I'm a new user. I came here by googling for GMT400 ABS delete" and found this interesting thread:
https://www.gmt400.com/threads/1990-c1500-abs-rwal-removal.11427/
After reading that I came up with a few questions so I thought I'd ask for some help from the experts here.
My questions are about a 1999 K2500 Suburban 7.4 that was built on the GMT400 chassis. My 99 Suburban was the last year to be built on the GMT400 platform even though the last year for the pickups was 98. I hope my post isn't out of place.
Although my K2500 is commonly referred to as the "3/4 ton Suburban" it is supposedly built on a frame derived from the K3500 truck and has the K3500's 1-ton chassis, suspension and brakes. For this reason some of us refer to it as the "1-ton Suburban." It has the 8600 lb GVWR and the JD7 brakes.
My 4WAL ABS is shot. It's got an internal derangement such that it won't produce fluid when pressure-bled and it needs to be replaced. I can't find a replacement. I'm thinking about removing the 4WAL setup and going back to a plain-jane multi-function valve setup like you'd find in the pre-ABS trucks.
I would like to avoid a discussion on the pros/cons of deleting an ABS system. My ABS has been non-functional for a long time and I've been getting by on foundation brakes. Due to a recent line rupture my MC rear reservoir ran dry and my ABS controller developed an internal derangement such that now it won't even produce fluid at the rear exit line when pressure bled. The foundation brakes can't even be made stable. My only options are a complete replacement of the ABS system or to delete the complete ABS system and move back to traditional brakes. Replacing the ABS system is not an option for several reasons: 1) I can't find parts for my VIN; 2) ABS sensors are chronically misfiring the system due to rust flakes from front caliper/pad changes; and 3) I can't get the front hubs off due to rust ... even with fire & impacts. My only option to change the hub would be to remove the whole spindle assembly and take it to a machine shop. I don't have time to mess with this due to an emissions testing deadline next week.
For reasons (2) and (3) the ABS was constantly firing at low speeds when coming to a stop. The 50A fuse has been pulled and I've been using foundation braking. The coup de grace for this ABS unit was a recent rear line rupture that caused the master to run dry. Although the truck now has completely new lines I can't get any fluid to exude from the 4WAL rear line when pressure bleeding at 35 PSI with a Branick 300 due to some sort of internal derangement in the 4WAL. Even if I replaced the 4WAL, the ABS still would not function properly due to the sensor problems mentioned previously. The ABS has got to go.
To further complicate matters the truck is an early OBD-II vehicle that has the combined powertrain control module and ABS computer. I think the system is called a VCM.
I want to completely delete the 4WAL system, replacing it with a new master cylinder, new multi-function valve, and completely new lines. (The lines are already in.) I want a rock hard pedal. If necessary I'll consider a Wilwood 260-11179 adjustable proportioning valve because this truck has always had very poor rear wheel braking due to an 85/15 front/rear bias.
https://www.wilwood.com/MasterCylinders/MasterCylinderProd?itemno=260-11179
So here are my questions:
1. What happens if I unplug all of the electrical connectors going to the 4WAL unit? Will that generate error codes and dash lights when the 4WAL is gone?
2. Is the fact that the powertrain control module and ABS controller are both situated in the VCM going to cause problems if I delete the 4WAL and tape off it's connectors? I guess what I'm really asking is whether the powertrain control module and the ABS controller are integrated to the point that unplugging the ABS controller will alter or adversely impact the function of the powertrain control module. I don't want to delete my ABS and have a powertrain controller that refuses to work.
3. What effect will deletion of the 4WAL have on my brake lights (stop lamps at rear end of vehicle). I need to know how the stop lights are triggered on this vehicle, and whether they are mechanically triggered or whether they are triggered by a pressure sensor in the 4WAL. I'm hoping that the stop lights are triggered by a mechanical switch on the pedal , rather than by a hydraulic pressure switch in the 4WAL/VCM system, so that ABS deletion doesn't cause my stop lights to stop working and create a new problem for me.
4. I don't have a schematic for the brake system electrical wiring. If anyone can help with that, or a real GM service manual, I'd appreciate it.
Thanks.
https://www.gmt400.com/threads/1990-c1500-abs-rwal-removal.11427/
After reading that I came up with a few questions so I thought I'd ask for some help from the experts here.
My questions are about a 1999 K2500 Suburban 7.4 that was built on the GMT400 chassis. My 99 Suburban was the last year to be built on the GMT400 platform even though the last year for the pickups was 98. I hope my post isn't out of place.
Although my K2500 is commonly referred to as the "3/4 ton Suburban" it is supposedly built on a frame derived from the K3500 truck and has the K3500's 1-ton chassis, suspension and brakes. For this reason some of us refer to it as the "1-ton Suburban." It has the 8600 lb GVWR and the JD7 brakes.
My 4WAL ABS is shot. It's got an internal derangement such that it won't produce fluid when pressure-bled and it needs to be replaced. I can't find a replacement. I'm thinking about removing the 4WAL setup and going back to a plain-jane multi-function valve setup like you'd find in the pre-ABS trucks.
I would like to avoid a discussion on the pros/cons of deleting an ABS system. My ABS has been non-functional for a long time and I've been getting by on foundation brakes. Due to a recent line rupture my MC rear reservoir ran dry and my ABS controller developed an internal derangement such that now it won't even produce fluid at the rear exit line when pressure bled. The foundation brakes can't even be made stable. My only options are a complete replacement of the ABS system or to delete the complete ABS system and move back to traditional brakes. Replacing the ABS system is not an option for several reasons: 1) I can't find parts for my VIN; 2) ABS sensors are chronically misfiring the system due to rust flakes from front caliper/pad changes; and 3) I can't get the front hubs off due to rust ... even with fire & impacts. My only option to change the hub would be to remove the whole spindle assembly and take it to a machine shop. I don't have time to mess with this due to an emissions testing deadline next week.
For reasons (2) and (3) the ABS was constantly firing at low speeds when coming to a stop. The 50A fuse has been pulled and I've been using foundation braking. The coup de grace for this ABS unit was a recent rear line rupture that caused the master to run dry. Although the truck now has completely new lines I can't get any fluid to exude from the 4WAL rear line when pressure bleeding at 35 PSI with a Branick 300 due to some sort of internal derangement in the 4WAL. Even if I replaced the 4WAL, the ABS still would not function properly due to the sensor problems mentioned previously. The ABS has got to go.
To further complicate matters the truck is an early OBD-II vehicle that has the combined powertrain control module and ABS computer. I think the system is called a VCM.
I want to completely delete the 4WAL system, replacing it with a new master cylinder, new multi-function valve, and completely new lines. (The lines are already in.) I want a rock hard pedal. If necessary I'll consider a Wilwood 260-11179 adjustable proportioning valve because this truck has always had very poor rear wheel braking due to an 85/15 front/rear bias.
https://www.wilwood.com/MasterCylinders/MasterCylinderProd?itemno=260-11179
So here are my questions:
1. What happens if I unplug all of the electrical connectors going to the 4WAL unit? Will that generate error codes and dash lights when the 4WAL is gone?
2. Is the fact that the powertrain control module and ABS controller are both situated in the VCM going to cause problems if I delete the 4WAL and tape off it's connectors? I guess what I'm really asking is whether the powertrain control module and the ABS controller are integrated to the point that unplugging the ABS controller will alter or adversely impact the function of the powertrain control module. I don't want to delete my ABS and have a powertrain controller that refuses to work.
3. What effect will deletion of the 4WAL have on my brake lights (stop lamps at rear end of vehicle). I need to know how the stop lights are triggered on this vehicle, and whether they are mechanically triggered or whether they are triggered by a pressure sensor in the 4WAL. I'm hoping that the stop lights are triggered by a mechanical switch on the pedal , rather than by a hydraulic pressure switch in the 4WAL/VCM system, so that ABS deletion doesn't cause my stop lights to stop working and create a new problem for me.
4. I don't have a schematic for the brake system electrical wiring. If anyone can help with that, or a real GM service manual, I'd appreciate it.
Thanks.
