QuestionHi Howard,
I have an early 1974 MGB. I just replaced the right rear slave cylinder, and am having a terrible time bleeding the system. I bleed the system first by following the "manual's process. Opening the bleed valve on the down stroke, and closing it just before the start and during the up stroke.(done to all 4 cylinders) Early in the process we accidentally ran the rear reservoir low for a few strokes but subsequently pumped a lot of fluid and pushed a lot of air out. I’m getting a soft mushy brake. But it will stop the car, feels like the rear brakes are almost locking up... no front nose dive when braking. When I press on the pedal I hear what sounds like air moving, "a throaty sound" in the brake lines near the master cylinder, at the beginning of the stroke, then it firms up and the air noise is gone...
I've tried running a long (12 ft.) tube from the brake bleed line(s) back to the master cylinder and pumping fluid continuously around the loop, no bubbles appear in the clear tubing, but still have a mushy brake
I've also attached a mity vac to the master cylinder and pulled a vacuum with the slave bleed valve closed and also with the bleed valve open (connected to the 12 ft tube full of fluid). Got some air out but still no luck...
I've also removed the rear brake line from the master cylinder, raised it up so there shouldn't be any "air traps” and pushed fluid with a 100cc syringe back through the line from the slave cylinder, re-attached it, still no luck...
Do you know of any tricks to get the air out of the upper lines near the Master Cylinder?
Could the air noise indicate a problem with the master cylinder, or something in the front brakes...
Any ideas on how to isolate the problem would be appreciated.
Thanks,
Jim
P.S. You had someone question how to put the C-clips back on a slave cylinder. A 2” long 3/8 24 bolt, nut, washer and an 11/16 socket can be used to press the C-clip onto the boss. Put the nut on the bolt, then the washer, then socket (nut end towards boss) (its inner diameter is just greater than the boss). Screw this into the boss, then slip the C-clip in between the socket and the boss, centering it on the chamfer and the socket… tighten the bolt till it bottoms, then use the nut to push the C-clip farther if necessary... finish tapping the C into place
AnswerHi Jim,
I am not convinced you have air in the system. When there is a lot of travel in any of the cylinders fluid moves rapidly and can sound like air moving.
A soft pedal can come from too much movement in any part of the brake system so you need to do some testing.
First test is to pump the brake pedal and note if the pedal is any higher from the first push to the pedal after pumping, then let off the brake and pull the hand brake up hard so the rear brakes are locked up and then pump the brake pedal again. Is there any change?
Next, jack the front up and remove both front wheels and with a strong light watch the relationship between the disk and the caliper while someone pumps the brake pedal in hard strokes. Check both wheels and let me know. Also let me know about the hand brake test. Also check for any free play at all in the front wheel bearings.
That is a good tip on the "E" clip on the rear wheel cylinders. They are always a hassle.
Howard
