I'm having a hell of a time bleeding brakes

#1

Howdy,

When i bought this car, it has a very stiff pedal. it felt great. records show it had a new master cyl put in about 20k ago.

Then i had to go and mess it up :stuck_out_tongue:

I rebuilt all four calipers and installed ss brake lines. new pads.

I used my trusty Motive power bleeder to bleed/flush a liter of fluid through. buttoned 'er up. test drive. whoa. i have what feels like a foot of travel before i hit ‘pad’.

repeat. repeat. repeat.

somewhere along the line i bleed the clutch and break that too. rebleed using the old fashioned way (loosen, press, tighten, pull up, etc) and get it back to decent.

Anyway, i’ve gone through about 6 liters of fluid now and my brakes and clutch both feel like crap. Slowly getting better, but still not good enough and nowhere near like it was originally.

My procedure:

Hook up power bleeder, bleed RR, LR, RF, LF. sometimes i do the clutch, sometimes i don’t. repeat. round and round till fluids gone.

I normally tap the calipers w/ a wrench or something to loosen up air bubbles. dunno if thats voodoo or not.

Any tips or tricks? Could something be wrong? I’m thinking maybe the bushings that seal the brake fluid res onto the master cylinder? I see no fluid leaks though…

Thanks

#2

I had a similar experience with mine. My pedal was very firm before I rebuilt my rear calipers and now the seem to go soft after sitting a day or so. The will pump up tight but during a session but they used to stay firm all of the time. Maybe someone has a suggestion for both of us.

#3

screwynewy wrote:

[quote]I had a similar experience with mine. My pedal was very firm before I rebuilt my rear calipers and now the seem to go soft after sitting a day or so. The will pump up tight but during a session but they used to stay firm all of the time. Maybe someone has a suggestion for both of us.[/quote]look in the bentley about engaging the ABS pump to bleed the air out of it.

#4

Have you tried the old fashion way of having someone pump the pedal? I stopped filling my power bleeder with fluid since I would constantly get a steady stream of "micro-bubbles". Now I just use the empty bleeder to pressurize the system and fill the resivoir more. Do you think you might have gotten air in the MC? Remember to properly bleed the clutch you have to turn the slave cylinder upside down since the bleeder is on the bottom.

#5

trentmw wrote:

This is the same way that I do it. I was never comfortable with leaving the excess fluid in the bleeder where it can absorb moisture.

The way I flush my system is in two steps. First, I use a mityvac to suck all of the fluid out of the master cylinder reservoir. Then, I add fresh fluid to the reservoir and use the power-bleeder to force it through. Alternate with clear and blue so that you know when you’ve sent enough fluid through the system. It’s really not that much, the lines are so small.

#6

Is it possible that enough fluid drained out of the lines to wind up with air in the ABS system? That will cause a soft pedal that won’t be cleared by ordinary bleeding. If that happened you’ll have to engage the ABS during the bleed.

#7

well. yes, it is possible. i had the brake lines open and dripping for two days straight. :slight_smile: wups.

One question i’ve always had though, If the abs valve wasnt open (ABS not engaged) while the lines were draining, how would air get in ?

#8

Hi,
what i had last year after replacing brakelines with a M3 is that the pressure regulator front /rear broke down. Brakes were great but after replacing the brake lines it was not working correctly ,resulting in a soft feeling brake pedal.
It is the round cylinder under your master brake cylinder
Bye chris
the netherlands

#9

The ABS unit is higher than the ends of the hard lines, so if they are left open the fluid will drain out of the ABS unit and be replaced by air…

#10

I see. well that then, is my prime target.

I looked through my Bentley, but didnt see anything on activating the ABS unit. Can you elaborate on that, nasaregistrar?

I’ve done it before by putting the car on stands, starting it up, and gently rolling the rear wheels and hitting the brakes. fools the computer. But maybe this is one of those things you don’t tell people about…

:whistle:

#11

I am having similar problems. You say your pedals feel "crappy". Does this mean, they are soft? When you get down hard on the brakes do the tires lockup and skid? I replaced the ABS pump because I felt it was clogged with old, gunky fluid. Maybe this was a mistake since it didn’t solve my problem.

#12

Trick if you have lines open on the car to slow the loss of fluid.

Take a piece of plastic bag. take the reservoir over off. remove the float assembly for the level sensor. put the plastic over the top of the MC reservoir. put the cap on.

Now there is no vent on the MC and your fluid won’t run out near as fast.

Make sure you remove it before you drive it.

#13

TXBDan wrote:

[quote]I see. well that then, is my prime target.

I looked through my Bentley, but didnt see anything on activating the ABS unit. Can you elaborate on that, nasaregistrar?

I’ve done it before by putting the car on stands, starting it up, and gently rolling the rear wheels and hitting the brakes. fools the computer. But maybe this is one of those things you don’t tell people about…

:whistle:[/quote]I will have to find the procedure. I thought it was in the bentley…it involves a jumper across terminals at the relay If I remember correctly.

#14

My brakes are great.

I do this:

hook a tube to the nipple…

put the tube in a jar with some old brake fluid in it…

crack the nipple…

wait till there isn’t any more bubbles.

that’s it.

#15

My brakes are great.

I do this:

hook a tube to the nipple…

put the tube in a jar with some old brake fluid in it…

crack the nipple…

wait till there isn’t any more bubbles.

that’s it.

#16

Can anybody add anything to this? I’m having the same problem (soft pedal), but I’m pretty confident the air is out of the lines.

#17

mskeen wrote:

I am still coming up to speed on the BMW vs. the Porsches that I have owned so maybe this helps, maybe not. The 911 has "monoblock" with pistons on both sides so nothing moved but the pistons and pads. One of the things I had to learn about and maintain on the 944 were the "sliders". The 944 has a piston on one side (like the BMW) and the frame slides to pull the outer pad against the rotor. I had a terrible time with spongy brakes and looked at everything. Didn’t solve the problem until I disassembled the calipers and cleaned off all of the rust on the sliders with a wire brush then lubed with a little bit of anti-seize. Worked fabulous after that. The reason that my brother gave me for the spongy feel was that the caliper wasn’t sliding and so when the piston pushes on one side, the moving part flexes. Haven’t closely inspected the mechanical setup of the BMW brakes yet but maybe this binding issue could also happen with the BMW brakes. Just a thought. Liquids don’t compress so it’s either air or a mechanical movement of some kind allowing the pedal to feel spongy.

#18

erupert66 wrote:

[quote]mskeen wrote:

I am still coming up to speed on the BMW vs. the Porsches that I have owned so maybe this helps, maybe not. The 911 has "monoblock" with pistons on both sides so nothing moved but the pistons and pads. One of the things I had to learn about and maintain on the 944 were the "sliders". The 944 has a piston on one side (like the BMW) and the frame slides to pull the outer pad against the rotor. I had a terrible time with spongy brakes and looked at everything. Didn’t solve the problem until I disassembled the calipers and cleaned off all of the rust on the sliders with a wire brush then lubed with a little bit of anti-seize. Worked fabulous after that. The reason that my brother gave me for the spongy feel was that the caliper wasn’t sliding and so when the piston pushes on one side, the moving part flexes. Haven’t closely inspected the mechanical setup of the BMW brakes yet but maybe this binding issue could also happen with the BMW brakes. Just a thought. Liquids don’t compress so it’s either air or a mechanical movement of some kind allowing the pedal to feel spongy.[/quote]

Thanks for the reply. I don’t think that’s it, as I had all the calipers off for cleaning/rebuilding this winter, but I’ll see if I can lubricate it somehow. I suspect there is air in the ABS pump somewhere (as suggested previously), but I can’t find any solid method of getting that out. Some people on other forums I’ve read suggest bleeding as normal, then driving the car to engage the ABS, then bleeding again. I’ve pretty much done this already. The other method I heard was pump the pedal 3 times, open bleeder, pump 10 times; that just sounds like a good way to put air in the system.

#19

Does this spongy pedal result in a brake lockup and skid? When I brake hard this happens to me.

#20

Does this spongy pedal result in a brake lockup and skid? When I brake hard this happens to me.