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MG Midget and Sprite Technical - Rear suspension bits

Thought I'd take a pic before they're bolted on :-)

Nick Nakorn

hi Nick. Where are you in Devon? what are you building
I am in Stoke Gabriel near totnes.
regards Pete K
P C Knightley

Hi Pete,
I live in Devon (Buckfastleigh) but have a workshop in London so I'm up and down the 303 every so often. The pic is the rear suspension I've been designing for my Midget 1500. Have I seen your Midget on YouTube driving through the S.Hams?
Nick
Nick Nakorn

Is that a 4 link rear end conversion ? Is it to work with an early or later axle ? Very interesting.
Andy Phillips (frankenfrog)

Is this something you would consider selling another set of or maybe specific plans and/or measurements so I could build a set? I am planning on building a new race car this summer for autocross and track days.
J Bubela

J Bubela, Hi. There are a large number of changes I'm making to the car and so it will be a while before I will be able to test the design. If all goes well I would certainly consider producing a kit for sale but, until it has been rigourously tested, I do not endorse or recommend it. Though I'm certain the handling will be greatly improved, the modification is mainly for reasons of comfort as the project is to produce a better road car, rather than a track car. I'm happy to provide copies of the drawings for a modest fee once the final-final design is throughly sorted but until then it's a work in progress.

Andy, indeed. I hope to fit it to the car soon. I have designed it around my 1977 Midget 1500 rostyle/steel wheel axle and the 1500 bodyshell.
Nick Nakorn

Nice... where are you going to attach on the axle assembly for the inner mount

P
Prop and the Blackhole Midget

hi nick, mine is a mk2 sprite with a one off body.
its been off the road for 3 years due life and illness
but i am trying to get it back on the road!
if you fancy a trip over to stoke and give me some
encouragement .
regards Pete
P C Knightley

Hi Prop, I've designed and fabricated a mounting that sits on the top of the differential casing. I'm aware that the standard casing is lightweight so time will tell if the casing is strong enough; I've spread the load as much as is practical.
Nick Nakorn

Pete, your Sprite sounds really interesting - do you have pictures of the one-off body? I'm making significant changes to the body of my Midget and will start those when the mechanical stuff is finished. Really I should have done it the other way around (body first then mechanicals) but I need to get the thing mobile and at the correct ride-height, wheel width and so-on. I'll let you know when I'm next in Devon.
Nick Nakorn

hi nick, I am at 14 pound field stoke gabriel(last right
off the Aish road) its on 205 60 13 wheels with no
flared arches. if you have a e=mail I have some
pictures. but your close enough to come and have a look.
regards pete
P C Knightley

Hi Nick,
This is something ive been mulling over for a while and have done some research.... i was looking at a bolt on annular ring using the diff mounting studs, i think we probably have a similar idea....
One thing i did find was the picture attached from an early Lotus, they used the same axle and had a welded on bracket for the third link... They had problems and ended up welding extra gussets on in red in the picture....

in my mind i was copying the lotus 3 link setup , but put the third link on top and split the bush into two so that the attachment points would be at around 11 and 1 o clock when looking at the diff.


however mine is just vapourware at the moment ! .So i'm very interested to see how you go with yours
Andy Phillips (frankenfrog)

sorry, picture now attached...

Andy Phillips (frankenfrog)

At some point I'll post a pic of it all bolted on (my computer went wrong and I lost all the build pics). I tried out the anular ring idea as a sketch but I could not get the geometry I wanted. With the current design I think I have all the advantages of a 4-link and tne geometry of parallel links. The pick-up points on the axle being behind the axle centre-line.
Nick Nakorn

Hi chaps, I'm feeling somewhat chuffed that the prototype rear suspension is now on the car and, though I say it myself, is looking good. I hasten to add that it is untested and may not work as well as it looks.

Nick Nakorn

hi nick , looking good. my beast has a similar set up
but uses the ottigina; 1/4 elliptical springs.
prtr
P C Knightley

Cheers Pete,
I'll swing by when I'm next in the area and take a look. My e-mail is nick@nagara.co.uk
Nick
Nick Nakorn

If it drives half as good as it looks it 'll be fantastic!

Did you only drill holes for the top mount?
And just welded the brackets to the axle?

Did you do anything to spread the load on the top suspension mounts?
Onno K

Is the shell laying on it s side? If so, could you put a floor jack under the end or the axle housing and check the lateral movement?
Trevor Jessie

Onno K, many thanks - I hope so. The top mounts on each side have very strong triangulated brackets inside the car that take the vertical loads to the side chassis rails and in addition there is a strong brace between the two to take any horizontal loads and improve the rigidity of the shell; the floor of the car takes very little loading, if any.

Trevor, ideed it was - I made a tilter for easy access. The car is now the right way up. I did not put a jack beneath the end of the axle as I'm very confident it simply would have lifted the whole rear of the car (the car is so light). The closest I got to that kind of test was to lift it manually and it seemed very solid. Chassis-side the rod-ends are bushed with performance polyurethene and axle-side the rod-ends are all spherical bearings so there's only the compliance of the polyurethene and the spring in the tubular arms in terms of lateral deflection; the latter is negligible in a static lift; on the road, though, it will be a different matter and that will be the proof of the pudding.
Nick Nakorn

Im impressed....very nice indeed

My plan.. at least a year away is to use a shortened 1st generation RX7 rearend that has LSD and disk brakes, attach lakewood ladder bars, my pan hard rod, and carrera adjustable tube shocks

But now that ive seen your set up, im definatly going with coil over springs instead of leaf springs

Where / how / from what did you come up with the coils... or was it a kit

Really blown away

Prop

Prop and the Blackhole Midget

Just a thought....

Did you consider making a plate that would bolt to the pumpkin hardware to mount the inner rods.

Would that work or was there an issue/flaw of some type in the engineering

Prop
Prop and the Blackhole Midget

Cheers Prop! Always great to have encouragement.

No, it's not a kit, I designed it myself than fabricated most of the parts around standard items. I made the bushed rod-ends to fit the bushes normally used for the leaf springs. The arms are just steel tube with threaded bungs welded to them (I bought the bungs) and I fabricated all the brackets. I spent ages choosing the Spring-damper units and decided on Gaz units because they're cheap (for the UK!)and have a very good range of sizes and spring rates (they also supply the springs)and they have adjustable dampers built-in. The main problem was getting info from their factory.

I thought about a mounting utilising the pumpkin bolts in the form of a ring with the mounts welded to it. But I could not get the geometry I was after with that set up (I only sketched it out but it was clear it wouldn't work and it would mean replacing all the studs (longer and stronger). Additionally, I really wanted the mountings to be double-shear with the tabs boxed and welded both sides. The only position that made sense for the geometry and the strength I was after was behind and above the axle line either side of the diff housing; but it took a lot of drawings to get it right.

Many thanks for all your kind comments!

Nick
Nick Nakorn

Prop, get a set or coil overs from a John Deere Gator. You can get them for nearly free when people upgrade. In a near vertical position the spring rate and dampening might be very good.
Trevor Jessie

Feels great to at last have the car sitting on the ground on its wheels. The ride height is about what I'd expected and it will settle down somewhat at the car is rebuilt.

Nick Nakorn

Are the coilovers adjusted all the way down for that photo?
Trevor Jessie

Beautiful work!

Idea: stroke it through its full travel without the springs installed so you can confirm there is no binding, and that the movement of the rear axle housing is as intended.



Norm
Norm Kerr

Hi Trevor - the coilovers were adjusted for finger-tight pre-load (zero,good as) so if it sits too low I can tighten it up.
Hey Norm, many thanks - I'm pleased with the way it's going. Before the shiny paint went on I assembled the whole thing without springs and it articulated perfectly with no binding at all. I tried all combinations of left-droop/right-bump etc.. etc.. and it was beautifully smooth. I think all the preparation in terms of lots of sketches and scale drawings has paid off.
Thanks again for the encouragement chaps, it's appreciated.
Nick











Nick Nakorn

Nice set up, been thinking about something similar for years but never had the time etc, going to follow with great interest.

Brian
brian s

Thanks trevor,

I will definatly look into the john deere gator, im assuming thats an ATV

Prop
Prop and the Blackhole Midget

Wow trevor,

I just looked those john deere coil overs up.on ebay what a great idea and very cost effective...lots of them for under $100 for the pair

Any ideas on how to figure out which ones to use ?

What a great
Prop and the Blackhole Midget

Nice work,....

With your design does the pinion angle change with the rear wheel bump ? or does the axle move parallel up and down ?

ive seen some designs where the top arms are shorter than the bottom ones to give this feature, but it maybe that there are for longer travel off road vehicles...

keep up the good work, cant wait to hear how she drives..
Andy
Andy Phillips (frankenfrog)

Hi Andy, the shorter top arms make matters worse in my view. My system (I think) is the closest one can get to 'vertical' movement in the space available and the exact positions of the mounting points (on chassis and axle) dictate whether or not one gets a tad of understeer or a tad of oversteer when cornering hard (extremes of bump and droop between each side). As Midgets will oversteer easily anyway, I've gone for a tad of understeer to make things as neutral as possible. But it's all a compromise because with a live axle the geometry is always flawed.
Nick Nakorn

When you welded brackets on the diff housing/axle tube, did it distort? If so, was it difficult to straighten?
Trevor Jessie

Trevor - a very good question. As far as I can tell, all is well. Put it this way, the half-shafts fitted with no problems and nothing looks out of line. I don't have any suitable equipment for measuring distortion so I don't actually know - but I was very conscious when welding to tack all over the place and not do any long seams, the brackets are fully welded but in short 'stitches' so I'm reasonably confident that everything is OK. It's a good question because, when stripped of everything, those axle casings are very light and not all that thick. If I get any trouble from the axle casing in use then I'll think again about the brackets and how they are welded.
Nick Nakorn

I watched a guy straighten an axle tube by welding a bead on the opposite side to draw it back in line. It was mounted to a welding table with jigs to check for alignment. Beyond my abilities, but wasn't sure if it was a concern on a spridget axle housing.
Trevor Jessie

Trevor,

You probably know Woody (if I remember his name correctly) who is from here and raced Spridgets. He had that warping problem with some axle housings. I think the result was breaking half shafts.

Charley
C R Huff

This thread was discussed between 10/04/2014 and 22/04/2014

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