BMW Luxury Touring Community banner
21 - 38 of 38 Posts

·
Registered
Joined
·
9 Posts
Bonjuor

Here is BMW's explanation of the system. The most important thing you can do is follow the brake fluid flush requirements. Annual on the wheel circuits and every two years on the control circuits. I have disassembled failed units and know pretty much what is going on inside.


These photos should give you an idea why the flush is so important.
I don't know if you can help me. When I had taken the solenoids out, I turned the case over and from the bottom of each solenoid void came an ally ring, a rod, a spring and what someone else has called a nipple.
I know that the rod goes in the side hole and the spring in the top hole, but don't know about the "nipple".
My guess would be that it goes in the top hole before the spring.
 

·
Wrencher Extraordinaire
2005 K1200LT
Joined
·
14,911 Posts
Pictures would help, but yes it can be put back together.
 

·
Wrencher Extraordinaire
2005 K1200LT
Joined
·
14,911 Posts
Maybe this will help. Each version is just a bit different even on LTs. The tiny pin with the spring is what pushes against a ball to seal the open loop fluid pressure loop and force the pressure out to the caliper. The Solenoid and armature is what evokes the ABS function to remove the pin from the ball.
173385


173386
 

·
Registered
Joined
·
9 Posts
That certainly makes more sense than having the pin and spring in between two parts that aren't moving.
I'll give it a try.
Thanks
 

·
Registered
Joined
·
9 Posts
I got it all back together with the spring and nipple in the top opening, and it all worked. Servo, ABS and residual braking all okay. Then the other day, I pushed the bike off the stand and the front brake barely stopped the bike.
Lots of investigation later, I conclude that the one-way valve on the outlet of the front pump is not working. Physically, where are these valves? Anyone got any idea.

Smiffy

(The symptoms are, with the ignition off, the front brake lever comes all the way back but the bike can still be pushed. If the ignition is on and the brake lever is pulled back the brake bites, if I then switch the ignition off, the lever comes back and the brake releases. If I do the same with the back brake, it works with the ignition off, and on and off again.)
 

·
Wrencher Extraordinaire
2005 K1200LT
Joined
·
14,911 Posts
The only valve in the wheel circuit is the one circled in red in post #25. But then I looked at my diagram and it shows a check valve after the pump. I suspect it is part of the pumps output port. It is open until you apply pressure in the control circuit to push it closed. Not sure why the lever is going all the way in with the key off. Do you get a very short movement of the lever with the key on?

This diagram may help you understand what is going on inside normally.

Rectangle Slope Font Parallel Schematic
 

·
Registered
Joined
·
9 Posts
Yes, short movement with ignition on.
There is no valve on the outlets of the pump, you can look in and see the pump rotor.
I think it must be in the part into which the brake pipe fits. This has a filter at the bottom which sits in the pump outlet chamber, a hole half way up which connects to the chamber behind the pistons (and also the pressure sensor) and at the top fits the brake pipe to the calipers. I'll try swapping that part front to rear and see if the problem moves to the rear circuit.
Thanks for the diagram.
 

·
Registered
Joined
·
9 Posts
The one-way valve does appear to be in that tube, but swapping them over made no difference.

With the top off the reservoirs, with the ignition on, pull the brake lever and the pump starts running, as I pull the lever, the piston (the shiny part in the red ring in your picture) moves a little and the lever stiffens as the brakes bite. When I turn off the ignition, the lever comes back to the bars and the piston moves forwards (to the left of the bike). When I release the lever the piston goes back.

With the ignition off, as I pull the lever the piston moves forwards but I feel no resistance until it is all the way forward. If I press the back brake as the piston moves forward I feel more resistance and the brake is applied.

It's as if there is some other way that the pressure in the caliper circuit is being dumped back to the reservoir. But I can't see any passages that come away from the caliper circuit other than from the pump and to the area that the piston goes into.

I have had it all apart again, put it back together and the behavior above is still the same except for one time when the lever held it's position when the ignition was turned off.

In the end I put it all back together so I could see how much actual braking I was getting with the ignition off.
On a medium downhill slope I let it build up speed to about 5mph then gently pulled the brake lever, I got a bit of braking, then a bit more, then a bit more (still not much though) then pulled it a little further and it reverted to the minimum braking I felt at first. Pulling the lever more made no difference. This was repeatable.

The problem MUST be in the back (left side on bike) block as the caliper circuit does not go anywhere else, So my next plan is to rebuild it using a different one of those.

Any thoughts?

Smiffy
 

·
Wrencher Extraordinaire
2005 K1200LT
Joined
·
14,911 Posts
Since the input is isolated the fluid movement that allows the lever to go to the bars is associated with the objects circled in blue. The only path for that fluid is in the primary input piston and the integral input piston on the other circuit. Now there are two pressure relief valves that are on the input side that could be causing this issue. They are the black domes you see on the ABS unit. Why they are letting the lever go to the bars is beyond me, but it is worth looking at it.

Gas Engineering Auto part Household hardware Machine
 

·
Wrencher Extraordinaire
2005 K1200LT
Joined
·
14,911 Posts
OK. Now I see how you are observing this. Interesting. I suspect that that piston is free to move that far when there is no back pressure from the pump but not sure why. I will have to dig one of my units and see if I can move it that far by hand.

In looking at the videos, I see the rear piston move slightly when you are applying the front (integral) but I do not see the front move when you are applying the rear. There is something wrong in the integral circuits blocking movement in the front circuit with and input from the rear. That may mean a seal is bad internally.
 

·
Registered
Joined
·
3 Posts
Here are pictures of the little parts concerned, in the orientation I think they go in, and a picture of the empty housing.
Hello,

Here a picture to confirm where these parts should be inserted:
I have remove the ring to show the location.
The small pin with the spring should be in the hole facing the big black pressure valve (at the top in this picture). The long small one in the other small hole.

Automotive tire Wood Rim Gas Fixture


It is easier to insert them if you remove the screw with the Allen key facing this long small part. Just be careful because there is a spring under this screw.

Automotive tire Rim Wood Bicycle part Automotive wheel system


Hope it will help you.
 

·
Registered
Joined
·
9 Posts
OK. Now I see how you are observing this. Interesting. I suspect that that piston is free to move that far when there is no back pressure from the pump but not sure why. I will have to dig one of my units and see if I can move it that far by hand.
I have just been experimenting using the spare back case (left side on bike) and the intermediate section, no pumps fitted and using the armatures to push the "pistons". I held the piston all the way in, dribbled fluid into the outlet then as it filled with fluid allowed the piston to come out. When the fluid drained away suddenly, the "piston" was still pushed in well past the window, so the range of movement in the video with the ignition off, the output circuit won't hold any pressure. So look at a pump again, if I dribble fluid into the outlet holes it drains through straight away. None of it makes any sense.

I also looked at the pressure relief valves on the spare, they are just pistons with springs behind them, probably there to absorb some of the kick-back when the ABS activates the solenoids.
 

·
Registered
Joined
·
9 Posts
Here a picture to confirm where these parts should be inserted:
I have remove the ring to show the location.
The small pin with the spring should be in the hole facing the big black pressure valve (at the top in this picture). The long small one in the other small hole.
Thanks for confirming that, that's how I've got them, and it WAS working.
 

·
Registered
Joined
·
3 Posts
I have just been experimenting using the spare back case (left side on bike) and the intermediate section, no pumps fitted and using the armatures to push the "pistons". I held the piston all the way in, dribbled fluid into the outlet then as it filled with fluid allowed the piston to come out. When the fluid drained away suddenly, the "piston" was still pushed in well past the window, so the range of movement in the video with the ignition off, the output circuit won't hold any pressure. So look at a pump again, if I dribble fluid into the outlet holes it drains through straight away. None of it makes any sense.

I also looked at the pressure relief valves on the spare, they are just pistons with springs behind them, probably there to absorb some of the kick-back when the ABS activates the solenoids.
Hi,
If you remove the pump and the DC motor and look the unit as that:


Light Gas Cylinder Machine Metal


I tried to draw the links between the piston, the pump and the outlet port. The location of the outlet is not aside but it is easier to put it there.

Handwriting Font Rectangle Parallel Circle


So when you push the piston (by hand or with the brake lever, the pressure should rise up. If not, it can be a problem with one of the seal (bold black in the draw).
Assuming the small ball in the outlet is ok.

With the ignition off and brake lever pulled, the brake should work (residual braking). If not, you may have an issue in the control part of the unit. I mean where the Integral piston is located
If you have this unit open, maybe some pictures can help to build some hypothesis.
 

·
Registered
Joined
·
3 Posts
hello,

It's always sad to not have any news after spending some time to figure out what could be the issue and how to help with so few information.

Anyway, for those who can be interested, I try to show how the control valve works in these I-ABS units and the dependency between the 2 separate fluid circuits: the one from the brake lever, in blue colour, and the one to the caliper, in yellow colour.

The main acting component is a small ball in front of the Control Piston ( in purple below). This ball split the whole area housing the failsave piston in 2 chambers.
I will explain later what is the role of the failsave piston.

1/ When the system is in standby mode, no brake activated, the gap between the 2 chambers is large and the pressure of the fluid is equal in both side (in yellow).

Product Font Parallel Technology Rectangle


2/ When the brake is pulled, the blue liquid will move the control piston, thus pushing the purple ball and reducing the gap between the 2 chambers.
At the same time the electric pump will raise up the pressure to the caliper and the green ball (a valve in the outlet port) will prevent the fluid to go back to the reservoir.
Usually, the failsave piston will not move. Only 2 mm of movement of the Control Piston is enough to lock the wheel.

Product Font Parallel Screenshot Rectangle


The ABS function is accomplished by the electromagnetic field forcing the Control Piston to move back and forward. This will increase and decrease alternatively the gap between the purple ball and the failsave piston, reducing the pressure and then re-applying the pressure to the caliper.

3/ When the I-ABS unit fails, there is still the possibility to have some kind of brake, called by BMW Residual braking feature and based on the failsave piston (but for me it is a cruel "joke").
The pilot will pull the lever to increase the pressure in the control circuit. The blue fluid will move deeper the control piston, the purple ball will completely close the gap.
Because the electric pump is out of service, the pilot has to increase the pressure at the lever and this will finally move the failsave piston.
This is how the pressure rise up to the brake caliper, in red colour below.

Product Font Parallel Rectangle Circle



Because we are on a forum and I spend time to write this text and do these pictures I have to add 3 things:
  • Sorry for my bad English, I'm quite better in my native language.
  • You are free to copy and use these pictures as long as you don't make any money with them. (yes, I'm a dreamer)
  • I really hope someone will found some help with this thread

By now, have a good and safe ride.
Cheers,
 
21 - 38 of 38 Posts
Top