Gearbox Issues

[JayW]

Back to this one again chaps!

Clutch & box change yesterday made no difference to the wobble issue.

Just to reiterate:

When cruising, i get a gentle pulsing through the gearknob, flooring it increases the wobbling to the point where at around 5k the whole car is shaking violently. During deceleration, it's perfectly normal. 1st is the least prevalent, up to 5th where it's at it's worst. However, the wobble goes away if you dip the clutch at any speed, so it's only when i'm on the power.

The wheels have been swapped front to back to rule out balancing issues.

Gearbox & Clutch changed.

Driveshafts inspected yesterday with no faults found (and no noises or clunks anyway).

Brake disks/pads were new last august and it's done very few miles since, no vibration/juddering under braking.

Wheel bearings free & smooth with no play.


Apart from changing stuff for the sake of it, i'm running out of thoughts!

If it were warped disks, i'd feel it under braking. Granted, the BX doesn't have a direct connection between th pedal and the calipers, but surely i'd still feel it in the steering?

The driveshafts were absolutely fine, in fact, everything under there attests to the cars low mileage.

All the mounts appear good, but somethings causing the engine/box to vibrate side-side and transferring this through to the gearstick and then the wheels under power.

Scratching head!

[Defender110]

I've had something very similar to this (not on a BX) with the front crankshaft pulley failing with the outer ring becoming delaminated from the inner boss. They are bonded together with a strip of rubber known as a silencer which is supposed to absorb engine vibration. Worth a look?

[mat_fenwick]

Did you manage to check the driveshafts for run out? I'd expect anything causing them to be bent to leave some kind of visual evidence (and for it to be at least detectable on the overrun if they were at fault), but...

The other thing is the orientation of the lower engine mount bush - are the solid sections in line with the way the engine wants to twist? I once didn't realise this was critical, and suffered vibration (felt through the car) under load afterwards. Can't remember if there was any gearstick wobble though, which I'd normally think of as a slow speed movement.

[NeilGP]

Is it possible that one of the cylinders is loosing power on load? (dirty injector, bad valve seal...)
The load in 1st is no where near the the load in 5th gear.

Just a thought...

[JayW]

I pulled the driveshafts apart, checked all the spiders and cups and thy all looked perfectly normal, no abnormal wear. Reassembled with new grease. Even the int. bearing was in excellent fettle.

The engine mounts never been touched and looks normal so can't imagine it's related. Interesting thought though.

The other idea i was toying with was: IF it's brake disk related, perhaps any available slack in the front bushes is allowing the wobble to transfer to the engine/box via the driveshafts at low speed so as not to make the car vibrate, but the slack can't cope at higher speeds? Seems hugely unlikely and wouldn't explain why it's much worse under power.

Think i'm just going to order more new disks and try them.

Looking at the date of the OP i was having this problem last september and we changed the disks at stratford shortly before. There was no issue immediately otherwise i'd hav gone straight for the disks and to be honest, the symptoms don't tie in!

It's like driving with a badly buckled wheel!

[NeilGP]

Have you tried getting the wheels balanced on the car?
This may show you if a brake disk isn't flat on the hub and offsetting the wheel.

[Jaba]

Tyre distortion, extreme wheel bearing wear or damage ?? If theres no vibration movement on the steering wheel what is the back end like I would check this as well.

I know its a BX but something like this SHOULD be easy to spot.

[MULLEY]

I was thinking engine mounts myself, does the gearbox have mounts as well?