I'm having some issues with the rear brakes on my 2001. It's a 2500 lifted 4.5". I've looked ata manual but it doesn't say anything about how the rear antilocks work. When I was replacing shocks this weekend (love the Bilsteins!!!) I noticed there is a 'rod' that connects to the drivers side lower shock mount and goes up to the brake lines. I was thinking this is what works the rear abs buy limiting the fluid when the rear of the truck is lifted under heavy braking. If so, could it be that when the previous owner had the lift installed and extension for this device was not installed causing the rear brake to not work at all?

If someone has a better manual that describes the rear abs system, could you maybe scan a couple of pages and send them to me at shcermak at yahoo.com ?? I'd appreciate any help you guys have!

 

actualy what you are looking at is the rear brake proportioning valve. what it does is allow more or less pressure to teh rear tires depending on load. the ABS system still works all 4 tires from the module under the hood.

 

DESCRIPTION The antilock brake system (ABS) is an electronically operated, all wheel brake control system. 2500 and 3500 vehicles have Electronic Brake Distribution (EBD) designed into the systen which eliminates the combination/proportioning valve. The system is designed to prevent wheel lockup and maintain steering control during periods of high wheel slip when braking. Preventing lockup is accomplished by modulating fluid pressure to the wheel brake units. The hydraulic system is a three channel design. The front wheel brakes are controlled individually and the rear wheel brakes in tandem. The ABS electrical system is separate from other electrical circuits in the vehicle. A specially programmed controller antilock brake unit operates the system components. ABS system major components include: [ul][*]Controller Antilock Brakes (CAB)[*]Hydraulic Control Unit (HCU)[*]Wheel Speed Sensors (WSS)[*]ABS Warning Light[/ul]
OPERATION Battery voltage is supplied to the CAB when a speed of 15 miles per hour is reached. The CAB performs a system initialization procedure at this point. Initialization consists of a static and dynamic self check of system electrical components. The static and dynamic checks occurs at ignition start up. During the dynamic check, the CAB briefly cycles the pump and solenoids to verify operation. An audible noise may be heard during this self check. This noise should be considered normal. If an ABS component exhibits a fault during initialization, the CAB illuminates the amber warning light and registers a fault code in the microprocessor memory. The CAB monitors wheel speed sensor inputs continuously while the vehicle is in motion. However, the CAB will not activate any ABS components as long as sensor inputs indicate normal braking. During normal braking, the master cylinder, power booster and wheel brake units all function as they would in a vehicle without ABS. The HCU components are not activated. The purpose of the antilock system is to prevent wheel lockup during periods of high wheel slip. Preventing lockup helps maintain vehicle braking action and steering control. The antilock CAB activates the system whenever sensor signals indicate periods of wheel slip. Periods of wheel slip occur when brake stops involve high pedal pressure and rate of vehicle deceleration. The antilock system prevents lockup during a wheel slip condition by modulating fluid apply pressure to the wheel brake units. Brake fluid apply pressure is modulated according to wheel speed, degree of slip and rate of deceleration. Sensors at each front wheel convert wheel speed into electrical signals. These signals are transmitted to the CAB for processing and determination of wheel slip and deceleration rate. The ABS system has three fluid pressure control channels. The front brakes are controlled separately and the rear brakes in tandem. A speed sensor input signal indicating a wheel slip condition activates the CAB antilock program. There are Two solenoid valves (Isolation and Dump valve) which are used in each antilock control channel. The valves are all located within the HCU valve body and work in pairs to either increase, hold, or decrease apply pressure as needed in the individual control channels. During an ABS stop the ISO valve actuates, Stopping anymore pressure build —up to the calipers. Then the Dump valve dumps off pressure until the wheel unlocks. This will continue until the wheels quit slipping altogether.


Not sure that this is of help... But I can get any more info that you need.....DAVID

 

Ok, so I was close. So if the tail of the truck is lifted then the lever here will not allow as much fluid to the rear brakes letting them spin freely?

What's happening is if it is slightly wet out I can press the pedal all the way down, the front will all but lock and the rear just keep spinning. Do you think in an attemp to test it I should unhook the connecting rod?

Part/Service- Wow! That's way more info than I think I could have ever guessed would be out there for a brake system.

Thanks for the help so far!

 

if a lift kit was installed there should have been another arm to put in its place. past that, I'm not sure of the geometry or proper placement of that arm.

 

Drew- I would bet the lever has not been adjusted correctly. I'm going to try and find a truck here locally that I can look at and take some measurements from. If I have to I'll make my own.