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MG MGA - Another simple measurement sought

Guys, I previously explained that on my my newly rebuilt chassis of my race car (now to be used soley for road use) the rear rebound straps were stretched to the limit and some of you said that once fitted the body weight would resolve the issue. Well my entire body is actually a lightweight fiberglass shell with 14 inch rims and I still find the straps stretched even with the body re-attached. I will need to get the rear re-set somehow. To assist me in working this out could someone tell me what the distance is between the upper and lower strap mounting points on a standard car. This will help me adjust the ride set up correctly,
regards
mark
Mark Mathiesen

The measurement varies with load. The only measurement that appears to matter is the length of the rebound strap less the amount of drop. In my 58 the car sits 1/2" to 3/4" down from full extension of the straps. How close to being able to install the straps are you now? I would guess you are fairly close, 1/4" to 1/2"? Take that number add to it the 1/2" to 3/4" and you get how far you need to drop the rear axle.
There are 2 ways to drop the axle. #1 reconfigure the spring (re-arch by a spring shop) or add a spacer and get longer u-bolts.
http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29226
A one inch block between parts 12 and the axle in this Moss picture should do the trick. Such a block could easily be made of aluminum stock by matching the width of the spring and the eye bolt hole. Longer U-bolts can be made by any competent spring shop if your are now too short.
R J Brown

RJ Brown, thanks for the reply. Just a quick question regarding the use of a lowering block. Whilst I can see it would raise the axle in relation to the spring wouldnt it also cause the shockie to be stretched even further move it further away from its upper mount?
regards
mark
Mark Mathiesen

The rebound strap mounts to the axle not the spring and would be raised closer to the body. The shock is mounted below the spring and it would be down further.
Re arching the springs would probably be a better way but lowering blocks would be easier.
Have you changed springs? some of the replacement springs are too "tall" See: http://mgaguru.com/mgtech/suspensn/rs102.htm
R J Brown

Hi R J Brown,

I will take the car to a suspension shop to get the springs re-set but will need to use your advice as a starting point. As I see it on my car the strap at full stretch is 225 mm from lower mounting point to upper mounting point. Assuming the slack in a standard unladen roadster should be as you say about 3/4 inch (19mm) then the correct length between the mounting points should be about 8 inches (205 mm). Is this what your advising?
regards
mark
Mark Mathiesen

Mark, I have just measured the length of the new straps I have in my garage. They are 225 centre to centre. Given that the straps only work in one direction, when they stop the axle dropping off, the measurement 205 seems reasonable. So if you set the springs as you suggest, that should be OK. My old roadster is considerably lower than that but it has covered about 400,000 miles and sags noticably.
Barry
BM Gannon

Yes. That said I was a bit surprised to see how little travel ther is in the rear suspension of these cars. One other thought would be to load the car down until it reaches a hight you are comfortable with and use that measurement. You said you are using 14 inch wheels so being at the same height as stock is really not the point. How it looks, how the tires fill the space. These may be more significant quuestions than where is stock.
R J Brown

R J Brown, yes I realised the wheel size could have thrown off the measurement that is why I chose a measuring point un-affected by wheel size (the strap point will be the same no matter what the wheel diameter or moel MGA). As it is going to be used for street/club run purposes I will set up as per yours and Bill's advice and work from there. Thanks to both of you for your input as this point has been holding up things such as getting the new driveshaft made and final stripdown for the final chassis/suspension painting,
regards
mark
Mark Mathiesen

This thread was discussed between 01/01/2008 and 06/01/2008

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