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another guy with locked front brakes

Discussion in 'XJ Technical Chat' started by eric.jones, Aug 22, 2008.

  1. eric.jones

    eric.jones New Member

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    My front brakes tighetend up on me today driving down the freeway at lunch time. I'm doing like 65 and I notice she doen't want to hold speed. I'm near an exit so I bail off. Thinking somethings going on the the motor but it seems to be running strong. Then I notice smoke coming from the frontend. It never completely locked up. I was about 7 miles from home. I took out my tool bag, opened the bleeder valve it squirted fluid and it loosened right up. I was able to ride it home using the rear brake only. The front disc was nice and cool by the time I got home, though it has turned a little gold/bronze color. I rebuilt the master cylinder and caliper a couple weeks ago, also replaced the brake hoses, pads and fluid obviously.
    XJ650J single disc, pretty simple.

    How tight is the caliper piston suppose to be with the new seal ?
    without the seal it dropped right in, was nice an loose, with the seal I could not push it in by hand even before I hooked it up and put fluid in it, should it be that tight? I had to push it in with a piece of wood and a c-clamp.
    It's been working great since I got it running on tuesday and I've put a little over a hundred miles on it.
    Is there a good way of knowing the master cylinder is releasing pressure correctly?
     
  2. stereomind

    stereomind Active Member

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    There is a relief hole in the master cylinder. it looks like someone didn't drill it all the way. there's a TINY passage in the middle that can get clogged up easily. you'll have to use something like a welding tip cleaner or a strand of some very thin wire to clean it out.

    The caliper... Did you clean out the groove where the big o-ring goes? it has to be spotless... also, it helps to wet the outside of the piston with some fresh brake fluid before pressing it back in. you should be able to press it in by hand (well, maybe both hands).

    if you can make the brake pads release by loosening the bleeder valve, I'd say the problem is in the master cylinder.
     
  3. eric.jones

    eric.jones New Member

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    Thanks, I'll check that tonight, I think you may be correct. I probably should have spent some more time cleaning it like I did my carbs, I bought the cleaning wires from Chacal so I do have them. The MC was a mess, the fluid was all dry and gunky. After disassenbling it I squirted it in and out with brake cleaner. Maybe it was really plugged?
     
  4. chadwickm

    chadwickm Member

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    Yeap! The 'spoonge' hole is clogged! You should be able to spray cleaner thru the hole once it't free of debris.
     
  5. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    The cleaning wires in the carb cleaning wires set do NOT have a wire small enough to clean the port in the master cylinder body.............

    For that task, take a piece of 14 or 16 gauge stranded wire and "un-strand" it down to one or two strands, and use that to clean it out.

    It's truly tiny....smaller than any size passge on a carb!
     
  6. jswag5

    jswag5 Member

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    i dont know how many guys have access, but i keep a few of my old guitar strings around to clean up stuff like that, they work excellent.
     
  7. eric.jones

    eric.jones New Member

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    Are you guys telling me the hole in the picture is really suppose to go through into the plunger cylinder with a hair line hole.
    I sure doesnt seem like it goes through to me.
    Ive probed it with a wooden toothpick a strand of wire from a small piece of stranded copper wire, Ive used carb cleaner and brake cleaner on it and shot it with 150 lbs of compressed air!!!
     

    Attached Files:

  8. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    Yes, that's the one!
     
  9. RickCoMatic

    RickCoMatic Well-Known Member

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    I think the problem is with the Caliper; not the Master Cylinder.

    The two Channels where the Caliper Seals fit often "Shrink" due to a build-up of Brake Fluid, Brake Dust and Moisture forming a substance that builds-up behind the Seals and effectively shrinks the Circumference of an already close tolerance of the Seals to the Caliper Pistons.

    The Struggle you had to get the Caliper Piston fitted back into the Caliper Body most likely results from there being some of that foreigm matter in the Channels making the Seals fit "Out of Round"

    Too tight.
    Too tight to allow the Piston to retreat when Hydraulic Pressure to them is released.

    That foreign matter has to be scraped-off the surfaces of the Channels until the Channels are absolutely free of any trace.
    Once the Channels are returned to a perfectly free of any foreign matter state ... the Caliper Seals will fit in them -- Round; again.

    There should be no need for excessive pressure placed on the Caliper Pistons to replace them back into the Caliper Body outside of normal use of the C-clamp when Caliper Piston is pressed into a Caliper Body which has no build-up to cause the circumference of the Seals to be reduced.

    In other words.
    Scrape the crap out of the channels.
    Let the Seals be round.
    The Caliper won't bind.
     
  10. eric.jones

    eric.jones New Member

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    Okay, thanks guys.
    It took some effort but I got the little tiny hole clear, it was there, just as you said it would be.
    I guess I should take a look at the caliper now too, just to make sure the seal groove is spotless.
    I just hate to drain the whole system of brake fluid again, and have to re-bleed... that was a 3 hour job two weekends ago!
     
  11. RickCoMatic

    RickCoMatic Well-Known Member

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    It'll be worth it. The brakes up front are an important component to have working right.
    Now that you know what you are looking at, it shouldn't be too hard to revisit the front brakes.
    Getting creative with making a scraping tool to do the whole circumferences of those two Seal Grooves is key.
    Just remove the crap and leave behind a perfectly cleaned Sealing surface.
    Your brakes will function like new again.
     
  12. Robert

    Robert Active Member

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    We need to sticky this photo! This question pops up just about every other week.
     
  13. schmuckaholic

    schmuckaholic Well-Known Member

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    Sure caught my attention... I didn't know that itsy-bitsy hole was there. This will come in very handy indeed once my parts arrive.
     
  14. southpaw

    southpaw Member

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    so does that tiny little hole exist in the seca R master cylinder I am still having dragging problems also who has rebuild kits for the 81 seca r ????
     
  15. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    Yes, all XJ series master cylinder have that port!

    REBUILD KITS:

    Master Cylinder Rebuild Kits:

    mc1) OEM and aftermarket brake Master Cylinder Rebuild Kits contain all the operational parts you need to correctly rebuild your master cylinder: piston, piston seal, piston spring, piston rubber sealing boot, and retaining circlip. NOTE: the piston seal does not come pre-installed onto the piston, and at first glance, you may wonder "how the heck do you get that small seal opening over that large piston?". Well, lots of lube (brake fluid) and patience and a small, dull pry tool works wonders. Make sure that you install the seal with the flared seal "lip" facing towards the fluid outlet!

    NOTE: be sure you very carefully clean and inspect your used, original master cylinder for any damage and rebuildability. If the pressed-in steel piston bore is badly scarred or pitted-rusted, then it must be honed to a silky-smooth finish before installing new components. If pits or scratches are too deep to be removed, it is best to obtain a replacement master cylinder (new or used) rather than to try to rebuild a damaged original. Remember, your life literally depends on your brakes....not always in day-to-day riding, but when it counts the most, in an emergency situation; and those always happen in the blink of an eye, and without prior warning.....

    Master cylinder rebuild kits contain the piston, the piston seal, the spring, the plunger end seal, the plunger dust boot and its retaining circlip.



    HCP3030 OEM front Master Cylinder REBUILD KIT, for all XJ550 models.
    $ 54.00

    HCP1694 Aftermarket front Master Cylinder REBUILD KIT, for all XJ550 models.
    $ 32.00
     
  16. southpaw

    southpaw Member

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    Chacal I knew i should have just called you but i didnt remember you have them. Ever thought about putting out a catalog????
     
  17. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    One of these days!
     
  18. RickCoMatic

    RickCoMatic Well-Known Member

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    Hopefully very soon!
    I pity the poor souls who still suffer with "Dial-Up!"

    You really ought to have your own site build and just post the appropriate link.
     
  19. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    I know..............!
     
  20. schmuckaholic

    schmuckaholic Well-Known Member

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    The issue has been discussed before. Long story short, it's not going to happen for a while -- the man's busy.

    The good news is, my itsy-bitsy teeny-weeny little polka-dot relief hole opened up with little trouble on my master cylinder. Had some small gauge wire laying around, shaved off the insulation, and it went right through.

    On the other hand, you do NOT want to know what the grooves for the caliper piston seals looked like.
     

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