no leaks, new master/RABS, still no brakes

[Panda]

I got a 91 ranger 2wd and a week ago my brakes decided to go out on me. I have a little bit of pedal when I hit the floor but nothing significant. I couldn't find any leaks in the lines so my Ford mechanic buddy and I replaced the master cylinder a couple days ago and bled the brakes and still nothing. Then he said it is most likely the RABS unit so I bought a RABS unit from Autozone and we installed it. We then bled the brakes again but still no pedal. We are currently stumped as to what the problem is. I can't think of any other place for the fluid to go so I'm thinking I got a bad RABS unit from Autozone because I seem to have a pedal when the truck is off but not when it is on (only thing I can think of that turns on with the truck brake-wise is the ABS). Does anyone here know if I'm missing something or is it safe to guess the new RABS is defective? I ask because I really do not want to have to take the RABS unit back and wait another week for a new one if i don't have to

 

[sblake01]

I used a power bleeder on mine when I replaced my master. I thought my RABS valve was bad but after I power bled them the brakes were okay. The way these systems are designed (badly, but I digress), I'm not sure a bad RABS valve would prevent you from being able to bleed the brakes anyway. If your RABS valve was working before the master went out, it was probably still good.

 

[tx3nc]

I'm wondering if there might be a short in the wiring harness or a problem with the RABS computer that is holding the dump valve in the RABS hydraulic control unit open. Maybe try unplugging the connector to the hydraulic control unit and see if the pedal firms up. I could then look at my schematic for a '93 (assuming the wiring is the same) and let you know what pin to check for voltage where it shouldn't be.

 

[06RangerXLT]

firts step... facepalm.


next tell your ford mechanic buddy he should get a new job. (why i dont take my truck to a dealership)

Now, remove your master and bench bleed it. if you do not bench bleed a new master, you will never get brakes. For a how to, use google.

 

[brinker88]

+1 ^

...Common sense would tell you to do that, since the directions that come with the new master cyl. SAYS to bench bleed it....

Also could be your booster.

 

[sblake01]

I assumed that he bench bled the master since that's pretty much standard procedure. If not, that's the problem. I also think that if the RABS valve worked before master died there's no reason it wouldn't still work. That's an expensive piece to replace especially if you don't need to. A bad booster would only cause you to lose the 'power assist'; not the hydrualics. I agree with 06RangerXLT; find someone who knows a little more about what he's doing to help you.

 

[Panda]

06RangerXLT:
We did bench bleed the master before putting it in. This isn't my first brake job and even I'm not that stupid let alone my friend. Next time I'll try to remember to put something that obvious in my post before posting.

tx3nc:
we tried unplugging the RABS computer after replacing the RABS unit and that actually made the brakes worse. It felt like I had even less pedal than before when I unplugged it.

sblake01:
And the master cylinder was the first thing we replaced but we had no brakes after so we moved on to RABS unit. I currently am out of a job that's why I haven't taken it into a shop to have it fixed, otherwise I definitely would have by now

But ya we were working on the truck last weekend and found that I had brakes when we crimped the rubber hose going to the front driver caliper. So we figured the caliper was somehow screwing with the brakes and replaced that. Still no brakes We noticed while replacing it that the wheel bearing was basically gone (the wheel could move an easy 10 degrees in any direction) but at the time figured it wouldn't affect the brakes. The next day my friend calls me up and tells me he talked to front end tech at the Ford dealer. They said the destroyed wheel bearings could cause the brake piston to over extend and cause my problems or something like that. I'm still having trouble wrapping my head around how that works out because in my mind that's what the other side of the caliper is for but either way we are planning on replacing the wheel bearings next weekend because it definitely needs them.

 

[sblake01]

Do you know for certain that the master was bad? I knew it was the problem on mine. Even after I replaced it and did normal bleeding my pedal was still kind of spongy until I used a power bleeder. Your situation sounds like it's a little different from mine. It's hard to diagnose in print sometimes. I'm not sure that I buy that scenario as laid out by the Ford tech either. Let us know what it turns out to be.

 

[Panda]

so we worked on the truck yesterday and replaced the wheel bearings along with the rotor/wheel hub or w/e the hell its called. Turns out the driver side inner wheel bearing decided to explode at some point (I'll guess it was when my brakes went out...) and blow a few chunks of the walls of the hub out. So yeah once that was replaced my brakes feel as good as new! Well as good as they once wer, except for the part where my RABS doesn't seem to want to work (Rears lock up like crazy). So I'll be putting the old one back on sometime during the week and returning the Autozone one.

 

[jharward]

Did you ever figure out the problem? I'm having similar issues with my truck?

 

[Panda]

Yeah it was the destroyed wheel bearing and hub. It allowed for a crazy amount of play in the wheel and rotor. The Front end tech at my buddy's ford dealership said that play allowed the caliper to overextend or something like that which meant no brakes (still not quite sure how that worked). As for the RABS, I put my old one in and it went back to working like normal. Aftermarket RABS modules are known for being hit or miss.