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Author: Subject: Top mounting shocks..... totally shocking?
DorsetStrider

posted on 18/9/05 at 05:34 PM Reply With Quote
Top mounting shocks..... totally shocking?

I've got a question for all the suspension experts out there....

I'm thinking of how I'm going to sort out my rear suspension. I'm building a mid engined car (NOT a 7) and would like to use a similar rear suspension design to that of the book front. However with the drive shafts going through the middle of the wheel mounting the damper is going to be a problem.... is there any reason I can't mount the damper on the top wishbone instead of the lower?





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quattromike

posted on 18/9/05 at 05:47 PM Reply With Quote
Good question! I'm doing the exact same thing at the rear(with the shock coming from the top A arm). I just hope the transit track rod is up to it. I think it'll be perfectly ok, the only thing is I'm only going to have 3 1/2" travel on my shocker which should be enough it'll just have to have a stiff spring on it.
As I say I would like to hear what everyones opinions are on this.
Mike

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gustavo_brum
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posted on 18/9/05 at 05:57 PM Reply With Quote
Not a very good idea... track rod ends are not designed for bending, only longitudinal loads. Maybe you should mount the track rod end to the lower arm instead. It´s simple and safer.

Gustavo

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JoelP

posted on 18/9/05 at 06:28 PM Reply With Quote
i see nothing wrong with it myself, at least the TRE is getting pushed down, not apart.

One alternative is to run a push rod off the lower arm, and mount it to avoid the driveshaft.

If you arent happy with a TRE taking the load, just use a different upper ball joint.





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britishtrident

posted on 18/9/05 at 06:45 PM Reply With Quote
Copying a front suspension for a rear is a really bad start -- even more so when it is the book front suspension with its massive bump steer problems.

A better start would be adapting MK style rear IRS.

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JoelP

posted on 18/9/05 at 07:14 PM Reply With Quote
what engine are you using, and are the hubs the matching ones? And are you using an insert to replace a strut?





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MikeRJ

posted on 18/9/05 at 07:45 PM Reply With Quote
The transit rod end works at the front of the car because it only has to resist sideways forces from braking. Even so, it's not really designed for this application and the conclusions from previous discussions on here suggest is that there isn't a very large safety factor as the thread is stressed in bending rather than tension/compression (though the failure rate would suggest it's strong enough).

However, putting suspension forces through it is a very bad idea, not only from the strength issue, but because force transfered through the balljoint in that direction will compress the internal spring that keeps the ball tightly in it's socket. This means the ball will be free to float around, giving unwanted movement in your suspension.

As you are presumably designing something from scratch, why not use a ball joint designed for this application, from e.g. a metro?

[Edited on 18/9/05 by MikeRJ]

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DorsetStrider

posted on 18/9/05 at 08:54 PM Reply With Quote
Ok well if the problem is in the TRE what about if I reveresed things? using a ball joint facing downwards at the top and a TRE facing up at the bottom? or is this an even worse idea?

The other option would be as someone pointed out working in a mounting for a push rod and having a cantilevered suspension.





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suparuss

posted on 18/9/05 at 09:44 PM Reply With Quote
am i missing something here? if it is the rear suspension you dont need balljoints at all.
just bushes or spherical bearings for up/down movement. no point copying the whole front suspension design. youd probably be better off modifying your upright with a bracket and using a polybush, or prefferably 2.

Russ.

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JoelP

posted on 18/9/05 at 09:53 PM Reply With Quote
i think he's using a FWD setup at the back, hence the hubs will be steerable. Id agree with you though, much easier to use different hubs that dont need balljoints.

does anyone do ally rear uprights for the sierra based 7s?

[Edited on 18/9/05 by JoelP]





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Rorty

posted on 19/9/05 at 03:41 AM Reply With Quote
The TRE is probably not suitable for the upper wishbone if you intend mounting the shock to the upper wishbone.
The Transit TRE or DLE is definitely not suitable for use on the lower wishbone.
Fit a propper balljoint (not a TRE or DLE) to the upper wishbone, and don't be tempted to use one that's normally situated on a lower wishbone (unless you pull one apart and examine its construction), as most balljoints are designed to work either as a lower joint or an upper joint, but seldom both. There are exceptions.





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NS Dev

posted on 19/9/05 at 07:54 AM Reply With Quote
quote:
Originally posted by Rorty
The TRE is probably not suitable for the upper wishbone if you intend mounting the shock to the upper wishbone.
The Transit TRE or DLE is definitely not suitable for use on the lower wishbone.



Why not?

I know what you are saying about compression or tension type balljoints, but the transit one is a steering joint so is neither.

I use the transit joints top and bottom on the grasser with no problem at all, though that is very light.

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Rorty

posted on 19/9/05 at 08:29 AM Reply With Quote
OK, if it works it works, but bear in mind you only do a few hundred yards in your car once or twice a month.
I would have thought the Transit TLE would not stand up to the rigours of long road use.





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Syd Bridge

posted on 19/9/05 at 08:29 AM Reply With Quote
Go to a Kit Car show and look at what all the manufacturers are doing.

The shock should mount straight on to the upright. Thence, no big balljoint probs.

The parts are all commercially available, so why try and reinvent the system?

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smart51

posted on 19/9/05 at 08:33 AM Reply With Quote
could you have the shock off centre? If you are worried about twisting forces, have one on either side!
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MikeRJ

posted on 19/9/05 at 09:00 AM Reply With Quote
quote:
Originally posted by NS Dev
Why not?

I know what you are saying about compression or tension type balljoints, but the transit one is a steering joint so is neither.


It may not be designed as one or the other, but it definately contains an internal spring to compensate for wear (virtualy all standard TRE's do IME). Pushing the taper up into the body of the TRE will compress the spring and lift the ball out of it's socket. Try putting one in a vice and you'll see what I mean. If no forces are put through the joint in this direction then it might be suitable.

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NS Dev

posted on 19/9/05 at 10:00 AM Reply With Quote
That's probably it, and as Rorty said, mileage is low and maintainance thorough on the grasser.

It's certainly had some biggish hits on the front corners now though (enough to take chunks out of the wheels) and the balljoints are fine.

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Stu16v

posted on 19/9/05 at 07:05 PM Reply With Quote
Interesting to note that folk using a Maxi bottom ball joint are, in theory at least, loading the joint differently to how it was intended as well...





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