Brake Master Cylinder Lube??

Discussion in 'Other Service and Maintenance' started by screwylouie, Feb 6, 2013.

  1. screwylouie

    screwylouie Active Member

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    Has anyone had any trouble with what seems like a weak spring in the front brake master cylinder? I noticed one night that my brake light was staying bright like I was still touching the lever but I was not. Upon closer inspection I saw that the master cylinder piston was taking a very long time to push the lever back far enough to turn off the brake light switch. The brakes otherwise work great and yes, the relief ports in the master cylinder are not blocked. I took the bike back to the dealer and in detail told him where the problem was. It was also very obvious when I shone a light at the master cylinder piston cap that it was moving VERY slowly. The service manager didn't listen to a word I said and must have been daydreaming when I showed him the piston cap because when I picked the bike up, they merely lubed the brake lever pivot. It was having the same problem on the way home. So, I bought the repair kit and replaced all of the internal parts myself, bled the brakes, and voila! Problem solved!.............. For a while:newsmile08:. I now think that the bore depth in the master cylinder was machined a bit too deep, bore diameter is slightly too small, or both. I checked the free length of 3 different springs and they all are within a few thousandths of an inch in length. This weekend I am going to install a spacer that I made at work out of stainless steel to replace the original. My new one is .125 thicker and so will provide .125 more return pressure(the pressure it takes to compress the spring .125) to my brake lever. I'm betting it will work like a charm but now for my question (finally right?). I don't want to buy another rebuild kit just to get the little packet of "lube" that supposedly must be used. Any one see this stuff? Looks like liquid graphite or something and it immediately turns the new brake fluid dirty looking. The instructions say to coat all rubber piston components and piston bore with this crap. Didn't do much to solve my problem last time so I'd like to skip it and save the cost of a kit just to get the mystery lube. Of course, they don't sell the mystery lube by itself. OPINIONS??:newsmile093:
     
  2. Jack Klarich

    Jack Klarich Expert Member

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    Is this an 012 model? It should be under warranty, I had a similar problem with an 07 model seems H D has had problems with some of the master cylinders, mine was replaced under warranty, thee tech originally wanted to just stretch the return spring in the cylinder imagine that
     
  3. Hoople

    Hoople Account Removed

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    I don't have it in front of me, but I remember seeing a part number on the packet for that lube. I had the same exact problem with my 2009. Piston sticking, brake light stays on, same as yours. A rebuild kit fixed up the problem quickly. Found a bunch of black goo inside bore. I wrote down the part number and will get to you with it.
     
  4. Jack Klarich

    Jack Klarich Expert Member

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    When I rebuild Hydraulic cylinders I use Napa Silglide on the rubber and pistons for assembly lube. The pivot on the lever you could use some moly lube, white lithium grease or some anti sieze
     
  5. screwylouie

    screwylouie Active Member

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    Thanks for the reply Hoople!

    The rebuild kit that I installed myself worked great too but only for a few weeks and it started sticking again. My bike is under warranty but the dealer service manager obviously doesn't know what he's doing or just doesn't care. My question is, do you think it's really necessary to use a lube at all? Especially since it didn't work long term anyways.
     
  6. screwylouie

    screwylouie Active Member

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    Thanks for the reply Jack!

    I think they have the right IDEA about the spring but stretching it, I think, is a bad idea. I think the root cause of this "problem" is that the spring is very close to its free length when installed and the only thing holding the assembly in the bore is the "wiper" on the piston "cap". If the spring length is too long it will pop the piston out before the lever can be put in place to hold it all together. I guess, bottom line is IMO, too little spring pressure, hence my 1/8 inch spacer idea.

    What I really want to know is, do you think a lube is necessary at all? Doesn't the brake fluid provide enough lubrication for the piston bore all by itself and wouldn't it dilute and wash away the additional "lube" anyways??
     
  7. Hoople

    Hoople Account Removed

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    It only lasted a couple of weeks.. . wow, that's not good.
    The part number (20-12425) that was on the lube packet doesn't convert to anything useful in the HD parts system. It must be some kind of internal vendor part number.

    I did not like what I saw when I took the front master cylinder apart. It looked like dried out factory assembly lube. Years ago a German company called ATE use to sell master cylinder assembly lube here in the U.S. that worked Great. When I rebuilt my master cylinder, I wanted to use that lube but could not find it anywhere. For some reason, it is no longer sold in the U.S.

    Since I couldn't find the ATE lube, I settled on WilWood # 290-11087 assembly lube.
    Wilwood High-Performance Disc Brakes - Brake Fluid & Assembly Lube

    In the back of my mind, I do not 100% accept mixing anything that may come in contact with brake fluid,, but I also feel that some type of assembly lube must be used. I bought the Wilwood lube from Summit Racing. Even though the bottle says it is synthetic, it is compatible with Dot 3 & Dot 4 Fluids. Go figure.

    Jack has a lot more experience on brakes than I will ever have. That lube may be the ticket.
    I didn't know of that lube until now. But so far the Wilwood seems to be doing the job and that was a good year and a half ago. The brake lever still snaps back like it should. I have a couple of unused HD lube packets if you need/want them.
     

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  8. screwylouie

    screwylouie Active Member

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    Hoople, you are the best, man!! I saw the same thing when I took mine apart, the piston bore had this black stuff on it, I thought I was looking at a really bad surface finish from the machining or something. I cleaned it up with 4000 grit emery cloth until it was spotless, reassembled with the repair kit and factory lube, and it worked great but not for long. I think this factory lube is drying up and binding up the seals in the bore. I'm gonna try the WilWood stuff, either that or skip the lube altogether. I'll let you know how it works out! Thanks again brother for the advice and kind offer for the lube packets!
     
  9. Jack Klarich

    Jack Klarich Expert Member

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    The initial lube is a must or your rubber parts would roll over and leak. The brake fluid will over time take over as the lube. I would be extra careful honing or sanding any anodized aluminum parts, this will remove the factory protective coating, IMO you should have the dealer replace the master cylinder at their expense, they should have a new and improved 1 now as they have had a lot of problems with their original vendor. The lubes Hoople has posted are good choices as well as the Napa silglide I posted and is readily available
     
  10. screwylouie

    screwylouie Active Member

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    Thanks again Jack!

    Anodized? Huh, must be a clear anodize finish then. I'll be extra careful but that 4000 grit stuff is barely abrasive enough to clean off the black junk from the factory lube. I think my brand of toilet paper is more abrasive than this stuff!

    I'd love to have the dealer replace the master cylinder but i'm not very impressed at all with their service department. If it comes down to it, I'll replace the whole master cylinder on my own dime.