Instant brake failure - '91 Ranger

Fairlaniac · Nov 4, 2015

To bring you up to speed, three weeks ago just before i got home the brake pedal went about half way to the floor and was stiff. It wouldn't push any further and it wasn't the whole way down. I ran along the curb to scuff it to a stop. So I buy a new master cylinder and booster. I installed them, checked everything out and all is good for the past week or so. Until today. Coming off the highway at 70mph I applied the brakes and they were working and then i head a click or something. It happened so fast I don't recall the sound exactly but the pedal stopped half way down just like the other week. I'm a strong 6'5" guy so I wasn't a wimp applying the brakes. With all my might I got it stopped a bit past the stop sign but on the shoulder. No leaks anywhere. I cannot figure this out. The exact same result one with an old M/C & booster, the other with new parts. any ideas?

thanks,

black_demon69 · Nov 4, 2015

suggestions as follows

1 check firewall for cracks. if cracked could be flexing and reducing movement of rod going into master.

2 check valve on booster

3 bad booster (i have seen bad out of the box especially reman ones)

4 check brakes for loose sticking or broken parts (all 4 wheels)

5 check for vacuum leaks especially on vacuum line to booster

6 check adjustment on rod to master

hope this helps

Mightyfordranger · Nov 4, 2015

My cousin had the same problem with a ranger he had it was a 98 4.0 4x4 one winter he had to blow through an intersection cause he couldn't stop. That was the second time that it happened its like it chose when it had brakes.
He tried putting all new brake M\C and booster but it didnt help either he ended up trading it in on another truck. So if this turns out to be a frequent problem I'd definitely like to know how to fix it as well

Fairlaniac · Nov 5, 2015

black_demon69 said:
suggestions as follows

1 check firewall for cracks. if cracked could be flexing and reducing movement of rod going into master. I could see this limiting the pedal travel but the pedal seems to have hit a brick wall, it is a firm stop?

2 check valve on booster check valve is new and I checked it with my Mity-Mite vacuum gun and it seems ok

3 bad booster (i have seen bad out of the box especially reman ones) anyway to bench test if the booster is bad?

4 check brakes for loose sticking or broken parts (all 4 wheels) nothing sticking, even if one caliper or shoe stuck I'd feel it. All four at once? I'd think a different issue?

5 check for vacuum leaks especially on vacuum line to booster new leak free vacuum hose from intake to booster

6 check adjustment on rod to master What is there to check here? Never did anything other than put a M/C onto a booster an make sure the rod is aligned. How do you check or adjust the rod?

hope this helps

Thanks for the help, still no clue to the issue but a good checklist. - Thanks!

black_demon69 · Nov 5, 2015

Fairlaniac said:
Thanks for the help, still no clue to the issue but a good checklist. - Thanks!

your welcome

did you clamp both ends of vac hose to booster?

to adjust rod length there should be 2 adjustment points one for pedal travel on the pedal ans the other on the end of the rod that actuates the mc don't mess with it unless you have to...

does pedal come back when rpm go up or idles for a min.?

if i had to guess i would say defective booster is your problem...

Mightyfordranger · Nov 5, 2015

Post up the fix if ya find it please

turbo91xlt · Nov 7, 2015

Check your RABS valve. On my '92 it failed why trying to bleed the brakes, resulting in an almost instant hard pedal. Easiest solution & what I did was just bypass it. Brakes have worked flawless since.

black_demon69 · Nov 7, 2015

turbo91xlt said:
Check your RABS valve. On my '92 it failed why trying to bleed the brakes, resulting in an almost instant hard pedal. Easiest solution & what I did was just bypass it. Brakes have worked flawless since.

yes i forgot about rabs valve check this as well

Fairlaniac · Nov 8, 2015

black_demon69 said:
yes i forgot about rabs valve check this as well

Can you fill me in "Rabs" is it rear abs? Where is such a valve?

Sorry if it seems obvious. Just got home from driving all day. Brain in numb.

Thanks,

cvar · Nov 9, 2015

See http://www.aa1car.com/library/abs_kelseyhayes_rwal.htm

RABS is underneath the cab, mounted to the left frame inside rail, under the driver's feet.

Fairlaniac · Nov 9, 2015

It may be safe to say the booster is bad. With the engine running I was down by the brake pedal. I used my hand to push on the pedal. A constant hissing of air is present and while the engine has a rough idle, it smooths out when I press the pedal and it hisses. I'll start by getting another booster.

Thanks,

Fairlaniac · Nov 10, 2015

So today I was checking things over. I didn't have a lot of time so I just "tested" things. The brake pedal still went down about half way and was solid as a rock and the truck still rolled. No brakes. One thing I realized is my booster pushrod was .280 short vs. the original booster. So I set it. Installed it and still the same deal. Half way and a solid pedal but no pressure. This is both with engine running and off. So I took my old master cylinder and installed it. Now it does need bled but the pedal goes to the floor. Is there a possibility there is pressure in front of the M/C to not allow any brakes to work? I don't see it as the front brakes go directly from the M/C to the distribution "Y" then to each caliper. The front brakes don't grab. I didn't get to check the RABS sensor but what is the worst than can happen with that? The back brakes won't work? If so I don't see how the RABS affects the front. Does any of this make sense? any ideas?

Thanks,

enjr44 · Jan 29, 2016

Did you get this fixed??

Fairlaniac · Jan 29, 2016

I got another new m/c and booster, reset push rod length and all is good.

Instant brake failure - '91 Ranger

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