Rear end Clunk

[240ZMan]

I've got the dreaded "clunk" in the rear end of my 73 240 when starting up and shifting, and reversing. Not always, but some of the time. From this forum I assumed my mustache bar bushings were shot. But I got under there last weekend and they look good. In fact I couldn't budge the front of the diffy at all with my hands. I even brought the floor jack over and applied a little lifting on the front and it didn't move.

I tried moving the different u and half shaft joints with my hands and nothing has much play in it, at least for a 30 year old 200k mile car :classic:

I'm wondering now if the problem is inside the diffy? And given that the PO says that's the way it has been as long as he can remember, should I even worry about it?

[ZmeFly]

for me at least is to raise the rear of the car and start it or have someone else do this and put it into gear to see whats going on.

One of many things it could be, diff strap, ujoints, shafts, diff mount.

One other thing, if you choose this route please be very safety cautious as you never know what can happen.

[zztom]

Could the rear end gears be sloppy? I read that lead grease was put in whenever there was a clunk...even when the cars were new !! I'm fighting the same noise and my next step is inside the diff. It only makes noise from a standing start. Just like the gears are "hooking up".

[240ZMan]

I've never heard of lead grease. What would it do for the gears?

Interestingly, the clunk only comes when I change the load on the rear end, such as starting up or reversing. But if I drive along in 2nd gear and alternately step on the gas and then lift off, often there won't be a clunk. Not what I would expect if there was too much play inside between the pinion and ring gears.

[zztom]

What I heard was that it was supposed to quiet the problem, not fix it.

[Zedrally]

That dreaded clunk is definately one of the joints on one of the half shafts.

It may not be apparent with the wheels on the ground, however most members on this list would be suprised if it was anything else. [possible, but not probable].

Jack up the rear [both wheels] and double check, it should be quite apparent from where the clunk comes from.

I think the "leaded" grease you mention is graphite grease.

[Zs-ondabrain]

After I replaced this, then I found one of my joints on my right half-shaft was bad and it was hard to find out which one to replace,

[haveljacken7]

my 72 did the clunk for awhile, it ended up being the strap

[Fun_in_my_z]

check your axile greas that could couse a clunk

[venom42]

When does the "clunk" occur? Mine seems to do it a little bit when I lift off the throttle from acceleration. Is that the same problem?

[Zs-ondabrain]

usually if the "clunk" occurs after lifting off the throttle, the diff mount rubber has ripped or in lamens terms, the diff mount is broken.

Mine has broken in the past and has just broken again, and it "clunks" when I let off the gas. the only thing to do is replace it with a stock replacement, or the metal one if you don't mind the insidious noise that rings through the car whenever you're in motion.

[Brett240]

i have the same problem and i (now) know what it is. i checked the front mount, replaced the u joints checked the bushings in the moustache bar, the diff has been recently rebuilt, i just couldnt figure out what was going on.

then out of frustration whilei was putting he-man force on thehalf shaft nuts i noticed the diff rock to the side.

the holes in the rear moustache bar that the diff bolts slide through have elongated so when getting on and off the accelerator the diff was rocking side to side, solution: new rear moustache bar.