Driveline clunk

[swindler]

Hi I'm trying to make the most of lockdown with some more fettling.

One issue I have is a driveline clunk/knock when I sharply come off the throttle after accelerating - esp in second gear. I've replaced the engine mounts to no effect.

Any thoughts?

[abowie]

Could be tailshaft U joints, driveshaft U joints or even your diff.

The driveshaft ones are the easiest to get at so look at them first.

If it's the tailshaft you can only get it out by dropping the IRS as there isn't enough room otherwise. People have replaced these U joints in situ but to bwe honest dropping the IRS is maybe an hours work and is the easier option.

Before you do any of this make sure your have the rear engine stabiliser correctly adjusted.

[politeperson]

Always worth having a quick look at the rear radius arm bushes. I have seen them wear out in as little as 3,000 miles. They press out pretty easily.

[swindler]

It's hard to say but I think the knock is coming from the centre of the car rather than the rear.
Daft question, but when you say check the stabiliser adjustment do you mean that it sounds like it's too loose? So the gearbox could be 'jumping' up on it's spring mount?

[abowie]

The opposite. The temptation is to overtighten the stabiliser. You only need wind the lower threaded disc up until it is in contact with the support then nip the top nut down onto the special washer.

If you do them up tight you can get quite alarming noises from them.

[Tom W]

The stabiliser can also end up too tight as the other mounts sag. This is true particularly of the gearbox rear mount, which suffers as it gets soaked from oil leaks and goes soft.

[mgcjag]

Just for info incase your not sure the stabiliser is connected to the engine bulkhead..open the bonnet and its at the rear of the engine....Steve

[Herzeg]

I don't know if this could be the problem, but I had a sort of clonking sound on the rear of mine. Angus had a look and eventually I think he tracked it down to a slight wear in the splines, giving some play. I can't remember the exact details, maybe Angus can fill in the missing bits. IIRC he put something like loctite on it and it cured it

John

[Heuer]

Yes, check the spinners especially if they are not originals. Repro's can be a poor fit and cause all sorts of clunking and graunching sounds.

[MarkRado]

[swindler]

thanks lots to be getting on with.

I should have mentioned I renewed the gearbox spring mount last year along with the front mounts (it's a late 3.8 so on the spring rather than fixed gearbox mounts).

Stabilser assembly felt fine - top bolt wasn't too tight and lower washer was just pinched, but I have ordered a new stabiliser mount as the rubber is rock hard.

Will do a full inspection of rear bushes but the spinners theory v interesting. The spinners are repros from 1989-90 restoration (only 3800 miles ago). Hub splines new at same time have always felt very tight, and look to be so if it's possible to assess by eye! I can't manually detect any rotational play in rear wheels, but they do have a slight fore and aft play when the car is off the ground...

Will report back!

[swindler]

My stabiliser mount was bolted to a thick (^6mm) plate underneath the bulkhead bracket. I've circled it in this photo - it's quite hard to see as its resting on the bottom of the stabiliser rod which I haven't taken off hence not being able to remove the plate.

I ask as I can't see any reference to this plate in the parts diagrams - just checking it's not some sort of modification for strengthening

InkedIMG_8063 (2) M.jpg (36.11 KiB) Viewed 3720 times

[rswaffie]

Hi,
I don’t think there should be any parts to that assembly other than those in the pic below.
If there are, it sounds like a p.o ‘fix’ for something!

[swindler]

Interestingly I think I have now estabilished it is a bone fide part C21201 'tapped plate' eg

https://www.etypeparts.com/c21201-e-type-tapped-plate

But I'm curious it isn't shown in most diagrams including the one you've highlighted,

I wonder if this is a mid production spec change. Anyway I'm hopeful that the clunk is the noise from the adjustable lower washer hitting this plate as the new engine mounts have settled a mm or two - makes sense & i'll be able to establish when the new mount arrives

[rswaffie]

This is the plate and it’s location from the XKs.com website.

[swindler]

A quick update on this just in case it's useful for anyone searching in future.
My issue was the horizontal bolt securing the lower end of the stabiliser bar wasn't tight enough, allowing side to side play between it and the gearbox. Replaced the rubber components anyway and it has solved it.