K75 Brake Service Question

[plock]

Hi Folks,

I'm am about to tackle replacing the front rotors and pads on my 94 K75 (w/ABS) and had a couple of questions.

1) I'm assuming it would be prudent to replace the hydraulic brake fluid while doing this work. The question is: Is there a particular order that these should be done in? I realize that I'll need to remove the calipers to get the wheel off in order to change the rotors. Should the brake bleeding happen 1st or last in this process, or does it matter?

2) Since I have never performed any of these myself, I have a question about the bleeding process: My Haynes Manual indicates that it makes sense to connect both bleed nipples to plastic tubes and release the fluid from both. However in looking at the setup on my bike, it looks like I only have one bleed nipple. I have the hose running from the master cylinder that connects to the right hand caliper. Then there is a rigid hose that runs out of that right caliper and runs over the fender and then down to the left unit. The bleed nipple for both appears to be the output on the left unit only. Is that correct and is it the only "drain point" I should worry about? Since this is all new to me, any helpful hints would be appreciated!

 

[PHMARVIN]

Hi, Plock,
The manual was written in the mid-'80's, when the bikes were fairly new. There were changes over the years. One change was the later bikes had the front brake calipers connected by the steel brake line. You are correct in your thought that you only bleed the left caliper. This is what I do. Suck out all the fluid from the master cylinder with an ear syringe, enema bulb, or the like. Refill with fresh DOT 4 fluid. Attach a plastic or rubber hose to the bleed screw on the caliper. The end of the hose is immersed in a small amount of brake fluid in the bottom of a jar, bottle, etc. Open the bleed screw, squeeze the lever (ONLY about halfway to the bar), close bleed screw, release lever. Repeat until no air bubbles emerge from the hose. Then leave the bleed screw open and let gravity move fluid through the system. MAKE SURE the master cylinder does NOT go empty. When fresh, clean fluid emerges from the end of the tube, shut the bleed screw, remove the tube, replace cover, top up the fluid reservoir (a little below the "full" line - remember the bellows takes up some space and you don't want the fluid spilling uver the top of the reservoir when you put the bellows in) and replace the top. Now do the same for the rear brakes.

 

[GILLY]

Are you sure it needs the rotors? My old K75 had 93000 on it and rotors were still fine.

Gilly

 

[plock]

Are you sure it needs the rotors? My old K75 had 93000 on it and rotors were still fine.

Gilly

Gilly, Not sure what else it could be..I can feel a pulsation in the brake lever and can feel the front end move up and down when coming to a stop. I assume that its reacting to the shape of the rotor.

 

[GILLY]

OK, I didn't see anywhere why you were doing the work. I assumed worn pads.
Gilly

 

[kayseventyfive]

.I can feel a pulsation in the brake lever and can feel the front end move up and down when coming to a stop. I assume that its reacting to the shape of the rotor.

I have had that. On one K bike, sanding the pads and rotor fixed it. Current bike did that when I bought it. Laziness and busy-ness kept delaying the fix. Then it went away. I think the previous rider was more gentle than I. That fits my theory that K bikes benefit from vigorous use.

Have you checked your disks for runout? Are your calipers releasing properly?

Sounds like a fork oil replacement would help with the exaggeration of symptoms, too. Maybe a little stiffer oil.

.

 

[plock]

I have had that. On one K bike, sanding the pads and rotor fixed it. Current bike did that when I bought it. Laziness and busy-ness kept delaying the fix. Then it went away. I think the previous rider was more gentle than I. That fits my theory that K bikes benefit from vigorous use.

Have you checked your disks for runout? Are your calipers releasing properly?

Sounds like a fork oil replacement would help with the exaggeration of symptoms, too. Maybe a little stiffer oil.

.

Changed the fork oil this past fall (seemed to help a little). The calipers may be a possibility. Is there an easy way to tell if their not releasing properly?

 

[deilenberger]

Gilly, Not sure what else it could be..I can feel a pulsation in the brake lever and can feel the front end move up and down when coming to a stop. I assume that its reacting to the shape of the rotor.

Sigh.. one of the fatal flaws of the K75S that resulted in me no longer owning it. I went through more rotors than tires. Every 6-7,000 miles this reoccured. Got so I didn't want to ride the bike since I *knew* it was gonna do it again soon.

Problem is variations in friction on the rotor surface. It can be caused by pad-poop (tech-term for stuff left on the rotor from a cooking hot pad left resting on the rotor after some vigorous braking) or - rust - caused by a damp/wet pad laying against the rotor overnight, or just plain damn stubbornness.

Apparently BMW had a bit of a problem with this - and on some bikes - they replaced the front rims. I also - once - had it go away for the usual time (about 6,000 miles) after replacing the wheel bearings. Then it came back, and replacing them again didn't make it go away. I think BMW replacing the rims did the same as me replacing the wheel bearings...

One of the real mysteries of K bikes IMHO. I finally went to EBC rotors and pads - these are a mild-steel rotor instead of stainless, so they will rust - but they also don't seem to cause the shudder you describe even if the pads rust to the rotors.

Oh - other fruitless stuff I tried to fix it - sanding the rotors. Made no difference. Using a ball-hone on the rotors. Made no difference. Braking rotors - lasted the same time as the stock rotors.

More than one person has left K bikes for exactly this reason, and it seems most prevalent on S's.. dunno why. Just does - never had it on my K100RT. Rarely hear of it on K100's - hear it way too often on K75's.

 

[mieczkow]

Rotors and Brake Pulsing

Went through the same drill as Don, only I went pretty quick to the EBC rotors. I tried all the other stuff - multiple changes of pads, sanding, cleaning like crazy, etc. I Finally replaced both of them with EBC (I have an '87 so no ABS) and put new EBC copper-sintered pads. I also rebuilt the calipers. Problem went away and it has not yet returned. I was so happy I replaced the rear rotor with an EBC too. So, the EBC change-out worked for me. That doesn't mean it will work for you, but if you're gonna do the rotors, the EBC are a darn sight cheaper than BMW rotors. when I bleed any hydraulics I use a MightyVac and I've never had trouble getting the air out and the brakes nice and firm - it usually only takes a few minutes and I never paid any attention to doing it in any particular sequence.

 

[plock]

Thanks for all the good advice everyone!

On another note: Tried pretty hard to puchase EBC rotors as the BMW's are crazy expensive. However everywhere I tried I was told that EBC no longer makes them for the ABS model.

 

[122832]

... I was told that EBC no longer makes them for the ABS model.

Strange. They still list them in their '09 Catalog EBC Brakes Catalog 2009 (PDF)

I'd suspect you have a bunch of parts people that don't want to bother making the special order.