Hey guys, long time no chat. Still having trouble with my brakes, seems to be a common story around here.
Just finished replacing both rear brake assemblies. New drums, shoes all springs and clips and new slave cylinders on both rears. Replaced RABS unit with a rebuilt one from Rockauto. Vacuum pump seems to be fine. Used a vacuum bleeder to remove all old fluid and air from system, adjusted rear shoes up good and still really soft pedal. Goes right to the floor if you push on it for a few seconds. Master cylinder is only 4-5 years old according to the previous owner but brakes have never been good since I've owned the truck. No visable leaks in the system or around the master cylinder. Will bench bleeding the master help even though its been in the truck for awhile? Should I just replace the master and make it a whole new system?
Any advice will be greatly appreciated as this has been ongoing for a while now and is really starting to be a pain.
Cheers, Frank
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Try bleeding the brakes the conventional way with a helper.
Get the helper to pump up the brakes and hold pressure on the pedal while right rear bleed screw is opened and pedal is pressed to the floor. Hold pedal to floor while bleed screw is closed. Release pedal, open bleed screw and repeat until all air is out. Do the same with left rear, RABS module, right front, left front and see if that helps.

 

I'd say the master cylinder is leaking internally past the seals. You "may" still have a bit of air in the system but that would not account for the brake pedal slowly sinking to the floor.

 

Does it slowly go to the floor if you hold a lot of pressure on the pedal or does it go down quickly? A friend bought a F350 new in 94 that the pedal slowly sank if holding a lot of pressure on it, Ford said it was normal for the RABS system. My 95 F250 has done it for the 5 years I have been driving it. The Ford rep I talked to said to try to move the truck when the pedal is all the way to the floor, I tried this with both trucks and can't move them with the throttle at WOT and the brake pedal down.

 

x2^^

I hate vacumm bleeders. i think they pump more air in than they do out.

 

I will try re-bleeding tomorrow. The conventional way is how my father and I always did our racecars as a kid but as I live alone a ways out of town getting a helper can be hard. I have a mate coming tomorrow so will get him to give me a hand. I am fairly sure the pedal goes down slowly under heavy pressure but the fact still remains that it goes most of the way to the floor before it gets any pressure. If I stamp on the brakes it does stop but just seems like it should have more feel.
Will see how I go in the morning.
Cheers guys.

 

I always though these trucks have a bit of a squishy pedal but i like that when you step on it it actually does something. Unlike some cars that have a stiff pedal but it doesn't equal the braking power. Speaking of which i need to bleed the brakes on my plow truck.

 

Righto, update time. Removed the master cylinder cleaned and bench bled it. Refited with the plugs still in and tested the pedal with the engine running for vacuum. Was perfect, good hard pedal so master cylinder all good. Reconnected the lines and bled the system and the soft pedal was back. On the suggestion of a mate I clamped the flexible lines to the frontwheels and all of a sudden good pedal again. Drove around the yard with just the rear brakes and pulls up on a dime with good pedal feel. So from this I find that the front calipers are the problem. Clamped the rear flexible line and tried with just the fronts and truck still stopped good but the pedal went right to the floor. Looks like I will be stripping the fronts.
Is there anything I should look out for while removing the front rotors from a 4wd with a ttb axle?
Does it involve stripping the front lock hubs and if so is this something I can do at home or is it a specialist job?
Will measure all the variables on the rotors and checkout the operation ofthe calipers.
Am glad I have narrowed it down to one end of the truck. Gives me something to focus on.

 

the locking hubs should be no problem. Remove the little cap screws and cap. Remove the inner and outer snap rings. The one around the inside of the hub may need a small screwdriver or dental pick to pry it out. The locking mechanism then pulls straight out.
You now have access to the bearing retainer nuts. You might need the pronged wrench to get these out but you could probably make one.
Once the bearing nuts are off and the caliper is out of the way the hub/rotor slides off the spindle. You can then press or pound the lugs out and seperate the rotor from the hub.

 

Sounds fairly straight forward. Will give it a go tonight.
Cheers LazyK

 

Did you figure out the issue with the soft peddle?

 

Most likely the flexible rubber brake line was getting soft and expanding. This can make the brakes very soft and unresponsive.