In my '94 convertable, when I turn a sharp corner and accelerate, such as exiting a traffic circle, something seems to shift in the drive train. Could this be a broken engine or transmission mount?

 

Possibly c-beam bolts are not tight or bad bushings.

 

I'm going to get the car on the lift and check everything including the "C" beam in hopes of finding the problem. It could also be a suspension issue. If and when I find it, I will post the results.

 

It sounds like your Corvette have what my 1988 C4 has. On my Corvette you drive for an hour or so and then you will notice that when you accelerate the nose shifts to the right side a bit. (maybe 2-4 *) If you let off the gas pedal the Corvette straightens out. I rebuilt every bushing and component in the steering and suspension front and rear.

At first I thought the whole "power train" shifted but later have learned it has something to do with something over the drive shaft that gets loosened. Probably the C Beam.

The first time it happened I almost wet my pants. Not a comfortable feeling. Turned out someone hit a curb on the right side and loosened up the C-Beam or something down there.

Be sure to post what you find but with my past experience replacing parts is NOT the answer. I changed shocks bushings and spent a lot of time and money to no avail in solving it until I asked here on the Forum.

Take it to a Transmission shop or a Corvette shop and have them check it out for you.

 

I do all my own mechanical work for two reasons: I enjoy it but more importantly, I don't trust the workmanship of other mechanics. Many of them don't even know how to lift a corvette without damaging it.

 

Hello again Richard!

I do as much of the work as I can physically do. I have had my C3 for 28 1/2 years and for most of the time I have lived with 5 crushed discs in my lower back and a right sciatic Nerve damage. I had my Differential rebuilt by a Shop as I have never "Set One Up" and did not want to hurt anything. Otherwise anything happens to my Corvettes is 99% done by me and my tools. I have a C3 and a C4 so I stay busy with just the two of them.

This place where the transmission shifted on my C4 Corvette is above the driveshaft and not someplace I can get to easily. While I had the transmission being rebuilt we had it tightened up. To do this work it has to be on a lift (for me) and it is not something I would try. No I don't rebuild automatics either but I am sure I could IF I needed to.

I live outside of Washington DC and there is an incredible Corvette Shop in Gaithersburg, MD called Tony's Corvettes. This shop can do warranty work for GM and they are absolutely amazing. I had them reinstall my 427 after rebuilding it. They made it look beautiful and exactly like it was built from the factory. Tony (the owner) and another guy spent a couple days making everything "perfect". They can do anything you want to anything from a 1953 up to a 2020 as far as Corvettes go. They are true "experts" in the field of Corvette Knowledge and offer nothing but the Best workmanship on our Corvettes. I TRUST Tony and his staff!

It is nice to know someone who can bail you out in case you get over your head.
Be Well and STAY Well!

 

Did you change your rear camber bushings? Mine were worn bad but we could not get any play in them while on a lift. Even the alignment shop didn't find it. It would shift under heavy pressure (as in accelerating coming out of a turn). The shift was as causing a temporary rear tow change which made the rear kick to the left. Scared the crap out of me several times. I was afraid to accelerate hard coming out of a turn. I only found it while replacing other bushings in the rear.

 

Checking the rear camber bushings is a really good idea and I will do so. Thank You.

 

[QUOTE=Richard Jinderlee;1601362014]Checking the rear camber bushings is a really good idea and I will do so. Thank You.[/QUOTE

On mine the left inner bushing metal sleeve was worn completely through on one side but the rubber looked good. I had to remove the camber strut before I found it.

 

By the way, are the "camber bushings" you refer to the same as the control arm bushings?

 

This is a pic of the camber rod, it has a rubber bushing on each end. One end is by bottom of differential, other is near lower rear shock mount. Either one being worn wear the rod can move more than designed can cause the issue you describe. This "may or may not" be your problem, but worth looking closely at.

 

I get it. My Haynes refers to this as the "spindle support rod" (There is no control arm like on the front). I should also check the "control rod" bushings. It so happens I too have a '04 CE Z06. I think it is # 1999. In fact, I have a video on YouTube- "C5 Harmonic Balancer Supplemental, Part 1 and 2" - which you may wish to watch. I also have a '93 40th anniversary edition with 7k miles (actually, this is my daughter's 16th birthday gift). The corvette I am looking at now is a C7 GS.

 

I removed the spindle support rods and found nothing wrong with the bushings (camber bushings). I checked all of the other rear suspension bushings and found nothing wrong with them. In the past, I found that the symptom I am experiencing was caused by a broken transmission mount. However, I don't believe this car has one. It seems the entire drive train is linked together by a rigid "C" beam and supported at four points- the two motor mounts in front and two differential carrier-to-body mounting bolts and bushings in the rear. I don't know where else to look.

 

Is yours a manual or automatic? With manual transmission where the shifter mechanism is mounted onto the transmission, as in 91 through 96 Zf equipped cars, the sign of a loose c beam, or one with the mounting holes worn oversize / oval, is the tendency of the shift lever to rise upwards during hard acceleration.

Unfortunately, after twenty five plus years of service, the C beam may not be quite as rigid as it was when new.

 

It is a manual transmission. Also, the car just turned over 40K miles. It looks like dropping the "C" beam to inspect it requires a great deal of work.

 

A 94 with only 40,000 miles? That's a great find

 

Richard, I have two suggestions. First, very carefully check the U-joints in your halfshafts. In a C4, those shafts also serve as your upper lateral suspension links (the camber rod you've discussed is the lower lateral link). When one of the U-joints in these shafts wears out, it creates clop, and the symptom I've felt is that the car slightly changes direction on power (nose comes up and steers just a bit to the left or right). This might fit the symptoms you're describing. If you jack the rear of the car off the ground and then turn each wheel forward and backward by hand (with the car in gear so the diff won't spin), you can probable observe a bad U-joint moving on and off the axis of the halfshaft as you change direction of turning the wheel. PS - ctmccloskey, are you reading this? This sounds like your problem!

The other issue is back to the camber rods. The bushings may be in good shape, but it's also possible for the camber adjuster cam bolt to move if it isn't cranked down reeeeaaally tight. And I've also seen video of someone's car where the brackets the adjuster bolt to were moving around during cornering. That video is somewhere on this site, and they used a GoPro camera attached underneath the car while driving to see the movement. That could easily cause your symptoms, because they'd change the rear toe and camber. If you have a small action cam like that available, I'd do the same thing to see what's happening underneath your car as you drive.

 

Hello there Matthew Miller,

On my 1988 C4 Coupe the car drives great for about an hour at highway speeds. Then when speeding up above ~72-74 mph or so the Corvette would suddenly shift to the right maybe 2-3*. When it happened you would notice it RIGHT AWAY. When I let off the gas it would decelerate until about 62 and then the steering would go straight all by itself. The steering just changes and when you slow down it "pops" back. When on the highway it wouldn't happen until I hit 72+ mph and the correction happens around 62-64 mph. It ONLY happens at Higher than 70 mph and is very consistent. I did it several times to determine if the Corvette was still safe to drive, as long as I stayed below the trigger speed it was not an issue so I drove the rest of the way home.

It doesn't happen until the C4 is HOT and been on a highway for a while. I had the differential serviced and it was in great shape. I then replaced the bushings on the front and rear of the Corvette. I have a lot of VB&P and Van Steel parts under my C4. I don't have the old camber rods as I have the aftermarket threaded adjustable camber rods. I went through both trailing arms and anything that might do the shifting at speed. Any bushing with ANY play was replaced with Polyurethane.

During Transmission rebuild we looked for anything loose and found nothing. To me as the driver it felt like the rear axle shifted making the movement. I would love to know it is gone for ever. I was sure it was the rear axle shifting and it scared the heck out of me.

Kind of like traveling at 75 mph while entering a banked 15 mph clover leaf turn and discovering your master cylinder "locked up" and realizing that you have no brakes. Thank God the Car was a CORVETTE with a tight suspension, manual transmission and a functional parking break as I made it home without a hitch. A couple more grey hairs maybe...

I would love to hear your thought on this issue. I respect your knowledge and background of auto-crossing. You are a valuable resource on the Corvette Forum
This Corvette is just Possessed, maybe I will call a Priest and see what they can do...

Be Well and STAY WELL!

 

That's it! We need a corvette exorcist!

 

Man, I was reading through your post and thinking the same thing: this is a supernatural problem and we are not equipped to deal with it! The only thing I can think of that would be heat and speed related, as you describe, is maybe something to do with the power steering valves getting hung up and sending too much assist on one side of the valve or the other. Perhaps it has to heat up to get the valve to hang and/or the fluid to the viscosity required to make the problem happen, and the pump has to be spinning a certain speed for a certain amount of time to create the right pressure? Maybe see if you can replicate it in lower gears at the same RPM after it's hot - that's the only way I can think of to diagnose that. It's a real grasp at straws, but otherwise I'm stumped. If anything pops into my head, I'll let you now.