In the 50s English motorcycle world, most makes now have available a Twin Leading Shoe front backing plate upgrade to help keep the riders alive in current traffic.
A while back I was converting my BSA to TLS and I thought “this would be a really good upgrade for my improved TC, I wonder what would be involved?” I know little about any MGs other than TCs. Later I stumbled on the fact that TDs had TLS front brakes and when I looked into it and saw that the brake shoes were the same width and the same diameter drum as the TC, I knew I could do something with them.
I borrowed a TD backing plate, it was obvious it couldn’t be made to fit, but I made a dimensioned drawing from it of the cylinder positions to modify the TC backing plates.
The TD had the cylinders mounted at 3 and 9 o’clock on a flat surface backing plate. I mounted them at 12 and 6 so the TC brake line could be used and the upper brake spring had clearance with the plate offset.
The conversion is pretty straight forward using all TD parts except the adaptors which I made new. (The TD brake line thread is 3/8, the TC 7/16).
This project is all about minimizing the amount the plate warps when you weld in the replacement piece after cutting out the raised portion at 6 o’clock and figuring out the best way to straighten the plate in a hydraulic press after welding. Going at this completely cold, I fumbled my way through the first plate, a lot easier for the second and the next time around should be a piece of cake as I feel I now have the job pretty well figured out. (those famous last words!)
The rule of thumb when going from a SLS to a TLS brake is a 25% improvement in efficiency. This isn’t earth shattering. In routine use, I can’t really notice an improvement without using my imagination.
However, in a hard or puckering stop, then I can really notice the improvement which is when it counts.
I’m glad I did this job. This was a good improvement for my car and an interesting project.
Charlie Mac Quarrie
Ed’s note: Andy King offers a kit for TA/B/Cs using your existing backplates and modified to take twin leading shoes as fitted to the TD/TF. The kit contains all new wheel cylinders, shoes, return springs and will bolt directly onto your existing drums. PRICE IN THE REGION OF £750.00 http://www.mgsparesandrestorations.com/home.cfm
Ed’s further note: For those who are interested, there is an article by Jeff Redman on converting to a twin leading shoe arrangement at the following link:
However, one downside is that it does not use the existing TC backplates and donor backplates need to be sourced (probably as rare as hens’ teeth).
For the uninitiated, the ‘text book’ explanation of the advantage of the twin leading shoe arrangement is as follows:
The twin leading shoe drum brake is a specific design type of drum brake that is typically found on the front of automobiles. Its advantage is that it provides maximum possible retardation in its intended direction of travel, i.e. frontwards. Everything else being equal, it is more powerful than a single leading shoe drum design.
The term “twin leading” is used because both shoes are “leading”, moving with the direction of rotation of the drum and thus exhibiting a self- applying, or self-servo effect i.e. being dragged into the friction surface of the brake drum and thus achieving greater braking force.