HARD brake pedal question
I had a hard brake pedal on my KP61 when i bought it.
I replaced the wheel cylinders, rotors, calipers, drums, lines and master and booster(everything) and at first all was well. It felt good, But after about 20 miles the brakes would start dragging. Now the pedal is rock hard again. The brakes don't appear to be dragging. But I'm affraid to drive it much because of how hard it is to stop.
Is there a proportional valve and what could be going on? The manifold vacuum seems to be strong BTW.
+hard brakes
If the brakes start dragging after 20 miles and then get rock hard again. Try reducing the length of the M/C push rod one complete turn. The M/C piston has to retract enough to uncover a port to release the brake pressure. You also need a return spring on the brake pedal so the piston can return to the original free state position. The internal M/C spring is not strong to push the pedal assembly rearward far enough. DaveW7
Thanks, Dave
Adjust at the pedal? At the inner master or booster pushrod at the master?
(The pedal does have an assist spring)
You should be able to adjust the push rod at the pedal. Try that first. Adjusting at the booster pushrod would be a PITA. The spec calls for 1mm clearance before contacting the piston. How you measure THAT??? Davew7
I've got the master off and I'm replacing it. (I don't trust it)
When I put it all back together, I'd like to use flexible stainless lines. Has anyone been doing this? Is it M10x1.0? I'd like to use banjo bolts like a motorcycle application because my lines at the master are getting old and have been bent back and forth many times and are harder and harder to align with the master each time.
If it is like all the other Toyota brake lines the threads will be M10-1.0 [same as GM when looking for parts]. Be aware that to use a banjo fitting you must have a flat machined surface to seal against. Verify that your new M/C attachment surface has a smooth finished boss for the crush washers to seal against. I've seen some M/Cs with a really rough surfaces on the brake line attachment boss.
DaveW7
I found it easy to buy steel bundy tube with copper coating and to bend up new ones. Its about a hundred bucks worth of tooling, for the cutter, bender and flaring tool, and then you can make endless amounts of new lines in various sizes. Id prefer that over anything flexible considering all oem uses rigid lines. You should be able to find a shop in your area that deals in industrial fittings and will have all this stuff. There's a great shop in Brisbane called IFS, Industrial Fittings Sales, if you get stuck.
Hard pedal could be as simple as a bad booster. I know you have manifold vacuum, but have you checked that the one way valve works and that the booster functions with the test procedure in the manual? The OEM manual also should have pedal height specs.
Good point about the machined surface.Originally Posted by davew7
I hadn't considered it.
I'll have an "extra master and booster now in hand and I'm going to try to make a gauge to set up the new ones.
The booster is new. (The old one was also doing the same thing and was probably fine) The check valves and tube are also tested and new. When I get the second master cylinder, I'll adjust the booster rod one full turn in and see how it goes.
The only thing I haven't replaced is the proportioning valve at this point.
It worked really well at first. Nice pedal. Nice feel. Then the brakes began to drag. Now they are hard like the booster is not at all working. If I pull the hose off of the booster, you can hear a "woosh" like it is keeping a nice vacuum. But it seems to me like the master is not moving internally to allow the fluid back into the reservoir. I never adjusted the booster before I installed it. (I measured it against the old one.) But the "new"master cylinder was already installed on the car when I purchased it. And I'm thinking it either has some old crud in it or it is otherwise defective.
Am I thinking o.k.?
If your the booster rod is like my AE86, then you should be able to adjust the internal booster rod. But that means complete removing the M/C.
The master cylinder piston only has to move a fraction, to internally uncover the port to allow the fluid to return to the reservoir. My guess is that you are seeing a stack up of tolerances in the booster and M/C assemblies relative to rod positions. You are just going to have to keep adjusting the rod until the brakes no longer drag. [ W/O a measurement method ] It is possible that you have deflective parts or your technical term "crud" in the system. Since you have to remove the M/C, it's not that much more work to remove the piston and check out the condition. DaveW7
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