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MG MGB Technical - Steering rack changes

Gents
I got some great advise from the archive, and have converted from RB Xmember to CB. I made a gig to
re-align/cut the RB rack/mounts to fit. This has all worked great.
Problem #1. the steering shaft has a very very slight curve, and when turned, tends to rock the rack ( has not been finally mounted yet). Will this mevement be taken up by the spring were the uppershaft comes through the bulkhead? I can get it straightened if required.
#2. Does anybody know what this spring does. It to slightly preload the steering shaft to stop it rattleing around?
#3. The inner upper shaft can be withdraw downwards and it looks as though there are 4 sheer rivets. Is this correct. I can not imagine this is a problem because the shaft is still contained within the outer housing?
Thanks
Brian
b bourne

1. Spring? What spring? Normally any misalignment that puts any sideways forces on the UJ as the steering wheel is turned will cause rapid wear of the UJ and pinion bearing.

If either steering shaft is curved such that it doesn't rotate about a fixed point in space but describes a circle, then it is bent and scrap!

Careful shimming of the rack mounts is required to get correct alignment, a long and fiddly process. Ideally you need the special tool which is a pair of cones that bolt onto the two shaft ends, and shim the rack so that the tips of the cones are just touching, but you can get away with blu-tack or stiff wire wrapped round the shafts, rotating the shafts to ensure that the point of the wire or blue-tack is aligned with the centre-line of the shaft *and* the correct distance from the end of the shaft i.e. the same distance as the middle of the spider when the UJ is fitted.
Paul Hunt 2

Hi Brian
There is no allowance anywhere to accomodate a bent pinion shaft. It needs to be straigntened or replaced.

The inner section of the steering column seems to be held in place by a couple of plastic injections. Mine are broken and cause no problems. It appears that these bits are to hold the inner section in place for assembly purposes in the factory.

Shimming at the steering rack may be needed, and as Paul says it can be a tedious job. I jigged my steering rack, and connected the pinion shaft to the steering column using the universal joint. The mounts were then made to fit and welded in place. Because the rack was in its final position at time of welding, no shimming was required. You may have a problem if you followed this method with a bent pinion shaft.

Cheers Ian F


Ian Fraser

Paul / Ian
Thanks for the replies. Its a bit dificult to visulize the rigging explanations, but I think I understand.
I have already made a temp jig to retain the original rack position and have rotated the rack to align with the upper uj. I intend to tack weld new mounts while it is all in this position.
I would be very interested if you could clarify the the cone/wire method... not sure exactly what we are trying to accomplish. It amazes me that the different positions the RB and CB racks are mounted, + when the cars use lowering springs, that so much attention is made to get the rack spot on??
Cheers
Brian
b bourne

Brian
There is a lot of stuff in the archives on converting steering in a conversion from rubber bumper to chrome bumper cross members. You should research that info.
Barry
Barry Parkinson

Hi Brian.

The critical part about the steering/suspension setup is to maintain the same vertical relationship between the rack ends and the upper inner and lower inner suspension mountings. A vertical movement will induce bump steer.

Lowered springs alone retain the relationship, all they do is to relocate the rest position of the suspension, and do not significantly induce bump steer.

A minor movement of the rack forwards or rearwards does not greatly affect the steering except at or near full lock in either direction. Generally steering accuracy is not required at full lock.

This tolerance enables the RB rack on a RB cross member to be mounted on a skew with no excessive ill effects, and also enables a RB rack to be mounted on a CB cross member (without shortening the pinion shaft) either by making new mounts, or modifying the existing mounts by use of a spacer that allows the rack to sit further forward and at the same level.

Another method is to shorten the pinion shaft, and with new mounts, mount the rack closer to it original position on the cross member.

Another thing to watch for is the lateral location of the rack. If the housing is closer to one side of the car than the other, this does not matter greatly - as long as the tie rods are of equal length. Any attempt to centre the rack in an offset housing by lenthing the tie rod on one side and shortening it on the other will induce bump steer.

If you have located the rack as you described (by jigging and attaching the pinion shaft to the steering column through the universal) you will have no need to carry out any other alignment. Just make sure the the pinion shaft is straight, and that you have used new cross member mounting pads, and the cross member bolts are fully tightened up.

Cheers
ian F



Ian Fraser

Just curious - why would anyone go to this trouble? What is the advantage of changing. I have a 71, so I am just curious about those of you who own the later cars - is there some reason for doing this?

Jeff
J Delk

Hi Jeff.

One of the hassles of a RB car is the raised ride height which reduces the handling capabilities. Lowering the car results in an improvement.

3 main ways.

Fit a CB cross member:
It is the 'best' way of lowering the front of a RB car as it involves the least number of compromises. The body is lowered on the top of the cross member. Full suspension travel is retained, standard ground clearance undr cross member is retained. More work is involved than the other methods.

Other ways:
Shorter springs - reduced suspension travel, reduced clearance under cross member.

Dropped spindles - Spring travel retained, reduced clearance under cross member, reduced clearance under lower wish bones.

Cheers
Ian f

Ian Fraser

Jeff,
The RB cars had a slower steering rack, ie, it takes a little longer to get from lock to lock, something like a half turn or so if I'm not mistaken...
Ron

This thread was discussed between 11/09/2006 and 15/09/2006

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