A brake rotor question - 1984 R100

[palerider5763]

Hello all -

I am going through a new-to-me 84 R100CS LE, trying to address a number of age-related and sitting-related issues. A point of contention between the bike and I has been the front brake. It's the brembo dual disc setup, with a 15" master, and the rubber-distribution piece-steel-rubber-steel hose/pipe configuration going down to the calipers. The rotors are the stock, fixed type (possibly also by brembo). Everything appears original to 1984.

Issue is the front brake keeps locking up, sometimes after it's stationary for a while, sometimes it's fine for a few miles and then begins to drag the bike slower (along with the smell). I've bled the brakes, replaced the fluid, attempted to clean the little holes in the master cylinder, but no dice. And since everything on it is original, and I don't want to die on it, I've decided to replace everything from the master on down to the calipers and rotors to give me piece of mind. And a project to do when my kids are away.

As I'm collecting my parts I'm debating whether to buy the OEM rotors again (34 11 236 005) or go for something potentially better, like EBC floating or semi-floating discs. Prices for either are around $220 each, more or less. Any thoughts on the pros/cons?

On one hand, I want to keep the bike original; on the other, I ride it and would appreciate better stopping power and/or more even wear. But with new Brembo OE single-pot calipers and pads installed (they still make them!), would semi-floating/floating rotors be better, worse, or have no effect? What would you do?

Thanks for your collective wisdom! Ride safe-

James

 

[ksdcr]

Not sure which set up would be “better”, but if I had a BMW R100 CS, I’d keep it OEM.

 

[m_stock10506]

It sounds like your original rubber lines have broken down internally - after 40 years - and they are blocking brake fluid from returning. You are replacing those hoses, so don't need to carry on about that more.

I have an '84 R100 - 170k miles. I recently replaced the original rotors, which had gone below the minimum thickness. I contacted Tom Cutter and got a set of Brembo replacement rotors. Reasonably priced, compared to rotors from BMW. They are fixed, not floating. They installed onto the OEM carriers without any fuss and they are providing good braking power with very linear feel.

 

[pglaves]

I contacted Tom Cutter and got a set of Brembo replacement rotors.

That is Tom Cutter - http://www.rubberchickenracinggarage.com/

 

[James.A]

I am fidgeting with a similar problem with a 1985 R80RT. I am convinced that the issue is the master cylinder. It is a handlebar master cylinder. I had cleaned the master cylinder and cleared the relief port that that relieves the hydraulic pressure when we grab the brake lever. About a year later the problem returns. I have already replaced all the brake hoses, so those seem to be eliminated as an issue. While I do not subscribe to the notion of throwing new parts at a problem, I am convinced that a master cylinder replacement is my next step. A bike with a front brake that drags is unsafe. That dragging front brake put me on my side executing a left turn at walking speed. If you want the best performance, put the best, all new stuff you can get. To my mind, originality does not override safety on a bike you want to ride.

 

[palerider5763]

Thank you everyone, appreciate the feedback.

I'm going to go OEM. Originality is one thing, but I also never thought the brakes were lacking, for a 70hp bike. For me, there are only a few things I will throw new parts at without overthinking the problem - and the front brake is probably at the top of that list. It'll stop well for another 40 years.

 

[kbasa]

I went EBC about 15 years ago and have floating rotors now. I replaced the lines with new stainless ones (Goodrich, I think? Maybe Spiegler?) The brakes, when combined with radial tires are far superior to what they were when I bought it. I also rebuilt the calipers with the kit from BMW, which replaces the seals internally where the halves meet to form the caliper, along with the seals and dust seals on the pistons themselves. You could have a rusty piston that's hanging it up, but I expect the problem lies higher in the brake circuit.

With regard to the brakes locking up, this can be an issue with fluid being unable to return to the master cylinder's storage reservoir when you release the brake. You may have a plugged return in the MC that is the source of your misery. I've had this happen on older Japanese bike brakes, but brakes are brakes and I'd be looking at your MC and cleaning the return passage first.

This is also on my 1984 R100CS LE.

Best of luck.

 

[ccolwell]

If you are riding the bike it makes sense to use modern brake parts for safety and keep the original parts in a box.

 

[kbasa]

If you are riding the bike it makes sense to use modern brake parts for safety and keep the original parts in a box.

Kinda my take. I like to ride mine, so I want to be able to stop, have decent suspension and good traction/tires, so I've modified all that stuff.

Some day, I'll probably get a wild hair and swap out the forks with some modern stuff for even better brakes, tires and suspension.

 

[ccolwell]

Some day, I'll probably get a wild hair and swap out the forks with some modern stuff for even better brakes, tires and suspension.

So, an R Nine T.

 

[kbasa]

So, an R Nine T.

Nah. Already had a couple hexheads. And I’m sorry, but the shape of the tank is odd.

 

[migrant]

Kinda my take. I like to ride mine, so I want to be able to stop, have decent suspension and good traction/tires, so I've modified all that stuff.

Some day, I'll probably get a wild hair and swap out the forks with some modern stuff for even better brakes, tires and suspension.

Suspension is next for my R90S, currently with old Progressive shocks and forks that I rebuilt with stock parts other than the progressive-wound springs that it came with. There are times I think I'm riding a rigid frame.

What suspension mods did you choose that made it ride-worthy?

 

[kbasa]

Suspension is next for my R90S, currently with old Progressive shocks and forks that I rebuilt with stock parts other than the progressive-wound springs that it came with. There are times I think I'm riding a rigid frame.

What suspension mods did you choose that made it ride-worthy?

I put RaceTech in the forks with a San Jose billet top plate. Konis on the back and they’re OK, but not great, so they’re probably next up.

Conti Classic Attack radial tires made a huge difference in terms of feedback. It’s the first time I’ve felt like an airhead was attached to the road.

 

[ccolwell]

I put RaceTech in the forks with a San Jose billet top plate. Konis on the back and they’re OK, but not great, so they’re probably next up.

That's a very good set up. I had that on the R90S. Ikons worked well enough for the riding I did (moderately aggressive).

 

[kbasa]

That's a very good set up. I had that on the R90S. Ikons worker well enough for the riding I did (moderately aggressive).

Thanks. I'm pretty pleased with it. I think the front end points out the relative crudeness of shocks from 30 years ago and something more modern is appropriate.

Kinda busy selling my house right now, so maybe some Ohlins in the future. These bikes have enough power and torque to be pretty quick on the backroads, but the rear suspension has a little ways to go. I don't really ride it loaded anymore, so even though frame braces are attractive and cool looking, I don't feel like I've got enough frame windup to either get noticed or make a difference.

 

[palerider5763]

A quick update on my front brake refresh...

For those looking to do a similar end-to-end replacement on an 81-84 R100CS or /T with the dual disc Brembo setup, here's what I've removed and re-installed so far, from top to bottom:

32 72 2 302 370 Master and piston, 15mm (x1). Removes from grip assembly with two small hex screws ("Fillister head screw"), electric disconnect is also there for the brake light.
07 11 9 920 057 Small hex/fillister head screws to secure Master to right grip assembly (x2)
07 11 9 933 060 Spring washer/crush washers for small hex screws, for above (x2)

34 32 1 241 563 Brake hose (x1) from Master down to Distribution Piece. There is a banjo fitting on one end, at the Master, and threaded on the other to go into the distribution piece. It threads downward from the bar through a gusset to under the tank.
34 32 1 242 205 Hollow bolt for the banjo fitting the Master to front brake hose (x1)
07 11 9 963 072 Gasket rings/copper seal washers for hollow bolt - need one on each side of the banjo fitting (x2)

34 32 1 241 568 Distribution piece (x1). Made of metal, it sits under the tank. It receives fluid from 563 above, and distributes brake fluid down to each caliper through 699 (x2) below. It also supports a heat sink and has the Bosch ignition module screwed on top of it. Adding/replacing heat sink paste is a good "while you're there" which I got from Brook's website. I reused to screws that keep all that together.
07 12 9 952 123 Hose clamp (x1). This secures the distribution piece to the top bar of the frame, under the tank.

34 32 1 234 699 Brake hoses (x2). I bought Cohline hoses, which look and are stamped almost exactly like OEM, from EME. These screw into the distribution piece on each side.
34 32 1 234 628 Hose clamps (x2). These hold each brake line securely against the frame as they head down. They "fold over" the grommets below, which protect the line. Screw the brake lines to the distribution piece first before clamping.
34 32 1 234 629 Grommets (x2). These fit around each brake line, and are sized so that the hose clamp fits nicely around them.

Continuing the downward path, my bike has two little, metal, wire-like "hose holders" that protrude a bit in front of the downtubes of the frame in front, one on each side. They have a rubber grommet around the loop end, which each 699 hose passes through. I couldn't find these on a fiche anywhere, but mine were in good shape, so I cleaned and re-used them. Each rubber hose goes through them on its way down to the next clamp, which is off the front fender.

34 32 1 241 561 and 34 32 1 241 562 Hose clamps (1 each). These clamps are secured to the fork/fender assembly, just above the caliper. There are two parts numbers, one for each side (L/R). This clamp holds a grommet which wraps around the "female" end of the 699 brake hose, and supports the connection to the brake pipe (which itself connects to the caliper). Each one is secured by the bolts supporting the front fender, on either side.
34 32 1 233 159 Grommets (x2). You need one each for each hose clamp above. Each side of the grommet is recessed a bit; note the shallower end goes on to 699 fitting first, and kind of settles into the groove on the hose fitting. I inserted the grommet into the clamp first, then fit the hose in after.

34 11 1 236 566 Brake disks/rotors (x2). I ordered mine from Motobins (Brembo code BR20200), price and delivery speed were great.
07 11 9 919 656 Brake disc mounting bolts. Also from Motobins, mine came with the required self-locking nuts and washers. I removed the original discs, cleaned the snowflake wheel as best I could (Simple green and some scrubbing/rinsing), cleaned the contact surfaces with brake cleaner, and installed the new discs and bolts (torqued to 30nm, IIRC, but do your own homework). I had the wheel balanced at a motorcycle shop nearby.

That's where I sit today. The wheel is back on the bike, axle greased, axle and clamp bolts hand-tightened, with the whole top of the brake system good to go, down to the bottom of the hoses. But I think I made a mistake with the brake pipes and calipers, which are the final pieces of the puzzle. Which I'll ask you about in the next post. If you see anything else wrong/missing, please let me know.

Other notes: I tend to clean everything as I go, so things take longer. I also tend to use "gummy fledge"/Sonax on all existing/new rubber parts to give them a bit longer life. I also have the habit of assembling everything loosely first, until I'm sure I haven't messed anything up. I put little pieces of tape on all fasteners that haven't been properly torqued yet, and I'll go through them all with the right torque specs at the end. It's rare that I get everything perfect the first time through...

 

[palerider5763]

So all was going great, but then I learned something many on here probably already knew: You can't buy the correct Brembo caliper made for 80s BMWs new anywhere, which I thought I could. What I ordered (from OPP) were Brembo calipers of similar year/vintage, probably for a Moto Guzzi or other marque. From a few feet away they're identical; but up close you see differences in the mold and shape that are off just enough that it can't mount them on the fork tubes and discs. So I think I'm facing a rebuild of my existing calipers, hopefully using the same or most components (seals, pins, pistons, pads, etc.) from my incorrect order. Hoping they share the same internals, going to open them both and check.

Here's what I ordered:
Brembo #20355640
Brembo #20355641


When you turn it, you can see that the markings and shape are different. Also, my originals have Brembo and a little BMW symbol underneath them, which I thought might mean nothing, but turns out it does. Any insights or experience with this?

Also: The brake pipes (x2) I ordered (34 32 1 241 957) came right from the MaxBMW fiche. These connect the 699 brake hose to the caliper. But they too are not exactly the same as my originals; the fittings are fine, but the bend angles are a bit different.

When I align my original brake pipes/calipers to the new hoses and new discs everything lines up perfectly on the fork. So I think I need to re-build my existing calipers and possibly bend the pipes a bit to get the right angles? Is that a good idea, or do I have the wrong part? And if anyone has a recommendation for what black paint I can use to paint the calipers, I'd appreciate it! Thanks for any thoughts...

 

[jimwjarmour]

binding brakes

probably too late now but if you can find a smaller master cylinder than 15 mm my friend got a 13mm gives more power to brakes, i went from 17mm i belive on my 1977 r100 s under tank type to 15mm made a hell of a difference ,also check your brake pad pins ,if pads new, for tightness, had this on my sons 2000 r1100rt just had to file around locating area on the new ebc pads ,also when you have it all built up or before you start pump up front brake lever put a rubber band round the lever holding it tight on , over night or longer will centralize its self , well hope this assists ,Jimmy

 

[88bmwjeff]

When I align my original brake pipes/calipers to the new hoses and new discs everything lines up perfectly on the fork. So I think I need to re-build my existing calipers and possibly bend the pipes a bit to get the right angles? Is that a good idea, or do I have the wrong part? And if anyone has a recommendation for what black paint I can use to paint the calipers, I'd appreciate it! Thanks for any thoughts...

I rebuilt my Brembo calipers for my 1988 R100 RT earlier this year. The rebuild was easy. Granted, I didn't repaint the calipers though. I used polishing compound and a toothbrush to rejuvenate the paint a bit. While they don't look nice and new as they would with a fresh paint job, they do look a lot better.

I too purchased new pipes (I believe they are a bit different on the 84 compared to the 88) and they needed to be adjusted a bit to have everything fit properly. I replaced the stock rubber hose with Spiegler stainless steel ones, so things did need a slight adjusting for the those too. I also found that assembling the calipers and pipes before mounting the calipers was easier and required less adjusting than if tried to attach the pipes after the calipers were attached.