Rear Coilover Mounts

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Rear Coilover Mounts

Postby streetsy » Wed Oct 14, 2015 6:50 pm

I will be fitting coil-overs to my Gold soon-ish, I have been looking at various styles, manufacturers, suppliers etc, I have noticed that coil-overs with a bush or bearing mount at both ends are much more commonplace and cheaper (as opposed to bush and rod type arrangement usually used on Midas'). Bearing this in mind and excusing the crude drawing has anybody tried to make a top mount to allow fitment of a double bushed coil-over.
topmount.jpg
Topmount
topmount.jpg (53.93 KiB) Viewed 8121 times

PRO's
>It would spread the load over its entire area which would be a larger area than the rubber bush on a standard coilover.
>The M12 rod could be as long as required to compensate for the fibreglass thickness.
>Rubber bushes could still be used but would be much larger, therefore spreading the load.

CON's
>Not sure of any

What are your thoughts/experiences.
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Re: Rear Coilover Mounts

Postby Rich » Wed Oct 14, 2015 8:16 pm

Looks like a good solution, particularly as the ones made for the standard fitting often don't have a long enough threaded section. I had to cut down the rubbers on the ProTec ones I had made for the car.
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Re: Rear Coilover Mounts

Postby Stuart » Wed Oct 14, 2015 8:27 pm

Just the job for my new dampers.

Image
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Re: Rear Coilover Mounts

Postby DavidL » Thu Oct 15, 2015 10:25 am

Two possible cons strike me.
The first one which popped into my head is that it could look a bit fussy, given that it's part of the car visible in side view. I appreciate that this is a minor point. However it wouldn't take much work to blank off the top couple of inches with some plastic/aluminium sheet.
The second, which took a few more hours for me to notice, is that this would give you two points of movement at the top of the suspension unit, unless the vertical M12 threaded part was rigidly mounted. Admittedly I was thinking that it would need rubber bushings where it passes through the car body, but I think that's because I'm used to seeing rubber bushes there...
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Re: Rear Coilover Mounts

Postby Hans Efde » Thu Oct 15, 2015 10:46 am

I like it. I have a few old Spax dampers and they are already leaking again. Maybe the cause is in what David says. If there is a bit of play on the suspension bearings (the ones that must be greased), the rigid mounted dampers (as we have now) will experience sideloads. I am quite sure it isn't designed for this. This design will prevent sideloads on the dampers so they may live longer. Only drawback is the limited space and access of the grp turret, but I think it's worth a try.
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Re: Rear Coilover Mounts

Postby DavidL » Thu Oct 15, 2015 12:03 pm

I think I may not have fully described what I meant by "two points of movement".
What I'd meant to imply was that the top mount as drawn by Streetsy could "rock" fore and aft if it isn't rigidly mounted to the wheel arch, and if it's rubber mounted, which is how I initially thought it would have to be, then the top of the suspension unit could also move forwards and backwards.
Also, given the limited access to the inside of the top mount where the suspension unit bolts on, it might be necessary to tighten that bolt before inserting the top mount through the wheel arch - unless you cut a hole through the side of the wheel arch to allow it to be tightened once it's in place.
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Re: Rear Coilover Mounts

Postby Hans Efde » Thu Oct 15, 2015 12:37 pm

The top mount must always be screwed to the body with plenty of rubber bushings, similar to the present shock absorbers. I wouldn't like a solid mount since I expect damage to the monocoque because of the hammering. Also I suppose it will be quite noisy with the unfiltered banging of the shock absorber. But I like the idea of such a mount because it is an extra hingepoint so the absorber isn't getting lateral forces when the suspension develops play. I have had so much trouble with leaking rear shock absorbers, it must be something like this (although my suspension is without play, just saying).
But indeed it may be wise to install the shockabsorber first to the mount and then install the assembly on the car. Although more fiddly than the direct fitting of the shock absorber, we'll have a wider choice in shock absorbers which will be cheaper as well. And installation problems due to the thick grp layer belong to the past. If there will be a group buy for such a mount, I am in.
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Re: Rear Coilover Mounts

Postby DavidL » Thu Oct 15, 2015 12:52 pm

If this top mount is mounted to the body with rubber bushings, then it would probably also have to have something to prevent it turning in the wheel arch hole.
I can't see how this mount would accommodate any lateral forces from worn suspension bearings which aren't already accommodated by the present system. Surely the rubber mounts on top of the existing suspension units already do that? Unless I'm missing something...
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Re: Rear Coilover Mounts

Postby Hans Efde » Thu Oct 15, 2015 1:14 pm

The present way the shock absorber is mounted both upper and lower mounts are fixed. There is a bit of freedom of movement in the rubber bush but it isn't much. It still has to absorb a bending moment if the rear suspension develops play. It has to work as a sort of McPherson suspension, but clearly the Midas shock absorbers are not designed to work as a McPherson suspension. If you take away the bending moment by making a hinge as the mount above, the bending moment in the absorber is gone. This would have positive influence on the life of the absorber. I've made a sketch to clarify my theory (view on wheel looking forward):
Image
Ofcourse I may be wrong, but there must be a reason why rear shock absorbers start leaking so fast.
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Re: Rear Coilover Mounts

Postby DavidL » Thu Oct 15, 2015 1:47 pm

I had envisioned the top mount being fitted with the bolt aligned east-west, rather than north-south as you have drawn it.
My thinking was that you have to allow for the amount of front-to-rear motion of the bottom suspension unit mount as the radius arm travels through its arc - do you think there would be more side-to-side movement in a worn radius arm than the normal amount of front-to-rear movement?
Ideally, you would have a ball joint mount at both ends of the suspension unit, of course.
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