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Ask GM Tech (Cam) Your Own Question

GM Tech (Cam)
GM Tech (Cam), GMC Mechanic
Category: GM
Satisfied Customers: 27661
Experience:  GM Grand Master Technician 2007. 11 years experience.
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04 GMC Sierra 2500 HD: brake lines..proportioning valve reset

Resolved Question:

'04 GMC Sierra 2500 HD, brake lines replaced, how is the proportioning valve reset, where on the unit is the reset access?
Submitted: 2 years ago.
Category: GM
Expert:  GM Tech (Cam) replied 2 years ago.

GM Tech (Cam) :

Hello, I'm Cam. Please include all the details about your issue so I can accurately advise you. I cannot see your vehicle so please be detailed.

GM Tech (Cam) :

There is no stand alone proportioning valve on this.

GM Tech (Cam) :

It uses the ABS to do that.

GM Tech (Cam) :

so bleeding through the abs unit can be tricky.

Customer:

While towing my boat I lost a brake line, rusted thru, towed truck home and bought pre bent stainless brake line kit for entire truck as the others were abourt to go. Replaced lines except rear as they were in good shape, tried to bleed calipers but can't get fluid to lft fron or right rear, I was told proporting valve has to be reset.

GM Tech (Cam) :

Did you bench bleed the master cylinder again?

Customer:

No, it wasn't removed

GM Tech (Cam) :

Also of you got fluid to the one rear, it may be a line issue to the other rear since there is a single line to the rear.

Customer:

actually I'm not sure if the rears are getting fluid, I bled them & only got the old fluid out, could tell by color

GM Tech (Cam) :

OK, do you have acess to a pressure bleeder?

Customer:

Road tested yesterday, pedal feels as if no power brakes and the left front locks up on brake application.

Customer:

No, vacuum bleeder

GM Tech (Cam) :

OK, try this, it make take a bit but I am thinking you can rig it up. Can you fill the master then some how put no more than 30 psi into the top ofcompressed air.

GM Tech (Cam) :

then bleed that way.

Customer:

That's gonna be difficult, why can't I get fluid out of the right front?

GM Tech (Cam) :

Because air is stuck in the lines and liekly the abs assembly.

GM Tech (Cam) :

the pressure will push it through.

Customer:

When I crack the lines from the master at the proportioing valve I get fluid by gravity but its not getting to the wheels. What if I crack the lines to the front one at a time and use the pedal pressure to see if I'm getting fluid thru the prop valve?

GM Tech (Cam) :

THat is not a prop valve, it is a pressure differential switch only.

GM Tech (Cam) :

But you can try that.

Customer:

OK, the ABS assy is under the drivers seat on the frame and has 5 lines to it, two from master, one each to the fronts and one to the rears, right?

GM Tech (Cam) :

yes that is correct.

Customer:

And if no fluid goes thru it to the right front how do I reset the switch, I was told the switch (valve)moved when I lost a line and it has to be physically moved (reset) to the normal position

GM Tech (Cam) :

There is no reset switch on these, it resets when it gets pressure from the master cylinder.

GM Tech (Cam) :

It is not like the old ones.

Customer:

Ok, if I open one line at the master and apply pressure I have a 50/50 chance of getting the correct line to reset the valve, then try again with the other line?

GM Tech (Cam) :

I would try both first.

GM Tech (Cam) :

Did you only try gravity bleeding of teh whole system?

Customer:

Apply pressure as in a panic stop?

GM Tech (Cam) :

The way I do it is pump the pedal 3 times them hold it, then person 2 opens the rear bleeder.

Customer:

Bleed rears first, then fronts? I get fluid from the left front, also, when I hold the pedal down with pressur I can feel the ABS kick in and the pedal drops a little bit then stops.

GM Tech (Cam) :

yes, rears first.

GM Tech (Cam) :

did you try bleeding after you had the abs kick in?

Customer:

OK, I'll try that, I have a vacuum bleeder that always worked well, no I didn't, I just ran out to get replacement bleeder screws and the fronts required vice gripps and the rears were on their way. Any other ideas before I leave and try your suggestion?

GM Tech (Cam) :

At the moment no, try that and get back to me.

Customer:

How?

GM Tech (Cam) :

Bookmark this page so you can easily navigate back to it, and so you know, you can reply at any time for follow up information regarding this issue, even after you accept my answer and I will reply. Please don't forget to click accept at some time as that is my only means of compensation for assisting you.

Customer:

Thanks

GM Tech (Cam) :

no problem.

GM Tech (Cam), GMC Mechanic
Category: GM
Satisfied Customers: 27661
Experience: GM Grand Master Technician 2007. 11 years experience.
GM Tech (Cam) and 3 other GM Specialists are ready to help you

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