Need the skinny on brake proportioning and function. '94 XLT 2WD

[ForgedCrank]

Hello all...
wondering if someone can give me a quick overview of the braking system (specifically, front/rear bias proportioning) on these. I've come to the conclusion that my rear brakes are doing very little or nothing during braking.
I replaced the brakes on all 4 corners when I got this a few months ago, new drums, cylinders, shoes and everything in the rear as well, even flushed out all the old fluid and bled a quart of new fluid through the entire thing.. Parking brake works great, but the fronts are VERY easy to lock up, and downright scary on wet pavement.
Is there an adjustable proportioning valve on these things, or a part of the OEM system that may have gone south on me? Is it done in the master cylinder or something? How would one go about testing to find the issue here?
OR... are the brakes just simply that shi**y on these things?

 

[Brain75]

Which Port On Master Cylinder is For Front, Rear Brakes? | VehicleChef

The master cylinder in your vehicle is responsible for controlling the brakes and the brake pressure. Ideally, you will find two ports connected with lines.…

vehiclechef.com

The front port on the master cylinder should go to the back circuit (back wheels) , and the back port should go to the front circuit (front wheels)....

I've never seen one different than that, but the possiblity exists I suppose...

Anyhow, just checking the basics - is it plumbed up that way?


To change the proportion it usually means pulling the brake master cylinder and rebuilding it on the bench (changing internal guts for a different proportion - some can not be changed).


Just curious if this is bone stock, someone replaced the rear axle and put in a really old style (not self-adjusting) and and... possibilities are endless when dealing with a used vehicle someone else has mucked about with.


Are the rear brakes adjusted to the point they grab? This may sound ridiculous, but the brakes only self-adjust when you step on the brakes while moving in reverse. I had a girlfriend who was deathly afraid of backing up, and never parked in such a way she had to - so the self-adjusters never operated for her.

If you just replaced the shoes, did you adjust them close or do a couple/3/4/5 stops in reverse to allow the self-adjusters to operate.


The parking brake has it's own adjustment and operates through the full range, so it does not depend on the shoes being adjusted correctly.

 

[Uncle Gump]

These trucks are prone to locking the rears. Rarely the fronts.

Is the brake pedal low? Rear brake shoe adjustment is directly proportional to pedal height. If the pedal height is low... poor adjustment on the rear brake shoes.

When you bled the system... was there a good squirt of fluid at the rear when you cracked open a bleeder?

Your truck should be equipped with RABS. The valve will be mounted on the inner frame rail below the drivers feet. This will regulate fluid to the rear.

 

[ForgedCrank]

Trying to remember all of the details because it started raining like hell and I haven't been willing to crawl under it yet today.
Here is what I know without question
- This truck does NOT have the factory diff in it, it does not match the door tag and was upgraded in the past for whatever reason and now has a 8.8" diff instead of the smaller one, and it has 10" brakes.
- When I bled/flushed the system, I did get fluid from the rear bleeders, but near the end of the process, less and less was coming out. It did flush completely though, and I say that because I could definitely tell that fluid changed from dark to clear. It DID slow way down through. I remember being frustrated with that, but never gave it anymore thought.
- I did adjust the shoes as is my normal method. I run them out until I can't get the drum on anymore, then little by little back them off until the drum barely fits, yet doesn't drag when turned by hand. They were Motorcraft branded new shoes.
- I did look, and yes the rear master port is plumbed to the front brakes, front port goes to the rear brakes.
- I have very good pedal, it is solid and is operating at the higher end of the travel, nothing alarming like not engaging until it's past half-way or anything.

The valve Gump explained is the one I had not yet found. From what I was reading, I was expecting it to be found on the inner fender below the master cylinder, but there is nothing there on mine.
I was under there looking around yesterday but I probably missed it. I was also looking for what people call an "anti-lock valve" (which I assume is what Gump is calling RABS) that is supposed to be mounted on the top of the rear diff, something that I do not have. So anyway, I'll have another go and trying to find it on the frame rail when things dry up a bit.
Let's assume I do find it. does this sound like the problem and is something that simply needs replaced? Or is it something you can disassemble and clean and/or adjust? I'm not finding any hits on google or YT specific to the Ford.
Also, if this is a mechanical anti-lock valve, does this mean my master cylinder has a proportioning valve built-in like some and is a potential source for the problem as well? i'm trying to think through the possibilities here and start hunting for parts while I'm waiting for it to A) NOT be 45 degrees outside and B) not raining

 

[Mechrick]

The RABS module is under the dash close to the ash tray. The RABS valve is in the driver's frame rail roughly under the driver's seat.

RABS uses the diff speed sensor to read the rate of deceleration of the rear wheels, and modulate rear brake pressure accordingly. There is proportioning built into the valve.

On my BII, I removed the proportioning valve (no RABS on that one) and installed an adjustable one close to the master, because the rear is now an 8.8" out of an Explorer Sport Trac with discs.

Not a good idea to do that with a pickup because the load changes, requiring a dynamic amount of brake pressure to the rears.

The fronts are always supposed to lock before the rears (understeer is safer than oversteer).

 

[Brain75]

The 8.8 is a "new" axle, so not really possible to be non-self adjusting.... We are talking 40's and 50's for that kinda ancient tech... (just eliminating the possibility someone put an old Ford 9" or something like that).

...I replaced the brakes on all 4 corners when I got this a few months ago, new drums, cylinders, shoes and everything ...

I was not aware of this till now (haven't had to), but anytime you replace the wheel cylinders or master, you have to bleed the RABS as well - or so I just read on FTE.

I found a video "how to bleed your brakes with RABS valve (Ford ABS)" - guy says he is working on a bronco.

Caveat: This is pure google results, no 1st hand experience... video might not be, etc, etc - caveat emptor.

 

[Uncle Gump]

Here is what i know about RABS... it will never work without the rear wheel speed sensor. So if it has a RABS Valve... it is non functional. It was never a good system anyway... that's why there were several lawsuits and the manufacturers moving quickly to 4 wheel ABS.

Did you by chance replace the rear flexible brake hose at the rear end? These have been known to collapse and severely limit fluid flow to the rear cylinders.

 

[ForgedCrank]

Here is what i know about RABS... it will never work without the rear wheel speed sensor. So if it has a RABS Valve... it is non functional. It was never a good system anyway... that's why there were several lawsuits and the manufacturers moving quickly to 4 wheel ABS.

Did you by chance replace the rear flexible brake hose at the rear end? These have been known to collapse and severely limit fluid flow to the rear cylinders.

No, i did not, I only replaced the front ones, but now things are getting gray. I need to get under there and do better recon before I can really tell what I've got to work with. I don't know this for sure, but what may be happening is that I don't have a rear wheel speed sensor anymore do to the diff swap at some point in the past. I'm afraid to say that for sure though until I get back under there and take detailed notes, then I can go from there.

 

[ForgedCrank]

Ok, I couldn't stand it so I suited up and got underneath the thing to look around. Well, I was wrong about a lot.
First, I DO actually have a sensor on the rear diff, I assume it is the speed sensor cuz i'm not sure what else it could be. Screwed into the front/top on passenger side. I'm not sure how I missed it looking for it, but I did and it's definitely there. If I am understanding correctly, this is called "Vehicle speed sensor" or VSS, is that correct?
I was also able to locate the valve thingy, right where you guys said it was, i'm not sure how the heck I missed it before either. Maybe I should lay off the beer when I'm doing this stuff. Na... crazy talk. Do I have this correct.. it is called "RABS Valve" ?
So now the question is how to proceed? You think I should just rip and replace all this stuff one by one? I'm not much into the parts cannon approach, but I'm not so sure how to even test this stuff for function. On the VSS, is a simple resistance check good enough? Not sure how I could tell if it was sending a proper signal to wherever it goes. Would I see a brake or ABS light if it were malfunctioning or dead?
And as for the valve part, I don't even know how I would test that. It's not a cheap part, so I hate to blow 150+ on a reman and that not be the issue. suggestions? Sorry if I appear lazy, I'm not really not, and I'm willing to do the reading, I'm just a lost on the nomenclature that is key to finding the right answers. Searching for "my 1994 ranger rear brakes might not be working" isn't going to get me far. I'm in territory where I only understand the very basic idea of what is going on and am clueless on how to troubleshoot the complete system. i'm also now wondering if this is somehow related to my cruise control not working.

Unless anyone has better advice, I think I'm going to start with bleeding everything again since I was unaware of this RABS thing when I did it before. If I have this correct, I first do the master cylinder rear circuit first, then the RABS valve unit thingy, then the rear brakes, then the front brakes.
After that, i'm not sure what else to do other than start swapping parts.

 

[Brain75]

One post on FTE says to bleed them after the rear brakes and before the front (so it follows the same traditional longest line first, then next to longest, etc up to shortest last).
Based on that I would consider the rear to be done, bleed the RABS, then front again and see how things behave.

 

[ForgedCrank]

One post on FTE says to bleed them after the rear brakes and before the front (so it follows the same traditional longest line first, then next to longest, etc up to shortest last).
Based on that I would consider the rear to be done, bleed the RABS, then front again and see how things behave.

that makes sense I recon.
i think i'm going to do the entire thing in that order, then do the rears again as a test just to see if fluid will actually come out of them better than it was before... if it is still acting funky, I think I can probably assume that this valve is messed up or stuck.
I am a bit confused on the part number though. The shop manual calls for part# "2B373", but looking it up, it doesn't look anything like what I have. Searching find a number "F87Z-2B373-ARM" that looks more correct. can anyone verify?
I'm wondering if it "looks" the same physically, if it will work, or if there are different configurations for different vehicles using the same base housing.

 

[Uncle Gump]

I just moved this to the brakes forum.

There was a very similar post on here not too long ago that dealt with this very issue. I think i remember there was an issue RABS Valve.

I'm gonna see if I can find it.

 

[Uncle Gump]

Can’t bleed after disk swap

I put SN95 mustang disks on my ranger months ago and had trouble bleeding them then as I am having now. Basically I cannot get any fluid to come out of the bleed. If I crack the lines almost anywhere else in the system I get fluid, although it’s not a super strong jet when cracked and the pedal...

www.therangerstation.com

 

[ForgedCrank]

Can’t bleed after disk swap

I put SN95 mustang disks on my ranger months ago and had trouble bleeding them then as I am having now. Basically I cannot get any fluid to come out of the bleed. If I crack the lines almost anywhere else in the system I get fluid, although it’s not a super strong jet when cracked and the pedal...

www.therangerstation.com

Ok, great. This is exactly the information I was failing to uncover on my own. Now that I have a basic understanding, I'll bleed the thing again and see how it behaves and if I'm lucky, it resolves the issue. To test, it looks like I have to be going more than 8-10 mph and try to lock up in gravel or something, right? I'm not sure I'll have wet roads to test with when I need to.
Mine looks different than most I am finding on flea-bay though. The one I have looks the same as what is commonly listed as for '98-2000 Ranger"... so I think I'm just going to order the re-man from O'Reilly. I generally don't trust part store reman crap and do it myself, but I'm not sure what I'll get into and how long I'll be down looking for parts and o-rings so meh. This stupid thing is expensive. I wish I weren't so sticky about keeping everything as-built, otherwise i'd just do as others have and bypass it with an adjustable valve in it's place.

Cardone Remanufactured ABS Hydraulic Assembly - 12-2029

 

[don4331]

Couple of minor corrections/additions:

The parking brake uses the same adjustment as the rear brake shoes. In fact, in addition to brakes adjusting when backing up, they will adjust when you apply the parking brake.
The brake light comes on during 1 of 2 conditions:

1. When there is large pressure differential between front and rear circuits​

2. When the speed from the VSS suddenly drops.​

If the RABS module is locked 'closed', i.e. stopping fluid to the rear brakes, there won't be a large pressure drop between the 2 circuits; and there won't be the sudden speed drop detected by the VSS (rear lock up case) Which is why brake light doesn't come on.

@Brain75 's video gets it 1/2 right - he's really just bleeding the main cylinder and hoping that the air migrates uphill to the main cylinder...it does work, but man do you need patience. The part he gets more right is you need to make sure the RABS module didn't get air in it/bleed it; for the model in the video, so removing the spring allows that (and as it is very short/very uphill to the master bleeding happens relatively easy. But he could have done it faster, by just opening the bleeder valve on the RABS...

If the RABS module gets air in it, the valve moves to the 'closed' position - its supposed to be a safety thing; if rear brake line fails, you don't lose all your brakes because the pedal went to the floor.​

​

The challenge becomes getting the air out of the RABS module.

If I remember correctly, there is a bleeder on the Ranger RABS module (under the black dust cap in the picture?)​

Once your bleed the air out of the RABS module, everything starts working again​

What I can't remember is if you have to reset the RABS module or not - for the 4 wheel ABS in newer Rangers, if you get air into the ABS module, you absolutely have to reset the module.​

​

The correct procedure for bleeding with RABS is to bleed:

Passengers rear​

Drivers rear​

RABS module​

Passengers front​

Drivers front​

Passengers rear​

Drivers rear​

Passengers front​

Drivers front​