E39 brakes "frozen"?

[ross1]

what do you guys make of this?
https://www.bimmerforums.com/forum/s...2#post30129432

[02Pilot]

Could be water in the booster - easy to check, so do that first. The drain under the cabin air filter housing can get clogged up, which I suppose could get bad enough to get into the booster.

[Breeze1]

I noticed that the "same thing" happens to my car but with the AC: whenever I use it while it's raining, it blows air that is at the ambient temperature and not cold anymore; since the rubber gasket on the plastic part at the bottom of the windshield is damaged, I'm suspecting that water freezes somewhere when making contact with the gas lines and prevents the gas from circulating; the same thing could be happening to you somewhere along the fluid lines (not necessarily the booster or reservoir).

[bmwdirtracer]

I'd go with the consensus, Ross: Water in the booster. Now, I'd add that since the brakes work fine the rest of the time, and swapping the booster on an E39 is a royal PITA, I'd be tempted to use a vacuum device through the hole, with a tube long enough to reach bottom, and suck all the water out......

[02Pilot]

I'd go with the consensus, Ross: Water in the booster. Now, I'd add that since the brakes work fine the rest of the time, and swapping the booster on an E39 is a royal PITA, I'd be tempted to use a vacuum device through the hole, with a tube long enough to reach bottom, and suck all the water out......

Absolutely use a suction pump to empty it (assuming it's the problem). If it were me I'd then refill with rubbing alcohol and then suck that out too, which will help to get rid of any residual water.

[ross1]

Well, here's what I've done.
The booster seems dry, I inserted ~3' cotton rope which came out dry, I did this several times. A small dia. vacuum hose netted the same, negative results. The compartment is dry with no sign of previous water incursion and drain is clear. I have no way to be certain there is no water as I cannot see where the rope or tube wind up. My recollection of the construction of these is a large spring one side of the diaphragm, perhaps I'm not touching bottom.
I power bled all four corners and the fluid wasn't terrible, very weak tea color so some rust/moisture was in there but I've seen WAAAY worse with no issues. Went through a qt of fluid, what comes out now is clear.
I'd like to run the ABS pump. Anyone care to guide this Neandertal without proper equipment how to achieve this? Found a thread relevant to E36s which states juming the pump relay is all. figured I should ask the wisened residents here.
Edit: This is (that F%^*ing bitchy) Bosch 5.7 so no pre-charge pump I can power on by jumping a relay

[ross1]

I'd go with the consensus, Ross: Water in the booster. Now, I'd add that since the brakes work fine the rest of the time, and swapping the booster on an E39 is a royal PITA, I'd be tempted to use a vacuum device through the hole, with a tube long enough to reach bottom, and suck all the water out......

Oh yeah!
I have a spare booster and a full shop beer fridge but still cringe at this.
I don't think it has water but am not certain, hoping the bleed will do it but not confident there either.
Can you guide this stooge on bleeding the abs with a hammer and tongs?

[02Pilot]

My approach before I got a scan tool that would trigger the ABS was to go out and try to lock the wheels with a few panic stops (much easier in the rain), then pressure bleed.

[ross1]

My approach before I got a scan tool that would trigger the ABS was to go out and try to lock the wheels with a few panic stops (much easier in the rain), then pressure bleed.

Yep, I've done that but it's very tedious, hard on the car and either pisses of the neighbors or attracts attention from John Law.
Hoping for a work around that won't rouse the ire of Herr Bosch.

[bmwdirtracer]

I use ISTA to bleed the ABS...like after changing a master cylinder....and it is a royal bitch. Takes 2 people four or five rounds of repeated activations, pumping, et al.

But yet, this really can't be your problem. You've got no boost, not air in the system. To freeze, you'd have to have nearly pure water in the brake system. As hydrophilic as brake fluid is, there ain't no way.

Try this: When you've got the frozen hard pedal next time, after starting the engine, shut the car off again, and pull the hose fitting out of the vacuum booster. Do you hear vacuum release? If not, check that grommet for cracking, and the hose....and then try replacing the (cheap and easy) one-way valve on the hose.

I promise you, you do not want to pull the master cylinder off an E39.

[ross1]

I use ISTA to bleed the ABS...like after changing a master cylinder....and it is a royal bitch. Takes 2 people four or five rounds of repeated activations, pumping, et al.

But yet, this really can't be your problem. You've got no boost, not air in the system. To freeze, you'd have to have nearly pure water in the brake system. As hydrophilic as brake fluid is, there ain't no way.

Try this: When you've got the frozen hard pedal next time, after starting the engine, shut the car off again, and pull the hose fitting out of the vacuum booster. Do you hear vacuum release? If not, check that grommet for cracking, and the hose....and then try replacing the (cheap and easy) one-way valve on the hose.

I promise you, you do not want to pull the master cylinder off an E39.

The reason I want to cycle the ABS is simply to be sure there is fresh fluid throughout. Driving and invoking an ABS stop will run the pump but with nowhere for the fluid to go won't accomplish anything unless I want to bleed the thing every stop.
I need to pay better attention to the symptoms. This happened last winter and I had forgotten about it as the car wasn't used until recently. First cold morning and I get a (familiar)surprise while backing out of my driveway.
I'm glad to hear you concur with the contaminated fluid not being at fault, I couldn't see this either.
I'm pretty well convinced the booster is dry and my frozen theory is a red herring. Lack of boost, as you've said, seems the issue. Maybe a shrunken grommet?
Another thought I have is that perhaps the troublesome oil separator lines have managed to back up moisture into the vac line for the booster. I'll examine that later today.
Below freezing ambient IS the catalyst.
EDIT: That one way valve, yeah, that's the ticket! Will investigate and advise.

[ross1]

NO smoking gun. Here is the latest, I have little confidence anything has changed, the next cold snap will tell.
Two one way valves, one on the booster another Y arrangement in the engine compartment, both flow one direction only. The one at the booster would only flow one direction but when compared to another I had on hand it seemed slightly restricted grommet was fine. Swapped out the questionable check valve, we'll see.