Double Leading Shoe Drums on a Trials Bike?

Discussion in 'Trials' started by gearheadE30, Sep 18, 2017.

  1. gearheadE30

    gearheadE30 Long timer

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    Thanks! I would probably use an aluminum or steel shaft collar instead of that tiny clamp if I went the clamp route, but you're right. It's a lot of load.

    My concern stems from finding someone to weld tabs on who won't damage the fork leg. I don't know any fabricators locally who would be up to that task, and the risk is very high since TY fork lowers aren't exactly a dime a dozen. Definitely a rare skill, but would be my preferred route if I can find someone to do it. Going to have to make some phone calls, I suppose.
    #21
  2. motobene

    motobene Motoing for 46 years

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    I have found 6061 aluminum tabs will weld to cast aluminum legs pretty well with 5356 rod. Fabricating the tabs well is the first priority. Having the parts really clean with no paint or oil or dirt at the weld site is the next. Alignment is critical too, so it's not only about great welding, the machining and fabricating needs to be great too.

    If it were me, I'd tack the tabs onto the legs on the bike, assembled, with the caliper clamped to the disc, then carefully disassemble and finish welding. It's a lot of careful, high-skill work to do custom stuff well!
    #22
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  3. motobene

    motobene Motoing for 46 years

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    IMG_20171010_125711692.jpg
    Yup. Custom work can be a real time sucker! I have a fresh example. Better footpegs, lowered and moved back on a pet KLR250 was added to a big maintenance overhaul. No biggie, right? Wrong!

    My idea of custom work is the result must be right and reliable the first time. That ALWAYS means more time up front.

    I found I had to machine a fixture to hold the forged steel mounts on both sides to be able to rotate them 90 degrees on the frame. They are slotted and bolted via the big bolt through the suspension linkage, so this small change was not at all easy to do.

    I had to make custom clevices. Thank goodness I had square tubing just the right size or that would have taken a LONG time. Machining in steel slows everything down, even on a full size Bridgeport-type mill.

    The result will be awesome, but it's like throwing pearls at swine. Pukie the KLR isn't a swine, but who really gives a crap about a 22-year-old kick start KLR? Me, apparently:flush
    #23
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  4. dmay

    dmay Been here awhile

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    Sherco uses a floating disc and a fixed mount caliper. Fixed mount disc and fixed mount caliper will likely have a inconsistent lever feel as there is always some flex in every assembly.
    #24
  5. gearheadE30

    gearheadE30 Long timer

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    Thanks for the tips. I'm really mostly concerned with irreparably damaging the fork leg; the fabrication part I can figure out, and will definitely be paying very close attention to alignment and pad swept area. With some care, I'm confident I can get that part right.

    Someday I will have the capability to machine things for myself as needed...but this early in my fledgling career, there's little financial sense in that right now. :( The feeling of polishing a turd, or throwing pearls at a swine, or whatever the case may be is always in the back of my head, as a lot of the people I ride with recommend I just buy a new bike. But I feel I hardly need to tell you that there's something to be said for optimizing a design and making it your own with attention to detail. It's quite rewarding, even if the end result can be bested by something new off the showroom floor.

    You are quite right. I realized that a few days ago when I was looking at caliper sources online - I've spent a bit of time looking for small sliding pin calipers with appropriate piston diameters, but haven't come up with anything great so far. All the MX stuff is too big, and it's a challenge finding something with an appropriate piston ratio. Closest I've gotten so far is the setup from a KTM Freeride, but there are some alleged design flaws with that setup as well. The search continues...
    #25
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  6. Brewtus

    Brewtus Buffoonery, Inc.

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    Not trying to spend you $$ for you, but did you consider buying another fork slider off of Fleabay to do the mod? If it works, fabulous, and you are ready to go. If it messes up, you still have the OE fork assembly to keep the bike going. :D

    Just my 2 cents, not trying to stick my fat snout into your bidness. :thumb

    BTW, kudos on your build. I really enjoy following the evolution of a long term project vehicle and seeing the well thought out engineering and fabrication of mods dreamed up by the owner. Sure new bikes are nice and will be SO much better than your old Mono will ever be, but at the end of the day they are bought not built. Your Yammie is well on it's way to being very special, even more so because you compete on it as well as just mod it. That's part of the reason I have a little bike crush on 'Bene's Fantic, keep modding TY80s, and am about to have 2 more Montesas join the Scuderia. Keep up the good work! :-)
    #26
  7. gearheadE30

    gearheadE30 Long timer

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    I was originally looking for a TY350 slider to try it on, but there aren't really any out there (even internationally, it appears TY Mono forks are either impossible to find or just in high demand). I'm not sure if this is what you meant, but yes, I have considered buying a cheap beat up set of forks for some other bike as a test set just to see how it goes. That would also give me an opportunity to do a test or two to failure just to make sure that the careful, temperature-conscious welding is still also strong welding. Since I've had to restart the search for a caliper, that's been the priority since it will determine bracket requirements. However, I will probably end up doing this. The money is worth it to make sure I don't screw up the original.

    I appreciate your 2 cents, and all the other spare change I've collected around here! I've learned a lot from you guys - about the only way for me to make up for lack of experience is to try to listen to the people who have already been through this stuff. Glad to hear you're enjoying following along; there's something to be said for fiddling with a bike and making it your own. That Fantic was actually part of the motivation for building this bike, so I know what you mean!
    #27
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  8. dmay

    dmay Been here awhile

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  9. Brewtus

    Brewtus Buffoonery, Inc.

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  10. Brewtus

    Brewtus Buffoonery, Inc.

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  11. UstaKood

    UstaKood Adventurer

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    This is off an it400 , same era . Don't know if it's any better or worse but could be an option .

    Modern disc would be nice though .

    Attached Files:

    #31
  12. gearheadE30

    gearheadE30 Long timer

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    Honestly, considering what I'll have into any custom setup, that doesn't actually seem too out of line.

    Downside is, like Brewtus brought up, the performance of the off-the-shelf conversion parts is not known to be very good. I couldn't tell you why, but most comments online say they're not any better than the drum. That caliper bracket is roughly what I had in mind though.... It would be nice to get ahold of just the bracket, but that's probably not any easier than just buying a TYZ fork that already has brackets.

    That brake backing plate is actually a good upgrade for sticking with drums, mainly because the actuator lever is so much longer. The rest of the geometry, from what I've been able to find, is actually the same as the TY. Just in case anyone else stumbles on this thread in the future and just wants to upgrade the stock drum, all of the following bikes use that backing plate. The YZ250 and YZ490 had the option for a double leading shoe setup during this time, with aluminum actuator arms and a different backing plate stop that puts the arms at an awkward angle relative to the cable on a TY. The IT could also be had with a DLS setup, however it used steel actuator arms and fits the TY forks correctly. The aluminum arms can be added to the IT setup, but as far as I've found were never sold that way from the factory.

    YZ125 1977-1984
    YZ250 1976-1981
    YZ400 1976-1979
    IT175 1977-1983
    IT200 1984-1985
    IT250 1977-1982
    IT400 1977-1979
    IT425 1980
    TT250 1980-1982
    TT500 1979-1980
    #32
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  13. lineaway

    lineaway Long timer

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    All the early trials disc brakes pretty much sucked. The stock ty350 brakes were still better than most. Alot of riders learned there nose wheelie skills on the ty350. I never saw anyone converting to a double leading drum backing plate. So has anybody done this?
    #33
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  14. lineaway

    lineaway Long timer

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    Lots of good information for a Dinosaur of a bike nobody wants anymore.:dunno
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  15. gearheadE30

    gearheadE30 Long timer

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    Yes to the external arm plate that Ustakood posted. Maybe to the DLS plate - I found one person who said they made it work (with the IT version of the plate), but no pictures or proof beyond hearsay. I stopped pursuing it once I started looking into disc brakes.

    I'm sure my drums are good enough to nose wheelie - I've seen others do it on my bike. My technique for that particular maneuver is sadly lacking - I'm only marginally more successful on a modern bike. In a section, though, one of the biggest differences I notice between a modern bike and my TY is that I don't have to think about the brake on the modern bike. Gotta plan ahead on the TY, and that's the real driver here. The more natural the bike feels to me, the better and more consistently I will be able to ride it. Plus, these projects and the associated research through the dark corners of history are enjoyable, for some reason. :beer

    Be that as it may, I get a kick out of this particular dinosaur. Maybe someone like me down the road and in the same boat will come along and happen to be looking for that info. I hate it when I'm searching for something and I find a thread where someone was figuring it all out....and then just never came back and posted the critical concluding piece of information, so I try not to let that happen in my own threads.
    #35
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  16. lineaway

    lineaway Long timer

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    Ha! Ha! I am actually having one delivered at our vintage event. I have not seen this bike in 30 years. But is supposed to be a good one. I always loved the TY mono.
    #36
  17. motobene

    motobene Motoing for 46 years

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    Some lateral float is needed in disc brakes. In the past on Euro trials bikes it was assumed more was needed than was in fact needed, so even with symmetry of pucks either side of the disc, the disc was floated, making for more clatter, loose feel rocking back and forth, and increasing high frequency squeal.

    I have early 2000s AJP wheels and brakes on the Fantic. These had fixed parts on the rear and a floating disc on the front.

    All the moderns now sport rotors fixed hard to the hub and fix the calipers fixed hard to the fork leg and swing arm. Rear AND front. This is the simplest and best arrangement, and it works great. It requires good process control in machining accuracy, however.

    My '16 Sherco had a tiny bit of lateral run-out on the rear hub, requiring me to Emery paper the disc more frequently than I like to stop a chirp noise every rotation. My '17s are all good on that score.
    #37
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  18. gearheadE30

    gearheadE30 Long timer

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    There's enough meat on that YZ rotor that I could pretty easily convert it to a floating rotor using mid-201X Sherco rotor slide pins if for some reason my fabrication doesn't live up to expectations, or if it's needed to really make the system work right. I've now tried almost all of the calipers I have lying around - none of them clear the spokes on the wheel. So I'm still in the process of figuring that out before doing anything else.

    The closest I got was a Wilwood PS1 caliper, but still no luck. And it's still physically a very large caliper.

    [​IMG]
    [​IMG]


    I got kind of frustrated, so I ended up making a case saver to replace the bent up and rusty leaf-catcher that the factory installed.

    [​IMG]


    EDIT: I know, I know, I need to wash the bike. Hard to get the motivation up with all the nasty weather.
    #38
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  19. lineaway

    lineaway Long timer

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    Got my Ty running today FYI 1984 and 1985 IT 200 front wheel is the TY350 hub with the outside longer arm. I ordered one off ebay today.
    #39
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  20. Brewtus

    Brewtus Buffoonery, Inc.

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    You want your Long Ride seat back? :lol3
    #40