A 'clunk' on pulling away

[The Beaver King]

Gents,

Some advice and suggestions if you could please.

My father has a 1989 350i (now a 460SE). Since the engine has been modified (circa 6/7 years ago) it has developed a 'clunk' when pulling away from stationary in 1st. We've spent a good few years searching for the source and we believe we have narrowed it down to the rear drivers A frame. Pic below:



Pic is from Google images and of a 390SE, but it's close enough.


With that in mind, we have replaced the 'stay bars/struts in case the noise was play in those. No change.
We have shimmed/sleeved the bolts on the wishbones in case it was play on those. It seemed to cure most of the problem, but it has gradually gotten louder. So, as a more permanent solution, we have replaced all the rear bushes with polys. This has made no difference.

So, has anybody else experienced this issue? I'm guessing the problem may have arisen due to the extra power going through the back end. Two years back it blew a gearbox, so the noise isn't from that.

Bear in mind that it has been through 6/7 MOTs (at various garages) since the noise developed, so it probably isn't anything obvious (wheel bearing etc).

Whilst it isn't serious (hence why it isn't fixed after 7 years....) I will be taking it to Classic Le Man in a month, so while I'm dealing with the usual TVR niggles, I'd like to have a look.

Thanks guys, all theories appreciated.

[mrzigazaga]

Hi mate...A "clunk" can be a telltale sign of either inner or outer drive shaft UJ's or a rear wheel bearing...Also which i found out nearly to my horror that the propshaft UJ can cause it...Ziga

[The Beaver King]

mrzigazaga said:

Hi mate...A "clunk" can be a telltale sign of either inner or outer drive shaft UJ's or a rear wheel bearing...Also which i found out nearly to my horror that the propshaft UJ can cause it...Ziga

Ziga, cheers mate.

I don't think it's the prop UJ as that has been out and back in again a year or two back. Drive shaft UJ's sound like a good place to start.

Ideas on checking them? I'm thinking getting it up on stands, brakes on and rocking the wheel backwards and forwards to feel for play. Maybe a 'clunk'?

Should there been any play?

Cheers

[ElvisWedgely]

You say since the engine was modified. Are you sure it's not the exhaust pipe hitting the body as the noise is very deceiving? The exhaust pipe is a very tight fit on these cars at the best of times. Or is it a crunching type of mechenical clunk? Diff crown or bearings maybe?

Tony.TCB

[The Beaver King]

ElvisWedgely said:

You say since the engine was modified. Are you sure it's not the exhaust pipe hitting the body as the noise is very deceiving? The exhaust pipe is a very tight fit on these cars at the best of times. Or is it a crunching type of mechenical clunk? Diff crown or bearings maybe?

Tony.TCB

I don't think so. The engine is only modified through boring out/stage 3 heads/uprated cams etc, the block itself is unmodified so the exisiting exhaust system was used. That said, it's worth a check to ensure a mount hasn't come loose....

The best way to describe the sound is it is similar to hitting the chassis with a hammer. It has that metallic 'bang' kind of noise.

If it were the bearings or diff, I'd have expected it to have given up the ghost by now. As said, this has been going on for around 7 years and probably 10-15,000 miles.

I'm conviced it is rear suspension related. Time for some serious detective work I think.

Thanks.

[mrzigazaga]

Well if you have replaced all the rear suspension bushes and the gearbox mount then it could well be a UJ..There are 4 on the rear in total and any one of them could cause it..There shouldn't be large amounts of play in the rear set so checking the UJ's and diff cradle/Bushes is a good idea..

Like you say if it was a wheel bearing i think it would of collapsed by now!...Hope you find it...Ziga

[jmorgan]

I used to jack the hub up with the wheel on (car already on stands), get the wheel to around normal travel and see where the play is. The UJ's are not at extended travel then and easier to manipulate.

From memory mind, not had a chance in this garage and always safe.

[hallsie]

My money would be on the Diff input shaft.

handbrake on, If you put it in 1st and it clonks, then put it in reverse and it clonks then you may have a bit af backlash to take up on the diff bearing.

Also, and its a long shot but does happen, have you looked at the diff hanger, notorious for breaking, especially with a bit mor power acting on them.

Stu

[The Beaver King]

Thanks guys, UJs it is.

I'll have a look in the next week or so and report on my findings

Actually, one last thing...

Accelerator pedal resistance, is anybody elses very 'weak'?

By weak I mean it has very little resistance, so the slightest pressure produces a fair amount of movement.

As mentioned above, it's not my car (yet), but the throttle is so light I struugle to drive it without releasing most of the power. I've bought a stronger spring for the throttle and checked to see if the pedal has a seperate return spring, but there doesn't appear to be one...?

My S has a much firmer throttle, but half the power. I find the reverse on the wedge and it is..... unsettling.

[The Beaver King]

hallsie said:

My money would be on the Diff input shaft.

handbrake on, If you put it in 1st and it clonks, then put it in reverse and it clonks then you may have a bit af backlash to take up on the diff bearing.

Also, and its a long shot but does happen, have you looked at the diff hanger, notorious for breaking, especially with a bit mor power acting on them.

Stu

Added to the 'to check' list

[mrzigazaga]

Hi mate...A weak throttle...Do you have any throttle return springs on the throttle return?...Two ideally...
Here is mine..There is only one in the pic but i now have two fitted..You can buy throttle return springs..Just measure the gap between and buy one thats 2" shorter..

[ElvisWedgely]

The Beaver King said:

The best way to describe the sound is it is similar to hitting the chassis with a hammer. It has that metallic 'bang' kind of noise.

That sounds very much like the exhaust or the engine knocking on the chassis. I used to have a 450 that made a similar noise only at certain angles when on a hill but would never make the noise on the straight. It turned out to be the exhaust.

Tony.TCB

[The Beaver King]

mrzigazaga said:

Hi mate...A weak throttle...Do you have any throttle return springs on the throttle return?...Two ideally...
Here is mine..There is only one in the pic but i now have two fitted..You can buy throttle return springs..Just measure the gap between and buy one thats 2" shorter..

Zig, there is one on there at the minute, but it is losing it's 'spring' a bit.

I bought a replacement already, so hopefully this will cure the issue. I've got another kicking around the garage somewhere, so I'll put another on if it is still too light.

Thanks.

ElvisWedgely said:

That sounds very much like the exhaust or the engine knocking on the chassis. I used to have a 450 that made a similar noise only at certain angles when on a hill but would never make the noise on the straight. It turned out to be the exhaust.

Tony.TCB

I'll check that out mate. We did fibre glass a SE rear spoiler onto it a few years back, so it could well be the exhaust hitting that. I'll give it a rattle and see if I can recreate the noise.

Thanks.

[jmorgan]

Good to have two springs on in case one gives up the ghost.

[superwedge]

should be a spring on the brake one ,under dash,

[njhucker]

I had a similar problem that had me beat for ages, so although this sounds completely unlikely it is worth checking. One of the rear springs was rubbing on the top mounting as I pulled away, and a coil was just clicking on the edge of the upper seat. When taking the damper off one time I noticed that the edge of the spring seat was shiny metal. I turned the spring through 180 degrees and the noise stopped. When I first heard the noise I thought I had left a spanner on the handbrake cable and it was tapping on the diff or frame.

[Jack Valiant]

I had a similar issue with my old 400 SE. I hunted and changed most things on the rear suspension to no avail. It turned out to be a broken diff carrier. Get the car up in the air and with a good light have a good root round with a decent size pry bar fella

[TVRleigh_BBWR]

Get the rear of the ground, and get someone to put there foot on the brake, and then try and rock the wheels round. if there is any rotation then you have a shot UJ, they are quite common to go, but you would get a clonk on every gear change, but may not hear it over all the other noise

[The Beaver King]

jmorgan said:

Good to have two springs on in case one gives up the ghost.

Yeah, I think I'll add another just in case.

superwedge said:

should be a spring on the brake one ,under dash,

The brake one is okay, but I did wonder if the accelerator pedal had a seperate spring under the dash. I had a look, but there doesn't appear to be one.

njhucker said:

I had a similar problem that had me beat for ages, so although this sounds completely unlikely it is worth checking. One of the rear springs was rubbing on the top mounting as I pulled away, and a coil was just clicking on the edge of the upper seat. When taking the damper off one time I noticed that the edge of the spring seat was shiny metal. I turned the spring through 180 degrees and the noise stopped. When I first heard the noise I thought I had left a spanner on the handbrake cable and it was tapping on the diff or frame.

The coils have been off a few times and we put a rubber mat on last time that sits between the coil and mount, so it shouldn't be that. A fair suggestion though.

Jack Valiant said:

I had a similar issue with my old 400 SE. I hunted and changed most things on the rear suspension to no avail. It turned out to be a broken diff carrier. Get the car up in the air and with a good light have a good root round with a decent size pry bar fella

This seems to be the most likely cause at the moment. I can't remember the last time we dropped the diff out (maybe 10 years ago), so this will be my first port of call.

TVRleigh_BBWR said:

Get the rear of the ground, and get someone to put there foot on the brake, and then try and rock the wheels round. if there is any rotation then you have a shot UJ, they are quite common to go, but you would get a clonk on every gear change, but may not hear it over all the other noise

Possible, I'll certainly check while it's up. I'm fairly confident I'd hear it though; as loud as the car is, it is quite a clunk and I can hear it when giving it a 'spirited' launch.

It doesn't happen if you pull away in 2nd gear though, which leads me to believe it is something moving when subjected to sudden power, as opposed to slowly pulling away.


I really appreciate the input guys. I will come back with an answer once I've got the little bugger in the air next week. Thanks.

[The Beaver King]

Just a quick update guys.

I finally got round to putting the young lady up on jacks at the weekend; Hallsie wins the mythical wedge point.

hallsie said:

My money would be on the Diff input shaft.

handbrake on, If you put it in 1st and it clonks, then put it in reverse and it clonks then you may have a bit af backlash to take up on the diff bearing.

Stu

Backlash in the diff, not too bad but definitely the source of the noise.

She's going to Classic in a few weeks, so no time to fix it but I don't imagine it will suddenly fail after this long.


A quick 2 hour job on Saturday morning (sorting the connections on a dim headlight), turned into two full days and yesterday evening! Apparently even looking at the electrics cross eyed causes all the rear lights to fail and the slave cylinder to blow a seal...

After much cursing, shaking of earth points, changing connections and getting coated in brake fluid; she has her MOT this morning. Hopefully she'll pass and then it's 2 weeks of shake down before Classic