Clonk on the over-run

[Robbie693]

Hello,

I think I asked about this before but can't remember, anyway it's now gotten worse...

I'm getting a clonk from the back end when I lift off the throttle abruptly. Doesn't do it pulling away or on acceleration. No noise when going over speed humps so I'm assuming it's not suspension related. Does this sound like diff mounts or tie bars or could it be either? Or anything else? How can I check?

Thanks

Robbie

[john.p.clegg]

Robbie

Prop shaft u/j's?

John

[oillite]

Also could be the diff housing mounts, especially the top ones, well it was on a +2s 130/5 that I once owned!

[Robbie693]

Thanks John - I think they're ok. I got PM to check them a few months ago whilst they had the car for something else...

Oillite - Is there any way to check the mounts? Would I be able to detect movement by shaking the diff or something?

Thanks

Robbie

[RotoFlexible]

The tie bars/torque rods (bottom of diff forward to chassis) will produce a nice clonk if the forward mounting points are loose (or the rear bushings are perished). In some incarnations, the forward ends are located on the chassis studs or bolts by a conical washer - I have not been able to locate such an item, however. If there are bolts through the chassis flanges, they can oval the hole. (To fix or prevent this, it is common to weld bolts in place to create studs.) In any case, put a wrench on the nuts (and bolts if they are not welded) to check for looseness.

[Robbie693]

Thanks Andrew - I'll check and tighten. I have a Spyder chassis which I think(?) are bolts through the chassis for the torque rods.

Cheers

Robbie

[fatboyoz]

In some incarnations, the forward ends are located on the chassis studs or bolts by a conical washer - I have not been able to locate such an item, however.

Andrew,
My torque rods have the countersunk holes in the forward end. Unable to source the special washers, I chamfered nyloc nuts, using a grinder, to match the countersink angle and fitted these.
Colin.

[billwill]

Thanks John - I think they're ok. I got PM to check them a few months ago whilst they had the car for something else...

Oillite - Is there any way to check the mounts? Would I be able to detect movement by shaking the diff or something?

Thanks

Robbie

I recall. A tiny amount loose on the Diff mounting bolts can produce such a clonk; I has one & cured it by tightening the bolts; as I recall the spanner moved merely an eighth of a turn.

You need a socket spanner set with a long extension bar to reach the nut from underneath and a ring spanner for the bolt head in the boot.

The diff is too heavy for you to reproduce the clonk by shaking the diff.

[kstrutt11]

It sounds just like the diff mountings, on mine one had cracked around the mounting hole.

Kevin

[Robbie693]

Thanks both,

Bill - now you mention it I remember a similar problem with my last Plus 2. When I bought it their was a humming from the rear at motorway speeds. Turned out to be the same thing, just bolts needed tightening.

So I guess it's tightening first and then replacement mounts second

Thanks again

Robbie

[Dave Fowler]

Thanks John - I think they're ok. I got PM to check them a few months ago whilst they had the car for something else...

Oillite - Is there any way to check the mounts? Would I be able to detect movement by shaking the diff or something?

Thanks

Robbie

I recall. A tiny amount loose on the Diff mounting bolts can produce such a clonk; I has one & cured it by tightening the bolts; as I recall the spanner moved merely an eighth of a turn.

You need a socket spanner set with a long extension bar to reach the nut from underneath and a ring spanner for the bolt head in the boot.

The diff is too heavy for you to reproduce the clonk by shaking the diff.

Having suffered just such a clonk since I installed Miller drive shafts, I was mightily pleased to find this thread. I imagine the Rotoflexes must have cushioned things enough to prevent any clonk.

Getting to the top of the diff bolts on a Plus 2 is harder, as you have to remove the rear seat to get to them. Even then, they're not easy to access as they're under the fuel tank, so you can only use an open or ring spanner. And with Miller shafts, there's no chance of getting a socket onto the bolt heads on the underside either. I know, it serves me right for buying a car with a rear seat in the first place!

But I got there and was able to tighten one of the bolts; the other wouldn't budge so I'll assume it's as tight as it needs to be. And just as Bill said, the amount of movement was pretty tiny on the one that I could tighten.

Now all I need to do is take the car out for a drive and see if it's made any difference...

Dave

[Robbie693]

So I've made a discovery...

The diff torque rods are missing one of the cup washers. It's the one that goes after the diff casing and before the rear bush:

Could this be the cause of the clonk? The nuts are tight but the bushes look to be not concentric with the diff ears. More importantly, are the cup washers available?

Cheers

Robbie

[rgh0]

The cup washers normally come in the kits for the rear bushes, they are the same as the cup washers used to mount the bushes on the roll bar to the bottom of the front shocks. The innner ones against the diff ears have a protrusion that centres them in the diff ears and keeps the rod from hitting the diff in metal to metal contact. The rear one does not have this protrusion but is flat to accept the nut.

regards
Rohan

[Robbie693]

Thanks Rohan, I'll see if I can get a kit. The bushes should probably be replaced anyway as they have been pressing against the diff case with no washer so they may have distorted or worn.

Cheers

Robbie

[ardee_selby]

The cup washers normally come in the kits for the rear bushes, they are the same as the cup washers used to mount the bushes on the roll bar to the bottom of the front shocks. The innner ones against the diff ears have a protrusion that centres them in the diff ears and keeps the rod from hitting the diff in metal to metal contact. The rear one does not have this protrusion but is flat to accept the nut.

regards
Rohan

Rohan (Guys)

The existence (or not) and need for (or not) of these inner cup washers were asked about (by me) way back in 2002.

elan-archive-f16/diff-torque-rod-bushing-washers-t7012.html?hilit= torque rod

elan-archive-f16/washers-bushes-torque-rods-longish-t7064.html?hilit= torque rod

I recall their existence was questioned as some parts lists didn't include them (and some had not found them during dismantling) whereas the unofficial "Mini-Manual" I referred to showed them.

So thanks for clearing it up for me.

(Note the loose spacer tube illustrated. Also discussed, but appears was subsequently integrated with the torque rods)

Regards - Richard