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Old 04-06-2007, 01:40 PM   #1
1-3-2-4
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Default Brake flush with ABS?

Let me start off by stating that yes, I searched, and yes I've read the FAQ...

That being said, I'm overdo for a brake fluid flush. It appears that the dealer wants to charge me $90 to use their fancy scanner and cycle the ABS pump.

Aside from the 'hit the brakes going fast enough to cycle the ABS', is there another way to cycle the pump while bleeding? I could just bleed the circuits like normal, but I'd like to do a complete flush. Any insight?

Thanks!
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Old 04-06-2007, 03:14 PM   #2
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there's no other way that I am aware of aside from the 'lock up the brakes' method.
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Old 04-06-2007, 03:39 PM   #3
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That's how I do it too.
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Old 04-06-2007, 04:57 PM   #4
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Great, thanks for the info. I was just hoping that there was a plug-in program that could be downloaded and run through the OBD cable. Any programmers out there want to do this?
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Old 04-06-2007, 05:27 PM   #5
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A simple brake bleed or flush does not require the pump be cycled that I am aware of. The simple transfer of fluid is constant. However...should you introduce air into the master and allow it to get to the pump this will be the case.

Crack a bleeder, top off the fluid and let it drain into a pan. Keep the fluid level up and when the color changes in the pan, you've flushed it.

*Having installed a number of BBKs on cars with ABS, I can assure I did it all by gravity and then a light pump bleed when done. No key on, cycle anything. And it's all new fluid.
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Old 04-07-2007, 09:22 AM   #6
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I didnt need to use the ABS system when changing mine. Just depressed pedal, opened one bleeder at a time, pushed the pedal to the floor, closed bleeder, pedal up and down again, open bleeder, etc until new fluid comes out of each caliper.
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Old 04-07-2007, 09:27 AM   #7
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Quote:
Originally Posted by TCE View Post
A simple brake bleed or flush does not require the pump be cycled that I am aware of. The simple transfer of fluid is constant. However...should you introduce air into the master and allow it to get to the pump this will be the case.

Crack a bleeder, top off the fluid and let it drain into a pan. Keep the fluid level up and when the color changes in the pan, you've flushed it.

*Having installed a number of BBKs on cars with ABS, I can assure I did it all by gravity and then a light pump bleed when done. No key on, cycle anything. And it's all new fluid.
Thanks for chiming in with that, because after my last post, the same thought occured to me. Obviously, if there is air in the pump, then cycling it would be the only way to remove it. However, I wasn't sure how the circuit was layed out and therefore, wasn't sure how the fluid in the pump was situated in relation to the rest of the system.
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Old 04-07-2007, 09:30 AM   #8
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If you don't cycle the ABS solenoids while flushing, the inlet valve stays open (which lets fluid pass through to the brakes) but the outlet valve stays closed (which prevents any fluid at all from flowing through the ABS control unit).

This is the normal operating mode with both solenoids de-energized:


If you energize both solenoids, the inlet closes and the outlet opens, allowing fluid to flow backwards around that circuit, flushing the entire control unit of any old fluid.
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Old 04-07-2007, 09:32 AM   #9
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Alright, does anyone has a system diagram and maybe a cross section of the master, pump, etc.?
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Old 04-07-2007, 11:05 AM   #10
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Quote:
Originally Posted by nhluhr View Post
If you don't cycle the ABS solenoids while flushing, the inlet valve stays open (which lets fluid pass through to the brakes) but the outlet valve stays closed (which prevents any fluid at all from flowing through the ABS control unit).

This is the normal operating mode with both solenoids de-energized:


If you energize both solenoids, the inlet closes and the outlet opens, allowing fluid to flow backwards around that circuit, flushing the entire control unit of any old fluid.

Well said and explained. I personally have not done so and probably won't but it appears from your desctiption that a small amount of residual fluid may be trapped in the system without the key on cycles. For the average street enthusiast installing hoses it's probably a minimal contamination of old fluid to new (thus reducing temp a bit) but for the track junky wishing to cover all the bases; probably worth the time. thanks for the drawing.
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Old 04-07-2007, 01:02 PM   #11
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Important to note: those check valves mean fluid can only flow backwards through the unit... from the caliper to the master...
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Old 04-25-2007, 12:49 PM   #12
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There is a procedure to run the pump to get air out but I don't know if it exchanges fluid. I did this when I thought I had too much pedal travel.

See page ABS-11 of the chassis manual for the 2002 Impreza, ABS Sequence Control. Put the two pigtails (grounds) in pin 3 and 6 of the diagnosos connector and follow directions (key on, mash the brakes within 0.5 seconds). It will do the sequence on page ABS-12. Fun to do the first couple times.
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Old 04-25-2007, 01:10 PM   #13
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Looking at this more closely the ABS Sequence Control test runs the pump motor and closes the inlet (3 in the diagram above) and opens the outlet (8) for 0.4 seconds. It then closes the outlet and holds the inlet closed for an additional second. Then they go back to the deenergized state.

Would this pump fluid from the caliper through the ABS circuit and back to the master cylinder?
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Old 05-24-2007, 01:21 PM   #14
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bump for an answer. also anyone have a pic of the abs connector. non drawing preferred.
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