Strange brake problem with odd code

[RMecum]

After the truck has sat for a while, especially overnight, the brake pedal will feel like it travels a little lower than normal then the Brake & ABS lights come on. The brakes function normallly and if i shut the truck off and then start again the lights go out and all is fine. I took it to my favorite diesel shop and they checked for codes and found none... inspected the system and all looks o. k. It's been doing this for a couple months. I've been busy with a bunch of other stuff so I haven't driven it much. I needed it today and the lights were on so I stopped in at Big O tires and they checked and found code #78 "Foundation Brake Partial System Failure"



They've never seen that code and had no idea what it could mean. They did a visual inspection and checked the fluid, all good.



I had an EGR disc brake conversion put on a year ago and they work great. My diesel guy thought maybe some pressure difference caused by the disc brake set up might be causing some anomally. The Big O guys thought maybe there was something electrically that was intermittent.



When the lights are off there's no code.



I haven't found brake expert in Sacramento yet but I'm looking and anybody with any thoughts would be appreciated.

 

[JLandry]

Check out the attached excerpt from the Dodge Chassis Diagnostic Manual for some trouble shooting steps. Looks like it could be caused by one of the following items:



LOW FLUID LEVEL

BRAKE PRESSURE SWITCH SENSE CIRCUIT SHORTED TO GROUND

BRAKE PRESSURE SWITCH SHORTED TO GROUND

CAB (ABS Controller) - INTERNAL SHORT TO GROUND



Good luck,



John L.

 

[RMecum]

Thanks John! I really appreciate it. I knew someone on here would have some ideas.

I'll post when when the problem's solved.

Mike

 

[RMecum]

Still got the problem

I'm bringing this back up because I thought this was fixed TWICE and I'm still getting the lights (ABS & BRAKE). My diesel shop blead the brakes real good and it was O. K... . for a day or so.



So I took it to L. A. and while braking on exit from the freeway for a pit stop the ABS & BRAKE lights came on AGAIN! I went on to L. A. and took it to a Dodge dealer. They said it was the portioning valve and that the master cylinder needed replacing also.



$950. 00 later and on the way back to Sacramento they came on AGAIN... same deal... cruising for a while, braking/slowing as I applied the brakes and they came on.



When this happens the brake pedal goes a little farther than normal and the lights come on. Then after I stop the pedal is fine. The lights will go out after I shut the ignition off then on and as long I'm stopping and starting all is well. It only happens when the brakes have been left alone for a while... 20/30 mins or so. It's like they lose a preload or something. Maybe the boost is bad.



I don't know squat about this so I'm going to the dealer as my regular diesel shop doesn't want to mess with it.



Any ideas?



TIA... Mike

 

[JLandry]

Any ideas?

Hi Mike,



How frustrating!



If this were happening to my truck, I think at this point I'd be tempted to just go ahead and replace the entire ABS unit. If you check eBay, you'll usually find a good selection of new and used units available there. I think I've seen used units starting at around $75, and brand new units for only about $250.



If replacing the ABS unit doesn't solve the problem, then what else could it be but a wiring or wheel sensor problem? But usually when anything goes wrong with a wheel sensor you'll get a trouble code.



One more question:



When this happens, do you hear or feel anything different other than the brake pedal moving a little more than normal? Any buzzing sound heard or a possibly a rapid pulsing felt in the brake pedal?



Regards,



John L.

 

[RMecum]

Thanks John

I kind of firgure it's going to be replace the whole system before it's over. There's no other symptom other than the pedal travel being farther on the first application. Then it seems to pump up and return to normal and stays normal as long as there's no idle period. If it sits for a few hours or driven down the road for a while the problem occurs.



There are no noises or any pulsing/vibrating of the pedal. There is less braking on the first application... like maybe the rear brakes aren't coming on or something.



I wish there was a brake specialty shop that I could take it to that could test the system and upgrade or fix and make it perfect. I'm sure this is somehow related to the AGR disc brake conversion but I don't know enough about how this brake system works to be able to say for sure.



So I'm gonna be busy for the next few weeks... possibly for the all October and November (I'm back on active duty in the Air Force and I've gotta make hay while the sun shines!) so I'll get to this as I can and any thoughts you guys can throw in on this are GREATLY APPRECIATED!



Mike

 

[SSolderitch]

Pull the wire off the switch on the porportion valve and unscrew the switch. Check with a mirror if the groove is in the center of the hole. Depress the pedal a few times, check if still in center. If not the master cylinder is bad. You can also re-bleed the master cylinder, it may still have trapped air. Also did you jack up each wheel and see if they lock up when the pedal is depressed. That way your checking that the abs solenoids valves are closed.

PS: I changed the abs controller, didn't need a vin #, changed the wheel speed sensor only to find out it was my master cylinder.

 

[SPearson]

I don't know about the brakes on these trucks specifically, but on cars I've worked on in the past, this could be caused be a rear brake self-adjuster being stuck. If the brake adjuster(s) aren't adjusting properly, it takes more fluid to make the shoes travel out to the drum. When you hit the brake the first time it pushes the shoe out most of the way, they when you hit it a second time (pumping the brake) it sends more fluid out to the brake so it engages the drum. The lights come on because the first time you hit the brake it travels farther that it's supposed to so the lights are tripped. When the pedal is 'pumped up' then the brakes work normally. As you drive it on the highway without using the brakes, or let the truck sit, the fluid is pushed back to the master cylinder starting the process over. Just my 2 cents worth.

Stuart

 

[RMecum]

The dealer in southern california changed the portioning valve and the master cylinder already.



The truck is at Swift Dodge in Sacramento now. I don't do much myself any more so they're gonna figure in out I HOPE! They charged me $118. 00 to tell me they couldn't find anything wrong. When I threw a fit the service manager said he would take on the problem, drive the truck himself for a couple days and get to the bottom of it.



I'm in the Air Force and I'm not in the states at the moment and I'm hoping to either hear from the dealer while i'm on the road or have a fixed truck when in get back to California.



Mike



P. S. I'm hoping I can get something back for Moss Dodge in Moeno Valley since they didn't fix it... . that was almost a grand!

 

[drag racer]

Sorry for veering off-topic, but THANK YOU for your service to America!

 

[fest3er]

Brake pedal going farther than normal sure sounds like ABS is being engaged. This can happen when the CAB (Controller, Antilock Brake) detects a sudden change in wheel speed. Or thinks it does.



Post exactly the conditions when it happens: what you are doing at the time, how fast the vehicle is moving at the time, and any other 'odd' things you may notice at the time, like speedometer suddenly dropping to zero when you slow to below some speed. Also note if you have rear wheel anti-lock brakes, or all-wheel.



When my '98 was new-ish, every time I braked hard-ish on a washboard-like road, the rear ABS would engage, the brake pedal would suddenly drop to the floor a 1/4 inch or so, and most of the braking would vanish. I believe this was due to the rear axle hopping too much; KYB Gas-Ajust shocks (stiffer) solved this problem.



When I was playing with the Abbott speedo adjuster box, the ABS would engage every time the vehicle dropped under 10 MPH, because the speed sensor signal would vanish. Solving this problem involved making guaranteed solid electrical connections from the rear axle speed sensor into the CAB, and between the CAB and the PCM.



Later, during a drive between VA and the midwest, the CAB died, leaving me without speedometer/odometer for around 1000 miles. The new CAB, from Dodge, isn't exactly the right one; the ABS light has been flashing for, what, five years now; I don't even notice it any more driving. Flashing means the PCM can't set the default parameters in the CAB. Neither can the dealer. Well, duh. But ABS works OK, so I ain't worryin' 'bout it. )



I'd be willing to wager a dollar that the problem is somewhere from the wheel speed sensor(s) to the CAB, and possible including the CAB's ground and power supply. Put differently, I would almost guarantee that it is an electrical problem and not a mechanical problem. I would almost guarantee that the vehicle speed sensor voltage is dropping too low to be reliably detected by the CAB; if not that, then the CAB is failing. And the CAB is about the only thing that will cause the brake and ABS lights to come on during normal operation.

 

[ARARAR]

abs

Found this link in tdr issue thirty-one, might help. The ABS Education Alliance.

 

[RMecum]

Well I'm back home and picked my truck up yesterday. fest3er my problem is pretty well described in post's 1,4 & 6.



The latest is the dealer mechanics say they narrowed it down to the CAB, anti-lock brake brains. The main kick in the head is the part isn't going to be available until Dec 1st! Apparently when Chrysler was in bankruptcy they stopped paying their bills which caused many of the parts suppliers to go out of business. So now it's taking forever to get parts. When I had the trucked worked on in southern California they had to get the portioning valve from Milwaukee!



So I ordered the part. They assured me the truck is ok to drive just that when the ABS/Brake lights are on the ABS is not functioning. Like I've said all along the brakes are working great just these freeking lights keep coming on!



That's the update. I'll dredge this up again when/IF this fixes it.

 

[RMecum]

All brake systems are FMC!

That's Air Force talk that means fully mission capable. The ABS controller came in two months ahead of schedule and I had it installed when I came back from an Air Force trip last week.



Everything is back to normal... probably better since I have a new master cylinder, new portioning valve AND and new ABS controller.



I don't mind so much about the extra work because they did find the master cylinder and the portioning valve were bad. Just the journey to get it all fixed has been rather painfull to say the least.



At any rate, thanks to you guys who made suggestions. I wish I had time to do some of this stuff myself.



Mike

 

[rotohead]

Don't know if the OPer (RMecum) is still around but I'd be interested in hearing from him if he is if the ABS/Brake light problem he was fighting was fixed by replacing the ABS module? I'm having the same frustrating issue with my truck and I also have the EGR disc brake conversion on my rear. I've done about everything to fix this and have the same exact problem you described with your truck. And did you replace the ABS module electronics only or did you also replace the HCU and soleinoid body too? I'm also looking into the possibility the El Dorado calipers used on the conversion kit have somehow gone bad or out of adjustment. Seems the improper adjustment of the parking brake feature on those calipers can give a long brake pedal travel problem that could in turn activate the ABS/Brake light. I know this is a dated thread but it's the only one that explains almost all my issues to a T. Any input would be appreciated.

 

[rotohead]

Seems this owner has departed TDR. It's sad as I now know the reason for his ABS/Brake light issue and I'll explain here for anyone searching this problem. I had the same symptoms for three months. ABS/Brake light after a initially excessive long brake pedal travel. I could drive around very short distances and apply the brake or even pump the brake and no light. But if I drove about 5-6 miles and then apply brake to a stop the light would come on. Longer pedal travel then normal and could reset light by restarting truck. Also let truck sit overnight and same problem first run of the day. Replaced everything, BMC, combination valve, front hubs-calipers-pads-rotors, brake switch under the dash, ABS module repair, bled 20 times including bleeding the ABS module with a DRBIII scanner tool as per FSM instructions (code 78). It wasn't until I started looking at the calipers on the rear axle conversion from EGR that OP and I both had (no hate to EGR, this is a commonly used 1978 El Dorado caliper with parking brake feature) and that is where the problem is. It's said you must use the parking brake often to keep this caliper in adjustment. More to the point the calipers in the conversion kit have to be adjusted and kept that way for the base brake function to work correctly. If not the brake pedal will travel too far before activating the rear brakes and trigger the lights. Many youtube videos on how to properly adjust the rear calipers and isn't that difficult but must be done every install and the use the parking brake with regularity to maintain this. I have a feeling this OP got tired (and broke) from trying to fix this ABS light issue and sold the truck. I've spent over $1000 before I figured out the problem. I love this year of truck because it's a truck a owner can work on vs some of the newer models. Wish I could've imparted this knowledge on RMecum to help him out. Hopefully it will come in handy for someone else. I don't care to go through this ever again.

 

[rotohead]

Just to finish, the brakes with the EGR conversion kit work very well. I've towed over 77,000 miles and the improvement from drums is worth the conversion. Delete the proportion valve at the rear and it is a much more balanced braking front to rear. I did the GM cylinder upgrade with the drums and this is much better. Well worth the price and hassle. Just wish I was more educated on how these 1978 El Dorado calipers need to be adjusted. That IS something EGR could put on their web site and make the consumer experience better. Including making the parking brake feature function. It's not that hard...just need some consumer help.