Conversion to dual circuit brakes

[hupshall]

I have a 1974 Sprint which I'm starting to tear down to restore. I've owned the car for a little over 7 years and have enjoyed it tremendously but it's time to fix the rot in the doors, clean everything up, and give it a fresh coat of paint. When I put the vehicle back together, I want to replace the single circuit master cylinder with a dual circuit. I want the added security. I'm located in Seattle, Wa so as you can tell, Dolomite parts are pretty much impossible to source locally. To that end, I'm looking to pick the forum's knowledge for dual circuit master cylinders that may be available to me that will work properly in the Sprint.

[Jon Tilson]

My first thought is don't bother.
The dual circuit system only separates front and rear brakes, so if the front goes pop your load sensing valve probably means your rear brakes dont work properly anyway.

I've had dolomites for donkeys years. I have NEVER had a single master fail on me. What the single system also does is give a quicker warming that all is not well with the rear wheel cylinders by going a tad soft. In contrast I have had to rebuild every dual master cylinder I have owned at least once and the seal kit on the GMC version varies from expensive to unobtainable.

Is your car lhd or rhd? If you do want to do dual I have a NOS lhd dual master you are welcome to.

Jonners

[Howard81]

As Jonners said! When my 1500HL brakes went pop I lost everything!

[triple tango]

I reckon you get a better feel to the brakes with the single circuit type too

[hupshall]

Over here in the states, single circuit cars are kinda viewed as a death trap so it is something I want to deal with. My car is RHD. What is the difference? Assuming that I will be making new lines anyway..

here is a picture:

[gmsclassics]

One critical component of the conversion you are thinking about is the simultaneous conversion of the rear brake slave cylinders to the later, smaller 5/8 diameter. If you leave the earlier, larger diameter ones on the car, then, in the event of a failure of the front system, you won't have enough fluid in the master cylinder to operate the rear brakes. That would be worse than sticking with the single circuit.

As long as you look after the standard system and ensure that corrosion and damage is attended to, then it should be fine. I suspect most of the safety systems are to protect that element of society that never maintain their cars, yet expect them to continue to be 'safe'.

With a dual cicuit system, you should be able to bleed one part yet still have the other part operate those brakes - a good check that the system is working correctly.

If you are thinking about using a dual circuit master from another car, it must dispace at least as much fluid, so a larger diameter is probably the way to go. Any work on the brakes, introducing other parts needs very careful thought to ensure it is going to work correctly in all circumsatnces.

Geoff

Geoff

[Howard81]

When replacing the 5/8" rear cylinders on my 1500 I found out the all suppliers will send out 3/4" cylinders instead. This is because the manufacturer of these parts has put the wrong part number in the catalogue! The problem should be solved by now, but it's worth taking the pistons out to check.