Thread: Disco Brake Booster into RRC - Help

Originally Posted by Skiboy

I am about to put a mid 90's disco brake booster and master cylinder into my RRC 89 but found the RRC has 4 brake lines coming out of the brake master (one of these to the front is not sealed off as have put on Defender calipers than only need one line to each corner).

BUT the Disco master cylinder/booster (Lucas type) has only 2 outlets for brake lines. Disco 2 brake lines RRC 4 lines? Do I just need a T piece?

What should I do? The current RRC has one line to each front corner and a single line to the rear brakes.

WHY doing this - booster on RRC not go enough vacuum so likely gone - I am told the disco master cylinder is bigger bore so will drive the defender caliper better - ie stop harder.

All advice welcome.

Very similar set up to whats going in mine.
Rather than stuff around adapting I'm going to use the Disco steel pipes with new flexible hose so is nice and tidy.

Isn't the twin diaphragm '89 booster & the 'mid 90's' booster the same?
If so, why not just change the boosters, re-using your original 89 master cyl & see if that makes enough difference.
Otherwise, I agree with Rangier Rover, don't use tee peices that weren't part of and orignal system, unless it's a bush/farm only car - a bit fiddley, but change all the brake lines over to the later Disco type if you use the 2 port master cyl.
Rgs, LR4WD

Originally Posted by Skiboy

... I am told the disco master cylinder is bigger bore so will drive the defender caliper better - ie stop harder.

All advice welcome.

A larger bore master cylinder will give lower fluid pressure for the same force on the foot pedal - this will give lower clamp force at the calipers.

The physics are pressure = load / area

The larger master cylinder will move more fluid for the same stroke, so the pedal wont travel so far.

Defender calipers with larger diameter pistons will give higher clamping force for the same fluid pressure. Force = pressure x area.

OK agree booster the same so could just swap.

My brake specialist guy seems to think he can set up for a 2 line not 4 line system with a t piece - I would not be doing myself.

Re using Disco lines - not need to for the back as one line goes to the back - would need that for the front as currently have 2 lines to the front (with one of the 4 lines sealed off due to Defender only have single fluid inlet). So currently I have 3 lines - 2 front and 1 rear and want to match these to a 2 lines master.

Also I do not have a set of disco brake lines - they and the booster all got crushed so had to re-buy a booster off a club member. Not sure it is worth the effort to find, remove and then install a disco set of lines when can adapt (professionally) the rangie lines.

But I will go look at a set of disco lines to check out the option.
Skiboy