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Bleeding the ABS pump?
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TOPIC: Bleeding the ABS pump?

Bleeding the ABS pump? 5 years, 6 months ago #35700

  • MMChris
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Hi all,

I thought I'd turn here to hopefully get some help. My ABS stopped working after working on the car all winter. I was at VIR this past weekend (HPDE group 3) and would have liked the ABS.

Situation:

I replaced my SS lines with new ones and in the process damaged the threads to the LF hard line. I replaced this hard line and probably introduced air into the ABS pump.

When I am rolling to a stop at very slow speed and lightly press the brakes, the pedal pulses like ABS and there is a strange sound like a motor running.

I have had all the wheel sensors tested, and they are good. I have also looked for the ABS relay which is near the ABS computer, but it is not there. I have also tried a replacement ABS computer and have not had any luck.

My car is an 89 325i sedan, and I was told the ABS relay may have been changed to an internal relay in the ABS computer... but I'm not sure if this is true.

Sean Thompson with NASA told me there is probably air in the ABS pump and there is a process to jump pins on the ECU and manually activate the ABS pump, allowing you to bleed it. Has anyone heard of this, and is there a process in doing it??

Thanks for any help, this has been a pain to deal with.

Re:Bleeding the ABS pump? 5 years, 6 months ago #35744

  • edavidson
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Chris,

I am in the same boat (damaged a hard line that connected to the ABS pump) and plan on working on it this weekend. I have been researching this and opinions are mixed. Several forum posts (like this one www.318ti.org/forum/archive/index.php/t-14322.html) suggest that you just bleed the system, go out and activate the pump, and re-bleed. I will be discussing with my local BMW master tech and get back with any further suggestions. Best of luck,
Ed

Re:Bleeding the ABS pump? 5 years, 6 months ago #35781

  • Randy87is
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When I changed my front brake lines to SS, I had problems with bleeding the brakes. I bled them and they seemed firm, but when I drove the car, the pedal went to the floor and had to be pumped to get the brakes to work.

During a second bleeding, I got a lot of air out of the left front. The pedal felt better, but when I drove the car it was still soft and had to be pumped to get the brakes to work. I then bled the brakes again. I noted that the Bentley manual said to pump the brakes at least 12 times on an ABS car. I did that and after a couple of times cracking the right front bleeder valve, got a huge gush of air out of that bleeder. That took care of the problem with the pedal firmness.

Don't know if my problems were because I got air in the ABS pump or what, but you might try bleeding the system as described in the Bentley manual to see if that helps.

Sadly, I have some other issue that is keeping my ABS from working, so I'll be going through the process of trying to track down the cause. On that note, how did you verify that your wheel sensors are working?

Re:Bleeding the ABS pump? 5 years, 6 months ago #35795

  • MMChris
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Thanks for the info, I'll try pumping the brakes a lot more when bleeding and see if that helps.

I had a shop test the sensors, so I'm going on their word that they are ok. If I make any progress on this I'll let you guys know.

Re:Bleeding the ABS pump? 4 years, 6 months ago #45423

I have a different bleeding issue. The previous owner of the car changed all the brake lines and the car sat for two years with no fluid. We added fluid and tried to pump the brakes with the pump and hold method, but the pedal is unnaturally solid and will not pump, even with a bleeder open. We tried this with the car on, the car off, the front brake bleeder open, the rear brake bleeder open, nothing changes. Any idea what causes this? When the car had no fluid in it, the pedal predictably dropped straight to the floor, but now with fluid it just sits there rock solid. I must be doing something wrong with the ABS pump or something. If I just put pressure on the master cylinder cap, would that necessarily push fluid through the ABS pump, or is there something that I am badly missing? It is entirely possible that I just don't know what I am doing bleeding on this car. Please advise.

-Scott
2010 NASA National Champion
2009 NASA National Champion
2008 NASA National Champion

Re:Bleeding the ABS pump? 4 years, 6 months ago #45427

Randy87is wrote:
On that note, how did you verify that your wheel sensors are working?


I just went through this too. From all the information I could gather, take a multimeter and read the ohms on each sensor. The front ones disconnect on the wheel wells inside the engine bay and the rears' disconnects are where the rear seat used to be. They should read between 800 and 1600 ohms. Mine all read around 1000. Then, with the meter still connected, spin the hub. The ohms should jump pretty erratically. When I did this, the two sensors on the left side made the meter beep like it had continuity but it wasn't constant, more like a fast pulse. The two on the right side made no sound whatsoever. I have no idea which is supposed to be correct, silent or beeping. Also, make sure you take the sensors out and clean them really well. You might also try sticking a rag down in the hole and cleaning the teeth of the abs ring on the hub.

However, after all of my sensors tested properly and my abs light still came on a couple minutes after I started driving, I got frustrated and just replaced the two front sensors with some junkyard ones and it now works. It's worth testing the sensors but just be aware that if they all test well, you may still have a broken sensor. As the saying goes, ask me how I know. I've also heard of using an oscilloscope but I don't have one so I'm not sure on that procedure. Typically, if the abs light comes on after you drive for a mile or so, it's a sensor, if it comes on immediately, it's the relay or the computer.

Re: the abs pump, the only thing I know about this is that the aforementioned 12 pump theory helped mine immensely.
-Matt, '90 325i sedan, #21 SoCal SpecE30

Re:Bleeding the ABS pump? 4 years, 6 months ago #45429

  • jlevie
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The R. Patton technique for finding bad wheel speed sensors is to disconnect all but one sensor, then drive the car. If the ABS light comes on that sensor is generating a speed signal and is good. Repeat for each sensor until you find one that doesn't turn on the ABS light.
Jim Levie, #38
MidSouth Spec E30 Series Director

Re:Bleeding the ABS pump? 4 years, 6 months ago #45431

  • Ranger
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BigKeyserSoze wrote:
I have a different bleeding issue. The previous owner of the car changed all the brake lines and the car sat for two years with no fluid. We added fluid and tried to pump the brakes with the pump and hold method, but the pedal is unnaturally solid and will not pump, even with a bleeder open. We tried this with the car on, the car off, the front brake bleeder open, the rear brake bleeder open, nothing changes. Any idea what causes this? When the car had no fluid in it, the pedal predictably dropped straight to the floor, but now with fluid it just sits there rock solid. I must be doing something wrong with the ABS pump or something. If I just put pressure on the master cylinder cap, would that necessarily push fluid through the ABS pump, or is there something that I am badly missing? It is entirely possible that I just don't know what I am doing bleeding on this car. Please advise.

-Scott


MC's can easily get damaged if there's no fluid in them. They either rust internally, or the piston gets pushed too far by the pedal and seals get damaged.

That aside, start removing brake lines and figure out where the fluid is stopping. Start at the ABS unit. Identify which brake line going in/out of the ABS unit does what. Then remove one of the in lines and watch for fluid to spurt when you press the pedal. Do the same with the out lines.

The ABS unit as 6 lines I think. LF in and out. RF in and out. Rear in and out.

Greg Moberg's Lemons car had similar symptoms. The ABS unit ended up being bad. We figured this out when we couldn't get brake fluid to come out of one of the ABS's "out" lines.
Your opinion counts.

Re:Bleeding the ABS pump? 4 years, 6 months ago #45494

Was the ABS unit bad, or one of the ABS relays.

I find it maddening that you can't just remove the entire ABS system on these cars and still be legal. I see so many posts about wheel sensors, abs pumps, abs relays, and everything else, it seems there is far more money being spent keeping ABS working than if we just yanked it off and modulated lockup the old fashioned way, with the driver.

-Scott
2010 NASA National Champion
2009 NASA National Champion
2008 NASA National Champion

Re:Bleeding the ABS pump? 4 years, 6 months ago #45850

I still can't get this thing to bleed. With the car on jacks and running, you can pump the pedal a few times and get a little squirt out of a bleeder, then the pedal gets rock hard and doesn't want to do anything. Frustrating. Is there a way to cycle the ABS so that the pump stays running, or what do I need to check on the ABS relay or whatever the little part is that seems to go bad on these cars?

This is the last issue keeping this car from going on-track.

-Scott
2010 NASA National Champion
2009 NASA National Champion
2008 NASA National Champion
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