Did anyone convert to dual circuit brakes?

Dmitry

Dmitry

New Member
Hi All,

I am thinking to convert a P4 90 to dual circuit brake system. Found a few master cylinders online. They must be compatible with remote reservoirs. There are products that have 2 separate cylinders working in parallel with a balancing link between them. As I understand I will need to connect rear brakes to the rear output for the master cylinder, and the front output must be connected to the servo. Artificial intelligence also mentioned the proportioning valve that is required to balance between rear and front brakes. A bracket will need to be manufactured for the new cylinder. I'd say the most difficult here would be to understand/calculate correct pedal ratio, bore size, etc.

Did anyone do something like that on P4s?

My handbrake, by the way, is working fine now, and I found that it does slow down the car. I got high friction low fade brake shoes from John Wearing. As I understood, the lining on them was not thick enough, so I had to make new and modified V-shaped metal strips in the mechanism, so they could extend the shoes farther. Those strips don't have a stop on the "parking brake ON" side.

I drive my P4 very often, so would like to make it a bit safer.
 
Any particular reason for doing this? Safety in case of failure of one circuit, or improved braking? I have some experience of a P4 fitted with early P5 twin trailing shoe drum brakes, and it was superb - smooth as can be, never faded on big descents, no issues at all. I suspect the work required to work out m/cyl bores, pedal ratios and suitable boosters will not be trivial...unless you find somebody who has done it and it works well.
 
Having thought about this overnight (and in the distant past to do similar). It depends on how much engineering you want to do, a complete system would mean dual circuit master, twin servos and proportioning valve. Working on the principle that the most likely component to fail will be a wheel cylinder an alternative would be existing single circuit master, then to the existing servo and then via a 'T' piece to a shuttle valve, which works on the principle of the good side shutting off the bad side. It could then be a case of doing a diagonal split instead of front/rear, this would eliminate the brake bias problem.
 
jp928, I want to do it to protect against a circuit failure. My current brakes are not too bad, with high friction shoes and a new master cylinder. Although the pedal is a bit spongy. It will be some amount of work to convert it, for sure.

colnerov, I like the idea of keeping the original master cylinder - no need to design and make the bracket, no need for searching for the new master cylinder with similar parameters. I attached the drawing, do I understand it correctly? I found this on Ebay, it has 2 inputs and 2 outputs. Land Rover Brake Shuttle Valve Pressure Warning Actuator Switch 90 110 NRC7871 | eBay

Capture.JPG
 
Dmitry said:
jp928, I want to do it to protect against a circuit failure. My current brakes are not too bad, with high friction shoes and a new master cylinder. Although the pedal is a bit spongy. It will be some amount of work to convert it, for sure.

colnerov, I like the idea of keeping the original master cylinder - no need to design and make the bracket, no need for searching for the new master cylinder with similar parameters. I attached the drawing, do I understand it correctly? I found this on Ebay, it has 2 inputs and 2 outputs. Land Rover Brake Shuttle Valve Pressure Warning Actuator Switch 90 110 NRC7871 | eBay

View attachment 26534
Click to expand...

Yes that's it. I did similar on a Land Rover series years ago. Although that shuttle valve is a bit spendy I manage to find one from a Volvo, I think, in the breakers yard. That of course had metric threads but if you're re-plumbing the pipework it's simple enough to use metric fittings where needed. Be aware also that that valve has different size unions for each half, the same as the matching M/Cyl but the same 3/16" pipe but that's not applicable in your case.
 
If we are a bit reallistic about chances of failure lets look at the most common failure modes in drum brakes. I suggest most common would be hoses due to age and cracking - at the rate most of us use these cars, age is unlikely to be a problem, especially combined with the amount of time we tend to spend pottering with them. Next problem I have seen is steel pipework which rusts, or copper which work hardens. Both of these problems can be solved with Cunifer pipe - a copper/nickel/iron alloy that is easy to bend and flare, but wont work harden or rust. If you do a reasonably thorough job on the master and slave cylinders I reckon they would see you out. Fitting the pressure warning switch you mention would certainly be worthwhile. There is plenty of scope to improve the brakes with either the twin-trailing set up from the 3litre, or the disc setup from late P4s.
 
Got it. I will need to:
- install the shuttle valve
- periodically inspect the flexible hoses and cylinders
- make sure that Cunifer pipes are installed everywhere

This will give me peace of mind, together with good parking brake.

Thank you very much for the detailed advice!! I learned something new.
 
You must log in or register to reply here.
Back
Top