Rear Brakes Locking Up

[IAmTodd]

I've done some searching and I can't seem to find a similar situation. The past few days I've noticed some weird braking. It seems as though the rear brakes are locking up on wet pavement. If I'm going slow enough the back wheels will drag, if I'm moving around 10mph the ABS will kick in.

It seems more of an issue on wet pavement for obvious reasons. I had the drums off when I first got the truck and they looked fine. The front brakes are new including calipers, system was flushed and the ABS light is off and as far as I can tell the system is operating as it should.

The only two changes were it getting inspected last week (may call to see if the brakes were adjusted) and it was rear ended on Monday (yay for hitch and steel bumper, no obvious damage).

Anything else to check for?

 

[Jason94sport]

Does it go away higher speeds? Cause my X has been doing this for a year. New front pads & rotors, drums were adjusted which helped for a little while but it returned. As well no ABS light.

 

[IAmTodd]

I have no problem at speed. It's only when traveling at parking lot speeds and seems to only happen when wet. We've been really wet so I've been unable to test it in the dry.

 

[IAmTodd]

I remember reading somewhere that there's some type of inertia switch on the frame that deals with the braking. Does anyone know what it is and if that could be my issue?

EDIT- evidently that's called a G-switch? Is there a way to test it? I'm not coming up with anything by searching.

 

[Anime]

Have you pulled the drums to inspect the brakes mechanically?

I'd suspect the rear ABS sensor though, since there is just one sensor on the diff and it controls both rear brakes.

Does the ABS light come on when you turn the key when starting? If not then the bulb is out and the ABS light isn't turning on because of that.


There is no G-switch on the 1st gen, the ABS is only controlled through the wheel sensors (sensor/rings on the front discs, sensor on rear diff at the rear) and ABS control module, and triggered when the sensor detects the wheels are not rolling with the brakes engaged. Acceleration switches/G-sensors are found on much newer vehicles, though there are some from the late 90's that have earlier versions as well.

 

[IAmTodd]

Thanks for the info. I suspect it's a mechanical issue.

The light illuminates and the self test can be felt through the brake pedal. After that the light goes out. I don't believe it's a sensor issue. If I am traveling at speed >10mph(estimated) you can feel the ABS pulse when the rear wheels begin to slide. If I'm traveling slower the wheels will simply lock. I am unsure if it is just one wheel or two.

This has been occurring for the past few days but I just verified it (and seems worse) today.

 

[Jason94sport]

If I am traveling at speed >10mph(estimated) you can feel the ABS pulse when the rear wheels begin to slide. If I'm traveling slower the wheels will simply lock. I am unsure if it is just one wheel or two.

Mine is exactly the same. And it started out of the blue a year ago. The brakes have been went through. Why it goes away at higher speed IDK. I have slammed on the brakes at 40mph+ & the abs kicks in fine & all seems normal.
One time I was able to trigger the abs light & it stayed on one key cycle. But haven't been able to do it since. That was over 6 months ago. Since it's not a DD for me I only use it 1 day a week or for a special purpose, I'm not worried about trying to fix it.

 

[IAmTodd]

Mine's going to be the primary car for the winter so I'd like to make sure it's running well. I can only imagine how bad this problem is going to be in the snow!

Have you had your master cylinder looked at?

I'll report back if I find anything.

 

[Anime]

If one side was locking up, I'd be more suspect it was a mechanical issue with the brakes themselves, but if BOTH sides are locking up, I would say it is either the rear sensor, or something in the ABS control module itself, because it sounds like the ABS is doing a 'pulse' to lock the rear brakes, instead of the typical chattering to slow a wheel down.

Could be the collision jarred the rear sensor enough to damage it, or might even be a wiring issue. Hopefully it's the sensor, because those are rather inexpensive. The ABS control module is not.

 

[IAmTodd]

So further testing (I have yet to tear into anything yet) there's a definite spike in the braking as it begins to slide. I can feel no change in the brake pedal (I would think there would be also some change in resistance if it were ABS). The most puzzling thing it seems after I use the brakes a few times it goes away, at any speed. I'm just wondering if the shoes are adjusted out a tad too much and the drum expanding from heat allows it to loosen up a bit? Just a theory until I can verify anything.

Maybe I'll pull the ABS relays before I leave work to see if it continues. Thanks for the ideas.

 

[Jason94sport]

Where is that located? I may pull mine to test it. I'm driving the X today.

 

[IAmTodd]

Under the hood in the distribution box, there's two relays and two fuses (I think two fuses). The lid is labeled.

 

[malohnes]

Check your parking brake assembly. I had a similar issue that also showed up in snowy conditions and I found that my passenger side cable was hanging up and causing the one side to drag a bit.

I ended replacing the whole system...cables and hardware and all. It was minimal expense and mostly time and dirty cleaning. I'm slow and it took an easy 4 hours to do the whole job.

 

[IAmTodd]

Thanks, I'll check that out as well.

If I have to go throwing parts at these brakes I'm going to the pick n pull and swapping in discs. If I can find a good donor I can do that for under $100. I've never been thrilled with the e-brake setup with the discs though. We'll see what this weekend brings.

I was out at lunch time running some errands and it had no issue at all, stopped as it normally has been.

 

[siguaw]

There is no G-switch on the 1st gen,

Is this different from the one that cuts off fuel? I have a 1994 and it tripped on me when I slid into ruts on a mountain trail a few years back. Passenger floorboard under the carpet?

 

[IAmTodd]

That's the fuel inertia switch. It deals only with the fuel pump circuit. Completely different.

 

[siguaw]

learn something new everyday. Explain how the brake one works?

 

[zippoz]

i had the same problem on my 94 explorer, the back drivers side tire kept locking up, and the shoes and drum were fine.

i just loosened the lower tensioner sprocket, and the problem went away.

 

[IAmTodd]

learn something new everyday. Explain how the brake one works?

You got me. It's some type of mercury switch.

i had the same problem on my 94 explorer, the back drivers side tire kept locking up, and the shoes and drum were fine.

i just loosened the lower tensioner sprocket, and the problem went away.

I have to wonder if that's all mine is. It's not doing it any more, shoes must have worn enough to allow proper clearance. Still going to check it out. I'm also curious to look at that sensor on the frame rail that I though was the g-switch.

 

[zippoz]

yeah, we have the same model and year explorer, funny i didnt notice that till just now. I had a hell of a time getting my drum off, had to beat it and pry it from the back from 2 sides simultaneously to get her free.

I probably backed the tensioner off way too much, but i dont even care, i cant afford to have that rear tire locking up while im coming down a icy mountain pass.