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MG MGB Technical - banjo axle vs tube axle

I have seen it written and heard it said that the tube axle is stronger than the banjo axle. These comments have not been very specific.

What breaks on the banjo axle?
David Witham

I've only ever heard of one definite failure, that was on a Salisbury/tube, a broken half-shaft. Very odd given that it was a 4-cylinder, the V8 uses the same axle, and Perry Stephenson puts 322bhp & 383 ft/lbs torque through his!

I understood the change from the banjo to the Salisbury was one of commonising with the GT, which always had the Salisbury because it is quieter in the enclosed cabin.
PaulH Solihull

Tube axles are stronger all around, but that doesn't mean banjo axles are weak. The tube axles found on later MGBs were actually designed for light vans and trucks. They are very heavy.
Steve Simmons

Steve-
Yup, In the case of the Salisbury tube-type rear axle which weighs in at a rather ponderous 175 Lbs against the 115 Lbs of the Hardy-Spicer banjo-type rear axle, this additional penalty in terms of unsprung weight is 60 Lbs.

David-
I put a Hardy-Spicer banjo-type rear axle on my car in order to shed unsprung weight. My engine is a 1925c with a Derrington crossflow head and a Piper 285 camsgaft. Compression is 10.5:1. This is about as far a a B Series engine can be taken and still be suitable for street use. The Hardy-Spicer rear axle has never given a moment's trouble in seven years of spirited driving.
Stephen Strange

I will be going back to the Banjo to save usprung weight. The Salisbury is bomb proof on a tuned fast road MGB , and quieter but the banjo is fine on racing cars, and in fact mandatory as they cant afford the unsprung weight. Paul is correct, it was standardising when the GT was introduced and the banjo would have been too noisy for the closed car. John Thornley's book I think
Stan Best

I installed a banjo diff in my late '67 after the Salisbury unit started to howl due to the po running it dry because of a failed pinion seal. The banjo axle has given me excellent reliability over 35 years of service and has never even required a single seal replacement. I'm running it now with a supercharger, 1860 cc engine, flowed head and Kent 270 cam. After 7 years of abuse with this setup it is still going strong. A heavy duty unit. RAY
rjm RAY

Anyone install a banjo in a GT who can compare the noise levels?
Steve S

Does anyone know how much the axles would have cost, back in the 1960's? I suspect the Salisbury was simply cheaper than the Banjo axle and all this noise reduction stuff was a smokescreen to let them put cheaper axles on the MGB and GT

The Farina cars (Magnettes, Oxfords, Cambridges etc.) all had the banjo axle, right up until the end of production. BMC was trying to produce a luxury car. Surely these would have been the candidates for a quieter axle.
Mike

"a smokescreen to let them put cheaper axles on the MGB and GT"

And why not? Nothing wrong with cost reduction if it doesn't reduce the reliability (which it didn't). The Magnette finished in 68 i.e. just after the banjo was dropped from the roadster. The Oxford/Cambridge went on a little longer to 71 but were way past any enhancements by that time, replacements already on the board. They had always been closed and so would always have had sufficient noise reduction to achieve the result desired from the start, whereas additional measures would have been required for the GT over the roadster to allow the use of the same axle. As new models were brought out expectations rose, and one of the criticisms levelled against the UK motor industry was that new models did not improve as much as they should have done. Even though the MGB V8 was nothing more than an engine swap, wind noise was a major criticism levelled against that car when it was launched.
PaulH Solihull

Mike-
The Salisbury tube-type axle housing has a cast iron differential housing while the Hardy-Spicer banjo-type axle housing is fabricated by welding steel stampings together. Although much heavier, cast iron is a much better sound deadener. The design of the Salisbury tube-type rear axle is not only quieter, but can be inexpensively made to accommodate different width needs by simply lengthening or shortening both the axle tubes and their corresponding enclosed halfshafts (quartershafts). This is a much lower cost solution than the labor-intensive method of fabricating different sheet metal axle housings for each needed width rear axle, plus the additional cost of inventorying and storing multiple sheet metal stampings until they are needed for assembly and welding in jigs. It is only necessary to make sure that the differential mechanism is strong enough to handle the power and weight of the biggest intended vehicle, and the payoff is as-needed production of an axle that lasts practically forever in lightweight applications (as in an MGB). The downside is that while such a generic rear axle design will withstand more power, it will be heavier, making for more unsprung mass for the rear suspension to deal with. In the case of the Salisbury tube-type rear axle which weighs a rather ponderous 175 Lbs against the 115 Lbs of the Hardy-Spicer banjo-type rear axle, this additional penalty in terms of unsprung weight is 60 Lbs.
Stephen Strange

I have a banjo axle on my GT - whilst I haven't heard a Salisbury to compare I don't honestly think I can hear the axle over the engine, road or wind noise.

Cheers,
Tim
T Jenner

Nothing wrong with reducing costs when you get a better component, I agree. I'm not sure if the extra 60 lbs can be called a better component. Good grief, it's over half as heavy again! I can see the advantages if you need to inventory various lengths of axle though.

The banjo axle has the handy advantage that you can swap the differential without intefering with the brakes and suspension. I'm sure it's usefull if you're racing and I was glad of it too when I changed my worn out differential for a new one.

Both axles appear to wear out, judging by this website!

Mike
Mike

I've compared the noise level between the two and can find no difference. As far as the banjo axle goes, I simply prefer the overall design. RAY
rjm RAY

Both axles wear out? How so? Wearing out to me is when something has to be replaced or have a major rebuild. Yes they can start to clonk and there is a repair kit for that, but they will clonk to the end of time without breaking. The oil seal can fail, but that is more to do with the oil seal than the design of the axle.

It's probably the strongest part of the mechanicals. The same axle was used on the V8, which pales into insignificance compared to Perry Stephenson's 322bhp & 383 ft/lbs torque
http://www.britishv8.org/MG/PerryStephenson.htm
PaulH Solihull

I agree they are very robust, but I've replaced two worn differentials and one bent tube axle housing. They're mechanical devices and won't last forever!
Steve S

If properly maintained and not subjected to extreme abuse, such as a collision, they should last almost forever. These axle assemblies were way over engineered for these cars. RAY
rjm RAY

This thread was discussed between 03/09/2010 and 19/09/2010

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