Presure Bleeding Question

[Dreamer52]

I have too much pedal travel now, I'll pull the pads & work on the pistons. By outward you mean extend the pistons towards the pads, correct?

[DRACO A5OG]

Yes, Rusnak means extend the pistons towards the rotor just enough to slide the pads in snugly.

[Dreamer52]

OK, drivers side outside extended, inner hardly moved The passenger side extended more on outside but I could push pistons back in. Drivers side outside piston almost appears stuck. Should I open bleed valve & push piston back in?

[Dreamer52]

Forgot to add drivers side extended too mch, can't fit padnow.

[DRACO A5OG]

Press the pedal 2"s and hold with a 2X4 in place against the seat or seat rail.

Open the valve and push the pistons back to where the need to be. ( hook up a hose and catch bottle if you do not want a mess to clean up )

Try to find pieces of wood a bit skinner than the pads and place between pistons and rotor and press. You should never press pedal with out anything between the rotors pistons, pistons may come out too quickly and damage the rotor.

BTW, when you rebuilt the calipers, prior to placing the inner seal, did you make sure the pistons dropped in on their own by gravity. I am thinking maybe it was not cleaned enough and causing you to bind the pistons?

[rusnak]

You can also buy an inexpensive brake pad spreader. They have them at your FLOPS such as O'Reily's. I should add that the way you use them is to take the caliper off, put the pads back in, and then you turn the spreader until it's the same thickness as the rotor, then slide the whole thing back on.

Of course, if one brake piston is stuck, you want to unstick it first.

[Dreamer52]

Yep I had a spreader but piston was too far out. Took the top off reservoir and with very large flat blade was able to get the pistons back in. Pedal feels good but will manually bleed later 1 more time. I was worried about the pressure I had to put on pistons so I called PMB & they reassured me it will take some pressure. Now I have some light scratches on rotor. Is that acceptable or should I replace while everything is up & apart? If I need to replace, any recommendations?

[WANNA930]

When yo run a master dry you are sucking air into the master and the system. Bleeding a master is usually needed after that occurs. Sometimes you can get passed it others your pedal will never feel right.

As far as the power bleeder you should block the pedal as if it was being depressed and then pump away. That way you are opening the ports in the master to allow the fluid to flow rather then forcing fluid past.

If the rotors are new or you did bleed the master dry I would tap on them with a wrench while you are bleeding. This helps get the air bubbles to the top and out.

If you can catch your nail on the rotor damage simply sand or file lightly all should be fine.

Slow down reevaluate and all should be fine. Also make sure those rotor surfaces are surgically clean now. I always say if you haven't gone through a roll of towels and a can of cleaner they aren't clean.

[Dreamer52]

Sounds like excellent advise. I'll leave it apart & do some light sanding & clean. I really appreciate all the help guys...now I need go and try to collect all the tools laying around.

[TheSt|G]

Get your rubber mallet out and hammer those calipers while each one bleeds. Air easily can get stuck inside the passages.

[DRACO A5OG]

Lite scratches are fine, it is the deep gouges that are an issue. I think you will be fine, Just bed those pads in evenly and do not sit at a stop with brakes on. This will help keep rotors from warping.

[Dreamer52]

Thx, I'll give that a try.

[rusnak]

Yep, if the scratches are huge, then you can have the rotors machined down. Personally, I don't ever do that because the rotors need the mass to work as a heat sink. I think you'll be fine. I stick with ATE or Zimmermann rotors.

[911pcars]

Originally Posted by WANNA930

When yo run a master dry you are sucking air into the master and the system. Bleeding a master is usually needed after that occurs. Sometimes you can get passed it others your pedal will never feel right.

As far as the power bleeder you should block the pedal as if it was being depressed and then pump away. That way you are opening the ports in the master to allow the fluid to flow rather then forcing fluid past................

All good advice, but when the pedal is depressed, the MC piston and cup moves forward. At some travel distance, the piston/cup blocks the port between the reservoir and the MC so pressure can build in the system, otherwise it would pressurize the reservoir.

If pressure bleeding, leave the brake pedal alone. Air pressure from the tank should be enough to move fluid through the system. Atmospheric pressure produces the same result but with less volume.

Was there a chance that when you pushed the piston(s) back into the caliper, it could have went in partially, then decided to jam at some point? If the pistons don't extend toward the rotor when the pedal is applied, there's either a mechanical issue (jammed piston) or a hydraulic failure (no pressure, no fluid). Diagnose this as an electrical circuit. Loosen the brake line a some mid-point location, press the pedal and see if the fluid path is clear. Then repeat up to each caliper inlet. The caliper bleeder screw(s) is the end of that corner's pressure system. Fluid should escape there too.

Typically, no system pressure is due to a leaking cup in the MC, or if pressure is present and just a localized issue, a blocked fluid path caused by a kinked line or internally failed flex line.

Sherwood

[DRACO A5OG]

Originally Posted by hinjin

Did a manual bleed and pedal firmed up but still spongy. Will try another power bleed tomorrow. And the bleeder valves are on top. Tried to do a clutch bleed, can hook up the tube but can't get a wrench on the bleeder. Anyone know what size the clutch bleeder valve is-same as the other valves?

7MM.

Spongy?, You still have air or air is getting in past the caliper inner seals or inner seals are leaking. I would also check for leaks.

[911pcars]

At this point, you have some unknown issue, and it's probably not because of a lack of brake fluid. In fact, I'm guesing you've run 2-3 liters of brake fluid through the system already. If brake fluid doesn't dribble out of the bleeder screw by merely opening it, you either have a supply or a flow issue.

At one point (post #8) it sounds like you had functioning brakes, then after you tried manual bleeding (post #12), you had none. You stated during the manual bleeding process, the pedal went to the floor. At that time, that motion could have torn the MC cup seal which seals that end of the closed system. If so, the fluid will merely bypass the seal when the pedal is depressed. It happens when overstroking the pedal during manual bleeding, thus the reason Jim (Drago) suggests putting a block of wood under the pedal during that process.

Some other observations:
- Pressure bleeding assumes the hydraulic system is in good condition. If you can't bleed the system after running a liter of fluid through it. Stop. Diagnose what's wrong.

To manually retract a piston back into the caliper body, install a worn (thin) brake pad (or equivalent) to provide more working space and to spread the load, then use a large pry bar so the prying force is exerted on the middle of the pad, not the rotor. This will push the piston evenly. The worn pad will also bear the brunt of any sharp edges of the pry bar.

To review:
- Confirm the master cylinder is operating correctly. You shouldn't need more than a liter of BF to bleed the system.

- Dedicate a block of wood to use for manual bleeding.

- Once the system is restored to working order (hydraulic seals good at each end, no restrictions in the system, etc.), confirm brake fluid freely flows through the system at each corner. If this is the case, air easily evacuates.

- Refer to the following link. All you need is a length of tubing attached to the bleeder screw.

Brake bleeding

Hope this helps,
Sherwood

[Dreamer52]

Yep, helps a lot Sherwood.
I've got a pretty firm pedal now. Just cleaning up and hope to get on the road tomorrow.

[rusnak]

If the MC seals ever do go bad, you won't have a spongy feel, but your pedal will slowly drop to the floor as you press on it. That's the worst feeling. It means a few hours of no fun.

[Dreamer52]

Hi All-

Just as a follow up. A week after the new caliper install the pedal firmed up. I bled them a few times when I had the soft pedal but read I could either drive it for a week or put a spacer for the piston to extend. It took a week and a little fluid to top off the reservoir and everything is like new. Never could have done it without the group.

Thanks again for all the help & suggestions