Weird brake problem

[Slapnutz]

2006 BMW X5 4.4L sport package

When i stop the x5 it seems to roll to a stop and if i push really hard it will stop fully but i have to maintain the hard push or it will roll again. This problem happened overnight also.

Some history: 1 year and 2 months ago had brake fluid changed and brake lines replaced, 6 months ago changed brake pads to cool carbon, problem started 2 weeks ago, flushed brake fluid with 1 liter of pentosin, no air in the lines.

Conditions: i live 12,500 foot up a mountain so dirt roads, steep inclines and declines, country roads

So i have researched quite a bit and i think it might be brake booster or master cylinder. Any test for these to see if bad? Also i want to rebuild the brake calipers also but can only find the seals for the front. Anyone know a place i can get the rear seals. I have checked autohisauz, bav auto, pelican parts.

[Slapnutz]

Also a couple more things, i have the creader 6 and there was no codes that showed up.

And i bought the motive power bleeder black label, has the aluminum attachment to master cylinder, and it doesnt fit the master cylinder. Anyone else had an issue?

[Omerta]

Is the pedal spongy or does it feel like you dont have enough friction?

Your pads could have gotten glazed, you could be loosing vacuum to your MC reducing your braking force as a few options.

[Slapnutz]

The brakes feel perfectly normal when slowing down at higher speeds it is just under 10 mph it starts feeling weird. Unless i step on the brakes really hard the car wants to keep rolling.

After bleeding the brakes i started up the car and the brakes felt fine. As soon as i put the car in reverse and moved a little it just did not want to stop. Weird how it happened overnight.

[thrillcat]

I had this same problem this summer. Could be 1 or more of 3 things:

Brake Booster, Brake Vacuum Pump, or the Master Cylinder.

I replaced both the booster and the vacuum pump and the problem is fixed. I would do the pump first, as I'm pretty sure that's what fixed my issue.

[LeiZ]

Also check the caliper piston if it got stuck towards the end of the displacement. Sounds to me the piston has no problem pressing in the beginning, but not cooperating at the end.

Good luck!

[Doru]

On my vehicle, when I almost came to a stop, if I didn't push the brake pedal hard, it felt as if someone was pushing the vehicle from behind - a sort of a "jittery" stop if you will (stop-go-stop-go by inches). The only thing I did was changing the seals of the vacuum pump when I did the valve stem seals. Haven't had the issue since. So it could also be some bad seals?

[thrillcat]

The thing that points me to the vacuum pump is that it stops fine at higher speeds, but at lower speeds, there's not enough vacuum built up from the engine speed and the vacuum pump is not functioning properly (or like Doru said the seals are bad) and it's not able to give the booster the oomph it needs to help you stop.

This is EXACTLY what mine was doing.

[Junkycosmos]

Hi. Agreed on either vacuum pump or brake booster. I just went though something similar. For me the key test was that I could still stop the X just fine but I had to press very hard on the pedal at engine idling. In fact it was same as if I had the engine off.

Not sure if common issue on the 4.4 but on the 4.8s (in X and 545 etc) non return valve going bad and oil going into the brake booster is common.

Would suggest you try to rule the vacuum boost side of brakes in or out. You could have something else going but here are my details
http://www.xoutpost.com/bmw-sav-foru...cuum-pump.html

[Cadburysx5]

What kind of brake pads do you have exactly I have seen problems on a wide range of vehicles where the brake pads need to be hot in order to work properly and city driving low speed braking they have this issue. If the brakes are meant for a more performance application they won't keep their set when u brake them in. And in a sense need to be broken in each time u drive. And also if u have a stuck piston that is dragging the brake pads they could be over heating because what you're describing is like brake Fade not necessarily loss in pressure.