Boxerworks.com

Dirtsurfer, check the bore of your master cylinder carefully for pitting. This is quite common and in some cases it can be honed to a useful condition. If the pitting is too deep you can get the bore machined and sleeved.

The refurb kits are stupidly expensive whether OEM or 'pattern'. With a good bore the only thing from the kit that you really need is the 'cup' seal that goes on the piston - but you can't buy this separately. The rest is just bullshit, in my view.

Before you buy anything check out the availability of a suitable used handlebar mounted master cylinder compatible with your model. You will get much better braking, particularly if you go for a smaller diameter bore, like 14mm. I have heard that it is possible to run a 13mm bore with twin disks.

O, and do check out prices of parts at Motobins in the UK. F'rinstance, the UTT refurb kit is UKP47.00 (AUD81.06) there. If you make up an order with a few items the postage doesn't hurt at all.

dirtsurfer wrote: ↑Wed Dec 27, 2017 12:59 am

Wobbly wrote: ↑Sun Dec 10, 2017 7:58 pm You have simply misunderstood. The act of dispersing brake fluid does not require conscious activity by a human. The OP's master cylinder is UNDER the fuel tank where it cannot be observed. When those master cylinders leak, they dribble fluid all over the painted frame and a host of electrical harness connections. Wind (from riding the motorcycle) will then loft the fluid and coat the underside of the fuel tank "tunnel". This condition can exist for months and create quite a mess before the fuel tank is ever removed.

Well I have removed the tank and found the master cylinder to be leaking onto paintwork on the frame. The underside of the tank looks ok.

1. The rebuild should consist of removing the m/c, complete disassembly, and then washing each part in hot soapy water. The water will neutralize the corrosive action of the brake fluid allowing the m/c body to be repainted. The soap will aid in removing the dried-in-place crusty bit, which will be there. A small swath of 400 grit emery cloth wrapped on the tip of a 5 inch wooden dowel will allow you and a drill motor to clean/polish the bore to make a proper assessment. Since standard brake fluids attract so much water, about 50% of the time rust will leave deep divots in the cylinder wall... thus making rebuild useless. In such a rebuild, it's all about what the water did to the bore of the m/c, and not how bad the exterior looks.

2. Hot soapy water and a Scotch-Brite pad will stop the rust on that section of frame. Spray black enamel will make it stay in good condition for years to come.

3. Last, and definitely to be treated every bit as seriously as the braking system is the damage to the electrical wiring and relays just below the m/c. All that wiring needs to be blasted with hot soapy water to stop the corrosive action of the brake fluid on the copper and brass electrical connectors. Inspect and clean the 3 voltage regulator terminals. Due to the side stand, it is typical for most of the damage to be on the left side. That's the side with the starter relay. If you have the elongated metal tin can starter relay (pre ~1978), you'll probably be OK with simple terminal cleaning.



If you have the plug-in "mini-cube" relay (as shown above), then the relay socket is going to need VERY close attention and the relay is most probably toast. Pop the metal or plastic cap off the relay to reveal a science experiment gone horribly wrong. I can render more detailed help if that is the case.

4. And don't forget to wash the bottom of the fuel tank with hot soapy water as prevention. Just becasue you don't see it, doesn't mean small speckles of brake fluid are not also attacking that paint.

Hope this helps.

This information won't help the riders in OZ, but here is a great source in the US to have the M/C sleeved.
Mark Frappier
82 Mountain View
Agawam, MA 01001
1-800-528-5235

He relines the units in stainless, I just received a M/C he did for me for my vintage Jaguar, beautiful job and really reasonable. I heard about him from a guy doing a resto on a R90/6 on Adv Rider. Price was $84.00 with shipping back to me. Turn around was good, it arrived back to 1 week to the day he received it.

I bet this explains why I had a lot of starter relay problems with the '78 R80/7 I had for years. Good stuff Wobbly.

Wobbly wrote: ↑Wed Dec 27, 2017 4:35 pm 3. Last, and definitely to be treated every bit as seriously as the braking system is the damage to the electrical wiring and relays just below the m/c. All that wiring needs to be blasted with hot soapy water to stop the corrosive action of the brake fluid on the copper and brass electrical connectors. Inspect and clean the 3 voltage regulator terminals. Due to the side stand, it is typical for most of the damage to be on the left side. That's the side with the starter relay. If you have the elongated metal tin can starter relay (pre ~1978), you'll probably be OK with simple terminal cleaning.

Thanks for your help and advice so far.
I have disassembled the m/c and the bore is pitted to perhaps .5mm. I had to knock the piston out from the other end such was the corrosion around the circlip end but that cleaned up ok.

In considering options: the handle bar mounted M/C would also require additional hose and splitter. Anything else?

dirtsurfer wrote: ↑Fri Dec 29, 2017 1:18 am In considering options: the handle bar mounted M/C would also require additional hose and splitter. Anything else?

One short hose MC to splitter, two longer hoses to the calipers. Crush washers.

dirtsurfer wrote: ↑Fri Dec 29, 2017 1:18 am I have disassembled the m/c and the bore is pitted to perhaps .5mm. I had to knock the piston out from the other end such was the corrosion around the circlip end but that cleaned up ok.

This is typical becasue the only "standing water" was inside the brake system. You can't trust a used Ebay part, becasue chances are it's in the same shape as what you already have. Time to look for a local bike breaker and inspect before you buy.

SteveD wrote: ↑Fri Dec 29, 2017 5:19 am One short hose MC to splitter, two longer hoses to the calipers. Crush washers.

Or, 2 very long hoses and a double-length banjo bolt.

In the USA we have on-line stores that sell race car parts (Summit Auto, Race Part Solutions, etc). One of the product lines they typically sell is Teflon (PTFE) lined brake lines with the braided steel exterior and ALL the fittings. I mention this becasue you can make up any type of brake hose assembly you like for typically much less than the pre-made motorcycle brake lines in the stores.

The maker I'm most familiar with is Fragola ( http://fragolaperformancesystems.com/ ) and they carry all the Tee's and other fittings as well. If one of their stock hoses won't fit, then they'll make one to your specs. BMW's use the metric 10-1.0 thread pattern on all bikes. "AN2" sized hose and fittings work best.

Hope this helps.

Hi all
Thanks for all the replies and related discussion. Last night I fitted the handlebar M/C kit from Motobins. The M/C itself is Magura and demands the use DOT 4 brake fluid on the reservoir cap so that's what I put in . I'm pretty happy with the result so far; I'm going to check all the connections again tonight to be sure there are no leaks; but the front brake now has a better feel and more convincing stopping power .


And the (new) brake light switch works too!