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MG MGB Technical - MGB-GT Rear Axle

I'm considering converting my BGT from wire wheels to disc wheels. Was/is the tube type axle a real improvement on the banjo axle? The banjo type seemed to be reliable and quiet on the MGA and early MGBs. Did the factory change axle types just because they got a better price on the tube type?
Fraser Cooper

What year is your BGT and what axle do you have? I swapped the rear from my '73 BGT for a '72 with no problems. Complete bolt on
william fox

It's a '67 BGT and the banjo axle is from a '65 roadster. Other than the BGT brake cylinders having a larger bore, I figure the swop is no problem. I changed my '58 MGA from wire to disc wheels back in 1964!
I was mainly concerned about whether the banjo axle was as quiet and sturdy as the tube type.
Thanks for the vote of confidence!
Fraser Cooper

I was reading the other day that the backing plates are different for the roadster and the GT (as are the tabs on the brake cylinders) so that you can't install the wrong rear wheel brake cylinders. You may want to make sure you get the right backing plate.

I swapped a 75 roadster rear end under my 67 GT. It took some playing around to get the ebrake right etc. but is relatively straight forward. A set of modern tires on 15x6 wheels will quickly show you how inadequate the orginal seats are. I've gone to Fiero seats and can actually go around a left hand corner without feeling like I am going to fall over.
Barry
Barry Parkinson

Fraser,

The banjo axle is lighter, but the tube axle is stronger. Most of the racers like the tube axle because it's also easier to change gear ratios. The banjo axle is still strong enough for everyday use.

The locating pin for the wheel cylinders might be a problem, as the roadster doesn't use it, but that can be overcome easily. Either take out the pin, drill a hole in the backing plate for the pin, or use roadster wheel cylinders. The swap is very doable.


Paul K

Fraser; The 67 GT and roadster used the same .800" brake cylinder up to #138400, I believe that number was the beginning of the 68 model. The wheel cylinders for the roadster and the GT have index pins. The .875" cylinder for the GT has the index pin at a different location. There isn't a lot of difference in their location so it's easy to drill and file the index hole in a roadster backing plate so the .875" GT cylinder index pin will fit, I did that a few years ago. You will also need the banjo axle handbrake cable and spring to axle mountiong hardware for a banjo axle, the rubber pads are the same. I don't know if the driveshafts will interchange. I'm sure Paul K means the banjo axle gear ratios are easier to change.

Clifton



Clifton Gordon

Thanks for the advice, Group. It's nice to have the collected wisdom (and I mean that sincerely) to fall back on.
About seats: I put a pair of TR7 (horrors!) seats in my BGT. What a difference! Very comfortable and one feels as if part of the car.
Fraser Cooper

Paul K
"Most of the racers like the tube axle because its also easier to change gear ratios"
I believe you will find it is the other way round, its easier to change ratios in the banjo axle, since you just pull the half shafts out a little, then the whole diff can be pulled out and changed for one with a different ratio. Its fairly easy to do and doesn't take long.

To change ratios in the tube axle you would have to completely dismantle using special tools, then rebuild with new crown wheel and pinion of different ratio. A job for a specialist only.

The GT was only ever fitted with the tube axle. The roadster had the banjo axle fitted on early cars until GHN3 123716, after then the roadster could have banjo or tube until GHN3 132923 after which only tube axles where fitted.

They changed to tube axle because it was supposed to be a better design and much quieter, it was also cheaper to produce, say no more!
Regards
Graham
Graham Cherry

Yes, I suspected the 'cheaper to produce' part! Having partially re-built (instal 'anti-clunk' kits) in two tube axles, I can agree that the banjo type would be faster to change ratios in.
Ta, Graham and the Group.
Fraser Cooper

I was contmplating going the other way.... swapping a disc wheel tube type ('73 GT) for a wire wheel banjo (from a roadster). Glad to know that this poses no problem. I did not know that the brake cylinders but was glad to learn that it is a minor detail.

My more serious concern was drive shaft length and noise (will be wife's MG).

I do love this forum... thanks.
J. A. McManus

To show my ignorance. Is there an advantage to going to solids? (other than not having to true up the wires)
Bruce Cunha

Bruce
For classic looks, wire wheels can't be beat. For reliability, strength and performance they don't measure up.

A 35 year old 14" x 4.5" out of round wire wheel that is worn and keeps loosening up and then slipping on the hub, doesn't compare in performance, let alone reliability, to an alloy 15" x 6" wheel with a modern low profile tire and wheel combo.

A compromise is a new 15" x 5"? spoke wheel with wider than stock tires. For the cost of the new wire wheels you could have two sets of alloy.

Barry
Barry Parkinson

Also wire wheels are a real pain to keep clean!
Simon Jansen

Clifton, thanks for catching my error. I did indeed mean to say it was easier to change ratios in the banjo axle.

Paul K

Brake cylinders - easy to deal with but potentially important. GTs used larger bore wheel cylinders to give more braking effort as the greater weight means they are less likely to lock. Hence the index pins on a tube axle. Getting them the wrong way round could result in either lowered braking effort on a GT or locking rear wheels on a roadster.
Paul Hunt

I changed my rostyle wheels for alloy mini-lite look-alikes 15 years ago. A very long time ago I had a midget with wires.

Wires look great but I would think that maintenance is a very big key to their performance. I also cannot see that wire wheels can posssibly have the rigidity of a one piece cast alloy wheel.

My experience in changing from rostyle to alloys is that you can never underestimate the need for rigidity in a wheel. The car is so much more sure footed with the alloys than it ever was with the rostyles. You can feel the difference.

If you like the great look of wires and don't mind the shortcomings, go for it.

If driving is more important than the look go for alloys.
Richard Smith

This thread was discussed between 12/03/2005 and 19/03/2005

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