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MG MGB Technical - wire wheel to alloys conversion

Just information gathering before my potential purchase of my first 'B. The one I'm considering has painted wires which will need refurbing. I can get some Minilites for the cost of a refurb so was wondering what it takes to change from wires to 'normal' wheels?
Steve Church

They make knock off disk wheels that will slide right on the wire wheel hub, but their very expensive, I mean VERY expensive! Other than that, you'll have to change out the rear to one with hubs for bolt on wheels. The rears are different in width so the hubs aren't interchangeable. Then the front disks will have to be changed also, but their easy, it's the rear that creates a problem. Paint the wires, the cost will be far less than converting to disk wheels. Or, buy a car with disk wheels already on it! Sorry. PJ
P.S. Jennings

Steve,

Sell your wires, hubs spinners and rear axle and replace with much cheaper ones via eBay or from somebody who wants to do the conversion the other way.

You should end up with money in your pocket.
D Balkwill

Steve-
You will need to switch the front hubs (no need to change the front brake rotors or any other brake components as they are the same for either disc wheel or wire wheel applications), plus obtain a rear axle of appropriate length. Both the Hardy-Spicer banjo-type rear axles and the Salisbury tube-type rear axles each came in two different widths. This variation was the result of the need to accommodate the fitting of wire wheels and steel wheels. Hardy-Spicer banjo-type rear axles for wire wheels measure 44.5” across, while the rear axles for steel disc wheels measure 46.25“ across. Salisbury tube-type rear axles for wire wheels measure 47” across, while the rear axles for steel disc wheels measure 48.5“ across. This measurement should be taken between the outer rings that have the four holes in the faces on the bearing caps that the back plate bolts onto, i.e., without the backplates installed.

It should be noted that 18G and 18GA engines with a three-synchro transmission and a Hardy-Spicer Banjo-type rear axle use a 30” (76.2cm) driveshaft (propeller shaft) without an overdrive unit (BMC Part # AHH 7488, Hardy-Spicer Part # 114H02771, Victoria British Part # 5-5921, MossMotors Part # 268-080). 18G and 18GA engines with a three-synchro transmission with an Overdrive unit and a Hardy-Spicer Banjo-type rear axle use a 31.125” (78.9cm) driveshaft (propeller shaft) (BMC Part # AHH 7487, Hardy-Spicer Part # 114H02776, Victoria British Part # 5-5922, MossMotors Part # 268-090) with an Overdrive unit. It should be noted that all driveshaft (propeller shaft) length measurements should always be taken Flange to Flange with the driveshaft (propeller shaft) fully compressed in length. Be aware that the protective rubber boot will attempt to extend the driveshaft (propeller shaft).

18GB engines with a three-synchro transmission without an Overdrive unit and a Salisbury tube-type rear axle use a 31.125” (78.9 cm) driveshaft (propeller shaft) (BMC Part # AHH 7487, Hardy-Spicer Part # 114H02776, Victoria British Part # 5-5922, MossMotors Part # 268-090). 18GB engines with a three-synchro transmission that are equipped with a D-type Overdrive unit and a Salisbury tube-type rear axle use a 32” (81.3cm) driveshaft (propeller shaft) (BMC Part # AHH 7486, Hardy-Spicer Part # 114H02779, MossMotors Part # 268-100, Victoria British Part # 5-5924).

All 18GD and later engines with the four-synchro transmission use the same 31.125” (78.9 cm) driveshaft (propeller shaft) (BMC Part # AHH 7487, Hardy-Spicer Part # 114H02776, MossMotors Part # 268-090, Victoria British Part # 5-5922) for both Overdrive and Non-Overdrive applications when used with the Salisbury tube-type rear axle (BMC Part # BTB 1106 for steel wheels, BMC Part # BTB 1107 for wire wheels).

However, the four-synchro transmission uses a 31.125” (76.2 cm) driveshaft (propeller shaft) (BMC Part # AHH 7487, Hardy-Spicer Part # 114H02776, Moss Motors Part # 268-080, Victoria British Part # 5-5921) when used with a Hardy-Spicer Banjo-type rear axle.


As standard Original Equipment, the differential mechanisms of both the Hardy-Spicer banjo-type and Salisbury tube-type rear axles found on the MGB equipped with a manual transmission both used crownwheel and pinion gearsets that produced the same 3.909:1 final drive ratio, although they were also available from the factory with optional crownwheel and pinion gearsets that produced different final drive ratios that were meant to be appropriate for special applications. Over the years, MG owners with special requirements have also used other ratio crownwheel and pinion gearsets from other model cars found in the BMC stable. The number of respective teeth of both the crownwheel gear and the pinion gear of the Hardy-Spicer banjo-type rear axle are often stamped onto the rear face of the differential casing to the left of the differential cover, i.e., 43 11. In the case of the Salisbury tube-type rear axles, the number of teeth of both the crownwheel gear and the pinion gear are often stamped onto the right hand side of the top of the differential casing.
Stephen Strange

Thanks Steve for that very full explanation!

Dave - I like your thinking. Definitely worth looking at.

One thing that puzzles me. What's the difference between 'banjo' and 'tube' type axles? I'm not too proud to admit that I don't know!
Steve Church

Steve-
During its lifetime the MGB was equipped with two different rear axle / differential assemblies: The Hardy-Spicer banjo-type three-quarter floating axle and the Salisbury tube-type fully floating axle. A three-quarter floating axle has its outer bearing positioned between the wheel hub and the axle, thus eliminating the bending loads of the car’s weight, while the fully floating type axle has an additional bearing between the hub and axle to handle the sidethrust of heavy cornering loads. In the case of an MGB powered by a B Series engine, either axle is quite adequate for street use, although the Salisbury tube-type rear axle assembly is both notably quieter and capable of handling heavier loadings, although it is of considerably heavier weight.

The Salisbury tube-type rear axle did not become standardized on all models until the advent of the more powerful MGC in 1968. Until that point, all Roadster models were equipped with the Hardy-Spicer Banjo-type rear axle, and the GT models were all equipped with the Salisbury tube-type rear axle. The principle reason for the higher noise level of the Hardy-Spicer banjo-type rear axle was the profile of the teeth of the gears. They transmit power more efficiently, but are noisier (much as straight-cut gears are noisier than helically-cut gears are). Another design feature that also makes a difference in noise level is the manner of construction of the rear axle housings. 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 them until they are needed. 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 absorb more power, it will be heavier, making for more unsprung mass for the rear suspension to deal with.

Here is an image of these two rear axle types. The top axle is a Salisbury tube-type rear axle, while the bottom two are Hardy-Spicer banjo-type rear axles. Their overall profiles explain the origins of their names.

Stephen Strange

Steve, I believe that that you meant to describe the Salisbury axle as a "semi" floating axle and not a full floating axle, whereas the Hardy-Spicer is, indeed, a 3/4 floating axle. RAY
rjm RAY

You only need to change the axle (and handbrake cable) if changing to *standard* stud-mounted wheels i.e. with the standard offset. I say 'need' but although standard offset wheels may well fit and not rub on the inner arches (going the other way tends to rub on the outer arches) they will be set a long way in and not look right. If you are going for Minilites and can get the appropriate offset the wire/wheel axle will be fine.
Paul Hunt 2010

This thread was discussed between 05/06/2010 and 09/06/2010

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