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If you mean the following, from the FAQ section on bleeding ABS:
"You never get the fluid completely changed on ABS cars as some fluid is in a storage accumulator that is not accessible."
I think the next sentence pretty much nullifies the concern about vintage fluid in the accumulator (assuming periodic fluid changes):
"If you periodically change fluid this is never an issue as the fluid left in these areas will be circulated eventually through much of the system and it will be diluted by the clean fluid and will pose no problem."
Also, the fact that the 200 and 700/900 brake manuals don't address the "completeness" of bleeding ABS systems seems to make it a moot point.
And the FAQ, while being an asset, does have some dated opinions from various sources, and IMO is not the bible some think it to be. Consider the information under:
Using Line Clamps When Flushing/Bleeding:
[Tip from Motor Magazine] Add the step of line-clamping the brake hose to the caliper when you retract caliper pistons. If you don't, you may be forcing brake fluid from the caliper bore (where rust and other debris may have collected) and sending this dirty fluid upstream.
It's long been standard practice to open the caliper bleeder screws to give brake fluid a place to go while retracting pistons. However, sometimes the bleeders are partially blocked. In these cases, they may not let out all of the fluid that you meant to let escape. Instead, the fluid may take the path of least resistance - upstream. Nowadays, that's likely to send it to sensitive ABS components.
• This makes little sense to me. Even a "partially blocked bleeder", would offer "the path of least resistance", when compared to the totally closed "upstream" path to the ABS modulator and Master Cyl. Does the writer assume there is empty air space "upstream"? IMO, this alone discredits the whole "tip", as presented.
If the vehicle you're servicing has a blocked bleeder, you may get around the problem by cracking open the fitting where the brakeline attaches to the caliper before retracting the piston. For added assurance, you may also want to line-clamp the hose feeding the caliper with genuine clamps designed for this purpose.
• With a "blocked bleeder", I wouldn't be trying to "retract the piston" I'd be trying to fix the bleeder or replace the caliper that can't be bled. Advice like this makes me question the writer's experience and credibility—and thus again the whole "tip".
"For added assurance, you may also want to line-clamp the hose feeding the caliper with genuine clamps designed for this purpose."
• I've never seen any "genuine" brake hose clamps. Probably because I've never needed any. I do have line clamps that I use on pliable fuel, vacuum, or coolant hoses. I just don't see needlessly subjecting brake hoses (with their semi-rigid inner liner) to any crushing forces.
And clamping a brake hose to prevent fluid loss when changing the caliper, is just not necessary. Fluid loss from an open line is easily prevented by blocking the brake pedal depressed (while bleeding off the resulting pressure). The MC piston seals will block the reservoir ports and no fluid will flow, except for a drop or two when the line is first opened. This method is from the 700/900 brake service manual.
This is what 2 of the Big 3 had to say about the subject in 2002:
BIG 3 BRAKE SYMPOSIUM 2002...
(excerpted clamping comments)
• GENERAL MOTORS PRESENTATION, Russ Dobson - GM Service Operations, Warren Tech Center
>CLAMPING BRAKE HOSES? GM says NEVER! Risk of damaging hose too great.
• FORD PRESENTATION, Garrett Van Camp & Chris Oakwood
>CLAMPING BRAKE HOSES? Ford does not recommend clamping hoses. . . This may damage the hose and increase the risk of hose failure.
I apologize for the rant, if that's what it reads like. I just don't like what I see as bogus info being offered as gospel.
--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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