Inoperative rear brakes

[MAKG]

Well, I'm more than a bit annoyed at myself for not noticing this A LOT earlier, but I don't have functional rear brakes in the '91 Exploder. In fact, I suspect they have been inoperative at least since I bought the vehicle over 3 years ago. The parking brake works just fine; I insist it hold the vehicle on the steepest part of my driveway, over 30% grade (I believe this rules out all the mechanicals, and requires a hydraulic solution).

I noticed the front brakes could be more easily locked up than I'd like, but I attributed it to the much heavier GVWR compared to the Bronco II I'd previously had. Wrong; it's that the front brakes are providing 100% of the stopping power.

I figured it out when I replaced a sticky caliper, and decided to flush the brakes since I had a bunch of brake fluid around and I hadn't done it before. I had no idea if the previous owner had ever done it (though I think I know the answer now). Opening both rear brake bleeders and having my wife stand on the brake pedal (with the parking brake off) yielded absolutely nothing. I completely removed the bleed screws and discovered they were full of rust. Still nothing. I cracked the fitting on the left right rear wheel cylinder (the left is a bit bent up, though it doesn't appear crimped, and I can't get a flare nut wrench around it because of that).

The master cylinder appears fine; with the pedal down, cracking both fittings yields some fluid.

The rear union fittings are accessible behind the spare tire, but appear to be rusted solid. Same for the rear soft-line connector. I can't easily get at the RABS valve without disassembling several parts in the way. Obviously, these will have to change, but before I go there, I want a stupidity check. Please verify my assumptions:

1. The problem is a hydraulic blockage somewhere between the master cylinder and junction atop the rear end.

2. RABS won't cause this problem without setting a DTC (the RABS self test does run).

3. Nonfunctional (disabled) RABS will have the opposite failure mode -- it will never disengage the rear brakes.

4. There aren't any mechanical (inside brake drums) problems that can cause this behavior.

Note that the rear brake line appears to be EMPTY. Not full of rust. And the pedal feel is quite firm.

I'm debating throwing parts at it (replacing the rear brakes including wheel cylinders and drums) because they are probably original and I know the rear wheel cylinders are full of rust. I doubt this would solve the problem, but I think it needs to be done anyway.

Now I'm much relieved I couldn't find the time for that drive up Pike's Peak I almost did two weeks ago....

 

[skippy]

same vehicle with worn out front pads awhile ago?wow,you have been fortunate.good luck.

 

[MAKG]

same vehicle with worn out front pads awhile ago?wow,you have been fortunate.good luck.

Yes. Well, at least the parking brake works....

And now the fronts do.

 

[Jspafford]

I say RABS valve.

 

[baddis]

i have seen where the wheel cylinders have plugged up with rust nothing in or out of them.

 

[MAKG]

i have seen where the wheel cylinders have plugged up with rust nothing in or out of them.

This is certainly true. At least the bleed screws are completely packed; the wheel cylinders probably are as well.

However, it's not the whole story. When I disconnected the right side brake line at the wheel cylinder and pushed the pedal, nothing came out. There has to be an additional upstream problem.

 

[MAKG]

I say RABS valve.

GOOD GOD!

$180 for a valve?

Do you suspect a plugged valve or electrically failed valve? Is that third connection a bleed screw?

Is there any way to clean this thing? Can it be checked in the field easily? Normally, I won't even consider junkyard hydraulic parts, but I might if I can know it's good.

 

[Jspafford]

Mike when my valve failed it leaked externally and I had horrible brakes. I would go get a straight connector and bypass the valve to see if your rears work.

I took my RABS valve out and left the splice in there. All is well, the ABS bulb burned out years ago so I have no indicator.

Your right, there was NO WAY I was going to pay that for a valve. My rears never even try and lock up as it is.

 

[MAKG]

Hmm, mine isn't leaking.

But when time allows, I'll remove the front driveshaft and get a wrench on that bleed screw.

If there isn't fluid there, I can try disconnecting the input side to see if there is pressure in front. That would confirm the valve.

I don't like to disable safety equipment, and RABS was put on these vehicles because they were prone to spinning out with hard braking on curves. Given that I live in mountains, this is a very likely situation. Yeah, there are techniques for recovering from a rear slide, but you usually don't have the freedom to turn the steering wheel against a curve on a mountain road. Of course, you can still "threshold brake," but you're still reducing options by disabling the valve.

 

[Evan]

Hmm, mine isn't leaking.

But when time allows, I'll remove the front driveshaft and get a wrench on that bleed screw.

If there isn't fluid there, I can try disconnecting the input side to see if there is pressure in front. That would confirm the valve.

I don't like to disable safety equipment, and RABS was put on these vehicles because they were prone to spinning out with hard braking on curves. Given that I live in mountains, this is a very likely situation. Yeah, there are techniques for recovering from a rear slide, but you usually don't have the freedom to turn the steering wheel against a curve on a mountain road. Of course, you can still "threshold brake," but you're still reducing options by disabling the valve.

Well, at least right now you don't need to worry about your rear locking when you go around a corner.

Once the rear on an Explorer or Bronco II had locked and starts swinging out it's almost too late to correct it by threshold braking. You have to abandon braking and work on throttle, which poses a problem when going down a mountain road as you're not braking anymore. I agree that RABS is a good thing to have in your driving situation. I removed mine only because it's undesirable on the trail.

 

[metalmacguyver]

I think the best option is to hit up the classifieds section and buy a RABS valve from someone. It is something that is very unlikely to be bought when parting out a truck so you could probably by several for cheap incase one isnt good or whatever.

 

[Simple_serf]

Personally, I'd bypass it. RABS has never saved my ass from sliding in snowy conditions/ice.

If you want to keep it, still bypass the rabs...then you can see if you can get the brakes working right.

My current problem is the rears locking up on the first brake application of the day. Given that I had to put $1400 in brake work in this truck last year...I'm just going to leave it for now.

How bout the junkyard option...i'll be they don't get too many people looking for these.

 

[Jspafford]

The rears lockup because the shoes are absorbing moisture and swelling against the drums. Changing to a different type of shoe corrects this.

 

[Jspafford]

Hmm, mine isn't leaking.

But when time allows, I'll remove the front driveshaft and get a wrench on that bleed screw.

If there isn't fluid there, I can try disconnecting the input side to see if there is pressure in front. That would confirm the valve.

I don't like to disable safety equipment, and RABS was put on these vehicles because they were prone to spinning out with hard braking on curves. Given that I live in mountains, this is a very likely situation. Yeah, there are techniques for recovering from a rear slide, but you usually don't have the freedom to turn the steering wheel against a curve on a mountain road. Of course, you can still "threshold brake," but you're still reducing options by disabling the valve.

As I mentioned my RABS didn't work when I got the truck anyway so I was not out anything by not fixing it.

My front brakes lock up LONG before the rears even try. I am always shifting into 4WD when I have to stop hard in snowy or icy conditions.

 

[Jspafford]

So Mike, did you figure out the problem?

 

[metalmacguyver]

About the RABS, I was playing around in the snow and I did manage to make it work. I had to stand on the brakes and when it did work, it only pulsed every 1.5-2 seconds. I was not impressed. That rate of response is not sufficient to provide much safety.

 

[MAKG]

Nope. The wife is out of town, so I'm on toddler patrol.

metalmcguyver, I thought the spec was nearly 10 Hz. Are you sure yours was working?

 

[MAKG]

OK, plugged ABS valve confirmed. Thanks, jspafford.

The cheapest price by far is autozone.com. $100 + $60 core. My usual Ford dealer (Mission Valley Ford Truck) wants $198 + $100 core. The gold plated Ford dealer (Palo Alto Ford) wants $275. So, it's on order.

 

[metalmacguyver]

I could definately feel it working but it was slow as heck. It definately surprised me how slow it was working.

Its not something that has me worried though.

 

[Jspafford]

OK, plugged ABS valve confirmed. Thanks, jspafford.

The cheapest price by far is autozone.com. $100 + $60 core. My usual Ford dealer (Mission Valley Ford Truck) wants $198 + $100 core. The gold plated Ford dealer (Palo Alto Ford) wants $275. So, it's on order.

No need to thank me.

I was hoping for your sake I was wrong. Those valve are extremely overpriced. Looks like you were able to find one cheaper than I was quoted.

If you don't mind my asking, how did you determine it to be bad?