adding second brake caliper-?

[doubletrouble]

650Skull got it right!! point 2 to be exact. The Caliper bracket slipped right over the second rotor. I also found out the front axle bolt has a shoulder that will hold the speedo drive in place even it the fork is out just a hair.
Everything worked out great and thanks for all the input from everybody. If I was going to start over I probably would have taken the advice of grizld1 and just improved the single rotor setup. Too late now.
What a great website!!
DT

 

[Timothy]

Hei Guys,

Have just signed up to the forum. Have been follwoing the discussion on "2 discs or not 2 discs". I have a 1979 650F Roadster (Standard in the US) which was imported from the US I think in the early nighties. I bought it in 1997. I have done most of the standard upgrades to improve the handling and steering and also decided to get an extra disc to have equivalent to Eurpoean spec (I live in Norway). I bought a left hand disc and caliper from an SR500 and as discussed found out it was 5 mm thick. I have been back and forth on whether to complete the conversion or not. The standard single disc works OK, but needs a good hard squeeze. I can't imagine the second disc will be that much better especially when adding so much unsprung weight? I have had the original disc skimmed, put on braided hoses and fitted sintered pads. In other words it's probably as good as it can get without actually putting a completely different brake on example from an R1 (I like that idea).

The other thing that's not mentioned is that the double disc models have a larger volume hydraulic reservoir. When I spoke to Tony Hall at Halco (sadly no longer with us) he said that the single reservoir had a different valve arrangement and that he'd experienced some pumping problems with that setup and recommended getting the bigger reservoir from a double disc model also (since mine was from the SR it's identical to what I already have).

I'm tempted to go the full change out the front end for something newer route and saw with interest the other posting regarding upgrading front forks. RD350 YPVS forks with double discs should do nicely although I do like the look of my wire wheels?

One final point regarding the thickness. I too reacted to the 7 mm thickness and the warning in the manual regarding a service limit of 6.5 mm when 2x 5mm are fitted to the XS1100. I concluded that the things are so over engineered, especially when compared to the much thinner discs you see fitted on today's sportsbikes.

 

[vntg-gearhead]

I'm a little late posting my opinion but here it is.

A single rotor/caliper system will generate more heat on it's single rotor than 2 caliper/rotors experinces on any 1 of it's 2 rotors. All the front braking on a single rotor system is done by one caliper/rotor. A twin system has the work load divided by 2. Therefore, half the work per rotor/caliper = less heat per rotor/caliper. This explains why you can use a thinner rotor. Also of note, your not stopping an 800 lb turd cruiser. With twin front brakes you'll notice using the brakes less (time on brakes) to get the same effect.

Another advantage to two rotors is the elimination of fork tweek under braking. A single rotor will tend to pull/twist the forks. This can be a handling issue and can upset the chassis when in "knee drag" mode. A single system will also wear out the forks sooner. A fork brace will help these issues, but they will still be there to some degree.

Master cylinder? Use the single brake system master cylinder. If you don't like it's feel, get the twin system master or an aftermarket 12mm. I believe this; if it works for you and you can operate it safely, don't listen to those that say "you can't do that." The key here is to ride it, sort it, repair it, then repeat the process.

Adjusting the forks to align the calipers!! It's hard enough to get some machines to have the forks run perfectly parrallel with each other. Example; anything old school British. Forks sliders need to move up and down perfectly parrallel. If you tweek the lower axle end of the slider in or out, your creating a wedge effect when the fork slider moves up, thereby creating a bind in the forks. Not only will your forks not work smoothly as they should, they will wear out quickly which will cause an addtional handling issue.

My 2.5 cents.

 

[vntg-gearhead]

Of special note!

A floating caliper should not be used with a floating rotor. You should use a solid mounted multiple piston caliper with a floating rotor or a floating caliper with a solid mounted rotor. Look at modern bikes.

 

[Stigda]

Hi there, about the calipers of -75. The clymer manual demands that whenever a caliper has been splitted in halfs, you should get new bolts when putting back together. I dont understand why(?), and they seem wery hard to find. I have splitted my caliper and that was about time, now some good cleaning and a rep kit will be placed before closing up again.
Can I use the four old bolts again?
Look at the drawing, the bolts are # 16, 17 & 18

 

[grizld1]

vntg-gearhead, re. floating rotors with floating calipers, you need to look at a few more modern bikes. What signifies isn't the number of pistons but whether both pads are piston-actuated of whether one pad is pulled into contact with the rotor by the action of the opposite pad (floating). Tokico dual-piston floating calipers are used with full-float rotors on quite a few of them (the Suzuki SV/Gladius series, for example). Admittedly dual-action calipers (both pads active) are a better way to go, but modern floating rotors perform very nicely indeed with the single-piston unit on 77 and forward XS650's.

 

[vntg-gearhead]

Hi there, about the calipers of -75. The clymer manual demands that whenever a caliper has been splitted in halfs, you should get new bolts when putting back together. I dont understand why(?), and they seem wery hard to find. I have splitted my caliper and that was about time, now some good cleaning and a rep kit will be placed before closing up again.
Can I use the four old bolts again?
Look at the drawing, the bolts are # 16, 17 & 18

If the threads are good, reuse them. If the threads were bad, most likely the caliper threads would be bad as well. I don't know for sure why they say to not reuse them but I have an opinion. I've always resused them. They are NOT "stretch or torque to yield" bolts which must not be reused. Use brake assembly lube (NAPA) or brake fluid to lube the piston o-rings. Make sure you have the caliper halves o-rings held in place when putting the halves together. I use a small amount of silicone brake grease (NAPA) for that. Blue Loctite on the bolts. Tighten on the bench, then temp mount on the fork to final tighten before the Loctite starts to set up. This is the best way to tighten the caliper halves bolts because it's hard to hold it on bench. I don't like to use a vise to hold them. I don't recall the torque spec for the caliper halve bolts but it's fairly tight
(24ft lbs ???).

 

[Tomterrific]

I just happen to have an XS650 and an SR500, both with dual front disks. Those dual disks on a 340 pound bike are way over kill. The SR500 will be going back to a single disk sometime this summer and the 14mm MC and thinner SR's dual rotors will be going over to the XS. The SR disks are thinner as mentioned.

I have a 16mm master cylinder on the XS and a 14mm MC on the SR. The 14mm is the prefered as the power and feel is just right. The 16mm is solid.

What is the number one reason for going to dual disks? They look powerful.

What bike can I steal a modern light weight rotor from to fit on my SR500?

Tom Graham

 

[vntg-gearhead]

vntg-gearhead, re. floating rotors with floating calipers, you need to look at a few more modern bikes. What signifies isn't the number of pistons but whether both pads are piston-actuated of whether one pad is pulled into contact with the rotor by the action of the opposite pad (floating). Tokico dual-piston floating calipers are used with full-float rotors on quite a few of them (the Suzuki SV/Gladius series, for example). Admittedly dual-action calipers (both pads active) are a better way to go, but modern floating rotors perform very nicely indeed with the single-piston unit on 77 and forward XS650's.

The term "floating" can understandable confuse. Single and sometimes 2 piston calipers are usually slider/floating mounted and use a rigid rotor (all the float needed is via the caliper). Those with 4 or more, are usually solid/rigid mounted. They rely on the individual >slight< float of the pistons and the ability of the floating rotor to >slightly< float (slight x2 = all the float you'll need). I'll look again at the SV. Although I put a Gixer fork and brake assembly on it (much better), with 6 piston calipers.

The issues I've had with floating/slide calipers and FULL floating rotors combo on the XS is; the slides tend to be loose/sloppy (not a bad thing if you have a rigid rotor) and cause too much flex to the full floating rotor thereby loosening the rotor rivet washer to much. Of course I ride my machines harder than most and can find a weak link in any design.

My large TDM/R1 type rotors w/dual action calipers, on my well flogged 650 Tracker, are so strong I could do "stoppies" if I was 30 years younger. However the full floating rotors rattle so much at idle it sounds like something is about to fall off. Bad loose, loud rattle. I've tightened the rivet washers twice (not a recommended procedure) only to have the problem return. I know they are supposed to move, but this is way too much movement. Next ride in "knee drag" mode they may fail. I'm currently searching for a pair of 298mm/11.7" rotors to fix this issue. Not an easy task as the 10.5" and 11.7" look the same in Ebay pics. Key here is to measure before you buy. Can't ride it now anyway. I've got a set of JBM intakes that must be installed be for I take it out again. Carbs keep falling off with the gasoline softened Mikes intakes.

 

[grizld1]

Never had issues with prematurely loose buttons on the old D, even clamping down with sintered pads and 11 mm. MC; but then again I don't ride as hard as I did a few years ago, LOL. Keeping the static pad fresh and positioned close to the rotor is important; you don't want the driven pad shoving the rotor way over before contact is made with the static pad, and if there's a big gap to close, that will happen.

 

[vntg-gearhead]

Your exactly right. On a full floating caliper, the piston pushing on the rotor pulls the static pad in place. With FULL floating rotors it will actually push the rotor aside a little until the static pad comes in contact with the rotor. This is what prematurely loosens the rotor buttons. The more rigid (not FULL) semi floating rotors may work but I'd prefer solid/rigid rotors with floating caliper. Keeping costs to a minimum, I used the single piston calipers (Mikes XS) and good but used TDM rotors (akin to Mikes XS). Rotors not being new may have added to the button loosening, but they were good when first installed 1500 miles ago.

I really like the dual brakes. Even though they are a little over kill. Don't understand using high tech calipers on these machines. I'd rather ride it verses it being in the garage for an unessasary upgrade. One of those K.I.S.S things.

 

[Stigda]

If the threads are good, reuse them. If the threads were bad, most likely the caliper threads would be bad as well. I don't know for sure why they say to not reuse them but I have an opinion. I've always resused them. They are NOT "stretch or torque to yield" bolts which must not be reused. Use brake assembly lube (NAPA) or brake fluid to lube the piston o-rings. Make sure you have the caliper halves o-rings held in place when putting the halves together. I use a small amount of silicone brake grease (NAPA) for that. Blue Loctite on the bolts. Tighten on the bench, then temp mount on the fork to final tighten before the Loctite starts to set up. This is the best way to tighten the caliper halves bolts because it's hard to hold it on bench. I don't like to use a vise to hold them. I don't recall the torque spec for the caliper halve bolts but it's fairly tight
(24ft lbs ???).

Thank you. I have now picked up all the tools and shit that I need and will put it together tonight.
The torque should be 43-72ft.-ib on the hex bolts, 53.5-68ft.-ib on the bridge bolts and the mounting bolts to the fork 28-36ft.-ib, all according to my Clymer.
I will also use acid-free ATE grease on the o-rings and Locktite on the four halves bolts.

 

[Spockwerks]

Sorry for adding to this thread at this late date, but I am currently assembling my '80 XS650G for resale, or maybe restreeting is a more tender term. Either way I will be riding it for a while so I figger I'll use up all these upgrade spares I've accumulated during the past 3 decades and make this one built to the hilt in a back to the '80s kind of way. Part of that being the dual disc arrangement in this thread, using both discs and calipers from an XS750, the year they all turned purple. I've put a new MC into the equation, so we have to wait and see how it works.
Anyway, the XS750 has 1mm larger fork tubes but a stem length that is much too short to call this a drop in fit.
But the XV920 known overseas as the TR-1 IS a drop in fit, right down to the neck bearings, BUT the discs are a bit smaller in diameter plus thinner & lighter. Triple trees are burly great aluminum castings that add substantial bulk visually, and I am quite sure they are more torsionally rigid as an assembly than the standard suspension.

So add XS750, XV920, and TR-1 to your shopping list next trip to the junk yard.

 

[Grimly]

If I can toss my 2c in here to add to the knowledge pool.
Mine is a 79 Special, European model with twin 297mm discs. As standard, the M/C is about 11/16" as far as I know.
After years of fettling worn Suzuki GS calipers, I was quite pleased to find the XS calipers were of a slightly simpler design and didn't suffer as badly from sliding pin wear (it was there, but minor).
However, I wanted some better feel from the brakes, so reading around I thought I'd try a 14mm m/c from a Kwack (iirc, it was from a ZXR400 - nice unit with span-adjust, dogleg).
That worked bloody well - gave me braking power that had me grinning from ear to ear, but there was one slight drawback - the slight caliper slider wear that was present was causing some lost motion at the handlebar lever. Not a huge amount, but got a little bit close to the bar for my taste.
I ended up fitting a Honda NTV650/700 m/c 16mm (5/8th) which is a perfect compromise. There's still plenty of upgraded stopping power, and the lost motion is trivial. In fact, the Deauville m/c has become my favourite upgrade for a lot of twin-disc bikes of that era, now. They're dirt-cheap, reliable and easily rebuilt. They're also all OEM, and made by reputable Japanese factory, and not some anonymous sweatshop in Guangong, with little or no quality control.

All the above was done on a fully rebuilt system with new seals, stainless-braided lines, etc..