Brake issue I just can't track down

[Hank]

When I push in my brake pedal I hear a whoosh noise and the pedal will go down easy about half way. During this time I have good/semi normal brake action. About halfway down the pedal gets real hard to push pretty much stops, brake action will increase slightly but you really have to stand on it.

Pumping the brakes makes no diff.

The brake pedal does not go to the floor. I can get it to the floor if I open up a bleeder so I don't think I am loosing pressure or fluid.

Front pads and rear shoes are new. The fluid is new. Rear cylls are new. Braking action is pretty good, as good as it gets with 33's and stock brakes. No fluid leaks, no pulling to one side, flex lines are new oem with no cracking or swelling.

Any ideas? Your Ex brakes do this?


UPDATE: Today the master cyll went out. Replaced it and hoped this would clear up but it did not. Same thing, open a bleeder and you can put the pedal to the floor. Close the bleeder and same situation as above.

Confirmed the pushrod from the booster to the master cyll is adjusted to spec .995 in.

I'd say braking is kind of weak, it is almost like I am running out of pedal travel and there should be more brake to go.

This is not a air/bleeding issue, I pumped a half gallon through the system again today with my power bleeder. And the feel is differant that if it was air in the line, remember I have brakes when you start to push the pedal.

Front pads are performance friction, rear shoes are Albany. Again, both new.

Only thing I noticed today was I can't get the RABS to trigger anymore. However not Antilock light on the dash. I pulled the fuse and it did light up.

Thought about a bad RABS valve but dont think that would explain the pedal stop. Thought about stuck calipers but no pulling and if they were stuck I would have serious rear lockup. I do have semi good front brakes.

Again, it is like I am running out of brake/pedal.

Bad vac booster?? How to test? It will hold vacuum for 4-5 pumps after stopping the motor.

Seriously baffled.....

 

[jimbo74]

sounds to me liek a bad booster..... however i am not sure by your description... a car i worked on once had a bad booster... but the pedal barely moved... i am a big guy, 250 pounds worth... and had to use both feet and stomp on it pushing myself into the chair to get the car to stop befroe hitting anything in the shop.....

 

[Hank]

I wonder if it is possible for the booster to have a tear or a crack in it where it looses vac pressure when extended?

Loss of pressure would explain a hard pedal but running into it halfway down is the baffling part. However I'm not so sure as it hold vac for a while and you can get 4-5 pumps out of it after shutting down the motor.

Thought about a bad check valve but the fact I have vac after shutting down negates that..

The feel is like you have normal brakes then you could say it goes to lack of pressure feel.

Question for you and other Ex owners as I see your avatar changed.

1. Do your brakes make that whoosh sound?
2. How far can you force your pedal down?

 

[Bronco638]

Like Jim suggested and based on the "whoosh" sound, I would guess brake booster. Sounds like it's not failing completely but there might be a tear in the diaphragm some place.

 

[Hank]

Yep, I think you both are right. I picked one up this am.

Here was my unscientific test I based it on.

Start car, sit at idle. Slam on brakes hard as I can till pedal stops. Hold position on pedal wait about 10 seconds and push some more, get a whoosh and about 2" of pedal travel then stops. Repeat 2 more times till pedal is way lower than it has ever been. Hold pedal and make sure no brake pressure is being lost. Put Ex in reverse and give it gas. Brakes hold.

On the way into work this am I got up to about 75, no one was behind me so I pushed slowely down on the pedal. Pedal stayed fairly firm and was able to go much farther than when I stomped on it. Very good brake performance also.

Will see if I can install the new booster tonight and post back.

Thanks for the extra brain power. I have seen this blow but never leak.

 

[Hank]

The old booster was flakey, I now have full pedal travel. Pedal is still soft and now that I have full pedal travel I can actually pump the brakes and they do come up with pumping so there must be a little air trapped in the system somewhere.

I'm bummed as my power bleeder normally can get the air out of anything. Might have to hook up the power bleeder and get a volunteer to pump the brakes up at the same time this weekend.

Any bleeding tricks to the RABS? I know ABS requires a dealer tool if you get air in it. But the haynes says nothing about the RABS valve.

BTW, getting some RABS action again with the new booster.

Thanks guys.

 

[Hank]

Status, have not had chance to bleed yet. Vac pressure holding overnight on the booster so at least one problem is solved. Getting the air bubble to move is a real PITA, can take 20-30 quick pumps to get to to move to where the pedal goes firm.

 

[Hank]

Some improvement:

Hooked up the power bleeder and pumped it to 20lbs. Started the Ex and got the wife in the driver seat. Started in the rear and had her kick the heck out of the pedal five times and stop but keeping pressure on the pedal. And then I would open the bleeder. The first few cycles came out clear and all the fluid in the system was new.

After the third or so cycle I got some air and a pocket of dark fluid out. Had her kick the pedal a few more times till nothing but clear fluid came out. There is some improvement in the pedal. My guess is that somehow I had a pocket of air and old fluid in the RABS. On stopping the Ex does not nose dive as much anymore so I suspect I am actually getting some rear brake action.

The front ran nothing but clear new fluid on all bleeds.

Saw some movement in the OEM lines, could not really tell if they were swelling under pressure but decided to replace them as that is about the last thing left to replace. OEM flex lines are 3 years old. Found the Russell stainless line kit at coximport.com for 91.00. Ordered the kit for the lifted Explorer. Supports up to 4" lift. Could be in by this weekend.

Will post back after install.

 

[XLT Xtreme]

Hank;

I have about the same problem with mine as you explain. Seems like I get the "whoosh" sound when im on the brakes more like in town. When on the highway and don't use the brakes alot it does not seem to be as bad. In town when I push the brakes seems like I can push them about a quarter of the way down but if I need to step on them a little harder is when I here the sound and the peddal seems to have alot more travel than normal to me.

I looked at the pads and everything looks good. Thinking of doing the booster myself. Looking under the hood mine looks like new but then again I keep it clean under there so hard to tell by a visual. How much did your booster cost and did you get it through Ford?

Mike

 

[Hank]

New master was about 90 from Autozone, same as the booster. If you need to do both the combo unit is cheaper. Wish I knew that at the time.

Was hoping the lines would have got here by now but it looks like sometime next week.

 

[CDW6212R]

Have you bled the RABS valve? I have read that it has a bleed screw(older 94down X's). Good luck,

 

[Hank]

So far I have not found anything difinitive on bleeding the RABS, it does not have a typical bleeder on it and the haynes does not describe any bleeding instructions. The only thing mentioned is about the ABS system requiring a dealer tool to bleed.

Anyone have good info on this?

 

[Hank]

Found this interesting article. Posted for info purposes only for others.

Dead Link Removed

Vehicles: 1987 through 1998 Ford Bronco. All engines with Rear Anti-lock Braking Systems (RABS).

System: Brakes/ABS.

Symptom/Problem: Brake pedal fade, low pedal. The problem is an internal leak in RABS valve.

Background: A common complaint on Ford light duty trucks with the rear anti-lock brake system is that the brake pedal will fade while under steady pressure. In a conventional brake system this would point to an external fluid leak or an internal leak (bypass) in the master cylinder. Generally, one and usually two master cylinders have been replaced already, leaving one very frustrated technician. In this system there is one other possibility - the rear anti-lock brake valve. This valve is the electro-hydraulic proportioning valve located on the left-hand frame rail between the master cylinder and the rear brakes. This valve controls the brake fluid during an anti-lock stop by restricting or bleeding off rear wheel cylinder pressure.

To better understand what's happening, let's take a quick look at system operation. The RABS module continuously monitors rear wheel speed by means of a sensor installed in the rear differential. When the sensor signal to the module shows a rapid decrease in speed - indicating rear wheel lockup will occur - it energizes the isolation solenoid in the RABS valve. By doing this, the normally open valve is now closed, blocking off the line to prevent further brake fluid from entering the rear wheel cylinders. If there is still too great a decrease in rear wheel speed, the module will then energize the dump solenoid in the RABS valve. This solenoid is normally closed and, when energized, will open a port to the accumulator and bleed off some of the pressure to prevent lockup. This fluid is then stored until normal brake functions are resumed and the fluid is returned to the master cylinder.

If rear wheel speed is now OK, the module de-energizes these solenoids to resume normal braking. If speed decreases too rapidly again, it resumes anti-lock control. The module will alternate between the two solenoids and normal braking until there is no further chance of locking up or vehicle speed is now under 5 mph.

The focus is on this dump portion of the RABS valve. Occasionally the seat between the solenoid and the accumulator will leak, causing the pedal to fade during normal pedal applications. This sinking pedal has no other abnormal braking characteristics and is usually not noticed (depending on severity) unless it sits for an extended amount of time with constant pressure applied. It may be due to physical damage or a buildup of contaminants in the hydraulic system, but the results are the same.

Some customers report that the brakes were just fine until a hydraulic component was replaced or repaired and the brakes were bled. Then the pedal started fading. Quite possibly this is due to a new problem that is created by "moving" some of the contaminated fluid into the valve. To diagnose this system, like all brake systems, first verify that there are no external fluid leaks. If visual inspection is OK, disconnect the brake lines at the master cylinder and plug the outlets in the cylinder. When the master cylinder is plugged, if a fade is still experienced, the master is at fault.

If, however, there is no fade, determine if it is coming from the front or rear brakes by blocking one port at a time at the master cylinder. If there is no longer a fading pedal when blocking the port to the rear line, go one step further and build a short brake line to splice between the inlet and outlet lines at the RABS valve to temporarily bypass the valve.

After bleeding the rear brakes and verifying there is a solid pedal, it's a good bet that the problem is in the valve itself. The next step is to replace and bleed the valve (if equipped with a bleeder) and the rear wheel cylinders. Verify the repair and road test.

Jeff Boskowitz, IDENTIFIX Ford specialist, is certified Ford EEC, MACS, ASE master and L1. He has 26 years of experience.


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[RanSit]

speaking of brakes i got a question

for the past few days b4 my tranny went about 2 weeks ago now well i would be driving and hit my brakes my rear antilock would come on and my brake light would come on...i guessed it was that it was time for new brakes...thats not a problem its like $30 but now when i turn on my truck just to let it run till i get my new tranny so its not just sitting there the brake light and antilock light wont go off...at first i thought it was my emergeny brake was in but thats not the case...any ideas?? could it be that i just need new brakes?

 

[Hank]

There are a number of reasons why the RABS light can come on, the simple ones are blown fuse and dirty connections, air in lines.... All very common.

The autozone site has a good chart on RABS codes if you are getting flashing and there are a bunch of sites out there with good RABS info. I would search google for Ford RABS light on for starters.

My issue differs as I don't have a light, it seems to be the internal seal leak/failure issue which results is pedal fade.

My 91 does not have a brake pad/shoe sensor. Something that grounds out and turns on a light on the dash when the wire in the pad grounds to the disk and the drum so I doubt you have a pad/shoe issue causing the light to come on. I once ran my rear shoes down to the rivets on both wheels and never got a light.

 

[Hank]

No good news, autozone shipped a 94 abs module not a 91 rabs valve...

Might try flushing the valve with denatured alcohol this weekend.

 

[Hank]

Long story short, went to local AutoZone store and got them to take back the wrong part even though it was a special order and credit the priority over shipping. AutoZone.com would not but the local manager did once I expalined the problem.


Found the right part at Advance Auto. Their system, even on-line shows photos of the part. So the mananger and I confirmed it before ordering. Side note, should be in tomorrow and no shipping charge.. I am so done with AutoZone.... Everything I do with them takes three trips..

I'm posting the following info incase others want/need to replace their RABS
-------------------------------------------------------------------------
Advance calls the RABS Valve an ABS Hydraullic Unit. Item number is 122029 and at the time of this post the cost was 89.88 and a 50.00 core. Manufacturer is Cardone.

 

[Rhett]

So in short, did replacing the RABS valve solve your pedal fade problem?

 

[Hank]

"So in short" funny, yeah I tend to babble a bit...
RABS due in Friday AM. Hoping to replace the flex lines and RABS Saturday.

Was that a bit better?

 

[Rhett]

No I like the babbling. It's very informative. I tend to do it myself sometimes...
I have the 4-wheel ABS...I wonder if my ABS hydraulic control unit is different than the RABS HCU like you have?