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Suspension adjustment and damper fixings
Slimy38 - 7/6/14 at 10:19 AM

I could do with some pointers please. I'm building a Haynes base, with MX5 running gear. The rear wishbones are causing me a little confusion, mainly because I'm using a Talon diff cover and not the normal two-armed MX5 diff. What it means is that I'm aiming to use the Sierra wishbone design but with alterations to fix to the MX5 uprights.

On page 77 it describes an adjuster that works the same as the Sierra adjuster, and it seems to make sense. The problem is the Sierra design has the suspension damper mounted on the upright, which doesn't work on the MX5 upright as there isn't a mounting. What I was going to do is put a plate on the upper wishbone, as seen on the Saturn plans. But then that puts suspension loads through an adjuster, and I get the impression that's a bad thing to do.

Is there any way of keeping an adjuster on the outboard end of the wishbone, or do I need to relocate it somewhere else?

rdodger - 7/6/14 at 11:45 AM

Have a look at roadrunner racing.

They have a bracket just in from the outer adjuster to mount the damper to.

I think westfield bolt it all through the upright. I guess that would be fine if you used a rosejoint on damper and top wishbone.

The MX5 upright is offset at the top so it should all align nicely.

Sam_68 - 7/6/14 at 11:59 AM

quote:
Originally posted by Slimy38...What I was going to do is put a plate on the upper wishbone, as seen on the Saturn plans. But then that puts suspension loads through an adjuster, and I get the impression that's a bad thing to do.

Is there any way of keeping an adjuster on the outboard end of the wishbone, or do I need to relocate it somewhere else?


Personally, I'd think about re-designing the wishbone so that camber adjustment is by shims, sandwiched between a clevis (attached to the upright) and the end of the wishbone, with a couple of bolts holding the whole lot tight together.

Slimy38 - 7/6/14 at 12:20 PM

quote:
Originally posted by rdodger
Have a look at roadrunner racing.

They have a bracket just in from the outer adjuster to mount the damper to.

I think westfield bolt it all through the upright. I guess that would be fine if you used a rosejoint on damper and top wishbone.

The MX5 upright is offset at the top so it should all align nicely.


The only pics I could find was these;





They've not got an outer adjuster on the top, it's solid. The adjusters are at the bottom outboard. That does away with suspension loading on an adjuster.

But I think you're on to something with the Westfield;





The u shape on the wishbone has been 'doubled up' to accommodate both upright and the suspension damper (which in this case is a standard polybush type). So to me, that's eliminated all suspension loading on the upper wishbone hasn't it? The load is transmitted straight into the upright.

Unless I've misunderstood, I think I'm going to adapt that and keep the adjuster on the upper outboard, just having the damper attached to the upright rather than the wishbone.

[Edited on 7/6/14 by Slimy38]

Slimy38 - 7/6/14 at 01:20 PM

quote:
Originally posted by Sam_68
quote:
Originally posted by Slimy38...What I was going to do is put a plate on the upper wishbone, as seen on the Saturn plans. But then that puts suspension loads through an adjuster, and I get the impression that's a bad thing to do.

Is there any way of keeping an adjuster on the outboard end of the wishbone, or do I need to relocate it somewhere else?


Personally, I'd think about re-designing the wishbone so that camber adjustment is by shims, sandwiched between a clevis (attached to the upright) and the end of the wishbone, with a couple of bolts holding the whole lot tight together.


Aha, yes thats a good plan. That would give me a bit more strength, compared to everything coming through a single screw thread. Time for me to get drawing methinks...

Sam_68 - 7/6/14 at 03:38 PM

quote:
Originally posted by Slimy38...That would give me a bit more strength, compared to everything coming through a single screw thread.

It also means that the shanks of the bolts are loaded in shear (acceptable) rather than in bending (bad).

Having said which, an equivalent to the 'Sierra' design shown on page 69 would doubtless be fine: One of Colin Chapman's favourite sayings was that you could suspend a double-decker bus from a 1/4" bolt*, so an M20 ought to be good for suspending a Challenger tank.




* Though that would have been in tension, and apparently disproved by calculation by Martin Ogilvie anyway, so don't try it at home, kiddies.

Slimy38 - 7/6/14 at 04:01 PM

quote:
Originally posted by Sam_68

Having said which, an equivalent to the 'Sierra' design shown on page 69 would doubtless be fine:


Yep, I'd had it straight in my head all along that if I stuck with the Sierra design I'd be playing it safe. But it occurred to me last night that I'd be plonking a suspension bracket on top that wasn't in the original design, and out of all four sets of plans that I have, none use a suspension bracket and a wishbone adjuster in close proximity.

To be honest though, your plan of using bolts solves a fair few issues that I had. It gets me away from having to deal with fine metric bolts, I don't have to undo the suspension or upright bolts to adjust the camber, and (in my head) it's a stronger fixing. So it's an all round win.