Hello

I'm trying to pin-point the source of my automatic '73 240z rear end clunk. I'm thinking it's the differential. Here's why:

1) I jack up the rear end and put the car in drive. Parking brake is off.

2) I'm noticing the passenger rear wheel is rotating (as expected) but the

driver side rear wheel is nearly motionless. Hardly any power. The half

shaft is connected and I'm not seeing any U-Joint play.

As far as I can tell, it's a stock R180.

Is this normal differential behavior or am I looking at a bad differential?

Any insight is greatly appreciated!

Tony

When I found 1 half shaft ujoint that was bad I just did them all. As it turned out when doing this there were two others that were on the verge of failing. So if I had done only the first one I would have been under do it again in short order . When I replaced the diff I installed new moustache bar bushings . My old diff had 250K + on it but was going strong and no noise. I just wanted a different ratio. I also did the Axel bearings and found one stub Axel with a slight amount of play, part of a clunk .

After putting up with clunks, squeeks and other cyclic noises, I had a major dummy spit and took the 260 to a "mates place". Having little time on my hands to do these mechanicals, I decided that it was the only way it was going to get "fixed".

Much to my surprise, the unis in the half shafts had actually frozen from lack of use. Replacing the half shafts with used ones in good condition fixed all those evil noises that I had put up with over all those years.

FWIW, don't just replace 1 joint, do them all....

Problem solved!

OK. I inspected each U-Joint and they were all good. Then I inspected and tightened every bolt (moustache bar, differential mount) but all was good.

Crawling deeper under the car, I discovered two bolts (forgive as I did last

weekend - I can't remember the size... 3/4"? ... big suckers) up on either side of the front nose of the differential where it connects to the driveshaft.

This is where Carl Beck points out that there is a "strap" that runs over the top of the nose of the differential. The passenger side bolt was loose and I mean loose! I don't know what's for. Strap tension? At any rate, torquing this back down solved the problem. No more CLUNK. Thank you all for your

thoughtful comments that helped me diagnose and solve this problem. It's a much more pleasant ride!

Best

Tony

Thanks for posting the solution , this is how we all learn. Good job. Gary

I'm interested in the other possible causes of rear end clunk - from reading the posts over the past year I was convinced mine was related to the fwd diff mount. Over Last few days I did some suspension work and replaced the mount while in there (did the mustache bar last year), only to find out on the road that the clunk remained.

I am wondering if it is related to backlash, mine is promenent when moving up in gearshifts.

Any thoughts?

I replaced my front diff mount two days ago. My clunk is greatly reduced, but not eliminated. I have good mustache bar bushings, new diff and tranny mounts, and all 6 u-joints are new as well. I believe that the remaining clunk is in the rear control arm bushings, especially at the spindle pins. Those will be my next replacements.

Certainly excess lash could be part of the issue, but I'd make certain that all the rubber is fresh before I went to that.

I discovered two bolts (forgive as I did last

weekend - I can't remember the size... 3/4"? ... big suckers) up on either side of the front nose of the differential where it connects to the driveshaft.

Sounds like the two bolts that hold the nose of the diff to the diff mount or "isolator" as it's called. See below.

Engima

Yes! Those are the correct bolts!

Tony

Arne

My clunk is diminished, but still obvious (to me anyway). As a matter of interest the mount that I removed looked perfect, except for a small amount of dry rot - when I rubbed it, a very fine line was exposed and a long screwdriver forced through the gap and twisted revealed the defect, it was fully let go.

As for bushings - I replaced everything last winter except the rear outer control arm units (spindle pins) - they were a major pain to remove. That would be too much like life if that was where the problem was.

Anyway If that solves your clunk, please post or let me know. I'll just have to take it apart again.

My clutch problem started as an upshift clunk and progressed to "clunk clunk clunk". It sounded like it was more of a differential sound, but I couldn't find any problems in the back after all the repairs I did, so I pulled the transmission. The clutch was not to the rivets yet but worn and was not oil fowled (my rear motor seal was fine).

I put in a new clutch, plate, throwout bearing, pilot bearing, flywheel surface, and rear engine seal while I was in there and put it back together expecting no improvement, I was wrong, it was the fix.

I think what was happening was the clutch disk wasn't slipping on the disk but bouncing off it. A new clutch disk has grooves for the pad dust to escape. I think the dust was accumulating and getting sticky and the clutch plate was bouncing. I saw a non Zcar discussion of clutch dust causing clutch chatter due to non-asbestos clutch materials, don't know... I put in all Nissan parts. No idea what was in there.

http://www.btc-bci.com/~billben/clutch.htm

So what does it mean if the diff howls??? Thans what mine does.... and it clunks really bad. For instance when I am driving normal, than I let off the gas, then tap it repeatedly.... it clunks with each tap of the gas. The bushings are nice and tight. Any solution??? The clunk is really bothering me, and my radio isnt loud enough to cover this noise up.

Justin,

That sounds like ring and pinion lash is off, that is how you are going to get that howl, I just had this issue with mine...

Typically it is due to wear and possible bearing fatigue.

~Brian