Hello everyone. I've been a 60's and 70's Pontiac guy forever but wanted to learn about the newer cars so I bought a '00 WS6 M6 Formula. Pretty much stock sans lid, bellows and exhaust with 73k miles. I noticed a slight clunk when shifting so I put it up to check u-joints. I believe it is in the rear itself because there seemed to be a considerable amount of play at the driveshaft. Any ideas what to look for?
Thanks, looking forward to your reply.
Joe

 

a 00 would have a Torsen 'posi carrier'. Torsen seem to have more 'play' than Auburns so you can't compare to the 60s/70s Eatons and Auburns.

 

Thanks for the reply. I would imagine not enough play to cause a clunk though...

 

I really don't know about these cars......but for what it's worth, my 15 year old Ford P/U has about 10-20 degrees of play and I can't feel or hear any driveline slop either cruising or pulling a trailer. Totally different because you have three differentials with two being housed in the same case, but in a semi truck...I generally don't like to see it go more then 45 degrees, however I've driven trucks where there is over 180 degrees of slop and despite the constant banging, they keep going and going and going. That's all I can add to the subject.....good luck.

 

Drive-line slop is almost always attributed to the axle splines where they some-what loosely insert into the side differential gears. As the splines normally wear a bit over time, the slop increases and this can lead to a bit more clunking from the rearend. Nothing worth worrying about.

If the ring and pinion had slipped resulting in slop, the gears themselves would be screaming like a raped ape driving down the road. This rarely happens especially on factory set gears.

Worn u-joints also result in drive-line clunking, vibes and growling especially on stick cars. I have seen joints that pass the "wiggle the driveshaft test" and were still slightly damaged. The only way to sure fire determine if the u-joint is bad, is to remove its caps and look for looseness. However considering that they are rather cheap, just replace them and rule them out if they have many miles on them and FWIW, never use cheap Chinese u-joints from any discount parts house. Find Spicer u-joints casue everything else is crap and will fail promptly. Ask me how I know.

One quick way to check u-joints on a stick car (must have a posi) is to jack the rearend up, put it in 1st gear, and forcefully rotate the rear wheel back and forth to induce the clunk sound. If the joints are good, the clunk will be low in frequency and not very loud. If the joints have wear, the clunk will be higher in frequency and much louder. Almost metal banging metal sound. This test can work on an auto car too but some noise will come from the tranny when its in park.

The amount of rotation at the yoke is rather meaningless and could give a false impression.

Hope this helps.

 

Thank you for the insight. I will put it up and check using the method described above.
Again, thanks

 

You have slack between the ring and pinion teeth. I've installed a few gearsets, and "driveline slop" has ALWAYS been cured or almost cured with a new set of gears. And when they start to wear over much time, the slop shows again. Unfortunately, there's not much to do for the gears, if you install them "tighter" they will wear quicker and cause slop quicker, and installing them to spec or even somewhat loose to spec will cause the gearsets to last longer. All from my experience, take it as you will.

 

You don't check gear clearance from the driveshaft side. While it is true the clearance can be elsewhere like the posi unit, to confirm the gear's are at an acceptable amount of backlash you need to remove the rear cover and measure them with a dial indicator.

 

I understand that a dial indicator is the only true way of measuring it, but when you say don't check from the driveshaft, does that only apply on vehicles with limited slip? The reason I ask is because on a heavy truck with open diffs and the lockers not engaged, you can get a pretty good idea of how old your diffs are, or how much life you have left in them, just by rocking the driveshaft back and forth. I've never tried it with the lockers engaged. If your getting over 45 degrees it'll start going downhill pretty quick....like within a year, and if it's over 90 degrees of play in your primary shaft then it's wise to baby it coming from a stop, otherwise it's just a matter of time before you're gonna snap your breakaway u-joint or be picking out chunks of metal from your pumpkin. I've snapped one before, and another time I got the joy of fishing out the metal from one that another driver shattered. If you baby it, it'll keep going for a long time. Just curious if there is that much difference between the cars and trucks or open, limited slip diffs. Thanks.

 

I would say if what's inside the pumpkin is fixed, like say a spool, yes you could get a rough idea of gear play but typically acceptable limit is .007-.009. No way you are coming close to feeling that by hand from the wrong side of the gearset. While in a rear with a posi or some other multi-part contraption, you could probably feel posi-slop from the driveshaft, you won't be feeling gear slop itself. It's beyond the realm of the palm of your hand especially when there are a dozen other pieces rocking back and forth at the same time..

 

Ok, thanks for the response. Having seldom crawled under a car to rock a driveshaft, I can't say what feels normal and what wouldn't. However, I've messed around enough with semis that you can see and feel it, thus get a good idea of how much life is left in it......must have something to do with the power divider in the front diff of a semi. Again, thanks for the response.