2nd Gen Non-Engine/Transmission ABS Function is Dangerous

[WrenchRat]

Please help me evaluate/solve this ABS problem. Let me preface by saying I have a tall camper shell and at least 500 lbs or more in the bed at all times. I run about 40psi in the back tires (dually)(except when towing/hvy load) and 65psi front. Tires are 255/85-16 Cooper ST's. Previous tires were Cooper AT 235's and before that the 215 factory issued Michelins. No real issues with the brakes when ABS is not activated. Computer has been corrected for tire size. (Being off as much as 10% never seemed to make a difference, just thought I'd mention it. ) Driving style is pretty easy does it and is decidedly NOT aggressive.

Whenever the rear wheels break traction (the least little bit) during braking, the entire brake system goes into a lower pedal/low pressure mode and the resulting braking force becomes fairly minimal. Subjectively maybe 50%. This happens with only modest braking force and the last time, it happened on DRY pavement and nearly caused me to roll through an intersection and hit someone. Very frequent occurrences on wet roads.

This has happened from DAY ONE. The dealer indicated this is 'normal' and no problems were found. No trouble codes. And the dealer refuses to give me any ideas on how to disable the ABS, which I can understand.

Interestingly the only time the brakes have worked without the slip-skid-soft pedal was when the rear ABS sensor failed. The ABS system was totally incapacitated and I had normal brakes. I was tempted to leave it alone. But being a stickler for keeping things correct, I fixed it. After replacing the sensor, the brake system went back to it's 'normal' operating condition.

I tried pulling the fuse for the ABS, but that kills the speedo/odo. So that's a no go. It seems obvious to me that the braking balance between front and rear needs to be more biased to the front. But of course there is no adjustment for this and I didn't want to add a control valve for fear of completely fouling up the poorly set up ABS system and possibly ending up with NO brakes at an inopportune moment.

I have had other trucks without ABS and a little skid on the rear axle was the 'indicator' to pulse the brakes. Just a little operator modulation and all is well. Never had an issue with this kind of system.

Is there a way to add a switch somewhere to turn the ABS system on/off? A TSB? Adding a flow restricting valve/orifice to the rear brake line(s) to bias towards the front?

Other ideas? Can't afford to guess on this one or experiment as equipment and family are at risk.

I'll add that I have driven several other vehicles (Pontiac, Honda, Chev, Caddy, etc) and model years with ABS and have never encountered an ABS system that acted this way.

Help please.

 

[sslechta]

This doesn't really give you helpful info but I have a '99 also and it behaves the same way. It's very unnerving when it happens! It you hit that little bump while braking and suddenly it feels like you have no brakes at all!

 

[Garlic]

My 96 had just the opposite issue, it was biased 90% to the front and the rear brakes did not work at all. The proportioning valve wound up being a part of the problem and as well as an engineering problem. The rear wheel cylinders were too small in diameter to put enough force on the shoes to be effective. On the SRW there was a bulliten on a fix that did not work real well. I don't know if this is of much help to you.

 

[WrenchRat]

Yep, sslechta, that's the issue. And yes, it is UNNERVING. I've gotten so I watch for pavement irregularities and sand/gravel/manhole covers/railroad tracks/pavement markers and momentarily relieve braking pressure so I don't trip the ABS into low pressure mode and effectively lose braking power. Once it trips, there is usually not enough time for release, reset, and reapply.

I gotta believe this is an issue that's been discussed here before, many times. I did a search, but so far have not found a solid answer. Maybe someone can point to a specific thread or three with specific info?

Seems several folks, particularly the RW only ABS only guys simply disconnected or eliminated the ABS system altogether and replumbed the brake system for conventional operation. I'm not quite to that point yet and frankly don't want to have to do that.

I'm thinking that some sort of rear to front rebiasing of the system could help make it function a bit more predictably and actually be somewhat useful in nasty weather as well as eliminate dry pavement hopscotch.

The other issue I have run into is while offroad. Going down very steep gravel inclines and using the brakes is a BAD idea as the system thinks I've lost control (well, not quite yet). I found the only way to traverse grades like that is to use Low range, the PacBrake, and an appropriate gear to match up with the desired PacBrake action to achieve the necessary 'anchor' effect without losing traction. All while using no service brakes. It actually works pretty good.

For now, I think I'll test things by disconnecting the rear ABS (as if it's bad) at the pigtail connection and see if speedo/odo gauges work. Not sure which speed sensor feeds them? (One of the front wheels?) It'll throw a trouble code and light the ABS lamp, but at least I'll know what's going on. If that works, I may just put a 'keyed' switch on the dash somewhere and label it off-road use only and maybe that will remove insurance liability. It might even be worth taking the ABS discount OFF of my insurance so that it is not a contractual issue. Friggin lawyers. Or just do the redneck thing and ignore the issue altogether. :-laf

 

[Gary - K7GLD]

I had the same problem with my '91 - washboard pavement at an intersection, or loose gravel would cause rear wheel hop and momentary loss of road contact, then what appeared to be total loss of rear wheel brakes - especially bad if carrying a load or towing!



I finally unplugged the rear wheel ABS sensor, and installed a fixed resistor across the leads to simulate the presence of the sensor - got the equivalent of a conventional no-ABS braking system, and all was MUCH better!

 

[WrenchRat]

Now we're talkin'. OK Gary, what was your electrical component set-up? Resistor size? Just match the ohm reading from the sensor? And did that keep the ABS lamp from lighting?



Thanks!

 

[WestTN]

The idea behind that system is that you press the pedal further down, utilizing more front brake and less rear brake. And the rears do reapply at a lesser force when you press down on the pedal. If they were reapplied at the previous rate, you could loose control of the rear when they are sliding. They were the best technology available at the time.

 

[WrenchRat]

That may be WestTN, but Chrysler executed the idea quite poorly in my opinion. There was better technology around (Caddy, Corvette, Pontiac for example), Chrysler just didn't want to pay for it, I'm guessing.



Trouble is they don't seem to modulate like higher end GM vehicles do, The Chrysler system just senses a slippage and goes into a low pressure mode. And that's all you get until release and reset. It is what it is, I'll just have to sort out something of a workaround...

 

[klaybus]

WrenchRat,

Here's a link. TSB 05-04-98



On my 99 I believe I lengthed the rod on the load sensing valve which simulates a heavy load. A word of caution should be mentioned..... If you go too far, your rear-end is liable to pass your frontend as the rears will lock up fast!



Clay

 

[Devil Black Diesel]

WrenchRat,



Welcome to the club. There's obviously a design flaw in our ABS systems and it's very dangerous... I have yet to find a fix for it. Removing the fuse cures the problem so I know it's the ABS system. But, it's just as dagnerous without ABS if you have to panic brake so I don't know what's worse... too much brake or brakes that give out on you when you need them most?



Hopefully someone will find a fix for this soon as it could take someone's life someday. Read this post:



https://www.turbodieselregister.com...ussions/170961-how-disconnect-abs-system.html

 

[JVackiner]

It happened to me twice with my '99. First time I hit a deer and the next I rolled through a T intersection, small trees (thank God) and a fence before I got it stopped. I unplugged the controller at the fenderwell and I at least know when I hit the brakes I will stop. Maybe this is a bit disconcerting to those who have only driven ABS controlled vehicles but for me, it is no different than all the pickups I drove before ABS. The only downside is the brake and ABS light on the dash. I have gotten used to that and will not risk an accident with the dangerous ABS system that Dodge put in their pickups and fail to recognize there is a problem.

 

[Gary - K7GLD]

Now we're talkin'. OK Gary, what was your electrical component set-up? Resistor size? Just match the ohm reading from the sensor? And did that keep the ABS lamp from lighting?



Thanks!

Yes, I measured the normal resistance of the ABS sensor, then just substituted a fixed resistor for it, a common 1 watt from Radio Shack will do - about 1800 ohms as I recall, but it's been a long time ago...



Be sure to thoroughly weatherproof all connections.



And again yes, that keeps the ABS light from lighting, and the brakes function FAR better, more controllable and predictable this way.



Good luck.

 

[WrenchRat]

Thanks for the replies gents. At least this does appear to be a design flaw that covers many trucks. I just hope no one is injured or worse because of this flaw. I'm rather surprised, given the severity of the problem, that Chrysler has not been called out for this by NTSB or some squirrelly civil suit. -With the idea being to FIX the problem. I'm guessing there has been and the suits were settled out of court and the root problem never got addressed. Ah well, glad I don't depend on goobermint or mouthpieces to solve my problems.



As for adjusting my load proportioning valve. Ah, sort of difficult as my '99 does not have such a critter. Just crawled under to verify and nothing in sight. Guess Chrysler saw fit to remove it since ABS was added. That might be a good thing to add? At least then I could drop the flow back a bit and shift the brake bias towards the front to keep the rears from skidding so quick.



Gary, at this point, I believe I'll run a trial test utilizing something along the lines of your solution. I'll drag out the VOM and check the resistance of the sensor. Your idea seems to be a viable solution to at least return the truck to predictable braking and keep the dash lamps out.



Seems like others here have adequate skills to sense slippage and modulate brakes in an E stop. I'm happy to go back to that. At least I'll regain control over an incorrectly programmed computer. A neat solution might be to buy another sensor, plug it in and tie it off out of the way? Hmmm. A bit more $ than a resistor, but a neat plug in solution.



In the meantime, I'll start asking around engineering circles to see if anyone has a lead on this issue. Somewhere, someone may know the right person... If I find anything, I'll post.

 

[2broke2smoke]

had a freind with similiar problems ...



he replaced the brake cylinders in the rear with the large gm pieces ...



lighter throttle would result in more rear braking ...



this may not help your situation but i thought i'd throw it out there ...



it made such a noticeable diff that i did it on mine when i swapped the dana 80 dually axle into mine

 

[WrenchRat]

2broke2smoke,

Actually, I have more than enough rear braking power. At this point, the brake bias is too heavy to the rear. If I were sitting in a dirt track/stock car with bias adjustment, I would 'dial in' a bit LESS flow to the rear. So if I were to add larger wheel cylinders, I would be getting even more braking power to the rear wheels, which is the opposite direction I need to go. Sounds like you guys with SRW had your own set of interesting problems.



Another consideration I have is to increase the braking power of the front brakes by increasing rotor diameter(best way) and/or adding better calipers. Given that this very likely means going to 17inch or larger rims and seven new tires:{, the idea has remained on the back burner and will likely stay there. I've done this on GM trucks and gotten considerable improvement in braking capacity.



I would entertain ideas for some better calipers for the front that would work with my factory steel 16inch rims.

 

[Steve St.Laurent]

This isn't just a problem with Dodge rear only ABS systems. My '94 GMC Sonoma did the exact same thing and I got into an accident with that because of it. Rear only ABS was a bad idea. For some reason my '98. 5 I've never had a problem with it happening and it has only rear wheel ABS - maybe I've just been lucky. On my Sonoma pulling the fuse disabled the ABS and the cruise control so I installed a switch on the hot lead coming out of the fuse panel so I could turn it on when I wanted to use the cruise. Then I pulled the bulb out of the dash for the ABS light so it wasn't in my face all the time.

 

[jkern]

i have had the same problem with my 99 ram AND my 01 durango... i have learned to live with it in my truck... but the durango always catches me off guard. i think we probably all have a "close call" story... mine was loaded with 4 adults, and some lugage and towing about 3500lbs. down hill thru a stoplight... thankfully no one was coming, i tried my hardest to get it stopped, but no way... even with the trailer brakes maxed out.