though I have never noted either of these conditions with the super servos.Not to say it cant happen just have never noted it.

Ralls

iTrader: (32)

Well if this is the problem, which sounds completely plausible; how could my chassis mounted torque arm create it? Do remember, this started happening the second after I installed the torque arm.

performabuilt

iTrader: (25)

Well you are completely changing the way the shift shock is distributed , before this play would have been absorbed to some exstent through the arm and rear end bushings etc Now its strickly through the driveshaft gears and AXLES no cushion there so it would tend to amplify the affect I would say considerably you would tend to feel the drive shaft stop the pinion then catch up and hit the gear again in a much more noticable way. You have to bear in mind that GMs design was only partially performance thought out but many things they do are to hide the little bumps and clunks as they are called for the drivers comfort.

Ls1Envy

iTrader: (6)

I have the same thing after installing a rebuilt tranny, shift kit, and used rear end. The clunk transmits from the tranny into the rear and is only done at low throttle 1-2 shifts and sometimes 2-3. I may just be my shift kit though and worn out auburn. It's a little too harsh for my likieng(sp?).

performabuilt

iTrader: (25)

Holler a me in private and ill help you decrease it some anyway

BlackHawk T/A

iTrader: (3)

Would changing from a poly mount back to stock rubber help some?

Or can you tweak the clearances again after it's been driven and developed this clunk?

Good information so far. I'm glad one of these threads is finally going somewhere.

performabuilt

iTrader: (25)

Changing back to the stock type mount may help some anything that increases isolation could help. And Im sure you could do some tweaking would be a bit of hit and miss though and considerable work

RevGTO

iTrader: (12)

I just added a little lube to the rear u-joints ... it eliminated the "clink" that used to accompany the "clunk." I've also found that tuning for faster 2-3 shift times is better for this problem than slower ones.

The latest TSB is just an updated version of the same info from GM that I posted in an earlier thread. It sounds like we can cushion the effects of it somewhat, but it is not internally serviceable.