Brakes Require Lots of Pedal to Work

[hamann318is]

I've had this problem for sometime. The brake pedal pretty much will not brake unless you pump it two to three times. There is no visible leak, and I don't lose any fluid. This is after a new master cylinder and bleeding the brakes a few times...

I used to have to push the pedal to the floor and then let off and push again to get a pedal feel. To resolve this, I bled the brakes, which only made it moderately better, and then the pedal went back to behaving like this. So, I then replaced the master cylinder, which I thought fixed the problem. Pedal was decent, so I thought nothing of it. I drove it back to school, and over the period of the three hour drive, the pedal became what it is and what I think is worse than before.

This is a '91 318is with ABS. I had it on the track, and I don't think the ABS was engaging at all. I tried to get the ABS to engage with the new master cylinder to no avail.

I'm not quite sure what's wrong, does anyone have any thoughts? Thanks in advance!

[Massive Lee]

Have someone experienced, or a shop, bleed your brakes properly. Especially after changing the MC, bubbles are most likely trapped everywhere.

[hamann318is]

After following that suggestion, I took it to a shop, they bled it and the brakes were fine. However, after I drove it on the highway for a few hours, I lost the brakes again, and they behave like they used to. The fluid level in the reserve tank has stayed at max, and I don't see any indication of a leak. I'm not trying to throw out that possibility, but I don't know what else could have caused the brakes to do this... Anyone have anymore ideas?

Another thought. I didn't bench bleed the master before installing it, but I have bled the system a few times along with a professional bleeding at a shop. Would that cause a problem still? It just seems like the brakes are OK for a bit, but when you have the car on a highway, the brakes just go away and don't come back. I have a hard time understanding that aspect because, typically, I'm not using the brakes a whole lot on the highway.

[Massive Lee]

It is strange that it worked fine, then agravated.

- Are calipers sliding properly
- Is booster working properly? Is it keeping vaccuum as it should?
- Is the ruber seal at the base of the MC installed?
- Has the shop tested/cycled the ABS pump?

Lee

[hamann318is]

It is strange that it worked fine, then agravated.

- Are calipers sliding properly
- Is booster working properly? Is it keeping vaccuum as it should?
- Is the ruber seal at the base of the MC installed?
- Has the shop tested/cycled the ABS pump?

Lee

- How would I check to see if they're sliding properly?
- I'm pretty sure the booster is good. The only thing I know about that is that the pedal would be too firm. In my case goes to the floor and comes back up, and then I have some more pressure to deal with.
- I remember that I checked for that. The MC I installed had a rubber seal on it when I installed it, but I'm not 100% sure that we're talking about the same seal.
- They told me that they could engage ABS, but that's all I know about it.

What would you recommend having them look at?

[jlevie]

With a new master cylinder in place, the brakes properly bled, and no leaks or loss of fluid, the only candidate left is the ABS unit or thin pads that are backing way out during driving.

If the pads are backing away from the rotors, you could experience this pedal behavior after driving for a while w/o use of the brakes. But once you pump the pedal things should be normal for subsequent braking immediately after pumping up the pedal.

[hamann318is]

Well, I had to drive the car back home, so over the course of that highway drive, the brakes have gotten much worse.

The best way I can describe how they behave is pushing the pedal all the way to the floor with a little initial brake bite and a little hydraulic pressure, and then I'd have to do that now 2 times before any sort of backpressure is established.

I also have to push the pedal to the floor and let it come back up. I can't just depress it a bit, that doesn't seem to work.

I'm not really sure why a highway drive would make the brakes worse, but that's the culprit every time apparently.

Any ideas?

[Massive Lee]

One thing that comes to my mind is a bad wheel bearing. It did happen to me last summer. I found that my brake pedal would be extra stiff after bleeding but that after backing out the parking area or after a corner, it would require two or three pumpings until they are good again, then bad again after a corner. I then found that the wheel bearings were loose, pushing the pistons back into their bore, requiring extra pumping to bring back the tight fit, then pushed back again after a corner. Arghh. Changing bearing solved the problem.

[hamann318is]

Another thing to add. For some reason, the brakes initially have some bite when I touch the pedal but not enough to really slow the car down. When the pedal is on the floor, it seems like the braking is somewhat normal, but when I let the pedal back up, it's mushy again until it is pumped a few times.

Not sure if that means anything, but I thought it could be important.

[Massive Lee]

Inspect the wheel bearings for play. All four.

[hamann318is]

I'm going to check the wheel bearing, but what checks can I do myself on the booster? I was having some vacuum problems - the Check light after idling a bit - for a while. However, that problem has gone away. I can say that when I pump and hold the pedal down with force when it has pressure, the idle does drop a bit.

We had the same sort of a problem on a Dodge that came down to a bad ABS computer, but the fuse had blown too. I'm not getting any sort of ABS light, except for the one at start up. Any other why I can run some checks on the ABS system?