97GMC kelsey hayes ABS rear brake bleeding

[topaz250]

blew out a rear wheel cylinder, replaced, can't bleed rear brakes.

done it may times old school without ABS, no issues.

what's the secret?

 

TIA

[BasketCaseSensitive]

blew out a rear wheel cylinder, replaced, can't bleed rear brakes.

done it may times old school without ABS, no issues.

what's the secret?

 

TIA

This is copywrited material that I brazenly robbed from another website.

 

KELSEY-HAYES 4WAL BLEEDING PROCEDURE

Brakes can be bled in the usual way manually or with pressure or vacuum equipment. The wheel bleeding sequence is RR, LR, RF, LF. If a pressure bleeder is used, the combination valve must be held open.

If the EHCU Modulator or accumulator have been replaced, or air has entered the ABS part of the system, the EHCU modulator will have to be bled using one of two special procedures:

The preferred method is to cycle the ABS system using a factory scan tool or an aftermarket pro-level scan tool that has bi-directional capabilities so it can access the ABS system and cycle the pump and solenoids. A basic DIY scan tool that only reads codes and sensor data cannot do this.

If you can't get your hands on the proper scan tool, you can use the following manual bleeding procedure:

1. First, bleed the entire brake system using a pressure bleeder or vacuum bleeder. Pumping the brake pedal also works but must be done carefully so air doesn't siphon back into the lines. Bleed the wheels in this order: Right Rear, Left Rear, Right Front, Left Front.

2. Once all the air is out of the master cylinder and brake lines (no bubbles in the clear plastic bleeder hose you have attached to each of the calipers or wheel cylinders), you can proceed to bleeding the ABS system.

3. Open the internal bleed screws on the modulator one quarter to a half-turn. These are the cap screws on either side of the modulator. Note: Some newer 4WAL systems do NOT have these bleed screws so you must use a scan tool to bleed the system or try loosening the brake lines to the modulator to vent air.

4. Connect special tools (such as Kent-Moore No. J39177) to hold open the high-pressure accumulator bleed valves.

5. Open the two bleeder screws at the BPMV and bleed the unit by forcing fluid through it with a pressure bleeder or by slowly pumping the brake pedal. Do NOT allow the master cylinder reservoir to run low (add brake fluid as needed during this procedure).

6. Bleed the wheels again as before: RR, LR, RF, LF

7. Tighten the modulator bleed screws and remove the tools from the high-pressure accumulators.

8. Turn the ignition on and start the engine. Press down firmly on the brake pedal several times. If the pedal does not feel firm, turn the engine off, pump the pedal to relieve residual pressure in the system, and bleed each of the four brakes as before to get rid of any air in the system.

It's a pain to go through all of these steps, but if you do not and air is trapped in the ABS unit (or pump on applications that have a pump), it will eventually get into the lines and give you a soft pedal.

 

 

 

 

In other words, if you're doing this in your driveway and it's cold outside, welcome to hell.

[topaz250]

thanks, i guess air must have got into the abs controller.

just couldn't bleed the brakes and brakes were non existent.

doesn't seem safe, one blown out wheel cylinder takes out the whole system.

 

i ended up taking it into GM, all good now.

 

moral of the story, do your best to make sure air doesn't get into the abs controller or you're fubared.

Edited December 21, 2014 by topaz250

[BasketCaseSensitive]

thanks, i guess air must have got into the abs controller.

just couldn't bleed the brakes and brakes were non existent.

doesn't seem safe, one blown out wheel cylinder takes out the whole system.

 

i ended up taking it into GM, all good now.

 

moral of the story, do your best to make sure air doesn't get into the abs controller or you're fubared.

You'll be thrilled to know that on some cars now, you have to attach a computer to the car to retract the caliper pistons so the brake pads can be changed. 

[pomoco]

Its not that complicated. The combination valve next to the master cylinder will close off either the front or rear lines if it senses a leak. So if you pump fluid out the rear lines (or it leaks out) the valve closes those lines to keep the other brakes working. When you bleed them, you take fluid from the other end of the car to move the valve toward the other end. That is why there is a sequence. As you bleed the rear, the valve moves to shut off the rear line. Then you bleed the front and the valve moves towards the front.

[topaz250]

Its not that complicated. The combination valve next to the master cylinder will close off either the front or rear lines if it senses a leak. So if you pump fluid out the rear lines (or it leaks out) the valve closes those lines to keep the other brakes working.

 

I had zero brakes. never touched the front. Master cylinder ran dry, just the front compartment.

No issues with the brakes prior to wheel cylinder blowing out.

 

GM replaced the master cylinder and power bleed the brakes. If it happens again, i'll give your instructions a whirl, 1st, thx.