The MGA With An Attitude
REAR AXLE DIFFERENCE and Substitute Housing - TC-209

At 09:07 AM 8/1/05 +0200, Bo Giersing wrote:
"I have used the rear axle numbers on Twin Cam to assist in identifying cars which have lost their original identities - I believe that there is a very approximate relationship between the axle number and the car numbers, similar to the engine number relationship. My observations are as follows:

The axle casings on cars with steel disc wheels are wider that those with wire wheels - the number are typically in the tens of thousands. [The wire wheel axle housing and halfshafts are shorter, by about 7/8 inch on each side, to accommodate the long spline hub for wire wheels.] The Twin Cam axle casing is identical to the wire wheel casing, except that the brake mounting flanges and holes are rotated about 15 degrees forward, which makes the brake mounting holes on the Twin Cam axle parallel with the spring mounting plates. This is presumably to get the brake pistons or handbrake mechanism into the best position. You can use the wire wheel casing on the Twin Cam without problems, but on one of my cars, which had a damaged casing, I machined up a pair of mounting plates with the mounting holes rotated by 15 degrees (I don't know why the factory did not do this)- it is a very simple job.

I believe that the numbering of the Twin Cam axles start at 501 and go up to about 2200 and then start again at 501, with a smaller number punch, presumably at the start of the involute splines. I have seen many axles, all in this range, and have also seen many numbers which correspond more of less to the car number. My early YM1 554 has axle number 544, which has been over-stamped on a standard axle number in the 20,000 range (do other early Twin cams also have over-stamped numbers?) My YDH5 928 has axle number 892 and Eric Clough's YDH5 1150 has axle number 1124. My much later 1600 style YD2 2387 has axle number 558 stamped in much smaller letters.

The way to identify a Twin Cam axle casing, is to see whether the brake mounting bolt holes are parallel to the spring mounting plates, and to have a number in the range of 501 to about 2200. I have also seen a Twin Cam axle with no number at all.

Regards Bo

The Twin Cam rear axle uses the same type and part number halfshafts as the wire wheel cars, but different hub extensions for the pin drive wheels. Inboard splines are 10-splines for the 1500 type cars and 26 splines for the 1600 type cars. The Twin Cam was out of production before advent of the 25 spline halfshafts.

The rear hub extensions were modified beginning with TC_1840 in April 1959 - Identified by either thin or thick casting behind knock on thread. Was AJC5182/3, became ATB7252/3. Edward Vandyk provides the following pictures:

A early Twin Cam rear drive hub (far left) beside a later hub. The later hub has a larger pilot diameter between the knock-off threads and the wheel mounting surface. This will pick up and guide the center hole of the wheel, where the earlier hub aligns the wheel only on the four drive pins.

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