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My neighbor is working on his 89 Ford RV chasis, and has been stumped for a while.
The chasis has new front calipers , rear cylinders and master cylinder and booster.
Everything bleeds by Da Book and the brakes feel very hard ,
BUT when the engine is started and the booster ( I guess) helps the brake pedal it goes to the floor , really easy.
My neighbor is working on his 89 Ford RV chasis, and has been stumped for a while.
The chasis has new front calipers , rear cylinders and master cylinder and booster.
Everything bleeds by Da Book and the brakes feel very hard ,
BUT when the engine is started and the booster ( I guess) helps the brake pedal it goes to the floor , really easy.
And there is NO brakes !
Anyone seen this before?
Any help would be a big plus.
FAST FRED
Fred, seen this only once, spent a half a day chasing down the problem. Since the RV has new calipers, that means it has new pads, OK? The unit I was trouble shooting had new calipers and pads also. The problem turned out to be that the rotors were worn like an axe blade, that is, they were thinner---not a heck of a lot-- more at the edge than in the middle. The old pads had worn to match this shape as the rotors wore down---the driver was really rough on the brakes. Anyway, just as you say, with no boost, the pedal was high and firm, however when boost was added, the pads would cock and move inboard, using up all the pedal stroke. Easy to see if this is what's happening, just get inverted flare blind nuts at FLAPS, (Favorite Local Auto Parts Store), to fit the master cylinder ports for the brake lines. Unscrew the line for the front brakes, install the plug, and see if the pedal now drops off under booster pressure. If it does, you've found what axle set is causing the problem and I suspect you'll find what I said to be the cause. Using these blind nuts and inverted flare unions, you can move along a brake system, isolating components while you're trouble shooting the system.
I have a 1987 lincoln mark 7 when the car is off the peddle is hard when the car is on the peddle is hard there is no power i have to stand on the peddle the relay was making a loud noise so i replaced it. the brakes still dont work
My neighbor is working on his 89 Ford RV chasis, and has been stumped for a while.
The chasis has new front calipers , rear cylinders and master cylinder and booster.
Everything bleeds by Da Book and the brakes feel very hard ,
BUT when the engine is started and the booster ( I guess) helps the brake pedal it goes to the floor , really easy.
And there is NO brakes !
Anyone seen this before?
Any help would be a big plus.
FAST FRED
Fred, seen this only once, spent a half a day chasing down the problem. Since the RV has new calipers, that means it has new pads, OK? The unit I was trouble shooting had new calipers and pads also. The problem turned out to be that the rotors were worn like an axe blade, that is, they were thinner---not a heck of a lot-- more at the edge than in the middle. The old pads had worn to match this shape as the rotors wore down---the driver was really rough on the brakes. Anyway, just as you say, with no boost, the pedal was high and firm, however when boost was added, the pads would cock and move inboard, using up all the pedal stroke. Easy to see if this is what's happening, just get inverted flare blind nuts at FLAPS, (Favorite Local Auto Parts Store), to fit the master cylinder ports for the brake lines. Unscrew the line for the front brakes, install the plug, and see if the pedal now drops off under booster pressure. If it does, you've found what axle set is causing the problem and I suspect you'll find what I said to be the cause. Using these blind nuts and inverted flare unions, you can move along a brake system, isolating components while you're trouble shooting the system.
OPPS!!!, should have said "if the pedal DOESN'T drop off" with the front brakes plugged off, then you've found where the problem is.
The rotors were turned , so there is only about 10 thou movement as the brakes get applied.
The fluid is going somewhere , just cant figgure out where!
FASTFRED
Fred, start at the beginning, the master cylinder. Remove both brake lines and install plugs in the MC ports, this eliminates everything but the MC. BTW, the MC was bench bled before it was installed, wasn't it ? If the falling away pedal still occurs with the plugs installed, and the MC was bled prior to installation, then it has to be the MC bypassing fluid between the primary and secondary pistons, I've run across this once or twice on new/rebuilt MC's where cup expanders weren't used. Rember, to find the cause, you've got to go about it logically and systematically, that means starting at the MC, working outward on one axle brake set at a time to find the cause---bypassing MC, a balooning hose, etc.
My buddy finally got tired of bleeding everything and dissassembled the master cylinder.
Crapola called Soft Touch.
There was two cylinder sections and the first pushed on the second with a spring.
Thats why the pedal went almost to the floor , IT WAS DESIGNED TO!!
Pure trash , another failed Ford experiment.
The cure was to make a spacer to replace almost all of the spring.
Now the unit goes doen a bit , rather than almost to the floor when pushing with power on.
Thanks for the great help!
It sure was a mistery.
FAST FRED
Fred, that's a split brake system master cylinder. It isolates the front and rear brakes so a failure in one axle will still leave you with brakes on the other axle. The two sections---pistons-- are hydraulically connected in the section that contained the spring. You've GOT to bench bleed these MC's before you install them in order to fill the center section with brake fluid. Bench bleeding consists of mounting the MC in a vise, installing two sections of brake line in the outlet ports, bending the lines around so their ends almost touch the bottom of their respective resevoirs, filling each reservoir with fluid, and then working the push rod in and out until no bubbles appear in the fluid. Put the lid on the MC, remove the lines, install the MC, and gravity bleed the front and rear brakes. You can buy a bench bleeding kit at most auto parts stores. It contains a handfull of plastic fittings and two plastic tubes. You can go ahead and do the MC bleeding now that it's mounted, just stroke it with the pedal, that'll get rid of the air in the center chamber and bring the pedal up. It wasn't Ford's idea to build a split system, give the Feds credit/blame for that.
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