If you like our site, please consider joining our club!
By joining you will help ensure that we can continue to provide this service
JOIN HERE!

Handlebar mounted Brake master cylinder on 1975 R90/6

Post Reply
willstone
Posts: 36
Joined: Wed Dec 30, 2020 9:11 am

Handlebar mounted Brake master cylinder on 1975 R90/6

Post by willstone »

What is the collective wisdom on changing from under tank MC to handlebar mounted MC? What is involved? Are there distinct advantages? Disadvantages? Worth the trouble? I've researched the Magura 17-9200 14mm mc and have heard that should work. Any other suggestions? My option is to have my present under tank mc bored and sleeved for $110 + shipping.This is for 1975 R90/6.

User avatar
schrader7032
Posts: 9016
Joined: Fri Oct 27, 2006 3:00 am
Location: San Antonio, TX
Has thanked: 2 times
Been thanked: 29 times

Re: Handlebar mounted Brake master cylinder on 1975 R90/6

Post by schrader7032 »

Welcome to the forum! I hear a lot of people make the change to the bar-mounted master cylinder. I think the advantages are less danger of missing a leaking one under the tank, and supposedly better braking feel. One thing that can be looked at is consider changing the brake line from the master cylinder to the caliper...even if you just go with another OEM rubber one, the old one might have broken down internally and expands under pressure. Some go with a steel line...various suppliers I think Spiegler is one.

Snowbum has a big discussion on brakes here:

https://bmwmotorcycletech.info/brakes.htm

Check Section 8A where he discusses the changeover...looks like there's quite a lot of parts. An issue you'll need to deal with is getting the right diameter master cylinder to work with the ATE caliper.

Might want to consider first a swap of the brake line...see if that improves things.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

User avatar
srankin
Posts: 1054
Joined: Fri Jul 14, 2017 8:45 pm
Location: Spencerport, NY USA
Been thanked: 14 times

Re: Handlebar mounted Brake master cylinder on 1975 R90/6

Post by srankin »

Comparing my two bikes side by side I find the set up on my 84R80RT with the handle bar mounted master cylinder is far superior to the set up on my 78RS with the cylinder under the tank. Mind you, part of the difference is obviously the much better Brembo calipers in the newer system versus the ATE calipers.

But, There is a better "feel" and more "grab" with the newer system. Part of it is the elimination of the cable from the handlebar to the MC. I also believe the better performance is also due to the much better Brembo calipers. The ATE calipers with the one piston also have to be adjusted just right at the caliper for them to work their best. Where the Brembos have no adjustment along with an extra piston.

To be honest, I have toyed in my mind with changing the RS set up to the same as the RT but, I can't justify the cost and time. With the ATE system all adjusted properly, It is not a HUGE difference in braking power as far as I can see.

Now, I have been talking about a two caliper two rotor system. I would perhaps if the parts were reasonable add a second caliper and disc system to a single disc brake bike. My first bike was a single caliper ATE bike and while it had adequate braking, it could have been better. One of the reasons I traded it in for a newer bike was to get the two brake system. St.
Owner of a 84, R80RT and 78, R100RS

ECJ
Posts: 21
Joined: Fri Dec 15, 2017 9:50 am

Re: Handlebar mounted Brake master cylinder on 1975 R90/6

Post by ECJ »

I recently performed this swap on my 1979 R80/7 and can say the difference is considerable. One of the best upgrades I have done for this bike. I can now ride when needed with two finger coverage on the brake lever, and not need a full hand squeeze as was the case with the under tank MC.

The only downside, is cost. The new right hand perch is expensive at around $350, plus maybe another $120 for custom SS brake lines (definitely worth it), and a few more bucks for other small misc. hardware. I ran a two line set up, going to a later K bike manifold under the tank for cleaner routing (rather than just running straight from on handlebar MC to caliper), and also so that if I were to choose a dual disc set up in the future, it would be easier to modify.

ECJ

Post Reply