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Axle bracket angles - is Ron dead straight?
LocoSprint - 26/5/13 at 11:10 AM

Hi, new to posting here and looking to canvas opinion on an issue with my 750MC spec race car - now being used for sprinting. I've had a diff nose bearing failure. The way I see it, the diff nose points downward and the drive shaft doesn't look to feed in as straight as it might. However, the brackets appear to be fitted as per Ron's instructions "ensure they are parallel with the forward face of the axle casing".

I've checked the length of the trailing arms and they are all 12" as per book, so far as you can measure with the arms on the car.

So, on a race car, is the standard Ron guide right or should we be running a different angle to bring the diff nose up a bit?

Thanks in advance for your help folks.

britishtrident - 26/5/13 at 12:30 PM

To minimise angular vibration the diff pinion centre line should be parallel to the engine crank & gearbox tail shaft centre line. As long as the angles on the propshaft UJs are equal but the variations in in angular velocity should cancel out.


The angles can be slightly out with out causing major problems ie as on cars with old fashioned semi-elliptic leaf springs.

If you have had a pinion bearing problem I wonder if the pre-load on the pinion bearing has been disturbed.

Angel Acevedo - 26/5/13 at 02:58 PM

quote:
Originally posted by britishtrident
To minimise angular vibration the diff pinion centre line should be parallel to the engine crank & gearbox tail shaft centre line. As long as the angles on the propshaft UJs are equal but the variations in in angular velocity should cancel out.


The angles can be slightly out with out causing major problems ie as on cars with old fashioned semi-elliptic leaf springs.

If you have had a pinion bearing problem I wonder if the pre-load on the pinion bearing has been disturbed.


What he said.
Just to enhance: At Running Ride Height, with driver and gas, both flanges must be parallel (sp?) or as close to as possible.
If yours is not, maybe you have to adjust the length of one of the Trailing arm pairs, either upper or lower, which will be easiest, or reposition the brackets.
Too much difference from parallel, wil cause unwanted load cycling on drivetrain components.
HTH

MikeRJ - 26/5/13 at 03:38 PM

quote:
Originally posted by LocoSprint
Hi, new to posting here and looking to canvas opinion on an issue with my 750MC spec race car - now being used for sprinting. I've had a diff nose bearing failure. The way I see it, the diff nose points downward and the drive shaft doesn't look to feed in as straight as it might. However, the brackets appear to be fitted as per Ron's instructions "ensure they are parallel with the forward face of the axle casing".

I've checked the length of the trailing arms and they are all 12" as per book, so far as you can measure with the arms on the car.


The main variables you haven't accounted for is how accurately the axle brackets were welded onto the axle, and how accurately the chassis member has been placed that the trailing arm brackets are welded to (the ones labelled M1 and M2 in the Ron Champion book).

If the trailing arms are equal in length length, and the axle brackets are correctly mounted, then the diff flange will be parallel to the M1/M2 chassis members.

LocoSprint - 27/5/13 at 08:47 PM

Just to say thank you to all responders. I have now checked the brackets on the axle and by eye they look to be 'as book' - that is, parallel to the face of the diff. I've also had a chance over the weekend to compare with another axle and again, can't see any marked difference. Not so easy to compare the chassis brackets though and maybe as suggested above this is the cause?

Talking to an experienced racer I know, he suggested an adjustable end on upper (and possibly lower too) swinging arms. It might be worth taking the opportunity to fit a rod end to the arm as well. Does anyone know of a source for adjustable arms, or would we need to make up our own?

I guess if we made all 4 arms with rod ends this would help considerably in truing the axle to the chassis in all axes as well as setting the diff nose angle correctly.

Thanks again for your input all.