Need some help with my brakes... I'm at a loss.

Recently did the rear drums (fronts were done about 6 mos. ago) because I had one side locking up occasionally. Everything went pretty smooth and I'm 99% sure I got them back together correctly, brakes bled and adjusters fairly close to where they need to be.

The issue I'm having is since putting it back together, the pedal feels very "mushy" - there's almost no resistance with the engine running unless I pump them a couple times, then it feels like I have pressure but slowly drops to the floor. Everything I've been looking at says master cylinder, but I'm wondering if it could be something else I did. I've tried bleeding three times and the last (yesterday) I saw almost no air bubbles. I dont see any other leaks anywhere. The master looks to be fairly new and maybe replaced before I got it.

**EDIT: I suppose what I am asking is - is there a procedure specifically to test the Master Cylinder to see if it is leaking?

 

The RABS valve can cause the same symptoms. If the valve goes bad, it allows the psi of the valve to bleed past the seals and the same symptoms of a mushy brake pedal. Be sure that you bleed it from rear passenger, to rear driver, then RABS, then from passenger, then finally front driver.

 

RABS was replaced a couple months back when I did the fronts. I had the ABS light coming on and now it is on for a bit after start, but then goes right out.

 

Sorry, duplicate post...my phone isn't doing the best..ughhhh

 

I'm not exactly sure what this (bold selection) means, but, ANY air bubbles are too many... Not trying to be an a$$, it's just a reminder....

 

No offense taken... what I meant was that when I *first* started the bleed process, there were two or three very tiny (pin-size) bubbles that came out of the RR drum cylinder. They could have been me bumping the hose on the bleeder or come from the cylinder itself - it was hard to tell. But regardless, I went through the whole bleed cycle for the third time and didn't see any air being released. So I'm thinking I got everything...

One item I forgot to mention... with the engine off, the pedal feels firmer during the bleed process. When I start the car to test drive is when it gets really mushy and I have to pump a couple times to get decent pressure. (which then leaks off)

Thanks for the replies so far. Its been kinda frustrating.

 

Do you have your drum brakes adjusted so they are just touching the drum?

 

Did the fluid ever get low in the master so where it could get air in the system.

 

I believe so, yes...

 

Nope. I was very careful about this during the bleeding process...

 

Bump. Anybody?

 

The time i had a problem (very same as your description) it was because i didn't have the brakes adjusted tight enough. Might want to try that first.

 

@westcoasting - I adjusted the drums. No difference.

I can't even find the replacement part number for a '92 F350 Dually with Cruise. The MC that is in there now doesn't have a port for the sensor, but there are cruise buttons on the steering wheel. So I'm thinking maybe it was replaced already at one point in time?!?! I asked the parts guy about how to test the MC and he told me "yeah, there's a way, I dont really remember how though..." WTF!

IDK, I'm beyond frustrated at this point...

 

Your 1992 F350 uses a vacuum - servo based Speed Control system, there is no Brake Pressure switch on the master cylinder or anywhere else. 1993 was the first year for the full electronic Speed Control. The Brake Pressure switch is located near the RABS hydraulic module located on the driver side frame rail. 1994 was the first year that Ford moved the Brake Pressure switch to the added port on the master cylinder.

The above pertains to OBS trucks, no clue when other models switched over.

 

I have always found if the brake pedal stays firm and no dropping with the engine off the problem is vacuum based. If the pedal does drop and/or softens up the problem is hydraulic. If you can find plugs for the master cylinder ports you could remove the lines, plug the ports then see if the pedal drops. If it does, the master cylinder is bad. If not, the problem is further down stream.