Clunking from the rear end - Huge enormous update with a video and everything!!!

Hi guys,

I pickeded up my zed yesterday in Gladstone and I'm pleased that it is safe with no damage.

I have noticed in the last few weeks of driving it that it has developed a pronounced 'clunk' when you accelerate then back off. Even when you do it slightly, as the drive changes the clunk is there.

I'm guessing this could be CV shaft related as I have an R200 with the CV's from a later model Z with the circular flange at the stub axles. Or it could be a drive shaft CV I suppose but the noise definitly from the rear left.

Is there a way I can check that a CV might be on its way out??

I'm without any of my tools at the moment. :'(

thanks

Could it also be your drive shaft of actual diff? I'm assuming you've got upgraded CV's?

An LS1 surely couldn't have the power to break these items 

Usually clunking from accelerating then backing off is backlash.

Front diff mount? Check the studs on the rear too, the nuts on mine come loose sometimes.

Hmm good call on the bolts undoing themselves. That could explain why it has gotten worse over a few weeks. I don't believe it is a backlash issue as this has always been fine and shouldn't progressively get worse. CV's are standard items too which doesn't help. What are upgraded ones worth these days. From the US I suppose.

+1 for backlash in the diff.

      My 260z had a clunk which was noticable even when stationery. Put in first gear and let the clutch out, clunk, change to reverse and let the clutch out, clunk. Changed out the R200 (3.9) last night and finished putting the R180 (3.7) in tonight. 100% better. I don't want to do that again in a hurry.

Cheers

David.  

I found early on i found my cv axles clunked when turning tight corners and the bolts to stub axles came loose ended up using loctite fixed the loose bolt issue

But clunk remained in end found the cv shafts which i shortened by turning cv races around as per recomendation on other forums With my car sitting low the outer races were binding up ended up moving inner circlip up shaft 15 mm and turned races around to orginal position this stopped the clunking was so glad to find a soloution to problem

Good luck on finding a stronger cv option that is short enough to fit only one i have found is the wolf creek option but on contacting them they would not recommend using them with the power and torque output of a Ls1

Have researched making shafts with porsche 930 cv joints and shafts which should do job also i Have been watching peters commodore diff conversion with interest let him do the hard work while the 300zx cv still working

hope its something simple for u

I agree that it could be a worn or cracked diff mount. Upon acceleration the nose of the diff goes up, but when you back off the accelerator it goes back down. If the mount is stuffed the nose could hit the crossmember and give a bang.

Hi Tim,

If you haven't yet got your tools and workshop gear delivered, drop over to my place and we can have a quick look.

I'm located half way between Gladstone and Calliope. I'll pm the address to you.

Scott.

Check all nuts/ bolts, in my cars ( racing mind!) the four tailshaft to diff bolts ease off, the rear of diff to moustache bar bolts, need a snig up, and the moustache bar to body nuts ,in there there is a "gap" I filled it with packed washers as a spacer trying to chase clunks sort of worked.

The culprit was the stock rubber band over the diff nose, it was fine, it stopped the nose of the diff trying very hard to join me inside the passenger compartment!

The front diff mount in our old greasy oily stretched rubber 30 year old cars don't last long.

I replaced it with a solid mount and no rubber band, now the whole thing is so solid it transmits horrendous noise into the cabin, but just stick a helmet on ya head, while ya drive drive around!!!

Big thanks to those who have repsonded here and expecially to Scott who let me jack up my car at his place today and suss out where this racket was coming from.

Turns out there are a few issues.

One of them which we solved was the front diff mount seemed to be a customised jobby and the rubber had gone on it so the mount was letting the diff move up and down. This was temperarally fixed by inserting a piece of belt coveyor rubber where the gap was. This stopped the mount touching the exhaust too which was causing a lot of vibration during acceleration (like bring your kidney belt). Not anymore.

The second issue was there was 'some' play in the CV's and possibly even some back lash in the diff which is still causing the initial clunking, although it isnt as bad now.

I got to see Scott's sweet ride and swap a few stories.

I'll look foward to doing it again one weekend soon to get that wicked engine into your car Scott.

Cheers

G'day folks, its that time again.

I've just been on a mission to find the issue with this rear end. I pulled the diff out (only took 6 beers) and I have concluded that the problem is something I dont know about.

The 'play' in the rear end is quite pronounced when the wheels are off the ground and you move them fowards and backwards. I have checked the CV shafts and they are rock solid. I've checked the play in the pinion to crown wheel and there is one millionth of an inch play but that probably supposed to be there.

The 'play' my friends, appears to be in the spider gears/LSD (Limited Slip Differential).

I have recorded this great video to show those in the know, so you can know me, so I can fix it.

Please.

Thankyou/.

Any ideas guys?

Or is there another test or symptom I could look for.

Sorry can't help but my R200 with a CIG locker, although bad on tight turns at slow speed, has performed flawlessy> Although I regularly change my oil and it stinks eveytime. Handled my LS1 admirably and it turns 255 semis.

(on a side note - what the hell happened in that other video at the drags?)

Ha ha. That would be my last run.

When ever I put the power down hard I get a bit if vibration as the clutch slips and the clutch pedal sits on the floor which you don't notice obviously until you go to grab the next gear. I leave it in neutral for a bit as it cools down then I grab fourth and cruise the rest if the way.

I've been waiting on CAPA to get an LS7 clutch in but it's taking forever.

I talked to Peter Mac last night and got some ideas on what to check, as that 'play' in the diff center that the drunken moron above was going on about is normal.

I checked the uni's on the tailshaft peter and they appear fine.

Which lead me to your next suggestion about the moustache bar.

I had a look at it and the bushes are good but I'm not 100% certain how the bushes and washers should be set up. Originally the car had the bar hard against the floor with two bushes at the bottom, but I changed it to one on either side. The only thing I'm thinking is if the washers arent set up correctly, with load the bar flexs and the bolt gets sloppy inside the sleeve in the bush??

I didn't read the whole thread, but there should NOT be clunking in the rear end. period.

Those bushes are supposed to be setup one on top, one on bottom, the way they were setup could have been the entire issue, it would also put the diff alignment out by having the rear diff mount bolts too high.

Check the front diff mount, they can tear and allow the diff to flop. Check that the leather strap isn't broken/stretched/tearing. With a good condition diff and proper mounting there should be no clunk. Also check out the moustache bar, I managed to crack mine which caused all sorts of slop and clunking.

If checking and fixing the diff mounts doesn't do it then check the uni's, a cracked/wearing uni joint can cause clunking as I found out before I blew two of them up...

I now have zero clunking in my car and can drop second with the only noise the sweet sound of tearing rubber against bitumen 

I just saw the reference to the Uni's: Just as a note, when they are off the ground the angle they are at causes the small play to become VERY pronounced. With my car jacked up off the ground with both wheels at full droop I can turn the wheels about 1/8 of a turn relative to each other. If you jack the suspension up tho to normal ride height you will find NO slop, so it is not likely to be a uni joint issue.

If you can't get the rear end off the ground with the suspension level, then just stick your head under the car and try and turn the CV shaft with the car stationary. You should not be able to turn it/a slight wiggle only. If you are getting slop in the cv shaft with the car on the ground that could point towards worn cv's.

Thanks for the reply Whittie. I don't have a front diff strap. I've only got this front custom cross member the previous owners made. You can see in the pics how much play there was when you lifed the diff up with a jack. This is where the piece of belt conveyor rubber went. Now the diff is out I will be modifying this mount to hopefully improve it. And like in this latest pic on the last page the Moustache bar bushes were in the right way.

Cheers

Don't know if it's too late for your set up, but the cheap easy fix for the front mount is to replace the leather strap with a chain. Has worked for me for about 10 seasons of racing and basically maintenance free and no clunks at all with standing starts at 3500rpm and locked diff with 240 wide slicks. Any more revs and I light up both wheels, locked diff, and sit there producing expensive smoke.

This only took me a few hours and bit more solid then a chain ( though obviously if the chain has held up for racing it should be fine). I also did it so I could set the angle of the diff to match my driveline.

Edit: Might help if I put the link in

http://www.performanceforums.com/forums/showthread.php?67267512-GAS-260z-RB26-Build-Thread&p=841141828&viewfull=1#post841141828

Thanks for your replies.

I guess the custom mount that the PO installed does the job of a chain or belt. It stops the front of the diff from lifting up as it hits the cross member. The problem being there was no rubber or anti-vibration installed as they assumed the factory rubber mount would not stretch enough. I have secured the piece of belt conveyor rubber I got from Scott to the bottom mount so under hard acceleration the diff really has no where to go, as it has rubber insulation in the up and down movement.

An easy mod to perform if you have a similar issue, or belt has failed due to higher horse power etc.

Factory mount and cross member

Factory mount rubber takes the weight of the diff reducing vibration but doesnt stop any upwards movement ie. diff mount lifting up away from cross member

Custom lower mount

Lower mount with belt conveyor rubber. Initially the belt wasnt there and the gap would close under hard acceleration causing metal to metal contact.

Counter sunk bolts to stop rubber falling out (hopefully)

Note: This did solve a noise and vibration under acceleration problem, but does not solve my current clunking issue.

Current bets are that is something to do with the moustache bar mounts??

Say the car is parked in the garage and you have the engine running and select reverse, as you let the clutch out before any rearwards movement there is the clunk which sounds like it coming from inside the LH strut tower, put the clutch in then out slowly again and clunk. When you are at cruising speed and back off, clunk, then slowly start accelerating and clunk. As the drive changes from gearbox driving wheels, to wheels driving gearbox etc.  Sounds much like a drive shaft/CV shaft issue but those appear fine???

Hi,

    (My 260z had a clunk which was noticable even when stationery. Put in first gear and let the clutch out, clunk, change to reverse and let the clutch out, clunk. Changed out the R200 (3.9) last night and finished putting the R180 (3.7) in tonight. 100% better. )

      Sounds like I described at the start. If you have a good diff change it out.

David.

So you think the clunk was from backlash in your old diff and the one that replaced it was set up better? I don't have a spare diff so in might check for backlash using that method I read in a Haynes manual somewhere with the paint etc. Maybe I need a new crush washer if that's how they work. The last one I did was a Borg Warner.

There is about 1 degree play between the pinion and crown wheel from spinning the pinion flange and watching the center start to turn.

I really like that idea of the metal "strap" under the crossmember filled with rubber.

I may go back to a rubber mount and do that. I am running a solid front mount right now, mostly because it was given to me.

More investigationing today.

I impressed myself by measuring the backlash in the gears. I got 0.18 which is at the limit of factory specs so it shouldn't need adjusting.

I had a thought while looking at some pics of aftermarket (mostly billet alloy) moustache bars. If there is some flex in the factory bar with increased horse power, could I simply weld some RHS to the existing bar to give it some more strength?

Did you fix up your mo bar rubbers as last pics I saw you had both on the bottom instead  of one top and bottom as they should be. Just a thought.