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MG MGB Technical - front springs

whats the difference in length of the front springs on chrome and rubber bumper cars.
bob taylor

According to Clausager, the main reason for the extra ride height was in the design of the crossmember, not because of much or any extra length in the springs. Apparently the GT always had slightly longer springs than the roadster and when the V8 was introduced they started using these longer springs on all types of MGB, but it was the modified crossmember that really made the difference.
Mike Howlett

CB springs also changed to counteract sag when tied down on long sea voyages.

From various sources:

Pre 72 Roadster 9.9" 348 lb/in
Pre 72 GT 9.1" 480 lb/in
72 Roadster 10.2" 348 lb/in
72 on CB GT 9.32" 480 lb/in
73 Roadster 10.2" 373 lb/in
RB GT 10.2" 373 lb/in
V8 9.32" 480 lb/in

So sometimes the free height changed but due to other characteristics the load weight stayed the same, and vice versa, and some RBs were the same as some CBs.

Full detail here http://www.mgb-stuff.org.uk/suspensiontext.htm#springs
paulh4

hi all,

its my friends rubber bumper factory v8. its had a not very good chrome conversion and he thinks its a bit high on the front.not sure myself but looks quite low at the back.the orange one in the picture.


bob taylor

I'm confused now and studying the Moss catalogue hasn't helped. I replaced my front springs on my 71 roadster a long time ago with the correct spring for the car. Within 6 months it has sagged to lower than it was before so I fitted rubber bumper springs which I thought were stiffer and gave a higher ride. They were too high initially but have settled now to be perfect. I also thought the rubber bumper cars had a 1cm spacer at the top which I haven't fitted of course. I have a 3/4" anti roll bar which has given the car very good handling in combination with the springs. If only my new rear springs hadn't sagged too. At least my exhaust hits the ground less often now.
Paul Hollingworth

Bob - if seeking advice we would need to know the ride height measured from the centre of the axle to the lower edge of the trim trip, many examples here http://www.mgb-stuff.org.uk/suspensiontext.htm#height

The only spacer I'm aware of is the one that is welded to the top of the cross-member. There is a spigot screwed to the underside of the crosmember in the spring housing but that fits inside the spring for location, and was on all models according to the Parts Catalogue.

Springs have been a nightmare for some time now. Three lots of nominally 9.32" have measured 9.125 after a few years on the roadster, 9.375" probably original off the V8, and 9.75" for a new pair. The first pair the counter-man got for me were different heights so I politely asked for a matching pair. He obliged but said "It won't make any difference", and sure enough free heights were the same but on-car after running, 0.1" difference with the old springs had become 0.5". 2 years later they had come down an inch and were back to 0.1" difference.

Ideally the A-arms should be horizontal to minimise bump-steer, but that's not going to happen with lowered springs. Some have had shorter springs made but unless you make then harder they will keep bottoming, and harder translates to the ride. As soon as you start messing with the suspension of a B you introduce compromises. There is a thread elsewhere about parabolics and some have found the height goes up to 17" when fitted as per the instructions.
paulh4

Paul Hollingworth
No there was no 1cm spacer on RB springs, the ride height was done by taller mounting pedestals on the X member

Bob
If he wants it lower just get some shorter springs-----------
All v8s, chrome bumper and rubber bumper had the higher pedestals on the X member-4cyl chrome bumper cars were the only ones without them
"
'They' say that it was to give the oil pump clearance as well as to raise the ride height to meet expected bumper bar and headlight height rules, also the steering rack is slightly further forward to clear the front pulley on the v8 engine
I have done a 4cyl.chrome bumper X member to a V8 conversion but it's a real pain to do properly with the different angle of the rack etc-The rack has to be machined off a bit and shimmed to get the angle happening-The oil pump clears and the rack clears(just) but the rack angle takes a bit of getting spot on.

Lot easier to just get shorter springs-or take yours into the springworks and get them pressed (reset shorter)-If you measure yours up--free length and spring rate, you'll know what you've got to start off with, then ordering new springs isn't a guessing game--If you get springs the same rating and 3/8" shorter that'll drop the car about an inch----there is not a bump steer issue with MGB suspension geometry

By the way, factory V8s are prone to breaking the rack brackets off the X member, so a good look around near the welds each service is a good idea--luckily steering isn't completely lost when they come off as the pinion shaft is semi trapped in place by the engine mounting bracket that it goes through.
Scarey experience though all the same, worth checking out-

willy
William Revit

Willy,
I assume the rack brackets break because they are longer and flex more. When re-building I aways weld fillets in to stiffen things up.
Notice the sun is shining AND it's warm!!


Allan Reeling

Ha ha ha---temperature reading please----?
That's it Allan--good move with the fillets
I think as well as the longer brackets, modern tyres probably put a bit more load on them, specially when parking etc
Nice Autumn day here today
11am-14deg.C
bright sunshine
flat as a pancake out at sea
Was going to get the engine mounted in my Y today but no, going for a ride while the weather's still good
William Revit

Willy, It was in the 20's yesterday, today a touch cloudy, but still 16c.
Agree regarding the tyres.
Go for the drive, but beware of the Devils!!!
Allan Reeling

This thread was discussed between 14/05/2019 and 16/05/2019

MG MGB Technical index

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