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Knock elimination - Half-Shaft U-Joints


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Going through the knock elimination process on the 240Z.

I've changed the front mount for the diff and the problem has not been resolved.

It looks like one of the U-joints in the left half shaft has some play in it and will need to be adressed.

So, a few questions:

1. Should I look into putting new U-joints into my existing half-shafts or should I try and find a decest used set?

2. Other than the play in the U-joint, is there anything else I should look at in the half-shafts to ensure they are viable?

3. Assuming I'm replacing the U-joints, I've searched the board and one consistent piece of advice was to get good quality U-joints. I've seen a few knocks on the GMB brand products, but no mention of which might be a good supplier.

4. On a scale of 1-10 (10 being most difficult), how difficult an operation am I looking at?


Edited by bigoak
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Before I address your question, are you absolutely sure it's the half shafts? After my car was up on stands to put in a clutch, it started making some knocking sounds in the rear when it was back on the road. I couldn't figure out what putting it up on stands would do that would cause it, but the passenger side half shaft had a little play (already did the driver side a while back), so I took it out and had the joints replaced, although the sound to me was more suspension than half shaft. Anyway, after putting it back in, the sound was still there, so I climbed in the back and had my wife drive me around while I tried to localize the sound. I'm 54 now, so getting thrown around in the back of a Z is not like it used to be when I was 20! I quickly found the sound in the right shock tower. Took off the shock tower cap and noticed the top of the shock moving up and down. The bolt had come loose. All it took was a few turns of the wrench and no more knocking!

Half shaft sounds are usually cyclical. That is, the thunk happens in a certain rhythm. If you speed up the knock gets faster, slow down slower. If that's not happening it's probably not your half shafts.

So, sorry for not immediately answering your question, but didn't want you to be disappointed if that's not the problem. As to replacing the joints, it's not that hard. You need to remove the half shafts. (8 nuts/bolts each). Jack up the rear of the car and put the car on jack stands in the rear.

Remove the inner bolts first and then the outer. You can have a helper apply the parking brake to hold the shaft while you remove the nuts/bolts. Seems like they were 14mm. Oddly enough, I had an old 9/16ths wrench that had very thin walls, and it worked perfectly.

The tricky part is finding the right place to turn the shaft to be able to get to the nuts. A box end with the thinest walls will work best. In my case, I could get to the inner bolts when they were between 3 and 5 o'clock (facing the differential). The outer nuts were best reached at 3-5 o'clock facing the outer arm assembly. You may even have to take a file to the box end to thin down the walls to fit. Don't give up, you'll eventually find the best angle of attack to get to the bolts.

Take the half shafts to a competent machine shop or someone who specializes in drive shaft repair/balancing if possible. I paid $40.00 to have both inner/outer joints pressed out and new ones pressed in.

You can try popping out the c clips yourself and hammering out the old joints, but I'm not much on hammering on parts to save money! Seems to always cost me more in the end if you know what I mean.

Anyway, good luck,



Edited by bobc
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I'd do new joints in the pair of shafts you already have, assuming the boots and splines are both good. I had Spicer joints installed in my halfshafts. Pulled the shafts and delivered them to a local driveline shop, they installed them for $30 per u-joint. Of course, that was 2 years ago...

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Bobc, that was almost a full sentence...but yes, there is definitely a problem with the U-joints. I put it up on stands yesterday and could see play in one of the joints.

Arne, easy to remove the half shafts? I can check the boots. How would I know if the splines are ok? Just visual inspection?

Edited by bigoak
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Got it. I am getting a cyclical knocking so I think it might be the half shaft. (I'll check the tower as well).

There is a lot of slop in that half shaft so it will need to be fixed at any rate.


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U-joints are a 3 on the 10 scale to replace . Spicer for my money are a good part. If one has gone bad , replace all four while you are at it. I bought my Spicers for about $20.00 each at the local parts store

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I'll chime in because I just replaced my u-joints last month.

It's a PITA, but only because there's not a great amount of room to wrench. You'll have to jack the rear up, remove the wheels, slide under and start wrenching (and spinning your body around).

There's 4 nuts to remove on each side of the diff, and 4 bolts at each wheel. Then some penetrating oil and well placed whacks on the flanges (don't damage the shaft itself!) and you've got em out. It'll take you a few hours to do the whole job.

I bought 6 new joints from MSA for $106 (about $18 per). Only ended up putting in the half-shaft joints, as that cured my squeak. The local drive line repair shop pressed in the new joints for $65 (works out to $15 per plus tax). The shop actually sold Spicer, which I had been looking for, but I already had my joints.

Overall, I'd definitely recommend you do it. I had exhaust in the way that made things more difficult, but it wasn't that bad. It was ultimately a lot of fun actually.

BTW, I'm not sure of the brand MSA sells. It's a japanese brand, I'll check when I get home though.

Edited by JonnyRock
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What great timing on this thread. I took the diff out of my car last night, and the half shafts. Just looking at them I wasnt sure if they were serviceable or not. How can I tell if I have to replace the joints in them?

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What great timing on this thread. I took the diff out of my car last night' date=' and the half shafts. Just looking at them I wasnt sure if they were serviceable or not. How can I tell if I have to replace the joints in them?[/quote']

Well if you can rigidly clamp the shafts you can feel for play in the joint. But that's not always possible (be sure not to squeeze too tight and damage the shaft). Also, you may have a bad joint and not get any feeling of play.

It doesn't hurt to go ahead and replace them. Then again if you have no reason to suspect they're bad than you might as well not. They're likely aftermarket already, so go ahead and grease them at least.

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