Brake Problem

[BobsMK4]

I'm assuming you've carefully checked everywhere and you don't have any leaking lines, right? The shop might be right about a bad MC, but since you didn't bench bleed the masters, you may still have some pockets of air floating around in the system. Personally I would start there before throwing parts at it. Bench bleeding on the car is an easy step. You will need to make up a short piece of brake line to reach from the MC to the reservoir. One at a time, remove the brake line at the MC, attach the short piece and put the other end in the appropriate reservoir. Now pump the brake pedal repeatedly until you have a solid stream of fluid with no air. Repeat for the other MC. If you note either MC doesn't work exactly right, e.g. not good flow, somehow intermittent, whatever, this might be a clue to an MC problem. But assuming they both bench bleed OK, now do the 4-wheel bleed again. Start with the farthest rear, then the other rear, farthest front, other front. If you're doing the traditional method, open bleeder, pedal down and hold, close bleeder, release pedal. Speed bleeders make this a little easier if you're interested. I'm personally a big fan of pressure bleeding using a pressure cap with the CNC reservoirs. A few pounds of air pressure in the cap, then just open the bleeder until it runs all fluid. No pedal pumping. Good luck.

I have checked many times for possible leaks and there are none. I will try to bleed master cylinders tomorrow. In order to pressure bleed, is there a special cap for the CNC reservoir? Do you have to install a fitting into the cap? If you reverse bleed the system, do you still need to bleed the master cylinders?

[edwardb]

I have checked many times for possible leaks and there are none. I will try to bleed master cylinders tomorrow. In order to pressure bleed, is there a special cap for the CNC reservoir? Do you have to install a fitting into the cap? If you reverse bleed the system, do you still need to bleed the master cylinders?

The CNC pressure cap is their part number CNC1459A. It's a regular style round cap with a Schrader type valve installed. I always do the MC bench bleed, and then use the cap to bleed each wheel. Maybe the MC bench bleed isn't necessary with this method, but I've never tried without it. Other than a problem I had on my last build with the wrong length pushrod between the MC and hydroboost, I've had perfect brakes every time the first time.