Rear-End Clunk - Seeking Confirmation

[Dondigital]

1972 240Z - original UK RHD

I just want to run this by you knowledgeable people here to confirm that my diagnosis and prognosis are, hopefully, correct.

I’ve had the dreaded ‘clunk’ when coming on and off the accelerator so I managed to get the car over a pit the other day to have a proper look at the driveshaft and the rear diff.

There was a huge amount of play on the driveshaft which would indicate that the U-Joints are shot. There was also a small amount on the play in the left-hand half-shaft.

On that basis I’m planning to replace all six U-Joints. Does anyone have any advice on what else I should replace while I’m doing that job?

There is still an oil leak from the rear Diff itself but I can’t work out where so is it worth renewing all the oil seals?

Any and all advice is welcome but please don’t overload me.

 

[240L31]

Also check if they spindle pin bolts are torqued correctly (check FSM). This cured my clunk issue after I replaced basically every item down the driveline.

 

[jonbills]

I think some oil might come out of the gearbox when you take the diff out, so you might plan to change the oil in the gearbox.
If you change the seals on the diff, you'll be changing the oil anyway. I'd advise not touching the front/pinion oil seal, unless it's definitely leaking. If there's not an obvious source of the oil leak in the diff, check the vent on the top.
In addition to what @240L31 said, all these can be source of clunks: moustache bar bushes, tighten the nuts where the diff mounts to the moustache bar, check the retaining strap and the mounting bush at the front of the diff.

 

[usurp]

Also check if they spindle pin bolts are torqued correctly (check FSM). This cured my clunk issue after I replaced basically every item down the driveline.

I currently have the same rear-end clunk, changed the u-joints even though the mechanic said they didn't need changing and i still have the rear-end clunk. What is the spindle pin bolt and where can I find it?

 

[Graham Palmer]

As an additional thought...the Diff mount upgrade stopped a rear end clunk for me...on and off power the diff/prop shaft could (pre-mod) can move up/down per the old 'strap' over the top 'bodge' from Datsun back in 'the day'....just a thought...

 

[Geoff-R]

I currently have the same rear-end clunk, changed the u-joints even though the mechanic said they didn't need changing and i still have the rear-end clunk. What is the spindle pin bolt and where can I find it?

Here, the bolt is what links the rear hub to the lower arm.

 

[240L31]

Here, the bolt is what links the rear hub to the lower arm.

View attachment 56789

Exactly, and it needs to be rather tight to not cause a clunk (I think it was around 60Nm, check the FSM).

 

[usurp]

oh, i didn't even think of checking that. thanks hopefully that's the culprit.

 

[Healey 12]

Just been looking into my cars rear end clunk . It seems I do not have the strap that goes over the diff or the brackets for the strap like the first picture . Is that normal on a 73 240Z . ?

 

[Graham Palmer]

Yours has had the new diff mount upgrade already fitted....you can see the side of the mounting bracket already fitted to the old strap mounting bolts

 

[Healey 12]

Yours has had the new diff mount upgrade already fitted....you can see the side of the mounting bracket already fitted to the old strap mounting bolts

thanks, that is a relief. On to the next thing then to find the clunk problem

 

[Graham Palmer]

that is of course.....assuming the poly bush on top of the diff has been secured correctly ...which it looks like it has,....as the nuts can been seen on the bottom on the long bolts (from my pic)

 

[AliK]

@Healey 12 , looking at your photos I strongly suspect you have the original design RT mount (see pic below) that prevents the diff from lifting. Where as the one listed by @Graham Palmer above is an evolution where the diff hangs from.



Now then, I too had a massive clunk sometimes and designed my own mount similar to the pic above. In the process of swapping my diff and fitting the mount, I found that the insulator was completely shot - >



This allowed the diff to "float" and on engine braking / gear changes at WOT and high revs it was doing nothing to stop the diff flange / UJ connecting with the ARB!

Furthermore, I had other clunks where the moustache bar rubber stops were missing.

Having said all that, I think your troubles sound like they are more UJ related but if you vet the diff off, be sure to check you don't have a diff mount insulator in the same state as my old one. It looked perfectly Ok with the Diff on the car - but revealed itself when the diff was out!

 

[Healey 12]

@Healey 12 , looking at your photos I strongly suspect you have the original design RT mount (wee pic below) that prevents the diff from lifting. Where as the one listed by @Graham Palmer above is an evolution where the diff hangs from.

View attachment 60158

Now then, I too had a massive clunk sometimes and designed my own mount similar to the pic above. In the process of swapping my diff and fitting the mount, I found that the insulator was completely shot - >

View attachment 60159

This allowed the diff to "float" and on engine braking / gear changes at WOT and high revs it was doing nothing to stop the diff flange / UJ connecting with the ARB!

Furthermore, I had other clunks where the moustache bar rubber stops were missing.

Having said all that, I think your troubles sound like they are more UJ related but if you vet the diff off, be sure to check you don't have a diff mount insulator in the same state as my old one. It looked perfectly Ok with the Diff on the car - but revealed itself when the diff was out!

 

[Healey 12]

Hi Alik
Thanks for additional pics and Info . Looks like I have one similar to yours > the insulator is new and the UJ,s have been checked and seem ok .

 

[Healey 12]

Hi All .
Thanks to Tim ( TB240) giving me a hand I have investigated further my rear end clunk. Have checked so far , exhaust mountings solid no clunks , Has the upgraded diff insulator as above , all the suspension bushes are new and correctly seated and torqued, and UJ are all good Wish bone moves up and down but even with a bar no side to side movement. . So onto the rear shock which we removed tonight .The car was fitted before my ownership Koni race adjustable. as per picture. There seems to be good resistance to in and out movement. No marks on bottom of shock or the spacer .
Has anyone fitted these before if so what t setting should they be on for normal spirited driving Hard or Soft?

HELP , what next should I look at !?
Thanks David

 

[jonbills]

Did you check a) the diff to moustache bar nuts b) the moustache bar mount nuts?

 

[Healey 12]

Did you check a) the diff to moustache bar nuts b) the moustache bar mount nuts?

yeah all tight and marked them with red paint to see if they moved and after a few hundred miles' no movement in the paint lines

 

[jonbills]

Have you checked how much play there is at the diff input? Maybe the clunk is in the diff.