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240 Manual brake bleeding taking forever and fluid/air going back in?

I never heard of the replace one, bleed one method. It was probably covering some other problem, and that's what we have here.


If the OP actually observes that the air bubbles move backwards toward the caliper even after the bleeder valve is closed, then he has a faulty bleeder valve OR his bleeder hose is not sealing tight enough around the valve. Obviously, the end of the bleeder hose must be immersed in brake fluid, not just hanging in the air. I used a pretty cool and simple method for years using the spare tire for "power bleeding". Then I got the cool IPD unit. Even then you might have to struggle with the master cylinder sometimes. Be sure to observe the correct bleeding order: RR, LR, RF, LF on American cars.



I have a TSB somewhere that states that problems arise if bleeding is not performed after a brake pad replacement. It claims that pushing the pistons open forces dirt into the brake lines. Just a thought.



-L

It's common sense, once you introduce air into the system it should be purged immediately or you will suffer the consequences of it moving around within the system.
 
Is the master bad? Why did you replace the calipers? I put a new master on once and spent hours trying to bleed. My wife will never help me bleed again. Turned out it was bad from the start. New master #2. Teach son how to “ pressure ,open , down, closed“ 15 minutes, done.
 
Ok so I got a solid stream of fluid out of all but the passenger rear caliper. Fluid goes through the hardline going to the caliper but evidently not through the caliper itself. What is causing that? Should I throw on new rear calipers?

Bleeder valve bore is going straight to the caliper halves mating surface, where the little square seal is. I think it is possible for that little bore to rust, causing no flow. Especially if there was a little air bubble inside for a long time. If this is the case and you are lucky, you can free it up with a pin (or small drillbit, but make sure to keep the edge untouched where the bleeder valve seals) with the bleeder valve removed. If not, maybe the angle bores (which go behind the pistons) are rusty too. Or there is heavy gunk buildup inside.
 
Bleeder valve bore is going straight to the caliper halves mating surface, where the little square seal is. I think it is possible for that little bore to rust, causing no flow. Especially if there was a little air bubble inside for a long time. If this is the case and you are lucky, you can free it up with a pin (or small drillbit, but make sure to keep the edge untouched where the bleeder valve seals) with the bleeder valve removed. If not, maybe the angle bores (which go behind the pistons) are rusty too. Or there is heavy gunk buildup inside.

Thanks for your advice. I?ll take the caliper off and inspect the bore.
 
If the pistons still move. You can remove the bleeder screw. Then compress the pistons and it will blow out a minor blockage. Be sure to cover it so you don't spray fluid all around. You'll make a lot of pressure pressing in the pistons.

The bleeder screw themselves can also block up with corrosion. The same kind of pin or hard wire probe can usually fix that.
 
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If the pistons still move. You can remove the bleeder screw. Then compress the pistons and it will blow out a minor blockage. Be sure to cover it so you don't spray fluid all around. You'll make a lot of pressure pressing in the pistons.

The bleeder screw themselves can also block up with corrosion. The same kind of pin or hard wire probe can usually fix that.

I was considering removing the bleeder and squishing the brake pedal while pumping with the pressure bleeder.
 
Now I am having pedal resistance problems. The car is in the air and when I put it into first gear, the rear rotors spinning, depressing the brake pedal yields no stoppage. The fronts will stop/prevent spinning. No bubbles coming out of any caliper. The driver side rear did require the old school method of bleeding WITH the power bleeder still hooked up. All other calipers bleed with the power bleeder by itself. Brake pedal goes to the floor with no resistance at all. What is going on?
 
Brake pedal goes to the floor with no resistance at all. What is going on?
That clue looks suspiciously like a damaged (bleeding-induced damage) master cylinder. When pumping the brake pedal during bleeding, it is too easy to depress the pedal beyond its historical normal range. This forces the MC's rubber piston seals further down the cylinder to where the bore surface may be rough, corroded, or gunked up, tearing up the old rubber seal. Now the seals may be shot, unable to create any usable pressure.

Back in post #6, dl242gt warned of this:

"Another thing to do is only use the part of the master cylinder that was being used to brake with. Otherwise you may tear a seal and you need a new master cylinder."

Could you or your helper have pressed the brake pedal beyond its historical normal range?
 
That clue looks suspiciously like a damaged (bleeding-induced damage) master cylinder. When pumping the brake pedal during bleeding, it is too easy to depress the pedal beyond its historical normal range. This forces the MC's rubber piston seals further down the cylinder to where the bore surface may be rough, corroded, or gunked up, tearing up the old rubber seal. Now the seals may be shot, unable to create any usable pressure.

Back in post #6, dl242gt warned of this:

"Another thing to do is only use the part of the master cylinder that was being used to brake with. Otherwise you may tear a seal and you need a new master cylinder."

Could you or your helper have pressed the brake pedal beyond its historical normal range?

I couldn?t say since the car has been sitting for at least 2 years.

Other thing I overlooked was the front calipers. I had them swapped. (Bleeder valve on the bottom). Swapped them back and rebled and now it feels better. Still a little squishy / weak, but it stops and will lock up the tires no problem.
 
^Shouldn't be. He noticed, after your post, that the calipers were flipped, so he swapped them, and now the brakes were bleedable to the point that the pedal is somewhat spongy, but the car stops.
 
^Shouldn't be. He noticed, after your post, that the calipers were flipped, so he swapped them, and now the brakes were bleedable to the point that the pedal is somewhat spongy, but the car stops.

This^^^

Sorry, I retract my earlier statement. Can't make sense of your situation.




Confused.

I had the bleeder valves on the front calipers on the bottom instead of the top (air rises) so there must have been an air pocket that was stuck in there. I switched the front calipers so that the bleeder valves are on the top ( as they should be) and I was able to get some resistance with the brake pedal. The car now stops as it should, albeit the brake pedal goes a little further than I would like. I am guessing some more bleeding is in order.
 
For sure with the calipers reversed there was such a large trapped air bubble that it probably absorbed most of the pressure so the back calipers didn't get any pressure. In the rear it would have to make enough pressure to get through the regulators and it didn't.

Nice to see you got that sorted and it's stopping. The other two things that I've had give me a slightly soft pedal but the brakes work is the warning light valve. A valve that has gotten some corrosion or something internal wrong caused a soft brake pedal on my 79 242dl. It didn't leak outright but there was suspicious traces of fluid inside where the warning light switch screws in. Some fail completely there and fluid will pour out. But this never did. Just made the pedal soft.

The second one is some trapped air that will come out after a week or so of driving and then you do one more bleed session. That happened to a friends 242 factory flathood some years ago.
 
For sure with the calipers reversed there was such a large trapped air bubble that it probably absorbed most of the pressure so the back calipers didn't get any pressure. In the rear it would have to make enough pressure to get through the regulators and it didn't.

Nice to see you got that sorted and it's stopping. The other two things that I've had give me a slightly soft pedal but the brakes work is the warning light valve. A valve that has gotten some corrosion or something internal wrong caused a soft brake pedal on my 79 242dl. It didn't leak outright but there was suspicious traces of fluid inside where the warning light switch screws in. Some fail completely there and fluid will pour out. But this never did. Just made the pedal soft.

The second one is some trapped air that will come out after a week or so of driving and then you do one more bleed session. That happened to a friends 242 factory flathood some years ago.

I have a backup octopus ready just in case that has failed. I was *this* close to replacing it, thinking it was the cause of my woes.

I think Neptune mentioned his having the same feel. I am going to daily drive it (to work and back at least) for a week or two then bleed them again. My gut instinct tells me there is still a little air in the lines somewhere.
 
Try leaving it over night with the rear way up.

:nod:

But you forgot the bleed the rear brakes while you tap on the proportioning valves with the handle of a screwdriver part.

Pro tip, gonna take two people and make sure there's a couple stacks of wheels under the back portions of the rockers while you're under there with it jacked up precariously at an angle.
 
:nod:

But you forgot the bleed the rear brakes while you tap on the proportioning valves with the handle of a screwdriver part.

Pro tip, gonna take two people and make sure there's a couple stacks of wheels under the back portions of the rockers while you're under there with it jacked up precariously at an angle.

I did do the tappity taps when I was first bleeding them and so I will do that tactic once again when the new brake fluid arrives next week.
 
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