RegisterSearchFAQMemberlistUsergroupsLog in
Reply to topic Page 1 of 1
ABS Module COMPLETE Fluid Flush ???
Author Message
Reply with quote
Post ABS Module COMPLETE Fluid Flush ??? 
Long motorcycle into example first, please bear with me...

A few weeks ago I was working on a friends vehicle, a 1996 BMW R-Series motorcycle.

Among others, we changed the brake lines and with that of course the brake fluid as well. Interestingly in addition to the usual bleeding procedure, that bike has the opportunity to bleed the ABS module via 2x extra nipples, that are mounted on the module itself. The bike has 2x independently working brake fluid circuits (front brake and rear brake) and each nipple on the ABS is for bleeding one of those circuits.

We flushed the brakes with plenty of fresh fluid and after that was done we were flushing the ABS module as suggested per BMW service manual.

The fluid that CAME OUT of the ABS unit was BLACK like TAR !!!

So that made me think.

How is our ABS system built? Are there areas inside the ABS unit, where the normal flush procedure won't flush the fluid and what can we do to change the fluid in those areas?

View user's profile Send private message
Reply with quote
Post  
Yes, there is. The correct way to bleed an ABS system is with a scan tool that opens the ABS valves. Without the scan tool to open the valves, the ABS system doesn't get flushed. So far as I know there is no way to flush an ABS without a scan tool.

View user's profile Send private message Send e-mail
Reply with quote
Post  
I understand and I do have the scan tool and I used it for the ABS bleed procedure. However I'm still puzzled.

The scan tool only cycles the ABS pump. Even if that were to somehow get some of the old fluid out (and mix with the fresh fluid within the ABS unit), that amount should be still very small.

Yet, the amount of old fluid that we got out of my friends bike was quite a lot. Probably 5-6 inches worth, measured by the length of the attached bleeding hose.

So where would such amount of fluid end up within the system, if the pump is only cycled with the scan tool. We don't seem to have a return line on the master cylinder from the pump to reservoir.

The way the ABS system works gives me a lot to think about.

View user's profile Send private message
Reply with quote
Post  
As I understand it, when the GM ABS system is put into bleed mode it opens and closes valves inside so as to make a single path for fluid to go through, and pushes the accumulation valves all the way in to get the fluid out. The ABS system itself has small reservoirs with pumps built in.



I can't speak for the motorcycle system, other than a guess that because a motorcycle is so small that the ABS system had to have a separate reservoir in order to have enough fluid to operate correctly. And, it sounds like this system has never been flushed before while the brakes themselves have been.

Where did you get your scan tool and what did it cost, if you don't mind me asking? My truck needs the ABS flushed but I don't like having shops do work for me. It never goes right for me.

View user's profile Send private message Send e-mail
Reply with quote
Post  
Thank you for the schematics. I'm going to take a closer look at it.

Speeder wrote:
Where did you get your scan tool and what did it cost, if you don't mind me asking? My truck needs the ABS flushed but I don't like having shops do work for me. It never goes right for me.

I used my SnapOn MT2500. I recently scored some newer cartriges for it.
http://www.pacificp.com/forum/viewtopic.php?t=11233

I got the latest 9.2 cartrige combo, but I believe any of the newer BLACK VCI/TSI combo cartriges should do it. I think I saw @JR96CK posting on another thread that he used a 2003 VCI/TSI combo and that had the bleed function already. The red 1999 combo does not have it for sure.

View user's profile Send private message
Reply with quote
Post  
Fond this explanation:

Quote:
Well I found out that the short answer is no - you can't bleed your truck's abs without the GM Scan Tool, .

But there are ways around it. The ABS system used on '95 through early 2000's GM trucks is the Kelsey-Hayes EBC310. It has three sections - one each for the left- and right-front wheels, and a third for the rear axle. Each section is divided into an Isolation valve and a Dump-Valve/Low-Pressure Accumulator.

When bleeding the brakes the low-pressure accumulator is 'hidden' behind the dump-valve and can't be bled. The only way to flush the fluid and/or air from these areas is to cycle the ABS. The factory-approved method is to use the Tech 1 Scan Tool to command the computer to cycle the ABS.

But the "shade-tree" mechanic method is to drive down a gravel- or snow-covered road and jump on the brakes, which will cause the wheels to lock up and... cycle the ABS.

There's an obvious flaw in this procedure - one has to get the brakes working well enough to safely drive down said road. Plus, when the ABS cycles any air in the accumulators will be dumped into the lines. This may have a dramatic negative affect on your braking ability. Assuming all goes well and you were able to get all three circuits to activate (LF, RF and one of the rear wheels), then it's time to gingerly drive back home and bleed the rest of the air out of the system.


So as the valve are cycled, you should be able to dump the old fluid from the abs system.

View user's profile Send private message
Reply with quote
Post  
Found this also:

KELSEY-HAYES 4WAL BLEEDING PROCEDURE
Quote:
3. Open the internal bleed screws on the modulator one quarter to a half-turn. These are the cap screws on either side of the modulator. Note: Some newer 4WAL systems do NOT have these bleed screws so you must use a scan tool to bleed the system or try loosening the brake lines to the modulator to vent air.

4. Connect special tools (such as Kent-Moore No. J39177) to hold open the high-pressure accumulator bleed valves.

5. Open the two bleeder screws at the BPMV and bleed the unit by forcing fluid through it with a pressure bleeder or by slowly pumping the brake pedal. Do NOT allow the master cylinder reservoir to run low (add brake fluid as needed during this procedure).


Probably for pre-96

http://www.aa1car.com/library/abs_kelseyhayes.htm

View user's profile Send private message
Reply with quote
Post  
Thanks for this info, I hope it will work.

When I cycle the ABS pump with the scan tool, the scan tool does not continiously cycle the pump (at least mine does not). It rather does so in intervalls, while the procedure calls for keeping the brake pedal depressed. So a second person would have to open the bleeder valve at the same time as the pump cycles.

I'm going to try this out in a few weeks and report back.
(I have too many things going on at the moment and can't risk loosing the truck or it's brakes now)

View user's profile Send private message
Reply with quote
Post  
1999 Tahoe 4x4 wrote:



So a second person would have to open the bleeder valve at the same time as the pump cycles.

I'm going to try this out in a few weeks and report back.
(I have too many things going on at the moment and can't risk loosing the truck or it's brakes now)



What I usually do is press down on the brake pedal and wedge a 2"x 3" of the appropriate length from the pedal to the backside of the steering wheel or to the front bottom part of the driver's seat, effectively holding the pedal down with no one's assistance.

View user's profile Send private message
Display posts from previous:
Reply to topic Page 1 of 1
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum