I had the car up on axle stands all afternoon yesterday after an unsuccessful investigation into the knocking on my Z31.

It occurs when driving over rough terrain, thankfully I live in Gloucestershire, so lots of shitty roads to test out. A mechanic who I have known for some time, took it for a drive on Friday and heard the knocking. He said it certainly sounded like suspension. Unfortunately, up in the air, he couldn’t find anything. His ramps simulate some movement, he can rock the car side to side a little turn the wheels etc. Nothing seemed out of place or loose.

 

Back to my investigations…I raised the car and tried to move anything that was a joint. The entire car has been poly bushed, which does make the car overall stiffer but all assemblies appear to have been put back as they should be. All suspension is aftermarket, with no movement in either top or bottom.

The only thing I did find although it’s doubtful it would cause any knocking, is the brake discs. Can someone confirm to me what if anything, should be in these thread holes?

Anytime I've removed a wheel, the is a countersunk hole in the disc to affix to the hub, usually just one.

 

 

Thanks

those holes are there to assist in removing the discs..you can screw long bolts in there and those will push the disc of the hub.

Most cars have these threaded holes in the brake discs in some form or another

those holes are there to assist in removing the discs..you can screw long bolts in there and those will push the disc of the hub.

Most cars have these threaded holes in the brake discs in some form or another

 

Thanks for clearing that up!

I had something similar a few years back on a Renault 21 Turbo.

 

Turned out to be the sub frame bushes.

 

Bushes looked fine from the outside, and didn't appear to move much if pressured with a pry bar, but on removal the insides were wrecked, and thus allowed slight movement, even went through Mot's OK.

 

D Bushes on the back of the daily driver Toyota Avensis where the same, looked fine outside, didn't move much, but on removal, clearly ****ed.

 

My Zed I had to change the rear diff mountings as they caused rattling/knocking noises, once again wasn't all that evident until they were removed.

I had something similar a few years back on a Renault 21 Turbo.

 

Turned out to be the sub frame bushes.

 

Bushes looked fine from the outside, and didn't appear to move much if pressured with a pry bar, but on removal the insides were wrecked, and thus allowed slight movement, even went through Mot's OK.

 

D Bushes on the back of the daily driver Toyota Avensis where the same, looked fine outside, didn't move much, but on removal, clearly ****ed.

 

My Zed I had to change the rear diff mountings as they caused rattling/knocking noises, once again wasn't all that evident until they were removed.

 

This is all great info, thanks. From what i can see, every bushing has been replaced with the hardened poly versions. Perhaps there could be something that is still original??

How are the diff's mounted out of interested, i thought they were affixed straight onto the body.

This is all great info, thanks. From what i can see, every bushing has been replaced with the hardened poly versions. Perhaps there could be something that is still original??

How are the diff's mounted out of interested, i thought they were affixed straight onto the body.

 

All the bushes on my current Zed had been replaced as well, except for the diff mounts.

 

Got a garage to do the job for me mate, so can't give too much info on that, 4 bushes in total, 2 front, 2 rear, one pair of them was easy, and another a bit of a pig according to the lad that changed them.

All the bushes on my current Zed had been replaced as well, except for the diff mounts.

 

Got a garage to do the job for me mate, so can't give too much info on that, 4 bushes in total, 2 front, 2 rear, one pair of them was easy, and another a bit of a pig according to the lad that changed them.

 

Problem solved!

Thankfully after a brief investigation by a local suspension specialist, the assembly of the suspension damper had not been correctly fitted. Basically a washer missing from below the mounting plate.

Although there was no movement side to side on the MOT testing ramp. Once the damper was disconnected from the bottom, it was very obvious it was up and down motion.

Glad you got it sorted matey.

 

That's the kind of obscure thing it sounded like.