Front Brake Pads K75S

[kentuvman]

Thanks in advance to all of you out there who have helped me so much in learning how to work on my K75 . . .

New project . . .

I'm on a mission to eliminate the brake pulsing on my K75S. My K only has 33,000 but the pulsing is annoying. I decided to do it right, short of buying new rotors - just yet.

So far I had the dealer remove and install new front bearings (maybe was a waste of money - I'll find out), removed the rotors, had them spec'd with a micrometer and they are good .16 and confirmed they're not warped. I used a scotch pad to scrub the crud off the rotors and then paint thinner to clean and finally brake cleaner. Reinstalled front wheel. Will clean rotors once I get the pads installed before the test ride.

Making progress . . .

Both calipers are off the bike - I've removed the old brake pads and am replacing with Carbonne Leon's. Hoping I'm moving in the right direction . . .

Here's my questions:

1. To clean the brake calipers - was planning to blow compressed air.
2. My Clymers book recommends some pad lube so I bought a small tube at O'Reillys.
3. Can I bolt my calipers back on the bike and then install the pads OR should I install the pads before I bolt calipers back onto forks? Front brake handle is blocked off so it can't be squeezed.

Am I moving in the right direction? Thank You again.

Ken in MN

[chuck_donahue]

Thanks in advance to all of you out there who have helped me so much in learning how to work on my K75 . . .



Here's my questions:

1. To clean the brake calipers - was planning to blow compressed air.
2. My Clymers book recommends some pad lube so I bought a small tube at O'Reillys.
3. Can I bolt my calipers back on the bike and then install the pads OR should I install the pads before I bolt calipers back onto forks? Front brake handle is blocked off so it can't be squeezed.

Am I moving in the right direction? Thank You again.

Ken in MN
Question #1 I would use brake cleaner and compressed air.
Question #2 Any good lube is good, just don't use to much, don't get it on the rorors.
question #3 You can't put the pads on if the calapers are mounted on the bike. Calaper need to be off the mounts, they can still be connected to the brake lines, just not mounted on the calaper.

Question you didn't ask. yes you should change the brake fluid, all of it.

[PHMarvin]

question #3 You can't put the pads on if the calapers (sic) are mounted on the bike. Calaper (sic) need to be off the mounts, they can still be connected to the brake lines, just not mounted on the calaper.(sic)

Question you didn't ask. yes you should change the brake fluid, all of it.

I have replaced front brake pads on my K75's while the calipers were still mounted onto the forks. I'm not saying I would recommend it nor that is easier than removing the caliper(s), only that it can be done. And I agree with the brake fluid comment!

[rlswim]

I eliminated the pulsing on my 92 K75S after purchase a few years ago by using a scrubbing pad (lots) and then taking the bike out to a deserted road to brake heavily from high speed and being sure to release the brakes before coming to a complete stop. Cool down and repeat. Over time (months), my pulsing has disappeared completely. I'm wondering if braking habits of keeping the binders on after a hard stop might leave residue on the rotors that cause the pulsing. I make it a point to roll a bit after a hard stop. No pulsing for the last year or so now.

[kentuvman]

These are all great suggestions - thank you!

I did change the brake fluid a few months ago when I replaced the front brake master cylinder - do I need to do it again if the fluid is clean and I'm not opening the valves?

Glad to hear the suggestion about driving at high speed and braking hard - hoping all steps I've taken will do the trick.

Will keep you posted!

Ken

[mieczkow]

I just changed the front pads today on my 87 K75S so what I have to say applies to a non-ABS situation. I also earlier dealt with the whole pulsing and squealing issue when I first purchased the bike. What I did to deal with the front brake pulsing was to replace both front rotors with EBC and that stopped the problem for nearly 10,000 miles now on those rotors and their EBC copper-sintered pads. I also replaced the rear disc and used an EBC rotor and pads. Also put stainless steel lines on all the brakes, and rebuilt the rear brake cylinder. I tried to save the original rotors - I did all the scrubbing and cleaning using every solvent known to man and every kind of mild or fine abrasives. I checked the rotors for warp (there was none) as well as thickness (it was well within spec). None of that worked. The new rotors and pads worked. No more pulsing, ever. I replaced all the pads today with Carbonne Lorraines from beemer boneyard. Though I've only been on a brief "test run" so far with the new pads installed - they are working fine with no squeal or pulsing.

As far front pads on my 87 it is absolutely not necessary to remove the front calipers and it is easy to remove the pins and pads and reinstall new ones. I just did that this morning. Just pop off the plastic cap, with a long drift knock each retaining pin out and remove it along with the spring. The old pads will come out through the top of the caliper, Clean everything up and slide the new pads into place (you may have to reseat the caliper piston back into the caliper to get it to fit), line up the holes, don't forget to place the aft spring on the aft pin, put the short center pin into the groove in the top of the pads, slide the forepin into the forward holes making sure to get the forward section of the retaining spring seated under the pin and sitting in the slot. Tap the pin to make sure they are fully seated and pop you plastic cap back on the caliper. And your done.

Maybe this won't work with an ABS bike - I've never owned one, but it sure works with a 1987 K75S!

Tom Mieczkowski

[kentuvman]

My S is non ABS - I appreciate the suggestions - I have a bench grinder and used the wire wheel to clean the bolts going through the wheel that hold the rotors together and the pins that hold the brake pads in.

What really is important to note it for anyone doing this job, if you remove the front wheel, mark each side - there is a TIRE ROTATION ARROW on one side of the tire and you have to put this back the same way you take it off.

I followed instructions in Clymer big book for K75 and used masking tape to mark which rotor came off on each side. In my case, S for starboard and P for port.
Also, my rotors must be original - they have a yellow dab of paint on each one and I can assume lining them up the same way the came off ensures they're in the same place. I also used a little dab of blue loctite on each bolt when ratcheting down the rotor bolts.

Also important to put a light coat of grease on the axle and couplers that cover the bearings.

I'm taking my time - I spun the wheel and it seems to be a lot smoother and turn longer with the new bearings (I have to rationalize my new bearing purchase somehow). But really, the bearings were relatively cheap and the dealer only charged me $45 to install them. The peace of mind factor of know how my front end is put together and secured is worth a TON.

Have a great day!

[deilenberger]

I'll just preface my comments with - this is the primary reason I no longer own a K75S - and it's the same reason a number of other people I know sold their K75S.

The brake shudder seems particularly a K75S problem. Why just the S? No idea, and no one I know has any idea.. but out of S owners - at least 50%, probably closer to 75% of the owners I know have experienced it.

Fixes (I tried, and some other people tried were):

1. New rotors - BMW rotors fix it for a while - then it comes back, usually at about 6-10,000 mile intervals. EBC rotors so far have been good, and people who have used them haven't experienced the problem again - yet..

2. New pads - does nothing. I tried everything from very soft pads to very aggressive track pads. Didn't help.

3. Cleaning the rotors - tried brake hones, sanding them with special rotor sanding disks - brake cleaner, pretty much you name it. Didn't help at all.

4. Fluid changes - no change. Didn't make any difference.

5. Different fork springs - thinking the springs may be putting the suspension in a condition where it was especially sensitive to it - no change.

6. New wheel bearings - fixed it for 6,000 miles, then it came back. A second set of new bearings did absolutely nothing but drain my wallet and piss me off.

What finally fixed it seems to be the EBC rotors. The bike had close to 6,000 miles on those rotors when I sold it, and I believe it now has over 10,000 miles on them - so far no shudder (I know the new owner quite well.. good friend who was warned ahead of time about the problem.) But - as I said above - it may just be a matter of time.

It usually seemed to happen after the bike had sat in rain overnight, or been washed and put away without taking it out for a ride - so the pads tended to stick to the rotors. I had one set of rotors (in all - I had 6 different sets of rotors on this bike) sent to a metallurgy lab at Penn State - and it was claimed they could see a change in the surface composition that was about brake pad sized. I never saw the final report on this.

There were some stories of BMW-NA authorizing wheel replacement on bikes that experienced this problem while under warranty. Appears to have been a silent warranty sort of thing - not made public.

What really fixed it for me was to buy first an oilhead, and finally an R1200R. Which has wonderful brakes.

Good luck with it. The S is a great bike except for that particular flaw..

[lostboy]

Many of the bikes/wheels made in that erra have rotor mounting flanges which are not perpendicular to the axle. You can frequently reduce pulsing by dial indicating the rotor, then rotating it one or two mounting holes. If you can't fix it that way, find a machinist with a big lathe and ask him to true the flanges. Vintage Brakes may be able to help.

[deilenberger]

Many of the bikes/wheels made in that erra have rotor mounting flanges which are not perpendicular to the axle. You can frequently reduce pulsing by dial indicating the rotor, then rotating it one or two mounting holes. If you can't fix it that way, find a machinist with a big lathe and ask him to true the flanges. Vintage Brakes may be able to help.Problem with this theory is..

1. We're talking rotors with only 4 bolts holding them to the rim. Rotation possibilities are actually quite limited.
2. No one has found excessive runout on the rotors, which would be a large clue that there is this sort of problem. Without runout, we don't have a bad mount, or a bad hub so rotating them wouldn't be correcting a problem we don't have.
3. When I had it happen - if I rotated one rotor relative to the other - say 180 degrees - it doubled the shudder frequency, meaning it was a spot on the rotor that was causing the shudder, not parallelism or runout.

I did look for large enough lathes to cut the rotor surfaces - but finding an 11" swing lathe is almost impossible, and parallel grinding them didn't work, made it much worse, even when thickness variations were less than 0.001".

Once when I put Braking Rotors on the stock hubs, I did convince a machine shop to make a fixture so the center hub of the rotors could be trued up before putting the new rotors on them. That worked - for a while, then it started pulsing again.

That's the real catch - it could be eliminated - new rotors sometimes, new bearings other times - but it ALWAYS came back, and there was no change in the rotors or hubs or wheel mounting surface the rotor bolted up to. After fighting it for a long time I just lost interest in riding the bike - the shudder was that annoying and IMHO dangerous.

[JHGilbert]

I've often wondered whether rotors should be glass-peened prior to mounting to relieve the internal stresses and possibly prevent warping. But thankfully, I've never had a warped rotor.

[kentuvman]

I believe I've done a thorough job on my K75S with 33k miles. New front wheel bearings installed by dealer, rotors removed, checked-out, scrubbed with scotch pad, cleaned with thinner and brake cleaner in spray can, new Carbone Lorraine pads. Did it in stages - now everything back together - no test ride just yet. Hoping this will improve performance of front brakes.

Clymer big book says I can change rear pads w/out removing caliper - I thought I'd have to remove shock to get to it but book says I can rotate wheel and change pads from the port side.

Any suggestions before I embark on this task later tonight or tomorrow?

Thanks in advance,

Ken in MN

[breyfogle]

Many of the bikes/wheels made in that erra have rotor mounting flanges which are not perpendicular to the axle. You can frequently reduce pulsing by dial indicating the rotor, then rotating it one or two mounting holes. If you can't fix it that way, find a machinist with a big lathe and ask him to true the flanges. Vintage Brakes may be able to help.

When I replaced my worn-to-the-limit OEM rotors with EBC's, this was exactly the recommendation my BMW mechanic recommended. (The OEM's never pulsed but YMMV). Unfortunately for me, I did not follow his advice and I ended up with EBC rotors that pulsed *VERY* badly after only a short time. The EBC distributor replaced my rotors free of charge and the second set were better. I did manage to minimize the pulsing by rotating each EBC rotor to the "best" of the four possible mounting locations. I suspect that the front wheel flange is not true to the axle AND the EBC rotors are also not quite true and the combination can be assembled to minimize the excess runout.

[kentuvman]

Front & Rear brakes done!

Test ride today @ 50 miles running errands. Noticable improvement on front brakes not pulsing - I won't say it's 100% but a major improvement so far. It's also nice knowing what I've got on the front end - new bearings, pads, cleaned up rotor and same for back.

I used to rent airplanes when I was an active pilot. Most of the rentals were good but sometimes we'd get a real dog. Knowing I bought this bike last year and I'm the 3rd owner I do have good peace of mind now about my brakes and how the bike was re-assembled. I believe I did it properly. I had her up to 80 and everything good!

Next task to complete (will wait until October) remove gas tank and radiator and replace the fried radiator fan. I have it just want to ride some ore before tearing her down again.

The dust cap cover on the rear caliper was missing. If any of you have one you'd like to sell me, please PM me.

Thanks for all you help as always! I've learned a lot from you guys!

Ken in MN

p.s. Don - I know you'll be skeptical about how long the honeymoon will last with the pulsing being absent - I'll just enjoy her one mile at a time!

[98lee]

The dust cap cover on the rear caliper was missing. If any of you have one you'd like to sell me, please PM me.


Dealer part:

BMW# 34111454120 Covering Cap (BREMBO) $3.73


:dance:dance:dance

[kentuvman]

EZ enough - thanks!