Healey Marque Brake Servo story

[RDKeysor]

A Texas Healey owner authored an interesting article in this month's Healey Marque regarding the upgrades he has made to the brake system on a Healey 100. Briefly, he had upgraded both the rear end and the front suspension on his car, which includes '70s Mercury Capri BJ8-style calipers, etc., on the front. More recently he installed an aftermarket servo kit because he still wasn't satisfied with his brake performance, only to find his new system gave him rear wheel brake lock up. His solution, and I hope he forgives me for this use of his article, was to install TR6 wheel cylinders on the rear brakes to reduce rear brake performance. I checked Moss's listing for the TR6 rear brake cylinders, and the bore dimension is given as .70". I just miked and used a dial caliper on the piston, not the bore, from a recently replaced rear wheel cylinder on my '60 BN7, and that dimension was .747-.749". That's modestly larger than the TR6 version which appears otherwise identical to the Healey rear wheel cylinder. I have a Victoria British servo kit on my car, the 7/8" master cylinder I understand was used on Healey's that came equipped with servos, rebuilt front calipers, upgraded soft brake lines and more recently replacement rear brake cylinders (one had a tiny leak). Upon driving this outfit, I also found it was very easy to induce rear-wheel skid under not particularly heavy braking. I'll add that my brake pedal requires more effort than I would prefer, albeit producing very strong braking. Actually, I could get rear brake skid on this car before all of my upgrades. Just wondering what the Forum thinks on this issue, and has anyone installed a brake bias device that might obviate going to the TR6 wheel cylinders?

 

[Bob_Spidell]

Ah, the 'whack-a-mole' approach to 'improving' an old car. I have a BN2/100M and the brakes are perfectly adequate for normal street/highway driving (but probably not for racing). Note that if your braking system is sufficient to lock up the wheels then tires are the limiting factor--unless you're racing, where heat dissipation becomes an issue--so next the guy from TX will be installing 225/50R18 tires on his Hundred, then he'll need ABS, etc..

 

[steveg]

RD -
I installed a proportioning valve in the rear brake pipe. IMO this is easier than swapping out wheel cylinders. Richard Mayor (Boy Racer) described an easy way of adjusting it with the car on jack stands. These are around $40 on Amazon. Requires some custom pipes:

A friend installed his on the rear axle tee, which required a custom hose from the chassis to the axle.

 

[Keoke]

I installed a proportioning valve in the rear brake pipe. IMO this is easier than swapping out wheel cylinders.

Good show!! Steve :
Volvo taught me that way back in 1960 :
I always use them but the valves were available in the salvage yards back then.---

 

[RDKeysor]

This looks like a good way to go, but the difficult experience getting a brake line flared for my servo installation makes me a bit cautious. I have full sets of SAE and Metric taps and dies, but I don't know if they have any relevance in what I am proposing here. I have the upgraded soft brake lines sold my Moss. Any possibility that a proportioning valve might be tied in using the threaded junction at either end of the rear soft line? Having spent a lot of time getting my old wheel cylinders off and the new ones installed make me hesitant to mess with them again, though Steve's response to my problem there got me through the process. I'll be checking Amazon!

 

[steveg]

Here's the rear axle setup. The valve is available on Amazon. The fittings can be had from https://www.anplumbing.com/

Suggest calling them on the phone - they are helpful.

 

[steveg]

I installed a proportioning valve in the rear brake pipe. IMO this is easier than swapping out wheel cylinders.

Good show!! Steve :
Volvo taught me that way back in 1960 :
I always use them but the valves were available in the salvage yards back then.---

Keoke -- wanted to let you know how much I appreciate your posts on electrical topics from which I almost always learn something.