F800GS single brake mod woes

Discussion in 'Parallel Universe' started by LostInTransit, May 10, 2016.

  1. LostInTransit

    LostInTransit Been here awhile

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    Hello everyone!

    I have been running a single right caliper and disk on my f800gs for some time with no problems. I had read that if yo use the MC from the 650 twin it has a smaller bore that can improve the lever feel. So I bought one on ebay and installed it last night. It was an absolute bitch to bleed until i worked out how to bleed the MC first using its bleed screw but then the whole system appeared to bleed fine. Lever felt great so i went to bed. So start riding to work today and then caliper starts smoking and then front brake goes hard on! i vented some brake fluid from the pee cup as i thought it was too full stopping the fluid flowing back up as it expanded but it did it again about a mile later. bought a pair of spanners from the hardware store nearby and cracked the top bleed nipple to release the excess pressure. I then used a spanner to lever the pads apart while i opened the caliper nipple. Then rode to work on just the back brake.

    Anyone had some direct experience of using the F650twin MC on a single f800gs caliper??


    Regards

    Dave
    #1
  2. dpm

    dpm Been here awhile

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    sounds like the lever isn't returning fully to it's home position?
    #2
  3. LostInTransit

    LostInTransit Been here awhile

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    Hey dpm! Lever returns fine which is weird. Its like it isnt releasing fluid back up into the reservoir after its pulled and it just keeps adding it the more you use it till the pads are hard against the disk. I took the mc apart and the inside looks fine but it is more complicated inside than the f800gs one. Appears to have a small valve that needs to open when you release the lever but it looks like it works. Gonna re bleed with fluid from a different bottle!

    Dave
    #3
  4. LostInTransit

    LostInTransit Been here awhile

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    master.JPG rebled with no change, gone back to the original for now. So annoying as the brake felt amazing till it got jammed on! Here is the piston with the little valve at the end. It appears the valve allows backward flow when pressing the brake but not when its in the rest position? So basically it just keep filling up the brake line till the brake jams?!
    #4
  5. LostInTransit

    LostInTransit Been here awhile

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    DSC_0080.JPG
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  6. LostInTransit

    LostInTransit Been here awhile

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    This is my weirdo bike by the way. Haha!

    Dave
    #6
  7. FinTec

    FinTec Been here awhile

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    I like it! Well done with the front end. Did all the things the 800 needed: no beak, high fender, single rotor, etc.

    I have no input on what is going on with the MC, sorry. But if funds allow, look at the Magura line of after-marker MC's. I used their 12mm MC for my single caliper 800 project (used with MotoMaster 4 pot Caliper), and it works fantastic. Can order with a small attached reservoir as well so no huge bobble head one as per stock.

    Who's triple clamps did you use? And are those the factory forks or some bigger WP's?
    #7
  8. LostInTransit

    LostInTransit Been here awhile

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    Hey thanks Fin333! I will have a look for those online. Does the motomaster use stock rotor diameter? The fork crowns are from twalcom and they are the standard marzocchis at the minute. The twalcom fork inserts will be on the way soon though once i can sort out the front brake. Got a list of other mods on the cards so will put them up on here. Will try get some more photos up too!

    Edit* do you have a part number or photo of the magura unit?

    Regards
    Dave
    #8
  9. Snowy

    Snowy Long timer

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    I researched different master cylinders used in single disc conversions. It all sounded waaaaay too hard.

    I used a master cylinder off a DR650 on my single disc setup. Because there was a spare one laying on the work bench.

    Works great. Never been an issue. Had to plastiweld up a brake light switch using the original BMW switch though. Still works years later.

    It even worked with the ABS perfectly....right up until the welding/lightning incidents. One of those killed the electronics in the wheel speed sensor circuits.

    Effectively with the single disc, you can't feel the difference between double and single disc. You have to be really moving with a load. Then you can feel that initially there isn't quite the same force. But at legal speeds....meh. No difference you can put your finger on. It'll lock the front wheel on asphalt if you get carried away.
    #9
  10. Reaver

    Reaver How Did I Get Here?

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    Did you use the 800 lever and push rod on the 650 MC?

    The pushrod has a factory set adjustment after its assembled. If it is not set correct (too tight) then the relief valve won't be able to relieve so as the system gets hotter, more pressure will remain in the line.

    See the Allen head screw with the red witness paint? BMW forbids you to tamper with it!

    I needed to adjust mine when I installed ABS on a non ABS bike. Don't know why, but I had to and it worked.

    If you look at the hidden end of the rod, you'll see an adjustment setup. Unscrew it to allow the piston to fully return home.

    [​IMG]
    #10
  11. LostInTransit

    LostInTransit Been here awhile

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    Hey Snowy if I cant get it to work then the DR650 lever might be an option but i'm not giving up yet haha!

    Reaver i saw that it had a hex head in it and even tried to move it but it was siezed so i left it! will get it in some wd40 and see if i can free it as that would make complete sense as the little valve activator only works when the piston is fully out and i had a bit of tension in the cylinder when putting the lever bolt in! so backing out that little allen head would relive the pressure from the lever resulting in the piston fully resting and activating the valve.

    Can't wait to get home and get the adjuster freed off!!!!


    many thanks everyone!

    Dave
    #11
  12. LostInTransit

    LostInTransit Been here awhile

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    bike.JPG

    here is the weirdo again!



    Dave
    #12
  13. Reaver

    Reaver How Did I Get Here?

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    The adjuster is Loc-Tited in there. WD 40 won't help. Use a bit more force and make sure the pushrod is still tight when you're done so it doesn't back out and get too loose!
    #13
  14. LostInTransit

    LostInTransit Been here awhile

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    ok thanks Reaver i will sort it when i get in. Once i position it i will try get some new locktite on!


    regards
    Dave
    #14
  15. LostInTransit

    LostInTransit Been here awhile

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    Reinstalled the 650 cylinder, bled it and then wound the piston prodder bit back out and i think its worked. Not ridden it yet so will see tomorrow. I did notice that the brake does feel a bit tight as you pull the wheel through the caliper but hopefully that will settle when i ride it

    Regards
    Dave
    #15
  16. FinTec

    FinTec Been here awhile

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    I believe the MotoMaster caliper will work for several sizes of rotors with-in a certain range. I use a 320mm single rotor and it work great. It all comes down to the adapter you use and does it line up everything just right. Talk to them, they are easy to talk to I found.

    I used the Magura #0120794 MC. Part of their "Radial 195 series" and comes with a 12mm piston. This was the size MotoMaster suggested. Snowy is right, you can lose you mind trying to figure out the math for the right MC piston size. Just call your local Magura rep/dist, tell them what caliper you are using, and they will tell you which model of their MC will work. Let them do the math.

    You can guess on MC piston size, but if you are off a lot, you either get a MC that feels like wood or a mosshy non-working brake.

    By the way, if you have the coin, go for Magura's new "HC3" series MC for motorcycles. VERY nicely made with a bunch of adjustments. But crazy expensive if I remember right.
    #16
  17. LostInTransit

    LostInTransit Been here awhile

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    Ok rode to work and provisionally the brake feels good! There is still a bit of overall resistance between the pads and disc but it feels like its settling down. Fin i will keep your recipe though as a possible upgrade if im not happy with the current setup. Dont think i would get the hc3 lever bit rich for my blood haha! I have some new sintered pads to go on and im ordering a wavey disc from twalcom to complete the upgrade so will post some snaps once they are all on! I have a new disc in the post for the rear brake and some sintered pads for that also. This is all in aid of ensuring my brakes are spot on before i order the tt long range tank as with that much fuel on the bike it will stop like a pig!

    Regards
    Dave

    *edit*

    Brakes feel great now and have settled in!

    Many thanks everyone for your support!!
    #17
  18. bing

    bing F800GS & WR250R

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    Updating an old thread.... my 800GS came to me with the single disc conversion done but with the original master cylinder. The feel at the lever was wooden and hard. I put the other disc on and straight away the feel and braking improved. I have just put a KTM 390 Duke master cylinder on with only one disc. The feel and power are very much like the std setup with 2 discs. Braking is very good with good and is 90-95% of the original. The 3kg reduction (which is both rotational and unsprung) can be felt and I am not a gun rider by any measurement. The power for dirt riding is much more suited with a single disc. I highly recommend sourcing a different master cylinder for the single disc conversion. I think the ultimate set up would be a 320mm disc but I'm not sure where to source this and a calliper re-locater. Back to the internets.... IMG_3469.JPG IMG_3468.JPG
    #18
    SuhoMeso and morfic like this.
  19. SuhoMeso

    SuhoMeso Two wheels

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    How is this working out for you? What did you do for the brake light switch?



    #19
  20. bing

    bing F800GS & WR250R

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    I put a piece of rubber around the arm that activates a KTM brake light switch. It was a bit of mucking around but it works.

    Attached Files:

    #20