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MG MGA - MGB Front Suspension & Brakes on MGA

I have to deal with some trunnion wear as I don't think my favourite garagiste is going to just mention it at a third MOT. I think it will be a fail this time.

I have become aware of the possibility of using MGB components on the front and have done a fair bit of research including Barney's articles on the subject, Doug Jackson's description of the work and Andreas Pichler's detailed instructions on the Scuderia Froschenteich website.

I have one unanswered question relating to the hubs. I have Minilite replicas rather than wires, so I'm not sure if the MGB hubs will be right. Aren't the studs (lugnuts) bigger on the B? If so, can I re-use my existing A hubs with the B brake disc on the B stub axle?

I know I will soon find out if I start to do the work but if anyone has dealt with this issue before it would be helpful.

By the way, I am a pragmatist not a purist, so originality is not really an issue for me. If it works and is both cheaper and stronger, I am attracted towards it as a solution. It is reversible and the original components will stay with the car.

Regards

Malcolm
Malcolm Eades

Malcom you have to use the B hubs on the B stub axle. Yes the lug studs are 1/2" instead of the 7/16" as used on the MGA, shouldn't be a problem with the alloy wheels, just need to get the correct lug nuts. It is a reversable mod except that the outer tie rod ends need to be shortened and rethreaded about 3/4" to be able to properly adjust the toe and the brake hoses have a slightly different mounting point than the MGA hoses. You could have custom hoses made up to solve that problem and not have to reposition the frame brackets.
That's about all I can add, you already have most of the research done.
Bill Young

Thanks Bill. That's a great help and by return too. Don't you just love this bulletin board!!

I understand that I can avoid trimming the tie-rod ends by using the negative camber lower arms sold for Bs so I was planning to try that.

I will check the hose issue and make sure the length is right once it's all fitted up and I can check it lock to lock and at the extremes of the suspension travel.

Thanks again!

Malcolm

Malcolm Eades

Do NOT use the negative camber A arms if you use the MGB shocks or you will have far too much negative camber.

Frankly, replacing the whole suspension because you need to renew some readily available MGA parts seems a bit over the top - why not just refurbish what you have?

That would probably be cheaper to boot.

The spindle is completetly different on the MGB and the hubs are not interchangeable.
Bill Spohn

Malcolm, I had wear in the threads of my O/S top trunnion. New one cost £91.96 from MGOC, an expensive item but a sight cheaper than replacing the whole front suspension and brakes. Takes just a few minutes to replace a trunnion, that's got to be better than having your front end up in the air while all this good weather is going on!
Lindsay Sampford

Thanks to Bill and Lindsay for their wise counsel. The warning about the B shocks is particularly useful.

I know there is a certain lack of logic to what I have in mind and I would not be contemplating it if I hadn't already acquired all the B hardware for £70 secondhand and in good condition! The "consumable" parts would have been replaced anyway so the cost for those would be the same.

I'm probably over-reacting to stories of broken king-pins and difficult A caliper overhauls but I also enjoy the challenge of this kind of parts swap.

Cheers

Malcolm
Malcolm Eades

Malcom, there have been bad runs of king pins, I suspect with incorrectly machined radiuses at the start of the threads, and they have broken, but the kingpin isn't notably weak and new ones should be just fine for anything but racing with wide wheels and slicks.

The calipers are no trouble at all to rebuild - just break the retracting pin out of there (it does no good anyway) and you can use cheap MGB replacement caliper pistons. Not scary or difficult at all.

The usual reason people swap to MGB is that they are working on a 1500 and they can't find the correct MGA 1600 parts. If you already have the 1600 parts, I can't see any good reason to swap out.
Bill Spohn

Nearly every weekend for several years through the mid to late 90's I thrashed the crap out of my MGA in very serious autocross competition with SCCA. The car was shod with low profile wide sticky race tires and subject to continuous harsh steering manuvers that would regularly crack steel disk wheels. I also regularly drive with vigor on rough roads during road rally or long distance touring (logging roads or Alaska trip). But never any problem with the original vintage swivel pins.

I have seen several instances where an MGA clipped a tall curb sideways resulting in destruction of a front wheel. This commonly results in mild bending of the swivel pin at the smallest diameter just below the knuckle, but not breaking. I have successfully straightened a few of these with a torch and a bump hammer, all successful in subsequent regular operation.

As Bill has noted, there have been some less than desirable aftermarket parts with bad machining and sharp corners and/or incorrect steel resulting in brittleness and tendency to break rather than bend. This is probably not a problem with casual daily driver cars. Racer types could do well to pay closer attention to aftermarket parts, visually inspect all parts whenever they are in hand, and maybe have them crack inspected (magnafluxed or dye penetrant checked) at least once.

I have replaced one lower swivel link that had a worn thread from prior neglect of lubrication (before I bought the car). MGB kingpins will suffer similar wear in the bronze bushings if neglected. Not many people drive an MGA harder then I do, but I have no urge to change my original suspension parts.

Barney Gaylord

This thread was discussed between 01/07/2010 and 07/07/2010

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