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Tech Week May 2013, Dual Master Cylinder Conversion

Discussion in 'The Hokey Ass Message Board' started by bri0057, May 8, 2013.

  1. bri0057
    Joined: Dec 2, 2008
    Posts: 48

    bri0057
    Member

    [FONT=&quot]One thing that Minnesota winters are good for is working out in your garage with the radio blasting and the heater on high. With that said, this years winter project was a full front suspension rebuild and disk brake upgrade. Along with that came all new brake components front to back with a dual master cylinder in between.

    This write up is for 1949 to 1954 Chevy sedans but can easily be adapted just about any vehicle with an under floor master cylinder.

    Now there are plenty of kits out there and lots of posts about how people have built new master cylinder brackets but I decided that tech write up was in order. Why buy something when you can make it for twice the price right? Its all about having fun in the garage.

    Lets get started...

    Materials Needed:
    3/16 Sheet Steel
    1 ID round tube
    1 Square Tube
    3/8 Rod End (McMaster Carr 60645K341)
    ¾ID 1OD Brass Bushings (2) (McMaster Carr 6391K269)
    3/8x1.5 bolt (2)
    3/8x2 bolt
    3/8x4 bolt
    3/8 Castle nut
    3/8 washer (4)
    3/8 lock washer (2)
    3/8 nut (4)
    Cotter pin
    ¼-20 Grease zerk
    ¼x3/4 bolt (2)
    ¼ lock washer (2)
    ¼ nuts (3)
    Master Cylinder (Napa M1922, 1969 Corvette)

    Tools Needed:
    Welder
    Grinder or jigsaw
    Drill
    3/8 drill bit
    ¼ drill bit
    1 hole saw
    2 hole saw
    Hack saw
    Metal File

    Instructions:
    Start by cutting out the templates included at the end of the pdf file. Trace each out on you sheet of steel and use a cutoff wheel on your grinder or a metal blade for your jig saw to get them cut out. If you're lucky enough to have access to a plasma table, there are also .dxf files available. After your plates are cut out, drill the 3/8s holes and 2 hole for the master cylinder as well as mounting and clearance holes in the base plate.

    Take the base plate and weld the two 3/8 nuts to one side. Using a square or clamps, weld the master cylinder mounting plate to the base. Finally, weld the side plates to the base trying to keep them as square as possible. Remember to keep your heat down so you don't have a bunch of weld distortion. Also remember to leave a skip weld next to the mounting holes for the two 3/8 master cylinder mounting bolts.
    [​IMG]

    Next, cut your round steel tube into two 1.85" long sections. Drill a ¼" hole in the center of each going through only one of the walls. With the holes drilled, lay each tube next to each other on a flat surface with the holes pointing upward at a 15 degree angle. Weld the tubes together by running a bead on each side of the holes as well as the full length on the other side. These holes will be the grease passage for the pivot.
    [​IMG]
    With the pivot portion and main mounting structure welded up, the hardest part is left. Using the temple for the square tube, trace and cut your tube. With your welded tubes laying on a flat surface, position the square tube on top so the angle cut end makes a 14 degree angle to horizontal and weld all around to the round tubes.
    [​IMG]
    [​IMG]
    Once the pivot tubes are welded to the square tube, drill another ¼” hole in each tube positioned in the center when looking at it left to right. These will be the holes that bolts go through to retain the pedal arm pivots. At this point, don't weld the ¼" nuts on just yet.
    [​IMG]
    Finally, tack weld the square tube to the main assembly by aligning the square in the center of the place and so the lower pivot holes is centered 3.5" off the base. This distance will allow the pushrod to align correctly left to right with the master cylinder as well as position the pedal pivots in the correct factory location. The center of the lower pivot tube should be 3.5" off the base mounting surface to ensure that there is no binding of the pushrod.

    [​IMG]
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    Last edited: Mar 13, 2015
  2. bri0057
    Joined: Dec 2, 2008
    Posts: 48

    bri0057
    Member

    Hang in there, you’re almost done. Take your brass bushings and cut them down to 1.85” long and drill a ¼” hole in the center of each. Then insert each into your pivot tubes aligning the holes you just drilled with the holes that will be the grease path. Drill the other 2 ¼” holes for the pivot retention bolts.
    [​IMG]
    Once you have your bushings drilled, remove them and weld on the three ¼” nuts to your pivot tubes.
    [​IMG]
    At this point it’s time to bolt in your master cylinder in and insert your pedal arms to check for pushrod clearance. Cut your 3/8” bolt to 3.5” long and install it on the pedal arm along with the rod end. With your bolt cut to length, assemble it onto the rod and check the angle of your pedal arm compared to what it is at when assembled onto the original master cylinder. By doing this on the bench, you will be able to get your pushrod length adjusted before it is all installed under the floor. If the push rod clears the master cylinder bore when you press the pedal all the way down, then you have set your pivot height correctly and you can finish weld the square tube to the mounting plate. If it binds on the top or bottom of the master cylinder bore, adjust the height by cutting it off and welding it on again.
    [​IMG]
    Take your ¼” bolts and file ¼” of the end so it’s a round cylinder. The diameter will be the width of the groove in your pedal pivot shafts. It should be roughly the minor diameter of the bolt but may vary depending on how much wear your pivots have. You can test fit these holding bolts in the pivot point to make sure they are not binding as the pedal arms are moving. File the ends of the bolts to a point where no binding is felt.
    [​IMG]
    Assembly:
    Now that you have everything fabricated, it takes a little bit to get this larger assembly installed. Because the master cylinder needs a larger opening in the floor to get the cover off, you might as well cut a hole slightly larger to fit the full assembly through from the top. It is possible to install the bracket from under the floor then install the master cylinder but it can be difficult to get the bolts tightened that mount the master cylinder. Bolt the master cylinder to the bracket and assemble the pivot arm so you can bench bleed it. Once you have it bled, remove the pivot arm and install through the opening in the floor.

    Once you have the bracket in place with the master cylinder bolted to it, install the pedal arms through the access panel in the wheel well. With the pedal arms installed into the pivots, tighten the ¼” mounting bolts and then position the full assembly in place by bolting the 2 3/8” bolts up through the frame rails.

    With the assembly and arms installed, you will be able to install the pushrod assembly that you adjusted earlier. The bolt for the rod end will face towards the inside of the car to give enough clearance to the clutch pivot arm. Install the castle nut and cotter pin.

    Depending on how much your parking brake rod has been tweaked over the years, you may need to put a slight bend in it to prevent it from rubbing against your new master cylinder bracket.

    At this point you just need to grease the pivot, install your lines and sit back for a cold one. This is also a good time to go through the rest of the brake system and replace anything that looks worn. For this master cylinder you will need to install residual valves in the lines to prevent drain back due to the master cylinder being mounted below the wheel cylinders/calipers (10lb for drums, 2lb for discs). You may also want to add an adjustable proportioning valve between the residual valve and rear drums if you have done a disc conversion on the front. This will allow you to adjust your brakes for optimal stopping performance.
    [​IMG]
     
  3. bri0057
    Joined: Dec 2, 2008
    Posts: 48

    bri0057
    Member

    Here is the PDF document that has the drawings to print out as well as the .dxf files.
     

    Attached Files:

    Last edited: May 8, 2013
  4. chaddilac
    Joined: Mar 21, 2006
    Posts: 13,860

    chaddilac
    Member

    That's pretty freakin' cool right there!!!
     
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  5. In other words, nicely done; replete with great CAD drawings......
     
  6. gregaustex
    Joined: Feb 20, 2009
    Posts: 136

    gregaustex
    Member
    from Austin

    Very professionally done. Do you have pix of this installed? Thank you for posting.
     
  7. bri0057
    Joined: Dec 2, 2008
    Posts: 48

    bri0057
    Member

    Yea final pics would be good wouldn't they...please hold
     
  8. bri0057
    Joined: Dec 2, 2008
    Posts: 48

    bri0057
    Member

    Here are a few more shots of it installed in the car. Never mind the Fred Flintstone holes in the floor, that's next winters project....hopefully with a new Baileigh's bead roller.

    In the one picture you will notice that you can reuse the brake line tee that use to split the front and rear lines now for the spit to the front left and right.

    On another note, for those of you have have pm'd me about cad work, I do projects on the side, just let me know what your looking for and I'll shoot you a very reasonable price.

    [​IMG]

    [​IMG]

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    [​IMG]
     
  9. Very nice setup!
     
  10. vtx1800
    Joined: Oct 4, 2009
    Posts: 1,049

    vtx1800
    ALLIANCE MEMBER

    Very nice job, I've done something similar using the stock 38 master with a dual mounted behind, I really like the push rod, I've fabricated one but I think I will copy yours, it looks better! Your drawings, and other supporting information make a very good tech article.
     
  11. bri0057
    Joined: Dec 2, 2008
    Posts: 48

    bri0057
    Member

    Thanks guys, glad you like it. It was fun to put it all together.
     
  12. mammyjammer
    Joined: May 23, 2009
    Posts: 505

    mammyjammer
    Member
    from Area 51

    Well done!! Beautiful drawings, good pics.
     
  13. damagedduck
    Joined: Jun 16, 2011
    Posts: 2,342

    damagedduck
    Member
    from Greeley Co

  14. eddie_zapien
    Joined: Apr 4, 2007
    Posts: 277

    eddie_zapien
    Member

    I should have looked here when I built mine last spring... looks great!:)
     
  15. COOL!!! RESPECT!
     
  16. bri0057
    Joined: Dec 2, 2008
    Posts: 48

    bri0057
    Member

    Just an update to this old thread.....I would make the bracket out of thicker steel next time because it has a little flex in it. I'm also going to play around with a different master cylinder because it takes a little more pedal effort than I would like like to stop the old Chevy.
     
    pharrand likes this.
  17. pharrand
    Joined: Sep 26, 2010
    Posts: 6

    pharrand
    Member
    from Michigan

    Pure Genius. Keep us informed on what MC you finally end up with. Thanks for taking the time to share this. Pat
     
  18. Dallis
    Joined: Oct 12, 2016
    Posts: 4

    Dallis

     
  19. Dallis
    Joined: Oct 12, 2016
    Posts: 4

    Dallis

    This is a great resource! Thanks for all your trouble. Two questions: 1) Re the bracket structure, the right side wall is cut low to allow the lines to be attached. Could the left wall be the same, or does its height have a structural purpose? 2) Did you find a better MC than the one you first mentioned in the post? Again, THANKS for your efforts!
     
  20. bri0057
    Joined: Dec 2, 2008
    Posts: 48

    bri0057
    Member

    Since the original posts, the car has been bagged to lay frame which means this style of mount doesn't work. Below it the new mount I made which bolts through the frame side rail. Much stronger than my original creation. I still have the master cylinder listed. It works but I would like something better...just haven't had time to play around with it.

    Dallis: I would leave as much structure as you can. The bracket takes a lot of force through the pedal. If you don't need to remove material, I wouldn't.
     

    Attached Files:

    lowrodderchev likes this.
  21. Dallis
    Joined: Oct 12, 2016
    Posts: 4

    Dallis

    Good advice, and thanks again!
     
  22. Dallis
    Joined: Oct 12, 2016
    Posts: 4

    Dallis

    I'm just about ready to weld mine together. All has gone according to the plan and I put the bracket together w/ welding magnets for fit & measure. The bottom pivot tube measured good at 3 1/2" (center to surface). Then I measured the top pivot tube at 4 5/8", which is a 1/4" more than the original brake MC pivot point at 4 3/8".

    In re-checking everything I took the tubes (11 gauge) and placed them over the original MC pivot holes. That's when I discovered that the tube thickness makes it impossible to reconstruct the original center-to-center measurement of 1 1/16”.

    I'm guessing you made yours out of 11 gauge steel tubing, so you must have had a similar measurement on the upper pivot point. If so, did you encounter any issues w/ the clutch lever and adjustment? Dallis
     

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