Okay, so you've bled the wheel circuits! Yay!
But--the bike is two years old . . . and now you want to do the control circuits. If you've got the tank off already for the wheel circuit bleed or the fuel filter change--you've already done the really hard part!
The actual bleeding of the control circuits is fairly easy.
There are no calipers to remove and re-install, no brake pads to shim out, no Mini-Stan to deal with, etc. I would still recommend that you read through the entire process here, check out the pics and follow along in the shop manual as well (especially the numbering/sequence of the control circuit bleed screws) to get a feel for the entire scope before proceeding.
So, without further ado . . . Leslie and "Arianrhod" proudly present: [cue trumpet fanfare here]Bleeding the Front Control Circuit:
Remove the dust caps from the six control circuit bleed screws under the tank on the starboard side of the ABS pump housing:
Have a 7mm open-end wrench handy for the bleed screws (some might be tightly snugged down and it is a bit of a tight squeeze to get to them, so a longish wrench might be helpful here). The control circuits are bled more like conventional brakes, i.e. not using the servo pump, so you DO NOT turn the bike on for this part (or use a Mighty-Vac). Remember to go easy on the bleed screws (especially the SpeedBleeders). They only take ~7-8Nm to seat and you do not want to snap one off--or worse yet--strip out the hole!
The SB's are made to snap off before they strip out the hole. See their helpful website for info on how to remove a snapped-off SpeedBleeder, should the unfortunate happen.
First, turn the bars so that the reservoir is level (nearly to full left lock) and secure them somehow so they can't turn back and slosh brake fluid all over whilst you are bleeding. Next, wrap some paper towels or shop rags around the front control circuit reservoir at the right hand grip, then remove the four Phillips screws and remove the cover with rubber diaphragm.
You may find that the rubber diaphragm has everted itself. I've been told that this is normal and not a cause for concern--as the pads wear the fluid level drops in the reservoir and can turn the diaphragm inside-out. Just turn it right-side-out again and wipe everything off well with a rag. Be careful not to spill brake fluid on any painted surfaces (it eats paint!
) or get it on your hands (absorption through the skin can be damaging to your kidneys). Also be sure to observe all the warnings and cautions in the BMW shop manual, etc, etc, etc, yada, yada, yada . . . you know the drill!
Clean the cover and set it aside. Pump the handbrake lever slowly
, but fully to pump any air out of the line (you may see bubbles float to the top of the open reservoir). Be careful that the brake fluid doesn't squirt out of the blow-by bore hole at the bottom of the reservoir--especially later on as the fluid level drops and there is less fluid covering the hole. (Remember that part about brake fluid and paint and your kidneys?) Draw off the old brake fluid with the syringe, then wipe out the reservoir and refill with clean, fresh DOT-4 brake fluid from a sealed container. There is a stepped, raised indexing mark on the forward inside sidewall of the reservoir. Fill the fluid level to this mark and be sure not to let the level drop too far to allow brake fluid to squirt--unchecked--out of the hole in the bottom or allow air to enter the system through that same hole.
The six control circuit bleed screws are numbered in a strange skip pattern and the number one screw is bled again at the end of each circuit (i.e. bleed #1, #2, #3, then #1 again to complete that circuit). Refer to the BMW shop manual for the correct numbering of the screws (they are not consecutive) and the proper sequence of bleeding. Basically, you bleed the three (four, actually) front control circuit screws till all bubbles are gone and the fluid runs clear, top the reservoir back off, put the cover back together then do the rear circuit the same way (but the sequence of screws overlap in the correct order of bleeding--don't worry--it will be very clear when you see the diagrams in the shop manual).
If you are using the nifty catchment bag from SpeedBleeder.com it makes it harder for air to backflow and enter the system between pumps of the lever(s). Another nifty trick (though certainly not as convenient) is to use some soft silicone hose to go from the bleed screw into a coke bottle or some other such container with a bit of brake fluid in the bottom (submerge the end of the hose in the fluid to help keep the air out of the system). If you are using the SpeedBleeder screws also, it makes it almost impossible for air to get into the system in between pumps and you don't need to be so careful to shut the bleed screw before releasing pressure on the lever(s). But--assuming you're using the stock bleed screws, since SB doesn't yet make the really long 7mmX1.0 (X 2" long!) SB's yet (though I guess you could still use the shorter ones): the procedure is as follows:
1. Set the handbrake lever to position "4" (furthest out) on its adjustment cog. Slowly
squeeze the hand brake lever until you hear the brake-light switch click (fluid initially squirts back out the hole in the bottom of the reservoir until the blow-by bore closes).
2. Crack open the bleed screw a quarter to half a turn. You don't have to open it that much--since the system is now under pressure, you'll know when it's open as brake fluid will start coming out the bleed screw--and hopefully into the hose and not all over the ABS housing!
3. Slowly continue to squeeze the lever to the full extent of its travel as the fluid comes out, and then quickly close the bleed screw just before you reach the end of lever travel.
4. Slowly release the brake lever.
5. Repeat steps 1-4 until the fluid is clear and bubble-free, from each screw in turn, topping up the reservoir as needed to keep a comfortable amount of fluid over the blow-by bore hole.
The mantra you chant whilst doing this is: "squeeze--click" . . . "crack" . . . "squeeeeeeeeze--close" . . . "and release". Easy, huh? It's not rocket surgery or brain science. ("Of course . . . a child could do it . . . a CHILD
could do it!"
Bonus geek-points awarded for the source of that last quote!
When finished bleeding the last screw, top up the reservoir to the mark one last time, wipe off the rim, replace the cap with the rubber diaphragm and retaining screws. Then move to the rear control circuit.Bleeding the Rear Control Circuit:
The rear is done almost the exact same way as the front. You can access the rear control circuit reservoir behind the black plastic fairing panel. Remove the right side bag, then the panel. Remember to go easy on that plastic pin which can snap off easily!
Nifty Beemer Trick #358: a little dab of grease on the rubber grommit or the post will make removal and replacement easier!
Remove the cap and rubber diaphragm and wipe them off well. Draw off the old brake fluid and wipe out the reservoir.
Refill with clean fluid to the "max" fill line (the raised line in the plastic housing running around the perimeter of the reservoir just above the one that says "min" :)> ). Follow the same basic steps as above being sure to check the shop manual for the correct sequence of screws to be bled.
When you have bled the last screw (actually, the first screw again
), top off the fluid one last time to the "max" mark, and replace the cap, rubber diaphragm and black plastic fairing panel. That's it--You're DONE!!!
Go easy on the brakes during the first test ride and until you get used to the new feel. Do some parking lot work (you do anyway, right??
) and panic stops under controlled conditions to get a feel for the difference. Leslie found out why everyone had been complaining about the 1150's brakes feeling "grabby". She said that hers had felt "mushy" previously in comparison to how they felt after the wheel and control circuit brake bleed. She automatically grabbed the brake with the same force as previously required in a similar situation in a low speed parking lot maneuver and almost dropped the bike when it suddenly came to an abrupt stop. She says the brakes have a MUCH more positive feel to them now.
Stay tuned for our next episode: Bleeding the Hydraulic Clutch Circuit!