MGCC

Hard working but ignored

Rear axles for MGs

When the enthusiast works away at his or her latest restoration, or strips down a components to carry out a repair, or carries out an annual service, or even just buys a component at an auto-jumble because it would make a useful spare, do they ever wonder if the item they have in their hand is an original 'MG' part? Over the years I have found it amazing just how few enthusiasts actually bother to see if other cars use the same items fitted to their beloved MG Like any division of a larger organisation, MG often used corporate components. In large manufacturers, economy of production items leads to greater profits, which means more money for the shareholders pockets. Conversely this fact also means better spares availability for the end user, you and I. The franchised garages are also happier as they need not stock such huge ranges of components, so not tying up cash in parts in boxes, on shelves.

1935-1952.

First version of the 1935-52 rear axle, banjo type

The rear axle on MGs is an excellent example of economy of parts in practice. The TA, TB, TC , YA and YT used the rear axle of the equivalent Morris Ten/4 and Twelve/4, also shared with the Wolseley Ten/40 and Twelve/48, and the Morris Commercial light van range. The type was also used on the later post-war Morris Eight Series 'B', Wolseley Eight, Morris Ten-Four Series 'M', Wolseley Ten and the Morris 'Z, van. This rear axle was the standard light-car item of the Nuffield engineering branch. Gearboxes followed a similar fate. The rear axle was of the 'banjo' design, with a pressed steel casing with the differential unit mounted on the front face. The design is the three-quarter-floating type, with spiral-bevel pinion and crown wheel.

Three-quarter-floating means the half-shaft takes no weight of the car, just the driving/torque stresses. This Nuffield axle is very similar to the later BMC banjo axle, and is a development of the earlier 1930's Morris rear axle as used on the TA/TB, notable by its riveted up banjo casing. Depending upon the vehicle it was intended for, things like leaf-spring brackets and case widths differed, as the rear track was not the same on all the cars and vans it was fitted to. Even brake back-plate mountings could differ as well, but the basic engineering suited all applications. The only major difference would be the actual ratio of the crown and pinion, dictated by their respective diameters and numbers of teeth. This banjo axle was a simple spiral-bevel gear type, the pinion meshing with the crown wheel centrally, the drive-line facing the centre of the crown wheel. The post-war casing was a steel pressing in two halves welded together, and the differential nose piece of cast iron. It did get a bad name for weak half-shafts breaking, especially in the heavier l2hp saloons. The worst thing to do is to roll backwards and then stop the car on the clutch, to move forwards again. Swapping ratios is easy though, as the whole differential unit is mounted in one casting. The name 'banjo' is because of the shape of the casing, like the musical instrument.

This axle was used with a 5.22 to 1 ratio in the VA, 4.49 to 1 in the TA, 5.143 to 1 in the YA and YT, and 5.125 to 1 in the TB & TC. In the Morris & Wolseley saloon applications it was either 5.375 to 1, 5.286 to 1, or 4.875 to 1.

1952-1956.

This shows the rivets used in its construction

By the time the TD and YB arrived, the rear axle design had been improved to a hypoid- gear type. This has the drive pinion meshing with the crown wheel near the bottom of the differential. The drive-line runs well below the crown wheel centre, the pinion meshing near the bottom of the crown wheel, (but not as in a worm drive which IS at the bottom.) This gives a stronger drive as two or three teeth are in mesh at any one time, and the transmission tunnel, hence the cars floor, can be lower. The design is of the semi-floating type, which means the half-shaft takes part of the cars weight through it. This rear axle was also a Nuffield design, and again it was fitted to a number of other models. The Morris MS Six, MO Oxford and Cowley used it along with the similar Wolseley 4/50 and 6/80, as did the Wolseley 4/44 and early 15/50. It was fitted to the MG TF. Ratio's of the axle were to suit the various applications, and again the spring pad widths differed. The axle is difficult to work on, as it splits in half, meaning any ratio changes are quite involved with shimming, and checking gear meshing of the crown and pinion. Get this wrong and the axle will howl away driving you mad with its whine. The axle tubes are riveted into the centre casting, and old age will show up as a damp oil area around this join. Hot oil has worked its way through, but it is nothing to worry about. The wheel hub and brake drum are a one casting on this model, and the hub locates on a tapered collar centralising it, with the drive being by square splines on the half-shaft and a huge castellated nut holding it all together.

This axle was used with ratios of 5.125 to 1 in the Morris MO series, Wolseley 4/44, YB, TD and TF 1250; and 4.875 to 1 in the TF 1500 and early Wolseley 15/50.

1956-1965.

1952-56 axle is built up on its two halves, this means special tools are required

In 1953 the Nuffield Group amalgamated with the Austin Empire, and called itself the British Motor Corporation, or BMC for short. This controlling company tried very hard to get the numerous smaller firms under its wings to rationalise their products. There were Austin bits and Morris bits all over the place. But by 1956 BMC had standardised most of their running gear. Wheel hubs used the same stud spacing, in three sizes; engine's were the 'A'. 'B' and 'C' series, all cars used SU carburetters, (except Austin who used Zenith until 1959.) The rear axles had been replaced by three standard BMC patterns, the smaller one of the banjo design with hypoid gearing, fitted to the Austin A30, A35, A40, Morris Minor, Morris 1000, Morris 1000 Scwt and 7cwt van, Riley 1.5, Wolseley 1500, and the MG Midget. A medium version of the hypoid-gear BMC banjo rear axle, with its steel pressing case in two halves welded together, and the differential case in cast aluminium fitted to the Austin A50, A55, A55 mk2, A60, Austin l0cwt and l5cwt van, Morris JU and J2 van, early Sherpa van; Morris Oxford Series 4, 5, and 6; MG Magnette ZA, ZB, ZBV, MGA, and early MGB open sports cars, MG Magnette Mk3 and Mk4 Wolseley 15/50, 15/60; and finally the Riley 4/68 and 4/72. The larger BMC axle was not used on any MG, being destined for the large BMC saloons such as the Wolseley 6/90, Riley Pathfinder and 2.6, and the farina Austin A99 and A110, and Wolseley 6/99 and 6/110. This BMC axle was based firmly on that 1947 Austin A40 design, and was of a three-quarter-floating type like the early Nuffield one. Once again axle tube lengths affecting the rear track differed, as did ratios and spring mounting pads. This is an easy axle to swap ratios on within the size range, as the differential case unbolts in one piece as on the earlier Nuffield axle. One problem is that after mid 1962, (upon the introduction of the MGB,) the spline's on the half shafts changed from a square design, to a star shape. As long as you have the right half shafts for the differential, you are safe, though it is not difficult to swap over the 'planet gears' of the diff to suit the shafts. Note only the early MGB roadsters used this BMC banjo axle, once the MGB GT arrived the later Salisbury rear axle, as fitted to the Sherpa van was used. The huge use of this BMC axle means there is a massive selection of ratios to chose from. Because it was in use so long it is possible to get a drain but no filler plug. The filler moved from the aluminium nose casting to the rear of the banjo casing about 1960 on both. The drain is in the bottom of the banjo. On this axle there were quite a number of braking systems used, but the bolt spacing's for the various back plates was standard. Another little glitch is whether the MG has pressed steel wheels, or wire spoked wheels, as the outer end's are completely different, the wire wheel axle casing being narrower than its pressed steel wheel equivalent. The basic engineering is the same, as the various end castings are welded to the axle tubes of the standard case. Diff s are not interchangeable between the three sizes of axle, but the designs are identical.

The addition of an oil seal to the half shaft stopped oil getting onto the brake linings

So not only the engines of BMC were from a basic stock, axles were as well. There were improvements, like a double-race ball-bearing for the outer end of the half shaft after about 1959, and an oil 'O' ring seal between the half shaft outer face to bearing holder. Prior to this seal being fitted, it was possible to centrifuge oil out into the brake drum. This was not much good for the brake linings, and was because mechanics tried to re-use the gasket. The design is clever in that if the bearings oil seal leaks, the oil drains out of a hole in the rear of the brake-back-plate, not onto the brake linings. The diff nose seal is common to all the BMC axles, and the same seal also fits the later Nuffield hypoid axle of the YB, TF, ext. Never assume your car is the only model that uses a certain item, (unless it is a MGA Twin Cam, but there is always one.)

In the mid-range of cars this BMC axle had ratios of, -MGA 1500, 1600 Mkl, Mk3 & Mk4 Magnette, Austin A60, Wolseley 16/60, Riley 4/68 & 4/72, Morris Oxford series 6, as 4.3 to 1.

MG ZA, Wolseley 15/50, Austin A50 & A55, as 4.875 to 1.
MGA 1600 Mk2 and MGB Roadster to '65, as 3.9 and 3.7 to 1.
Austin A60 Countryman, Morris Oxford Traveller Series 6, Austin A60 van, MG ZB,
A55 mk2, Morris Oxford series 5, Wolseley 15/60, as 4.55 to 1.
Austin A55 van, Morris JU and J2 vans, as 5.125 to 1.
Morris Minor pre-1956, Austin A30, as 4.55 to 1.
Morris Minor 1000, Austin A35 & A40, early MG Midget, as 4.3 to 1.
Later MG Midget, Wolseley 1500, Riley 1.5, as 3.9 to 1.
Later Riley 1.5, some Midgets, as 3.7 to 1.
Morris l000 vans, as 5.125 to 1.

1965-1980

Whilst the Midget carried on with the old BMC banjo rear axle, the MGB swapped over to a Salisbury type, a design much stronger than the basic saloon car BMC item it was using. This coincided with the introduction of the MGB GT, so only early MGB Roadsters had the BMC banjo axle. Whilst the older axle was satisfactory, it had been originally designed for an Austin A40 with just 42bhp and 50lb torque back in 1947. The Salisbury axle was used also because fewer cars within the company were rear wheel drive, (the Austin 1800 had also arrived, along with the five-main-bearing 'B' series.) This axle was from the commercial side of the firm, from the Sherpa van in fact, and the MGB post 1965 four-synchro-gearbox came from the same source. The construction was again different as the centre main part was a casting, with steel tubes each side, the differential and gearing being built in from the rear cover. The design was of the hypoid-gear type with semi-floating half-shafts, like the later Nuffield design. Logically this is the best axle of the bunch, being by far the quietest and strongest.

In the MGB this axle had a 3.9 or 3.7 to 1 ratio.

The 1965-80 Salisbury rear axle. A very strong item.

All Axles.

All axles whine. When they are built up, the gears are made to mesh as best possible by using shims or selected bearings, gears, etc. The whine is 'adjusted' out of our normal hearing range, but other animals like dogs, can still hear it. It is vital the correct oil is used in hypoid axles, and these run very hot indeed. The special additives that lubricate the hypoid-'rubbing' motion as the gear run over each other only works when hot. Earlier spiral gears 'roll' over each other giving very, very high stress at the tiny point of contact. Crown and pinions should always be fitted as matched pairs or you will be in for a noisy axle. Hypoid gear oil smells like Tom-cats pee. (Do not use gear oil in the three-synchro BMC 'Z' Magnettes, MGA, early MGB, Midget, & Farina MG gearbox. The extra drag ruins the tiny synchromesh cones.) Take car over buying half-shafts at auto-jumbles, as virtually every model uses a different length; also second hand shafts must be used on the same side they began, or breakage is possible due to the reversal of the stresses. Look at the splines, the worn side will be the driven side. Also look at the edge of the splines for 'twisting', as the splines fade into the shaft. These are only fit for scrap.