2nd Gen Non-Engine/Transmission Rear anti-lock brakes and oversized brake cylinders

[JGK]

A few months ago I replaced the brake cylinders in my rear drum brakes with the larger GM version from NAPA auto parts. A popular modification based on what I’d read in various forums. However, since then, I’ve noticed my rear brakes seem to want to lock up and skid during hard, panic stops. My truck supposedly has anti-lock rear brakes. There is a brake controller box near the master cylinder under the hood. The truck also has the rear proportioning valve for the brakes.



I’m thinking the new cylinders are not working correctly with the anti-lock system. Either the anti-lock has failed or needs adjusting, or perhaps the proportioning valve needs adjusting. No problems are indicated by any warning lights on the dash.



Has any one else done this mod and experienced this problem? Is there an easy way to test or check the anti-lock system? I haven’t looked, but I assume the proportioning valve can be adjusted. Has anyone done so?



Thanks,

-Jay

 

[CarlJensen]

Search the threads on brake cylinder replace. Some have come up with good data on readjust of the proportioning to help with the lock up problem.

 

[Tom W]

I just did mine last week and it will lock up on very hard stops. Overall I am very pleased with how it works, much less peddle pressure and you can tell the rears are helping to stop. I do have something that has me puzzeled. When slowing normally ( fairly light braking) I feel a severe pulsating from about 30mph to 10mph. I don't think it is the anti lock braking as it is slower, about once every wheel rotation. It is from the rear and the drums and shoes are new, and seems to go away if I press harder.

Anyone have any ideas?



I'm not sure if this would be a good mod for ice and snow.

 

[DEickhoff]

I, too have the same pulsating when braking from 30 to 10mph but mine seems to do it only when going down hill. My brakes are stock. Any ideas?

 

[JGK]

Carl,



I did the search using your suggested keywords. You weren't kidding about lots to read! Since I hadn't noticed much on this issue in any threads lately, and I've had limited success searching for data on some issues, I didn't do my "due diligence" with a proper search. I think I'll look into putting a turnbuckle on the rod to the valve to make it adjustable in length.



Tom,



Not sure what you're experiencing. Perhaps a drum out of round? Though that would be odd since they are new. Have you removed the drums and inspected them and the brake shoes for odd wear patterns? Also, double checked the installation? I agree that having the rears lock up on slippery roads would be no good. I have to figure out how to adjust mine so they won't lock.



I was under the impression there was some sort of sensor in the axle that the controller uses to detect lockup and modulates the brake line pressure to avoid skids. However, it appears that's not happening, or is not working correctly with the new oversized cylinders. Maybe the controller works in conjuction with the proportioning valve. In any case, something needs to be adjusted here.



Thanks,

-Jay



PS: Oh, now another with a pulsation! I'm wondering what you'd find if you jacked up the back end to get both rear wheels off the ground, then adjusted the brakes using the access hole on the back of the brakes to turn the star wheel until the shoes just started to contact the drum - spinning the tire as you did this to see if you find any "high spots".

 

[DEickhoff]

Thanks for the advice. I'll try that this weekend. Its just odd that it only happens when going downhill from 30 to 10mph. Can't seem to get it to do the same thing anywhere else.



Dawna

 

[y-knot]

The rear wheel brakes can be very much improved over stock my the addition of the use on larger wheel cylinders. The ones EGR sells are approximately 10% larger then stockers, and give the rear brakes the added pressure to make them feel as though they are now part of the overall system. Before, they never grabbed.

Your pulsating peddle is not caused by the addition of the rear wheel cylinders. Pulsating pedal is a function of drum or disk out of round. This can be caused by worn disk or drums, which may need to be turned or replaced. Sometimes drums or disk can be made out of round by installing the wheels and zigging down the lugs without slowly taking them down and using the proper torque sequence and method. This pulls the drum or disk down hard to one side and distorts the disk or drum surface. Loosening the wheels and re-tightening them in the proper sequence to the proper torque will help.

Finally, most people do not understand the rear wheel anti-loc braking system on the Dodge trucks. It matters not it you have 4wheel anti-loc or the more common rear wheel anti-loc braking system installed on your truck. The two systems are identical when it comes to the rear of the trucks. The system is not designed to prevent the rear wheels from locking up, instead it is designed to prevent both wheels from locking at the same time, their by allowing the driver to maintain control. The Rear Wheel Anti-Loc Brake (RWAL) control system uses a rear wheel Speed Sensor and Tone Wheel , and Rear brake Anti-Loc valve assembly to control brake fluid pressure to both rear wheels.

I do not know what type of system you have, I have the 4 wheel anti-loc braking system on my truck and I have not had a single incident where the rear wheels locked when they should not have. Further more, I have had nothing but improved braking force since the installation of the larger rear wheel cylinders. I have had to use the 4 wheel anti-loc system a few times, once with a heavy trailer in tow, and it functioned perfectly each time. Before you can say for sure there is a problem with the anti-loc brakes, you need to fix the pulsating pedal problem first. Good luck



PS, Most people do not know that the Controller Anti-Lock Brake (CAB) module is programed with the correct tire size for the vehicle when it leaves the factory. This module uses the Revelations per mile of that tire size to compare the signal being sent from the rear wheel speed sensor, for all of it's actions. If you changed tire sizes, this module must be re-set to reflect the new tire size, other wise the anti-loc braking system will not function properly.

 

[JGK]

... Finally, most people do not understand the rear wheel anti-loc braking system on the Dodge trucks. It matters not it you have 4wheel anti-loc or the more common rear wheel anti-loc braking system installed on your truck. The two systems are identical when it comes to the rear of the trucks. The system is not designed to prevent the rear wheels from locking up, instead it is designed to prevent both wheels from locking at the same time, their by allowing the driver to maintain control. The Rear Wheel Anti-Loc Brake (RWAL) control system uses a rear wheel Speed Sensor and Tone Wheel , and Rear brake Anti-Loc valve assembly to control brake fluid pressure to both rear wheels.



... PS, Most people do not know that the Controller Anti-Lock Brake (CAB) module is programed with the correct tire size for the vehicle when it leaves the factory. This module uses the Revelations per mile of that tire size to compare the signal being sent from the rear wheel speed sensor, for all of it's actions. If you changed tire sizes, this module must be re-set to reflect the new tire size, other wise the anti-loc braking system will not function properly.

You obviously have a pretty firm grasp of this system. Cool! I thought I'd read there was a sensor/tone wheel in the differential for the anti-lock system. But the tire size thing, and the fact that it wasn't designed to prevent wheel lock-up completely, is new. Though it tends to make sense given that it applies to the rear axle as a whole and not the individual wheels.



OK, so new question: How does one reset the CAB to adjust for my bigger tires, if that is possible?



Thanks,

- Jay

 

[y-knot]

It is pretty easy, only problem is you will need to have a scan tool to access the CAB module and input the correct wheel revolutions per minuet. My Mitchell manual has the procedure listed and even gives a chart showing the various rev's per minuet for the popular sizes, but the scan tool is needed. You can weightier get your own scan tool and access the CAB yourself or go to the dealer and have them do it. I know to do it yourself requires the initial outlay of several hundred dollars for the scan tool and supporting software, this might not be the route you take? But I can tell you that it would be money well spent, you would have the ability to diagnoses and fix your truck as well as others, and I still believe no-one is better equipped to care for and fix anyones truck like the owner. He is emotionally attached, and will take the time and care to do things right, at least that is how I feel. You know yourself better then anyone, so that is your judgment call. Good luck with your vehicles braking system.

 

[DEickhoff]

Thanks y-knot. Your knowledge of this system greater then my own. I will first try to re-torque the lug nuts first and see if it solves this frustrating problem.



thanks



dawna

 

[Tom W]

I am now thinking the pulsating on my truck is caused by the drums. I will get them checked Saturday. They were made in China. I'll let you know.

 

[y-knot]

I was looking at possibly selling truck parts on the side, in my search for suppliers I found that many, many, many parts are made in china and other Asian countries, as similar to "Cummins" brand stock replacement parts. While they look the part, I doubt very much if they have the quality control or material of the True Cummins replacement parts. Cummins is a brand of diesel engine manufacturer that is recognized and used around the world, consequently there are hoards of manufacturers that sell nothing but Cummins replacement parts. Not sure about the legalities of these parts or if Cummins cares about their copying and supplying replacement parts for many of the versions of Cummins diesel engines. My thought would be yes Cummins cares, but in certain International markets their is nothing they can do? Not sure. Does anyone else know? These parts are for the most parts what you see advertised a listed on E-bay. While they list mainly starters, alternators and the like, I found everything from complete engines to crankshafts to turbos. Any and everything Cummins makes seems to have been reproduced somewhere else for much less. Have any of you bought such parts?

 

[JGK]

y-knot,



Your point about buying a scanner so one can diagnose codes himself and so forth has a lot of merit. But for me, at this point, I can't justify the cost.



But I did call one of the local dealers this morning to see what they'd charge to reset the anti-lock brake module. $40. Says it will take about 45 minutes and will do it while I wait (maybe they'll let me watch!). Says it will also adjust the odometer and speedometer for the larger tires as well. Assuming they won't mess things up, this seems to me to be the best solution in my case.



Thanks for the info.



-Jay

 

[JGK]

Follow-up on ABS reflash

The dealer took only about 20 minutes to reset the rear ABS controller and they only charged me $28. I've stomped on the brakes only once or twice since and got no lock-ups. Just a slight noise that indicated the rears were close to sliding but not quite.



Yesterday I hauled 2 loads of rock bark - a ton each - and got on the brakes a bit hard to see how they reacted. Very predictable with no lock-up.



One thing, while I knew the bigger tires were changing my indicated speed by about 8% (read lower than I was actually traveling), I didn't realize just how bad I was exceeding posted limits. Now the speeds I normally drive are indicating I'm begging for a ticket! This re-flash should help me avoid that.



-Jay

 

[Tom W]

I had my new drums turned, said they only removed about . 006" but it fixed the pulsating problem. I really like how it stops now, not as good a 4 wheel discs but a whole lot better than when it was new.

 

[JGK]

Two fixes down, one to go...



Dawna?