Could I ask, when did they move the front brake master cylinder from under the tank to on the right handlebars?
I'm looking at a bike claiming to be 1977 R100/s with master cylinder on the handlebars. Is that right?
Thanks guys.
Mal
No, that would have to be an upgrade. The R100 first had a handlebar mounted master cylinder in 1981, in the US at least.
Back to the /6, in case you're thinking of one of the smaller displacement bikes, the R60/6 has a front drum brake and Bing slide carbs, while the R75/6 has a front disk brake and Bing CV carbs, like the R90/6.
They moved the master cylinder out from under the gas tank in 81 as mentioned. At the same time, they switched from single piston ATE front brake calipers to two piston Brembo calipers.
On the 78 and newer RS, RT and S, models the rear brake became a disc unit with a Brembo caliper.
I don't know what model years or models of /7 bikes kept the rear drum brake. I do know my 84 R80RT has a drum rear brake.
So I will as many know me, stick my two cents in regarding the brake systems. My 78 RS had the ATE front brakes with the master cylinder under the gas tank. This system works pretty good as long as the cable to the master cylinder from the handlebars is adjusted properly and (the big and) the ATE calipers themselves are adjusted properly. They had a cam system in the caliper to adjust one of the pads in relationship to the rotor.
The Brembo front brakes with handlebar mounted master cylinder I have on my 84 R80RT are superior to the ATE set up for both stopping power and ease of maintaining. The Brembos have opposing pistons and are self adjusting unlike the ATE units.
In my case, I did a partial upgrade on the RS in that I replaced the ATE front end with a Brembo system. Not an easy job as it requires changing forks and braces along with brake lines and calipers.
In this upgrade I did not (as some other do) move the master cylinder to the handle bars, I left it under the tank. I do have parts on hand to do so but have found I don't need to. The Brembo system on its own is so much better than the ATE system.
Also, with the master cylinder under the tank, less sunlight gets to it and I find brake fluid seems to last longer than it does on my handle bar mounted cylinder on my RT.
OK, LOL, I have gassed on about front brakes, now I will hot air some more about rear brakes. In MY opinion the drum brakes on airheads are far better than the disc brake system BMW choose to install on some of the bikes. In my experience stopping power with a properly adjusted drum brake is better or just as good a the disc system. Also, I had well over 150K miles on my drum system before I had to replace shoes. (This is on my R80RT). On my 78RS, road grime and crap gets sprayed into the caliper and onto the rear discs causing fast wear and corrosion. So, Every 50K, I need to replace pads. Also, I have to flush the fluid every 30K miles.
So if I had my way, I would ditch the disc rear brake on my RS and go to a drum system. Sadly it is not as easy a task to do as was the front brake conversion, so I doubt at my age I will do it.
LOL, now that I have put you all to sleep, wake up and go for a ride. St
In MY opinion the drum brakes on airheads are far better than the disc brake system BMW choose to install on some of the bikes. In my experience stopping power with a properly adjusted drum brake is better or just as good a the disc system. Also, I had well over 150K miles on my drum system before I had to replace shoes. (This is on my R80RT). On my 78RS, road grime and crap gets sprayed into the caliper and onto the rear discs causing fast wear and corrosion. So, Every 50K, I need to replace pads. Also, I have to flush the fluid every 30K miles.
So if I had my way, I would ditch the disc rear brake on my RS and go to a drum system. Sadly it is not as easy a task to do as was the front brake conversion, so I doubt at my age I will do it.
That's great intel on the front brake. I did the opposite and just replaced the master cylinder with the handlebar mounted unit. I can't say it was an improvement. I did it because someone told me it was the "trick" thing to do and younger me believed it. Your solution sounds far better, and a bit more involved.
I agree regarding the rear disc. I'm not a fan. The drum has better feel.
I switched to a drum on my '78 R100S and much prefer it. I don't recall it being a big ordeal though. Going from memory, I needed a new wheel with a brake drum (I was already switching to spokes from mags, so not a big deal), rod and connectors for the brake pedal to the actuator on the final drive, and the actuator and brake shoe hardware in the wheel, on the final drive. I believe my '78 final drive already had all the castings and threaded holes for the drum brake hardware. Mine was plug and play. I also cut off the welded retainer bar on the swingarm that keeps the caliper from rotating. Then you just need to get rid of the caliper, reservoir and brake lines. It's been 15 years, so I may be forgetting some things, but I recall being surprised that it was not more difficult. I could be repressing something horrible that happened and maybe it's a PITA, but I don't remember it that way:)
That is some good discussion on the braking system. While I had worked out from the link to the sales brochures that the handlebar mounted brake master cylinder did not appear before 1980, I had no idea about the other matters. Though I do remember adjusting the ATE front calipers on my R90/6.
A long time back I rebuilt a mates R60/5 when he did a big end bearing. Put in a new crank and pistons from memory. I thought the engineering of the internals was substantial and I was sort of disappointed when I was told that BMW had dropped the double row cam chain for a single row unit. I'm not sure when that change occurred, do any of you know?
I don't know the date, but the '77 model should have an under tank master cylinder. My '78 does. But if I read the RealOEM info right, the under tank was used up to 09/1980. So beginning with the 1981 models it was moved to the bars.
Now having it on the bars is a modification that many have done. Supposed to be more effective, better feel, and less chance of missing a leak due to being hidden under the tank.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.
What was being said about the rear drum brake fits my experience with the drum front brake. I had a 60/6 and changed the motor for a 75/6 after 100,000 miles, because the pundits kept saying the fuel mileage was better and the 750 was the best motor.
The fuel mileage was not better, 45mpg against 55 (UK gallons, 20 fl oz.) the motor was certainly lower compression, so no detonating but I was working with the bike, so speed was not an issue. The brake shoes I would get refaced at about 25,000, twice was the most as the operating arm would wear the surface on the shoe. The drum went oval at 180,000.
The next bike was a 75/7. Discs would last 30,000, pads 3 to 4,000, cast iron discs performed better. Obviously, most people don't do those sorts of mileages and better brake performance may be worth the cost but, since it was my business, I found the drums cheaper to run, needing less maintenance and the performance was sufficient.
I now run a 50/2 and, after 40 years of disc brakes, I've had to relearn to leave more room for braking.
My RS which has the disc brake does have all the holes needed to switch over to a drum brake rear end. LOL, I haven't done it yet because of laziness in collecting the parts and cheapness in not wanting to pay for the parts.
Yes, I would need a new rear wheel with the drum, the brake rod, shoes, adjusters, a few bits and bobs. I do think one of the parts is NLA new from BMW and like hen's feet to find used. I believe it is the shaft that passes through the final drive with the cam to move the shoes.
When I did the front brake conversion, I found a guy making a custom bike who was selling the entire front end of the bike forks, brackets, calipers, everything to do the job for less than $400. I got the parts and was very pleased they were from a sub 40K mile bike that was well cared for.
The same guy had all of the handlebars stuff needed to move the master cylinder from under the tank to the handle bars. As I did the job in two parts (0r was going to do the job in two parts), I did the forks and brakes first and found the stopping power was equal to my RT which has the handlebar mounted master cylinder. LOL, since I like the look of my handlebars and controls without the master cylinder on them, and the one under the tank provides equal effort and power, I figured there was no real reason to do the swap.
As for seeing leaks in the handlebar unit faster, yep, it is right there so yep it is faster to see a leak. LOL, my smart arsed comment to that is the owners of the bikes with the under the tank units should as part of regular maintenance take the gas tank off and look things over. Frankly, the only time I ever see a major problem at my friend's shop with damage done from a leaking master cylinder is on the bikes where the owners have stored them for long time or buy them second hand and get a case of previous owner's disease, because the previous owner was too lazy to check and change fluid on a regular basis.
As I said earlier and I don't have the numbers or solid proof to back up the claim, I believe the fluid in the under the tank units lasts longer than the handlebar mounted units. Scuttle butt is this is due to less sun and less moisture from rain or washing.
So. LOL, forgive me for writing a mile long winded post. I am right now off the bikes with a case of bronchitis and as Kurt knows, when I can't ride, I pester people on the forums. Ride safe and happy. St.
I may switch back to the under tank master cylinder after this discussion. I don't really like the look of it up on the handlebar either. Fun discussion for sure.
And, I do recall having bought that actuator arm, that goes through the final drive to the brake rod, from the dealer back in the day. Funny that BMW went back to a rear drum in later bikes.
Mal,
The single row timing chain started in 1979 at the same time BMW went to the "bean can" points and the shorter cam with the indexing slot. I haven't heard anyone mention that they had found the single row cam chain to be less robust than the older double row version.
The 1974 models with the /5 handlebar switches are difficult to convert to a handlebar master cylinder due to the mounting system for the switches. 1975 and newer models allow the switches to easily attach to the handlebar master cylinder perch.
In my opinion the ATE brakes and the under tank master cylinder are a more than adequate brake setup but they do require careful setup and regular maintenance.
The bikes from 1974 to 1980 do not have any particular glaring problems that need to be avoided when searching for a bike. Other than avoiding the R60 due to the low power and slide carbs, the biggest factor in making a choice will be the condition of the individual bike and how the previous owner has cared for it.
I have enjoyed reading your posts and watching your work on the /2 bikes. I am sure that when you find the /6 or /7 bike that is right for you we will be treated to some more of your innovative solutions to BMW's designs.
I thought the engineering of the internals was substantial and I was sort of disappointed when I was told that BMW had dropped the double row cam chain for a single row unit. I'm not sure when that change occurred, do any of you know?
Mal - I poked around on Max BMW's microfiche parts catalogue and it shows that the double row timing chain was used from '70-'78. In 1979 BMW changed to the single row chain. The site doesn't display parts by year, necessarily, but in looking at the double row timing chain, there is a note indicating that it was used only through 1978.
