98 Trans Am Shaking above 60MPH

[jtredd]

I just purchased a 98 Trams Am /automatic in excellent shape with around 40,000 miles on it and noticed a slight shaking and shimmy on the highway from 60MPH + in the body, the passenger seat shakes pretty good. I have since rebuilt the brakes and bought new tires but the mid-body shakes did not stop. It has recently become much worse. I can't feel it's origin in the steering wheel or the gas pedal...it's definately in the mid-body to rear region. I have it up on blocks and have inspected the u-joints and aluminum driveshaft to see if and weights came off and for any cracks. I plan to drop the driveshaft to see if the u-joints are locking as they are not loose. The differential yoke seal is leaking so I guess I will fix that too. The wheel bearings seem fine. Anyone have any ideas as to what this could be? Tracking the RPM vs MPH in different gears provides no change among them.

Thanks.

[98LSGUN]

Does it continue to shake above 60 or is there a mph that it stops?

[jtredd]

I ran it up to 110 MPH and the shake just got worse. I pulled the driveshaft today and it appears the front u-joint has some play in it and the rear u-joint is locked up. I have been trying to press them out all day with no luck. There are no c-camps as these are the factory joints. I took it up to the parts store to use their vice and it broke trying to pres them out, yea..... I broke their vice!! These suckers are in there. I guess I will have to get a machine shop to heat them up and use a hydraulic press to get them out. When I finally get the new ones in I hope the vibration is gone so this will be worth it.
Thanks...

[MadSeason]

GL, I'd check the torque arm to see if that's bent out of shape at all. I've seen one go on a stocker and cause shakes like you're describing

[jtredd]

I checked the torque arm and it does not appear to be bent but the bushing appears to be somewhat dryrotted. This TA is a '98 with only 40,000 miles on it and it was kept in a garage a lot, so some rubber parts need replacing. I'll check the arm bushing for play after I get these u-joints replaced. After breaking the vice at the parts store Saturday I fought with them yesterday again to press them out and broke MY vice too ! These u-joints are really stuck. I am taking the driveshaft to a shop to have them removed. I'm very concerned that they will crack the yoke since it is an alloy driveshaft...they want over 800 dollars for a replacement. I have replaced many a u-joint in my day, mostly on old GTO, Lemans and Firebird's around late 60 and early 70 models and have never had this much trouble getting them pressed out!!

Thanks,

[MadSeason]

for 800 bucks if you gota replace the driveshaft get carbon fiber

[jtredd]

Well I got the u-joints safely out and the new ones pressed in. I just installed the driveshaft and went for a test drive. The vibration is still there but different. It seems to be tighter...like the bad u-joint is the result of something else allowing play. Could the transmission tailshaft be allowing the spline yoke to wallow around? I can't see any anything but minor play when I rock it back and forth. Any ideas?

Thanks,

[MadSeason]

hmm take a look at the crush sleeve, a friend changed gears on his car and over torqued the nut when he put it on and it caused a lot of clunkin and vibration before he blew the rear out. maybe yours is smashed a little

[jtredd]

Well, driving it home from work resulted in a clunk from the differential when slowing down at stop lights around 15 MPH when the transmission downshifted before stopping. There is also a series of clunk sounds coming from the rear drivers side wheel when I turn left...but only when I let up in the turn allowing slack, not when I accelerate in the turn. No popping or clunking from the other wheel when I turn right. I did some dughnuts in the mall parkig lt in both directions to confirm it is only clunking on one side and in the center at the chunk. Not sure if it is a wheel bearing yet but tomorrow I am pulling the plate off the rear end to inspect the ring & spiders & crush & axles. I guesss I'll pull and inspect the wheel bearing too. This is progressivly getting worse. Any ideas??? Is my rear end just going???? The vibration is now a tight roaring rotary sounding feel at high speeds. The clunk is at low speeds.

Thanks...

[MadSeason]

Probably the Rear going out, check the pinion, backlash, ect. hopefully its something that can be fixed easy

[jtredd]

Pulled the rear end plate and inspected the gears. No noticable damage. The ring gear seems to have even wear, but pretty worn. Not sure how much play there should be between the ring gear and pinion gear. It looks like about 3/16th of an inch of slack and taps pretty hard when rocked back and forth by moving the driveshaft. Does this sound right? The axle bearing on the drivers side looks fine. This is not what I expected to find.

[01LS1]

It could either be one of the following:

1. Out of balance drive shaft

2. Out of balance wheels and/or a tire with a flat spot.

3. Bent or damaged rim...those can't be properly balance. The previous owner may have hit a big pot hole or curb and bent the rim.

[Too Slow]

I agree with with 01LS1. It sounds like something is wrong with the tires. What kind of tires did you purchase? Were they used or brand new. Tires mean a lot.

[jtredd]

I just purchased 4 new BF Goodrich G-Force T/A 245/50 ZR16's but the problem existed prior to their purchase. I am going to spin the driveshaft 180 degrees and see if I get any improvement before getting it's balance checked. Thanks...

[MadSeason]

any luck finding the problem yet

[98LSGUN]

BTW where in the ATL are you?

[jtredd]

The 180 spin seems to have helped but vibration persists. I guess I'll bite the bullet and get it checked out for wheel balance, alignment and driveshaft balance. Just got new shocks and am going to put them on first.

98LSGUN, I live up in Dawsonville but work in Alpharetta.

[surfinjoe]

I have a 00 SS and have recently picked-up a vibration after 70 mph. It is a really wierd thing. Sometimes it is there, sometimes it is not. When I corner, it goes away. It kind of feels like a tie rod, but will have to confirm this w/e. Anyone got any ideas?

:dunno: