1987 K75C 34.6K Oldest Karibic Bleu Brake Rotor Nut question

I'm a bit embarrassed to have to ask this but here goes.

I'm replacing the front brake rotors. The new nuts have a knurled side that is a smaller diameter than the non-knurled side. Which side rests against the washer and why is one side knurled?

Pic attached. Not very sharp but you should get the idea. The knurl is on the bottom in the shown pic.

Thanks in advance,
Pete

Pete,

The nuts are self locking nuts (no lock washer or loctite required when new). You may be more familiar with Nylock self locking nuts with the nylon insert.

The nuts you have, have a slight crimp in the diameter at the smaller end (the end facing down in your photo). When new, this causes a slight interference fit when the bolt reaches those threads. The bolt is started on the large diameter (top) end of the nut and after a few turns, gets tighter. These nuts, being all steel, have a higher temp capacity than nylon locking nuts (probably a good thing near brakes).

These are officially intended as a one use nut, as the deformation (locking capability) is reduced slightly after even one use, but a drop of red Loctite will let you reuse these with no worries.

After all that; necked down side out.

As always excellently explained. Many thanks Lee!

Pete

pjar said:

I'm a bit embarrassed to have to ask this but here goes.

I'm replacing the front brake rotors. The new nuts have a knurled side that is a smaller diameter than the non-knurled side. Which side rests against the washer and why is one side knurled?

Pic attached. Not very sharp but you should get the idea. The knurl is on the bottom in the shown pic.

Thanks in advance,
Pete

Click to expand...

What does the rest of the bike look like?

Rotor and Pad replacement update

Hello,

R&R went fine. I work slow and methodically so it took me a fair amount of time. The only temporary hitch was with new rotors and pads the pads would not insert with calipers mounted and torqued.

I removed calipers, made sure pistons moved easily and were fully recessed, mounted calipers lightly (bolts tightened by hand) and then inserted pads while jiggling calipers as needed. That worked. After torquing the caliper the pads slipped up or down easily.

Lee if you have another super slick black magic solution please share it. Thanks again for you help.

The brakes perform well with no squealing or pulsing after a test ride. It was refreshing!

Pete

Attached is a pic

36654 said:

What does the rest of the bike look like?

Click to expand...

Picture attached with previous owner.

The original owner added a fuel gauge (left) and temp gauge (right peeking out behind the brake fluid reservoir). The fuel gauge is unnecessary IMHO, but the temp gauge is nice and enables you to know if the fan engages at the right temp.

Enjoy!
pete

Pete,

Are you putting in new STOCK rotors or AFTERMARKET rotors?

If they are aftermarket, if you have the capability, measure the thickness. Aftermarket rotors may be a few thousandths thicker than stock, which might make it a little harder to install new pads.

Which pads are you using and are they FA-18 pad size? What is their thickness?

Stock pads with stock rotors: remove pads, retract pistons, install new pads. Nothing special.

98lee said:

Pete,

Are you putting in new STOCK rotors or AFTERMARKET rotors?

If they are aftermarket, if you have the capability, measure the thickness. Aftermarket rotors may be a few thousandths thicker than stock, which might make it a little harder to install new pads.

Which pads are you using and are they FA-18 pad size? What is their thickness?

Stock pads with stock rotors: remove pads, retract pistons, install new pads. Nothing special.

Click to expand...

Hi Lee,

EBC rotors with EBC organic pads (FA-18). Thickness of the rotors is .2005" I'm thinking I may not have had the pistons completely retracted on the initial try. I haven't checked the thickness of the pads, but there is no binding when I spin the wheel. It feels normal.

Pete

pjar said:

Hi Lee,

EBC rotors with EBC organic pads (FA-18). Thickness of the rotors is .2005" I'm thinking I may not have had the pistons completely retracted on the initial try. I haven't checked the thickness of the pads, but there is no binding when I spin the wheel. It feels normal.

Pete

Click to expand...

This is why I'm not a mechanic because I sometimes overlook the obvious. The prior rotor/pad set up squealed a lot. I used CRC Disc Brake Quiet to try to stop the squealing. That worked for about 24 hours. When I removed the calipers I noticed there was build up of the Disc Brake Quiet on the outer edge of the piston and on the dust cover. That too may have contributed to my initial difficulty inserting the pads.

Pete

Pete,

Sounds like your detective work has ucovered the likely suspects.

pjar said:

This is why I'm not a mechanic because I sometimes overlook the obvious. The prior rotor/pad set up squealed a lot. I used CRC Disc Brake Quiet to try to stop the squealing. That worked for about 24 hours.

Pete

Click to expand...

They all do that, really. The trick is to brake harder, really. Just like pre-loading the shifter, it's a BMW feature, not a quirk.

Bobmws said:

They all do that, really.

Click to expand...

Not really.

Less than 2% of the K75/100s that I've seen or worked on had squealing brakes. The ones that wanted that fixed were corrected with new pads and proper break in.

Squealing indicates SOMETHING is not happy at the pad/rotor interface. Usually the problem is glazed pads. Sometimes it is just the pad material (I like the EBC HH pads). Sometimes it is the rotor surface that has developed issues.

98lee said:

Not really.

Less than 2% of the K75/100s that I've seen or worked on had squealing brakes. The ones that wanted that fixed were corrected with new pads and proper break in.

Squealing indicates SOMETHING is not happy at the pad/rotor interface. Usually the problem is glazed pads. Sometimes it is just the pad material (I like the EBC HH pads). Sometimes it is the rotor surface that has developed issues.

Click to expand...

Lee, you are spot on again. I previously bought used rotors, one of them had some run-out, but much less than the ones that I was replacing. What I didn't know and didn't thoroughly research was to replace the pads when replacing the rotors. I used the original 29-year-old pads and they squealed like hell. So yes, they were most likely glazed. So far the new set up is working great (new pads and rotors). It was worth the expense. Thank you!

pete