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MG Midget and Sprite Technical - Axle Location

Have been having a think/sketch for rear axle location on the midget. It'll be on coilovers that come up through the rear floor just inboard of the "chassis rails" (almost straight through the square bumpstop plate) and am leaning towards either:


C-Type Jaguar style 3-link, using the original spring mounts on the tub for two lower links, making use of the triangular brace between rear bulkhead and rear chassis rail (that the lever arm would normally bolt to) and an extra, smaller, triangle mounted laterally outboard of that for a 3rd link on the right hand side of the car. Plus panhard, watts linkage, or mumford linkage. Problem - I can't see a structurally nice way to mount a panhard rod on the chassis tub.

(Old) Lotus Seven style 2-link plus a-frame, where the two upper links attach where the 3rd link would on the above design, and the a-frame mounts to the front leaf spring mounts and some bracketry around the sump plug.


These may help visualise:
<snip for language filter>
Anybody here have/that's seen either a 3-link or a-frame setup on a Midget? How was it done?


This mount is not so nice:
<snip for language filter>

This is too complex for my tastes, and I'm not keen on adding a crossbeam to the rear of the car:
<snip for language filter>
ma cosic

First snipped links:
http://www.miracerros.com/mustang/t_suspension2.htm
http://www.sandsmuseum.com/cars/seven/assembly/sevenm.gif
http://www.sandsmuseum.com/cars/seven/assembly/sevencut.gif
ma cosic

second snipped links:
http://spriteparts.com.au/photogallery/gremlin/Panhard%20rod.JPG
ma cosic

Thris snipped link:
http://www.moss-europe.co.uk/Shop/ViewProducts.aspx?PlateIndexID=8111
ma cosic

Any idea why the forum wouldn't let me post the whole message, with links in place? Some language filter shouts at me...
ma cosic

MA,

I think the BB software prevents posts with large numbers of links in it, I have had the problem before also. Yesterday I also had posts go missing when posted in too quickly on the same thread, OK if I waited a few minutes between posts.

Regarding axle location I would have gone for the Watts or Mumford link as location geometry is better than a Panhard. One I did years ago http://www.metal-arts.co.uk/~djb/Watts/ . A mate has a Caterham and was is not shown or not clear in your links is the strengthening plate across the back of the axle diff area. Using an A frame at that position applies most of the force driving the car forward to the centre of the axle at the fixing point for the A frame.
David Billington

My dad ran a S2 Seven for a while when younger and the A-Frame to Axle fixing was a terrible weak point. The axle just isn't designed to take those particular loads at that point.
Dean Smith ('73 RWA)

Take a look at the new 4 link coil over suspension for the MGB developed by Bill Guzman, I think it would convert well to the Midget chassis with a couple of tweeks on the bar length. The mounts would be almost identical. Here's a link to some information about this product. The lower links mount in the same location as the front of the original leaf springs and the upper links mount to a bracket that bolts on in place of the original shock. http://www.mgexperience.net/phorum/read.php?40,713791,717194#msg-717194


Bill Young

DB: Your watts link is neat enough - I guess there's no way of escaping having to add structure to the chassis to do this properly. Perfectly usable as a three-link too.

A-frame needs to be sized/mounted properly agreed. Lotus Seven was fine on tossply tyres with 35hp, really only dies if you add stickier tyres or more poke.

BY: Would that setup bind if made using properly rigid bushings/mounts? Probably not. Loads in the upper tubes will be nontrivial as you corner mind - they're not at a huge inward angle.

I guess I should appropriately size an a-frame/two link and watts link/three link and see which puts mass where/choose that way.
ma cosic

MA,

A mate has a Caterham with sticky Yokahams tyres and 1.7l 135bhp engine and the axle and A frame are fine, but the axle is reinforced. You do have the option of mounting the A frame the other way round so the apex connects to the back of the floor pan. You end up with the roll centre moving with the chassis rather than the axle that way, IIRC thought to be better that way, and the loads on the axle are at the ends.
David Billington

A '62 S2 Seven with Cosworth 1340 had 85 bhp.

I dont think any of them had 35hp.....even the A series ones :-o
Dean Smith ('73 RWA)

Dave B, that is the first time I have seen a watts linkage done in that manner, I think if it is alright with you that I may copy that to fit over next winter, along with your anti tramp bars.
Bob (robert) Midget Turbo

Bob (Robert),

I have no problem with you copying it and if you have any questions please ask. What is unusual about it?, possibly the centre link mounted to the chassis. It was an idea mentioned to me by a guy I used to know that worked for Ray Mallock and Arthur Mallock used that on his cars before switching to the Mumford link IIRC for better ground clearance/lower RC. It gives a constant distance between the CG and RC.

The Watts linkage shot is the one off my frogeye, the other shots are of a mates Austin Sprite. IIRC the only differences were the linkage was higher on his car, the links came forward slightly from the centre to the outside, the centre fixing was a countersunk screw rather than hex bolt due to clearance issues, and the mounting bracket had a cutout to clear the fuel pipe into the tank.
David Billington

Bill adapted the same basic suspension design used by GM on most of their RWD passenger cars from about 1965 on up into the 80's know as a triangulated 4 link. If properly placed there isn't any bind on the links, but most use urethane or rubber bushings just in case it's a little off and for quietness on a street car. As I understand it has good characteristics of low roll center and no need for a panhard rod. It may not be the best or most adjustable suspension for a race car, but great for the street.
Bill Young

Bill,

That system has been used by a number of cars in Europe as well, the Ford Cortina Mk3 and Mk4 spring to mind as good examples. Regarding the roll centre, that layout actually results in a higher RC than the standard suspension with cart springs, as the RC is governed by the locating links, the upper ones as far as I can see in this case. It looks nice but I would keep an eye on the aluminium and stainless interface as they don't usually make good bed fellows in contact with one another if the environment is prone to promote corrosion.

Bob,

One thing not shown in the details for the Watts linkage is a 1/2" spacer IIRC that spaces the bracket off the boot floor on the off side and wraps around the edge of the fuel tank.
David Billington

This thread was discussed between 28/04/2008 and 30/04/2008

MG Midget and Sprite Technical index

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