MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - a frame

Hi
Is any one using an A frame to locate the rear axle?
tim
Tim Dalton

Not me.
David "it always seems to be right where I left it ;-)" Lieb
David Lieb

I've used a dowsing rod to locate water, but never a rear axle. They're almost always behind me.

Peter "David started it" Caldwell
Peter Caldwell

You might try looking under the car to see if the axle is still there....pulling the roof off the house is just to much work.


Prop...I dont live in an A frame house...Prop
Props Black Hole

To add some seriousness to the thread...Granted it is friday so who wants to do that...LOL

what is your thinking about an A-frame...Im unaware of this concept, luckly Ive never had to locate the axle as I just used the rust lines to bolt everything back up. probably not the best idea, but I think its a common one.


Prop
Props Black Hole

Hi Tim
i was going that way untill i spoke to a very good race engineer who builds midgets and sunbeam tigers,
he said the roll centre would be to low and the spring rate would need tobe very high good for track and hillclimbs but not for road.
Gary
gary knowles

I think the concern is about the point of the A and short bearing/bush life.

I don't except the roll centre being 'too low' would be a problem on a road car. Besides how low is too low and is that lower than Frontline's mumford link system?

Still I don't claim to be a suspension expert and willing to learn something new or argue about it on this one!
Daniel Thirteen-Twelve

One of the points about an A frame is which way round you mount it.

I would go for the apex at the back edge of the floor as this gives a RC fixed to the chassis and with the outer ends fixed to the axle near the spring mounts, doesn't stress the axle.

The lower RC issue can be corrected with a rear ARB as the issue is the increased roll moment, stiffer springs being a simple fix with the drawback of high bump rate, a rear ARB being far more effective at increasing the roll rate without effecting the bump rate so much.

Fixing the apex to the centre of the axle has the problem of imposing bending on the axle which could lead to the casing failure. The Caterham live axle uses this set-up and has strengthening behind the axle. In the Caterham case, with a lower A frame and 2 upper links, the A frame take the majority of the force accelerating the car through the centre bottom of the axle.
David Billington

I had an early Lotus Cortina which originally had "A" frame location for the rear axle with radius arms, coil springs and tube dampers. As per David's post above, they were a disaster on the road, great for race tracks but on the road they would tear up the rear axle.
Most were modded with leaf springs and tube shocks, which mine had when I bought it. So "A" frame possibly not the best idea for a road car without a great deal of reinforcement!
Graham.
Graham P 1330 Frogeye

IIRC the yellow midget of John Britten reg no SS1800 had an A frame rear suspension. Its on Martin Ingall's ecellent Sebringsprite.com website, I have some mag articles somewhere, will check it out, can anyone confirm ?
Ian
Ian Webb '73 GAN5

Please clarify.
The problem with the A Frame locating the axle is potential damage to the axle housing?
I think I have that covered. I shaped a piece of 1/2" thick steel to match the curve on the housing and welded it all around. It has a 1" hole in the center for the drain plug. There are two 3/8" thick tabs welded to this for the "apex" rose joint. The axle housing is much to thin to support the load-about 1/8" thick. The "apex" rose joint is a heavy duty 3/4"

Regarding the stress to the leaf springs I'm hoping to be able to remove my rear sway bar.
Carol Smith mentions this in one of his books but I can't remember which one right now.
Tom
TCW Tom Westcot

Tom
With the amount of load that is going to be on the centre joint it needs to be fitted so that the mounting bolt passes through the joint verticaly. Also the cross bar of your A frame needs to be as close as possible to the front joints so that the load is shared by both joints Cheers Willy
WilliamRevit

Tom,

Is your post wanting clarification of what issues can be caused by mounting the A frame from the centre of the axle or a statement of how you worked around it.
David Billington

This pic re lotus 7 rear suspension may be of some assistance:
http://kit-car.org/Files/suspension/lotus_s2rear.jpg
Graham
Graham P 1330 Frogeye

David Shannon's Class A Midget Challenge car ran with Caterham A frame rear suspension (and had a bracing plate exactly like the one suggested in the above link). David won Class A of the Midget Challenge in 1995 in the car, but the suggestion about the rear roll centre may be correct as that car always had too much rear grip compared to front - i.e. it understeered quite badly...
J A Bilsland

This thread was discussed between 21/08/2009 and 31/08/2009

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.