Help! $6500 and 2-3 months in the shop... and the drive train whine persists...

[Skant]

Please... I know this is a very long description of the history of this problem... but particularly if you know corvette drive trains, I hope you'll read this.

I'm feeling stuck. I need help. At this point, I'm so frustrated that I'm starting to become tempted to sell my previously beloved vette.

Okay... here's what's been happening.

I had 4.11 gears (Tom's Gears) installed in the car along with a number of other mods. The shop that did it guaranteed me that they would be quiet (I've heard 4.11's are prone to whine if not installed juuust right).

Got the car back after the mods. The shop warned me that they were concerned about the transmission. It was noisy. And they didn't like the metal content in the transmission fluid they had replaced.

Followed the breakin instructions to the letter. The car produces a warbling whine sound cruising on the freeway starting about 65mph. Mostly present between 65-80mph. Loudest at 70-75mph. Letting off the throttle stops the sound. Giving it more throttle lessens or stops the sound. Pushing in the clutch stops the sound. The sound has a sort of omnipresence. The sound seems to come from the rear, but it is most audible near the shifter.

I took it back to the shop that did the mods. They did a road test with me and decided that, because the sound went away when the clutch was pushed in and because of the metal they had found in the transmission fluid, it was not the rear end. They say they spent a lot of extra time setting up that rear end, and it must be perfect. The transmission needs to be rebuilt.

I am not so certain. I take it to a transmission specialty shop and another corvette specialty shop for other opinions. For both of them, on explaining the problem over the phone, they thought it would be the new 4.11 gears. And for both of them, when they actually road tested the car (the tranny shop actually put it up on a lift and used a stethoscope, too), they agreed with the first shop that the noise was from the transmission.

The first shop also claims that the car made these sounds before their modifications. And two of my friends say so as well, though they think they may have become louder. I think if it was as loud as this, I would have noticed. But the sound may have been present (quiet) before.

Okay. Well, everyone seems to be in agreement that it's the transmission. So I have the first shop rebuild the transmission. Two months pass while they have it because they broke a specialized tool and had to wait for a replacement. Then, when they're finally supposed to be done, they call me and tell me I'd better come look at this.

The car is on the lift with its transmission and driveline removed. They tell me to rotate the flywheel back and forth by hand. It moves freely. It shouldn't be able to move like that. That's bad. They say they've never seen such a damaged flywheel and clutch. It gets worse... they show me in the partially disassembled transmission where there's a lot of metal shards in it. One of the dogs is missing a tooth. The shafts and certain gears are losing their hardness and need to be replaced. And they're not even all the way into it yet... already the cost of replacing the damaged hard parts is prohibitive. The transmission is too damaged all over to be worth rebuilding.

The idea here is that, for whatever reason, the springs in the dual mass flywheel have broken. So each shift is slamming hard against the drive train. This has done a lot of harm to transmission. Probably before I ever owned this car.

The shop bails me out by installing another ZF6... out of a 1992 (earlier style, straight cut gears)... for the same cost as I would have for rebuilding the one. Using the owners personal backup transmission for his car. But the flywheel and clutch must also be replaced. A single mass flywheel setup is actually _much_ cheaper than the stock dual mass, and it's more performant so I go for that option. So all this costs about $6500 and takes another week or so.

I get the car back... the transmission sounds different. Several noises have been deleted. The single mass flywheel makes it's rock grinding noises (they don't both me). However... the annoying warbling whine it made on the freeway remains exactly as it was. Not changed at all. Maybe a little quieter... maaaybe. But it's been more than two months since I last drove this car.

I take it back to them. They're surprised it's making the same sound. They still believe it's the transmission. I'm skeptical, but they tell me they're so certain of it that they're going to replace the transmission with a third transmission out of a 94 for free.

In a large way, I can't fault this shop. As expensive as it has been for me, they've been taking losses to do this stuff. An entire tranny swap for free is not a small sacrifice on their part. So I have to believe they are sincere!

Unfortunately, when I brought the car in for this, they said that the tranny appeared to actually be out of a 90 or 91. It was sold to them as a used 94. It has the older style shifter with the lockout, so it couldn't be a 94. They're doing the swap anyway.

When they're done, the warbling whine sound still persists.

They say they don't want to install a fourth transmission in this car. 'It must just be the nature of the beast'. So they've ended up calling it normal and letting it go.

So here I am. I can not believe that this is a normal sound. I drove two other C4's... including another LT4 like mine... they made a lot of the same sounds mine does... they made the sounds that don't bother me... but they didn't make this annoying warbling whine sound at all.

I have had three different ZF6 transmissions in my car. And I can say that each of them have had related but different characterstic sounds to them. Different personalities. Just by listening to them, I could tell you which tranmission was which. _However_, the warbling whine sound has remained exactly the same in each case. So I have a doubly hard time believing that all three transmissions are producing this exact same sound when all the other sounds they make differ somewhat.

I don't know what to do really. Maybe the obvious thing is that it's the 4.11's. My original thought. But if my friends are right, and it was making such a sound previously and it just got louder with the 4.11's... well... I don't know. The vette makes a lot of various noises, so I think that may be confusing.

My research on the forums shows a possible match for the wheel bearings or the u-joints. I have noticed, with the car on a lift, that I could rock the rear wheels in the 12 and 6 o'clock maybe 1/16th or 1/8th of an inch. The fronts do not have any such movement at all. The shop says they've checked my wheel bearings and they're fine.

I guess maybe what I need is a shop which really specializes in corvette drivelines that's somewhere near San Jose, CA to take it to. Or... just someone to turn to. Some super expert I could show the car to and they could say "Oh yeah, that's the u-joint on the left side."

The shop where I had all this done is supposed to be one of the best corvette specialty shops around. And, as much as they've failed to fix my problem, I think that they still are. They sure tried, and then some. I've just been in very bad luck. Plus, they did show me the old transmission and fly wheel and all... they were quite damaged, so the money I've spent so far is maybe not in vain.

I think the problem may be elsewhere in the driveline. Possibly also caused by the flywheel. If the jarring forces wrecked the previous transmission... they may have also done damage elsewhere. However, the shop said the rear end looked good when they put the 4.11's in. And they applied a rebuild kit to it as well while they were at it for the various wear parts (they recommended I do this since it wouldn't be much more expense and it would already be open).

Anyway... I'm just feeling pretty bad about all this. I've spent so much money on it, and the irritating noise persists. It makes me not want to drive my vette anymore. The noise is annoying in the first place, but becomes extra annoying with the emotional baggage attached. I'm so frustrated!

Any advice? Help? Please? If I can't resolve this somehow, I'll probably end up selling this car. It's my first taste of vette, and I liked it before. But maybe it's all just too expensive and problem prone for me.

- Skant

 

[Ken]

It's hard to believe that the Corvette shop's expert technicians, performing a road test of the vehicle, would not be able to pinpoint the location of the disagreeable noise. They should at least be able to narrow it down one step at a time until the cause is located.

The fact that the noise abates when you disengage the clutch makes me think that it's in the flywheel/clutch assembly area, possibly the throwout bearing.

I don't know if you remember, but I spent quite a bit of money trying to get my overdrive to function correctly on my 4+3, to the point of installing a rebuilt unit which I immediately trashed. The root cause for the overdrive malfunction was a fifteen dollar relay, which none of the so-called "technicians" could find.

Hang in there, we have a lot of LT-4 owners who'll be able to help ya Skant, including shop recommendations in the San Jose area.

 

[Skant]

The fact that the noise abates when you disengage the clutch makes me think that it's in the flywheel/clutch assembly area, possibly the throwout bearing.

Three different shops pointed at the transmission as the culprit for this reason. But it's been replaced three times with no success. So it seems to me that it's a red herring. And the diagnosis of this particular problem is a tricky one.

Some aspects I forgot to mention above which are likely pertinent... The pitch of the warbling whine varies directly with road speed. It is unchanged by gear selection. It only occurs under a slight load... exactly the load needed to maintain speed (it's warbling sound is continuous under cruise control on a level freeway)... letting off the gas pedal and pushing in the clutch both have the same effect on quelling the sound. I think pushing in the clutch may be a red herring pointing to the transmission just because... like letting off the gas... it also removes the engine power from the equation... which also quells the sound. On occassion, I've heard a quieter burst of the annoying sound even with the clutch pushed in or gas pedal totally out.

I think that's the really tricky part about it... it requires speed and specific throttle and specific load to make it happen. Unfortunately, the particular combination that does it is the most common one! So it does it pretty much all the time while crusiing on the freeway.

The transmission itself makes a much higher pitched sound which is quieter and solid and doesn't really annoy me (and changed slightly with each of the three transmissions). In fact, it's about two octaves higher than the annoying warbling whine sound which sounds to me like it really comes from the rear. That makes sense to me since the transmission output and driveline are spinning 4.11 times faster than rear end. Two octaves = 4x the frequency. (I'm a musician on the side...)


Hmmm... I seem to have convinced myself that the annoying sound is coming from either the pumpkin or something after it. I've thought that since the very beginning, actually. And particularly now since everything between the engine and the driveline has been replaced at least once to no avail. But then, I'm not a qualified mechanic.


Thanks for the encouragement, and your example. I need to feel some hope that this problem will be solved. I guess sometimes diagnosis is very tricky.

- Skant

 

[Ken Anderson]

EVERY symptom you initially described pointed to the differential! And your story gets worse & worse re: the transmission debacle. Some experts these guys are.

 

[taegdh]

I agree with the diagnosis that it is driveline or differential related! When the noise changed with the speed of the car and not the rpm of the engine or transmission, that is the big clue.

From what you've listed, in the back of my mind I wonder if the ring gear is properly aligned. If it isn't evenly aligned you'll get the rough noise. I'd also check the carrier mounts, if the input to the differential is out of alignment, horizontally or vertically, to the output of the transmission, noise and other problems are bount to rear their ugly heads, and it doesn't take much, just a degree or two.

Just a thought!

 

[Ken]

What gets me is the fact that none of these so-called "experts" were able to determine this noise, and its origin, while riding or driving the car on the freeway, where you say the noise is always evident, as well as being most noticeable.

 

[Chas]

I had a noise too....

I went to a trans shop that has done work for me before , on a 4x4 truck and a 86 Camaro...the guy has always done a good job for me in the past, so i had no reason to fear going to him with a really nasty noise in my rearend.
The first time it happened was a week following the CAC cruise fest.I drove it about 5 miles during the week following and then came saturday and a local show. i was basically ideling down the street and it sounded like i ran over a cinder block , and thrn rolled it under a few times. It seemed to change the speed of the car, im not sure as i hit the brakes and it didnt happen again as i went home and parked it. monday morning i go to the shop, didnt hear the sound at all. he drove it and didnt hear it , so he put it on the hoist and said the U-joints on the passinger side were toast, and the emergency brake was falling apart. he fixed the joint and removed the e-brake....i have an auto trans so i dont use it anyway. i then took it to a friends brake shop to be sure it was done right. he finished the job on the brake and told me that on the hoist with it in gear he could hear bad things in the diffrential. i told him about the work i had done and he said he felt the guy was doing a good job on cars but this is a Corvette and maybe he didnt understand the thing .
he told me of a diffrent shop that he had vette work done at , and personally knew this guy. the new shop puts my vette on a rollback truck and takes it to fix. seems the ring bolts had backed out and had trashed the insides, rendering the core worthless in the process. he told me i had a 308 gear, and now is the time to change if i want. he told me the same things about the 411 gears that you stated, and said a 355 would be really sweet and not loud at highway speed. he also was able to change the gear and calibrate my speedometer. it runs great and i love the way it snaps now. i was running 2600 rpm at 70 mph with the 308...now im at 3400 at 70...and its wound up tight and ready to go. it dont make noise that i can hear at that speed either.
so my point is, maybe the guys just dont know the thing. this is just my experience. this ordeal cost me $2200 to finish. i lost the core deposit. that is my only real regret.that was $300 im out. i hope this works out for you soon .
good luck.
Chas

 

[sothpaw]

Skant,

I'll have to agree with the others--it's the diff. I have had that whine (I call it a high frequency burble) for over 30 k mi now in the stock diff.

The key characteristic of mine is it's speed dependence. It is not present under 50mph. It is present in every gear regardless of rpm. However, it is most noticable in 6th while cruising at 60-70 mph since the engine is pretty quiet at the low rpm in 6th.

 

[tlong]

I can relate to how you feel. I have a suggestion. Could you put this up on a rack, jack the rear wheels up a bit and take it up to 70? It would be easy to literally put your finger on it then. There would of course be no load but a bad diff would still probably sing its ugly song. Just an idea.

 

[Skant]

What gets me is the fact that none of these so-called "experts" were able to determine this noise, and its origin, while riding or driving the car on the freeway, where you say the noise is always evident, as well as being most noticeable.

To think of it... the transmission, clutch, and flywheel really were damaged. Three seperate shops did successfully diagnose that problem from driving car and listening to it. It was still working okay at that time, but catastrophic failure was on the horizon.

Replacing the transmission did eliminate several sounds it was making that had never really bothered me. It just didn't eliminate the particular really annoying sound I had brought it in for.

Maybe it's not so unreasonable for them to figure that... if the tranny is bad... it could easily be making all of the bad sounds. That needs to be fixed first before casting blame on any other component.

However...

Once that was taken care of and the freeway warbling whine noise persisted anyway... methinks they should have turned back to the rear end again rather than just giving up on it and leaving me with a car that I don't enjoy driving anymore. The shop that did the rear end is so certain that it was perfect that they won't accept that the fault could be there.

Maybe I should take it to the other two shops again and see if their '2nd opinions' are different now that a dying tranny should no longer cloud the issue.


Or...


I think what I really need now is some shop near San Jose that really knows how to do 4.11's in a vette. A shop that can positively diagnose this drive line issue and that can eliminate the problem... whereas I know that installing 4.11's without a whine is difficult, and takes a very good shop to manage it.

You see... part of the problem is that I've been driving this LT4 around with 4.11's in it... it's really crazy fast. I... can't go back... even 3.73's aren't going to feel satisfying to me now... I must have 4.11's without a whine.

So... anyone know a shop that can do this which is located within a reasonable driving distance from me?


Also... I imagine that redoing the 4.11's means completely redoing them. They can't just adjust the previous gears or anything. It would have to be an entirely new set?

- Skant

 

[Vettelt193]

what kind of fluid do you have in the diff and the tranny?

Many times, swapping to a better (synthetic) fluid will help take care of odd noises. If you don't have a good synthetic in there already, try red-line or other... i have heard excellent things about them. I usually stick to Mobil 1 products, but if I were in your situation, I would spend the $$$ on red-line before rebuilding the rear.

 

[Skant]

Vettelt193: The transmissions have been using Redline MTL. In the 3rd transmission (the one that's in the car now), they switched to Redline MT90 on Redline's recommendation that the heavier oil may quiet noisy ZF6 transmissions. But it didn't help. And actually, I think this 3rd transmission may be a little noisier than the 2nd one. I wonder if the MT90 could actually be worse for noise. But... anyway... those noises aren't a big deal.

For the rear end... hmmm... *checking my log book*... ah... Redline 75w-90 was used. I was instructed to bring it back to have the fluid changed again after 800-900 miles. I did so. At that point... I don't seem to have recorded this in my logbook... but I remember the freeway warbling whine sound actually stopped almost completely for a couple of days... but it was replaced instead by a different problem... it started moaning when turning around corners after it was warmed up. And then the freeway whine came back, too. So it had both noises.

The rear diff fluid was changed again, but that didn't eliminate the moan. Then one bottle of GM friction modifier was added, and that eliminated the moan entirely. The freeway warbling whine remained with no change.

Supposedly, the Redline fluid should not need the friction modifier.

If there's a chemical solution to this problem, I'd sure love it. But I suspect I'm already using the very best chemicals.

- Skant

 

[taegdh]

Got a question, Does this have Posi-Traction / Limited Slip Differential?

If so, you may want to also have that checked out. Toward the end of their lifetime expectancy, when you have clutch facing material starting to crumble, you get the axles wanting to be "locked" all the time, which could also give strange noises as you described.

You gotta check it all out..... You don't need to loose the rear-end when you're out on the highway by your lonesome at O'Dark thirty.

 

[Moonunit 451]

Vettelt193:

For the rear end... hmmm... *checking my log book*... ah... Redline 75w-90 was used. I was instructed to bring it back to have the fluid changed again after 800-900 miles. I did so. At that point... I don't seem to have recorded this in my logbook... but I remember the freeway warbling whine sound actually stopped almost completely for a couple of days... but it was replaced instead by a different problem... it started moaning when turning around corners after it was warmed up. And then the freeway whine came back, too. So it had both noises.

The rear diff fluid was changed again, but that didn't eliminate the moan. Then one bottle of GM friction modifier was added, and that eliminated the moan entirely. The freeway warbling whine remained with no change.

Supposedly, the Redline fluid should not need the friction modifier.

If there's a chemical solution to this problem, I'd sure love it. But I suspect I'm already using the very best chemicals.

- Skant

Red Line does make two diggerent 75-90 rear end lubes. And to read about them on there site I found very confusing. This business of "limited slip Posi Track" blew my mind and still does. I thought you had one or the other type of rear end.

At any rate the dealer gave me the wrong one when I installed my D44 and I quickly developed the grinding when turning that you described. It went away immediately when I put the right fluid with the additive in there.

I'm running 3:33's so I can't really relate to your main problem, but perhaps a fluid change, being certain that the right fluid is added would be a cheap place to start. Heck you might even just throw in a bottle of the additive for about $5 from the dealer and give that a try. Good luck Skant

 

[rrubel]

I have a similar whine in my non-Vette daily driver. It varies directly with how much throttle I give it, being most noticeable when just cruising. I'm told it's the bearing where the driveshaft enters the rear diff. I'm also told it's not really worth worrying about; I have over 100k miles with this issue and, while mildly annoying, there's been no big mechanical problem.
[RICHR]

 

[DkBG]

Hi Skant . First of all , let me tell you that your read end was built in the factory where I spent 30 years . I don't know much technical stuff as my job wasn't in that area . But , I can tell you that making ring and pinions run quietly is the hardest part of the differential business . It's a constant battle that continues right out to the assembly lines . Lapping changes and shimming adjustments are made all the time . What worked on the last 2000 units might not be good enough on the next 2000 . I'm not familar with Toms Gears but even if they do everything well and even if your installer does his best work you could still end up with noise . It's a real problem in the industry . Lightweight carrier assemblies , unibody construction , the stiffer parts mounts , quieter interiors and other such things can all make noises seem louder than they were in the old days . I'd look around for someone who specializes in differential repair and ask him to check it out . And by all means , go ahead and try some different lubes . Little things can make a sound difference . Cliff

 

[Ken]

To me, it's no big deal - I love the sound of straight-cut gears! I actually miss the sound the old Buick manual transmissions used to make.

 

[Skant]

Well, it sounds like the only remedy is to get it redone by a shop that really specializes in rear ends. So can anyone recommend such a shop anywhere near San Jose, CA?

- Skant

 

[Ken]

... can anyone recommend such a shop anywhere near San Jose, CA?

I'm really surprised that no one has spoken up yet with a referral for you.

Hang in there, we have a lot of LT-4 owners who'll be able to help ya Skant, including shop recommendations in the San Jose area.

 

[SPANISHVETTS]

I am a bit late popping in on this but here is my $.02 worth anyway. I have never seen a set of quiet 4:11s after they have a few thousand miles on them. Even the ones from the factory start to whine while they are still ¨new¨.

The 2nd thought about 4:11s is the daily drivability; it is almost as uncomfortable as driving around town with a 3000RPM TC. Of course if your daily driving is on the strip with an 8000RPM engine and close ratio 4 speed the 4:11s are the way to go.