ABS bleed

[Tapio]

Could it be surface tension?
It's probably the same phenomenon that can be seen in a carbonated soft drink or mineral water. CO2 bubbles stick to the bottles inner wall.
I think they can get loose from where they sit if you work the brake lever/pedal rapidly. Sudden rushes of fluid back and forth might get them to start wandering upwards in the system.

I'm much more interested in how you can set carb float levels with a manometer. The pressure in the float bowls should be as close to ambient pressure as possible at all times.

[Corvus]

Could it be surface tension?
It's probably the same phenomenon that can be seen in a carbonated soft drink or mineral water. CO2 bubbles stick to the bottles inner wall.
I think they can get loose from where they sit if you work the brake lever/pedal rapidly. Sudden rushes of fluid back and forth might get them to start wandering upwards in the system.

I'm much more interested in how you can set carb float levels with a manometer. The pressure in the float bowls should be as close to ambient pressure as possible at all times.

It might be surface tension. Maybe it is a function of the ratio between the air volume and tube diameter. Maybe if the tube is small enough the molecules of water can build a kind of membrane, at molecular level, which the air can't shear? I'm guessing. One thing for sure, even the simplest thing is much more sophisticated than meets the eye. All the more fascinating for it.

The carb manometer. The manometer is formed by attaching a tube to the fuel drain hose tail found underneath the float bowl on most old jap bikes, then bending it upwards above the float bowl and leave the tube end open to atmosphere.

The carb float chamber is vented to atmosphere so that forms the other end of the manometer. When the drain screw is opened the tube fills with fuel and, because each side is vented to atmosphere, the fuel level in the tube is exactly the same as in the float chamber. As long as the carb is held at angle it would operate at, then you can see how much the float is out of position.

Incidentally, not all carb float chambers are vented to atmoshere. Some, more sophisticated set ups, are vented to airbox. Even so, with the engine not running, it is then atmospheric pressure anyway, so the makeshift manometer still works.

[Mitch1100]

Thanks for info guys, first bike I've owned with ABS...had a slightly spongy feel due to small amt of trapped air, (previous owner had done fluid change.) My mechanic said bleed would have to be done through ABS unit if line is broken..I assume he means new lines fitted. Tuning, brakes etc I leave to experts due to mechanical incompetance

[DaveH]

[quote="Herb"]

The 1200s design is very different to the older machines and there is no servo.

The reason for the dealer recomendation is because in the service book BMW have added a diagnostic test, which I understand merely consists of a check for error codes.


I will admit that I did bugger up a buddies 12RT.......removed all the fluid........installed new fluid, but could not get the air out of the system...........had to send him to the dealer........oops!

quote]

A mixture of facts here.
The newer abs system does not require any special tools or complicated prodedure to change the fluid.

The diagnostic (bleed) test doesn't test for diagnostic codes. It modulates (i.e. pulses) the abs unit VERY rapidly which allows it to gauge whether there is air entrained in the system.

If its just been a 'normal' fluid change, there won't be so all is well.

If air has been allowed into the system as per the last comment above, then problems can arise in shifting the air bubbles. That is why the diagnostics are needed - not to test for codes, but to pulse the unit and purge the air out of the system.

The GS911 is able to perform this function

[Droptarotter]

Dave;

So I could have been able to bleed my buddies 12RT with my GS-911??
Damn........wish I had known that!

Cheers

[Herb]

Every day is an education. Good to know for sure for future reference.

[DaveH]

Dave;

So I could have been able to bleed my buddies 12RT with my GS-911??
Damn........wish I had known that!

Cheers

Yes the GS911 would have done the job

The bleed test on the later abs units is different to the old servo type where you are manually pressurising the circuit to check for entrained air.

On the newer systems the abs unit modulates (as if the abs were activated)
to dispel any air bubbles and then the circuits are bled again until it's all been purged.

[Droptarotter]

Thank you!

Cheers

[Sandy]

Thankyou for that information DaveH, I went ahead and changed the brake fluid in my 1200s yesterday, and all went well!

[DaveH]

Great stuff...glad to help

[dysondiver]

i have the procedure for he r1150 , mine had a front hose replaced ,,,, ith abs and the servo , it was crazy , i removed the lot ,,, if the procedures any use pm me and ill mail it to you.

[DaveH]

i have the procedure for he r1150 , mine had a front hose replaced ,,,, ith abs and the servo , it was crazy , i removed the lot ,,, if the procedures any use pm me and ill mail it to you.

There's a full write up on how to remove the servo type abs system from 1150 models on my Web site. Biggest hassle is re wiring the brake light activation circuits as the abs system uses NC switches as opposed to NO switches on conventional systems. It can be done by reusing the ABS relay in the circuit.

[dysondiver]

hi , thats probably where it came from ,,,
i used the old electronics , just made up a nice alloy housing for it all to sit in , no prob ,,,, any way , bit off topic , but thanks for the original info on servo and abs ectomy.

[The Teutonic Tangerine]

I believe some systems with ABS and Servo also have another fluid reservoir near the control unit and opening the bleed valve at the caliper and expecting the fluid to drop ant the handlebar don't work.

[Justcruising]

Correct! The servo-assisted EVO ABS on BMW models circa 2004-05, have this arrangement and require a more sofisicated fluid change / bleed procedure ... available on the net if req'd.