Brake Distribution Block and Switch Cleaning

Discussion in 'General IH Tech' started by MyScout800, Feb 27, 2008.


  1. MyScout800

    MyScout800 Binder Driver

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    Is there a way to actually clean one of the early blocks from an 800 (or similar) which only has drum brakes. I beleive this to be only a brass junction block, without proportioning, but with the integrated brake light switch. The problem is the Brake Light Switch no longer operates (frozen in the center, I think) and I would like to still use it. Is a thorough cleaning even an option or would I just make matters worse?
     
  2. Brian K.

    Brian K. Binder Driver

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    YES! Yes! Yes!

    I just did this project on both my '70 1100 truck and '67 Mustang this past weekend!

    As soon as I can get to the other computer, I'll post the pictures I took. It's an easy and worthwhile job.

    Brian
     
  3. kingben01

    kingben01 Farmall Cub

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    If you have a tandem mastyer cylinder (2 chambers, 2 hoses) them that block contains a metering valve and a pressure differential valve (brake light switch). the only way I know to test one is to remove one brake line and hit the brakes. You see, in order to keep the brake light ungrounded, it requires pressure from both sides. When you lose pressure on one side, the spool shifts and grounds the switch and the light comes on.

    If you have a single chamber master cylinder like mine (1 chamber and 1 line), then it's just a junction tee. the problem with this is that if you blow a line, you got no brakes at all. It's like the pedal's not there.....
     
  4. MyScout800

    MyScout800 Binder Driver

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    Thanks guys!

    This is actually for my 69 Mustang with drum/drum brakes, but I know this subject applies to the 800 dual reservoir with brake warning light switch as well. As I understand it, there is no metering within the block, but only a shuttle valve of some kind that produces the safety and warning light aspects of the gizmo. Mine has failed to "light" in over twenty years with numerous brake changes and fluid replacements leading me to believe it probaly is frozen although I suppose it could be just an electrical switch failure. (yes I have tested the bulb :D) In any case, I am planning a Master Cylinder swap in a few short weeks and figured I would delve into the distribution block/switch to see if I can clean and repair at the same time.

    Cant wait to see those photos and lessons learned Brian... I presume there are lessons learned. At least in my case, there are always quite a few and sometimes they are real doozies (sp?) :whistling:
     
  5. Brian K.

    Brian K. Binder Driver

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    Here you go!

    The International Block will be different than the Mustang Block. Interesting coincidence that I did both of them last weekend!

    The International Block:

    Easiest of the two, here's why: Basically you just remove each endcap and push the pistons, springs, and caps out. Simple. You are going to very carefully clean everything, including the bore of the block. (Ensure nothing is scored.) Mine was filthy and totally gunked up and it would not move position, thus the switch could never reset.

    The copper washers and "O-Rings" must be replaced. The easiest way I've found is a Harbor Freight O-Ring set and a copper washer set. They are about $7 each and have all washers and O-Rings neatly organized by size. There's enough in each kit to last a lifetime! If you must choose between O-Rings to find a match, (I/E, you aren't confident the match is absolutely exact) always go with the SMALLER of the two choices. The slightly larger will not seal well. The smaller O-Ring will expand slightly in the bore giving a good seal.

    The Mustang Block:


    Much more of a pain as there is only access on one side of the block. If your piston is a gunked and frozen as mine, it isn't going anywhere easily. If you can't draw the piston out of the bore with very small needlenose pliers, here's the solution: The design of the Mustang block is a single piston with an indentation in the center for the switch pin. It has a brass protuberance you can see when you take the end cap off. Drill a very small hole in the brass, very carefully, dead center. Using the smallest Easy-out you have, carefully work it into the hole. Begin to spin the piston carefully as you apply a "pull" to it, it will come out. (Another hint: Soak the thing in penetrating oil overnight the evening before, it helps.)

    Both are back on their respective vehicles and working great!

    Brian
     

    Attached Files:

  6. MyScout800

    MyScout800 Binder Driver

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    Sweet!! Nice succinct and informative write up. Sounds I will be tackling mine with a lot more confidence thanks to you. :)
     
  7. Greg R

    Greg R Dreams of Cub Cadets

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    Great write up Brian, thanks.

    As a note on maintenance, you're supposed to pull the switch(electrical) when pressure bleeding the brakes because the spool shifts. Then when finished, reapply the brakes with firm pressure to re-center the spool before re-installing the switch. This is an item often over-looked when bleeding the system. I use a vacuum bleeder, so that part doesn't apply. If you apply brakes with out re-centering the spool, and the switch is in, the little plastic tip that trips the switch can break off.
     
  8. usugarbage

    usugarbage Farmall Cub

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    Good thread. It took a little persuasion, but I got mine apart last night and gave it a thorough cleaning. I'm pretty sure it had never been apart in its life and I thought I'd note the sizes of the bits I replaced.

    o-rings: 3/16 ID, 5/16 OD
    copper washers: 33/64 ID, 45/64 OD

    Also, CTS 2470Q p7 has some decent pics of the pressure differential (or combination) valve. It even shows how the warning light switch closes the circuit to trip the dreaded break light warning.
     

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