My 1974 R90/6 never-ending project, with plenty of pics.

kstoo said:

?
I think that the EBC just bolts on.
I have had good report about them, they wear less because they are drilled/slotted properly, they are "floating" to compensate for heat growth, ...
they look cool

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I did a search, and you're correct. They do just bolt on. Some replacements provide only the rotor and not the carrier. My memory was incorrect with regards to the EBC rotors.

However, the EBC's are $247 each (at Bike Bandit for my 88 R100RT) vs $112 each for the Grimeca's. Big cost difference. Whether or not they're worth the additional $135, I don't know.

Dennis Kirk was less than that if I remember right but the link that PMonk listed above is the best; $189. Pre-1985 are cheaper, too.

OK, now, do we have to pass the hat for CDD?

Nathan, I think this is not un-common. I've seen another 70's drilled rotor that started to show hairline cracks at the drilled venting holes. Let's face it, a rotor is a wear part not unlike brake pads or tires. Maybe you could check out the microfiche on the MAX BMW website or RealOEM.com to see the exploded view of the caliper mounting. I checked my old parts book and it doesn't clearly indicate that the caliper floats or if there is an eccentric adjustment to get perfect alignment. It seems reasonable that if the caliper put a bind on the rotor when the brake was applied, the rotor would be stressed. Surely someone here knows more about disc brakes than I/we do.

Brake Rotor Crackages - Ugh!

crazydrummerdude said:

I've got good news and bad news.

Good news: I rode 19.4 miles today. Ran like a top. Just pulled me right along..

I knew I had to adjust the front brake, because it was more of a "slow suggestion lever" than a brake lever. So, after the ride, I shut the bike off and removed the tank for an adjustment. I bent down and and saw the bad news:

Now how the hell does that happen? It was cool to the touch.. and nothing was rubbing. When I aligned the rotor last night, I made sure everything was lined up properly and nothing was rubbing or hanging up. I distinctly remember hearing a "tink tink" as I was riding, so I guess that explains the sound. Anyone seen this before?

Now I've gotta 1) find out why it happened, and 2) find a new (used) rotor.

Arg! I'm bummed.. and broke.

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Real sorry to hear about that, Nathan!

But I have my suspicions...!

First of all, there are the EVIL BRAKE SPIRITS!



There is a FACE in that pan of goo, Nathan! Don't you SEE it??? It looks a LOT like that face on MARS!

'Tis the face of the EVIL BRAKE SPIRIT!!! Mark my words (er, rotors...)

(the Evil Brake Spirit is invoked when you leave your valve cover washers on the head, before installing the cover) but I digress...

OK, OK, OK...

I have an ALTERNATIVE theory, just in case...

There is a recent Airhead post entitled: Rs brakes, posted by 9842.

The reply (by lostboy) tells it all:

"Chances are the vent port in the master cylinder is plugged. Look down into the resevoir and you'll see the top of the cylinder. In it are two holes, one relatively large and the other is tiny-about .013-.015". The tiny one is the vent port. If you are brave and careful, you can open this hole with a wire drill. You have little to lose; the alternatives are rebuilding or replacing the master cylinder, which you may have to do anyway."



Now I think I remember that you rebuilt your front brake master cylinder, yes?

You could STILL have that problem. Here's a clue:

"I knew I had to adjust the front brake, because it was more of a "slow suggestion lever" than a brake lever."

That 900cc engine has PLENTY enough giddyup to pull you along smartly, EVEN WITH the front brake on!

I believe that the reason it seemed like a "slow suggestion lever" is because that front brake was ALREADY ON.

That's why it didn't "do more" when you pulled the brake lever - you already had the front brake on and didn't know it.

Now before anybody says: "Aw, that's a bunch of BS!" I will tell you this:

I have experienced this on my RS. Sometimes the "vent port" is also known as a "compensation port."

On my bike, if I ride outside in the cold (say 40 deg. F) for a while, then park inside a warm garage (60 deg. F) for a couple of hours, I can come back to "tight" front brakes. I can still (barely) roll the machine and there can be enough pressure trapped in the system to turn-on the brake light! There is PLENTY of smoke to power right through this. Mine will usually correct itself in a block or so of riding (I'll overhaul my master cylinder this Spring.)

I think your rotor cracked because it got hotter than the hinges of hell. Failing that, go back to my first theory.

Good luck and I hope you will find enough bucks to fix it soon!

*** Ah, yes! I nearly forgot - the BAILOUT! That's it! ***

I'll bet your BRAKE BAILOUT CHECK is already in the mail. Nuttin' to worry about!

Fascinating! No, not that goofy mechanical stuff. The Oil Pan Spirit I mean.



Hang in there Dude, I am sure everybody is checking their piles of spare parts. Hopefully, something will turn up.

orbitangel said:

EVIL BRAKE SPIRITS!

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Hahaha.. I like the way you think.

I believe that the reason it seemed like a "slow suggestion lever" is because that front brake was ALREADY ON.

That's why it didn't "do more" when you pulled the brake lever - you already had the front brake on and didn't know it.

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I see what you're saying. The only problem is: the bike rolled just fine in and out of my shop. In neutral, with the engine off, the bike rolls fine. So, it seems that the brake wasn't on, at least in that environment.

I rolled it down the slight slope from the shop to the garage, and tested the brakes and determined they were more suggestive than movement-prohibitive. But, they were enough to go for a spin on the backroad that I take.

I think your rotor cracked because it got hotter than the hinges of hell. Failing that, go back to my first theory.

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How fast can a rotor cool? I thought (and maybe still think) the same thing, but the hole in our theory was that the brakes were cool to the touch when I pulled back in from the ride. Seems like during a ride, a lagging brake would heat up (and eventually lock up), instead of cool down and free up.

In fact, when I was riding home from school a couple months ago on my R75, I noticed I had no-go. I pulled in the clutch to coast down the hill, and actually slowed down! So, I rode the 1 more block to my apartment and investigated the front brake.. and it certainly was hotter than a.. somethingreallyhot. When it cooled from sitting, it freed up, and I could adjust it more accurately. That's the hole in our theory mentioned above. A rubbing brake gets hot (and hot things expand) during a ride. (But your personal experience is interesting.)

But, like I said, I like the way you think.

..

Oh, I forgot to address the master cylinder.

I believe I got all passages clear. I have a handy little "poker" tool that I was using in there to clear out the gunk, then compressed air to blow out all the remainder. Then again, maybe I was just teasing the evil brake spirits such that it re-clogged all my passages! Sounds kinda nasty.

Is the solid rotor stock on your bike?

Metal fatigue is a peculiar thing. A piece of metal can look normal and break suddenly from a very small amount of force. I almost died once proving this to be true. The story is too long. Let's just say tall stepladders, 250 lb. light fixtures and concrete floors can be a bad combination.

Hope you find a rotor at a good price.

Possible spare rotor

Hello from Michigan, Crazydrummerdude.....I have a spare rotor that came off of a 1984 RT. If it is compatible with your R75 you are welcome to it. Some of the folks following this thread can probably answer the compatibility question.

Great job...regards, John

Oops.....and if it's compatible with an R75, it'll be OK for the R90/6 also...

moose738 said:

Hello from Michigan, Crazydrummerdude.....I have a spare rotor that came off of a 1984 RT. If it is compatible with your R75 you are welcome to it. Some of the folks following this thread can probably answer the compatibility question.

Great job...regards, John

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HERO!

moose738 said:

Hello from Michigan, Crazydrummerdude.....I have a spare rotor that came off of a 1984 RT. If it is compatible with your R75 you are welcome to it. Some of the folks following this thread can probably answer the compatibility question.

Great job...regards, John

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Ooohh ooohhh! Yes, I'm interested. How much do you want for it?

I just got home and sumran's damper knob was in the mail.

You people are awesome.

R90/6 Rescue

You can have it for the cost of shipment.... It's good to see a neglected bike returned from the dead. Sort of like rescuing a dog from the pound. Send me a mailing address and I'll get it out this weekend.

PM sent. Thanks!

School starts back up on Monday.. so work will dwindle off on the bike for a couple weeks.

moose738 said:

You can have it for the cost of shipment.... It's good to see a neglected bike returned from the dead. Sort of like rescuing a dog from the pound. Send me a mailing address and I'll get it out this weekend.

Click to expand...

moose738 said:

Oops.....and if it's compatible with an R75, it'll be OK for the R90/6 also...

Click to expand...

Looks like the same part number on the RT and /6's.

Sumran's steering damper knob and moose's rotor arrived. Thanks again!

I went to install the damper knob, to turn this:



into this:



But, to my intrigued non-surprise, it seems to fit similar to my R75's. What I mean is, when I got a new knob for my R75, I couldn't get the little screw to grab onto any threads. So, I carefully Dremeled the inside of the knob and the screw portion of the outside to the right dimensions so it could slide down further and catch, as shown:



So, I might have to look closer at the R90's and Dremel it, too, or realize what I'm doing wrong.

Then, on to the disc brake. If anyone didn't know it, to remove the front wheel is just a nut and a bolt.



After that, it's literally just a few more bolts to remove the rotor/carrier. If you look closely, you might be able to see the 6 or 7 cracks throughout it.



Turned it into:



..and installed it. Now I've got a safe bike! ..and hey, it's even a drilled rotor! Never had one of those before.

I'll probably say it again, but.. I hope this thread will be inspiration for anyone out there who's considering doing their own maintenance (or saving a similar old bike). It's incredibly straight forward and easy. When you get the job done, you'll say to yourself: Wow, that's it?

Took it for a few laps around the field today. Still gotta adjust that front brake. Maybe I'll bleed it again, too.

I've been meaning to look into the horn situation. It doesn't work. Any place(s) I should check first, before getting frustrated?

Easy stuff first. After checking power and ground and button continuity. I don't know if you have one, but the horn relay mebbe?

The "Keep 'em Flying" article in this month's ON magazine is about trouble shooting and fixing horn problems on airheads. It seems the entire club is revolving around your project!

Life is busy during the semester. I don't really get to wrench much, but thank God this thing is ride-able, so I can at least enjoy the fruits of my labor so far.

Came back to town for the weekend, so I had some fun in the snow today. Almost wiped out 5 times. Hahaha..







Hopefully tomorrow I can work on a few things.