Avalanche brake failure

[Timtruck]

A friend of ours, not me, has an '02 Avalanche that has no brakes at all, he replaced the master cylinder, yes it was bled, but the pedal still goes to the floor and wont even pump up. No leaks anywhere either.
I bled the master cylinder for him and it had a good firm pedal then but, when the lines were connected, nothing, right to the floor, I'm stumped. Could it be the ABS, module, pump or sensors?

[95 S_Trucker]

Did you bleed at each wheel after the master cylinder replacement? Did you perform an automated bleed on the abs unit?

[rpmerf]

Not sure if this is the same / similar to my 97 Burb. There is an automated bleed that needs to be done on the ABS unit using a Tech II scan tool. An alternate way is to bleed it as good as you can, then try to lock the brakes on a dirt or gravel road. You might be able to try bleeding out the back of the ABS unit first before connecting the lines to the brakes.

[hatzie]

There are other scan tools that will initiate an automated bleed.
I've done the washboard road trick but it doesn't work as well as the scan tool, if at all, because it's not operating the ABS valves in sequence.

[Timtruck]

Ok, so a scan tool will be needed. this gets me on the right track, Thanks!

[izzy_Britton]

i fought my brakes with the same issue for a month. kept asking the same question and kept getting a funny responding question: "did you center the proportioning valve?"

i thought it was one of those funnies, like muffler bearing aand blinker fluid. ya know the kind?

anyways yes, a good scan tool should have something in the menu about an automated bleed or an abs bleed. it is a real thing and yes it will most likely fix your issue, as odd as it sounds. I have an old Solus II from snap-on and it was able to do this.

good luck. update us please. thank you.

[hatzie]

Originally Posted by izzy_Britton

i fought my brakes with the same issue for a month. kept asking the same question and kept getting a funny responding question: "did you center the proportioning valve?"

i thought it was one of those funnies, like muffler bearing aand blinker fluid. ya know the kind?

anyways yes, a good scan tool should have something in the menu about an automated bleed or an abs bleed. it is a real thing and yes it will most likely fix your issue, as odd as it sounds. I have an old Solus II from snap-on and it was able to do this.

good luck. update us please. thank you.

That's a valid question for folks that are used to working on antiques without ABS brakes.
On the older vehicles you remove the brake warning lamp switch from the combination valve and install a plug after you center the valve shuttle.