Rear Axle Tramp in reverse

[timbigden@icloud.com]

Hi all, I’m new to the A7 gang having purchased my 1933 PD about a month ago, so sorry if this has been covered before.
The car judders (tramps) violently when reversing, especially if turning at the same time. I’ve been told that it’s a characteristic of A7s but I’ve not seen any as bad as mine.
Having read some guidance on the Cornish club forum I suspected the flange on the end of the pinion being loose, but having removed the prop shaft, it isnt loose. The hardy Spicer joint is good, and the attachment of the front of the torque tube to the chassis is firm.
Any wisdom would be appreciated.
T

[Howard Wright]

Hi Tim

Welcome to the world of Austin Sevens.

The symptoms you describe are normally associated with the Torque tube being loose.
If you get hold of either the prop shaft or torque tube and push hard upwards there should be no discernible movement.

If there is, two things could be amiss, firstly the castellated adjusting nut may need tightening and secondly the clamping sphere at the bottom of the torque tube bracket is loose.

Unfortunately it is often difficult to tighten the castellated nut on the torque tube without causing the large ball joint on the end of the torque tube from snagging (this is often worn in a non concentric way). Also the wear on the ball might be such that the nut has reached the end of its thread. I’ve taken up to a 1/16” off the surface of the bracket to allow the nut to tighten more.

The big nut on the bottom of the bracket has often acquired a spacer under it to allow a tighter grip on the chassis ball.  An additional penny washer might help achieving a better grip.

Good luck

Howard

[Nick Salmon]

Don't slip the clutch any more than necessary as it will contribute to the judder.

[Bob Kneale]

There may be a simpler solution................
Check that you haven't got a brake shoe return spring problem, either a broken spring hook or worse a broken hoof securing lug o one of the aluminium brake shoes.
I had exactly the same symptoms on my RP, and it was the resultant brake shoe dragging on the drum that was the cause.
Good luck with your investigations........Often there is a simple solution to what you might imagine to be more serious!
Bob

[andrew34ruby]

I find that a different technique is required when setting off from rest. Forwards and backwards are different.

When setting off in reverse make sure the engine is warm and the choke fully in to give a slow tickover. Engage reverse, don't touch the throttle pedal, let the clutch up gently, fully up, and reverse without jerking.

[AustinWood]

Another cause can be play on the joint where the radius arms meet the chassis. If there is play here any drag on the front brakes the axle will move forward as the car reverses. This causes the brakes to be applied more heavily. Sometimes the ball itself is loose where it meets the cross-member. If so the rivets should be removed and replaced with HT bolts.

["Slack Alice" Simon]

Assuming the mechanics have been checked and fixed if necessary .... and it still does it.

Find an open space, and practice being bold with the clutch.

Judder is often made a lot worse by the driver being (understandably) tentative.

[squeak]

Another cause can be play on the joint where the radius arms meet the chassis. If there is play here any drag on the front brakes the axle will move forward as the car reverses. This causes the brakes to be applied more heavily. Sometimes the ball itself is loose where it meets the cross-member. If so the rivets should be removed and replaced with HT bolts.

Tim in the OP did mention the problem was was worse when turning in reverse. The front brake lever position can cause a cable drag when turning.

[timbigden@icloud.com]

Thanks for all the advice, I did manage to tighten the castilated nut, and that improved it a bit. I’ve also improved my reversing technique. The problem is now more manageable.