TR2/3/3A Brake System Performance Expectations

[glemon]

Randall, not sure about a TR3, on a TR6 you are supposed to swap to a slightly bigger rear wheel cylinder to do the swap right, I thought it was because you needed to balance the front and rear. I did the conversion and never liked the way the brakes felt. Pedal went down too far as described in the original post, went through quart of brake fluid, adjusted the rears as tight as I could, no improvement, went back to stock.

 

[Geo Hahn]

FWIW, I finally gave up on the hydraulic switch and hid a mechanical switch on the pedal. The hydraulic ones kept taking more and more pressure to activate, I had 3 of them fail in less than 3 years...

I added a relay to the (DOT5) brake circuit and so far it has been fine. Searching for my old post on this I see:

... I'll be in the test group on this one as I have DOT5 and the switch sold by Moss -- Intermotor brand p/n 51620, made in England.

Switch installed 9/9/2009, 87,853 miles. Now at 92,997. So far, so good.

To update... now it has been 7½ years and 13,000 miles.

But the mechanical switch also works out well - that is what I use on my E-Type.

 

[TR3driver]

Thanks, Art.

Yeah, I've heard about fitting the larger rear cylinders as well. But there are a lot of other variables as well (eg pad compound vs shoe compound) and from what I've seen, most TR6 could benefit from larger rear cylinders anyway (under most conditions).

 

[mastaphixa]

Ok, to close the original loop of this thread, I went back to the two person "Push and hold" method of brake bleeding and after getting tons of air out of the system now really have brakes that I can trust! I did carefully adjust the rears to minimize "the first stroke gets you nothing" effect, but I had a bunch of air in the system that vacuum bleeding just didn't get out. I still standby vacuum bleeding for a system that has already been bled properly (for changing the fluid every couple of years if you're using DOT 3/4) but to bleed a system that has been completely drained or for a new system coming together, the old standard method is the way to go.

 

[RonR]

I have the same problem as "mastaphixa.

The first engagement of the brake pedal goes about two thirds of the way down and activates the brakes. Lifting and reapplying pressure on the brake pedal results on the brakes engaging after less than 2 inches of movement, with a rock hard pedal.

The only component of my TR3A’s braking system that has not bee replaced or rebuilt are the steel brake lines, rotors, and rear drums. I have rebuild front calipers, new rear wheel cylinders, new master cylinder, and new flex hoses. The 5-way union and the associated restrictor valve have been cleaned. The brakes system and master cylinder have been bleed numerous times (DOT 4) by me and my a friend that restores british cars. Also, though unrelated, the front suspension has been rebuilt including new wheel bearings.

I am confident the pedal adjustments are in accordance with the Service Manual listings.

 

[TR3driver]

Did you check brake rotor runout? The spec is only .004" (which I assume is total, not plus/minus) and I found it was very easy to have more than that when changing rotors. It's not unheard-of for new rotors to be already warped, and also easy for problems to creep in like the wheel bearings not being installed just right.

Wheel bearings adjusted to the disc brake spec? The clearance in the workshop manual (1.5 to 2 flats) is huge, and was later updated to less than 1/2 flat. (Eventually given as .003" to .005")

Were the rear shoes "arced" (ie machined to match the exact diameter of the drum) ? They wear in eventually, but having them arced makes a big difference to initial operation. Basically if the surface of the friction material doesn't match the inside of the drum, the shoe has to flex when the brakes are applied; which takes up part of the pedal travel.

 

[TR-3rg]

Hi, I chased the same issue on my TR-3a. Try pumping the brakes up and leaving the car over night. Do not move the car. If the pedal needs pumping in the morning, its probably not from loose wheel bearing, flexing stub axles, etc. I put a 2 pound residual pressure valve in the rear brake line. It keeps the rear brake springs from pushing the brake fluid out of the wheel cylinders. Wilwood makes them and they are about $15. Its probably doing what the factory valve was meant to do 60 years ago. If you are having trouble bleeding, I use one of the kits with a short length of hose and plastic cup. I replaced the 8" hose with a 2 foot length. I hang that up so its 15" above the bleeder screw. Its easy then to bleed, the air escapes but the fluid prevents air from getting in.

Good Luck, RG

 

[Andrew Mace]

RG, I thought the original residual pressure valves were to keep the front caliper pistons and, therefore, pads closer to the disc. I can't imagine that 2lb. would be anywhere near enough to overcome the rear brake shoe springs!