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MG Midget and Sprite Technical - front end rebuild

This weekend i rebuilt the front end suspension.
new polybushes all round, new lower A-arm/Springpans, new grease nipples, new bump stops and rebound rubbers and a good clean and lubrication all round.

Steering much smoother/easier now and nice and quiet.

I've not yet put the GRP front back on, just taken it for a spin around the carpark near my house but i notice that on the drivers side there is about 3mm clearance between the rebound rubber and the shock arm, but on passenger side the shock arm actually sits on the rubber.

I wouldnt have thought that correct ?....
Will the suspension bed in after a while?
Is it because of the weight difference (i suspect so) and is the best thing to lower the passenger side a little with some spacers to even it up?

Part of the reason for putting new arms on was to try and even the suspension height, the old arms had seen some welding and action in their past and weren't straight..

ive got the original longer springs with the 271lb (i think) rate..
Andy Phillips (frankenfrog)

There should be MUCH more clearance than that.
Dave O'Neill 2

You've used the same coil springs? Did they go back on the same sides? I might have fitted new ones, or at least swapped side to side to even out the weight difference vs, wear.
Also, re poly bushes, did you leave the lower inner and top outer fulcrum pins loose, put the car back on its wheels, and tighten them afterwards?
David Smith

Hi Dave x2, yes, same springs.
To be honest i didnt keep track of them when taken out so they might or might not be on the same sides..

No, didnt slacken off the bushes then retighten them once on the ground, i'll try that...should have thought of that myself...

However looking at an old picture from an old post i think its been the same for years now, just showing up more now i have the correct rebound rubbers on...

See pic below from a year or two ago... the difference from one side to another is now not so marked due to the straight new A-arms, but the angle of the top suspension arm is about the same as on the RH side when looking at the picture, just that now with proper rebounds it is more obvious.

i think some lowering spacers should sort it out...its probably just a weight issue.. The whole car only weighs about 500kg as its mainly made of plastic...
i'll machine some this week, ive got some bar lying around.

What should the normal rebound rubber to shock arm clearance be ?



Andy Phillips (frankenfrog)

I remember this thread from some time back ... what did we decide was the issue, was it a bent chassis rail?


Prop
Prop and the Blackhole Midget

At the time i was told it was quite normal, but it still seems wrong to me... i would have thought the lever arms should point slightly down with the car stood on its wheels and no one in it, then be nearly level with passengers included.

See my old thread
http://www.mg-cars.net/mg-midget-sprite-technical-bbs/front-suspension-and-ride-hieght-201304301231082107.htm


See new photo of the rebuild assembly below, this is the LH side , viewed from being sat in the car.
Car is stood on its wheels and has been for a thrash around the carpark. You can see the lever arm sitting on the rebound rubber.

i think maybe i just need to get shorter springs.
When i measured them before they were 9 3/4" long.

I think i'm going over old ground from the previous thread above, but now with new A-arms fitted to take out that variable.. at least it'll be safer now, and the polybushes seem great...and with the new A-arms i have the possibility to add an ARB.


Andy Phillips (frankenfrog)

anyone know the weight of an all-steel frog front end? I'm wondering if the reduction to a GRP one (or nothing at all as your 1st post ) makes the difference?
David Smith

I read somewhere about 50kg saving by going from steel to GRP front....
50kg = 110 lb, so if the spring rate is 271lb/in (so 542lb/in for 2 springs) then that would translate to 0.2in extra spring compression = 5mm.

also, i have an aluminium radiator and aluminium cyl head so extra weight savings, so lets say with steel front and normal engine/radiator then the shock arms would be 7mm off the rebound rubbers....

Would that be about what other people have ?
Andy Phillips (frankenfrog)

Andy,

That doesn't take into account the spring being about half way along the wishbone which gives you about a quarter the spring rate at the wheel due to the lever halving the force at the wheel and the spring displacement halved compared to that at the wheel.
David Billington

Good point, so if we double the figure i got then a normal car would have about 14mm clearance with no passengers... that seems a reasonable figure to me....

So it looks like its just down to weight.
Shorter springs are available but stiffer, and given the weight difference i'm afraid they would be too stiff for the road.
Easiest/cheapest thing to just use spacers i think....
Andy Phillips (frankenfrog)

The frog was originally fitted with shorter springs than the later cars.

When I rebuilt mine, I bought later springs (albeit with apparently the correct spring rate) and the car sat far too high at the front. In the end I put spacers (about 1/2 inch or so thick) between the wishbones and spring pans to make the car "look right".

If you take this approach you may also wish to think about the fact that the rebound buffer (on the chassis) will now be further away from the top of the spring pan and thus the wheel will travel further into the wheel arch on full deflection, so check the limits of travel before fitting the springs and make sure that no clashes occur.

I fitted a 1/2 inch packing piece on top of the spring pan to compensate.

Simon
SA Wood

If you've been driving it like that, I'm surprised your steering rack hasn't failed. The track rods are working at an extreme angle.
Dave O'Neill 2

New TRE's 2 years ago, they still seem ok though the gaiter has split, and of course the suspension does go down with my weight in the car.
I had some 4mm thick spacers under the passenger side before i did this rebuild in an attempt to level the suspension. I was hoping that the new A-arms would sort out my problems.

I'll make some new spacers, 12mm" thick for the passenger side and use the old 4mm ones on the drivers side, That should even things up for when theres just me inside.

Another happy weekend lying on my back with two long screwed rods then... I tried the 'jack' method to release the springs but the car is so light that the jack lifts the car off the axle stands before compressing the spring...
Andy Phillips (frankenfrog)

When I reassembled the midget front end with all new parts, I couldn't get the bump stop rubbers in. We left it without until the engine was in, and they still wouldn't go in. Eventually I jacked the A pan up and squeezed them in and dropped the car down again. After a few weeks it all settled a bit more, and being driven has brought everything to the right position

I did the front springs on my A about ten years ago, and going over the first bump at speed made the springs settle into the A pans with a noise that sounded like I had dropped a grand piano

dominic clancy

Andy, after looking at your pictures, I went and looked at my car ('74 Midget and I have lowered the front by putting spacers between the spring pan and A-arm). With no one sitting in it, the TRE and damper lever arms are pretty much horizontal and the space between the lever arm and rebound rubber is approximately 30mm. Don't have an answer as to what's going on, but wouldn't think 110lb. would make that much difference.
Jack Orkin

Hi Jack,
Can you remember what thickness of spacers you used ?

Hi Dominic,
Yes i got the piano sound when i went over the speed bump on the entrance to the carpark, luckily i wasnt driving a morris marina........(top gear joke!)
Andy Phillips (frankenfrog)

Andy, the spacers are about 1/2" or 12mm. Moss US sells a kit (#49) http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29294
but I didn't see it in the Moss UK catalog. The Moss UK catalog is different and much better than the US one. Why is that? Aren't they the same company? Anyway, the spacers are simple round bar stock with a hole drilled in it and a longer bolt.
Jack Orkin

Thanks Jack, 12mm it is then,
i can make my own so can experiment from that starting point.
Andy Phillips (frankenfrog)

OK, back home this weekend so installed 15mm spacers on the passenger side and 3mm on the drivers side.
both shock arms now at a similar height and about 10mm off the rebound rubbers.
before and after photo below...

A quick spin and happy with the results, though may lower a bit further in the future...
now on to the next project... ARB....


Andy Phillips (frankenfrog)

This thread was discussed between 19/10/2014 and 27/10/2014

MG Midget and Sprite Technical index

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