1990 Olds CC shaking from 55 on up.

I have a 1990 Custom Cruiser and it has been shaking starting around 55 on up and worse with speed. I feel it mostly through the seat, not much in the steering wheel. I've had the wheels rebalanced and the tires inspected and nothing changed. I replaced the rear shocks with air shocks but that didn't change anything. I haven't replaced the front shocks yet but they don't seem bad. I couldn't find any steering play or loose linkage. Could the U-joints or driveshaft cause the car to shake? They don't clunk when shifting. What else should I be looking at on this style Custom Cruiser?

Trans mount, u-joint, driveshaft balance come to mind, but an out of balance tire on the rear can do that sometimes also.

my dad had a 90 suburban growing up that developed a shudder and shake that got worse with speed.... they replaced a carrier bearing and u joints , trans mount, and didnt make it go away, turns out it was something with the lock up torque converter that caused it to shudder/shimmy. We discovered it because it wouldn't do it in 3rd... only OD... may try that to see if it is by chance something along those lines? They had the trans rebuilt and it fixed it.

I'll have to check, haven't tried it in 3rd on the highway.

What did they actually do to the tires besides balancing, and have they been rotated since this started? It could be one of your tires, try rotating them and see if the shaking changes that will only cost you your time if you do it yourself. Or try a different set of tires if you have some.

All good suggestions, and it probably is time for him to do the power on/power off/coast test to see if the shake changes, as well as the converter test in third gear and/or pushing the brake lightly to release the lockup. These test should be able to isolate the issue to fewer possible problems.

Power on/power off coast test? Not sure what you mean. I know the converter test, I haven't had a chance to drive it lately. I rotated them a couple months ago hoping it would have an effect but it didn't. That's why I had them rebalanced.

Does it shake when accellerating?

Does it shake when off the throttle completely?

Does it shake when coasting in neutral?

All at a speed that you know it shakes at.

booster wrote:

Does it shake when accellerating?

Does it shake when off the throttle completely?

Does it shake when coasting in neutral?

All at a speed that you know it shakes at.

Thats what I was going to suggest also... is it a speed only dependent shake? If it varies with slight throttle vs coasting but at the same speed, it would indicate a driveline issue vs a rotational issue from one or more corners...

Ran it through the tests today on a back road on the way home. I did run a fresh paved freeway section at 65 and it was still shaking just the same but I couldn't do the tests there with the traffic.

Does it shake when accelerating?

Above about 53 it will shake harder the harder I accelerate and will reduce back to a lesser steady shake when I let off based on my constant speed above 53.

Does it shake when off the throttle completely?

Yes, above 53. I didn't go over about 68 based on road conditions.

Does it shake when coasting in neutral?

I ran up to 68 or so and crested a hill and coasted down a mile or so in neutral, it shook until about 50 but lessened as the speed backed off and was nonexistent below 50.

All at a speed that you know it shakes at.

Yes 53+, I went as high as 68 but the road I was using was not super safe. Unfortunately most roads out here have chip seal which makes the cars vibrate anyway, but I could tell the difference.

I know my 91 CC needs u-joints because I can twist the driveshaft in my hand and they clunk shifting gears. This one doesn't do that, although the shop that rebuilt the tranny last year said they were getting worn and may need replacement in the future. Can they wear enough to vibrate but not clunk or turn in by hand?

I tried again checking the ball joints/bearings and still no play. I can twist the tie rods slightly but I don't feel it in the steering only the seat and some vibration in the gas pedal. The engine doesn't miss at stop lights and the only time it has an issue is fast idle, sometimes it surges. I did a full check to make sure all hoses, vacuum lines, and plug wires were correctly attached. Nothing wrong there.

We did replace the worn out rear shocks with monroe air shocks which are holding air perfect at 50 lbs and the car sits at the correct height. It shook before we did that and they had no effect on the shake. I haven't gotten to the front ones yet but they don't sag or bounce.

I don't see any rim damage and the tires are holding air after they were rebalanced and one had a valve stem replaced.

hmm.. frustrating... i hate it when things arent cut and dry easy to find..

did you try it out of overdrive just by chance? i may have missed it in the write up...

maybe a u joint... seems like the lease expensive and easiest thing to try first... maybe to rule things out rotationally , swap wheels with your other wagon for a test drive to rule it out for sure? hopefully its not an out of balance drive shaft or something...

I think the more shake with more load would point to u-joints or torque converter. Try lightly holding the brake on to release the converter and try it in third gear which I think was mentioned earlier.

Sorry, forgot, I did drive in third and made no difference.  I've done the check to kick the converter out and it works just fine.

Kicking the converter out had no effect.

did you ever figure out the shake? my 91 has a slight shudder/ shimmy at around 40 mph and I think its u joint related...

No I have not. Things got busy and now with the Washington rainy season it doesn't come out very much. I did notice with the air shock pressure raised to tow a trailer the shimmy was reduced some

smparr wrote:

No I have not. Things got busy and now with the Washington rainy season it doesn't come out very much. I did notice with the air shock pressure raised to tow a trailer the shimmy was reduced some

That would change the driveshaft angle a bit so might be indicating U-joints.

Thats what I was thinking... mines lowered and has the shimmy... i bet my angle is a little off from OEM causing it to shimmy if the angles arent right....