Help! Noises after 4.11 installation!

[Skant]

I know this is a long post... I'd really appreciate anyone with ZF6 transmission or D44 rear end experience to read this and reply. Thanks in advance!

Previous thread was:

http://corvetteactioncenter.com/forums/showthread.php?t=44966


I'm not really sure what to do now...

I had a shop install 4.11's in my 1996 LT4 CE. They installed Tom's gears 4.11's in it and also did some replacing of various wear items in the rear end that they advised made sense to do as long as it was already open.

Ever since I've had it back, it makes a warbling whine sound at 65mph and higher when cruising (maintaining speed on level ground). It sounds like it comes from the transmission (might be telegraphing). Giving it more gas quiets it down a lot. Taking your foot off the gas completely quiets it down a lot (to nothing or nearly nothing).

I took it for a test drive with the shop, and they said since the sound stops when you push in the clutch, it must be on the input side of the transmission... mostly likely the infamous input bearing.

I'm not so convinced. The pitch of the sound varies directly with road speed, and is not altered by gear selection. Plus, I've found that under some circumstances, I can get it to make a little bit of the sound even with the clutch in. It is my observation that either throttle out or clutch in have the same effect on squelching the sound.

The shop believes I should have all of the bearings in the transmission replaced ($$$). They told me to take it to transmission only shop that they know for a second opinion if I'm concerned about their diagnosis. I did... the other place put it on the rack and listened with a stethoscope... they concluded that most of the noises were coming from the middle or front of the transmission. But they thought there might be some smaller noise from the rear end as well. The drive line is definately transmitting sound between the two, but they couldn't determine for certain which direction. But the noise was definately much louder at the transmission. They wanted to do a test with the driveline out to isolate the two and verify. They recommended that this might be done when the rear end was serviced (scheduled 900 miles after the install). They would talk to the first shop and exchange information.

When I talked to the first shop again, they seemed a little miffed that I was still doubting their diagnosis (and they do have the credentials and come highly recommended by other vette folks... but this is the first I have worked with them)... why can't I just believe it's the transmission? The rear end install, they said, went very well. And they spent a lot of extra time making sure the contact pattern on the gears was extra sweet for me. Further, they had talked with the second shop and discussed it and both come to the conclusion that it was the transmission.

They also told me that the car was making this noise on their test drive before the install. I don't know about that, but two of my friends have told me that indeed they think it was. It just wasn't nearly so loud. So maybe I just never really paid attention to it before. I'm really not too sure now. There's no way it could have been as loud as it is now... I couldn't possibly have missed _that_. Frankly, I don't want to strain my relations with my friends at this shop... so I don't want to really question their diagnosis. But I'm also fearful that it might be wrong, and it's going to cost me a lot of money to fix the wrong thing.


So... to add to this mix... today I took it in for the scheduled rear end service after the install. Everything seemed to go great. I noted that I thought the noise was quieter than it was before on the freeway. I'm not at all sure of that, but it seemed maybe a little better. Could easily be psychological... I had hoped that somehow changing the rear fluid might fix things.

So when I'm just about home, I turn around a corner, and it makes a moaning sound. Now anytime I turn sharply (make the differential work), it makes this sound. It didn't do that during the shop's testdrive before or after service. It didn't do that when I left the shop (and it would have). But after driving on the freeway it did.

Turn tightly... doesn't have to be fast. It's not intermittent. Happens with or without throttle (though I'm guessing a lot of throttle would stop it... by locking the tires totally together and spinning out). If you do it just right, it makes a very good impression of a big dog howling. Never thought my vette could sound like a canine.

I called the shop with my observations immediately. They said they didn't know what that was about. Advised me to check the obvious stuff (like power steering fluid, make sure it's not dumping fluid, etc) and then maybe drive it a bit more and see if it's a fluke or goes away with a little mileage. I can bring it in whenever I like.


So here I am... I have a lot of reasons to believe this is a really good shop that really knows its stuff. But my car has had these issues ever since they performed the mods on it. I guess it's just noise... it's not affected drivability so far... but it's not a subtle amount of noise. It's very annoying.

I really need some good advice here. I don't want to burn my relations with the shop. The most obvious course is to do as they advise... just leave it with them for a week or two and have the transmission done.. plus whatever else for this new thing? But what if they're wrong about the diagnosis? I've had people tell me it just has to be the new 4.11's.

But are the 4.11's having a problem? Or did the change just expose an issue with the transmission... and make sounds worse? Certainly, the driveline is spinning faster than before, so it's reasonable for it to at least exxagerate the sounds by that much.


And here I want to go to my first autocross on April 4th. If I take the car in to the shop, I'll certainly miss it. My friends at the shop advised me that I should probably run it in the autocross as is and then do the transmission afterward (might as well beat it up when you're about to rebuild it anyway). They don't believe the tranmission is in danger of failure any time soon... in fact, they recommend that if I can tolerate the noises, I should wait until it has another problem first.


I dunno. What do you guys think of all this? I'm feeling real uncertain of how to get to a good car. I feel like my vette has just been messed up now... and yet it's soooo fast. It really cooks with the 4.11's...

Maybe I'm just being freaky, and I really aught to just trust in the shop.

- Skant

 

[garycr14]

Tranny

You need to take it to a different transmission shop for a completly neutral opinion. I know the guys you are talking about, and I believe they are all honest people, but to for you to feel good about this you need another opinion. I recommend the following shop: Grant & Dans Transmissions at 37555 Centralmont Pl, Fremont. (510) 742-8726. Tak to Grant, he is a Guru when it comes to such things, I know it's a bit out of you way, but your car is worth it. And no, I have no relationship with the guy whatsoever. He fixed a rear end for me about 10 years ago, but he has been recommended to me by several car restorers in the bay area.

I also have my own theory on such things. Just like your own body, illness always finds the weakest link. You probably had some noise comming from your tranny as you friends have confirmed. A slight very change in a noise when you drive a car every day can go unnoticed. All of the parts in the driveline are the same age, and are weakening, even in a small amount. You put in a new rear end, which is stronger than the other components, now the weak link in the chain has additional strain placed on it, as does the rest of the driveline, so something else breaks. In your case could be the clutch, throwout barring, or maybe even the tranny itself.

Well just my theory, might be right, might be wrong, but either way the only way you will feel comfortable is to have another qualified opinion.

Good luck!

 

[Skant]

Well, just finished driving the car around for quite some time. And things have definately changed.

The warbling whine on the freeway has diminished substantially. In fact, my friend thinks it's about the same as it was before the 4.11 swap now. The range of speeds where it was audible has narrowed quite a lot. Now it's really only between 70-75mph... where previously is was pronounced between 65-80mph. And considering changes in driveline speeds, 70-75mph would have been 85-90mph before... which are speeds I never cruise at.

The new sound... this groan while turning corners... only happens when the car is warmed up after running on the freeway (does not happen when cold)... and can be made while going quite slowly... so I took a friend to a parking lot and went around him in slow circles. Even while inside the car, he believed the sound to be coming from the right rear wheel. And listening to it from outside as I circled, he was quite sure of it.

I have previously noted an occasional squeak from the right rear wheel at low speeds. It had been doing that for months. I haven't heard that now... perhaps it has been replaced by the new sound.

The freeway sound changed at the same time this new turning sound appeared. Is it possible that _all_ of this is coming from the wheel bearing going bad? Could it telegraph all the way to making it sound like it's coming from the transmission?

The notion seems to make sense to me. Initially, I hadn't really thought the sound was from the transmission area... it really sounded more like the rear... or omnidirectional really... hard to tell.

But in any case... right this moment it seems unlikely that the transmission is the actual culprit. The freeway sound seems to have been altered either by changing the diff fluid... or by the wheel bearing progressing to a more advanced stage of wearing out... Nothing changed in the transmission.


Gary: I really appreciate that. Depending on how the wheel bearing thing turns out exactly, I think I will be taking your suggestion. I do think the guys at the shop seem quite honest. If they're wrong about the source of the trouble, it's because it seems to be quite difficult to accurately diagnose the source of a sound like that.

But in any case, you're definately right. I need to seek a condition where I can feel confident about spending the money on some solution to the problem. I've been nervous about it because there are some symptoms that just don't seem to add up with the diagnosis. But now... I'm thinking the wheel bearing may add up correctly with all of the symptoms.

That may well be it.

- Skant

 

[Ken]

Well, at least you're thorough Skant. (Ain't you got a prettier name? I always think first of "Skank." :L)

... changing the rear fluid

it makes a moaning sound ... anytime I turn sharply

Are you sure of the mechanics working on the car. A shop is only as good as its mechanic, and if the mechanic is having a bad day ...

I've had my share of disappointments in people who came highly recommended, believe me. Maybe the guy forgot to add the GM Posi-Additive or similar. Maybe he didn't really check the lash as close as he's letting on. Maybe he did, and it's simply the gears developing their wear patern (breaking-in).

At any rate, I'd have to be throughly convinced it wasn't the rear end before I'd start into transmission work.

 

[Ken]

Gee, maybe I should read the entire thread before I respond, eh?

 

[Skant]

Another piece... with the car on a lift, I had recently noticed that the rear wheels had play in the 12-6 o'clock direction... maybe 1/16th or 1/8th of an inch. No play at all in the 9-3 o'clock direction. The front wheels had no play in them whatsoever.

I have read elsewhere that if there's any play in the wheel in 12-6 direction, it's a bad bearing.

Does this all add up?

- Skant

 

[WhalePirot]

Giving it time seems like it's working, to some degree. The moaning made me think of the posi additive, too, until I read from the manual.
The '87s GM manual (p.4A-5) says, ""noise most pronounced on turns-- differential side gear and pinion". It says elsewhere, that these components rarely give trouble. It speaks of a 'whirring or chattering' noise with improper lube Also, rear axle noises change with 'coasting' or 'pulling', unlike front bearing noise. Failing U-joints can make noise, too, but no noise at 10mph, coasting would seem to indicate they're okay..
The whining, sounds like gear noise, by GM's paragraph and your description. The characteristics vary, depending on how the shop set your rear grears, and with the noise diminishing, they are likely just wearing in, as the shop suggested. It is always possible to get bad parts, too. These noise do travel well in all that heavy metal.
I cannot find a spec for allowable 'wobble'. The best way I know to check is to pull the caliper and see if the vertical and horizontal wobble is the same. I cannot define excessive movement, but worn bearings will wobble the same, excessively, about both axes. The caliper restricts movement on one , so it must be off.
I wish I couild be more help, but more drive time likely will not hurt anything.

 

[BigRed]

Sealed bearings should have NO wobble in them.

When they start wobbling that doesn't exactly mean run and replace them either, just means they are getting worn out and the ball bearing to race marrage has gained a little ground.

Now when the "ground" has gotten to big, pieces of race OR ball' will stop the bearing from running smoothly.

Add this up over 60 MPH and you get a Whirrr or Whine or GROAN etc..

Change your wheel bearings and your U-Joints if this is at all in doubt.

The guy with the stethescope might not have heard this either because there was no weight on the bearing, therefore passing the buck over to the next loudest thing...the NOTORIOUSLY noisy ZF-6.

Personally Id lose the transmission from thought at this point (IMHO of course)

Now as for your friend noticing the problem before thats extremly possible. However is should not have changed due to a gear swap....wheels are still turning at the same speed.

If I were you Id go to GM or where ever and get a POSI additive and just throw it in yourself or by a neutral party just curiosity's sake.

Also a wheel bearing will ring out tone through-out the entire car the bloody sound is hard to diagnose sometimes where its coming from.

Thats where I would start..Bearings and U-Joints, If im wrong you got a new bearing package and you've eliminated the possibility. If Im right your a hero.

Hope that helps you

 

[Skant]

Thanks for the responses so far. I'm pretty well thinking it is probably the wheel bearings and/or u-joints at this point. I expect that the transmission really is louder than usual since the corvette shop says so... but I don't think it's actually the source of the really objectionable sounds on the freeway. And heck... the shop even recommended that if I could tolerate the noises, it's better to just leave the transmission alone and work on it when it develops some real problem.

I had scheduled to bring the car into the shop on Wednesday to check out/repair the noise while turning. However, I've realized that my first autocross is supposed to be on April 4th... a corvette only event, too. I've been wanting to get into autocross so bad, I really don't want to miss it. But if I took it in, unless the shop was done by Friday... I would miss it. They probably could finish it earlier, but complications will happen due to murphy's law.

Would it be crazy to just go ahead and autocross this car as it is? Just for my first autocross here. And then straight after, have the servicing done. Might as well thrash the parts I'm about to replace anyway, I suppose. Unless it's really in danger of coming unglued. But it's nothing but annoying noises at this point. No actual drivability issues.

Does that sound reasonable?

- Skant

 

[garycr14]

AutoX

I would say do the AutoX, then see what happens. It's supposed to be a very fast course this time, which will mean heavy on the straight aways, short on the turns. If something were to happen, we usually have a couple of people who trailor their cars that would drive it home, and let the broken car be a "trailor queen for a day". See Ya at the Races!

 

[Skant]

I took the vette to the shop today to show them this new sound while turning around corners. It looks like it's actually coming from tire rub.

Unknown to me, there had been a miscommunication... I had asked to have the front end lowered an inch... they lowered the entire car an inch. The rear tires can now rub against the inside of the wheel well. So warming it up on the freeway increases the tire pressure... and takes up the remaining clearance. Thus why it doesn't happen when the car is relatively cold.

They want to do a thorough inspection of the whole rear end now... including the wheel bearings and everything. I'm all for that. I mentioned my theory that the freeway noise might be the wheel bearings going bad.. so with everything, they want to inspect it good.

This car has stock tires, so I'm thinking that lowering the rear an inch shouldn't be causing wheel rub. So maybe a combination of worn wheel bearings and the lowering is doing it.

But also... I haven't had an alignment since the lowering. So I might expect.. if it's an inch down, that would cause a camber change wouldn't it? The tires would be tipped inward at the top. So maybe it's just a matter of needing an alignment (I've been waiting for the car to settle all the way before having this done).

Still... they're going to check out the whole rear end tomorrow. So we should know for sure what's up there.

Looks like I'll be at the races on Sunday. A little wheel rub isn't a critical issue.

- Skant

 

[Skant]

So I took it in... The owner looked at it on the way in and thinks the sound on the freeway is from the wheel rub, too. He commented that I should probably do nothing and just let it radius out the inner wheel wells on its own... it's already most of the way there anyway. He thinks the inner wheel wheel looks a little warped, and that's why it's touching. I think it looks a little warped, too.

He says it won't actually hurt the tire. He showed me on his own car that he uses for autocross where he's had 335's on all four corners, and he just let it rub out the inner wells. Didn't hurt anything.

So... I left it there for them to inspect it all. They've inspected it. They think the wheel bearings aren't in perfect shape, but are okay. They've checked all around the rear end, and they think it's good except for the rubbing on the inner fender. They're cautioning me about driving it. They're not totally sure about where the sound is coming from on the car, but they know the transmission is a problem, and think that needs to be dealt with first. They cautioned that it just might let go if I drive it more. But they seemed uncertain what was actually going on with the car now. It's real hard to diagnose where the sounds are coming from.

Myself... I don't think it's about to let go. It's been making the same sounds all this time and hasn't gotten any worse. And I haven't been soft on it at all. In fact, the sounds seem to be slowly getting better. Which really inclines me to think that most of it is just from that wheel rub... and it's going away as it radiuses out the inner wheel well.

I think I've pretty much gotten into 'I'm going to that autocross come hell or high water!' mode. I wanna race!

And then after that... we'll see. I'm leaning towards just dropping the car off with them and not taking it back until it's all good. Yet I'm resistant to having them go into the transmission while there's still any uncertainty. And it seems like the longer I drive the car and examine it, the more information is revealed about what's going on. I just don't want to dump thousands of dollars unnecessarily, ya know? This car only has 50k miles on it... it's too early for a ZF6 to bail...

I may go to that Fremont shop for that disinterested 3rd party opinion after the autocross. We'll see. I fairly expect that... surrounded by corvette nuts at the autocross... more insight may become available _at_ the autocross...

- Skant

 

[Ken]

... do nothing and just let it radius out the inner wheel wells on its own... it won't actually hurt the tire.

I had the same problem back in the mid-nineties; it worked itself out. :cool

 

[Skant]

Ken: Were your symptoms similar? And how long did it take? Thanks!

- Skant

 

[garycr14]

Idea

Skant, may I suggest that you replace the suspect tire with your spare, drive it and see if you still hear the noise. I assume you have a spare tire in your bay, or tucked in the garage somewhere. If not get another tire from somewhere and give it a go.

Good Luck!

 

[Ken]

Ken: Were your symptoms similar? And how long did it take?

Sounds, from what you describe, to be a similar situation. My inner wheel well liner was rubbing the tire on the inside edge. I never noticed when it quit making the rubbing sound, but if you look at the liner you can see where the tire wore a half-moon shape in the liner away. Mine must have been warped, or mis-installed, when it was repaired after the crash.

 

[vettered91]

Skant,

Immediately After I went from 2.59 to 3.54 in my dana 36, I did have those horrible canine loud sounds everytime the rear end warmed up. Every time after a short ride on the highway when I turned right or left to park there it was!!!

Two little bottles of GM Positraction aditive, (4oz each) and all my problems (wird noices) went away!!!

I hope it'll help you (almost sure) before you spend more $$$

 

[WhalePirot]

inner wheel well liner was rubbing the tire

Mmmmmmm, the smell of burning rubber!

I know it well, from lowering onto 315x17s and road dips.

Sounds like the seriousness has diminished quite substantially.

 

[Skant]

Thanks for the help, folks!

The friction modifier completely eliminated the noises it was making while turning around corners. So that problem is fixed. Thanks much for the advice about that!

Unfortunately, the freeway sounds weren't affected by that fix at all. That's a seperate issue. I've taken the car to two other shops for independent analysis of the problem. Both thought that it would be the rear end by the description of the problem... and both decided that the problem was a bearing going bad in the transmission after actually inspecting and road testing the car. So that's two corvette specialty shops and one transmission specialty shop that have all made the same diagnosis: Bad bearing in the tranny.

The diagnosis is consistent. Guess I can't argue with that. Time to empty out my wallet... :cry

- Skant

 

[warren s]

How do like the change to 4.11s?