1994 c/k 1500 2wd w/ rear abs bleeding

[mphmilkman]

I was hoping someone had the GM bleeding instructions for a 1994 chevy 1500 w/ rear abs. I have vaccumed 2 qts through the system after replacing hoses, master cillinder, adj brakes, etc with still having a spongy pedal. I bled the master per instructions as well as blocking off the bias pin in the proportioning valve. I assum the air to be trapped in the proportioning valve or the rear abs metering valves

[mphmilkman]

I think i have stumped the group here

[2000CAYukon]

Originally Posted by mphmilkman

I think i have stumped the group here

I have the 90 Factory Service Manuals (at home) and my 90 K1500 has rear ABS. I can post the procedure later tonight after the kids are in bed.

Having bleed my rear brakes recently (and a few times over the 17 years I have owned this truck), it is real important to adjust the rears to get a good pedal. You should feel some drag when you spin the drum. You should recheck the adjustment since the shoes may have shifted while bleeding. Also see how far the parking brake drops when you set the parking brake. If it goes to the floor, you probably do not have them adjusted enough.

The other thing that I would recommend getting a helper to pump the pedal instead of a vacuum pump (I have done it both ways but I have heard it is not good to use a vacuum for ABS vehicles - this may only apply to newer vehicles).

Have the helper pump 3 times and hold. Then open the bleeder making sure the helper holds until you close the bleeder.

You also want to start RR, LR, RF then LF for an order.

Let me know if you want me to post the directions out of the FSM.

//2000CAYukon

[2000CAYukon]

mphmilkman,
I got your email and here are the factory directions:

Manual Bleeding:
1) Fill the Master Cylinder and maintain the level during bleeding operation.
2) If air is suspected in the Master Cylinder bore, it must be bled first.
If bleeding the Master then do the following and Steps 3, 4 and 5.
- Remove the forward brake pipe connector (at the Master)
- All brake fluid to flow from the connector port
- Connect the brake pipe but do not tighten
3) Slowly depress the brake pedal allowing the air to bleed from the loose fitting.
- Tighten the fitting before releasing the pedal
- Wait 15 seconds, repeat including the 15 second wait until all air is purged.
4) Do the same for the rear pipe as defined in Steps 2
5) Do the same for rear pipe as defined in Step 3
6) Bleed in the Sequence: RR, LR, RF and LF for wheel cylinder and caliper bleeding for Steps 7 and 8
7) Attach a hose to the bleeder screw and immerse the other end of the hose in a condainer partially filled with clean brake fluid
8) Slowly depress the brake pedal one time and hold
- Loosen the bleeder screw to purge the air
- Tighten the bleeder screw and slowly release the pedal
- Wait 15 seconds and repeat Steps 7 and 8 until all of the air is purged
9) Continue to the next wheel in the sequence as outlined in 6
10) Bleed the Isolation/Dump Valve (Power Brakes only)
- Slowly depress the brake pedal one time
- Loosen the bleeder screw on the Isolation/Dump Valve
- Tighten the bleeder screw and slowly release the pedal
- Wait 15 seconds and repeat until air is purged from the valve
11) Check pedal for sponginess and Check if Brake Warning Lamp is illuminated indicating an unbalanced pressure. Repeat the entire bleeding procedure to correct either condition

On my 90, the Isolation Dump Valve is located under the master next to the combination valve. Hopefully, it is the same on your 94. Either way, you should be able to see a bleeder screw on it.

Hope this Helps!

//2000CAYukon

[maxwedge]

Also watch for the combo valve being stuck internally, I've had to manually pull out the bypass button on the end of the valve to bleed the rear, actually there is a clip expander tool to do this for you.