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MG MGA - Convert to MGB banjo differential.

I am thinking of converting my 1962 steel wheel MGA roadster to wire wheels. I have obtained a complete 1968 MGBGT wire wheel, 3.9 ratio banjo type differential with worn out hubs. My question is can I order stock 1600 MKII MGA type hubs with fine threads or do I have to buy MGB hubs with the corse threads. I will buy stock MGA front hubs with fine threads and I would like to have all the hubs with the same thread pitch. Thanks for your help.

John
John Progess

The easiest way is obviously to just buy the coarse thread spinners. Externally, they can be purchased with an external appearance identical to the fine thread variety.

The width of the MGB housing is about 1/2" narrower than the MGA version. In addition, the splines on the spider gears in the differential are different between the A and B (and even among different A models). These engineering changes pose potential problems with an axel swap. I don't personally know the spine configuration of the hub end, bu it may be possible to swap the pressed hubs or, alternatively, change the spider gears (the latter assumes that the 1/4" longer MGA axel can be fitted directly or without major modification), but all in all, having two different threaded spinners front rear is the least work. I've had that set up on my MGA for many years.

Steve
Steve Brandt

John,
The '57 MGA that we just finished used the following:

MGA was originally a wire wheel rear axle. MGB rear axle (banjo style of course) was also a wire wheel unit.

MGA parts used:
Axle housing,
Hubs w/7/16" hub bolts
(New) MGA fine Spline hubs
fine spline knock off's (knock on's to those in GB)
Drums

MGB Parts:
Axles shafts (half shafts)
rear brake backing plates
(new) MGB rear brake wheel cylinders, shoes, springs, adjusters and all brake parts
MGB 3.909 gear ratio in original MGB pumpkin

MGB Brake hose- but this required a bit of modification to fit and was used since we have a MGB front suspension and brakes on it, otherwise i would have used the MGA brake hose on the system.

How to switch from steel wheel to wire wheel is a little bit different since the sw and ww is a width difference... I think that the MGB rear axle could have been put in complete, but did not attempt it since the MGA axle housing was cleaner... The shafts were the identical length, but i do not remember if the housing and bolt-down/angle (pitch) locations were the same.

FWIW,
-BMC.
BMC Brian McCullough

There are three different splines on MGA. From car #82749 (wire wheels) on it is the same as MGB; as a MKII, yours likely is in this range - if it hasn't been changed.
These cars use the exact same axle shaft as the B, BTB153. From what Brian says, the difference in hubs is that A had 7/16 studs (B has 1/2" I think), so inner and outer hubs must match. The splined hubs were changed to coarse thread because it is stronger. Early B hubs are fine thread, just like the A, but with the larger studs to match the inner hub.
BTW, NO GT came with banjo axle, so it must be from a roadster.
FRM
FR Millmore

Yes I thought that FRM, but must admit to not being an authority on the MGB. I also thought that the roadsters changed to Salisbury axles before 68?
Bob (robert)

What are the strengths and weaknesses of the banjo housing compared to the tubular (Salisbury) style? Another way of asking the question is, why was the change made?

Thanks,
Steve
Steve Brandt

The tube axle is stronger and significantly heavier than the banjo. In addition it is generally considered to be quieter than the banjo. This may be why it was introduced with the BGT where internal refinement will have been an objective.

Essentially the tube axle was the new common axle design for BMC's heavier duty RWD applications. So the B was being brought into line with general policy.
David Witham

Roadster came with either axle from 65-67, then all Salisbury type.
FRM
FR Millmore

The Moss book shows that the MGA MKII and the MGB banjo axles have the same part number. It also shows different part numbers for the MGA inner hub for steel wheels and wires. Does anyone know what the difference is? I checked the MGB wire inner hub and an MGA steel wheel inner hub and they look identical except for the stud size (same bearing and seal). So the question is can I use a MGA inner hub and new MGA wire wheel spline hub with the MGB wire wheel banjo housing and shaft and pumpkin? I also checked the brake backing plate and the MGA will fit the MGB banjo housing. I would like to use my MGA brake parts as they are new. Thanks again for your information.

John
John Progess

This thread was discussed between 19/09/2005 and 21/09/2005

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