[sonoma_tom]

I just finished running new NiCop and stainless gravel guard (where necessary) all the way around the truck after the intermediate line sprung a leak. Obviously, the master cylinder piston shut off fluid to the back brakes. I understand that. So, I was searching the forums to find a procedure to reset the piston in the master cylinder, and I found success! This is such a great community. Anyway, what I found was this from a post from 2005:

Special Purpose Pressure Differential Switch
There are a number of pressure differential switches that perform a second function. In
addition to completing the ground to the red warning light, they also shut off the fluid
flow to the rear brakes if a rear hydraulic failure has occurred. The fluid flow to the rear
brakes is through the ports in Figure 21. If a rear pressure loss occurs then the pressure
differential piston moves toward the rear brake circuit and closes off the fluid passages to
the rear brakes as in Figure 22. When dealing with this type of valve you must re-center
the valve before the rear brakes can be bled. Bleed the lines at the master cylinder and the
fitting on the valve. Open a front bleeder and spike the brake pedal a couple of times
taking care not to exceed half pedal travel. This usually will re-center the piston. If it
won't re-center, the combination valve will have to be replaced. END!

So here's my question...what does this procedure from a shop manual mean by "bleed the lines at the master cylinder and the fitting on the valve"? I mean, I know that it's probably obvious, but what would this procedure look like that's different from me hooking up my pressure bleeder after creating the pressure loss in the front? If this is elsewhere in the forum, I apologize. I also didn't want to resurrect a zombie post. Thanks for any help!

 

[Rhotpursuit]

I just finished running new NiCop and stainless gravel guard (where necessary) all the way around the truck after the intermediate line sprung a leak. Obviously, the master cylinder piston shut off fluid to the back brakes. I understand that. So, I was searching the forums to find a procedure to reset the piston in the master cylinder, and I found success! This is such a great community. Anyway, what I found was this from a post from 2005:



So here's my question...what does this procedure from a shop manual mean by "bleed the lines at the master cylinder and the fitting on the valve"? I mean, I know that it's probably obvious, but what would this procedure look like that's different from me hooking up my pressure bleeder after creating the pressure loss in the front? If this is elsewhere in the forum, I apologize. I also didn't want to resurrect a zombie post. Thanks for any help!

If your master cylinder went dry, you'd need to bench bleed it.

 

[sonoma_tom]

If your master cylinder went dry, you'd need to bench bleed it.

So, just to make sure I have this right....the portion of the reservoir that went dry was for the back while the portion for the front kept fluid. So, that would necessitate a bench bleed? If so, would the procedure still be 1) bench bleed 2) create loss with bleeder screw in front 3) bleed brakes with pressure bleeder or would the bench bleed mean that I will have corrected the internal piston positioning that locked out the rear? I guess while I am thinking about it, I plan to have a shop with the proper ECM tech (Tech1?) re-bleed and take care of the ABS unit. Would that be warranted or is that overkill? Thanks again!!!!

 

[Rhotpursuit]

I had a friend bleed my ABS with a Tech 2. I'm sure there are YouTube videos that explain how to bleed and center the master cylinder.