Did a SAS on my '94 Explorer years ago and the brakes were always mushy afterward (build thread in sig). Axles were a Dana 60 and Sterling 10.25" from an '87 F-350. I put a new master cylinder for a '79 Ford on and bypassed the Explorer's ABS pump. Finally lost brakes the last time I had it out 2 years ago and it's been parked since (too many other priorities). Finally noticed it would leak brake fluid from the driver front caliper and passenger rear wheel cylinder after sitting a while. My wife and I replaced both calipers and wheel cylinders (and rear brake shoes) and we bled the system this morning. Still seems to have the same problem--firm pedal until you start it then it goes to the floor but the brakes are still working but I haven't been able to really test them yet (I have to get a Jeep moved out of the way to really drive it). I'm stumped about what the problem could be. I'm left with line diameter too small since they're the Explorer's 3/16" lines. Any other ideas?
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mushy brakes after SAS
- Thread starter SVO42
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Man I hate this problem with a passion. I feel for you, as I wouldn't wish it upon anyone. There has to be over 10 pages in the BH registry covering this issue. 
A little something I learned is to Make sure that master has the same setup as the explorer master for the front/reverse ports. Some are opposite, and could cause it to be bypassing instantly with too much pressure to the rears.
Now since I mentioned bypassing and rears, did you install an adjustable prop valve for the rears when you deleted the ABS system? I had to install one when I did it, and took me forever to figure out I had it set too high. there is a small happy place setting on mine between 450 & 475 psi to make the master happy and not bypass.
Simple trick to test.
1) Engine off. Pinch the soft lines with small vise grips ever so gently if they are new enough. (nevermind if they are old and frail) Pump up the pedal until it is firm. Engine on, push the pedal. Does it stay up or fall to the floor?
2) If it stays firm... Ease it into gear and Test the brakes on a side street and see if the pedal stays up. You will feel the loss of the braking power with no rear brakes, but this will tell you if your system is connected right, and/or if the rears have too much pressure to them.
If this results in your pedal working, you need a prop valve in-line for the rears and set it accordingly. Let us know if this helped any. Good luck!
A little something I learned is to Make sure that master has the same setup as the explorer master for the front/reverse ports. Some are opposite, and could cause it to be bypassing instantly with too much pressure to the rears.
Now since I mentioned bypassing and rears, did you install an adjustable prop valve for the rears when you deleted the ABS system? I had to install one when I did it, and took me forever to figure out I had it set too high. there is a small happy place setting on mine between 450 & 475 psi to make the master happy and not bypass.
Simple trick to test.
1) Engine off. Pinch the soft lines with small vise grips ever so gently if they are new enough. (nevermind if they are old and frail) Pump up the pedal until it is firm. Engine on, push the pedal. Does it stay up or fall to the floor?
2) If it stays firm... Ease it into gear and Test the brakes on a side street and see if the pedal stays up. You will feel the loss of the braking power with no rear brakes, but this will tell you if your system is connected right, and/or if the rears have too much pressure to them.
If this results in your pedal working, you need a prop valve in-line for the rears and set it accordingly. Let us know if this helped any. Good luck!
jmdirk
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Still sounds like an air problem. Did you bench bleed the master?
This kind of problem is more often than not, having air or a a leak in the system. With the engine off, you only have the force of your foot on the pedal. When you start the engine, you know have the extra vacuum assist boosting the line pressure. the result is:
1) being able to further compress the air in the system than you could under your own power
2) being able to force fluid past a leak due due the extra pressure where it wouldn't leak with the engine off
My guess would be that the MC wasn't bled. It's virtually impossible to get all the air out of a master by trying to bleed it from the calipers. You have to bleed the master first, then connect the lines and then bleed the lines from the wheels.
Bleeding sequence is supposedly RR, LR, RF, LF. Some will recommended tapping the calipers lightly while bleeding to 'loosen' the air.
You could also have a leak somewhere, either at one of the connection points, but it could be a corroded line itself. Particularly up where the brake line to the rear runs in the frame rail beside the gas tank. Mud can get packed up in there causing the line to rust out creating pin hole leaks. My Ex had that problem when I bought it and then again a couple years later. ended up using cupro-nickel brake lines which are supposed to be much more corrosion resistant.
I'd say that since the 79 MC you're using is pre-ABS, it probably has the pressure reduction valve and residual pressure valve built into it. Pinching off flex lines is really going to tell you if you have leak after the pinch point or not. Not having proper bias to the rear would result in locking up the rear brakes rather easily.
This kind of problem is more often than not, having air or a a leak in the system. With the engine off, you only have the force of your foot on the pedal. When you start the engine, you know have the extra vacuum assist boosting the line pressure. the result is:
1) being able to further compress the air in the system than you could under your own power
2) being able to force fluid past a leak due due the extra pressure where it wouldn't leak with the engine off
My guess would be that the MC wasn't bled. It's virtually impossible to get all the air out of a master by trying to bleed it from the calipers. You have to bleed the master first, then connect the lines and then bleed the lines from the wheels.
Bleeding sequence is supposedly RR, LR, RF, LF. Some will recommended tapping the calipers lightly while bleeding to 'loosen' the air.
You could also have a leak somewhere, either at one of the connection points, but it could be a corroded line itself. Particularly up where the brake line to the rear runs in the frame rail beside the gas tank. Mud can get packed up in there causing the line to rust out creating pin hole leaks. My Ex had that problem when I bought it and then again a couple years later. ended up using cupro-nickel brake lines which are supposed to be much more corrosion resistant.
I'd say that since the 79 MC you're using is pre-ABS, it probably has the pressure reduction valve and residual pressure valve built into it. Pinching off flex lines is really going to tell you if you have leak after the pinch point or not. Not having proper bias to the rear would result in locking up the rear brakes rather easily.
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Too much rear pressure will cause the master to bypass and the pedal to the floor. The diaphragm in the master gives way to high back pressure. When was the last time anybody can remember a rear tire locking up on dry pavement other then the result of the E brake engaged?
jmdirk
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There is no diaphragm or bypass in the master. The two pistons are inline and designed to bottom out so that you still have either front or rear brakes in the event that one of the circuits fails.
Not so hard to lock up the rear brakes. That's the whole reason that early first gens only had rear ABS. Once the weight shifts forward under braking, it's extremely easy for the rears to lock up.
Not so hard to lock up the rear brakes. That's the whole reason that early first gens only had rear ABS. Once the weight shifts forward under braking, it's extremely easy for the rears to lock up.
SVO42
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I bench bled the MC when I did the swap. Looking at some other info I think I might also have a fluid volume issue. My awesome wife and I worked on it and got the new parts with a quick redneck bleed last weekend. Finally tested it and while the pedal still goes to the floor (or almost) the brakes at least work again! Tested on a gravel road in front of our house and, even though the pedal goes down too far, it stops! Pretty sure at least one pair of wheels is locking up since I could hear the gravel sliding.
Did some part spec research and I got a new MC for a '98 Super Duty. That was the last year for a front disc Dana 60/rear drum Sterling and had the largest MC bore at 1.25". Hope to get the new one plumbed (ports are on the opposite side and now I need a new fitting thanks to it being almost seized and having to break out the vise grips) and then I'll do a proper bleed and see what happens.
While I'm working I'll check for failed lines. I'm hoping that does the trick but maybe next will be a trying a proportioning valve. I'd like to do hydroboost eventually, and full hydro steering, and a NP-435/Dana 20 swap, rollcage...but one thing at a time.
I'm a little busy since we also have to finish re-decking our trailer and replacing the worn out springs on out Excursion tow rig!
Did some part spec research and I got a new MC for a '98 Super Duty. That was the last year for a front disc Dana 60/rear drum Sterling and had the largest MC bore at 1.25". Hope to get the new one plumbed (ports are on the opposite side and now I need a new fitting thanks to it being almost seized and having to break out the vise grips) and then I'll do a proper bleed and see what happens.
While I'm working I'll check for failed lines. I'm hoping that does the trick but maybe next will be a trying a proportioning valve. I'd like to do hydroboost eventually, and full hydro steering, and a NP-435/Dana 20 swap, rollcage...but one thing at a time.
I'm a little busy since we also have to finish re-decking our trailer and replacing the worn out springs on out Excursion tow rig!
jmdirk
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Keep in mind - going with a larger MC will make the pedal feel firmer, but you'll actually end up with a loss in pressure and the caliper, reducing the effectiveness of the brakes.
I used a larger MC, but also went with a larger diameter vacuum booster from a mid-ninties super duty. It's a really tight fit, but that will give you both a firm pedal and not loose the pressure.
There's a thread stickied in the Under the Hood section
I used a larger MC, but also went with a larger diameter vacuum booster from a mid-ninties super duty. It's a really tight fit, but that will give you both a firm pedal and not loose the pressure.
There's a thread stickied in the Under the Hood section
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