QuestionQUESTION: 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
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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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QUESTION: Hi Howard, Well, I took the bleeders out of the calipers and put them in the Master Cylinder. Got a rock hard pedal. Reinstalled bleeders and bleed the brakes with a Mighty Vac. Still very spongy pedal. Almost goes to the floor. But if I pump it about 10 times I can lock up the fronts. Where can the air be trapped? Thanks for all the help. Andy
AnswerHi Andy, if you bled in the order I advised and were not getting any more air from the bleeders than it most likely is not an air problem but a movement problem. You can use the same method of isolation by using a caliper bleeder to block off the front calipers at the master cylinder and if the rear brakes are set up correctly you will have a very good brake pedal and that proves the problem is in the calipers. If you have a soft not so great pedal you need to correct the rear brakes first before proceeding to the calipers. The common problems in the rear are (with new shoes) shoes don't fit the drum or incorrect adjustment.
If however you do have a good hard pedal with only the rear line connected, you need to reinstall the bleeder valve in the caliper and have someone pump the brakes slowly and with a hard push while you look closely with a bright light at the relationship of the brake disk to the caliper. If you see any flexing of the disk it means most likely that one of the pistons is stuck and the other is forcing the disk over to meet the other brake pad. Thus the soft pedal because even the smallest amount of movement of a caliper piston displaces more fluid than a master cylinder can pump in one stroke. Both sides must be looked at carefully.
If you see no movement of the disk do this. (especially if you just installed new pads.) remove the brake pads and put in place an old worn out pad or any hard object (flat plate material) that is a little thinner than the new or present pad. (you are not going to drive the car so it does not matter what you put in there. Now, pump up the brakes again and remove the plates. now you will find that the new or present pads do not fit in unless you pry the pistons back into their bore BUT DON'T PRY THEM BACK. Pry the piston a very little at a time until you can just force the pad in. If you pried the piston in and the pad slips in easily you need to start over.
The objective is to have the pads forced in so they are in place but tight so the disk is not easy to rotate and both pads are in place. Do both front calipers that way. Now check to see if you have a good pedal. If you do you can not drive the car that way of you will overheat the disk and calipers so what you do is to drive the car in 1st gear only and make hard "S" turns in the road or if you have a large parking lot available close just drive the car hard in circles in right and left hand turns a few times. Now jack the car up and try to hand spin the front wheels. If they spin free you are finished, if not you need to repeat either the "S" turns or circles and check again. There are no retraction devices (except on older Jaguars) to keep the pads off of the brake disks so the caliper manufactures designed the seals so that they hold very hard onto the pistons and when you apply the brakes you force the piston out and it applies pressure on the pad and when you release the brake the seal on the piston flexes back to retract the piston away from the pad. Some times when working on calipers the piston seal flexes too much and and requires two or more pumps of the master cylinder to make the piston reach the pads so thus the procedure I out lined corrects that. It does not happen all the time but I found it to give a soft pedal about one in every 10 cars done.
Let me know how you do.
Howard
