Hello there,
Am new here but thought I would ask the membership for some insights.
Have a 84 R80G/S and want to make it a dual front brake runner.
Hopes that one of you might know the thickness of the spacer needed to place the second disk (off a R90S),before I get a bunch of washers out.
Also any of you out there tackled this "addition" ? Any ideas, warnings or suggestions - experienced based best of course - are greatly appreciated.
Cheers
RA

Here are a couple of sites where you will find people who have made this mod before and will be only to glad to assist.
Search both sites before sticking up a post..

BM Bikes & BM Riders Club Forum • Index page

Airheads - ::. UKGSer.com .::

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The electric monk always has faith.

Thanks for the heads up, will take a good look.
Cheers
RA

You need a new left front fork (or was it the right one...).
A disc.
A caliper.
Brakehose and split.
=> bolt on.

Fits right on.

Kits are available from Willkommen bei WÜDO Motorrad, Ihrem Spezialisten für BMW Motorräder. Bei uns finden Sie alles rund um BMW Motorräder, seine Fahrer und Beifahrer. Hier stehen Sie und Ihre Wünsche im Mittelpunkt. and I think hpn also have an option. www.speigler.de probably have a kit as well. The best system is however from ISR Brakes: ISR Brakes .

Curious:
-why do you want dual disc on a GS? Just enlarging to 330mm will do the trick, and is a bargin in comparission...

I've seen that Down-Under they use Japanese bike brake parts.

Have you been in contact with Motorworks - BMW Motorcycle Spares - home they do have a lot of experience concerning fixing the bad airhead breaks.

Just noticed yesterday as I swapped to my winter rims that Motorworks was proven correct (again...) - warped discs -

The main reason for the -poor- brakes is the construnction of the wheels. The grease from the bearings is flung out onto the discs... lubricates the pads very well... the result is a very long life expectancy of the pads... I have been unable to figure out a solution to this problem less one rebuilds the wheels for standard ballbearings instead of the tapered bearings...

Note:
- when you get an original dual 280mm disc system to work on your GS... be carefull or you may be flipped over the handlebar as the forks are pushed down during hard braking... the original braking system is quite good when it works... then after some miles you have the standard original BMW ABS system at its full potential and operational excellence...

I use Motorworks cast fully floating discs at summer - miles ahead of the warping cracking crappy original discs -

__________________
Drive Safely,
Albert

Hej Albert,
Thank you for the sites, I will take a good look.
Why a dual brake on my G/S ? well I have most of the parts already and really enjoy stopping. What I was hoping to figure out through the membership was the thickness of the plate I need to bring up the disk to line them up with the pads. I must say that the websites I have been directed to will help me a great deal so thank you all for that.
Cheers
RA

If you have most parts you should be able to see that they should fit right on - no spacers needed.

However, if you do as I have been forced to do due to lack of 19" tires, to install a different rim, R45-65 front rims, then one must have spacers.

The original disc and bowl are the same to R45 through to R100.

What you need is a corresponding lower leg = then it is just a bolt on issue -

Let us know how it goes! -

__________________
Drive Safely,
Albert

I have twin disced my '83 G/S and from memory had to turn up a spacer 5.5mm longer than the original. I also use the original master cylinder which is a little spongy but will still screech the front tyre, it is a big improvement.

Maybe an Alternative option to think about might be to fit a Harrison billet mini 6 pot brake - this is a very effective brake, it is well made, simple, light and works well it has lots of feel and is progressive in both the dry and wet - two up with luggage in the wet it is good enough but not overpowered, snatchy or grabby. It does however need fairly regular cleaning (every 4000 miles minimum). It may not be as powerful as the twin set up your talking about but to date I have not found it to be a problem. (except replacement pads are expensive but they do last a very long time) would probably work out as cheap or cheaper than the option you are looking at.

Greetings Sunlune

In the past I added a second disc to a 1986 R80RT and changed the original calliper on my R100GSPD to a Harrison Billet Mini 6 to get more stopping power with both bikes.

I can't exactly remember which gave me the better improvement and it was on two different bikes but I found that the Harrison was the better/easier option for the following reasons.

1) Mechanically the Harrison is a much easier to install and bleeding the system was simpler.

2) The unsprung weight is virtually unchanged. A second disc/calliper is fairly heavy.

3) I remember it also being more of a pain to change the front wheel with the second disc as I couldn't unbolt and move the calliper out of position due to the inflexible steel brake line that ran from the calliper to the fork leg. I don't know if that applies to your bike.

4) When I added a second disc to my R80RT the master cylinder needed to be changed to a larger diameter to help push the extra fluid required for the second disc and there was a bit of guess work involved in finding the correct size. It would still stop but there was a lot of travel in the lever. Even with the six posts on the Harrison there is virtually no difference in the feel of the brake from original, except that it stops :-)

I understand your wanting to add the second disc to your bike especially since you have most of the parts and the Harrison is not cheap but it does work well.

I agree with the comment by adv950 about the Harrison although I haven't had any issues with cleaning.

Good luck

Ian J

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Hi Ianj just to clarify the issue with the cleaning, I use the Gs throughout the winter in the Uk and have found the accumulation of salt and dirt seem to get one or two of the pads sticking or hanging on maybe a bit quicker than a standard system - its no big deal just need to drop the pads and pins out give them a good clean, clean up round the edges of the pistons and pop it all back together 15 to 20 mins and they work as new again. Tchus.

Second that finding.
On my /7 1984 it seems to be mainly the righ caliper and the outer (the far right) pad/piston that gets jammed every so often at winter; salt and dust/dirt caused. No big issue though as Adventure950 points out - takes a coffe-brake to fix/clean; and then is all set to go again -

__________________
Drive Safely,
Albert

Greeting Sunlune

I just reread your original post and I've thought of a possible issue.

From what you describe you have two different callipers. One from an R90S and the original from the G/S

Do both these callipers have the same diameter pistons?

The reason I ask is that I'm not sure how the pressure from the fluid from the master cylinder would be distributed across the two sets of calliper pistons if the pistons are different sizes.

Either one calliper would press against the disc rotor with a greater pressure than the other this would reduce the braking effciency and/or cause one set of pads to wear much quicker than the other or the fluid pressure would balance across the two callipers.

It may not make any real difference, I don't know.

Is there a hydraulics expert out there who can give a definitive answer?

ADV950 - I'm not surprised about your cleaning, not a lot of snow and no road salting in Oz

Regards

Ian J

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Always have plan B, and maybe plan C
www.travelswithkitty.com

Have you mixed an ATE single piston with a Brembo dual piston caliper???
Yes = problem. Different size and different displaced fluid volume.

Simple equation:
Pressure divided by square area equates pressure on surface.

I would even expect pulsations to arised between the calipers as they adjust for the different surface area pressure - a kind of a wobbling.

Looking forward to a better and deeper explanation from/by a hydraulic expert -

__________________
Drive Safely,
Albert

I have been away for quite a bit ( long project ) and now with a little bit of time before the next one I can attend to the importance of Moto life.
So to answer some of the thoughts and to update.
First in terms of calipers, they are both Brembos, the left ( sitting on bike ) one is from the G/S and attached and the right one is from an ST no R90S... as you all know two different of a type to fit.
The one from the ST is a perfect match only flipped to fit the right side of the fork.
Now what I do have from the R90S is the brake rotor and the mount which is not as deep and after doing quite a bit of dry mounting ( watch the grins ) of all the pieces, turns out the spacer I would need to overcome the difference is too great for me to set up the dual system with the parts I have, to make this work I would simply need to buy the bits from an ST....
So here comes the thought ?
Do I get a 320mm disc ?
Do I figure a way to mount my 2nd Brembo on the single disc ?
Do I get a 6 pot ?
Or do I simply chuck it all and simply put metal plates on my boots to aid in stopping ?
Other than that the bike is grand, getting lots of bits done on it and quite happy with the sexy beast.
Cheers to all.
RA

Go for the Harrison 6 pot and a HPN rear drum shoe and cam upgrade - then you have an excellent allround brake system - which can be put back to standard in a jiffy if you sell in the future and the Harrison and HPN brake bits will sell very well - getting your investment back. Ps the HPN rear brake really makes a huge difference to the back end - so if your feeling flush it is a good investment.

Its all works out cheaper than failing to stop and hitting something solid.