clutch replaced on'96 LT4, now shifter vibrates more >4500rpm.

[dmd]

I've got a good bit more vibration in the shifter than I remember having before the clutch replacement. The manual talked about aligning the clutch cover to the flywheel when reinstalling, and there was a yellow paint mark on the cover, but since I had a new clutch and a used flywheel, there was nothing to align that mar to on the flywheel. Looking at the uneven spacing between the bolt holes, I crossed my fingers and installed the clutch cover in what seemed to be the only way. Did I miss something?

 

[Hib Halverson]

If you have vibration around 4500 that you didn't have before and the only thing you did was change the clutch, then the clutch is probably out of balance.

You need to remove the clutch and return it to the vendor and ask for one that is "neutral balanced".

 

[dmd]

If you have vibration around 4500 that you didn't have before and the only thing you did was change the clutch, then the clutch is probably out of balance.

You need to remove the clutch and return it to the vendor and ask for one that is "neutral balanced".

I spoke to the techs at Valeo yesterday and confirmed that I have the right part for my car, so I am back to trying to understand the mysterious paint mark on the clutch cover. Can anyone elaborate on its purpose?

 

[roger longman]

Why couldn't "the techs at Valeo" tell you, I assume it was from them you bought it ? Roger.

 

[dmd]

Why couldn't "the techs at Valeo" tell you, I assume it was from them you bought it ? Roger.

All he could do is confirm a part number. Not particularly helpful beyond that.

 

[G Winter]

Yours is an LT4 ? mine is an L98 in a 90 . My clutch cover had no such marks. Only alignment was the disk to the pilot bearing. Did you tighten the cover (pressure plate) bolts evenly , a little at a time all the way around ?
If not you can twist the pressure plate.
Another thing , is that flywheel used to balance the engine. On the L98 ther are 1/4 in pins placed in holes around the outside of the flywheel . When changing the flywheel you have to match the placement of these
weights to the old flywheel. I don't know if this is the same on the LT 4


Glenn

 

[dmd]

I don't remember anything like that, and after reviewing my pictures from the job I don't see anything like that either.

 

[G Winter]

Be Monday before I can do it but will take a pic of my old flywheel and try to point it out.

Glenn

 

[dmd]

 

[G Winter]

Now that I see your flywheel , I think my weight holes were around by the starter ring gear.
Don't look like you have them,so that shouldn't be your vibration problem.

One last thing. I talked to the ZF Doc early this summer and if the pilot bearing isn't installed perfectly straight it
It can cause a problem with misalignment . Don't remember what the symptoms are.

Glenn

 

[c4c5specialist]

HI there,
There is no mention of the balancing pins in the flywheel here.

They MUST BE SWAPPED FROM THE FLYWHEEL TO THE OTHER ONE YOU ARE INSTALLING>

IF YOU DO NOT< vibrations will occur.

As long as the pilot bearing and flywheel were installed correctly per FSM guidelines, you will be just fine.

Allthebest, c4c5

 

[dmd]

Let me be clear that this is NOT something I can't live with. If it won't hurt anything I would be happy to leave it as-is because of all the work to take it apart again.

Glenn, I have considered your input very valuable through all this, but I have to tell you that I am hightly skeptical of "zfdoc". His site is full of misspellings, grammatical errors and use of vocabulary which is in excess of his actual knowledge. These types of errors from someone who wants to be considered an authority are inexcusable and engender my distrust. I also think that the noises he describes as being problems worthy of having him rebuild your transmission for $5,000 are normal for the ZF and intended to take advantage of overzealous ZR-1 owners who think the neutral gear whine means it is about to explode. It's just noisy. Learn to appreciate it, or trade for a C5/C6.

Having said that, I yanked out the old brass pilot bushing with a slide hammer and pounded in the new bearing the only way I could: with a mini-sledge and a deep impact socket, until it was flush. If it had been even slightly crooked it simply wouldn't have gone in at all, those are hardened metals with tight tolerances. I didn't even dimple the bearing shell and I must've hit it at least 50 times.

As for installing the flywheel, it was keyed with a peg and would only go on one way. I torqued the bolts to spec in the star pattern, and installed the clutch cover turning each bolt one turn at a time in a star pattern as well, until it stopped, then I torqued them in a star pattern. It was painstaking but I know the price of cutting corners. I hope there wasn't anything else I was supposed to do.

 

[G Winter]

According to C4C5 specialist , who I trust , the flywheel is supposed to have the weight pins in it. I couldn't see the holes in your flywheel The flywheel I replaced on my 90 L98 had the holes , but no pins in any. So I didn't put any in. I have never noticed any vibration, and is smoother than it was before clutch replacement.
Did you replace the pilot with a bearing or a bushing ? The bushing you could cock in the hole. If this was the case I would think you would have a vibration or noise at low speed.The way you installed the pressure plate I can't imagine you caused a problem there.
I would be concerned about any vibration in the drive train. If you feel it at 4500 there is some at lower speeds.
Did you look at your old flywheel to see if it had the weights?



Glenn

 

[dmd]

Yeah, the old one had holes and pegs on the back. And this replacement flywheel came from a 90.

 

[G Winter]

Interesting, didn't know the L98 and LT had the same flywheel.
For all things to be right the weights should match. Not sure if you can cause damage from vibration.
We should be reprimanded for not making sure you knew that.
Glenn

 

[c4c5specialist]

HI there,
If you had pins in the L98 flywheel and didnt remove them, THERE IS YOUR VIBRATION!!!

Allthebest, c4c5

 

[dmd]

Thanks Paul, I figured that out. Didn't know they were even there when I had it all apart, neither of us had ever dealt with a DM flywheel that was balanced like this before. It would've been nice to know going into it, but it's done. What I need to know now is if I can live with it without hurting anything or if I have to park it for a couple months until I'm ready to do this job all over again.

 

[gmjunkie]

Thanks Paul, I figured that out. Didn't know they were even there when I had it all apart, neither of us had ever dealt with a DM flywheel that was balanced like this before. It would've been nice to know going into it, but it's done. What I need to know now is if I can live with it without hurting anything or if I have to park it for a couple months until I'm ready to do this job all over again.

It won't be very good on the Rod and Main bearings!!
I wouldn't run it that way!!

 

[dmd]

Okay, then how is it all the other less-fortunate LT1's and L98's out there that aren't so lucky as to be able to call the Corvette their home keep from tearing themselves apart without those weights? Is it not safe to say that this is just NVH tuning, because I don't feel it in the car, just the shifter.

 

[Hib Halverson]

(snip)"...because I don't feel it in the car, just the shifter."

Well....DUH!

You don't feel imbalance "in the car" because the powertrain is soft mounted.

As someone who seriously-flamed ZR51 Performance (the ZFDoc) for making statements which were...

"...in excess of his actual knowledge",

...I am astonished that you didn't know that.

Some basics for you
1) When you change flywheels on 89-96 L98, LT1 and LT4 engines you need to deal with the weights (those pins in the flywheel) in the manner that "c4c5Specialist" has suggested. Information on those pins is, also, in the 90-95 FSMs but, strangely, was omitted in the 89 and 96 books.

2) When you change to an aftermarket clutch, even units which are claimed to be "neutral balance" by their manufacturers, be prepared for imbalance. I never install an aftermarket clutch (ie: Fidanza, Centerforce, McLeod, etc) without having its balance checked.

3) Flywheel/clutch imbalance will peak between 3000 and 4000 rpm. The reason you feel it most in that range is a) humans' sense of touch/feel tends to be more sensitive to those frequencies and b) the car's structure tends to resonate at those frequencies.

4) The reason imbalance might be felt through the shifter (a buzzing sensation) but not through your butt is that while your imbalance exists, it's not bad enough to get the car's structure to vibrate. Because of the damping effect of hydraulic and rubber powertrain mounts, the amplitude of the vibration must be higher to be felt "in the car" than it needs to be to be felt just "through the shifter". I recently had a similar, but worse, problem with an aftermarket clutch in a C5. The manufacturer had made an error in its balance work leaving the clutch 40-grams out of balance, which is a ton of imbalance. Yep, you could feel it in the shifter for sure and, between 2500 and 4000 rpm, you could feel it and even hear it in the car's structure.

Now, back to ZR51 Performance, the ZFDoc...today, there are few engineers left at GM Powertrain who worked on the S6-40 and not many at ZF Industries, but there is a small group of rebuilders around the country who specialize in the transmission, and one is ZR51 Performance. Through the technical writing and service work I've done with the S6-40, I became familiar with Bill Boudreau, the "ZFDoc," about a dozen years ago. While it is true that Bill is not an expert writer or web designer, he is an expert on the ZF S6-40. The vast majority of information on his web site, while it may have misspellings or improper editing, from a technical standpoint, is accurate.

I am qualified to assess the accuracy of information on that site because few people, outside of those engineers from ZF and GM who developed the transmission during the late 80s and early 90s, know more about the ZF S6-40 than myself. I covered the engineering of the ZF six-speed extensively for magazines in the early 1990s. I did two long interview sessions in Michigan with engineers at GM Powertrain and at ZF Industries during 1992 with resulted in articles in "Corvette Quarterly" and "Vette" magazines. I've owned and maintained not one, but two cars with ZFs in them.

In 2000, Bill and I worked on an article about ZF service work and during the preparation of that article, together we disassembled, photographed and reassembled one of my ZFs along with several others he had in his shop. All this experience with the ZF S6-40 allows me to comment upon that web site's content.

ZR51 Performance, the "ZFDoc," is one of the best choices in ZF S6-40 service and rebuilding. In my opinion, the slanderous statements expressed by "dmg" that Bill Boudreau makes statements which are...

"....in excess of his actual knowledge"

...and that he is attempting to misrepresent transmission problems to unsuspecting ZR-1 owners with the intent to profit fraudulently, are so much shear speculation on "dmg's" part that they are laughable.

"Dmg" has no basis in fact to make such statements. What he posted about the ZFDoc is pure B.S.