Good evening...

My 95 Z28 has developed a strange vibration when it shifts hard from 1st to 2nd. It feels alot like wheel-hop to me...a 3-4 second vibration from the R rear wheel. Up until 3 months ago, it would chirp at anything over 1/2 throttle, or grab hard/slightly fishtail at WOT during this shift.

Last weekend, I put it up on jack stands, hoping to find a dead shock, missing torque arm bushing or lower cntrl arm bushing, but everthing feels tight and the rubber seems intact and shock still has it's gas charge. Also checked all the mountings on my SLP subframe connectors, but everything was secure.

I'm starting to lean toward the differential failing, but it's not making any noise whatsoever and drives perfectly at part throttle. When it's raining, it will spin the R rear tire w/o any vibration or noise (ie..just like normal)

My questions are:

1) Who has had these same symptoms and were they related to the OEM differential failing..?

2) What ways would you suggest to test it further..? (I'll pass on the 'Go peel out and see what it does' advice)

The history:

95 Z28 A4 (bought with 42k miles, now has 90k)
SLP Subframe connectors
Factory 10-bolt 2.73
Kuhmo 712's on 17x9.5 rims

Nothing has changed on the car in the last 8 mos, never abused, never run slicks/drag radials, changed fluid/additive regularly. Thanks for you help...

 

first I would look at the trans mount real good make sure it hasnt split it apart.

2nd try to maunally shift the car from 1-2 my car broke a piston in the trans and it shuttered from the 1-2 shift. and wasnt as bad if I maunually shiffted it.

If neither of them are the case I dont know.

 

My trans developed exactly the same symptom - a harsh vibration or shudder in the driveline on some full throttle upshifts. It was bad enough to trip the low traction light. The shop that had originally overhauled and modified the trans, pulled it apart. The forward clutch apply piston had developed a radial crack that lowered the shift pressures, and that allowed the band to "slip-stick" during the shift, causing the shudder. I knew the first time it happened that it was probably the band, but I had no idea how. Now I know. The piston (stock aluminum) was replaced with a steel one, as was the sun carrier shell, or whatever it is called. No problems since.

 

I started to have those symptoms, then there was a knock everytime i accelerated hard. turned out to be tranny mount. Easily fixed. 28 bucks at kragen, one hour do it yourself labor

 

I had the exact same symptoms. Thought mine was the tranny mount also. So I bought a new poly one. When I checked it out the stock one was just fine. Turns out my tranny was shot. I bought a used replacement from someone on here and everything was just fine. Installed th poly mount at the same time just in case. I've never had the original tranny taken apart to see what's wrong with it but I was told the main drive gear had some teeth broke off. The reason was if I was driving around in 1st gear and let off the gas. Instead of it doing the normal engine braking like all cars do the idle would go back down like I pushed in a clutch. I was told it was because that drive gear was allowed to turn in both directions instead of just the one like it was supposed to. Also after some real hard 40mph floor stompin' downshifts the clutch bands couldn't hang. I was waiting as long as I could until the tranny died. I went with that shifting "shutter" for months. The car shifts much much better now.

 

Thanks for the responses...

I've replaced my tranny mount before, due to a loud 'thump' right under the console, and it's something I looked closely at when I had it up in the air, so I don't think that it's it...

I've also got only 35k miles on this tranny (done by a reputable guy locally, who also put in the Trans-go..see sig), so I don't want to belive that's related...

Also the noise seems to originate from the right, rear side of the car...and each time it does this, it throws any ABS Inop light...which must mean it's detecting a wheel sensor that's not agreeing with the rest. I've got no guess if this means the R rear is really hopping...or if the L rear isn't balancing the load like it should on a posi-track RE....

I apprecite the thoughts thus far.....

Anyone else been through this..?

 

You might have a caliper acting up. If I'm correct I think the rear calipers on our cars are known for locking up. Both of my rears did within months of each other. I had my passenger rear lock up and couldn't afford new calipers and rotors since I needed and wanted to do it all at once. So I just let it go. A couple months later the other one did the same thing. The second one could have failed because the first did I don't know, but I do know the first one failed on it's own. I replaced them with used ones I bought from someone else and they work just fine. Plan to upgrade to a whole new slotted 4 piston setup on all 4 before spring. Also I think that would contribute to your abs inop light. I'm very vague at remembering this but I think around the time my tranny was acting up it did the light also though. Just check the cheaper things first I guess. Hope it's nothing major

 

Unique, I think your problem is exactly like mine. The ABS light is what happened to me as well (low track or something like that), caused by the vibration in the ring gear as the trans tries to lock up and chatters the driveline. It is isn't a wheel brake. And the noise did appear from the centerline and the right rear, but that is just because you sit on the left. Because it occurs during the shift, it can only be tire shake or the trans, and it isn't tire shake. When it gets worse, and it will, you will be pulling the trans. My trans had only 15k on it when this problem occured, and it has the trans-go kit in it as well. Then it came out again. The problem is unrelated to the trans-go parts, although stand by for some to post that it is. The piston failure is a GM design fault. Also the these cars have 3 channel ABS, so it is the entire rear axle, and not a side to side variation that trips the light. The front wheels are individual.
It seems on these cars it is rarely the simple stuff. I wish it was.

 

Thanks, Vader...

I wish I knew the name of the broken piston (size of a saucer (3.5" wide x 1.5" tall) that was replaced with the first tranny rebuild, as it broke a hard part inside when the first failure (22 mos ago) occurred.

Although I really want to believe it's the rear-end, I've twice encounted some slippage when punching it on a corner (much like when you're low on trans fluid), which makes it hard for me to buy the problems all in the differential...

I'm not rear-end expert, but I don't believe there's any way the differential can slip and cause the engine to spin up like it's slipping....by it's own design, either it works or it doesn't...since the gears are always interlocked, and the clutches only affect the posi-track side of things...

*sigh*....

At least the tranny guy is local and independant - Perhaps I'll let him drive it/test it and see what he thinks...

I appreciate it...

Lates..