Brake bias on crewcab?
05-25-2017, 05:22 AM
#1
Brake bias on crewcab?
Is there a particular reason a crewcab would have brakes biased to the rear?
I recently changed out rotors and pads on the Denali. The rears were completely gone but the fronts had a good bit of life left. Since I bought the truck used, I do not know how many miles were on them. I noticed after bedding the new pads, the rear rotors had significantly more wear than the fronts as if thee rears are clamping harder. Now that they have been on for a while, the rears are dusting much heavier than the fronts. Doing a little searching on the web, I found a number of GMT900 crewcabs and Avalanches that have complained of wearing rears out faster than fronts but no conclusion as to why.
I recently changed out rotors and pads on the Denali. The rears were completely gone but the fronts had a good bit of life left. Since I bought the truck used, I do not know how many miles were on them. I noticed after bedding the new pads, the rear rotors had significantly more wear than the fronts as if thee rears are clamping harder. Now that they have been on for a while, the rears are dusting much heavier than the fronts. Doing a little searching on the web, I found a number of GMT900 crewcabs and Avalanches that have complained of wearing rears out faster than fronts but no conclusion as to why.
05-25-2017, 07:32 AM
#2
TECH Fanatic
My rear pads on my 08 denali always start squeaking way before the fronts are worn.
05-26-2017, 01:50 PM
#3
Anyone ever heard of this or have an opinion on it's validity?
I am not aware of any level sensors on the truck that could tell the EBCM that the truck is loaded. However, if there are, mine is lowerd and level so it could be a contributing factor in the increased rear bias. 
Just remembered the truck has hill assist braking so the EBCM does infact contribute to the braking circuit. Not sure about the rear height/load validity though.
Originally Posted by from another truck forum
Enjoy the new brakes! I verified the theory of EBCM controlling the rear brake bias by lowering my rear suspension setting cali style (simulating heavy tow load) and rear brakes would almost instantly lock up and trigger abs on hard brake. When I lifted the rear(hotrod rake) I could stand on the brakes on a hard brake and rears did not lock up. Pretty crazy how smart these vehicles have become.
Just remembered the truck has hill assist braking so the EBCM does infact contribute to the braking circuit. Not sure about the rear height/load validity though.
Last edited by BigKID; 05-26-2017 at 02:02 PM.
11-08-2017, 02:33 PM
#4
I'm not giving up on this. I just had the wheels off and rear pads are about half gone, fronts still look like new. I also had to scrub the brake dust off the rear wheels. 
Anywho... based on lots of reading, modern electronic brake force distribution (EDB) or Dynamic Rear Proportioning (DRP) as GM refers to it, is all controlled instantaneously thru the ABS system based on wheel slip. Here is an excerpt from GM's 1997 patent on DRP:
I cannot find anything validating the above claim that rear height contributes to rear brake bias in any way. I have read some philosophies on applying more force to the rear on initial and light braking to reduce nose dive and keep the vehicle more level. This makes sense to me in a truck that cannot incorporate anti-rise rear suspension geometry due to leaf springs. However this doesn't hold water for the Avalanches that have a 3-link rear suspension. I am thinking now it is simply a caliper volume/pad area issue. In the heavier Crew Cabs and Avalanches, the EBCM is not restricting the rear as much as in say a lighter RCSB this presenting 100% of the master cylinder force to both front and rear. By nature the single 54mm piston rear caliper with a smaller pad will apply sooner and exert more force to the rotor with the same displaced fluid volume as the dual 51mm piston front caliper. This now has me thinking a swap to the SUV dual 45mm piston caliper will help restore some balance to front/rear bias during light braking before DRP kicks in.
Anywho... based on lots of reading, modern electronic brake force distribution (EDB) or Dynamic Rear Proportioning (DRP) as GM refers to it, is all controlled instantaneously thru the ABS system based on wheel slip. Here is an excerpt from GM's 1997 patent on DRP:
In accordance with the present invention a dynamic rear proportioning (DRP) system is provided that is integrated with an existing vehicle anti-lock braking system (ABS), utilizing the sensors and control devices necessary for those systems. The DRP system utilizes the anti-lock braking system to perform the function of the rear brake pressure proportioning. The rear brake hydraulic channel(s) can be isolated from the master cylinder by activating the rear isolation valves, provided in the ABS. DRP provides the optimum brake force balance, regardless of vehicle loading, without the use of a load sensing mechanism. The system monitors wheel speed and estimates vehicle and wheel deceleration, vehicle speed, and lateral acceleration as well as the rear wheel slip to dynamically control the rear brake force. By continually updating these control parameters, the system can further increase or decrease the rear brake pressure to maintain the optimum brake force balance throughout the braking maneuver. If the braking conditions change, the pressure can be increased incrementally by pulsing the isolation valve(s). As conditions permit, the pressure can be increased to a maximum pressure equal to that of the front channels (or master cylinder pressure). Since the only system activity is the shuttling of the solenoids, there is no perceptible change in the pedal feel and no discernable noise during DRP control. There are numerous benefits to such a system. The need for rear proportioning hydraulic components is eliminated, saving cost and weight. Brake force is more evenly distributed, optimizing vehicle stability, adhesion utilization, lining wear and temperature stress.
I cannot find anything validating the above claim that rear height contributes to rear brake bias in any way. I have read some philosophies on applying more force to the rear on initial and light braking to reduce nose dive and keep the vehicle more level. This makes sense to me in a truck that cannot incorporate anti-rise rear suspension geometry due to leaf springs. However this doesn't hold water for the Avalanches that have a 3-link rear suspension. I am thinking now it is simply a caliper volume/pad area issue. In the heavier Crew Cabs and Avalanches, the EBCM is not restricting the rear as much as in say a lighter RCSB this presenting 100% of the master cylinder force to both front and rear. By nature the single 54mm piston rear caliper with a smaller pad will apply sooner and exert more force to the rotor with the same displaced fluid volume as the dual 51mm piston front caliper. This now has me thinking a swap to the SUV dual 45mm piston caliper will help restore some balance to front/rear bias during light braking before DRP kicks in.
