knock in drivetrain

[nielsl]

Hello,


My audi s2 3b have a knock in it's drivetrain, and you feel it the most when you kick down the gas pedal and release it direct.

I first started with a new rear diff mount (from powerflex) but it made no differance. Then I put new gearbox, diff and engine mounts, but the knocking is still existing.


It's just like the front axle and rear axle have to much slack relative to each other. Can it be the driveshaft between the gearbox and rear diff? Or the rear diff self?

Thanks for helping

[4WDrifter]

Check that the bolts that attach the front left drive shaft at the engine are tight asap

[rynaqui]

Around 2 years ago I had to pull the handbrake whilst driving due to a car which swerved in front of me, this was in order to correct the car as I skidded across the road. After that I had a constant shunt/knock in my drivetrain. It is most likely being caused by the propshaft centre bearing, I would recommend inspecting but probably replacement would be required if it hasn't been already. Whilst I was there I replaced the centre joint and outer joints as well so it is fully serviced. That is your best bet .

[nielsl]

Check that the bolts that attach the front left drive shaft at the engine are tight asap

is this a joke?

[nielsl]

Around 2 years ago I had to pull the handbrake whilst driving due to a car which swerved in front of me, this was in order to correct the car as I skidded across the road. After that I had a constant shunt/knock in my drivetrain. It is most likely being caused by the propshaft centre bearing, I would recommend inspecting but probably replacement would be required if it hasn't been already. Whilst I was there I replaced the centre joint and outer joints as well so it is fully serviced. That is your best bet .

but it doesn't knock when i drive at constant speed, it's when I kick down and release the gas brutal. and it looks like it comes from the back of the car

[4WDrifter]

is this a joke?

No joke. Did you check them? Are they tight?

[LHD_Kid]

there will always be some driveline shunt if you are aggressive with the pedals.

If it really is excessive and all your bushes are ok, I would get itbin the air and check all the cv joints... so the cv and spline at each end of each rotating component...

[nielsl]

No joke. Did you check them? Are they tight?

yes i checked them and they are tight

[Vauhtiveikko]

Not sure about the coupe but in the Avant this type of lock ring made the biggest difference by removing the unwanted movement:

https://www.ringer-racing.com/product.sc?productId=14

[Rom7650]

Hi nielsl, did you found the solution to your knocking noise?

[nielsl]

Hi nielsl, did you found the solution to your knocking noise?

nowp, but I have not much time to work and drive the car due the build of my house. But I think that the engine is moving to much, but the engine and gearbox mounts are all new.

Are you from Belgium?

[Lago Blue]

Niesl,

Here's perhaps another possibility. I have neither an S2 or currently said knock (and also be aware I do have widgets to flog to prevent the following issue, so grain of salt, etc.), but IIUC, a 3b would be an early car which as a B3, shares much chassis-wise with my 7a.

If you think the noise may be yet coming from the rear of the car, it is pretty simple to check the A-arm bushings for condition. You would need to gauge their resistance to fore/aft A-arm displacement. Left to themselves, they will eventually go metal (the rubber faces wear off the bushing's flange faces) to metal against the sub-frame brackets. In the stock condition, the brackets are the fence that the A-arms constantly threaten to bump into, eventually striking as the A-arms move trombone-style (on the bushing's mounting bolts) during torque reversals precisely such as you've described. Basically, when you lever on them (with a suitably wide, carefully placed flat-blade screw-driver or similar), the arms should not move fore/aft whatsoever.

I have tried to describe this “lift-pause-thump; press-pause-thump” drive-line noise in the 2nd last 'While cruising' paragraph here:

https://www.s2forum.com/forum/technical/suspension-steering/81502-a-primer-on-“stops”-mod-bushing-a-arm-theory?p=1265117#post1265117

Below are two photos of A-arm bushing's (these are front-axle bushings from a single A-arm, but no matter, it's the same issue) flange-face's, the 1st looks as new, however the 2nd, which has already begun to regularly strike the sub-frame bracket, note the wear (missing lettering and tearing) to the thin rubber coating of the steel flange-face, belies the fact that the pair of them are each already weakened.

Audi A-arm bush face A.png Audi A-arm bush face B.png

[Rom7650]

Niel,
Yes I'm in the south of Belgium.

We have to chec the Lago Blue possibiliti...