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MG MGB Technical - Geometry

After taking my car for tracking today whilst it was on the machine we could see all of the measurements.

The tracking is easy enough to sort but obviously nothing else is really adjustable.

We did come up with an intuitive way to move the rear axle round so it points the same way as the front wheels though.

Is there any modifications available to make any of the rest of the geometry adjustable?
K Goldup

You can change camber with different A-arms and I think there is a kit to reduce the castor on the B.
Art Pearse

How did you move the rear axle round?
Ian
Ian Buckley

K,
There are panhard rod kits available that are adjustable and locates the rear axle.
Joe G
J. E. Guthrie

Ian, We managed to move it round a fair amount by undoing the nuts on the 'U' bolts round the axle and levering it in the direction it needed to be.

I'm going to attempt to remove the plates from the bottom of the axle and elongate to the centre bolt hole which could well produce enough movement to locate the axle to 'almost' where it needs to be.

But shhh don't tell anyone. If it works I could make thousands selling this this service!
K Goldup

I think you would need to make some packing pieces if you elongated the holes. Can you be sure that the U bolts would hold the axle in one place. There's quite a few forces acting on the back axle casing.
Steve Church

When I had changed the rear springs, and took everything apart. I naturally assumbed it would all go back together in the same place. After reading past threads, from individuals whom had done the same and encountered tracking problems, differences in ride height etc, I was actually happy that indeed all did go back together well. Guess I was lucky? Mike
J.M. Doust

I always assumed it would go back in the same spot too. When you say you moved the axle, do you mean from side to side? In other words you moved it to get more clearance between tyre and wheel arch on the left side?
Ian
Ian Buckley

Adding to my previous thread. When I had the tracking checked and altered, I was impressed with the tecnology avilable now; The mechanics mounted on all 4 wheels, a laser sighting devise so that one could alter all wheels if necessary( I presume.) Providing all is adjustable. So in the MG's case the rear axle is not adjustable, but you can get this 'square' with the front wheels, ( These being the ones to adjust.) prior to then adjusting toe in? Must admit it ran very straight afterwards and steered better.I think they would use this also to check camber. Mike
J.M. Doust

Adding to my previous post and upon reflection, elongating the holes for the U bolts would not achieve anything because the plate welded on the diff housing accommodates the centre bolt of the springs?
Ian Buckley

There is the rubber pad between spring and axle mounting face so there can be a certain amount of squish in that, but perhaps 1/8" forwards or sideways max. One of the functions of the centre bolt on the spring is to locate the axle, if you just elongated the holes then it is quite likely to move around unless you welded up to make them circular again. But then that is the same as moving the mounts on the axle casing, or the mounts on the body, both of which have been done in the past to centralise the wheels in the arches. But if that puts the rear wheels out of line with the fronts, it is no solution.

The panhard rod kit is probably adjustable more so that it fits, rather than the adjustment being used to force the axle in any direction. I'd imagine that would put a lot of stress in the rod and its fittings - as Abingdon found when testing the intended suspension for the MGB which broke and flipped the car over. That entailed a rapid redesign (de-design?) back to cart springs, which required the 'hulls' under the rear lights.
PaulH Solihull

Paul/Buckles
I've been toying with an idea for a while now

Spring centre bolts with offset heads

If you had centrebolts with say 1/4" offset heads they could be swivelled around to move the diff back/forward for tracking adjustments as well as sideways for guard clearance and then locked up when the desired position is achieved

How many points do I get for this fantastic idea

Willy

William Revit

Well, my ancient Celica had just that arrangement for altering the front camber ...
PaulH Solihull

By moving it I don't mean side to side I mean we managed to move one side forward and one side backwards.

We did make a fair differences even with the U bolts done back up (but still not perfect)

Also something else we wondered about, is there a way to reduce the front suspension droop?

K Goldup

K Goldup

Please define front suspension droop.

Willy, you are a winner. I did not think of that - full marks. You are almost qualified to live on the Australian mainland!

Paul refers to relocating the mounting points on the diff housing. I did toy with that idea but have not done anything. Also, as Paul says a panhard rod is not for centralisinging the axle. I do not believe there is a suitable mounting point on the body which will stand the strain anyway.

One thing I have been thinking about lately is changing to parabolic springs. I imagine they would give a more progressive ride and perhaps reduce the tendency to skip around on choppy road surfaces?
Ian
Ian Buckley

As I have learnt to my cost, parabolics, which I think make for a more comfortable ride, are not recommended where engine output exceeds 100 bhp at the wheels. Need to be used with tube shocks on a very soft setting.
Michael Beswick

'Droop' is probably just spring sag. I changed mine a few years ago as the A-arms seemed to be pointing upwards as well as outwards, instead of (ideally) being horizontal, and I couldn't get the trolley jack under the crossmember. However new springs added 2" to the front height, thankfully reducing by 3/4" after a short tour of sleeping policemen, and a further half-inch two years later which is where they are now two years later still at about 14 3/4" from the bottom of the trim strip to the wheel centre. A-arms are very slightly angled downwards and outwards i.e. possibly fractionally too high, and the suspension seems too hard to me as the front of the body seems to bounce whereas I'd rather have more compliance.

A pal has just replaced his parabolics under guarantee as the first set wound up like springs (the second case I have come across in recent months), apparently they are not recommended for more than 100bhp at the wheels, although it is torque that winds them up rather than bhp. He has a supercharger. They *are* more compliant than the original multi-leaf, but it's usually recommended that the dampers are uprated at the same time, which is going to restrict rate of movement again i.e. increase the likelihood of them skipping.
PaulH Solihull

Ha! Said pal typing slightly ahead of me.
PaulH Solihull

I didn't know about the 100 bhp recommended limit for parabolics. That counts that idea out for me as my car has 140 rwhp. I thought the R V8 had parabolics or are they different in some way?
Ian
Ian Buckley

MGOC "will intercept orders for parabolics to ensure they are not being used for V8"....

They are asking the supplier (ie distributor) to look at producing parabolics for V8s. My guess would be that with such a wide variation of power outputs of "V8s", it will not happen soon!
Michael Beswick

The RV8 has torque-control arms that prevent winding-up, apparently http://www.v8register.net/FilesRV8WN/RV8NOTE312%20suspension%20UG%20concerns%20AM.pdf
PaulH Solihull

Paul - Further to your post concerning front suspension height, I noticed some while ago that my A arms were pointing upwards, and have just checked the height, bottom of chrome strip to wheel centre, at 14 inches.

My car is an ex-U.S. '77 roadster, and had been lowered, probably shortly before I bought it, a couple of years ago. Looking at the MGOC site I note they offer 'lowered' and 'standard' springs, so I'm wondering which to go for, thinking that 'standard' might have the front up in the air, r/b style. Is two years long enough for newish lowered springs (assuming that's what's on there) to settle to give me my present ride height?

Considering I'm losing ¾-inch travel the ride is ok, but I'm guessing it goes onto the bump stops fairly often (car looks ok though!).

Is there any way of telling what's on there?
John Bilham

I have fitted another set of parabolics (needed for a trip). I think they offer a more comfortable ride and would prefer not to fit ("harder") V8 springs on what is only a midly tuned car. Noting Paul's reference I looked at Moss's Anti Tramp Bar Kit. It would seem to prevent the spring going S shape, whilst retaining the characteristics of the (parabolic) spring. has anyone had good/bad experience of them. At £190 they ain't cheap!
Michael Beswick

If you are going to fit anti-tramp bars the floor immediately in front of the forward spring mount needs to be considerably re-enforced. Ideally as far as the cross member, a la RV8. The kits I have seen have a grossly inadequate bolted plate.
By the way my 200hp V8 roadster has RV8 parabolics, without anti-tramp.....never a problem. As for the "available" parabolics, I've heard many tales of their failure.
Allan Reeling

Do the RV8 parabolics fit straight on to a B (Roadster)? I have been offered a pair of "V8 Single leaf" springs by a pal. I though they might be composites but perhaps they are RV8 parabolics. I'm just a bit concerned that anything designed with V8 power in mind may be a bit "bouncy" for my Chrome Bumper roadster with about 110 at the wheels!
Michael Beswick

So is the entire force taken by these 4 bolts through the floor or does the bracket fit round the front hanger with the bolt thru the front spring eye?

http://www.moss-europe.co.uk/Shop/ViewProducts.aspx?PlateIndexID=13350
Michael Beswick

This thread was discussed between 16/07/2011 and 21/07/2011

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