Lets Talk Caliper Rebuilds

[Icecream]

The air comes from water in the brake fluid boiling off. During a track day, this is more likely to happen due to the amount of heat generated.
Once it's in the lines, I found it's a PITA to remove.

Did you flush out the clutch line?

hmm, this might be a fun experiment with heating up some brake fluid/water to boiling point to see what the bubbles do and if the water vapor condenses again after cooling. It should, I would think.

[elbert]

hmm, this might be a fun experiment with heating up some brake fluid/water to boiling point to see what the bubbles do and if the water vapor condenses again after cooling. It should, I would think.

You know what, I need to stop posting while I'm trying to work. The water lowers the boiling point of the brake fluid, which is what boils. Not the water itself.

[Estoril]

OK, then do you still think there is air in the system, and if so, where did it come from?

I have no idea. I once got air in the system from a front pad/rotor swap. Full MC. No bleed.

I would try what another poster said: Do a bleed and beat on caliper during and carefully note if you any tiny air bubbles.

Otherwise you either bleed again (incl. ABS activation) - or you look at the master cylinder. I assume your MC seal is solid (visual inspection) and cap firmly tightened.

[timmo]

I have no idea. I once got air in the system from a front pad/rotor swap. Full MC. No bleed.

I would try what another poster said: Do a bleed and beat on caliper during and carefully note if you any tiny air bubbles.

Otherwise you either bleed again (incl. ABS activation) - or you look at the master cylinder. I assume your MC seal is solid (visual inspection) and cap firmly tightened.

OP if you do this, let me know how it goes. Because I used a mallet on the calipers, and bled the ABS using INPA, and my pedal still doesn't feel as good as it has before

[eacmen]

When I bled the brakes I used a mallet and I also did an INPA bleed procedure. I did the INPA bleed early on in the bleed process since any air that would have been trapped in there would take a while to reach the caliper while bleeding.

This is going my approach in this order:

1. Take the car out for some hard threshold braking to get the brakes nice and hot. Basically re-bed them in. This might alleviate some of the pad taper with the new brass bushings. Crossing fingers that is all it is.
2. New front pads, repeat #1
3. Rebuild the calipers with new seals.
4. Either bbk or new mc.


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[eacmen]

Just measured the travel with a tape measure to get some actual numbers to compare to. Using just my arm to actuate the brake pedal i get 7/8 inches of travel with the engine off. With the engine on I get 2.5 inches of travel. If i used my foot that distance would be longer obviously.

Not that i need to worry about such things with SMG but i don't know how anyone could heel toe with a brake pedal that goes that far beneath the throttle.


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[elbert]

Agreed. I had the same symptoms. I did a two-man bleed with the Motive pressure bleeder (i.e. used together). Make sure that second person knows what they're doing (you'd be surprised).

I forgot to mention this -- I also changed the bleeder screws on all four calipers.
The bleed screws seal using a taper fit, and mine were fairly cruddy.
Not sure if this or having a decent helper made the difference, but it worked.
p/n 34116758107

[eacmen]

I forgot to mention this -- I also changed the bleeder screws on all four calipers.
The bleed screws seal using a taper fit, and mine were fairly cruddy.
Not sure if this or having a decent helper made the difference, but it worked.
p/n 34116758107

Yup. New bleeders here as well. Mine were leaking.

[sapote]

All I can think of to try next is caliper rebuild then MC replacement. I don't think its an MC problem. With the engine off I can pump the pedal and it gets hard. Maybe 1/2 inch of travel before it gets hard. Once you start the engine the pedal travel becomes *very* long. I would think that if the booster was failing then the pedal would get harder not softer.

engine off ---> short travel
engine running ----> very long travel.
reason: when engine running the booster provided amplification to the MC which compress the fluid with much more force as compared to engine off.

I don't think the booster or MC is at fault. I bet air in the system is the problem. air is compressible leading to longer pedal travel.

The key to a seccessful bleeding: The new fluid from the resevoir must flow out to each caliper bleeder screw, starting from the caliper with the longest pipe (Left rear?).
I don't understand why you said seeing no bubble going out from the bleeder bolt but seeing bubbles in the tube from bottle to the bleeder. If you used a power bleeder at 20 psi, then there was no negative pressure in the system to suck air in through the bleeder bolt threads as when doing with 2 person method (one pushing the pedal and one open/close the bleeder screw.)

[eacmen]

engine off ---> short travel
engine running ----> very long travel.
reason: when engine running the booster provided amplification to the MC which compress the fluid with much more force as compared to engine off.

I don't think the booster or MC is at fault. I bet air in the system is the problem. air is compressible leading to longer pedal travel.

The key to a seccessful bleeding: The new fluid from the resevoir must flow out to each caliper bleeder screw, starting from the caliper with the longest pipe (Left rear?).
I don't understand why you said seeing no bubble going out from the bleeder bolt but seeing bubbles in the tube from bottle to the bleeder. If you used a power bleeder at 20 psi, then there was no negative pressure in the system to suck air in through the bleeder bolt threads as when doing with 2 person method (one pushing the pedal and one open/close the bleeder screw.)

Since I was using IL of fluid what I did was mark thr bleed bottle with 200ml marks and bled each caliper until 200ml came out. Leaving 200ml left over.

You're saying that the Right Rear caliper needs a longer bleed than the Rear Left? If so how much more?


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[sapote]

Most cars the right rear caliper pipe is the longest, but the M3 has the ABS system located at the drug bin and so I guess the LR is the longest. In your case I think the air bubbles are not just in the calipers but they maybe in the middle of the long pipe. To really flush out the air, I would use a very long clear tube connecting from the bleeder screw and feed back to the resevoir and not to a bottle -- never run out of fluid -- and keep bleeding until seeing no air bubble in the tube, then repeat for the next caliper.

If test drive and happy with the pedal, then you can flush out again using new fluid if you like.

[heinzboehmer]

Most cars the right rear caliper pipe is the longest, but the M3 has the ABS system located at the drug bin and so I guess the LR is the longest.

Brake lines run down the left side of the car, so rear right is still the farthest.

[eacmen]

Most cars the right rear caliper pipe is the longest, but the M3 has the ABS system located at the drug bin and so I guess the LR is the longest. In your case I think the air bubbles are not just in the calipers but they maybe in the middle of the long pipe. To really flush out the air, I would use a very long clear tube connecting from the bleeder screw and feed back to the resevoir and not to a bottle -- never run out of fluid -- and keep bleeding until seeing no air bubble in the tube, then repeat for the next caliper.

If test drive and happy with the pedal, then you can flush out again using new fluid if you like.

This is a very interesting concept. So run the tubing from each caliper to the MC reservoir. Crack the bleeder and just keep pumping the pedal?

We have an MK60 so all the brake/ABS piping is near the ECU box.

This is basically how you would bench bleed the MC, just with a much longer tube...


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[sapote]

This is a very interesting concept. So run the tubing from each caliper to the MC reservoir. Crack the bleeder and just keep pumping the pedal?

We have an MK60 so all the brake/ABS piping is near the ECU box.

If using pumping the pedal method, make sure to close the bleeder screw before let up the pedal for the next pump. It's to avoid air being pulled in (via the bleeder threads) during the pedal moving up. Doing this rapidly to help flush out the air bubbles trapped in the middle of the long pipe. (Doing slow would allow the bubbles to slowly move back the high part of the pipe.)

[eacmen]

If using pumping the pedal method, make sure to close the bleeder screw before let up the pedal for the next pump. It's to avoid air being pulled in (via the bleeder threads) during the pedal moving up. Doing this rapidly to help flush out the air bubbles trapped in the middle of the long pipe. (Doing slow would allow the bubbles to slowly move back the high part of the pipe.)

How would you keep the system pressurized while feeding the fluid back into the MC without the pedal?


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