the dreaded brake bleeding thread for a 71 C-10

[bmxbang]

alright guys here's the backstory. Brakes of course worked fine before I screwed with them. I overhauled the front suspension over a two month time span and left the front master cylinder dry because I took the brake calipers off it. now everything back together and low and behold my brakes suck. I have bleed them by hand with a vacuum pump and also with a pneumatic pump and no big difference. they have gotten slightly better but not by any means safe for the road. they will in fact stiffen up after I pump the pedal a few times so that makes me think I still have air in them. If I where to hop in the truck now the pedal feels very soft and will go all the way to the ground with out changing dramatically in pressure resistance. No leaks that I am aware of. ill take any advice. The front brakes are disk.

[SCOTI]

No advice beyond what you're already doing. Sometimes it just takes more attempts before you can purge all of the air out of a system.

[rpmerf]

#1 - you said the master went dry, did you bench bleed it?

[rpmerf]

Next thought. I've found the best way is the 2 person method.
Person 1 - Start pushing the pedal down
Person 2 - Open the bleeder
Person 1 - Push the pedal about 80% of the way down, then stop and hold
Person 2 - close bleeder
Person 1 - release

Repeat.

If you are using a vacuum bleeder, they tend to suck air from around the threads. Wrap the threads of the bleeder in teflon tape. Make sure you use a good connector on the bleeder.

Some prop valves do not like when there is an imbalance, and need to be reset. Make sure there is good flow everywhere. If not, you either need to reset the pro valve, or look for another issue.

[SCOTI]

I also use a 2 person method:

Person 1 - Slowly pushes the pedal down
Person 2 - Opens the bleeder
Person 1 - Push the pedal until travel stops, then holds it there
Person 2 - Close bleeder
Person 1 - Slowly release

Repeat.

I have the person that modulates the pedal do it slowly & consistently (both on compression & when letting off) to reduce the possibility of aeration/foaming.
Person 2 also checks & refills the master cyl. between each round of bleeding.
And for those that might not know.... Always start @ the farthest bleeder valve from the master cyl & work your way to the closest bleeder valve.

[SunSoaked]

I replaced all the bleeder screws front and back with Russell Speed Bleeders. One of the easiest and cheapest mods I've done. Eliminates the two person method and vacuum pumps. Just make sure you keep the M/C full.

[LEEVON]

I have a small cheap pump that pushes fluid (and air) backwards from the bleeder to the master cylinder. It's a last resort but it has helped with this situation at least once.

Also, did you isolate and bleed the master cylinder first? You should block the rear port, then put a tube on the front port to recirc back into the master. Very short strokes until no air comes through. Doing it on the bench is ideal though...

[rpmerf]

That is known as reverse bleeding. It really helped me on my 97. I rigged togetehr a setup using a clean glass jar, some clear hose, and the air compressor with a regulator to only push about 3-5 psi. Fill it up with brake fluid, connect the hose to the beeder and open it a little, apply pressure to the jar, and it pushes fluid toward the master. Makes sense to me as this way you can push the bubbles up, rather than trying to push them down. Before doing this, bleed the normal way first to make sure you are only pushing clean fluid toward the master.

[CMars45000]

Originally Posted by rpmerf

#1 - you said the master went dry, did you bench bleed it?

This... I would "bench" bleed master first, the reinstall lines and bleed normally with a 2 person method (One pumps pedal, one cracks bleeder, starting the farthest from the M/C, working to the closest. The only vehicles this has NOT worked on for me are vehicles with ABS that sometimes need to have have the ABS pump bled with a scan tool.

Only other thought, the master have been known to fail after sitting for a long period of time or being asked to operate outside of their normal stroke range. If you have an older master that may have some internal corrosion, but it is using consistently, the master cylinder piston keeps a tie, corrosion free area worn in the bore. Then you need to bleed the brakes and ask the master cylinder piston to drag itself over the corrosion because your are making the piston go full stroke, and the old brittle seal can give up the ghost.

[bmxbang]

Originally Posted by CMars45000

This... I would "bench" bleed master first, the reinstall lines and bleed normally with a 2 person method (One pumps pedal, one cracks bleeder, starting the farthest from the M/C, working to the closest. The only vehicles this has NOT worked on for me are vehicles with ABS that sometimes need to have have the ABS pump bled with a scan tool.

Only other thought, the master have been known to fail after sitting for a long period of time or being asked to operate outside of their normal stroke range. If you have an older master that may have some internal corrosion, but it is using consistently, the master cylinder piston keeps a tie, corrosion free area worn in the bore. Then you need to bleed the brakes and ask the master cylinder piston to drag itself over the corrosion because your are making the piston go full stroke, and the old brittle seal can give up the ghost.

I'm thinking something like this may have happened I have no bubbles in the system at all currently that I can see from normal bleeding. the pedal is still very soft and will take about three pumps to harden up and get back to what I recall was normal braking. it will last for a very short time 1min max and then go back to me having to pump the brakes a few times to get them feeling solid again.

[bmxbang]

Well after taking a few days off and going back and re tracing all my steps with a clear head I realized I put the calipers on the opposite sides and the bleader valves that should be facing up where facing down probably trapping all sorts of air in the calipers lol. Can’t believe I let that one happen but I got them flipped today. And immediately they felt better after getting them bleed again. Have yet to drive it but I’m pretty sure I got the problem solved!
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[rennat_2006]

Originally Posted by bmxbang

Well after taking a few days off and going back and re tracing all my steps with a clear head I realized I put the calipers on the opposite sides and the bleader valves that should be facing up where facing down probably trapping all sorts of air in the calipers lol. Can’t believe I let that one happen but I got them flipped today. And immediately they felt better after getting them bleed again. Have yet to drive it but I’m pretty sure I got the problem solved!
Posted via Mobile Device

That'll do it for sure