Spongy brakes w/ new fluid, help?

[Robin-535im]

Hi Everyone,

This weekend I installed new rotors and pads. ATE rotors and Jurid pads - same as the PO put on the car and I liked the feel so I kept it.

NOW - I used a pressure bleeder, new ATE gold fluid, and pumped the brakes. Bill R showed us this: http://www.bimmer.info/forum/showthread.php?p=66978#post66978

which I didn't follow properly... I kept the system pressurized and pumped with the bleed valve closed, then opened it with the brake pedal held down all the way on the last pump.

But I'm pretty sure all the air got out, we flushed a lot of new fluid through the lines.

Tried the brakes, very spongy, no decrease in sponginess with pumping the brakes.

Then went on some lonely road and did 5-6, 80mph to 5mph stops, then drove for 20 minutes. All the while, fully spongy, couldn't even press hard enough with my manly legs to get it to almost lock up, it took full force to get it to stop.

Brakes look bedded just fine, but STILL SPONGY. Before they were rock solid, now it's like the system is half full of air.. Except for the fact that pumping doesn't bring back the pedal at all I would think it is air in the lines...

Does not change from start of drive to end - spongy on the first application, spongy all the way to work, spongy when I stop for the last time.

Any ideas? Could I have messed up the booster or cylinder by pumping with the pressure bleeder hooked up?

TIA!

- Robin

[Tiger]

I would say master cylinder is gone.

[mikeythekidd]

you still got air in the lines is all I can tell ya

[Robin-535im]

you still got air in the lines is all I can tell ya
Well.... all the times I've ever had air in the lines, pumping the pedal would gradually bring the stiffness back. I can pump that puppy all day and nothing... Now my experience is with old american cars, not BMW's... does air in the lines act differently with an ABS system?

[Robin-535im]

I would say master cylinder is gone.
That's what I'm thinking. No excess heat on the disks, doesn't look like anything is stuck (brakes feel even from side to side) but what I do notice is the backs seem to be doing a lot more stopping work than the front but that's just an eerie feeling I get, I don't have any proof of that.

[Bin_jammin]

Doesn't sound like a master to me. Usually when a master goes bad, you'll lose your pedal will bleed down while you're at a stop. A spongy pedal usually means you've got low rear shoes when you've got drums in the rear. Personally, I don't like using pressure bleeders, the only time I ever use them is when I've got a car that's just stubbornly refusing to get a pedal, and odds are it won't work. Get a friend, have them help you. There's nothing like actually actuating the brakes via the pedal when you're bleeding, and I'd be willing to bet that's what you need to do.

Before that though, go through your brakes and inspect them, make sure you don't have a stuck piston in a caliper, or something else isn't binding.

[gale]

Robin, does yours have the vacuum booster or hydro-boost?

[Robin-535im]

Robin, does yours have the vacuum booster or hydro-boost?
Vacuum booster I THINK... How to tell?

"Girling Brake Servo Unit" ala RealOEM, has a big 1/2" vacuum line from the manifold.

[Blitzkrieg Bob]

ABS pump may have air trapped in it.

You'll need to get it hooked up to a special system that runs the pump while bleeding...off to the dealer$$$

[Martin in Bellevue]

Robin, I'm thinking the abs should be induced with a few hard stops in a remote area. Then bleed the brakes again. Does anyone know how to cycle the abs pump manually, without the dealer-only modic peecee?

[Robin-535im]

Robin, I'm thinking the abs should be induced with a few hard stops in a remote area. Then bleed the brakes again. Does anyone know how to cycle the abs pump manually, without the dealer-only modic peecee?


I will try that... always fun to make ABS come on! I'm wondering how would air get in the system, the pressure bleeder pushes in the fluid, I could see small bubbles but it didn't run dry (I've mastered that trick in the past, believe me!)

Now that I think of it, the first time I used the brakes it seemed to catch, while I had my foot on the brake to back out of the driveway it felt like there was an obstruction or a little nub the pedal was catching on, but the weight of applying the brakes seemed to pop it through that spot. Wondering if that was an air bubble or a broken valve in the MC, or just my imagination. Strangely the back brakes seem to work better than the front, could the front circuit on ABS or master cylinder go out and the rear still work...

[Bin_jammin]

It's possible that your old pads have worn a groove into the holder. That would make the pads lock into place (in extreme instances, I've seen it happen though)

Check for that too.

[DanDombrowski]

Try putting the power bleeder back on the cap, pump to about 20 psi. See if the pedal firms up then.

I'm not sure what this would actually test for. If the MC is bad, Im not sure that adding pressure would firm the pedal. It would certainly firm the pedal if there was air in the lines though.

[632 Regal]

not to repeat everything stated here I do know that once the ABS unit catches a breeze its a MO-FO to get out. You do need pressure to get it out but also like mentioned the self bleeder might not do enough volume fast enough to push the air out of it. Might need a pro system to get you back to the mark.

[Ross]

I'm guessing the pads aren't yet bedded in or that they have become glazed.

[bsell]

Now that I think of it, the first time I used the brakes it seemed to catch, while I had my foot on the brake to back out of the driveway it felt like there was an obstruction or a little nub the pedal was catching on, but the weight of applying the brakes seemed to pop it through that spot. Wondering if that was an air bubble or a broken valve in the MC, or just my imagination. Strangely the back brakes seem to work better than the front, could the front circuit on ABS or master cylinder go out and the rear still work...

I vote for the pressure bleeder pushed some trash into the bore of the front brake half of the master cylinder, causing the 'catch' sensation in the pedal. After you pushed the cup for the front brakes through the trash, cutting the cup in the process, every return of the brake pedal sucks air into the front brake system.

Take a look at the back end of the master cylinder where it joins the booster. If you truly cut the cup, you might be pushing fluid back out the pushrod seal and into the booster. This might show as some wetness at the junction.

Or you could have spring clips installed incorrectly causing a 'catchy' feel during brake application as the pads snap over the incorrectly installed springs.

Good luck,

Brian

[Robin-535im]

I vote for the pressure bleeder pushed some trash into the bore of the front brake half of the master cylinder, causing the 'catch' sensation in the pedal. After you pushed the cup for the front brakes through the trash, cutting the cup in the process, every return of the brake pedal sucks air into the front brake system.

Take a look at the back end of the master cylinder where it joins the booster. If you truly cut the cup, you might be pushing fluid back out the pushrod seal and into the booster. This might show as some wetness at the junction.

Or you could have spring clips installed incorrectly causing a 'catchy' feel during brake application as the pads snap over the incorrectly installed springs.

Good luck,

Brian
Thanks Brian (et. al.) appreciate the comments.

My plan of action now is to do another careful bleed per the BMW instructions and if that doesn't fix it, get a new MC. $160 bucks or so from BMA, $420 from the dealer!

I checked the pads and they all appeared seated properly, and the wear pattern on the rotor is even, so I'm concluding that the pads are contacting correctly. Plus the bedding process resulted in the bluish tint I expected, evenly across the rotor.

I'll post again if/when it's resolved...

[Blitzkrieg Bob]

It's probably not the master cylinder. so don't spend the $$ yet...

they usually creep to the floor at stops, lots of pedal travel before they bite, or leak out the back of the bore down the booster.

spongy sounds like trapped air or a cracked & swelling brake line.

[Barney Paull-Edwards]

Try the following: with engine off,pump hard four or five times and release rear right nipple,repeat on rear right.Repeat on front,idea being to blast air out of system,sometimes works.See if clamping off vacuum pipe to servo improves pedal,if so theres your answer.

[Robin-535im]

I rebuilt the front calipers and that helped the issues I was having with one of the calipers dragging and heating up the left front rotor too much. I used a thermocouple to check the temps after the evening commute and found the left side ~40C hotter than the right. I rebuilt both calipers (which is basically cleaning them up nice and replacing the two rubber parts) and they now slide much easier, and no more binding that I can tell.

Bleeding didn't fix the sponginess much, but the new master cylinder seemed to. Brake booster tested out okay per Bentley's troubleshooting.

The "proper" BMW bleed procedure uses about a quart of brake fluid though! Actually, a bit more if you do the clutch too. Thanks everyone for the suggestions.

One real smart thing I did, while holding the old master cylinder, is push on the rod a little bit. It gave way and shot a snotload of brake fluid out into the garage, and of course on to the car. I had a pressurized bottle of hot soapy water there for just that reason... don't trust myself around brake fluid... so it wasn't too big a deal.