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Technical Mechanical brakes

Discussion in 'The Hokey Ass Message Board' started by sgtlethargic, Jul 1, 2020.

  1. Another thing about old Ford mechanical brakes--the parking brake applies the brakes on all 4 wheels instead of the rear wheels only.
     
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  2. jaracer
    Joined: Oct 4, 2008
    Posts: 326

    jaracer
    Member

    I believe that Hudson had both hydraulic and mechanical brakes. The mechanical brakes were a fail safe.

    Someone said that most of the air brakes on heavy trucks are improperly adjusted. Heavy truck have had self adjusters since the late 80's. With proper maintenance they keep the brakes properly adjusted.
     
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  3. You can still use the wide 5 wheels and run the hydraulic set up from 39 up....
     
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  4. Boneyard51
    Joined: Dec 10, 2017
    Posts: 4,018

    Boneyard51
    Member

    Self adjusters, like many automatic items are prone to failure, especially on trucks that drive a lot up North in the salt. Or trucks that set a lot. I have seen many self adjusters fail and since the driver /owner thinks they are working, they fail to check adjustment. And it usually takes tow guys to check mechanical brake adjustment.
    Any lever operated brake that does not have the shoes adjusted properly will not work effectively. Just my experiences being in that area for over forty years.








    Bones
     
  5. Ned Ludd
    Joined: May 15, 2009
    Posts: 4,004

    Ned Ludd
    Member

    I suspect that air brakes came in around the time diesel started to be a significant thing in heavy vehicles. I'd guess that that was around the same time the semi-trailer came in? Presumably spark-ignition heavy vehicles had vacuum servo brakes? Diesels don't really generate vacuum, so they'd need an ancillary vacuum pump to operate a brake booster, and once you're there it might as well be a positive-pressure compressor, which opens up a lot of other possibilities.

    I've given a lot of thought to engine-driven OBA on a rod or custom, powering a lot of stuff in addition to air suspension in the same way as Citroëns had a lot of stuff powered hydraulically. I wouldn't do air brakes because I'm not convinced of the pedal feel (though I believe there was a company offering air brakes for high-performance passenger car applications?) but a positive-pressure booster should be devisable.
     
  6. squirrel
    Joined: Sep 23, 2004
    Posts: 46,101

    squirrel
    Member

    That would be my concern, too.
     
  7. As has been mentioned they are commonly out of adjustment for the rust reason. Part of a CDL License holder's responsibility is to check their brakes via pulling the slack adjusters to check adjustment. Often overlooked as the result of self adjusting slack adjusters resulting in a ticket for improper equipment adjustment for the driver.

    Actually diesel engines in heavy trucks were not really endorsed by the trucking industry until the early 1960's. Air brakes were standard on F-8 Ford trucks and other makes since back in the 1950's when gasoline engines reigned supreme on the U.S. roads.
    In reality air brakes are a mechanical brake system with the air lines replacing the rods and cables as are hydraulic systems. Air brake systems eliminate the contamination and bleeding factors already addressed. Air brakes are a pressure system where pressure is needed to release the shoes from the drums unlike hydraulic or conventional systems that need pressure to apply the braking force. Application of the treadle valve, brake pedal releases air from the system applying the shoes to the drum. When pressures fall below 90 Lbs. your Maxi Brakes or parking brakes are preparing to apply so be ready and stop or slow to a manageable speed to prepare for wheel lock up. A fail safe for heavy load carrying vehicles so when you hit the brakes you are not suddenly aware when your pedal goes to the floor that there are no brakes as in a hydraulic system. There is no brake feel as in a hydraulic system and actually a safer system than hydraulic for heavy loaded vehicles.
     
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  8. This thread made me think of an air-powered engine, air suspension, and air brakes.
     
  9. Boneyard51
    Joined: Dec 10, 2017
    Posts: 4,018

    Boneyard51
    Member

    Not quite right Warhorse, you have to build about 90 lbs to release the spring brake( parking brake) that is correct. But when you press the brake pedal you are applying air pressure to a diaphragm that then pushes the brake shoes against the drum. Not all trucks have the parking brake. And a lot of trailers don’t have parking brakes( spring brake) .

    And I don’t get this “ no feel” thing. The trucks I drive definitely have a feel on the air brake .


    The “ fail safe” system in most air brake systems is in case of a hose rupture or compressor failure. If you are losing air, the spring brake will start to apply at around 60 psi and will come on 100% below about 60 psi.





    Bones
     
    Last edited: Jul 2, 2020
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  10. Yes you are correct I just said it all wrong. As far as the brake feel I can feel it also but for the newbie to air brakes you have probably seen them jam the pedal and lock them up while learning. They have came a long ways for sure to also introduce anti lock into the systems now. The old original air brakes were a thing to get used to. Like an acquired taste for Scotch or good shine.
     
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  11. Ned Ludd
    Joined: May 15, 2009
    Posts: 4,004

    Ned Ludd
    Member

    I think diesel had been making inroads in Europe since the '30s. I'm not sure about articulated vehicles at that time, though.
     
  12. Atwater Mike
    Joined: May 31, 2002
    Posts: 10,084

    Atwater Mike
    ALLIANCE MEMBER

    My Dad drove big rig since before I was born (1942) Before his passing in '54, he referred to the two types he drove (both types being 'semis') as 'Gas jobs' and 'smokers'.
    The more 'financially secure' firms ran 'Smokers', most of the others were 'gas jobs'...
    This was up and down the west coast, from San Jose south. His favorites were Diamond Ts...
     
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  13. Yes, particularly Germany. They were in use in German tanks in WWII while the American Sherman used anything from GMC's to radial engines whatever there was available was utilized and adaptable.
     
  14. junk_yard_jack
    Joined: Mar 4, 2009
    Posts: 10

    junk_yard_jack
    Member

    model a Fords have rods and clevises. I think it's a great system. Sometimes you gotta push hard tho
     
  15. Wrench97
    Joined: Jan 29, 2020
    Posts: 62

    Wrench97

    Vacuum brakes predated air basically used the same principles but instead of adding a air compressor they tried capturing engine vacuum and storing it......................................

    Semis today all have self adjusting slack adjusters they work well until some knucklehead replaces a brake chamber and cuts the rod too short or too long or in someway shape or form misaligns brackets, installs wrong parts even manually adjusting them constantly can damage the slack.

    New school are air disc it's a step up but most major fleets have not moved to them as mismatching tractors and trailers are an issue(you do not want the tractor to stop faster then the trailer) since trailers last longer it's always an issue.................................
     
  16. rusty valley
    Joined: Oct 25, 2014
    Posts: 1,505

    rusty valley
    Member

    many years ago i was driving for a company that would occasionally lease out a driver to deliver new semi trucks & trailers. its amazing how good they work when its all new
     
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  17. Shutter Speed
    Joined: Feb 2, 2017
    Posts: 801

    Shutter Speed
    ALLIANCE MEMBER

    Old Fords, at least Model A’s, parking brake/linkage is independent, and only locks rear wheels. A good emergency go-to. Has own separate shoe from service brakes in rear drums.
     
  18. Automotive Stud
    Joined: Sep 26, 2004
    Posts: 4,035

    Automotive Stud
    Member

    There's another important factor in the widespread changeover to hydraulic brakes that has not been mentioned. Aside from being self equalizing, in a hydraulic setup you can apply more force in a smaller space than you can with leverage from mechanical levers. This becomes more important as cars and roads allowed for higher speeds and brake linings got bigger.
     
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  19. Boneyard51
    Joined: Dec 10, 2017
    Posts: 4,018

    Boneyard51
    Member

    I disagree, you can get almost the same force with mechanical as with hydraulic, less a little for friction. And if mechanical are lubed right, you won’t lose that much to friction.
    Force is force, hydraulic or mechanical!









    Bones
     

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