Brake Combo Valve

[jor]

87 Suburban, Disc Front, Drum Rear

I finally got my brakes working properly after having replaced the combo valve and bleeding them with the little button pushed in. Does anyone have a trick for keeping the button in. I ended up wedging it with some wood wedges and a flat washer. Thanks.

Here's a photo of the original and its replacement with an arrow pointed to the button and another photo with a close up of the button.
jor

 

[dremu]

The FSM says to use special factory tool number J-1234567 or whatever.... or, it says, you can cut a slice in a piece of flat stock and bend or weld it, so it looks like this:

The piece sitting on the aluminum strip, if that's not obvious. Dimensions are given in the FSM but aren't critical -- I can go dig mine up if you need, but the width is 3/4-1"+, and the distance to the cut is given by where it sits (see below.) The bent end should be, I donno, 3/4"-1" or so as well, basically slightly shorter than the thickness of the valve body.

Loosen (don't remove) the bolt closest to the arrow, one of the two holding the valve onto the crossmember. Slide this piece onto the valve with the bolt fitting into the slot, until the welded/bent end presses against the button ... then push it in until the button is held in, and tighten the bolt. Voila.

If that doesn't make sense or you can't sort out measurements, LMK and I'll go dig the thing out and take some pix. I've mostly been bleeding my other truck (i.e. the one without the factory combo valve) so I've not had to use it in forever.

-- A

 

[jor]

Thanks, Dremu. I got it! And I'll rig up something similar. Great tip.
jor

 

[sunnyc123abc]

Whats that button for? I didn't know you need to have it pressed when you bleed your brakes.

 

[dremu]

Whats that button for? I didn't know you need to have it pressed when you bleed your brakes.

Part of the combo valve function is a pressure sensor, so that if one brake circuit (front or rear) has much less pressure than the other (i.e. due to leakage or other catastrophic hydraulic failure), that circuit is bypassed and the brake light in the dash comes on.

The push button resets the sliding mechanism. You'd do this while bleeding as it's possible, especially with manual bleeding (i.e. old school foot-on-the-pedal), to have one circuit open enough to look like a failure to the valve.

I've not always had to reset the thing, especially with the garden sprayer pressure bleeding I'm such a loud proponent of =)) ... but the FSM says to do it and with the right tool it's easy enough to do.

-- A