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Lower shock attachment point on IRS
Fred W B - 6/3/06 at 08:51 AM

I am fabricating rear uprights, which are complicated by the fact that if you don't mount the lower shock attachment point on the top of the upright, you have to offset it to the front or back, to allow the shock to clear the drive shaft. I see that some kit manufactures do it like in the photo below, with the shock mounted on the wishbone. So all the loads to the shock go through one rodend. Surely this can't be a good idea, in that the rod end shaft will be in constant bending stress?

Cheers

Fred W B
upright
upright

[Edited on 6/3/06 by Fred W B]

britishtrident - 6/3/06 at 09:26 AM

The rod end is a rod end so can't transmit bending moments, the problem is because the lower shock mounting is horizontally offset from the wheel centre the reaction form a twisting couple putting the lower wish bone in torsion.

A few ways round the problem include twin shockers as per Jaguar, a forked end shocker going over the drive shaft as per Honda and larger Rovers. Personaly I don't like the idea using normal wishbones on a driven rear axle, if room is available trailing link style wishbone suspension as on 60s and 70s single seat racers is better.

Syd Bridge - 6/3/06 at 09:45 AM

quote:
Originally posted by britishtrident
The rod end is a rod end so can't transmit bending moments


Maybe it can't TRANSMIT a moment, but the male thread is certainly subjected to a bending load in the picture.

Only useable solutions to even things up is:-
- mount the shock up top

-twin shocks, one either side

- pushrod with the rod mounted on or near centreline at the bottom, and angled enough to clear the driveshaft on its way up to the bellcrank.

Mr.Ison has been through this exercise, I believe.

How did it end up, Jon?

Syd.

NS Dev - 6/3/06 at 10:25 AM

That looks like a Stuart Taylor setup, the same as on my 7 except that mine has a bush at the rear of the wishbone and a rodend at the front. I don't like the look of it but I guess it works, just make sure the rodends are top quality jobbies!!

What I don't like with the whole setup is the shimming of the upright between the rodends. The slightest inaccuracy with the shimming puts the rodends in sideways bending stress too, and will obviously wear them fast as well.

Fred W B - 6/3/06 at 11:13 AM

Ultima also mount to the wishbone, with the shock offset to the rear.

Cheers

Fred WB
ULTIMA
ULTIMA

Bob C - 6/3/06 at 12:24 PM

Fred, in that top picture it would have seemed sensible to mount the shock bottom to the side if the upright rather than the bone. No twisting moment in the bone & no sideways stress on rodend.
top bone mounting means short shock = no suspension travel (ie very hard springs)
cheers
Bob

Fred W B - 6/3/06 at 07:17 PM

This is my very rough mock up, just to get the pivot positions right.

Cheers

Fred W B
[img][/img]