Ok I have a 1990 F-150. It sits most of the time. The other day I gave it a tune up and when I went to go for a ride, I lost the brakes, then all of a sudden they came back. They were not as strong as I think they used be. So I had my dad take it for a ride and it wouldnt do it for him then all of a sudden he went to slow down for a corner and the peddle went to the floor, hit the peddle again and they were back. So a long story short, is it the master cylinder or something else? Any Ideas?


Thanks

 

first check your fluid level. these trucks do have a valve that will block a blown line (not very well though) also check for fluid leaks. i would suspect a blown line before a master going out.

 

Sure sounds like the master cylinder to me.... "Worn out cups/seals"

 

Relatively easy to replace. Just did mine last month. Bench bleed the new MC before installation. Used a mighty vac at the wheels.

It's really cool to see new DOT3 fluid in the master cylinder reservoir for a change instead of that cola colored crap that was probably in there for 20 years!

Good luck.

 

As long as there is no actual outside fluid leak I vote for the master cylinder. A bad RABS module will usually result in a soft pedal, not a complete drop to the floor.

If you are leaking fluid, start looking for leaking wheel cylinders in the rear or caliper pistons in the front as well as leaks in the lines/hoses leading to them.

 

No there is no fluid leaking and all the lines look good, that was one of the first things i checked. Thats why i was thinking master cylinder. Now what is a RABS module, ive never heard of that before?

 

RABS = rear anti-lock brake system

Sounds like the master to me as well.

 

I'd check the vacuum line to it for cracks and such...before you start throwing parts at the truck.

 

Cut from my Ford Service Manual:

Anti-lock brake control module (dual solenoid electro-hydraulic valve) located on the left frame side rail (5015) just behind the No. 1 crossmember.

Left frame implies driver's side of the truck. I just noticed your truck is a 1990. I am not sure when Ford introduced the Rear Anti-Lock Brake system. Yours may have the standard brake proportioning valve instead of RABS.

 

Im thinking it does, it has the rear abs light that lights when you start it then goes out.

Hopefull saturday i can tear into it....was planning on it tonight but my job has bigger plans for me.....lucky me! LOL