I'm working on a 1993 Jeep YJ, 4.0, 5-speed. I have swapped in a 1989 Grand Waggy front Dana 44, and a rear 1994 Honda Passport Dana 44 (disk brakes).
I recently installed a 1978 Mercury Grand Marquis master cylinder and a 1998 Grand Cherokee proportioning valve for 4 wheel disks. Stock vacuum booster. I thoroughly bench bled the master cylinder and gravity bled all 4 calipers several times. I ran about 3/4 of a quart of fluid through each caliper. There are no leaks in the system.
With the engine off: The pedal is very soft. It feels as if it has two stages; at the top it's very soft, and then I can feel it come to a hard spot with a thunk/click/tap, whatever you want to call it, then it gets very hard. Pumping It will not build pressure. I am 95% sure there is no air in the lines. I also get a whooshing noise when I push the pedal.
With the engine on: The pedal is still very soft, though I can't feel the second "stage" I mentioned above. Occasionally, it feels close to normal near the end of the pedal travel. I get the same whooshing sound when I push the pedal, and there is a slight change in engine idle.
I replaced the "new" master cylinder today, thinking maybe the reman unit I got was bad out of the box, no change. I had the wife push the brakes with the engine off while I watched inside the master; the pistons don't move until the pedal passes the soft section I mentioned above. I measured the depth of the MC bore where the push rod contacts it, it's the same as my stock YJ master, so I know the push rod is the right length. I checked the check valve at the booster, it seems good, only allows air to pass one way.
I've been trying to study boosters, and to me it sounds like there could be a tear in my booster diaphragm. The whooshing sound and engine idle change seem to point to a vacuum leak. Also, I should mention that when I had the master out to change it the very first time I pushed the brake pedal to the floor by accident, which could have damaged the booster?? I had to re-seat the push rod back into the booster, is there a way to screw that up?
I've ordered a new booster, does that sound like the culprit? Any thoughts? Thanks in advance!
I recently installed a 1978 Mercury Grand Marquis master cylinder and a 1998 Grand Cherokee proportioning valve for 4 wheel disks. Stock vacuum booster. I thoroughly bench bled the master cylinder and gravity bled all 4 calipers several times. I ran about 3/4 of a quart of fluid through each caliper. There are no leaks in the system.
With the engine off: The pedal is very soft. It feels as if it has two stages; at the top it's very soft, and then I can feel it come to a hard spot with a thunk/click/tap, whatever you want to call it, then it gets very hard. Pumping It will not build pressure. I am 95% sure there is no air in the lines. I also get a whooshing noise when I push the pedal.
With the engine on: The pedal is still very soft, though I can't feel the second "stage" I mentioned above. Occasionally, it feels close to normal near the end of the pedal travel. I get the same whooshing sound when I push the pedal, and there is a slight change in engine idle.
I replaced the "new" master cylinder today, thinking maybe the reman unit I got was bad out of the box, no change. I had the wife push the brakes with the engine off while I watched inside the master; the pistons don't move until the pedal passes the soft section I mentioned above. I measured the depth of the MC bore where the push rod contacts it, it's the same as my stock YJ master, so I know the push rod is the right length. I checked the check valve at the booster, it seems good, only allows air to pass one way.
I've been trying to study boosters, and to me it sounds like there could be a tear in my booster diaphragm. The whooshing sound and engine idle change seem to point to a vacuum leak. Also, I should mention that when I had the master out to change it the very first time I pushed the brake pedal to the floor by accident, which could have damaged the booster?? I had to re-seat the push rod back into the booster, is there a way to screw that up?
I've ordered a new booster, does that sound like the culprit? Any thoughts? Thanks in advance!