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MG Midget and Sprite Technical - Suspension lean question.


Following the midget run from Toddington last week, I noticed that starting was getting more problematical, a bit like a battery with no go. That seemed unlikely as the car had had 6 hours of running the previous day. Anyhow it got worse and had to be push started to get back home, terrible graunching noises:-(
Got home and found that the only problem was the starter motor was so loose that the pinion could not engage. Even better the teeth on the ring gear were pristine, so have a new pinion on order as the that has wear.

So being as how the car was jacked up and on stands, I thought that I may as well do something about changing the springs. Mark Baldry had suggested Peter May 400lb springs, Anthony reckoned my dampers would not cope with that poundage, so I got a pair of standard springs.

Reading through the archives, I could see the pros and cons of the different methods of changing springs - swing lower wishbone down, or long bolts and wind spring pan down.

I opted for the swing wishbone down method, and got old spring out with a bit of struggle. Unfortunately there was no way I was going to able to get the new one in, just too long and I was unable to compress it. So I changed over to the long bolt method. That would have been OK except that a PO had very kindly welded two of the bolts in place, so not able to use the long bolts as specified. I had put the two long bolts on side of the spring pan and use a scissor jack on the other side. I could not use the jack on its own to put the spring pan up as the car was lifting off the axle stands, and I had no one heavy to sit on the wing for me.

So that was the off side spring installed, time taken - 4 hours!

Went to do the near side and used the long bolt method, this time no welded bolts, time taken 30 mins.

Car now sits suitably higher and the off side tyre no longer hit the top of wheel arch when turning left over sleeping policemen (there is one at the end of my road).

But, I still have traditional lean (as discussed to oblivion in the archives) to the off-side (right). It is a 1" lean. I have read that some people have packed the higher side spring pan down.

The question is, do I need to make a packing piece that is a ring to fit under the spring pan, or can I get away with packing with washers, which is a much easier solution? Also what thickness of packing would I need to reduce the 1" lean?

Thanks

Roly

Roly

Hi roly --- pacing with washers is a standard method, and it is what is supplied in the lowering kits!!
Mick - She's off the rotisserie

Roly, I would be interested in hearing why Anthony felt that the dampers would not cope with 400lb springs..... Ours work perfectly well.

As for leveling up the car, if you can afford the lower the 'high side' then that would be the way to go. If you usually drive the car on your own, then you should level it with the equivalent weight of yourself in the driving seat (drums of water are often good for this). Also there is a leverage ratio to take into consideration, as the spring sits apprx half way along the pan, if you lower it by 1/4" at the spring, you will lower the car by about 1/2". It'll require a bit of playing with....

Good luck,
Mark.
Mark T. Boldry

Ant reckoned that the standard dampers would not be able to damp the force of the 400lb springs effectively and that one was likely to have a lot of bouncing. I am sure he will be along presently to discuss!

I will have a play during the week at levelling the car up.

Thanks

Roly

Roly Alcock

...trundle...

I've had experience of fitting uprated springs with std dampers, and the result can be 'bouncy', i.e. the dampers take several oscillations to absorb the additional energy that is stored in the sping (decay); and the oscillation frequecy is higher. The interaction between spring rate and damper rate is complex - but the feeling of the under-damped spring is uncomfortable (as is the maths: 2nd order differential equation...! )

The original design brief would have included matching the oscillation decay and frequency between front and rear.

IIRC the std spring rate is around 270lb/in. IIRC (e.g. from old Moss catalogs) also uprated road springs are often around 330 lb/in, that is ~20% uprated and are 'OK' to use with std dampers. The 400lb/in springs are 50% updated... quite a bit for the std damper to cope with.

Given the quality of dampers these days, I would not recommend uprating to 400lb/in without the caveat that it's likely that the dampers would need to be uprated. I didn't say - don't do it; but like all such conversations I feel obliged to discuss the likely (+ve and -ve) impacts of any change. It's only fair to the 'victim'. Roly's damping to me seemed to be adequate for normal road use but nothing special.

Mark - you have the knowledge of where to buy good or how to uprate std dampers that may not be available to all.

BTW - my top recommedation for fsusp upgrade is 11/16 ARB; a tremendous improvement in stability and cornering with very few -ve side-effects.

Ride height: I packed mine with 4 nuts of the next higher dia; very easy and quick to do (one bolt at a time) esp if you don't have the FL conversion with the bar underneath the pan.

HTH and sorry for the long post.

A
Anthony

This thread was discussed between 14/09/2008 and 15/09/2008

MG Midget and Sprite Technical index

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