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thunking sound when letting out the clutch


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i'll shoot off some simple causes, the guru's can rip through you for more details later:)

It can often be caused by just a worn diff mount or strap, allowing the diff to move a little, as obviously it it will as the amount of force applied on it varies.....

Or you may have my problem where the exhaust is resting next to the diff, and when you launch hard they bend apart before clanging together:) but i doubt you have a 3 inch exaust, and this only happened after putting the r200 in. but none of this helps you!

Personally, i'd say its just sitting a little loose, i when wepulled my r180 diff out, there were teeth lying at the bottom off the diff that had snapped off, and it still wasn't making any sounds! (just glad we got it off when we did)

Charles

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Check the outer passenger side half shaft u joint--good bet it's shot, and very loose...just jiggle the half shaft, and it should move if the u joint is worn out...pretty easy to just look at it as well...I have had a couple go out on me, and what happens is all the needle bearings fall out of 1 of the 4 joints on that u joint, causing the whole thing to fail....

Good luck on finding the problem.

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I have just a couple of things to add. To check the diff mount , an easy way is to put pressure under the diff it's self. Put a floor jack under it and raise it while watching the move ment . if there is upward movement before the car starts to rise , the mount is shot. When you look at the ujoints and twist the shafts , look closely at them and see if you can see any rust particles near the little rubber sealls by each of the ends. This also goes for the drive shaft. If you find one half shaft ujoint that is bad , replace them all . Other wise you will be doing it again in a short time . Gary

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Would the same cause of the rear shift clunk hold true in the '75 280Z?

All 240Z's, 260Z's, and 280Z's have front Diff mounts, and the clunk is most often caused by the failure of this FRONT DIFF MOUNT. Other possible causes are the U-Joints, and/or Moustache bar bushings, but the most common cause is the FRONT DIFF MOUNT. It is a notorious and very well known weak link in the system. Those of us who have worked on 240Z's for 30+ years have seen it many times.

yep..

1970 - 1978 240Z's 260Z's and 280Z's...

just the 280Z's have a moustache bar.. but other than that.. same setup..

NO, ......240Z's and 260Z's have ALWAYS had moustache bars. The ones on 280Z's may be different, but 280Z's aren't the only Z's to have moustache bars.

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Check the outer passenger side half shaft u joint--good bet it's shot, and very loose...just jiggle the half shaft, and it should move if the u joint is worn out...pretty easy to just look at it as well...I have had a couple go out on me, and what happens is all the needle bearings fall out of 1 of the 4 joints on that u joint, causing the whole thing to fail....

Good luck on finding the problem.

I can second dogma on that. Exactly what made my rear clunk.

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Please see my comments on another thread called: "Bald rear tires". I have no better opinions than anyone else on this great site, I've just dealt with this very problem... very often, and yes 240s have mustache bars.

See yous guys!

72' 240z

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Essentially, if you haven't replaced the front diff mount since the car was new....I would just go ahead and replace it first, (along with shaking the ujoints)...if the diff mount hasn't been replaced, its dead....you could almost bet the mortgage. An original or one you're not sure of is pretty easy to replace, and doesn't cost a leg either. Get the rubber mount, not the metal one, as the metal one will transmit that 'clunk' into your butt when your driving! (it is very much stiffer)...use the metal one for racing where you want less cushioning.

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  • 1 year later...

Resurrecting an old thread....

Does anyone have a picture of this front diff mount? I can't picture it as I am at work and I think I might have this issue. I thought it was the u-joints and replaced all 4(not the ones on the drive shaft) and the car still makes the sound. Especially when I start to back up.

Tx,

Bill

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Hey Bill, just a heads up for you: I recently picked up the dreaded clunk as well. Having been on this list for a while, the first thing I did was get under the rear and try to move the front diffy mount. But it was solid. Lot's of head scratching...

After a few weeks, I tried the same thing again. Still "solid". But I noticed that the diffy is canted to the passenger side and is hitting/rubbing against the mount where the strap attaches. While I can't push the front of the diffy up, I can slide it side to side. So I have a new mount on order... Just be careful to not be fooled like I was if you can't move it up with your own strength.

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