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MG Midget and Sprite Technical - steering / suspension settings?

Hi,

hopefully a quick question...

I've just put peter may negative camber top trunnions on my 74 rwa midget. All the rest of the suspension is in good shape with new poly bushes on the wishbones, but otherwise standard.

I've not altered any other settings and its gone from a nice handling, light steering car into an incredibly heavy steering that you have to wrestle with and no self centreing, and it handles awful.

I'm guessing that the tracking will now be way out...

Does anyone have to hand the figures that I need in order to get it set up properly?

Thanks,
John


John Collins

You front wheels will be towing out... looks comical, drives aweful.

I set my tracking using a long ally bar; must be many descriptions in archive... you need to go for slight toe-in.

A
Anthony Cutler

do people often run this much camber on the road - I was under the impression they were beneficial for track cars only?
David Smith

Hi John
Something seems wrong.
I fitted the pm trunnions to my car and it transformed it, as you say it did throw my tracking out alot, the best setting I found was to set the track at zero or may be 1mm toe in each side.
Hope this helps
Rob Newt

As Ant says, it will be toeing out quite a lot.

Either set it to standard - toeing in slightly - or zero, as Rob says, although the latter will make it a bit twitchy in a straight line, but it will have a much sharper turn-in to corners.
Dave O'Neill 2

This is why I love this bbs, quick answers from those who have done the mods already.

Thanks for the info, I had a useful evening in teh garage tonight, and made 2 steps forwards but 3 steps back....

1 - tracking is way out, and my rack obviously wasn't centred when I fitted the car (learning as I go on with it!) so backed off both track rod ends off the rack, centred the steering by counting lock to lock turns of the wheel and am tightening each end of teh rack gradually by the same amount until I can start measuring it more accurately.

2 - snapped a wheel stud ! (annoying)

3 - found out that the steering was too heavy as I'd locked up the kingpin due to missing one of the shims that was still in the old trunnion - both stub axles turn easily again now.

4 - noticed a huge amount of sideways movement on one of the shock absorber arms (on a car that passed MOT 6 months ago and has done less than 1200 miles since) - annoying again!

5 - lack of self centring due to locked kingpins but also due to brake disc back plate fouling on the new trunnions - 2 mins with some tinsnips and sorted.

so will now have to remove hub and change wheel stud, then get roughly tracked before taking it in to be set up again. will let you know how I get on over the coming weekend.

Thanks,
John


John Collins

John,
At least you are moving in the right direction!!!

If it's anything like my old mini - Negative camber bottom arms in that case - once set up made the car feel great - much more confident in the corners!!!
Jon White

My tracking gauge

when do you want it?

It needs a flat area to use it on

I know you have that so when?
Bill 1

Hmmm where has he got a flat area ...???? It's too hilly for a Fen-lass at his place - some of us get altitude sickness when buying parts ;)

Glad you got it sorted - was wondering if it was tracking - or hoping as I'd not noticed in a car I drove with them on but wasn't going to fit mine without seeing!!
rachmacb

for people with the PM negative trunnions - as they are brass bushings - is the car now ruff as a badgers wotsit to drive? or does it not make much of a difference?

I'd like some -ve camber but not if it's going to shake my teeth out...
Rob Armstrong

There is a company here in the states that make an offset trunnion that can use the standard shaped bushings.
Trevor Jessie

As I said, mine aren't fitted just yet, but the car that I drove with them on was as smooth as a baby's backside!
rachmacb

I'd like someone to lighten Peter May negative camber trunnions so they looked and weighed a bit more like the original. I'd also like a modified Peter May negative camber trunion that takes a polybush.

Hit a pothole with the solid bush trunnion and you know you've hit a pothole otherwise they'e ok.
Daniel Thirteen-Twelve

Further to what Daniel suggests about lighter neg' camber trunnions I have a set of Aldon negative camber trunnions I bought approx 30 years ago, they are made in cast aluminium and take the standard rubber or poly bushes (similar to what Trevor mentions). I have never heard anybody mention them so must be resonably rare. Somebody needs to remake them, I believe they would be very popular, and with CNC machining these days, once somebody has set up a programme for the machine they could easily be repeated, its not a complicated part really. I used them for years until I fitted F-Line conversion, they were excellent on my rally car (in my youth !!)

I have a set of the solid P May ones, I would never fit them on a road car, smooth race track or sprint/ hillclimb only IMO. Actualy I would sell them if anybody wants a pair.

Ian
Ian Webb '73 GAN5

You can get nylatron bushes which are a compromise netween PM solid and polybush. They also come with an off-set so you can adjust the amount of -ve camber.
l snowdon

I fitted a set of PM trunnions, but have since removed them, as the ride was as hard as hell. Anyone know if the solid bushes can be removed, and polys fitted ?.

Dave
Dave Barrow

I was aware of the offset nylatron ones - but what stops them from rotating in the housing?

I think Ian is right, some offset ones with polybush ability would be well received :)
Rob Armstrong

as I said in post #3
I was under the impression they were beneficial for track cars only?
David Smith

"some offset ones with polybush ability would be well received"

Try www.speedwellengineering.com , they used to list them on their website.
Trevor Jessie

Upper trunion bushes have very little effect on the ride quality. Most of the impact force from road irregularities is absorbed by the lower inner A frame bushes. We don't concern ourselves with the ride quality that the solid lower trunion give because of the soft inner A frame bushes. If you change to a nylatron or other hard inner bushing then you'll get a noticable increase in ride harshness but the upper trunion bushing doesn't add much harshness at all. I've run my car for years now with nylatron upper trunion and lower inner A frame bushings and it's still fairly comfortable on the road. The tires really absorb most of the harsh impacts anyway.
The offset upper trunion bushes do have a problem with rotation if the trunion bolts are not well lubricated. The nylatron bushes are supposed to be self lubricating, but when using the offset ones I'd add some grease or silicon lubricant to the bore to help prevent binding on the bolt.
B Young

Well upper trunion bushs may well have very little effect on ride quality BUT if you go over a bump or across a pot hole it's quite a difference compared to polybushed trunnions.

I've never see the Aldon trunnions in the metal and am surprised they are in aluminium as if they break.... I noticed that PM didn't make his from aluminium.

How much camber do the Aldon ones produce compared to the PM (can only really be tested on the same car by swapping from to the other).

How about having the Aldon one used as a pattern to have some forged/cast in steel??
Daniel Thirteen-Twelve

I honestly couldn't tell the difference in ride harshness after fitting the Peter May trunnions. I'm sure they could be modified to take poly bushes if required though. The PM ones are machined from a solid block of steel so having a batch made to accept the profile of a bush should be easy for a decent machine shop.
John Payne

Daniel
I would be happy to supply mine as a pattern for making a new ones, but it is probly cheaper these days to machine them from solid, as CNC machines are plentiful and once set up can knock out these parts all day (bearing in mind a casting has also to have proably 50% of the same machining anyway.
I will dig them out and post a photo at the weekend.

Ian
Ian Webb '73 GAN5

Gents
Photo of Aldon negative camber aluminium trunnions as promised.
Ian



Ian Webb '73 GAN5

Very nice, first time I've ever seen these.
Daniel Thirteen-Twelve

from the looks of it, the shape seems rather simple.
I bet that a machinist could make them out of a block of aluminum, or steel, whichever was desired.

The only trick would be doing the math to make sure you had the horizontal hole located just right, to get the camber one was looking for.

Actually, once you had the geometry figured out, it would be possible to have each side machined accordingly to balance out any imbalance in the frame (RH/LH).

Norm
Norm Kerr

Technically, the hole is tapered for the bushings, but it would still be easily accomplished. You could even make them taller to accommodate the spritfire rotors of a brake conversion.
Trevor Jessie

OK,

interesting reading on this thread,

But I actually got a few spare minutes to work on my car this week,

got the tracking set to 1mm toe in, what a transformation, light steering, no bump steer as before, seems much more stable on my favourite roads, and sharper turn in. But makes the rear end feel looser, so perhaps need to fit the panhard rod thats lurking in my spares shed!

definately a good upgrade, just need an 11/16th arb if anyone has one spare?????

John
John Collins

This thread was discussed between 14/03/2011 and 29/03/2011

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