2004 Yukon brake bleeding issue

[stuffs2936]

Rear pads were wearing faster than front, removal of caliper seem to indicate the caliper was semi frozen and almost impossible to compress with C clamp. I replaced both rear calipers and can't get brake fluid flowing during either manual bleeding or vacuum bleeding. The vehicle has stability control. Countless attempts and no fluid at either rear caliper. I am pretty old school so I am not sure if the vehicle needs to be running or whether something else needs to be done to get fluid back to the new calipers. Brake pressure can't even move the calipers enough to seat the new pads. Any help on procedures or troubleshooting will be greatly appreciated and I thank you in advance.

[davester]

First, I would suggest examining the brake lines for rust, as they have a tendency to rust badly and suddenly the pedal will go to the floor and you go into the vehicle stopped for the red light.

 

Second, for this specific problem, I would suggest moving up the line and seeing where you get fluid coming out.  So, separate the rubber hose from the metal brake line on the rear axle, and see if fluid comes out the metal line.  If not, move to the jounce (rubber hose going to the middle of the rear axle), undo that and see if fluid, and so on until you get to the master cylinder or you get fluid.

[stuffs2936]

Thank you for your comments. Steel brake lines were replaced a few years ago, rubber line to the rear caliper was replaced just now with new caliper. The jounce hoses were not replaced. I was getting braking with rear caliper prior to replacing it. I guess I am asking whether the JL4 stability control is blocking the fluid when I try to bleed with the engine off? Or if the stability control is in any way affecting the flow to the rear. The new caliper was of course empty and maybe it just takes a lot longer. I have never heard of priming a caliper. I have been unable to get the caliper to respond at all to move the pads tight against the rotor.

[stuffs2936]

In all of the frustration with this, I almost forgot that when I first attempted to vacuum bleed the rear caliper with a mighty vac, I did get a significant amount of fluid but then it seemed to stop for no apparent reason. I have monitored the master cylinder religiously and it's level never dropped low. This led me to believe a valve in the abs stopped the fluid going to the rear. Unless the fluid I did get was what was retained in the lines after the abs unit. 

[davester]

I would think the fluid you sucked out is probably just the fluid in the caliper (or perhaps the caliper on the other side of the rear axle).

 

Go and work forward from the rear calipers until you can pump fluid out of a given connection, making sure not to run the master cylinder empty (as it's a hassle to bench-bleed it, then bleed everything).  Working from the rear to the front means you have to bleed the least about of stuff...

 

The ABS controller doesn't block the flow of fluid to the rear lines at all.  It provides ABS action by pulsing fluid in/out of the line (like a small master cylinder pump connected to a T connection to each line).  The ABS controller valves can completely fail internally (short of venting fluid to the ground) without impacting regular braking performance.

[stuffs2936]

Davester, thank you again very much for your insight into this issue. It was a great help to me. I guess the ABS seems a lot scarier than it is in reality. Knowing it was not a factor greatly simplified things. I seem to have a good pedal now and was able to get fluid coming through the rear calipers. I attribute much of the problem to two things. Giving a rest between bleeds for the system to stabilize seemed to help quite a bit. And using the Mityvac hand pump to vacuum the air out was deceptive as I believe I was pulling air from the threads when the bleeder screw was loosened not allowing me to see a solid stream of brake fluid. I was pulling air out of the system but also ambient air through the threads. When I loosened the screw less, I prevented brake fluid flow.  In my research I discovered the Motive products pressure tank at an affordable price and think this will be a better option for future bleeding. There is no substitute for experience and thank you again for sharing your expertise. 

[davester]

If you do get the Motive Pressure bleeder (I have it), if you get the plastic cap for the reservoir, keep the pressure low, like under 15 psi (maybe double check with Motive to confirm what pressure you should use).

 

Alternately, you can get the system with a metal cap for the reservoir, and you can use a higher pressure with that cap.

 

I made the mistake of getting the plastic cap, but using the pressure specified in the full-service manual, which was 25psi (around there, it's been a couple of years), and it worked for a short while, but then tabs on the cap failed, it blew off and sprayed brake fluid everywhere.  After this, I got the metal cap, as I needed to get another one anyway as the plastic one was partially deformed from when it blew off.

 

I liked how it worked, but the instructions could have been clearer about what pressure to use.  The only other negative thing was that it took 3 times for them to properly write my address on the package for the metal cap, I had to email them a picture of a random letter delivered to my house before they could get it right.  It's the only time something like this has happened to me when ordering stuff.

 

 

[stuffs2936]

Again, many thanks for the heads up on the pressure and the cap situation. Sorry you had to experience that disaster, that would have been the icing on the cake for this job for me.  That is strange about the address thing. Google maps has my address wrong and despite at least 4 attempts they refuse to change it and with no surprise they don't even have a way to talk to someone directly, you send in a request(s) and that is it. I will be super glad when this job will be buttoned up. Started out as a simple pad replacement and ended up with pads, rotors, new calipers, new backing plates, new axle seals and oh yes new axles with a new diff cover.  How does a rubber seal wear a groove in steel, lol. These days parts costs add up so fast even when purchased at a discount. Lucky I could do it and thankful for those willing to share their experiences.