Discussion with my mechanic: Dual or Single front disc brake?

[MauriceNL]

Hi guys,


For months I am drooling over all your bikes and posts regarding the XS'. I descide to buy one for myself and i just registed on this forum.

I've recenly bought a '79 xs650 which i brought to a garage for adjustment of the valves and a brake check-up.


I've noticed the brake power is quite poor and therefor i've asked the mechanic if he could check it.

He called me that it was no surprise that the brake was poor becaus i was missing 1 front disc brake. According him the previous owner removed 1 disc but did not exchange the and the brake pump (the one on the steer). So, appartenlty there is not enough pressure in the brake line to push 1 single brake.


I find this hard to beleive since 1) previous owner drove with it for years and 2) i know there were some models in the past which have a double brake and some with single brakes. But I don’t know how my bike was built back in the days.

Unfortunately i am not able to check my serial/frame now (it’s at the garage) so can someone tell me if the mechanic is right?


Can I check somewhere if my ’79-er was built with 1 or to discs?


Hope you guys can help me out.


Thank you and I hope to contribute a lot in the near future.

 

[joebgd]

It's my belief it always had one disk. You are exactly right some, i believe more the European midels, had two disks. Im r i ght now working on upping the front breaks. There are many ways. I ordered steel braided brake line. You sound like you read on here. You can change master c to lil smaller add a disk....
Welcome glad to have you abord. I am sure more experienced xsers will chime in also.

 

[gggGary]

For a single disk 1979 the master cylinder should have been 14mm I believe the double disk models used a 16mm master cylinder. But a smaller master cylinder gives better power or feel. Many use about an 11mm with a single disk I run a 10mm and am happy with the feel. A stainless steel brake line is also a performance and feel upgrade that is often done. The old rubber lines are often failing inside. But when properly adjusted and maintained the stock brake is OK.

 

[member3480]

Most bikes in the late 70's and 80's had poor brakes because single puck brakes were used. I have built many XS 650 and most are poor stopping and upgrading to dual front will help but I would also look at upgrading brakes to newer style if you are concerned. Top speed of a XS 650 is not fast compaired to todays bikes and there are many upgrades that you can do but no madder what you do dual disk and rear disk the bike is still very light and will slide if you lock up the brakes. So yes there are upgrades to make it stop better. Dual pucks stop better and more money for up grade but if that is what you feel will be better then I would look into it. Many kits and styles out there and I know there are threads on hear about brakes. You are dealing with a 20 year plus old bike so upgrades are needed.

 

[gggGary]

Old brakes need rebuilding! Junk gets behind the rubber piston seal, and a sticking slider, both common issues. The pistons are chrome plated steel and the chrome will be rust pitted. If brake pads have gotten oil on them from a leaking fork seal they are junk and must be replaced. Master cylinder should be stripped and cleaned.

 

[ThatXS650Guy]

My 79 had a horrible stock brake too. Get rid of the 14mm MC and go with a new 11mm. That will kill two birds with one stone.
Upgrade the pads, go to a SS line and clean up the rotor. The brakes will be much improved.
Plenty of brake info on this forum if you search.

 

[MauriceNL]

Greaaaat! Thank you guys! This very helpful!

 

[5twins]

Measure the diameter of your single disc. That will tell you whether your set-up was originally a single or double disc. The single disc set-up used a larger diameter disc @ 298mm. The double discs were smaller, about 267mm I think, but I'm not 100% sure on that size. No matter, if your disc is smaller than 298mm, it was a double disc set-up originally. Your MC should have it's size stamped on it somewhere, check that too.

 

[Paul Sutton]

I am a slow rider mainly running at 50 to 60mph on the open road. I replaced the 14mm master on my 81 Special with a Virago XV250 12.7mm. It is not a big change but definitely a noticeable improvement i.e. approximately a 20% increase (Changing to 12mm is approximately a 35% increase). The Virago has the correct master cylinder shape to match the original handlebars on the Specials. In practice the original 14mm was very hard to bring the bike to a quick stop. The 12.7mm brings me to a much quicker stop but will not lock the wheel up on a dry road. I bet 12mm would be a very good change to make without the risk of locking the wheel up too easily.

 

[nighthog]

I'm going to replace the one on my SJ Special with an 11mm one for a Honda CG 125. I've got a stainless braided line, rebuilt master cylinder and caliper and new EBC pads and disc but braking is like gripping a piece of wood, and very much the 'period' experience. Needs improvement, but hardly surprising for a bike of its age.
11mm or 10mm? I've agonized over that but 11mm seems the most popular choice. Or you could toss a coin .....

 

[Paul Sutton]

From the Technical Section we have the following link:
http://www.xs650.com/threads/fazer-blue-spot-caliper.197/page-2
At entry 24 Travis has a link to master/slave cylinder ratios for selecting the optimum cylinder sizes. The ratios are based on the surface area of the master and slave pistons because that is what is important with hydraulics: Kind of equivalent to tooth ratios on gears. This will help you decide if 10mm or 11mm is optimum. If the master cylinder is too small the brakes will feel spongy and may get failed even though they are good. Spongy isn't always due to trapped air.

 

[650Skull]

Euro Standards had a twin disk set up with the smaller rotors.

Euro US custom Specials had a single disk set up with the larger rotor.

The twin disk smaller rotors front forks are different where the caliper mounting lugs are lower to account for the smaller rotor.

If the bike was a US import then it would in all likelyhood have a large single disk set up be it a Special or standard.

Euro 79 Standard.Euro 79 US Custom