Hi Guys,
Car is stock. Just enjoy driving with the top down but now I have a vibration which I think is the u-joints. I'm wondering what is a good brand to replace the stock ones with? Should I buy the same, or upgrade to a better type? If so, what are the names. I don't race and I drive it in the summer only for the occasional acceleration rush.
Thanks!

 

You can't go wrong with a Spicer.

 

Not to deter you from a u-joint (you may well need it), but take a look underneath first. There's a brace that secures the tranny, and is secured by bolts. If you notice more vibration when you step on the gas, those bolts could be loose. Happened to me ~15 years ago--nasty vibration w/ a thump when I stepped on it. Jacked it up, found the loose bolts, torqued 'em down and never did repl. the u-joints. Worth checking, anyway.

 

Thank you. I'll check this first for sure!

 

Hi Injuneer,
Thanks again!
Would this be what youre thinking of for the spicer part? And will this fit both front and back? I believe they are same...

 

The link is the correct joint, a replacement for the factory Saginaw 3R. If they say it works in both positions, it should. I replaced my rear axle assembly (Strange 12-bolt), driveshaft (Mark Williams chrome moly), and transmission (TH400/Gear Vendors O/D) about 20 years ago,, using heavy duty, solid u-joints, so I can’t say with absolute certainty that both are the same.

Are you planning to have a shop replace the u-joints? The stock joints require that the nylon that is injected into the joint to lock it in the yoke has to be melted out with a torch. I did replace the factory rear joint with a special “crossover” unit to connect the factory driveshaft to the Strange 12-bolt. I just took the shaft and the joint to a local shop and they removed the old one, installed the new for $10.

 

Thank you, Injuneer for all the info. I think I like the idea of non-greasable which would be the link above (5-795X), plus this is the life version of spicer with the specs from the website saying they are much better than the greasable versions (5-3147X). From the Spicer webpage both the front and back ujoints are the same for the 95. Spicer® Light Vehicle U-Joints | Spicer Parts

I was thinking of bringing in the driveshaft and new ujoints to replace them for me like you mentioned. I did think about heating up the plastic injections which I may still try depending on how things look once I drop the driveshaft. Can shops straighten drive shafts that are not overly bent. This is the original driveshaft and I don't know what it will look like. I did change the clutch on my own ten years ago and felt the driveshaft removal then was very easy.

Also, I was reading on the forums here, and guys were talking about measuring the pinion angles as they may be causing the vibrations we can sometimes get. What are your thoughts on that?
Thank you!

 

You have to find a shop that specializes in driveshafts to have it checked for straightness and balance. Typical auto parts store doesn't do it.

There was actually a GM technical service bulletin (TSB) that allowed owners of cars still in warranty to get a new aluminum driveshaft. The steel driveshaft can produce vibrations at high RPM, because the rotational velocity exceeds the "critical speed" - the RPM at which it becomes unstable. The stock driveshaft critical speed is seldom a problem, unless you go to a 3.73 or 4.10 rear axle gear, or drive the car at insanely extreme speeds. It was mostly people who had opted for the numerically higher rear axle ratio that experienced the problems, and then had to argue with the dealer whether they were driving the car in excess of the legal speed limit. Obviously, no longer available, but it was a good way to get a free 1LE aluminum driveshaft at the time.

Pinion angle is seldom a problem on stock setups. And it is not adjustable with the stock suspension. It might be a problem is you have replaced the transmission mount with an Energy Suspension polyurethane mount, which is a bit taller than the stock mount, or if the torque arm front bushing is worn and allowing the front of the torque arm to move upwards too far under hard acceleration. The object is to insure that the trans output shaft and the pinion shaft are parallel under heavy load, so that the angle the driveshaft makes with the trans shaft is the same as the angle the driveshaft makes with the pinion shaft. Typically, a stock or slightly modified power level setup sets the angle at the rear end at 1 or 2 degrees negative. For a high powered application, you might set it as high ar 4-degrees negative, but onlly when it's on the track. Aftermarket torque arms are typically "adjustable".

Interesting reading:

https://www.markwilliams.com/driveshafttech.html

 

As Fred noted, if you have 3:73, or lower gears (4:10) the critical speed of the stock shaft is exceeded generally around 65mph and the DS will vibrate. Only way to fix is buy a wider, better balanced, DS....and Denny's is the preferred source for that

 

I phoned a couple shops. One said 1 hour labour per ujoint and they'll only install they're own parts. And a balance and straighten is 100.00USD.
Another shop said maybe 1 to 1.5 hour labour for both joints, but he'll install the parts I bring and recommended Spicer...said only get Spicer without me even asking.

I read that TSB a few years after they posted it in 2004. My car vibrated when I reached about 70mph and wished I was sooner to know about the TSB. I changed the clutch and I'm wondering if I didn't mark the driveshaft properly...it's a long time now so I don't remember if I did or didn't mark it. The car was only driven as a DD in low speeds after that and then life happened and I never did anything about the vibration. I had the clutch changed again in 2013 when the clutch fork arm broke, the shop convinced me to change the clutch while they were in there. I am wondering if the driveshaft was just marked then, with the shop thinking that was the right way for it to be on, and so continuing my possible error from 2005 when I changed the clutch. Is there a way to know if the vibration I'm getting is just the placement of the driveshaft...I'm guessing this would be corrected by rotating it 180 degrees?

My seat vibrates, steering wheel, and not all the time. When I speed up or slow down. That's why my brain started thinking ujoints, but I'm also wondering about the driveshaft placement. The ujoints are 25 years old now. Would it be a good idea to just put new ones on, either way? Do they last this long? Are they a part that should normally be replaced after this many years? I haven't owned a car this long that's why I'm asking.

I haven't changed the transmission mount nor the suspension. I don't know about the torque arm yet...I can check it. From what you're saying then, the pinion angle shouldn't be an issue then?

Thank you!

 

Thanks, Chimera96.
I think I have a 3.42 rear end in place as stock from the factory when I bought it new in 1995. I'm trying to remember how many options there were when we ordered back then...two choices in rear end? 3.42 and 3.73?

 

From 1994 model year on up through 2002, there were no “options” with the M6. All M6 cars left the factory with a 3.42 rear axle. That can be verified on the Service Parts label as RPO code “GU6”. From the link below you can see there were two rear axle ratios offered on the 1993 M6 (2.73, 3.23), and the A4 tranny could be either a 2.73 or a 3.23. Anything numerically higher than 3.42 would be an aftermarket install.

4_3

I went with 3.73 gears, and had no problems with the stock driveshaft (car was originally an M6).

 

stock 3:42 and DS "should" not have a balance vibe issue....unless the car has been lowered affecting the DL angle.

U joints do wear but typically last well over 100k mi. Spicer is considered the go to brand for replacement

The drive shaft could have been hit over its lifetime affecting balance but that kind of thing should be visible at point of contact (road debris, going over curb)