TR4/4A TR4A Handbrake

[Foura]

I have had a vibration at the back of my TR4A for some time. It has CV joint driveshafts. On our recent 4600km trip from Melbourne to Perth, my wife and I shared the driving. I noticed that the vibration was worse on the right hand side.

When we got home, I jacked the car up and rotated the wheels. I noticed that the right hand brake was binding slightly as I turned the wheel, so I backed off the adjuster and this has reduced the vibration.I am getting the drums machined today. I also noticed that the handbrake cables are not fully releasing, so I will do some lubing of those as well.

One of the articles on rebuilding the rear brakes mentions that the brake cylinder should be able to slide freely in the slot in the backing plate. Mine is not able to move, partly from slight corrosion, but more from the solid brake pipe which does not allow the cylinder to move. I have ordered new mounting plates and return springs and will put these in with suitable greasing. I notice that because the cylinder cannot move, the handbrake only applies one shoe on each side, which possibly explains the lousy performance of the handbrake. It seems to me that if the cylinder could slide, it would apply the other brake shoe, thus doubling the friction on the drum.

Can anyone enlighten me as to how the system SHOULD work?

 

[trrdster2000]

Rocky, they should move. Use some brake grease on both sides, just a light smear of 1/8 inch on each side should do it for the full length of the slot. That is after you have wire brushed the plate on both sides. Use the grease on the flat spots on the backing plate, it's a 1/4 inch by3/4 inch place about half way in the circumference of the shoes, both sides.
Some grease on the adjustment rods at the four flat spots will make for easier times for the length of the shoes cycle.


Wayne

 

[HerronScott]

One of the articles on rebuilding the rear brakes mentions that the brake cylinder should be able to slide freely in the slot in the backing plate. Mine is not able to move, partly from slight corrosion, but more from the solid brake pipe which does not allow the cylinder to move.

The metal brake line shouldn't be restricting the brake cylinder from moving.

Scott

 

[TR3driver]

I'll disagree, they don't move "easily". But they should move under the amount of force the brakes apply, or with a determined nudge from a mallet. The hard line has enough flex to accommodate the limited range of the slot.
Just curious, how can you tell that the handbrake is only applying one shoe? Or is that an assumption based on the cylinders not moving "easily" ?

 

[trrdster2000]

Randall, I see where his thinking is. A wheel cylinder with only one piston on a stable frame could only move one shoe, but we both know that there is so little movement if everything is working, it would be hard to pick it up.

Wayne

 

[Foura]

Thanks for all your help guys. I had the drums off for machining, so I could see that the handbrake linkage was operating one shoe only. The other shoe requires the brake cylinder to move and it isn't able to move. So I am probably only getting one shoe to move when the handbrake is applied which is why it only holds (barely!) on a flat surface. It also means that I am probably only getting the other shoe operating via the brake cylinder.

The drums were machined yesterday and came up well. Hopefully the new return springs and retaining plates will arrive in the next couple of days and I can reassemble the brakes and get them working properly.

 

[TR3driver]

Note that many of the diagrams on how to install the retaining plates are wrong. The outermost (also smallest) and innermost retaining plates get installed first, before the handbrake lever. Both plates have the opening away from where the lever will go. Then you install the lever (which will just slip under the end of the cylinder assembly), and tap the third plate into place between the first two, with the opening towards the lever.