Replaced hard brake lines on my GMT-800 pickup where they all rust through. I still have a soft pedal. Even though the lines were pre-bent, I can imagine that there are high spots well before the calipers. I have both pressure (Motive) and vacuum (HF) bleeders and have run a ton of fluid through. Any good brake bleeding tips? Oh, and it's not related to the ABS module - the RF refused to bleed at all and I didn't have a scan tool to cycle the module so I bypassed it to get back on the road.
I just literally did this same job this weekend on my GMT 400 (K2500). All new hard and soft lines. Since mine had been completely bled dry by a failed line for a few months until I got around to it, I couldn't get a good go out of the vacuum bleeder I normally use.
What I ended up doing was hooking up the vacuum and then pumping with the brake pedal. It worked very well. I still have the ABS unit inline.
Remove the bleeder screw for the RF. If fluid oozes out of the caliper, the bleed screw is blocked. Get a paper clip or piece of wire and unblock it. If caliper does not ooze, poke small bladed screw driver into the bleeder screw hole and see if anything breaks loose. if so, you may want to rebuild or replace the caliper. If still no fluid from the poking, remove brake line connection at the caliper. Do the same look and poke process. If no fluid out out the brake line, go to the tee where the brake line meets the LF line (should get fluid there as the LF bleeds OK). But if no fluid replace the tee. If fluid is there, replace the line between the tee and the caliper. Once the RF is working, re-do the LF bleeder. Good luck.
Related but on my 61 Pontiac I've got new master cylinder, new lines, new front calipers, new rear wheel cylinders . I did a successful bench bleed but can't seem to bleed the brakes. Nothing comes out the passenger front. Just a dribble out the rear lines. Ugh.
If the master cylinder was empty in either chamber it is pretty common to get air stuck there. I usually have an assistant (or a long prybar if no assistant is available) hold the pedal down and crack the lines loose at the master cylinder. This usually helps a lot.
I chased this problem on my 96 Ram after replacing all the lines. Turned out my home made flares suck. Since you have prebent lines the flares should be OK but make sure they are super tight. Like tighter than you think they should be. I was sucking little bits of air at every joint and couldnt get it bled. Remade a few lines with a better flaring tool (Mastercool Hydraulic Flarer FTW) and rebled and was good to go.
I was able to trigger the ABS on my 2000 Chevy by having a helper monkey hit the brakes lightly while I spun one wheel and kicked on the ABS, you can also take a few rips down a gravel road to kick on the ABS and then rebleed.
Or just beg/borrow/steal a scan tool. Thats the proper way to fly. A $200 Snap-On MT-2500 from Ebay will do it if you get the right cartridge and cable, most will come with them as the right cartridge and cable is the common one.
The ABS accumulator could be bye-bye if none of the above works.
In reply to Jerry From LA :
Try this - crack the bleed screw, then push the caliper piston all the way in. Then bleed / flush that corner, with the piston seated. Repeat for the other corners. Air can remained trapped in the piston bore and give a spongy pedal otherwise.
Dave said:Related but on my 61 Pontiac I've got new master cylinder, new lines, new front calipers, new rear wheel cylinders . I did a successful bench bleed but can't seem to bleed the brakes. Nothing comes out the passenger front. Just a dribble out the rear lines. Ugh.
I had the same problem as above after completely replacing the brake system on my truck last weekend, I could not get anything from the lines even with my vacuum system.
What I did was put the system under vacuum on one bleeder, and with the rest of them closed I started pumping the brake pedal. I had to pull it up a few times at first, but it quickly filled the system then.
In reply to Emdrei :
Best done with the caliper off the rotor and a very large C-clamp holding the piston in place. Do it while holding the caliper with C-clamp as high in the wheelwell as you can. If that doesn't work, the accumulator may be tango unifom.
I got mine sorted. There was a tiny bit of debris in the line that stopped the flare from seating. Thus a small leak. Ugh.
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