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Topic-icon R90S, 3rd disc brake parts

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3 months 4 days ago #5834 by mikethebike
R90S, 3rd disc brake parts was created by mikethebike
First off, I thought I had posted this yesterday, but I don't see any sign of it on the Forums, so here goes!

Last year I bought a '76 R90S that needed a lot of work to get it back on the road. It had been idle for more than 20 years (only has 16k miles on it). Its a one owner bike and when he bought it in Seattle he had a set of Morris mags installed at the dealer. This option for $400 gives you a 3rd disc brake!, what a deal. However I'm now having problems sourcing parts for that 3rd brake set up. The components are all from Hearst Airheart. They still produce brakes but they are mostly manual brakes for Go-karts. I've located a set of brake pads from Speedway Motors, but I cannot find seal kits for the master or brake cylinders. I've been in touch with Tolomatic who took over the line, but the 5/8" bore model is not even in their files anywhere.
So does anybody know of someone who may have parts, I'd appreciate the help.
Thanks in advance

Michael

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2 months 4 weeks ago - 2 months 4 weeks ago #5837 by Wobbly
Replied by Wobbly on topic R90S, 3rd disc brake parts

mikethebike wrote: First off, I thought I had posted this yesterday, but I don't see any sign of it on the Forums, so here goes!

Michael -
Welcome aboard ! First time posters need to have their first post cleared by moderators. That's why your post didn't appear right off.

mikethebike wrote: Last year I bought a '76 R90S that needed a lot of work to get it back on the road. It had been idle for more than 20 years (only has 16k miles on it). Its a one owner bike and when he bought it in Seattle he had a set of Morris mags installed at the dealer. This option for $400 gives you a 3rd disc brake!, what a deal. However I'm now having problems sourcing parts for that 3rd brake set up. The components are all from Hearst Airheart. They still produce brakes but they are mostly manual brakes for Go-karts. I've located a set of brake pads from Speedway Motors, but I cannot find seal kits for the master or brake cylinders. I've been in touch with Tolomatic who took over the line, but the 5/8" bore model is not even in their files anywhere.

So does anybody know of someone who may have parts, I'd appreciate the help. Thanks in advance.

► Just because a system is old doesn't automatically mean you need new seals. Take it apart, completely disassemble every piece, all wash internal parts with warm soapy water, air dry, sand pistons and bores, and re-assemble wet (wet with BF). Usually what you'll find is that most of what you thought was rust, was really simply caked-on antique DOT3/ DOT4 brake fluid. This will look like amber and can be up to 1/8" thick. The only reason to stop is a badly pitted bore... which even then isn't really a dead end.

There's a mental transition to be made here. You're no longer working on a hot-rod BMW, you're working on a nearly half century old vintage motorcycle. Parts don't need to look like they are going on an F1 racer for the World Championships. The truth is... this motorcycle will probably never go faster than 70MPH for all its remaining days. Average speed is more likely 50-55MPH. I'm talking realistically; not about what you see in your head. So lets act realistically.

► Here's how a professional restorer thinks... Airheart was a small company supplying rear brakes mostly to dirt trackers. They were never on any production bike. Therefore, the best they could do (most probably) is make the metal parts of the system, and BUY the rest. (Nobody spends $250,000 on a mold to make a part they can buy for 3 cents.) That means that they most likely designed around off-the-shelf standard parts and purchased the rubber seals. That means there's a high likelihood that you can walk into any NAPA (or any really GOOD auto store) and do the same. Look for one that's been in that same location for 50 years and has old guys with books, not pimple-faced kids on computers.

The corroborating evidence for this type logic is that the bores are in inch sizes. That is to say... it is pre-Asian invasion.

► One last bit of advice, which you can take or leave. You may wish to investigate a non-corrosive, non-varnishing, non-hardening, low friction, low maintenance brake fluid that goes by the name of DOT 5 Silicone for use in your restored system. I mention this because after spending 6 months to track down all these parts, I doubt you'll be looking forward to doing this again in 2 years... just so you can use BMW approved DOT4 brake fluid. No, I rather suspect you'll be looking for a fluid that helps you maintain your classic with minimal effort, rather than become an on-going maintenance nightmare. Let's face it, you've already got to contend with keeping Ethanol fuel out of the fuel system during storage, keeping the valves adjusted, and battery maintenance... my thinking is why add to the list ? But now you have my 2 cents.

Hope this helps.

Don't hide 'em, Ride 'em !!
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Last edit: 2 months 4 weeks ago by Wobbly.

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2 months 4 weeks ago - 2 months 4 weeks ago #5842 by mikethebike
Replied by mikethebike on topic R90S, 3rd disc brake parts
Thanks for the response, funny you should mention all of the above!
Over the weekend I soda blasted all the parts except the pistons. I now have a shiny black master and caliper, Coates’s with caliper paint.
After spending best part of Friday trying to find new seals, I re-examined the existing parts and they are now installed also.
So all I’m waiting for now are the brake pads and in they go.
But I hadn’t considered DOT 5, I assembled with smears of 4. So I’ll go ahead and use 5 for the fill.
I assume I can useDOT5 with the rebuild of the front system ( I have new SS lines coming from Germany this week and master seal kit locally)
Thanks again
Michael
Last edit: 2 months 4 weeks ago by mikethebike.

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2 months 4 weeks ago - 2 months 4 weeks ago #5845 by Wobbly
Replied by Wobbly on topic R90S, 3rd disc brake parts
► Yes, the very best time to cut over is when you are assembling the brake system from clean, naked parts. This because DOT5 Silicone does NOT mix well with any of the others. My understanding is that it forms a gelatin. I have converted working systems over by blowing though the entire system with compressed air for several minutes, then bleeding the brakes every couple of days to flush out any jelly that might form.

► Yes, it's good in your stock front system. I've been running it in a 1979 RT/RS for 5 years without ANY issues. If you are just adding the lines, then I'd pull the piston on the M/C and pop out the pistons on the calipers to get rid of the bulk of the old fluid. You can wash all the parts in warm soapy water, then warm the parts with a hair dryer. You'll undoubtedly find crusty DOT4 there and be glad you took the extra time. Refill the system from the calipers going UP to the M/C.

You need to be very careful. DOT5 Silicone will not mix with DOT3, DOT4 or DOT5.1 brake fluids. DOT5 Silicone is NOT the same thing as DOT5.1, which is often sold for ABS systems. The naming conventions for brake fluids make you scratch your head.

► You should not use DOT5 Silicone in an ABS system. It was invented in the early 1970's before ABS came into use. It's great in the R90, but not your late model BMW.

DOT5 Silicone is colored purple so that you can easily recognize it, and not be mixing it.

► For all the "gotchas", it is really excellent in a classic bike. It reduces brake system wear, is kind to the seals, negates the need for annual fluid replacement, and when you might need to bleed... you needn't worry about it destroying your $1000 paint job on your fuel tank. You can just bleed away without covering anything because it's so inert.

Hope this helps.

Don't hide 'em, Ride 'em !!
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Last edit: 2 months 4 weeks ago by Wobbly.
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