[Tim in CT]

Hello, i just became a new member of the forum and i also became a new owner of a 94 ford 7.3, turbo diesel, all wheel drive masons dump.
The truck had bad calipers when i received it and i replaced them.
everything bled fine and if the truck isn't running the pedal is firm.
However when it starts, the pedal faded. I have read the discussions about this and find it hard to believe they all seem to do this and there is no fix.
I have put new master cylinder and booster on. I have not replaced the vaccume pump but the low vaccume lite is not lit on the dash.
Word of wisdom?

 

[M.L.S.C.]

A low vacuum will make your brakes hard, not cause brake fade, so you're good with that vacuum pump you have. I always bleed brakes with the engine running, the proper order is RR -> RL -> RABS -> FR -> FL. Yes, the RABS has its own bleed screw on it, and that does need to be cracked open to truly get all the air out. And just so you know, these trucks do take LOTS of fluid to be ran through them to bleed them entirely.

 

[chuckster57]

A low vacuum will make your brakes hard, not cause brake fade, so you're good with that vacuum pump you have. I always bleed brakes with the engine running, the proper order is RR -> RL -> RABS -> FR -> FL. Yes, the RABS has its own bleed screw on it, and that does need to be cracked open to truly get all the air out. And just so you know, these trucks do take LOTS of fluid to be ran through them to bleed them entirely.

I didn't think it made a difference if the engine was running or not.

 

[rollfj]

If the valve inside the RABS is sticking, it can cause brake fade as well. I beat my head against brake fade on my truck for over a month, I just didn't think it could be the RABS, I finally replaced it and re-bled the entire system and all is well.

I believe there is a test procedure floating around the forums for the RABS valve.

 

[M.L.S.C.]

I didn't think it made a difference if the engine was running or not.

Believe it or not, it actually does make a difference - this is especially true with Broncos, they have been plagued with this for years, the '78-'79 ones as well as all of those with RABS, the '80s seem immune to it due to the design of the proportioning valve. Our trucks have RABS, they need the extra pressure push the air out every single crevice it can get.

 

[bigblue250]

My old 76' needed over a quart run through to get good brakes, same with my dads Ford chassis step van. 10-4 on bleeding out the RABS valve.

 

[chuckster57]

Believe it or not, it actually does make a difference - this is especially true with Broncos, they have been plagued with this for years, the '78-'79 ones as well as all of those with RABS, the '80s seem immune to it due to the design of the proportioning valve. Our trucks have RABS, they need the extra pressure push the air out every single crevice it can get.

:thumbsup: learn something new every day :thumbsup:

 

[M.L.S.C.]

My old 76' needed over a quart run through to get good brakes, same with my dads Ford chassis step van. 10-4 on bleeding out the RABS valve.

Yah, your '76 has the same prop-valve design like what the '78-'79 Broncos had, or shall I say the Broncos have the same valve as the F-series trucks, they all suffer from the hard bleeding virus.