Beck TD, Part 70: The 4.3 Rear End

 Back in 2018, Part 34 reported how Cor Engelen and Troy Nace helped me convert Beck from the stock 5.125 rear gear to a much more highway-friendly 3.9 ratio. That dropped the RPM at 60 miles per hour nearly 1000 RPM, from about 4100 to about 3100. Here's a photo of Cor as he was doing some of the detailed work in that conversion:

That rear end has worked superbly well ever since, and I've put about 2500 miles on it in various cruises. But... I love to experiment, and I wondered if a ratio somewhere between 5.125 and 3.9 would give better acceleration while still being comfortable to cruise. And when I rebuilt an overdrive transmission, my desire grew, since the overdrive gear would lower the cruising RPM by another 25 percent.

When Jake Roulstone told me that he had a 4.3 rear end from an MGA ready to sell, I couldn't resist. Especially since Jake is a very skilled fabricator, and he volunteered to set up the spring mounts for the TD before sending it! Jake lives all the way across the country in California, and he sent a couple of pictures of the process. He noted that one of the trees in the background of this photo is an avocado tree - don't have those in Pennsylvania.

Jake used an angle gauge to very precisely align the spring mounts. His welding is superb, and he noted that his installation was actually more precise than the factory welded mounts. 

I was still working alone due to the pandemic, but I managed to get the 3.9 rear out by myself using a transmission jack. Note that the brake drums are off - that was the only way I could get the rear out without dropping the springs. Also note the expensive Koni tubular shock conversion, installed by prior owner Mark H., peeking out from under the fender. It will play a part in the story later...

Once I had the rear on the bench, I began to figure out the other things needed to complete the installation. Jake had already reversed the backing plates so that TD handbrake actuators would work, and when he had the rear end in his TD, he just mounted the cable to the stock MGA bracket and said it worked fine. But I was being fussy, and noted that the stock TD location was more like this. The photo has captions because I had posted it to the Volvo Powered MGs Group for comments.

I decided to make a mount that would lock into the stock MGA bracket and put the cable right where I wanted it. Here are a few fabrication photos. I used the 20-ton press with my homemade bending jig to bend the heavy steel plate to match the inner profile of the bracket.

A test of the bracket worked perfectly, and I was pretty pumped. I later sandblasted and painted the brackets. 

That sense of pride lasted until Troy and I installed the rear end a couple of weeks later. That fancy bracket tried to go right through the middle of those expensive Koni shocks I mentioned earlier! The perils of designing on the bench instead of in place. By the time I had whittled to get enough clearance, it was hardly better than the stock MGA location. But I'm still proud of the fabrication, and glad I tried. UPDATE: See Part 75 for a better solution to the problem.

The next thing to figure out was the routing on the hydraulic lines for brake fluid. On the TD rear end, there was a drilled hole in a web on the back side, specifically to mount a three-way fitting to route the pipes. That didn't exist on the MGA.

Jake had figured that out, and I mimicked his installation with a custom bracket that fits under the studs for the rear "pumpkin." I also mimicked his routing around the pumpkin, with brackets under other studs.

The final bit of fabrication was actually a tool. When I first saw the rear, I thought that MG had been very clever to make the drain and fill plugs a square recess to match a 1/2" drive ratchet wrench. That notion persisted until I tried it and the wrench didn't fit! Turns out it was some other odd size, and worse yet, the hole was tapered. A quick web search yielded a variety of tools that were made for the job. Here's my version, designed to work with a 9/16" socket.

And here are a few photos of the fabrication of that tool. It works great!

Because Jake's MGA rear had the brake drums on and the brakes already adjusted, and also because he had crafted some very special adapters to allow the use of my 5-lug TD wheels, I didn't want to remove the drums as I did when I removed the old rear. Troy came over and helped me with the tricky task of maneuvering it into place. On the first side, we could tilt the rear and slip the drum through, but on the other we had to drop the front of the leaf spring to make clearance.

All this work was actually completed before my previous post, because I needed the brake plumbing all in place before completing the MGA master cylinder conversion. I somehow failed to take the final picture of everything back together, but be assured that there is a rear end in place with brakes ready to go, Mobil 1 synthetic gear lube in the pumpkin, and no leaks in early testing. Can't wait to button it up and go for a spin.

At 60 MPH, the RPM will be about 3400 RPM, compared to 3100 for the 3.9 gear. But once I get that D-type overdrive installed, the RPM at 60 will drop to 2721. And to be honest, I drive this car at 50 a lot more than 60 anyway. At 50, even with the 4-speed that's currently installed, the engine will be spinning a very comfortable 2845 RPM. 

Cor thinks I'm crazy to do all this work to change something we've already done, but if I'm going to have a project car, I have to have projects!

Continue on to Part 71....