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MG MGB Technical - 67 Banjo Axle Brakes for my GT
|I am rebuilding a 67 BGT and want to use a Banjo axle with disc wheels that I have. I know the factory only used Salisbury axles for the GT and was wondering if it was a weight issue or perhaps braking or just marketing. Any safety reason not to use the roadster banjo axle with disc wheels that I have? Thanks|
Most 67 had the banjo axle. The change to the tube or salisbury was in 68. No problems with using a banjo. Should bolt right in. Be sure that it is from a GT, the roadster rear wheel brake cylinders were different. The GT's are larger.
|Ron, thanks for the information. The larger rear wheel cylinders are listed in the MOSS catalog from GT # 138401, which I suspect is 1968 on. Do you think they bolt up to the banjo axle disc wheel rear axle or can i use the larger ones on the old axle assembly? Ralph|
|All GTs left the factory with tube/salisbury axles.|
Following the introduction of the GT the roadster continued to use the banjo axle for a while before moving over to the tube axle.
As has been said by Ron, the roadster and GT use different sizes of rear slave cylinders.
The banjo axle will work on a GT. It is not as strong as the tube axle but it should be strong enough. The tube axle is considered to be quieter than the banjo which may be why it was used on the GT from the start of production.
|I've heard the same thing David. The banjo axles are a bit noisy so they went to the tube type for the GT since it's an enclosed car.|
The banjo is lighter weight and more easily servicable, but that's about it.
|I remember reading "the Banjo axle would just be unnaceptably noisy in the closed car." So I would not recomend it, the ratio of sprung to unsprung weight wil be similar GT/Salisbury "roadster/Banjo. If you have ever moved both styles of axle in quick succesion though, there a big difference.|
|A friend of mine has a Banjo axle fitted to his 68 GT which has a highly tuned 1950 engine & is used for sprints & hillclimbs with no problems. He fitted this for the considerable weight saving.|
|The MGB GT rear wheel cylinders were bigger at some point but not until car 1968.... right? Prior to that, are they not the same for the roadster and GT? The MOSS catalog show them as changing with car #138401. Does that sound correct? Can the bigger (post 67) ones be used on the early cars? Perhaps they won't fit on the backing plate etc? Thanks|
|Ralph they will not fit, mounting pin is in different location, can be made to work by redrilling hole.|
|My bad, memory is not always what one would like. The Bajo later than the GT introduction was a roadster thing.. The rear brake cylinders were changed or were always different on the GT axles. I did have a 67GT with a banjo, no problems as I recall. The rear brake cylinders were larger compared to the roadster to provide a different brake bias front to rear. Again as I recall the later will fit but the locating pin as mentioned is in a different location. |
|My experience is that there are 3 sizes of rear brake cylinders: 1/ the small roadster, 2/ a little larger for the early GT, and 3/ yet larger for all later GTs.|
I converted a late roadster rear end for my '67 GT (so I could convert to alloy wheels) to the large cylinders by grinding off the locater pin on the cylinder. Works great.
My theory is that the new hi performance disc pads have a higher cf (more friction) and that you could probably use the larger rear wheel cylinders even in the roadster and still have no problem with rear lock up.
The difference in pedal pressure between an early brake pad and the ferro hawk pads, for example, is dramatic. It takes less pressure to lock the front wheels. The rear brake shoes cf haven't meaningfully improved, and the pedal pressure even with the large cylinders should not produce unpredicatible rear lock up.
Because of leaking rear oil seals, I drove my GT for a while without any meaningful braking from the rear. It was a little extra pedal pressure, but not that bad.
The argument against the above thesis, is that brake shoes are in part self energizing (while disc brakes are not) and that the increase in pedal pressure for the rear brakes increases the brake shoe friction dramatically on a non linear scale for hi pedal pressure.
This problem of non-linearity of drum brakes versus the linearity of disk brakes has made the combination of the two brake systems less than satisfactory.
The self actuating effect is most apparent at high brake pedal pressures -- the transfer of weight from rear to front is also most apparent at high stopping rates. The solution historically has been rear brakes that regularly doing less braking than would be optimal -- just to avoid the rear lock up problem.
With an anti locking brake system you can avoid this problem. Pickup trucks with large rear drum brakes needed to stop with a big load were among the worst offenders especially when lightly loaded. Anti lock brake systems for the rear wheels became standard very early on even in the less expensive models because of this critical problem. Apparently, rear anti lock brakes were less expensive than rear disc brakes.
If memory serves me, I think the banjo has 2 different axle hubs, 1 for wire wheels and the other for disc wheels. The earlier disc wheel hub may not match the hole pattern on the later Rostyle wheel type. You should ask around the list for more opinion before spending money.
Good Luck: Rich Boris 67 B roadster (banjo w/w)
This thread was discussed between 14/10/2005 and 19/10/2005
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