Brake bleeding nightmare

[E30is90]

Tried to have a local shop replace my old, but still in decent shape, brake line with stainless steel hoses I picked up. After he looked at the old lines he convinced me it was more trouble than it was worth to pull off the original hoses.

I begrudgingly agreed and asked him to just go ahead and bleed my lines to replace with new ATE Super Blue, since the wheels were off and it was already up on the lift. He used a vacuum bleeder and started on the appropriate rear right. Within seconds the fluid stopped running from the bleeder valve and he couldn't get it to resume. He then tried my rear left and it trickled out before stopping. Moving to the fronts, they bled fine.

Fast forward 3-hours and no brake pressure, I'm dead in the water. I insisted that he managed to get air in the lines, he insisted that he kept the reservoir filled and the master cylinder never came close to running dry and that he's bled thousands of brakes over the past 30-years. He then started trying to convince me that my rear brakes likely haven't been working and that I simply didn't know about it. I told him my brakes were working perfectly when I drove here and now they're shit.

Then out of the blue I see this guy come in and start pulling off my coolant overflow reservoir (he was called in by the shop manager, from another service center). He has this 12VDC powered probe and he starts touching it to the accumulator, which starts to suck the brake fluid from the fill container. Blue fluid shoots out from each bleeder valve, in-turn when opened, and my brakes are back in service.

I don't know how my accumulator managed to run dry even though they had kept the fill container well over the min line during the initial bleed. I hadn't read anything about this problem in the Benley manual. I asked this guy how he knew exactly what had happened and he said, "because I owned an 88 and 89 E30" and the same think happened to him when using vacuum bleeding. He only uses his own modified manual bleeding method.

I tell you, my car would still be sitting in the shop if it weren't for this guy and next time, I will swear off these maintenance items being performed by some yahoo at a local shop! The question is, would this have happened to me too? Why did the accumulator run dry when the fill reservoir had fluid? Questions, questions...

[jlevie]

It sounds to me like the problem was stuck valves in the ABS unit, which means that you probably didn't have any rear brakes. The ABS unit is what the other tech fiddled with and cycled with his 12v probe. His cycling of the ABS unit apparently freed up the stuck valve.

[E30is90]

It sounds to me like the problem was stuck valves in the ABS unit, which means that you probably didn't have any rear brakes. The ABS unit is what the other tech fiddled with and cycled with his 12v probe. His cycling of the ABS unit apparently freed up the stuck valve.

That's what the shop owner tried to convince me. But, when I drove the car that morning, the brakes were firm and feeling just like it always had. I had just replaced my rotors and pads a couple of months back. I get brake dust on my fronts and backs after each drive. I'm certain my rears were working.

After this issue occurred during the bleeding, I had no brake pressure at all. The brake peddle simply dropped straight to the floor. The shop manager said, you won't be able to drive the car until this problem is fixed. Obviously, I drove the car there with brakes.

The mechanic that fixed the issue indicated that the same thing had once happened to him on his 89 E30 when he had bled his brakes. He indicated that if air gets into the accumulator, it won't prime itself and brake fluid won't be pressurized throughout the system. After manually drawing the fluid into the system, one of the mechanics back by the rears heard air being forced out the bleeder valves, when he opened each one during the procedure, before the fluid was pushed through.

All 4 mechanics now working with it agreed that they had inadvertently gotten air into the system during the bleed process. In fact, because of all the grief they put me through and the time they had me there (from 10:30am to 6:00pm) the shop manager apologized and said I'm not going to charge you for any of the work they did on your car today. (They also didn't ever want to do a brake bleed on an E30 again).

[whysimon]

I think I might have the same problem. I can't seem to get the air out of my brakes (MC change) I bench bled and hooked up a pressure bleeder and still can't seem to get my brake pedal firm. I think its starting to fuck with my slave as well.

[whysimon]

^^^^^ so how does one probe the accumulator?

[E30is90]

^^^^^ so how does one probe the accumulator?

I couldn't fully see what this guy was doing, but after he pulled up the coolant reservoir container, he remove what looked like a metal box relay that plugged into I believe the ABS unit (just behind the driver side headlights). He then attached what looked similar to a DC circuit tester to the front battery terminals and touched it against one of the exposed contacts. I heard what sounded like a little motor sucking fluid from the brake fluid container. When the guy in the back opened the right rear bleeder valve, he heard air being pushed out followed by a full stream of brake fluid. Same on the left rear and pressure was restored– brakes back in service.

I would have liked to talk with this guy a little further, but he scooted out pretty fast. The only thing he told me is that it's easy to happen when vacuum bleeding if air gets pulled into the accumulator. He said he wouldn't use vacuum bleeding on his E30, only some modified manual method that he came up with.

[jlevie]

The only place that air can be sucked into an operational brake system is by draining the reservoir. The "accumulator" you mention is actually the ABS unit and it is very common for its valves to stick. Sometimes cycling the ABS, which is what the tech did, will free up the valves are return the system to normal operation. In other cases the only fix is to replace the ABS unit.

You may have thought that you had normally operating rear brakes, but in my experience you just didn't know that they were barely working, if at all.

The best way of bleeding brakes is to use a pressure bleeder. Partly because it can't suck air into the system like a vacuum bleeder can and partly because with a liter or more of fluid in the pressure bleeder you won't run the reservoir dry while flushing/bleeding the brakes.

[nmlss2006]

Shouldn't the brake torque test they do at inspection time catch this though?

[jlevie]

I don't know how that test is done. If on a four wheel dyno, the yes it should if their data is accurate for an E30.

The rear brakes on an E30, or most any other BMW, don't do a lot. Probably 80-85% of braking force comes from the front wheels with a stock system. So even if the rear brakes aren't working properly most folks won't be able to tell as they never get into threshold braking.

[nmlss2006]

I hear you, but let me ask a question: given that brakes have overheating problems by definition, wouldn't shifting the bias to the rear help matters, on the track? Of course, this assumes you keep ABS to avoid embarassing situations. Heck, it might even help with turn-in...

[E30is90]

You may have thought that you had normally operating rear brakes, but in my experience you just didn't know that they were barely working, if at all.

Honestly, I can't buy the belief that my rears weren't working. I just replaced my rotors and pads on all fours and just placed on a new wheel/tire package. I've been driving this car for 21-years (original owner) and would absolutely feel a change in braking behavior. I get brake dust accumulation on each drive and brake fluid bled from the rear calipers when the bleeders were first cracked. I'm certain, beyond doubt, that the vacuum bleeding method sucked air into the system. I lost all brake pressure as a result of the bleed procedure. It wasn't until the purge procedure was performed that pressure was restored. When driving the car after the brakes were restored, everything felt just the way it did before the problem had occurred.

The best way of bleeding brakes is to use a pressure bleeder. Partly because it can't suck air into the system like a vacuum bleeder can and partly because with a liter or more of fluid in the pressure bleeder you won't run the reservoir dry while flushing/bleeding the brakes.

I completely agree. I had always had it done this way in the past. A friend who works in a tire center told me he'd do my brake flush with his vacuum bleeder so I could see how its done and do it myself in the future. Well, I definitely saw what not to do...

[nrubenstein]

Yes, you want to shift bias to the rear with sticky tires and a stiff suspension. Remember that the E30 stock bias is set up for a super, super soft suspension with absolute shit tires.

[jlevie]

Increasing rear brake bias in an E30 can help on the track. As can twiddling ballast weights to improve front to rear and cross weight balance. Without introducing some form of cooling, you don't want to go too wild with the rear brakes. Ducts are easy for the front brakes, not so easy to for rear brakes.

[jlevie]

Honestly, I can't buy the belief that my rears weren't working. I just replaced my rotors and pads on all fours and just placed on a new wheel/tire package. I've been driving this car for 21-years (original owner) and would absolutely feel a change in braking behavior. I get brake dust accumulation on each drive and brake fluid bled from the rear calipers when the bleeders were first cracked. I'm certain, beyond doubt, that the vacuum bleeding method sucked air into the system. I lost all brake pressure as a result of the bleed procedure. It wasn't until the purge procedure was performed that pressure was restored. When driving the car after the brakes were restored, everything felt just the way it did before the problem had occurred.

Unless the reservoir ran dry or there was a fault elsewhere in the brake system I don't see the vacuum bleeder drawing air into the system. And I've never heard of one moving the valves in the ABS so as to cause the valves to stick and block fluid flow.

[E30is90]

Unless the reservoir ran dry or there was a fault elsewhere in the brake system I don't see the vacuum bleeder drawing air into the system. And I've never heard of one moving the valves in the ABS so as to cause the valves to stick and block fluid flow.

Hey, I hear you. The guy who did the bleed had said the same thing. I really need to talk with the mechanic who told me that this happened to his own '89 E30 and that fixed the problem doing the purge procedure. I'd like to have all the facts about what occurred and try to make sure that whatever did happen doesn't happen again. It was a shitload of grief, driving in with breaks and then losing all brake pressure with air stuck in the system. I'm pretty certain that if this was done using the typical pressure bleed, by a braking specialist, this never would have happened.