Axle Tramp

[jonny_c]

Hi guys - I'm chasing a bit more advice...

When I 'light up' the rear wheels under acceleration i get really bad tramping/knocking. If I stand on the brakes though - chav standing burnout style - the wheels spin up fine, also under light wheelspin. Normal driving is fine. (I've got very old P6000 on which i hate - partly why I've all tried this out, i need an excuse to change them!)

I did search this and from what i gathered this can be caused by worn bushed and rear shocks. I in the middle of winterising my chassis at the moment so took the opportunity to have a good look round. All seems well with bushes, as i expected as it was re bushed last year, including the diff which has purple bushes (powerflex?).

The shocks seem fine if you push the corner of the car but they do look original. I was wondering if the stiff new bushes could theoretically exaggerate the condition of the old shocks/springs and be causing the tramping. It is quite bad.

Any thoughts appreciated

Jonny

[WokingWedger]

Mine tramps to.

Has not original, but standard shocks, but I havent looked at the bushes yet.

Anyone know the most likely suspects ?

How does braking and spinning the wheels work then ? Is it just the front brakes are more powerful than the rear and the engine overcomes the rear ?

(cant do anything any good !)

[Else]

I think they all to under certain conditions. Mine does and its got fairly sophisticated rosejointed Protech double adjustable shocks and polybushes everywhere including the diff.

I think you have to learn to live with it, i have, would still be interested in the reason why though. In the old days of soild rear axles it was explained by the leaf springs winding up and then releasing. This was instantly cured by anti tramp bars.

I can't find any significant movemeent in any of the suspension components, maybe its the engine/gearbox twisting in the mounts, anyone care to enlighten us?

Andy

[jonny_c]

The way i see it, it must be a combination of wheel speed and a weak shock which leaves the 'system' underdamped. Worn bushes, especially in the diff must excite this underdamped system, but not necceserily cause the bounce. However I don't have any experience with axle tramp- my theory is only that - a theory!

It does appear to be realativly common though....

Yeah - standing on the brakes while pulling away meanes the engine torque overcomes the braking power of the rear wheels and they spin. It takes a bit of practice- but it is quite easy in a chim due to the torque. I'd only ever do it in the wet and a degree of mechanical sympathy is required...!

[StreetDragster]

On my friends 200sx' and RX7 their axle tramp was chased down the the diff bushes. The 200sx had urethane bushes put into the diff carrier and it solved the problem, the rx7 had to have the urethane bushes and some sort of damper arrangement that he got from japan.
Maybe our TVR's are similar?
Thanks

Matt

[jonny_c]

Could there be a possiblity that stiffer diff bushes could make the problem worse? That's what i was thinking when I first posted. Instead of absorbing the torque, they rebound quicker and set off the bouncing.

[Laird]

I used to get this on the Griff in certain conditions. I think the tyres have a part to play as the tramping is caused by the tyre spinning then gripping etc. A sticky tyre will reduce the chances of it happening so I guess a hard compound tyre won't help or an under inflated one?

[jonny_c]

Never thought about the spinning/gripping thing. This would explain why I don't have any problems if I do a 'burnout' on the brakes - because the wheel is always skidding.

Interesting...

Maybe the lightness of a TVR, combined with the torque, make axle tramp unavoidable in some conditions without additional damping on the diff.

[Laird]

Possibly, I think tyre width also plays a part as an 'overtyred' car will tramp like a bastard. My old boss took me out on the freeway in his 550 Viper, I waited with anticipation as he floored it only to have the bloody thing hop like a demented march hare. The rear tyres were massive though

[Else]

Laird said:

Possibly, I think tyre width also plays a part as an 'overtyred' car will tramp like a bastard. My old boss took me out on the freeway in his 550 Viper, I waited with anticipation as he floored it only to have the bloody thing hop like a demented march hare. The rear tyres were massive though

I wouldn't have said a chim/griff is 'overtyred', if anything they could do with a bigger contact patch, especially the bigger engined versions.

Andy

[Laird]

Else said:

I wouldn't have said a chim/griff is 'overtyred',

Andy

Neither would I