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WELDED REAR MOUNT for MGB GEARBOX in the MGA - GT-303

AH-HAAII! - An MGB Transmission Mount for the MGA
by Bill Stewart

As originally appeared in Texas Chapter News - October 2002 (with addendum).
Reproduced here with permission of Bill Stewart and TCN.

My car is a '58 MGA coupe in the process of a ground-up restoration (I have drug this car around with me for over 20 years). Wanting an air conditioner and overdrive, I decided to go with an MGB 1800cc engine to overcome the added load and improve the ride at highway speeds. Mounting the MGB transmission on the MGA frame, however, became a real challenge. The MGB 1800cc engine mounts are identical to the MGA and that installation was effortless; the transmission mount for the MGA and MGB are not the same and this was not a trivial installation. For this reason, many installers of MGB engines use the front half of a MGB transmission and the back half of an MGA transmission so they can then use the stock MGA transmission mount. Unfortunately, no overdrive is available for this combination, so it was not pursued.

MGB O/D gearbox on new welded rear mount
MGB O/D gearbox sitting on new welded rear mount

Searching for an MGB transmission mount took me to the MGA 1800 interest group as listed in the back of MGA! magazine. Steve Chaffee of that group sent me a drawing of a mount which utilized the 'ears' cut from a MGB cross member. The 'ears' were then welded to a flat plate which is bolted to the MGA cross member. Steve also mentioned that there was an 'engineered' solution also but that one I have not seen. Having a potential solution in hand, I proceeded to search for yet another solution that I felt would be how it would have done by the masters at Abingdon-on-Thames.

New welded rear mount, right side
New welded rear mount - right side

After putting the engine in its mount, I kept the transmission blocked up over the frame. I would return from time to time to this void between the transmission and the frame while continuing to work on other parts of the frame and suspension restoration. Months came and went and no happy solution came to mind. I tried to think of something new. I reconsidered the 'ears' on a plate. I wondered what the engineered solution was. I worried. I wondered. I worried!

New welded rear mount, left side
New welded rear mount - left side

Then, Ah-haa! What if I took the MGB member and cut it away until it fit on top of and into the MGA frame? I had a vision of the MGB cross member melting and sinking until it held the transmission 1/2" above the MGA frame. With that in mind, I bolted the transmission to the MGB cross member as it lay across the MGA frame. Taking measurements, eyeball and otherwise, I began to cut with a reciprocating saw and fine tooth blade with the cross member mounted in my shop vise. The first cuts were to the ends, A-A and B-B as shown in Figure 1. The next cut was to the base of the rear 'ears', C-C in Figure 1. A rip cut of the base, D-D was then made as shown in Figure 1, 1/4 inch behind the three holes in the base.

MGB gearbox cross member rough cuts
Figure 1

Two notches were made on the ends as shown in Figure 2. The lower bracket for the transmission mount pin was cut 1/2 inch from the rear as shown in Figure 1. The lower rubber bushing was trimmed 1/8 inch on the bottom lip to fit next to the square cross member. The mount was then welded in place to insure a fit without having to remount the transmission.

MGB gearbox cross member final cuts
Figure 2

My concern for making a mistake was realized when I mounted the new A/B the first time. When the transmission was swung down on the frame, it also moved forward leaving a 1/4 inch gap at the A square cross member. Also, the left end needed to be longer to reach the floorboard frame. With these corrections made, the second mount fit nicely. Yes, I cut a second cross member.

The engine restraint rod to the rear of the transmission was not made. A round cross member is in the way. Something else to work on! Now another Ah-haa!

Addendum, late November, 2002:

Barney, here are the photo's. Glad to help with this. I'm winging it and hope to be happy when it is complete. Yes, the right tunnel guide channel was removed. A large hole (to be larger) has been cut in the middle right side of the cover for the OD. I plan to cut the top of the cover forward of the top hole for the shift and move the small cover forward a couple of inches. This will allow the cover to sit on top of the floor boards. Will get back to you when I have a final fit and reconstruction. The B drive shaft fits with no changes. The OD switch will be mounted in the shift knob as a push on-push off under the MGB logo and an OD 'on' light will be added to the dash low center between the tach and speedo'. Wayne Kube, our president, has done this and is building mine. Same light as the turn indicator. I am very interested in what works and doesn't. Appreciate the dialog. Bill.

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