71 240Z rear diff questions, clunking

[Zedyone_kenobi]

Well, I decided to try to tackle my rear clunking I heard on my new baby. I crawled under her today and poked around at what it may be. Before I tell you what I discovered, Let me explain the noises.

When you put the car in 1st or reverse and let out the clutch, no matter how gently or slowly, you hear something mechanical make a very muted thud. Its just one thud, but it makes it each time you go from 1st to reverse. I also hear a thud from the back end each time I get on and off the gas in 1st or 2nd gear, like the diff is torquing up.

That about sums up my clunking issues: So I crawled up underneath to see what I could see. This is what I found. The car is in neutral this whole time with the emergency brake on and the front wheels blocked.

I can grab the driveshaft and turn it about a half inch. It does not translate up or sideways. This has me thinking that the ring and pinion has some slop in it, how much is normal I do not know, but this seems excessive, but the bearing on the pinion seems fine.

Item two, I can grab the fat part of the left and right driveshafts/halfshafts and I can physically move them up and down with my hand a little. I am thinking that the bearings on both sides are probably worn badly, or something greater is amiss inside the R180. Keep in mind the Ujoints felt solid and did not move, I could see the whole drive shaft coming out of the diff move up and down just a little.

Other than that, all else looked fine. All fuel lines feel soft and supple. The CV boots felt good with no cracks.

I am thinking I may need to start looking for either a new R180 or a new set of bearings. What worries me the most is the ability to turn the driveshaft so easily. Keep in mind I am on ramps, not on jack stands. So the wheels did not move.

In the vast world of clunk investigations, how does this rate? Any opinions, before I start ordering the parts I think I need.

[Grim]

How do the rubber parts look on the mustache bar and where the diff. mounts to the mustache bar? Sometimes this will cause the clunk. Just a guess. Good luck

[xray]

to measure backlash at the ring gear, you'd have to remove the diff cover. Here's a good relevant thread from the brilliant minds of hybridz...

http://forums.hybridz.org/showthread.php?t=110197&highlight=differential+rear+end+backlash

[Arne]

Speaking as someone who fought a similar clunk for many months, it doesn't sound like diff lash to me. I think the diff itself is rocking -- one way in first, and back in reverse. Just a stab in the dark, but make certain the two nuts that hold the diff to the mustache bar are tightened to spec. I've seen the whole diff torque back and forth there.

[Zedyone_kenobi]

I checked the mustache bar nuts, and they are TIGHT!

however, I have not verified the integrity of my diff front mount. Thats today when I have time.

AS for the half shafts. How much play should there be in the yoke coming out of the diffs in the radial direction, as in normal to the axis of rotation? When I grab mine, I can make it move, but just barely. I dont know how much slop there should be in those splines?

[speedracer906]

I too have the dreaded clunk. No high tech spec's from me but so far I have replaced all my Rubber, all my U joints and had every nut and bolt off and then on so I know there tight. Still the "BUMP". A lot of noise in the drive train was the U joints though.

Moving at the U joint is never a good thing. Use Spicer brand U joints to replace if you love your car. For me I plan in confirming that the Mustach bar is'nt banging against the body where the mounting bolts are. New bushings or not movement could occur there. Look for clean spots on the car indicating movement or rubbing. A friend that trusts you could help too, Check, re check and be cool then get some body underneath to feel for the clunk.

[sblake01]

Did you (speedracer906) replace the front differential mount?

[Poindexter]

Isn't there a concern with the slightly off-axis nature of the drive train? Something that was addressed and corrected by- I seem to recall- moving the diff backwards something like 35 mm?

I have the usual clunks and groans too, but none of them are particularly annoying or demanding of immediate attention- certainly not with a To Do list as long as mine.

Is this perhaps a lead?

[sblake01]

Hadn't considered that. May be true on Stephen's car, it's a 71, but Jim's is a 73 and I believe that change was made for the 72 model year.

[speedracer906]

"Did you (speedracer906) replace the front differential mount?"

Uuhhhm, I don't think I did. Tourque from the driveline could bottom out (top out in this case) the mount. Now I'm going to look at that.

[speedracer906]

"Did you (speedracer906) replace the front differential mount?"

Uuhhhm, I don't think I did. Tourque from the driveline could bottom out (top out in this case) the mount. Now I'm going to look at that.

Follow up:

It had a Nissan sticker still on it and took it for being a newer piece.

[sblake01]

Mine old one still had a Nissan sticker on it too. When unbolted the diff., the mount came apart in two pieces.