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MG TD TF 1500 - TF rear brake operation

I'm re-doing the rear brakes on the TF, and having the shoes relined and arced to the respective drums. That got me wondering about the operation of the rear brakes, as there is only one forward wheel cylinder to actuate them. Since the aft brake lining ends rest on a stationary block and don't make contact with the drum when at rest, does the aft portion of the brake linings ever come in contact with the drum? Obviously the forward portions of the linings do with actuation of the wheel cylinder, so is there some dynamic I'm not grasping that would also cause the aft portion of the linings to move outward as well when you depress the brake and make contact with the drum? There is a lighter spring in the aft position attached between the brake shoes.
I don't know if that acts as an actual return spring...or just a way to keep the aft portion of the brake shoes fixed against the stationary block while the front portions pivot outward under brake pressure.

Thanks!

Jim
Jim Rice

the cylinder slides in the backplate and pushes against both shoes. The lower shoe is leading (self servo effect) and gives most of the braking force.The top shoe is force back as the front edge hits the drum.
Arcing the shoes makes a massive difference to the initial braking and no bedding in.
If you powder coat the back plates, make sure the paint is remove from spring sheet that the cylinder slides on.
Ray TF2884
Ray Lee

Thanks Ray...that explanation helps me understand the inner workings of the rear brake system. I guess it's my 2 dimensional thinking at work as opposed to the engineers 3 dimensional thinking when they designed the system. I've never been able to observe well worn brake linings to see the wear pattern on the linings due to the rear oil seals having leaked a fair amount of fluid into the brake assembly. (addressing that as well with new oil seals, collar, etc.) No plans to powder coat the backing plates, and aware of the need to be sure the cylinders can traverse freely with no binding on the backing plates.

Jim
Jim Rice

Don't forget, 150 ft/lbs torque on the axle nut or you will wreck the splines.
Ray
Ray Lee

Regarding the torque values...I printed out a torque value chart for various nuts/bolts that David Dubois created years ago. In it, he listed the torque for the rear axle nuts at 85 ft. lbs. wet. (threads lubricated with oil). Do you know if the 85 wet torque value is ~equal to the 150 dry torque value?

Also, between 40 - 70 wet for the front axle nuts. I don't know what the dry value for those is.

Jim
Jim Rice

There has been a lot of traffic on this site about the axle torque and 150 seems to be agreed on.I have never heard of a failure at this level.
My torque is me standing on a 1 foot spanner oiled thread. If you do not get near the split pin hole try the nuts on the other side.
For wire wheel owners it does not matter if the splines damage because you can get new parts., Disc wheel brake drums are no longer made so damage must not be done.
Ray
Ray Lee

Ray, there was a discussion some time back about Orson mfg. in the UK being interested in making rear drums for steel wheel TDs and TFs if someone would loan them one to copy, did this ever go any further than a discussion? PJ
PJ Jennings

If the only hold-up is the loan of a set of drums to be copied, I have a full set from an abandoned TD donor car. Let me know if the project progresses and if my drums would be useful. Jud




J K Chapin

I sent them a drum and left it with MG Octagon Club to pursue. Nothing seems to have come of it.
Dave H
Dave Hill

This thread was discussed between 18/04/2022 and 19/04/2022

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