ABS pump and solenoid pack replacement

ah yes.....the GM Training Center.....been there many times, right next to the GM headquarters here in Warren Mi

Least your local is still there. They closed the DC training center a few years ago. Heck, for that matter, both the Buick dealers I worked at closed up shop even before the en masse recent purge.

Rickw wrote:

Nigel,
For what you are doing, I have found that a lengthy gravity bleed will work the best initially and sometimes be adequate for a complete bleed.
If after an hour or two of gravity bleeding doesn't give you the firm pedal you are looking for then do a two person bleed starting from the bleeder screw furthest away from the master cylinder reservoir and work your way toward the master cylinder.
i.e. LR, RR,RF then LF.
If after all this, the pedal is still soft then a simple, but good quality vacuum bleeder that attaches to the bleeder screws themselves will draw the air and fluid out of the hard to get places.
Remember if you are trying to use a Dot 4 or 5 Synthetic fluid you may have bleed the system then return the next day and bleed again. Something with the synthetics that they have a tendency to produce very small air bubbles that attach themselves to the internal lines and hoses and need time to find there way up to the master cylinder reservoir.
If this is what you are using (Dot4 or 5) synthetic and you can not get a firm pedal after a couple of days due to the lack of proper equipment, then just use DOT 3 and the process should go smoother.

wouldn't it be better to do a pressure bleed?

Albertj

Scott (Abaddon), I'm trying to come up with a plan for a brake line lock using the OEM abs/tcs equipment since it does look like the valves are a simple solenoid type that just need to be energized to function. I'm looking in my FSM and from what it says, there's inlet valves that are normally open and outlet valves that are normally closed for each wheel and then isolation valves for the front wheels for tcs only. I know I cannot use those isolation valves because they are overridden by manual brake application so I'm trying to figure out if it's better to energize - close the inlet valves for the front wheels to be cut off from the brake pedal or, instead, energize - open the outlet valves to that fluid is [and now I'm assuming] recirculated back making no pressure and thus disabling the front brakes which gets me to the same place. I'm not sure about what exactly makes more sense from a hydraulic standpoint but I'm leaning towards cutting off the inlet valves for the line lock. The next thing is to try to test it out when I get some time but do you have input on this whole thing with your experience? Or anyone else of course

Well, you're right about the simple solenoid part. However, they are energized based on a couple of different inputs. Without trying to explain it all, here's what GM says.....

The traction control system is designed in order to maintain traction and reduce wheel slip at the front drive wheels on slippery surfaces during acceleration. The system is designed in order to operate at all vehicle temperatures. The traction control system reduces wheel slip by the use of engine torque management and brake intervention.

The electronic brake (and traction) control module (EBCM/EBTCM) monitors the front and the rear wheel speeds through the wheel speed sensors.

If the EBCM/EBTCM detects front wheel slip at any time during acceleration, the EBCM/EBTCM will request the PCM to bring excess engine torque into a specific range. This is accomplished via two high speed pulse width modulated (PWM) circuits between the EBCM/EBTCM and the PCM.

The PCM will then adjust the spark firing angle and the engine fueling. The PCM will report the modified torque value back to the EBCM/EBTCM.

At the same time, the EBCM/EBTCM will complete the following actions:

•Energize the BPMV isolation valves.
•Turn ON the BPMV pump motor.
•Apply brake pressure to the over-spinning wheels.
The isolation valves isolate the front brake hydraulic circuits from the master cylinder and the rear brake hydraulic circuits. Once the front brake hydraulic circuits are isolated, pressure can be applied to the front wheels without affecting any other brake hydraulic circuit. The EBCM/EBTCM turns ON the BPMV pump motor in order to apply pressure. The EBCM/EBTCM begins cycling the BPMV's inlet and outlet valves.

The inlet and the outlet valve cyclings aid in obtaining the maximum road surface traction in the same manner as the antilock braking mode. The difference between traction control mode and antilock braking is indicated in the following list:

•Traction Control Mode — The brake fluid pressure is increased in order to lessen wheel spin.
•Antilock Braking Mode — The brake fluid pressure is reduced in order to allow greater wheel spin.
There are two pressure relief valves in the BPMV. This is because the BPMV pump motor supplies more brake fluid volume than required during traction control modes. The pressure relief valves allow excess brake fluid volume to be returned to the master cylinder reservoir.

If the brakes are manually applied at any time during the traction control mode, the BPMV pressure switch and the brake switch signal the EBTCM. The EBTCM disables traction control and allows manual braking.

Manual braking also overrides the traction control system through the use of the isolation valves. The isolation valves act as one way check valves. This allows manual brake fluid pressure to be applied to the brake hydraulic system.

It would be awesome if you could electrically energize the isolators and use them as a line-lock, but I fear that doing so would result in an ABS light and a TCS light, accompanied by some codes, and as most of us know, a disabled ABS/TCS system. I don't think there's a feasible way to fool the logic.
However, I think that if you install/tap into the brake lines nearest each front wheel, creating your own "isolators", you could pull off the line lock. I think that you'd just have to make sure that the TCS is disabled before you go ahead and lock the lines up. You'd have zero wheel speed to interfere with the ABS, and the TCS is disabled. The system wouldn't be monitoring really anything at that point. Torque it up, release the lock, and all is well. It may or may not throw some sort of BPMV pressure code though. I'm not really sure. There are so many things being monitored......

Linelock? On an FWD car? Why don't you just use the ebrake pedal? I pump it on at staging, then press and hold in 'release' but don't let off yet, use the right foot to heat up tires, and release the ebrake pedal as I desire.

BTW unless you have some really sticky tires, locking the rear tires doesn't work all that well anyway. They'll just drag along once the front really starts to pull.

That's exactly what my fsm has in it as well. I'm not terribly worried about the electronics portion of it yet. I can play with that after I see what it does but the worst it can really do is fail the abs as soon as i meet the selftest criteria which doesn't matter at the track.

Derek I haven't had a functional parking brake in a few years. Unfortunately the cables and everything all seized up gradually. I don't see any practical way to fix it. I want to be able to do a solid stage though so i can pull off some serious passes

Here's an idea. If you wanted to totally get rid of ABS and TCS on your car, you could pop open the ABS Module on the BPMV itself and try to find which wires excite the Isolator valves. If you find them, we could completely bypass the BPMV's normal function. By doing this, and adding an external switch to power the Isolators, you could apply the brakes hard while sitting still, and turn on the Isolators. I believe this would lock the pressures in place hence locking the front brakes. As long as you took your foot off the brake pedal, as soon as you turned the power switch off, line pressures would return to normal.
I talked to 2 of the senior guys in the shop about it last night while we were washing up. All of us agree that that'd probably be the only way to do it electrically utilizing what's there, but it would disable normal TCS and ABS functions....