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You are here: Experts > Home/Garden > Auto Repair > MG Car Repair > Brake Bleeding
Expert: Howard M. Fitzcharles III - 11/7/2009
Question
QUESTION: Recently replaced all brake components. Unable to get a pedal. Tried vacuum bleeding, pressure bleeding, and old pump and release. Not sure if I replaced the brake lines properly. The line nearest the pedal goes to the front brakes and the farthest goes to rear brakes. If I plug front brakes, I get a firm pedal. When bench bleeding, I notice the farthest line works first and then the nearest starts to work. Is this correct? If I reversed the lines would this cause lack of pedal?
ANSWER: Hi Andy, first thing I need is what kind of MG is this?
Howard
---------- FOLLOW-UP ----------
QUESTION: Howard, its a 1970 MG Midget, 1275 engine
Answer
Hi Andy,
On a dual circuit system I found that if you get two bleeder valves that match the line fittings in the master cylinder and remove the lines and put the bleeder valves in place of the lines you can do a 100% sure test of the master cylinder. Check one of the front caliper bleeder valves first and if they don't fit you can usually get a bleeder valve assortment in a kit from most auto parts stores.
With both bleeder valves in place of the lines fill the reservoir (DOT 4 fluid) and pump the pedal and bleed both valves and you should quickly arrive at a rock hard pedal with very little free play in the pedal (about 1 in.)
This is a 100% effective test of a master cylinder and is necessary before continuing with trying to get brakes. After you have this test complete, Then you can continue down towards the brakes.
As far as which line went to which hole as best I can remember the line to the front brakes is the one closest to the driver and the line closest to the front of the car is the rear brakes but I also seem to remember that the lines only fit one way and without a lot of bending couldn't be switched.
After you have confirmed that you have a good master cylinder then connect up the lines and start bleeding at the right rear wheel first, then left rear and right front and last is left front.
You said "farthest / nearest" reference to what? The way that the master cylinder works is when you push the piston in and the cylinder is already bled, you push on the first piston and it pushes on the fluid which in turn pushes the second piston in against it's fluid. If the first piston has air in the system that piston has a long nose that hits the second piston and pushes it against it's fluid. If however the first piston had been bled and the second piston had air then the first piston would push it's fluid and that fluid would push the second piston all the way to it's stop because it had air in second system. This way if either system failed the other still had brakes even though the pedal was only about half. A valve down the brake lines has a switch that is pushed if either of the systems has less pressure than the other, thus turning on a warning light so the driver is alerted that one of the systems is failing.
I recommend Dot 4 fluid only.
Let me know how you make out with it.
Howard
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