Making A Right Fork Leg For Dual ATEs

Discussion in 'Airheads' started by disston, Nov 3, 2011.

  1. disston

    disston ShadeTreeExpert

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    I have been rebuilding the front forks on my R90/6 the last few days. Working with all these things I look at the fork lower legs and it's plain the the right leg for a single disc is not easy to convert to a dual disk set up. But If one had two left lowers one of them could be converted for use on the right leg. And it doesn't look hard to do at all.

    The axle hole in the left lower is smaller so it can be drilled to fit the right side. There is the same amount of beef to the area of the fork lower of the two legs. In fact they appear to have started life as the same rough casting. The axle hole needs to be larger on the right leg.

    The pads for the caliper appear to be cast with a wide seat area. This is machined flat and the outside edge is cut off. When the left fork lower is put on the right side the cut off portion will now be on the inside. Merely cut the pad area on what will be the outside when placed on the right leg and weld this small piece to the other side of the pad. It will have to be machined flat again. Maybe some filling because of lost metal in cutting but not a big deal.

    That is it. Drill one hole larger and change the caliper pad, cut ,weld, machine flat.

    Is this not as easy to do as I think? I am not a machinist so it is entirely possible that something I don't see here is going to cost too much money or there is some reason why this just won't work?

    Charlie
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  2. crazydrummerdude

    crazydrummerdude Wacky Bongo Boy

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    If time is money, and money is money, most people will tell you that it'll be cheaper/easier to just buy the right parts from the get-go.

    I would like to see your progress if you do decide to go through with this, though.
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  3. wirewrkr

    wirewrkr the thread-killer

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    It's been done, I think it's a great solution to a very expensive dilemma.
    Let me just put this "wrinkle" in there....
    Don't ask your machinist to "drill" out the axle hole, (he'll cringe and turn funny colors) ask him to "bore or ream" to the correct size.
    There once was an old guy in Gaithersburg that had done some custom triple clamp work for me once, not far from the airpark, I can't remember his name, but the work was good and the price was right.
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  4. disston

    disston ShadeTreeExpert

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    I appreciate the input. I'm rebuilding the front forks of my R90. It was while I was comparing the two styles of fork lowers that I saw this was possible. It comes up all the time but I never do see this solution suggested. I have the much needed right side fork lower piece but I can't use dual brakes till I fix the hydraulics. So I guess I'll have an empty fork lower on the right side till I do that.

    I know that machine practices and operations are not what amateurs like myself think they are. Boring or reaming the hole would be relatively easy I think. But creating the flat pad for the caliper seems a bit harder. Still I'm glad it can be done and some day when the price of usable right lowers is exhausted we may see it happening more often.

    Charlie
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  5. wirewrkr

    wirewrkr the thread-killer

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    i should check with my favorite welding AND machining guru in SanJose and see if he wants to do some of these.
    He's done it already, (iirc) and is WELL versed in BMW motorcycle modifications.
    I should check to see how many i have. It might be "cheaper by the dozen" so to speak.
    #5
  6. Rob Farmer

    Rob Farmer Long timer

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    Are the correct ones really that hard to come by in the states? I've got two sitting under my bench. nobody wants them over here.

    Just have a look on euro ebay
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  7. wirewrkr

    wirewrkr the thread-killer

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    The price is astronomical when you find one over here.
    I am guilty of charging a premium when I sell them, but the market is the market, (I never twist anyones arm and force them to buy)
    they don't last long when I advertise a set or just one.
    #7
  8. PaulRS

    PaulRS Dutch fool

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    Why bother upgrading a marginal brake by adding another one?

    I'd get me a set of Brembo sliders, calipers, disks, or whatever comes along, dump the cable operated MC and fit a bar mounted one.
    And if it isn't a straight fit, you can always mix/match/machine to make it fit.

    BMW is like Lego for big boys. :deal

    Paul.
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  9. disston

    disston ShadeTreeExpert

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    I like the Lego analogy. But there is some difficulty with using the Brembo lowers. Then you have to use the later style dampers. Or something like that. I don't know. But usually when mixing parts you have to make more of a mixture than you wanted. I also like the idea of using a K bike front end on Airheads. I almost did that because I owned a K bike and I wanted to tear it up but I sold it instead. I hear you can even put a GSXR front end on an Airhead!

    I get enough braking out of a single ATE. I don't tail gate or charge into turns I don't know. I'm really a prettey sedate rider any more. So I guess it's just a matter of style or looks. It's very popular in the States to add a second caliper. Even if the ATE is marginal two of them must be better than one?

    I'm not kidding. I subscribe to a couple of motorcycle lists. Just a few. I see requests for the right fork leg about 4 times a year. On Ebay the whole front end goes for at least $250, usually higher. I think the last one I tracked a couple of weeks ago was almost $500. The right leg only is the only part needed if your single brakes, front end are good. Add another caliper, a MC or a line splitter. There are all kinds of theories about how to do this the proper way, a better way, a way that works.

    So yeah. Don't throw away those extra left ATE legs. They can be made into right legs. Might not be the right time but I'll bet it's not far off. Doing a dozen or more is a good idea. I say make all the extras you can find into right legs. The buyer would have the left and he would get the other parts also.

    WW, I met a guy in Gaithersburg that had a shop selling mostly choppers. Some was resales but I think he was building them also. Not the fancy unridable type but the workingman faster Pan Heads and Knuckles. Is this the machinist you know? Forget his name. It was around Airpark somewhere.

    Charlie

    BTW, what machine, attachment, procedure is needed for building the flat area for the caliper? Is this the difficult part of the conversion?
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  10. Max Headroom

    Max Headroom lost in the '70s

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    ATE r/h fork legs are getting harder to find in my little corner of the globe too Charlie, so I took a similar approach.

    I took a l/h fork leg to a mate and got him to cut the tang off the r/h side of the caliper flange and weld it onto the l/h side, thereby duplicating the dimensions, function and appearance of the stock r/h fork leg. I simply dressed the welds with a Dremel and it's now indistinguishable from a genuine item IMHO.

    I haven't drilled the axle hole yet, and it's the bit I'm looking forward to least. I'd been thinking about making a jig to support the leg, to ensure correct (and repeatable) alignment, and have already begun making one. The urgency has now gone from completing this exercise though, as the owner of the bike which required it has since decided to take a different path.
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  11. disston

    disston ShadeTreeExpert

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    WOW! A Dremel Tool. I love low tech machining. I imagine the guys who built the first internal combustion engines making parts with a file by hand.

    I do realize the hole has to be round.A drill will probably not make a truly round hole so I don't know how to do this part either. It also has to be plumb? I think the edge is square so maybe just clamping it on a flat surface will square it?

    So square, round, straight, right size. But to what % .

    I have at least one extra left leg. I think I'll send it to WW sometime next spring when I finish using it. Unless I try to remanufacture it with a hammer and chisel. :D
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  12. Rob Farmer

    Rob Farmer Long timer

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  13. Voltaire

    Voltaire Bored Of The Rings

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    Here is a fork leg that has been done. Its yet to be tested as the bike is wip.
    My mate who is a plastics engineer, cut of the tangs and welded them back on the other side. I suspect BMW only make one type of leg and cut the unused side off.
    Have also swapped out the pre 81 internals for later 'Brembo" leg ones.Since then have decided to go for Racetech Emulators so could have used the original internals as you just drill the damper rod holes out.
    The later internals drop in and you only have to drill out the base fitting.
    As for the brakes themselves, going to use a Ducati 'coffin lid' 13 mm master cylinder and braided hoses. Should make the ATEs work quite well. I want to retain the early disc look for the bike which is only going to be used on the track.
    I looked at using the Brembos but they don't clear the spokes of the wheel as its the wide hub not the narrow one used. The narrow one looks to be a wide one machined down as the hubs are in two halfs.
    Hope the pic helps. You can cut and fab up the tang yourself, just need it welded. I could spend a bit more time on it and you'd never know...

    Attached Files:

    #13
  14. Boxer Metal

    Boxer Metal Mad Scientist

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    I know this is an old post. If you are running a spoke wheel it is nothing like Lego's. I am curious to know if you have finished your conversion. I just did one and I'm starting another(spoke wheels and Brembo calipers).
    #14
  15. thewhistler63

    thewhistler63 Adventurer

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  16. Foot dragger

    Foot dragger singletracker

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    Yah,but putting real brakes that stop pretty hard on forks barely strong enough for what they already have could be an issue with flex. I do agree the ATE's are kinda goofy and weak though.
    It also seems like welding on the lower fork area could lead to warpage issues,I guess an machinist/welder would contend with this.
    #16
  17. Stan_R80/7

    Stan_R80/7 Beastly Gnarly

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    I am considering (i.e. in the process) of doing this conversion. My reasons are: cost and availability - $400 for a Brembo front set of lowers is a bit high and left lowers are easy to find; better brakes - I can live with decent (still, not great) ATE dual brakes; it's period correct - not that the bike has any collector value, but it looks right; it is not permanent - the original right lower can be reinstalled. Drilling and reaming a new hole is no problem and cutting off the tang to weld on the other side may just be the excuse I need to get a spool gun. I think the tang has no function - other than looks.

    I have another brake line and rotor with pads, so another ATE caliper, a piece of M10x1 steel brake line, and a brass brake line tee are needed. I got a set of /7 lower forks for $80.00 shipped and can live with losing that amount if this doesn't work out. I'll probably swap the ATE caliper to the right side to test the modified fork and rotor operation before finishing the conversion.
    #17
  18. disston

    disston ShadeTreeExpert

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    You need five (5) longer bolts that hold the rotors on.
    #18
  19. Voltaire

    Voltaire Bored Of The Rings

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    After racing my conversion for a year I'm happy with it, can't ever see myself converting to Brembos.Although ATE's in their original form combined with age are not flash, once you go to 13mm m/c, stainless lines and CAST IRON discs they work a treat.
    #19
  20. Kai Ju

    Kai Ju Long timer

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    +1

    I got lucky on my conversion, a gent had an NOS left leg for sale that I was going to do the conversion on, but when it arrived in the mail it turned out to be a right side leg........
    I modified my 13mm under tank M/C to run a double banjo line out of the original hole and I'm pretty happy with these 37 year old brakes.
    #20