94 Montero Master Brake Cylinder & Vacuum Booster
#11
JC.....Good idea, and I had thought about that also.......blocking off the rear lines and trying. The trouble is that the original design had a return brake line going from the rear proportioning valve back to the front ABS system. I guess I could make plugs and plug off both the going and the coming rear lines.
Naeos.....Im thinking you are probably right about air still being in the system. I know air will compress whereas brake fluid will not......but would it compress enough so as to make the pedal go all the way to the floor w/o even a hint of braking? I test drove the brakeless rig yesterday, and driving through a field, I was pumping faster than a Jed Clampett Oil Rig in Texas, and I had no brakes at all.....pump, pump, pump, all the way to the floor board.
Regarding bleeding, I first used the vaccuum pump and went from the rear brakes to the front brakes, and sucked alot of fluid out of each bleed screw, and I was confident that there was no air/bubbles coming out. I then bled again with a helper pumping the brakes as I bled the screws (Open....down, Close....up, over and over), and I once again removed alot of new/clear brake fluid from the system.
Now, "what-if" one of the lines going to the back brakes is holding air for some reason.......would a section of air in a line cause total failure of the brakes?
If the rear brake lines have any "U" or "N" shaped lines that can trap air as you bleed, would that be enough to cause total failure?
I now am thinking that the darn "return" line from the rear brakes might be the problem......maybe by deleting this line, I will solve the issue?
Naeos.....Im thinking you are probably right about air still being in the system. I know air will compress whereas brake fluid will not......but would it compress enough so as to make the pedal go all the way to the floor w/o even a hint of braking? I test drove the brakeless rig yesterday, and driving through a field, I was pumping faster than a Jed Clampett Oil Rig in Texas, and I had no brakes at all.....pump, pump, pump, all the way to the floor board.
Regarding bleeding, I first used the vaccuum pump and went from the rear brakes to the front brakes, and sucked alot of fluid out of each bleed screw, and I was confident that there was no air/bubbles coming out. I then bled again with a helper pumping the brakes as I bled the screws (Open....down, Close....up, over and over), and I once again removed alot of new/clear brake fluid from the system.
Now, "what-if" one of the lines going to the back brakes is holding air for some reason.......would a section of air in a line cause total failure of the brakes?
If the rear brake lines have any "U" or "N" shaped lines that can trap air as you bleed, would that be enough to cause total failure?
I now am thinking that the darn "return" line from the rear brakes might be the problem......maybe by deleting this line, I will solve the issue?
#13
I doubt there is air trapped in a line at this point seeing as you've bled enough fluid to fill a kitchen sink via different methods. I suppose there exists the possibility that you have a bad master cylinder, it may bench bleed fine but issues arise when being used on the vehicle. If all else fails, try replacing it again. Check the lever action of the brake pedal as well, I have to wonder if something has come disconnected somehow.
Sorry for the late reply, I was out of town for the last week.
Sorry for the late reply, I was out of town for the last week.
Last edited by Naeos_Valkarian; 04-28-2023 at 03:32 AM. Reason: Shenanigans
#14
Naeos.....No worries mate, for the slow reply.
Yep, it did feel almost as if the brake pedal was not connected to the Booster lever......but I installed it, and put the pin and cotter key back in, and the brake pedal is definately hooked up to the Booster. The Booster is good, as it is new and the tests show it is fine. The one-way vacuum valve to the Booster is fine also. The Master Brake Cylinder should be fine as it does have power to pump fluid out all the 4 brake bleed valves.
What do you think about what I described earlier.....about the strange set-up of having a "return brake line" coming from the rear brakes. This is tied back into a brake line block where output fluid is coming from the Master B.C.. From this block, the line goes to another block which supplies brake fluid to all the brakes. I am thinking that this return line from the rear is causing a wierd "do-loop" in the system and I am in essence just pumping fluid in a big circle when I hit the brakes. Your opinion?
My next try would be to cap off that return brake line from the rear and see if that solves the problem.
Yep, it did feel almost as if the brake pedal was not connected to the Booster lever......but I installed it, and put the pin and cotter key back in, and the brake pedal is definately hooked up to the Booster. The Booster is good, as it is new and the tests show it is fine. The one-way vacuum valve to the Booster is fine also. The Master Brake Cylinder should be fine as it does have power to pump fluid out all the 4 brake bleed valves.
What do you think about what I described earlier.....about the strange set-up of having a "return brake line" coming from the rear brakes. This is tied back into a brake line block where output fluid is coming from the Master B.C.. From this block, the line goes to another block which supplies brake fluid to all the brakes. I am thinking that this return line from the rear is causing a wierd "do-loop" in the system and I am in essence just pumping fluid in a big circle when I hit the brakes. Your opinion?
My next try would be to cap off that return brake line from the rear and see if that solves the problem.
#15
Naeos.....No worries mate, for the slow reply.
Yep, it did feel almost as if the brake pedal was not connected to the Booster lever......but I installed it, and put the pin and cotter key back in, and the brake pedal is definately hooked up to the Booster. The Booster is good, as it is new and the tests show it is fine. The one-way vacuum valve to the Booster is fine also. The Master Brake Cylinder should be fine as it does have power to pump fluid out all the 4 brake bleed valves.
What do you think about what I described earlier.....about the strange set-up of having a "return brake line" coming from the rear brakes. This is tied back into a brake line block where output fluid is coming from the Master B.C.. From this block, the line goes to another block which supplies brake fluid to all the brakes. I am thinking that this return line from the rear is causing a wierd "do-loop" in the system and I am in essence just pumping fluid in a big circle when I hit the brakes. Your opinion?
My next try would be to cap off that return brake line from the rear and see if that solves the problem.
Yep, it did feel almost as if the brake pedal was not connected to the Booster lever......but I installed it, and put the pin and cotter key back in, and the brake pedal is definately hooked up to the Booster. The Booster is good, as it is new and the tests show it is fine. The one-way vacuum valve to the Booster is fine also. The Master Brake Cylinder should be fine as it does have power to pump fluid out all the 4 brake bleed valves.
What do you think about what I described earlier.....about the strange set-up of having a "return brake line" coming from the rear brakes. This is tied back into a brake line block where output fluid is coming from the Master B.C.. From this block, the line goes to another block which supplies brake fluid to all the brakes. I am thinking that this return line from the rear is causing a wierd "do-loop" in the system and I am in essence just pumping fluid in a big circle when I hit the brakes. Your opinion?
My next try would be to cap off that return brake line from the rear and see if that solves the problem.
Last edited by Naeos_Valkarian; 04-29-2023 at 01:45 PM.
#16
Naeos......I suppose that with the ABS system, that return line from the rear was needed for some reason......but with the ABS gone, I think that capping off this line on both ends is well worth the try. If that fails, guess I will have to get out the sawzall and cut a big hole in the floor board so I can do a Fred Flintstone and stick my feet down on the road when I need to stop.
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