R90S ATE caliper rebuild

Discussion in 'Airheads' started by craydds, Nov 12, 2011.

  1. craydds

    craydds Long timer

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    Putting it back together with new parts. Stock "bumpers" in bottom caps. Tossed the anti-dive springs.
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    One of these years I might get my MC onto the bike.
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    #61
  2. supershaft

    supershaft because I can

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    Those bars are too narrow on so many levels! I wouldn't run a junction. Why have three lines when two will do. They make a line fitting so that the line goes straight into the MC versus using a banjo. That is always an option. At least when you make your own lines.
    #62
  3. craydds

    craydds Long timer

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    I've seen that connection. Any advantage of fitting going into the MC vs. a banjo? Seems like a banjo might be easier to remove and replace (???).
    #63
  4. supershaft

    supershaft because I can

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    They are suppose to let the line spin. The only advantage is space if you need it. They are just like fitting on the other end of many lines but they seal with a crush washer versus an interference fit.
    #64
  5. Hawk Medicine

    Hawk Medicine Coyote's Brother

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    Just in case you're interested:

    Here are a couple of photos of my Bar mounted MC installation.

    As you can see, I used a stock BMW under-tank splitter. The lines I ordered came straight from Spiegler. They're great suppliers and all I had to do was to describe what I was doing and they sent me the right stuff first time.

    Is the splitter installation better than using a double banjo fitting? IMO, no. The two approaches are interchangeable and which one you use will be a completely personal decision.

    Both systems work very well but when I was building my bike, my intent was to build my personal version of "Pre-R90S" R100S, so I pretty much duplicated the stock BMW system with the brake switch in the handgrip. The double banjo set-up just looks too non-stock for my tastes and the splitter allows the brake hoses to follow the same routes as the stock R90S/r100S installations. SShaft likes the double banjo set-up and that OK but I've never had a leak or any other problem with my BMW brake system. It's all plug and play and the performance is exactly the same but theres something to be said for keeping the visuals as close to stock as possible.

    Lastly... The handle bar MC will fit under the "S" fairing if you're using BMW "S" bars but I doubt that you'll be able to run anything higher. The K75S bars that are so nice on the RS might work but I haven't tried that trick. If they did work, I think we'd know about it by now and I like my "real deal" "S" bars just fine.


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    #65
  6. craydds

    craydds Long timer

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    That looks good. Nice upper triple clamp, too. I think I've read that a double banjo with two lines is a tight fit. Yours looks like there is plenty of room.
    #66
  7. surtees

    surtees Adventurer

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    Almost done with my own conversion so thought I would show a few pics - also a question or two of course.
    took off my single 38 caliper and replaced with lower sliders and two 40mm calipers from a 79 R100R that I rebuilt.
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    I went with a new 13 mm handle bar MC so my switches and double throttle cables would all fit.

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    As you can see I didn't have room for the double banjo so I did similar to mymindsok using the under tank distributor (used from Repsycle). Since it was there I just used the brake switch from my old MC and had new SS lines made all around.
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    Overall went together fairly easy in large part due to the outstanding info in olds cool (and snowbum). However I have run into problems with the bleeding. I used speedbleeders on the calipers and after quite a bit of lever pumping was able to push brake fluid without bubbles through first the left and then the right caliper. I did notice that a few minutes into the process some dark liquid swirled into the reservoir from the master cylinder but only for bit and then no more - anyone know what this might be? I thought maybe it was just residue from a new rubber washer or gasket in the MC and probably no big deal or at least I hope so.
    Anyway main problem is after this standard bleeding there was no resistance on the brake lever - the pistons moved in the calipers against the rotor but no real pressure.

    So I tried all the various inmate tricks (tapping to chase bubbles, pulling fluid with a syringe, lifting the calipers up, etc) but not much luck. Finally put the bike on a left lean to increase the down angle of the MC banjo, released the distributor and put it to one side and angled up so the line would go continuously up to the MC and the brake switch would be the lowest point to free any trapped air in the distributor. And left it overnight with the lever strapped against the handle. After the first night a bit better but no magic as I had heard about. Next day had a few beers while I did more tapping (and cursing) and left it again overnight with the lever strapped. Today there is pretty good pressure although I can still pull the lever all the way back to the grip if I really try. I hope this evenings Jamison toast to the old R90 and one more night with the lever strapped will do it - I will let you all know tomorrow or yell for help.
    #67
  8. craydds

    craydds Long timer

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    Nice job, surtees! Looks great. Sounds like the bleeding process is a struggle. That is one reason I want to go with a simple brake-line setup - no under tank splitter. My plan is to go with one line from the MC, straight down to the right caliper, then a second line from the right caliper over the fender brace to the left caliper, using speed bleeders, too. Two lines, four connections, fewer spots to trap air, easier to bleed I HOPE.
    #68
  9. Xcuvator

    Xcuvator Justa Venturer

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    One of the things that isn't mentioned much is the position of the pistons in ther bores. If they are fully retracted there isn't enough stroke in the MC to push them out enough to contact the rotors. When you pump the MC, what travel you get out of the pistons is reversed each stroke by the dust seals pulling them back.. This problem is made a little worse because of the smaller than stock MC bore. I think that by tying the brake lever overnight, the dust seals relax (slip) a bit and not retract the pistons as far when the brake is released, leaving them in position to push farther on the next stroke,

    When I assemble calipers, I leave the pistons extended so that when the pads are in, the assembly fits over the rotor with little clearance and find bleeding goes much easier.
    A way to get more MC piston travel when working with a stock under tank MC, is to diconnect the linkage and push the MC piston with a big phillips screwdriver when bleeding. This added stroke is often enough to push the caliper pistons far enough to slip into a new position on the dust seals and the seals can't retact them as far.
    #69
  10. craydds

    craydds Long timer

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    Interesting, makes sense. Let's say we're doing the bench bleeding, calipers removed from the forks and elevated above the MC. How do we help the pistons to adequately extrude?
    #70
  11. Xcuvator

    Xcuvator Justa Venturer

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    I'm not sure I have done this on a Airhead, but I have held the piston or pistons in between strokes. All you want to do is keep the dust seal from pulling it back.
    #71
  12. surtees

    surtees Adventurer

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    Interesting thought on the piston - not sure what it means but checked the gap between the rotor and the outside (movable) brake shoe and it was between .006-.008" at rest. Have not seen that value anywhere to compare to so does it seem correct? May check it again after some riding to see if it changes with feel of the brake.

    As to my saga, as Scotty would say 'Captain, there be brakes here!' After another night of lever engaged rest this AM the pressure felt pretty good - progressively more pressure as lever was pulled with max about 1/2 inch from grip. Went for a ride and what a world of difference from before the makeover - front brake grips with authority and the bike stops. Beautiful day so rode the coast highway a bit and one of my favorite canyons to test the brakes on down hill twisties. All was good - I am another believer in the dual ATE, handlebar MC combo.

    A few comments in case someone is planning this; I might consider the 14mm over the 13mm MC to give a bit more solid feel and less possibility of pulling the lever all the way to the grip, although the 13mm seems to work just fine so far,
    Also really make sure the bleeder valve seats on the old calipers are really smooth. They looked clean and I wire brushed them but still I needed to tighten the speedbleeders more that I would normally do to stop a small amount of fluid from oozing out with repeated braking. Not a big deal and this may be in part due to the speedbleeder shape but when they are apart I would recommend doing more surface prep or even honing to get it really smooth.

    Just a few pics (still sans the S fairing. - sorry for those caught in a bad winter (like my friends in Birmingham) and not to gloat - but 70 deg in Jan and empty canyons = motorcycle heaven.
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    #72
  13. craydds

    craydds Long timer

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    Great looking bike, and nice photography. Sounds like your brakes are working well. What brake pads are you using? I have the 14 mm MC, 38 mm ATE's, and EBC pads, not yet on my bike so I am jealous of your ride, too.
    #73
  14. craydds

    craydds Long timer

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    Killing time, waiting on other parts, can't finish my brakes yet. So I removed the tired old Konis. (sorry about the fuzzy picture)
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    Got some new YSS shocks from Tom Cutter, http://rubberchickenracinggarage.com/ .
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    Shocks installed.
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    #74
  15. supershaft

    supershaft because I can

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    They look short in the photos?
    #75
  16. surtees

    surtees Adventurer

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    I like the looks of those shocks - how did you know you needed new ones? I used EBC FA22 organic pads - I have 40mm calipers and the 13 mm MC - So if my calculations are correct I have an MC/piston ration of about 14. 7 while your system would be 18.9. I was aiming for around 14 but it is a pretty long travel. When yours is together it will be interesting to compare notes.
    #76
  17. craydds

    craydds Long timer

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    I measured them against the Konis, they are the same. Guess I could measure the old stock Boge's and compare, I'll do that this afternoon. I ordered through Tom Cutter, gave him all the required info (rider wt., passenger wt., etc.) and he had them set up for my bike.
    #77
  18. craydds

    craydds Long timer

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    One of the old Konis was leaking. Looked into rebuilding the Konis, but Tom Cutter had a better idea. He said the old Koni is an outdated technology and the new YSS shock is better.
    #78
  19. craydds

    craydds Long timer

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    How does one calculate the leverage? Seems like it is a simple ratio of (area of caliper piston)(2*) / (area of MC piston). I don't know how to type out arithmetic formulas on my keyboard --- pi x r-squared = A.
    *for two calipers
    #79
  20. craydds

    craydds Long timer

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    I measured the stock Boges, the Konis, and the YSS's, they are the same length.
    #80