Help! Rear End Shudder

[mfowler]

Ok, so I recently purchased a 1990 Corvette L98 convertible hard top. Automatic transmission, 108,000 original miles and garage kept. Needless to say its in mint condition. Even the interior leather is pristine. No fluid leaks anywhere either.
Anyway, the first couple months I was a good boy and never really got down on it. Recently I had it out and was running about 25-30 mph and decided to pass a slow car. I really punched it for the hell of it and noticed a fairly pronounced shudder. It seems to be coming from the rear end area. Normal driving (take off's, road speed) I don't notice it. Car runs very smooth. The shudder is only felt when I punch it from a slow speed. Any ideas on what can be causing this?

Thanks

 

[vett boy]

After this many years and miles I'd change the rear end fluid .Use synthetic and after changing find an empty parking lot .Place the car in reverse and do figure 8's at 10 mph for a few minutes .This might not cure a rash but I'm betting it'll fix your arthritis

 

[LLC5]

Ok, so I recently purchased a 1990 Corvette L98 convertible hard top. Automatic transmission, 108,000 original miles and garage kept. Needless to say its in mint condition. Even the interior leather is pristine. No fluid leaks anywhere either.
Anyway, the first couple months I was a good boy and never really got down on it. Recently I had it out and was running about 25-30 mph and decided to pass a slow car. I really punched it for the hell of it and noticed a fairly pronounced shudder. It seems to be coming from the rear end area. Normal driving (take off's, road speed) I don't notice it. Car runs very smooth. The shudder is only felt when I punch it from a slow speed. Any ideas on what can be causing this?

Thanks

It could be the diff fluid as vette boy suggested, if it hasn't been changed recently start there with the correct amount of LSD additive.

As far as low speed shudders at 25-30 mph the most common issues I have found (but not limited to these for sure, it could be a lot of things) are lean misfires, secondary low voltage to the spark plugs, and less likely but very noticeable when active is a bad lock up torque converter, which admittedly is rare. Since you believe it is from the rear check all the rear suspension components for wear or loose fasteners.

 

[mfowler]

Thanks guys, one thing I failed to mention is that the shudder is very momentary upon acceleration. Maybe 3-4 seconds max and then it smooths out. Its just on that initial kick of the accelerator. I'm not feeling a hesitation in power during the shudder. Thats what leads me to believe maybe a rear end problem vs. engine but then again I am no mechanic by a long shot. Could it also be a transmission problem?
Thank you both for your advise, I need all I can get!

 

[LLC5]

Thanks guys, one thing I failed to mention is that the shudder is very momentary upon acceleration. Maybe 3-4 seconds max and then it smooths out. Its just on that initial kick of the accelerator. I'm not feeling a hesitation in power during the shudder. Thats what leads me to believe maybe a rear end problem vs. engine but then again I am no mechanic by a long shot. Could it also be a transmission problem?
Thank you both for your advise, I need all I can get!

I would get it on a hoist and check all your power train mounts, engine, transmission and rear diff. Next up would be tune up maintenance items: spark plugs (looking carefully at the old ones for any kind of color problems or fouling), plug wires, cap and rotor, fuel filter, air filter. If you have an HEI dist look carefully for burn marks through the rotor button and coil, and carbon tracking on the coil itself, all are known issues. These are all maintenance items and wouldn't be a waste of money if the problem is still there. Next would be fluids, most notably ATF and rear diff., again maintenance items.

 

[Robertwav1]

I remember reading something years ago and believe it was on this forum about a shutter in the transmission. My car will do it occasionally but only like say your cruisin around 70 or so then hit the gas gently you would notice a shutter for a few seconds and then it would disappear. If you hit the gas harder it don't do it. I believe it was some kind of valve in the trans but I never pursued it. If I can find any information on notes I may have, I'll be sure to post it. Mine is a 4L60 Hydra-matic, not sure if yours is the same? It doen't happen all the time and I haven't noticed it over the last 3 or 4 years, highway driving. Does not do it low speed at all so, don't know if it's related or not?

 

[mfowler]

Thanks for the replies guys. I changed the transmission fluid and filter as well as the rearend fluid and seems to have stopped. For now anyway.