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I've had the clunk in an 89 C1500, a 92 C1500, a 99 Yukon and now I have it in my 01 2500 HD with the Allison.

 

I had thought all along that the problem was in the 4L60E/4L80E transmissions but now that it's shown up in my HD with an Allison I'm not sure what could be causing it.

 

I went to the dealer on Monday and they said the nickel plated yoke fix doesn't apply for the Allison.

 

Funny thing was as I was telling my story to the girl writing up the service request she just blurted out "That's normal".

 

I said, "You don't even know what type of truck I drove up in. How can you say it's normal?" Then I told her what type of truck I had and she decided she'd better get the Shop Manager involved. She was well trained to spout out the standard disclaimer.

 

When I started discussing the transmission with the Shop Manager she said, "It's not in the transmission, it's in the drive train."

 

I said, "The transmission is an integral part of the drive train." I wanted to slap her into next week.

 

Anyone heard of any TSB's for an 8.1/Allison 2500 HD with the "clunk"?

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How many miles are on the truck?  And do you have a one- or two-piece driveshaft?  How about U joints?  

 

Fitz

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And if it makes you feel any better, I had a girl (she wasn't old enough to be a lady) at the service counter at my dealer tell me that warm spark knock under load was "normal . . . "

 

I just asked to speak to the tech who was going to work on the truck . . .

 

Stupidity knows no bounds. . .

 

Fitz

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This vehicle has been like all the others.  I can first detect it around 10k miles and right now it has 19,755.  

 

It's got the two piece drive shaft.  U-joints are in perfect condition.  It's been babied and pampered all it's life.  I'm crazy about the truck but a clunk thats been going on in the GM product line since 1988 is bordering on the absurd.

 

I don't now what it is... every where I go if there's a gal behind the counter, I always get her even when I go to the other end.  I wouldn't mind this but they NEVER know anything.  They always have to go ask "Joe".

 

I'm not sexist and I know some women are knowledgeable regarding mechanical systems but not the ones that wait on me!

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I don't get the clunk while I'm driving but occasinally, I get a real loud one when I stop and put it into Park.  Sometimes I get another loud one when I put it into Drive after parking it.  The two don't always coincide either. (clunk on park does not mean a clunk on drive).

 

I never gave this much thought as I know a lot of 'larger' trucks with automatics make these kind of noises.  

 

I am by no means an expert, but if you have a 4x4, could it be something in the hubs?

 

bummed...

 

'02 8.1 Allison  Crew cab 4x4 (18,000 miles)

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I agree w/ bummed the allison is a commercial tranny and has a lg parking pawl.  My does the same thing when going from park to drive and vice versa on a regular basis.  I ask my dealer and he said it was typical of the tranny.  Lucky for me I have nothing but good things to say about my dealer he has bent over backwards and has solved all my problems on the first try. :cheers:

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This vehicle has been like all the others.  I can first detect it around 10k miles and right now it has 19,755.  

 

It's got the two piece drive shaft.  U-joints are in perfect condition.  It's been babied and pampered all it's life.  I'm crazy about the truck but a clunk thats been going on in the GM product line since 1988 is bordering on the absurd.

 

I don't now what it is... every where I go if there's a gal behind the counter, I always get her even when I go to the other end.  I wouldn't mind this but they NEVER know anything.  They always have to go ask "Joe".

 

I'm not sexist and I know some women are knowledgeable regarding mechanical systems but not the ones that wait on me!

Hey man, dont limit idiocy to just women.

 

I dont even know how many dumbass Service Mgrs ive spoken to.

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There are TCM updates that address 1-2 and 2-1 shifts with the Allison, which can sometimes result in a clunk. I don't think there's a TSB for it.

 

Describe your clunk a bit more- when does it do it, taking off from a stop, or when stopping? Does the transmission seem like it's not fully engaged in a gear, then clunks into gear? If so, you need the TCM updates.

 

Driving two footed can also screw up the Allison's shifting characteristics.

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There were 2 TSB's for my vehicle

 

01-07-30-034 Escessive Shifting while using Cruise Control and Towing.

 

02-07-30-020 Harsh or Delayed 2-1 Downshift, Neutral feel at a Stop, Shift Busyness.

 

I had all the reprogramming done.  The clunk is still there.  It wasn't there when I first left the dealers but as it warmed up I could begin to feel it coming back and by the time I got home it was back to the usual.

 

As I am stopping, right before I reach a complete stop I can feel a clunk in the drivetrain.  And as I start off again it happens.  It's like there is some sort of slack or play in the drivetrain.

 

Another symptom occurs when I am backing out my driveway in the morning.  When I shift from reverse to drive it shifts very hard.  It's like I had increased the rpm's in neutral then dropped it into drive.  I'm not doing that but it feels like that.  After it warms up everything is fine.  This may have been solved by the reprogramming.  I haven't driven it since I had the reprogramming.

 

Dihappy, I'm definitely not limiting idiocy to women.  It's just that I have yet to meet a knowledgeable one behind a parts store counter.  And yes, I've met lots of stupid guys behind the counter but so far the gals are batting 100%.  What I can't understand is why I always get waited on by the woman.  I must be a "dumb babe" magnet

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I started getting the clunk at about 75000 miles and at 77000 my 4L60E flew apart. I talked to AAMCO and they said that what broke in mine is a weak link in the tranny. Don't matter if it's 4 or 2 wheel drive. The Mechanic told me he had never seen on come apart like mine. I was turning about 5000 rpm when it hit 2nd gear and all H##L broke loose. But the truck next to mine was driving easy when his broke. Not as much damage to his as mine but total rebuild anyway. I'm still without my baby but hope to have her back next week.

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It's the weirdest thing.  All mine started around 10k.  My 92 had 206k when I got rid of it and had not had any problems other than being irritating.

 

I thought sure it was the trans and by going to the Allison I would not have to deal with it again but...

 

I'm getting my wife a video camera for Christmas.  I think I'm going to tie it up under the frame and see if I can spot what's moving.

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:angry: I have a 2002 1500HD with this problem, and they tell me there is no fix for the two piece drive shaft, or the slip yoke fix either. Is there any one out there with help for me to take to the dumd A$$ dealer.

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Well I had the Mech. Locker (G80) installed in the Diff. and then started to hear the clunk as you have explained. It never made any noise with the open diff. I also had the same guy who sets up the rears for my drag car do the install, so I know the install was done correctly. I didn't trust the dealer to do it, if it is beyond changing a fuse I don't bother going to the dealer, I either do it my self or take it to an expert. I even had it back so it could be checked out, and was told all clearances were dead on. He added that Eaton’s have a tendency to make noise.

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