chrisf
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| posted on 22/10/08 at 12:59 PM |
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Suspension Idea <OT>
Hi gents:
This is a bit off topic, but you guys have been more than helpful in the past. I hope this is no bother...
OK, so I'm building my wife a MX-5/Miata powered MG Midget (check the website for details). I'm going
to try to stay with the stock rear axle and 1/2 elliptic leaft springs--yes, a buggy suspension. Anyway, to control lateral movement, I'm
considering the following.
 
MG Midget Suspension Idea
The green lines are the proposed links to control lateral movement of the axle. What are your thoughts on this? Will this idea work OK or should I
bite the bullet and design a panhard bar?
Understand this car is for my wife to dash out with friends for shopping, wine, etc.; it's not going to be a roadracer. The Miata engine only has
120 hp and was selected for the fuel injection and reliabilty--nothing more.
Again, apologies for the off-topic question.
--Thanks, Chris
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Mr Whippy
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| posted on 22/10/08 at 01:08 PM |
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I don't think I'd do that as the distance between the axle and the chassis will change as the springs compress, that will pull on the twin
link bar and probably cause the axle to rotate, also make the bushes wear out very fast. You can use double links with trailing arm suspension. If you
are finding a lot of lateral movement then check the sping bushes for wear, ususally the springs stop sideways movement.
Fame is when your old car is plastered all over the internet
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chrisf
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| posted on 22/10/08 at 01:14 PM |
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Hi:
I should have stated this car has never been driven--by me anyway, so I'm just predicting lateral movement. All the bushings in the leaf springs
will be replaced with poly.
So what if I used rod ends on each side of the link? Same issue?
--thanks, chris
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mookaloid
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| posted on 22/10/08 at 01:17 PM |
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I agree with the above - I didn't think there was a problem with the rear suspension on a midget anyway - maybe go for improved shockers to
tighten things up and maybe slightly wider wheels and tyres if they will fit.
The power may not be much from the mazda engine but it's nearly double what the midget had originally, so I would make sure that the brakes are
up to the job and that the rest of the suspension is in tip top condition.
Cheers
Mark
"That thing you're thinking - it wont be that."
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tegwin
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| posted on 22/10/08 at 01:17 PM |
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Why do you want to add the bars?
The standard rear suspension setup would be adequate to stop lateral movement....
If you want to make it more "interesting" convert it to IRS...I know of several cars that this has been done to
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Mr Whippy
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| posted on 22/10/08 at 01:22 PM |
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well having thrashed the life out a friends midget showning him how to drift roundabouts sideways. I can tell you lateral movement is not an issue.
It'll be noisy mind with the poly bushes and you'll really hear the diff whine like you need a new one. Put grease in the bolt before
fitting as poly bushes squeak 
also the brakes suck
[Edited on 22/10/08 by Mr Whippy]
Fame is when your old car is plastered all over the internet
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chrisf
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| posted on 22/10/08 at 01:42 PM |
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Thanks Gents! That is actually encouraging news. I dreaded f-ing around with controling lateral movement.
I have a rubber bumper car with the 4x4 ride height. I plan on dropping it 2" all round. Is this a bad idea? I figured the chrome bumper cars
rolled out of the factory 1.5" lower than the rubber bumper cars. So what's the harm in dropping it another 1/2"?
Oh, I lost the rubber bumpers and I'm doing sheetmetal work to convert it back to CB specs. I'll also look to replace the brakes  And
I'm doing telescoping shocks as well--front and rear. Those lever arms seems like an awful idea.
--Thanks, Chris
[Edited on 22/10/08 by chrisf]
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Mr Whippy
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| posted on 22/10/08 at 01:55 PM |
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I'd say fit the new dampers then try it out on the road and see what you think before guessing what you need. They have normally got quite soft
suspension so I found it bottomed out quite easly on country roads, which is what they were designed for after all.
Fame is when your old car is plastered all over the internet
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HAL 1
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| posted on 22/10/08 at 02:24 PM |
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I once owned 'B'GT with rubber bumpers, after some heavy use the rear springs sagged so i just replaced the front ones with chrome type to
bring it down a bit, seemed to work ok.
could be worth asking around with regard to replacing springs, the ride height was only for U S regs and i doubt whether B L spent vast amounts on
re-development of the bodyshell
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MikeRJ
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| posted on 22/10/08 at 02:37 PM |
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The 1/2 eliptic rear suspension is a lot better than the earlier 1/4 eliptic, but still suffers from the same issues as most Hotchkiss type
arrangments i.e. axle tramp and location. A panhrad rod and anti- tramp bars would be a wise addition to any tuned Midget IMO. They are available
through e.g. MOSS, but are rather expensive for what you get.
However, it would be quite simple to replicate the design yourself.
The other addition I would consider is a front damper conversion kit. The standard lever arm damper doubles as the upper wishbone, and to say
it's rather flimsy is putting it nicely. A proper upper wishbone conversion and telescopic dampers really help calm down the Midgets
nervousness.
EDIT: Just read you are ditching them anyway!
[Edited on 22/10/08 by MikeRJ]
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Memphis Twin
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| posted on 22/10/08 at 04:38 PM |
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Chris,
The twin radius arms as per your drawing would work very well. I would Rose joint one end and rubber bush the other.
I once hillclimbed a Sylva Leader kitcar with a similar arrangement for lateral axle location. It worked just as effectively as a panhard rod
arrangement, except perhaps off the line with sticky tyres, where it wasn't quite as good at controlling the torque reaction of the axle. But
I'm just splitting hairs there...you'd probably never notice the difference. I would go ahead and do it, and I'm speaking from
experience.
Cheers Chris.
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MikeRJ
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| posted on 22/10/08 at 07:16 PM |
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quote:
Originally posted by chrisf
MG Midget Suspension Idea
Looking at that I diagram reckon the first thing you need to do is find a wider axle or fit some wheel spacers!
Actually the more I think about it, the more I think a panhard rod would be a superior solution all round. Compressing the elliptical springs will
cause the axle to move backwards (which is why one end of the spring needs a shackle), and those links will be trying to resist that motion and will
cause binding if they are mounted in the same plane as the springs on the bottom of the axle.
If they were mounted on the top of the axle then they would give you the benefit of some anti-tramp, but you'd have to get the mounting points in
the right place to prevent the whole axle rotating in bump and droop. This would be simmilar to the later Cortina rear axle location, and it's
still over constrained (i.e. causes binding). This is fixed in the Cortina by rubber void bushes (which used to fail regularly).
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