97 F350 brake problems

[nepatternmaker]

Brake problems on 97 F350
97 F350 4x4 CC 7.3. Over the winter the brake pedal has gradually started to bleed down when you are on the brakes. To me this is a bad master cylinder, leaking internally. There is no apparent fluid loss at any off the wheels or around the master cylinder itself. I replaced the master cylinder and couldn't get any consistent pedal at all. It would pump up just a little, then go completely away if it sat for just a few seconds. Sometimes pumping the pedal would give you less pedal pressure, and you could feel a step 1/2 way down where the pedal would release some of what little pressure it had. I took it off and returned it for warranty and put another one on. This one I could not bench bleed right because the cheesy plastic plugs that come with it for that purpose stripped out. I put it on the truck and bled the master cylinder with a mityvac. I can now pump up some pressure, (I think I'll have to bleed the whole system) but the pedal STILL bleeds down! You guys know of anything else that will cause that. I don't think the 97's have the rear ABS and I don't see any fluid anywhere that would indicate a leak. I'm supposed to haul 4 cars this weekend, but I gotta have brakes.

Any ideas?

dave

[nepatternmaker]

Here's what I've learned in the last 2 weeks about F350 brakes. There is a Ford TSB on the master cylinder for F250 and F350, '92-'97. The OEM mc does not have enough volume to operate the front dual piston calipers after the truck gets some age and wear on it. The OEM mc was a 1 1/8" ID bore, the new one is a 1 1/4" ID, so you can push more fluid and get brakes before the pedal almost bottoms out. The OEM in a Cardone reman# is 10-2690, the updated mc, also cardone reman, is 10-2828. I put 4 mc's on this truck, bled the brakes 3 times and bypassed the ABS valve. The pedal bled down and it was almost to the floor before I got any brake action, until I put the last one on, the 10-2828.

Ford also has a TSB for the vacuum brake booster on diesels only. The OEM booster allows the pedal to bleed down when the engine in running but the truck is stopped, like waiting at a stoplight. They specify a booster part number that is only available from Ford and is not searchable by application; you have to specifically order that number. I need this also, however have not ordered one yet.

For more info google "Ford truck brakes TSB", you'll get a number of responses with more details.

dave