RWAL ABS & e-brake lights-on... chronic condition - Page 2 - Dodge Diesel - Diesel Truck Resource Forums

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RWAL ABS & e-brake lights-on... chronic condition

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Old 01-11-2018, 03:44 PM
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The reason I mention the differences in the model years is because of the replacement CAB you got, perhaps it was the wrong one. Also don't rule out the parking brake switch as it also puts on the red light. Also if the wires to the rear diff sensor are damaged and need to be replaced don't forget they are a "twisted pair" and not just any wire. One other thought after reading the thread again, are you using a digital multi meter as they "sample" and it's possible to miss an intermittent fault.
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Old 01-11-2018, 09:58 PM
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Originally Posted by Busboy View Post
One other thought after reading the thread again, are you using a digital multi meter as they "sample" and it's possible to miss an intermittent fault.
Very good point, regarding these brake light switches. I have seen cases (not for this specific problem) where the contacts just get a bit of resistance between them that can cause troubles like this. This resistance can often be intermittent, and can be dependent on the amount of current passing through the contacts at the time. Just be careful of ruling out that switch too quickly.
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Old 01-12-2018, 02:46 AM
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Thanks, guys.
- new CAB has same p/n on it as my original, and as the junkyard one I bought, so I doubt there's any problem there
- brake-light switch was definitely misadjusted via my replacement of the hydroboost, but once I refreshed my memory of how it's supposed to be reset (simply one-minute procedure) the brake-lights returned to normal status
- I was briefly excited when I found no (audible) continuity between pins 13 & 14 at the CAB connector (that's the twisted-pair that heads back to the sensor in the diff), for some reason having jumped to the conclusion that I should be seeing something like zero ohms. I even bypassed an unnecessary inline connector set because shorting through the pair just ahead of them gave me the continuity "beep," but then of course once I'd spliced the cut ends back together, there was STILL no audible signal...that's when I realized no one had told me it was a near-zero resistance. I'm getting 1900 ohms, seeing that some others have reported 1300 ohms, and I suspect there's a broad range of passing resistance values. I'll dig out my old spares (it's been replaced at least twice) and see what those meter, but I think that's another wrong tree.)

Oh, and though my DVM does have a couple of memory options, I almost never use them so as to see the dynamics in any reading.

To be thorough, I do need to recheck for continuity/open on stop-switch terminals 1/2, which (going back in this post) should have pin 1 grounded via pin 2 normally (with pedal at rest), and with pedal pressed, that pair is supposed to be open, telling the CAB that the brakes are on, so it better start looking for any wheel-slippage. This worked flawlessly when I tested it before - and I tested it many times then - so I don't see this being a new problem or a metering failure.

I do owe myself another bleeding session (front-brake reservoir dropped rather fast, and it doesn't help that I back up an insanely-steep driveway daily, which spills that fluid forward into the rear-brake reservoir IIRC).

But failing alla that...swap out the proportioning-valve? Then yank out the ABS valve and see what I can see with it on a bench? I dunno what's in it - any orifices to clog? There were times when the fluid in my old MCs was really nasty-looking - no idea why - and I figure that gunk accumulates worse in some low-point in the system, maybe even after many bleeding sessions.

Thing with the proportioning-valve is that the only electrical communication it has with the rest of the system is that one "grounded-when-bad" switch. And that's always tested as un-grounded. So although the valve might screw up at times and explain my grabby rear brakes (sometimes), it can't convincingly explain my forever-on ABS light. The grabby rear brakes are actually relatively recent, like...the last six months. The ABS light has been on for more like a decade.
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Old 01-12-2018, 10:04 AM
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Mine was similar and it was the light switch. There are 4 or 5 different sets of contacts in that switch and it is quirky in its set up. If the plunger is set up wrong some of the contacts can still be open, not necessarily the ones that light up the tail lights. Then the system thinks there is a problem and shuts down the ABS. With an empty bed that means rear wheel lock up when you even think about stopping.
I fiddled with the old switch for days then just gave in and bought a new one. DO NOT PULL THE SHIPPING PIN BEFORE YOU HAVE IT INSTALLED.
Once you get the switch in make sure the pedal is up in it's resting position THEN pull the pin. The plunger will pop out until it touches the pedal and that sets up the switch.
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Old 01-13-2018, 10:20 PM
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VADSLRAM - OK, I give...got a switch on order. It's $10. Guess I could crowdsource for that...seriously, though, it's nothing in my spectrum of costs in time and dollars spent on this, though I have about a half-percent hope it will make a difference, since the contacts all checked out OK.
-----
I tested wheel speed-sensor output conclusively (I believe): pins 13 & 14 at the CAB connector give me an 1800ohm reading, and today I drove with my meter (AC volts) connected to the same pins. It varies smoothly from zero V to around 16V at 60MPH. I can't see that being a problem. I also can't find any specific testing data in the FSM; they just describe connecting it to do testing at the factory, on a set of rollers, but it's just not going to fail in a way that I get some "wrong" voltage out of it.

Looking further to the proportioning-valve, the FSM says this:
COMBINATION VALVE
Metering Valve Metering valve operation can be checked visually and with the aid of a helper. Observe the metering valve stem while a helper applies and releases the brakes. If the valve is operating correctly, the stem will extend slightly when the brakes are applied and retract when the brakes are released. If the valve is faulty, replace the entire combination valve as an assembly.
Is that "stem" accessed/ probed with a tiny screwdriver or dowel, if I pop off the rubber cap at front of the valve and put the dowel into the hole there? If that checks out, I'm inclined to skip messing with that component and go directly to the ABS valve, where unknown peril lurks.
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Old 01-19-2018, 03:48 PM
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the long nightmare is over.

I'm happy to report that I've got brakes like never before (I think literally since I bought the truck) and almost as importantly: no freaking RWAL/brake warning-lights!

UN-satisfyingly, though, I can't point to any one clear smoking-gun, in the end.

Installing a new hydroboost: this left me with same warning-light conditions, but while changing it, I'd been noticing that when on the steep hill where I have to work on it (I know, I know - great place for brake work), the MC reservoir for the front brakes was dangerously low due to the inclination, and the fact that the port into the MC itself was on the higher end. It's conceivable that it managed to suck in some air there, and I'd not re-bled the brakes for a few months...and I still didn't, because I just didn't really believe that could have happened.

Next, I did some other electrical testing, confirming things like the brake-pedal switch were operating as expected.

I moved on to the diff speed sensor (again.) Here's where my diagnostics went out of round; I for some reason had been thinking the speed-sensor would appropriately be "beep-tested" for continuity, meaning a very low resistance would give me a "beep" from my DVM, and I'd be able to work through the wiring checking for continuity without having to keep my eyes on the meter in the cab. So when that test gave me no beep, but shorting through the insulation across the sensor leads just cabward of the last plug DID, I jumped to the conclusion that, as some others had reported, I'd lost continuity (broken wire) in the last few inches of harness before the plug. So I cut out that redundant plug/jack and solder-spliced the wires there...and then was greeted with STILL NO continuity-beep from my meter.

It was only then that I began to question my assumption that the sensor resistance should be nearly zero, and googled to find that actually, there should be about 1800 ohms of resistance across the sensor.

So did I fix anything there? Well, not according to the warning-lights, which stayed on.

When I next got into it, I was heading towards replacing the proportioning-valve, since the symptoms lately had been as if the brakes were biased heavily to the rears. I posted to ask precisely how to test the proportioning-valve per the incomplete instructions in the FSM, using a dowel or whatever, but didn't get a reply. While test-driving after the hydro-boost, I could hardly help but lock up the rear end - it was insane.

So before replacing it, I owed it to myself to re-bleed. Having replaced my bleed-ports with those aftermarket check-valve types, it's a bit easier, too.

This would be far from the first time I'd tried to bleed my way out of the problem, but given the low-reservoir condition, and the mysterious dirty-looking fine debris that keeps accumulating in my reservoirs, I figured it was warranted again.

I couldn't position myself to be able to see if/how much air was coming through during bleeding, but when I was done, I held my breath and keyed over. The ABS light self-tested and went out, as often. It came back on immediately after I started...but then went out, as did the red e-brake warning light! I've not seen either light misbehaving since, which really amazes me, since I think this has been going on since about a year after I bought the truck, around 2005!

-----
If there's anything to complain about now in the realm of my brakes, it's that they're 'sticky.' When I took my wife out the other day, having released the e-brake and then barely teasing the beast to get in motion down our insane-steep driveway, it was like the brakes were 'stuck on.' And they released with a jerk that made my wife gasp, giving me that look...

The stickiness also appears from time to time while driving, especially when coming to a complete stop with foot on brakes: it requires a whole new level of finesse, so as not to get that minor whiplash sense that novice drivers go through when learning how to brake smoothly to a stop.

But hey - I have SERIOUS brakes now, better than ever, so I'm not complaining, at least not very loudly. I'll have a spare brake-light switch when it comes in, too...and probably a spare speed-sensor or two if I look around in my junk hard enough.

Thanks all for the contributions to my Decade of Diagnosis.

Dave
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Old 01-19-2018, 10:23 PM
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Glad you got it working. Your last post got me thinking, your steep driveway may have had a lot to do with your difficulty in successful bleeding. The air likes to rise to the top, and if the incline was making your bleeders that much lower than the master, it may very well have allowed a difficult bubble of air to have been trapped somewhere. I have experienced a difficult bleeding job or two, where raising the rear end of the vehicle on the hoist, to almost vertical, was necessary in getting the last bit of air out of the system. Just a thought.
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Old 01-20-2018, 09:11 PM
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Same problem, but - locking rear wheels was caused by leaking axle seals greasing the brake shoes and drums. I feel your pain. It's tempting to tape over the warning lights and forget them.
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Old 01-21-2018, 03:18 AM
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I had some vehicles with that "stickiness" on brake release you describe, and found that in some cases going to DOT 4 .SL6 brake fluid cured the problem.
.SL6 has about half the viscosity at cold temps than standard DOT3 or DOT4.
It is mainly used for vehicles with electronic stability control where quick filling of the pumps is important.
It is compatible and mixable with DOT3 and DOT4.

HTH

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Old 01-21-2018, 09:26 AM
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Originally Posted by DRam11 View Post
Same problem, but - locking rear wheels was caused by leaking axle seals greasing the brake shoes and drums.
Sigh. I prolly have that going on, too. Any visible evidence outside the drums, eg oozing oily stuff? My working facilities suck in the extreme, so even the notion of jacking it up (on a dirt slope that's only occasionally not soft & muddy) don't support my mechanical interest in getting eyes on it.
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Old 01-21-2018, 09:31 AM
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Originally Posted by AlpineRAM View Post
I had some vehicles with that "stickiness" on brake release you describe, and found that in some cases going to DOT 4 .SL6 brake fluid cured the problem.
.SL6 has about half the viscosity at cold temps than standard DOT3 or DOT4.
It is mainly used for vehicles with electronic stability control where quick filling of the pumps is important.
It is compatible and mixable with DOT3 and DOT4.

HTH

Markus
I actually swapped over to DOT 4 a couple of years back, not on any really sound basis, just the sense that it might be of higher quality and less hygroscopic than DOT 3. I don't think I really did my homework on that, though - something I'd picked up from a pre-internet-age buddy, so it might or might not be true. (I definitely didn't do it to winterize my truck, here in Honolulu...)
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Old 01-22-2018, 01:17 AM
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Well, in the cases where .SL6 spec did help it was because the fluid would get out of the brake cylinders quicker when releasing the brake.

Since you will have a bit of salt in the air, maybe you should check your calipers and the mechanics inside your drums for rust that makes them sticky.

Sometimes the front brake hoses degrade on the inside and swell shut, also delaying the release of the brakes.
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Old 01-23-2018, 02:05 AM
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Originally Posted by 'pants View Post
Sigh. I prolly have that going on, too. Any visible evidence outside the drums, eg oozing oily stuff? My working facilities suck in the extreme, so even the notion of jacking it up (on a dirt slope that's only occasionally not soft & muddy) don't support my mechanical interest in getting eyes on it.
That was so long ago I don't remember if there were external signs. It seems that the brakes grabbing created suspicion so I opened things up to look. It doesn't take much oily stuff on the shoes to cause the brakes to grab.
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