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How good are the brakes on a 1981 XS650 Special?

Discussion in 'The Garage' started by Focus Research, Nov 20, 2020.

  1. Focus Research

    Focus Research XS650 New Member

    I've been helping a friend resurrect an '81 Special. We bled the single front disk and put in new pads. The disk does not have any deep grooves. The lever feels very firm, and I certainly cannot pull it back to the grip. I'm not new at bleeding brakes, from cars to motorcycles. No bubbles, fresh fluid coming through, etc. I don't feel any squish.

    Taking the bike for a test, I found I could not lock the tire, even on gravel. Feels about the same as my '71 drum-braked Triumph.

    A caliper and MC rebuild are on the docket, along with a replacement brake line. But how good were the original brakes? I don't have another reference point except for my '93 twin-Brembo BMW, which will lock up the front tires too easily. The rotor appears to be stainless steel, which is a poor choice of material, and I remember the magazine reviews of that era complaining about wet performance. Is it worth having it reground? Is there a cast-iron replacement?

    I'm presuming I should be able to lock the tire, yes?

    Carl D.
    Raymond likes this.
  2. Jim

    Jim Beyond the edge is the unknown. Here be Dragons XS650.com Supporter Top Contributor

    While the XS front ain't a powerhouse by any stretch, it should easily lock on gravel. Sounds to me like the pads either need bedding in, or maybe a poor composition.
    The stock rotor isn't stainless, it's cast iron or steel.. not sure which.
    .. and welcome to the forum. :D
    Raymond likes this.
  3. arcticXS

    arcticXS XS650 Guru Top Contributor

    Not being familiar with the 81 Special, but I suspect it suffers from the same problem as most other vintage Yamahas. Too big master cylinder bore. On my RD350A, I use a 13 mm bore Brembo master cylinder. The RD caliper has 2 opposing pistons, 48 mm diameter. The later XS caliper has a single, smaller piston. If it was me, I'd look for an 11 or 12 mm master cylinder.
    Maybe from something like a Virago 125or 250.
    gggGary and Raymond like this.
  4. 5twins

    5twins XS650 Guru Top Contributor

    The rotor would get all rusty if it was iron or steel. It's some sort of stainless I'm pretty sure. I think this front brake can be made to work pretty well with a few tweaks. You'll want a stainless line and a hole pattern drilled in the disc. A slightly smaller than stock MC will improve the feel but the original works OK too. It can certainly be made to work better than what you're experiencing.
    gggGary, Paul Sutton and Raymond like this.
  5. Paul Sutton

    Paul Sutton Still Looking Good Top Contributor

    My 81SH front brake was very "wooden" in feel even with stainless brake lines. It behaved as you described. I fitted a Virago 400, or was it 250, 12.7mm master cylinder and it instantly felt much better. If you change to another master cylinder then remember to get one that matches the angle of the handle bars. The Virago MCs are sloped to match the original buckhorn type bars so fit an XS Special nicely with original bars. Lower bars may require an MC that sits more horizontally.

    The disk/rotor is a special grade of Japanese stainless for brake applications and you will seldom see any staining on them. But being a stainless grade they will stain a little if left dirty in storage for a long time, but clean up well with a light wipe with steel wool. There are better metals for rotors but for motorcycles there is a balancing act between brake performance and their decorative aspect.

    Second hand Yamaha master cylinders are usually a top quality purchase and at worst just need a new rebuild kit and new paint job. The last one I bought didn't even need a rebuild kit, just a damn good clean inside. Be very wary of those cheap Chinese MCs. They have a bad reputation as I found out.
    arcticXS and Raymond like this.
  6. gggGary

    gggGary I'm listening, change my mind XS650.com Supporter Top Contributor

    Hmm the stock brake works "pretty good" when everything is working as intended.
    And yes a full tear down of MC and caliper, new SS line is the correct way to proceed.
    Some possibles
    Check the master cylinder bore, it's printed on the body facing rider below reservoir. should read 14mm, some other dual disk Yamahas of that era used 5/8" bores, bikes are 40 years old no telling what parts swaps have gone on in that time.
    Like 5T sez bed the pads new pads need a bit of time to take on the contours of a used rotor. I find 6 to 10 good hard hauls down from speed will get the pads into contact enough for the brake to act properly. A look at the rotor after a ride will give you an idea of how much contact you are getting.you can see shiny vs dull area.
    a stuck "caliper slide pin" is a possibility also. Push the slide bushing out of the rubber boot clean any corrosion, sparingly apply brake grease, reinstall.
    I usually go to a smaller bore MC from a smaller Yamaha dual purpose machine. I also tend to swap to a later, much lighter brake rotor but this requires a rotor spacer to regain correct offset.

    MC and caliper rebuild how to's found in the tech section. https://www.xs650.com/threads/how-to-bleeding-the-brakes.11205/
    Raymond, Paul Sutton and GLJ like this.
  7. motormike

    motormike XS650 Junkie XS650.com Supporter Top Contributor

    Caliper sleeve... ?
  8. gggGary

    gggGary I'm listening, change my mind XS650.com Supporter Top Contributor

    Paul Sutton likes this.
  9. ThatXS650Guy

    ThatXS650Guy More Sparky than Speed Racer XS650.com Supporter Top Contributor

    North GA
    Big improvement can be had with just the smaller MC and a stainless steel brake line.
    Raymond, Paul Sutton and gggGary like this.
  10. motormike

    motormike XS650 Junkie XS650.com Supporter Top Contributor

    Caliper rubber.jpg The happy face is a new caliper rubber sleeve.. the unhappy face is a sleeve rubber that as been subject to.. most likely fork oil... it swelled... which if reused... will cause the caliper to drag and perform poorly. Also use " brake lube " for assembly in this area... wheel grease will cause the new rubber to swell... I lube the sleeve.. insert.. then place lube inside the sleeve boot.. both ends.... before I slip in the groves.. this helps prevent condensation build up... as evident by the pitted sleeve in the photo. I also lightly add a small about on the surface of the caliper bore before I insert the dust boot.. again to help prevent condensation .
    grizld1 and gggGary like this.
  11. Jim

    Jim Beyond the edge is the unknown. Here be Dragons XS650.com Supporter Top Contributor

    They'll rust...;)

    Last edited: Nov 21, 2020
    madmax-im and Paul Sutton like this.
  12. Paul Sutton

    Paul Sutton Still Looking Good Top Contributor

    Perhaps stainless steel is not the correct term to use. TRW describe their motorcycle discs as being made from "an extremely high-grade steel alloy that protects reliably against corrosion, maintaining a good appearance as well as strength, safety and performance."
    gggGary and Jim like this.
  13. Machine

    Machine Race the wind Top Contributor

    Stock XS brakes just require a mindset other than say, a sportbikes braking ability..
    gggGary, Paul Sutton and Jim like this.
  14. XSLeo

    XSLeo XS650 Guru Top Contributor

    I found that at times even with a new rubber sleeve there still can be sticking issues.
    Sometimes the bore the rubber sleeve goes into gets some corrosion build up. So when the new sleeve and pin are installed it's a tight fit.
    You some times have to ream this crud out. I found using a drill and a 1/2 bit and a bit of reaming gets this crud out. Go just far enough to get clean metal. Don't enlarge the bore any.
    Now with the new parts it slides better.
    Raymond, gggGary and Paul Sutton like this.
  15. Jim

    Jim Beyond the edge is the unknown. Here be Dragons XS650.com Supporter Top Contributor

    Stainless steel uses a high chromium content to prevent corrosion. That actually allows it to "heal" itself when scratched. If I'm not mistaken, that also makes it more flexible :umm:... so there's a trade-off for it. Increasing the nickel content also helps. That's what makes ss non-magnetic. These rotors ain't. My magnet sticks to it just as good as it sticks to my anvil. I'm guessin' it is actually stainless... with good corrosion resistance traded off for some other strength properties.
    gggGary likes this.
  16. Grimly

    Grimly XS650 Addict

    Yep; different grades of stainless, all the way from never-rust to something that looks like it's spent a month at the bottom of the dock.
    gggGary, Paul Sutton and Jim like this.
  17. xjwmx

    xjwmx It's just the unknown. Top Contributor

    If nothing's obviously wrong and the parts look okay, I'd bet that the pads just need bedding in. Resurfacing the rotor might speed it up and I think there's a minimum thickness spec in the manual that you can download. When I first put new pads in, the regular performance was a lot like wet performance and it took a couple of months of riding for them to get as effective as they were going to get

    I haven't read anyone's experience with a resurfaced or new rotor on here but I have a gut feeling it would give a good improvement. Maybe like 2 or 3x...
    gggGary likes this.
  18. kshansen

    kshansen XS650 Guru Top Contributor

    Can't speak for the 1981 XS 650 But I do recall the time I put new pads on my RD400 many years ago. First time I grabbed the front brakes I almost thought the bike sped up!

    After that I rode around dragging the brakes off and on and after a bit started to get some action. Once good and broke in one time managed to lock up the front wheel on nice dry pavement while slowing down to pull in driveway on the way home from work. After that I was a bit more careful, locking front wheel is not recommended! At least I didn't go down!
    Paul Sutton and Raymond like this.
  19. motormike

    motormike XS650 Junkie XS650.com Supporter Top Contributor

    Back when I turned a wrench... we'd turn the rotors..drums... besides true'n the items.. it also removed the brake material that builds up on the surface... so now you're stopping on the rotor-drum ..not the built up material. At our shop.. we tape up the rotor... and just media blast the brake'n surface.. does a excellent job of cleaning the rotor surface and provides excellent brake'n.
    Mailman and gggGary like this.
  20. fredintoon

    fredintoon Fred Hill, S'toon. Top Contributor

    Hi Carl,
    Rest of the World's XS650s got dual front brakes but North American XS650's only got got one (Effin' stylists)
    All XS650s.got the same size front brake lever hydraulic piston (Effin' cheapskate production managers)
    Add left side brake disk & caliper OR swap in a smaller piston brake lever to get better braking.
    Find several upgrades to XS650 stock brakes in the search box.
    XS650 stainless brake disk has a lower friction coefficient than a Guzzi's cast iron disk but it don't rust as you ride in the rain.
    And yes, I have seen Guzzi brake disks rust on a wet ride.
    Raymond likes this.

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