A Poor Man's Master Cylinder Upgrade

Brakes, Suspension, Rims and Tires

  1. Gerald Morris

    Gerald Morris Senior Member

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    The Poor Man’s Master Cylinder Upgrade

    by: Gerald E. Morris

    Brakes first concerned me just 3 days after purchasing Mathilda (our 2 door ‘66 Chrysler Newport). I had to replace drums, studs, shoes, springs all within the first month of owning Tilly. Front wheel cylinders and hoses followed a year later. By the second year’s end, I had GOOD brakes which stopped Mathilda’s hurtling 2.1 tons quickly, reliably and consistently, with but ONE fly polluting the DOT 3 fluid: the single pot master cylinder.

    The lethal potential of this system manifest itself after I had replaced the front hoses. I neglected to tighten the left hose sufficiently (probably due to distraction from my get running amok while I worked), making a leak just dangerous enough to nearly drain the brake system the following evening as we returned home from worship. The brakes went suspiciously soft by the time I stopped for a Sunday supper of fried chicken. THANK GOD FOR CHURCH’S CHICKEN!


    All but a couple tablespoons of the brake fluid had squirted out that loose hose fitting, as I saw from the telltale brake fluid under the fender. Carrying all sorts of tools, fluids and stuff in the trunk made it easy to refill the master cylinder. I tightened the hose and thanked the Lord and St. Joe for the timely warning, then drove us all home safe and sound. This convinced the wife that a few dollars on a master cylinder upgrade would be MOST WISELY invested. Despite having no further brake trouble, that business remained in mind until I got a good chance to effect the upgrade this summer.

    I. By 1967, Mopar adopted dual pot master cylinders with strong encouragement from newly empowered Federal bureaucrats motivated in part by accident statistics on brake failure due to the inherent flaw of the venerable single pot design. For the majority of their vehicles, still equipped with drum brakes all around, the Bendix 2660809 succeeded resoundingly for 3 years.

    MC1323__02940.1446059657.400.500.jpg
    The Bendix 2660809 Master Cylinder
    I chose this because with a 1” bore, and the same piston stroke length as its predecessor, I could bolt it in without some booster complicating my brake system. Both Babushka and I alike loathe the FACT that brake boosters rely on a running engine to provide ready braking power. I’ve experienced several times in my misspent youth having the engine suddenly quit while thundering along the Interstate at some respectable multiple of the posted speed limit. I prefer to have brakes which work as well CONSISTENTLY without dependence on any extra power system.

    This unit merits respect to this present day; so much so that its copied by those swinging capitalists in the “Peoples Middle Kingdom" or "Republic.” Had there been a shiny new U.S. made one readily available when I shopped for what I bought, I would have likely ponied up for it. As things are: I’m going to trust that the cast iron body of the unit I purchased has been competently poured. It seems so anyway. These sino-repops run between $65-75 on ePay. At least I didn’t have to pop for an adapter plate to bolt it in, as I would have for a Wilwood. It also works very nicely with the original pushrod.

    II. Aside from the MC, one needs a few other bits of hardware to upgrade.

    upload_2020-7-29_16-45-49.png
    (Note: this table had to be inserted as an image to preserve formatting --G.M​

    III. Disassemby
    Remove the single pot MC as per your FSM. A 7/16” tube nut wrench should do to remove the ¼ inch
    line from the old master cylinder to the 3 line junction block strapped to the front frame rail below.
    Remove that line from the junction block now too. Take special care to use a proper 3/8” tube nut wrench when disconnecting the rear brake line from the junction block. I
    PM-MC-upgrade_html_9e4604dcd7a5b27a.gif
    Old Re-purposed Junction Block, plugged rear port.
    STRONGLY advise one to remove the junction block from the frame rail by loosening the big sheet metal screw holding the strap down on the inner side of the rail prior to the attempt. This permits one to slip the tube nut wrench over the tube nut. Removing some of the wire wound around the tube as reinforcement and insulation near the nut also helps. (I HAD TO!)

    Grasp the junction block with vice-grips, apply torque to the tube nut with your wrench, and pray that you don’t round off every one of the 6 hexagonal corners as you attempt breaking that nut loose. I JUST managed this, after much PB Blast, and several false starts which rounded 4 of the 6 corners off. After a prayer and BEATING the tube nut wrench back onto that tube nut, I FINALLY got it to turn. Decades of old, baked on hydrocarbons polymerized to hold that nut fast and I suspect my beating the wrench back on cracked this super-molecular bond enough to free the nut with further work. Oddly enough, neither front line nut gave half so much trouble.

    After removing the rear line from the junction block, plug that rear hole with that 3/8-24 plug With a little blessing, you’ll never need to remove it. Make sure both front line nuts are snug in at this point also. If everything else came off and out, you can commence installing the new master cylinder.

    IV. Installation.
    Fill the new MC with the brake fluid of your choice and bench bleed it, then close the lid and plug the ports with your bleeding hoses or tubes. Hang it on the 4 studs meant for attaching to the firewall and tighten them to 100 inch-lbs. Leave off on the push-rod until all the lines have been securely installed and tightened.

    Cut a 15 inch length of 3/16 line, slide on a 3/8-24 tube nut, double flare the end, then snug in the union. If all went satisfactorily thus far, screw the other female end of the union onto the tube nut on the rear line. Slide on the ½ -20 (blue) tube nut, double flare the other end of the 15 inch extension, bend a 90 degree turn about 2 inches from the end of the tube nut, then snug this into the front port on the MC, which will be labeled with an R for “Rear.”

    PM-MC-upgrade_html_86b8c0fa01228567.gif
    Frontal view, Bendix (repop) MC w brake-light switch tee connected on fender.
    Note how the rear brake line sweeps smoothly down to the union, visible just right of the gear selector at the bottom center of the picture above. Given that distance from the exhaust manifold has been optimized here, using the MC itself to shield this line, I deemed it unnecessary to put a cooling curve in this line. Given how the front line must connect to the junction block directly beneath the MC on the frame rail, it comes marginally closer to the manifold, so the cooling curve between the brake light switch tee and the cylinder serves to insure against vaporizing the brake fluid in this most important line.

    IFF one cares to adopt a hydraulic brake light switch as I have, then one should next obtain a 7 inch length of 3/16 tubing, double flare one end, slide on a 7/16-24 tube nut and loosely start this into the top of the line junction block on the frame rail. Now slide down a 3/8-24 nut facing up, then flare the top end of the tube. Snug this into the hydraulic switch tee. If the switch hasn’t yet been screwed into the 1/8 inch NPT port at the middle of the tee, do so now.

    Take about 15 inches of 3/16 tubing, flare one end, and slide your last 3/8-24 tube nut over that. Loosely screw this into the end of the tee, slide the 9/16-20 nut onto the other end, and flare that. Now, make a full 360 degree loop starting about 2 inches from the top of the green 9/16 nut. This bend will give a nice bit of flexibility to the tube as you then snug the 9/16 nut into the REAR port of the MC, which has a capital “F” for FRONT labeling it. Now snug down the last nut in the tee, but leave the 7/16-24 nut loose, or even back it off and put the end of the line into a clean jar for bleeding.

    [ If foregoing the hydraulic switch, then you can connect directly from the top of the junction block to the front brake port on your MC. It takes a 15-20 inch piece of tubing to do this, depending on how much of a cooling loop, if any, you want to put in the tube. This way, you will have a VERY LOW material bill for your upgrade, though the hydraulic brake light switch isn’t too costly, and sure makes life easy. ]

    NOW attach the push rod to the pedal after making sure it will slide smoothly into the master cylinder, pressing the pistons. If all went well, you now should slowly pump the brake pedal ONCE to bleed the new front brake line as far as the junction block. Once the line is air-free this far, you can snug the 7/16-24 nut down for good in the top of the old junction block. I found VERY FEW bubbles from either front brake cylinder after hooking everything up, I happily report!

    The rear requires some serious bleeding. Go to the passenger side rear wheel, and place your bleeding reservoir and hose there. Open the port. Pump the brake a good 3 times. This will pump most of what little fluid the rear pot holds on the Bendix 2660809. Note how much dirty fluid and big bubbles turn up in your bleeding jar. Replace the lost fluid in the rear brake reservoir up front with new stuff, then pump again. Repeat this procedure until new, clean, bubble free fluid is ALL that fills the bleeding hose. Now, close the port, pump up pressure after filling the pot again, then, with a good weight on the pedal, go back, slowly open the port and watch for bubbles. If bubble-free at this point, close the port, bleed the other 3 wheel cylinders, then take your upgraded asphalt yacht for a cruise!
     
    Last edited: Jul 30, 2020
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  2. FURYGT

    FURYGT Senior Member

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    Well done! Your post will help many pre-67 C Body owners.
     
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  3. volksworld

    volksworld New Member

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    great...now that you're done throw some fuselage disc brake spindles on the front....
     
  4. mr. fix it

    mr. fix it Old Man with a Hat

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    Nice write up.

    Did you do a moderate speed brake speed test to make sure that the system is properly balanced?

    I did exactly what you did back in 2014 and found that the rears locked up under hard braking...
    Found a distribution block from a 67 dual system and my issue was gone...
     
    Last edited: Aug 1, 2020
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  5. Kristof

    Kristof New Member

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    Thanks for your write-up! This is on my agenda for next winter (66 Fury with manual drum brakes), should have been done last winter, but I lacked the courage to start... Your description will be a great help!! :thankyou::thankyou:
     
  6. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    FWIW, a lot of guys with older cars (prior to early 50's) with hydraulic pressure switches have eliminated them because they are slower to work. That means, in traffic, you have the brake lights coming on that much slower, giving the folks that aren't paying attention AND the young ones are actually now being trained to look for the third brake light, just that much less warning that you are stopping.

    IMHO, i wouldn't replace the standard brake switch, that can be adjusted to activate the brake lights as soon as you touch the pedal, with the slower acting hydraulic switch.
     
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  7. 70bigblockdodge

    70bigblockdodge Old Man with a Hat FCBO Gold Member

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    Do you have the rubber ring on the push rod? Otherwise there is nothing keeping the push rod from pulling out of the master cylinder if it ever gets pulled toward the driver. Anyone with manual brakes should check there car if they have never had the master cylinder off. Many not so bright mechanics do not realize what it is for or if it stays in the old MC. Everything will work normal until that push rod pops out. Then you are going to hit something.
     
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  8. cantflip

    cantflip Old Jagoff with a Hat FCBO Gold Member

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    I wonder how that's supposed to work here where there's always one car with one functional bulb left or painted over lenses to "look cool"...
     
  9. Gerald Morris

    Gerald Morris Senior Member

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    NO! Should I do so, I would have to 1.) replace the master cylinder I've chosen which doesn't have enough "throw" (piston volume) to drive disc brakes. 2.) use a BRAKE BOOSTER to DRIVE the MC w increased throw.

    Such would utterly betray my purpose with this upgrade, which is to maximize the ability of a MECHANICAL DRUM BRAKE SYSTEM. I don't like disc brakes as they DEPEND on a RUNNING ENGINE to pull the vacuum necessary to drive the booster. Yes, a vacuum canister MIGHT retain enough vacuum to allow ONE braking, but that's all they were good for. I'll rely on my quadriceps still instead.

    This issue arose and bit me about 20 yrs ago when outfitting an old 68 Mustang with disc brakes all around. I'd then discovered that the manual system which had driven the drum brakes admirably LACKED THE VOLUMETRIC DISPLACEMENT, called "throw" by brake men, to drive disc caliper pistons. While Fuselage and Formal disc brakes were more efficient than the early Budd prototype systems, they still require extra volume which only a power brake system can deliver.

    The Babushka and I agree; well adjusted drum brakes suit our safety needs better with this vehicle.
     
  10. Gerald Morris

    Gerald Morris Senior Member

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    YES! and THANK YOU FOR ASKING! I saw that shit when I got the old MC out; a vestigial remnant of the old rubber ring and boot. The kit I bought for mechanical hookup included a nice new boot and ring. I'm still missing the second spring which the catalog shows in the boot to give the pedal firmer return I guess.
     
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  11. Gerald Morris

    Gerald Morris Senior Member

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    I took it on Nogales Highway up to 70 mph, did a quick brake, and had no pulling or such. I checked yestereve with a second bleeding, just to be sure: NO BUBBLES ANYWHERE! The hydraulics are good. They were good before. I've now put about 40 miles on the new system with it working as nicely as it ever has. Next improvement will be to replace the crap "green" brake shoes with the NOS asbestos ones I acquired for their superior quality. They LAST much longer too.
     
  12. Gerald Morris

    Gerald Morris Senior Member

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    I composed this with folks like you in mind bro. It's really absurdly easy. Just attend to ALL the details and it will go nicely. Stay with a 1 inch bore master cylinder too if you plan to retain a mechanical system. You might be able to cop an old Bendix in a barn or junkyard and rebuild it, or get this re-pop like mine. It works well enough for the present and I think it will for a long time. Chinese stuff often is badly flawed, but I've found those flaws to be immediately obvious. They learned to cast iron about 2400 yrs ago, and actually can do that when their rulers want them to. Just have to keep in mind the proper caveat when buying anything from any asiatic slave state.
     
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  13. Gerald Morris

    Gerald Morris Senior Member

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    BTW, I plan to put that third brake light in up near the top of the rear window after I finish the exhaust job I've got going today. With the help of angels, I'm making this demo-derby escapee safe.
     
  14. Gerald Morris

    Gerald Morris Senior Member

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    I suspect the old switch bracket in mine. I went through 3 replacement switches before going hydraulic. The JEGS rig lights up quite promptly, so long as there is full brake fluid. The old MC has a VERY slow leak in the old top gasket I guess, and I discovered that when fluid level was down it indeed failed. I admit the cheap crap switches from Oh REALLY-Vatozone-Peppy-doodz all sucked. Lets see how long the JEGS switch performs well. I MAY yet try another direct switch.

    Using all LEDs for my tail lights has helped with response time. They require MUCH lower current! The middle bar is also LED.
     
  15. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    Maybe try a microswitch, like this one, wired normally closed. Mount it so the brake pedal arm contacts it when your foot is off the brake. Work up a bracket that adjusts, maybe using what's there.

    Should be pretty easy to source a good switch that will outlast the car. Probably cheaper than the cheap replacement automotive switch too.

    Micro-Switch-with-Roller-Lever-600x600.jpg
     
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  16. Gerald Morris

    Gerald Morris Senior Member

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    Good thoughts! I may also look about for another bracket. Saw an NOS one on ePay about 6 mos back. For the nonce, I'll roll w the JEGS switch. It does respond decently, for the present. I always appreciate your tight adhesion to the original design principles the folk working with Virtmann had in mind. (And his own genius!) I try not to deviate much from their work.
     
  17. twostick

    twostick Senior Member

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    An electric vacuum pump like GM used in the 80's and 90's would give you the redundancy you desire.

    Kevin
     
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  18. volksworld

    volksworld New Member

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    a 1 inch bore master should operate manual discs just fine...most people just automatically upgrade to power at the same time with a larger diameter master (usually 1 1/8)...the larger diameter requires power assist so the pedal isnt too hard to push...but the discs themselves dont require power if the master is sized correctly....the other thing that makes a disc brake master is a larger resevoir for the front because of the larger volume of fluid that the caliper will hold when the pads are worn...but as long as you keep an eye on the fluid level its not an issue...drove my truck for 20 years with a manual drum master and front discs
     
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  19. mr. fix it

    mr. fix it Old Man with a Hat

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    What M/C would be the choice to do this for disc brakes?
     
  20. Gerald Morris

    Gerald Morris Senior Member

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    Hmmm, I will have to research this matter of manually driven disc calipers. IFF they can be driven with the Bendix MC without further complication, then such a solution would be desirable. I need to attend to other suspension issues first at any rate, and also the cylinder heads, but I will put researching manual disc brakes on my Agenda. That would be gratifying.

    Yes, but at the price of added complication, which always increases the probability of something failing, though hopefully not anything of direct importance. The better solution here is to find disc brakes which can be driven by the Bendix cylinder in use. The front reservoir is larger than the rear anyway, suggesting that the designers had the proportion for drum brakes in mind. Looking in the 1967 catalog, one can see that the Bendix 2660809 clearly was intended to drive all drum systems with no mention of disc brakes. The cylinder at the top of the page was meant for that.
    upload_2020-8-1_11-52-43.png

    I remain suspicious of the notion that any disc caliper can be as well driven with the same fluid volume displaced by the front piston of this cylinder as the drum brake cylinder it was meant to drive. I may research this matter at some time, but doubt I will change my mind.