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Syncro vs. Non-syncro?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by fortcollinsram, Mar 14, 2002.

  1. fortcollinsram

    fortcollinsram 1/2 ton status

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    What does it mean exactly for a tranny to be syncro'd I know the 465 is syncro'd in 2-4 but not 1 and reverse...Can somebody explain what syncronizing the gears means and how it affects how you shift the tranny...

    Chris
     
  2. marcus

    marcus Registered Member

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    Most (all?) modern gearboxes are synchroed. Basically this means there is a bit if wizardry that ensure that the input and output are spinning at appromately the same speed when the dog clutchs engage. If this didn't happen, you'd get some nasty grining noises as your engine tried to slow down the truck's momentum.

    Most most boxes aren;t synchroed in first, because generally you are stationary when you engage 1st gear, same goes for reverse.

    Hope this helps

    Mark
     
  3. TX Mudder

    TX Mudder 1/2 ton status

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    Yeah, what he said.
    Because 1st (or low, depending on what you like to call it) is not synchronized, it is very difficult to shift into it at any speed much above 1mph.
    -- Mike
     
  4. m j

    m j 1/2 ton status

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    I have seen 2 definitions to syncho'd
    the one that I think is the correct one is countershaft is constantly engaged to the speed gears so the gears stay synchronized as opposed to a transmission where you have to move the gears to mesh.
    <a target="_blank" href=http://community.webshots.com/storage/1/v4/8/94/71/14689471XgBCsWTogn_ph.jpg>like this dana transcase</a>

    the other is the common version refering to a tranny with blocker rings to help match gear speeds during shifts

    the syncros(or blocker rings) are usually a brass cone style clutch
    that when you push the shift clutch towards a gear, will engage the speed gear and cause the 2 gears to reach the same speed before the shift clutch engages the the speed gear teeth.
    when someone says the syncros are gone it usually means they are worn down to the point they no longer contact the speed gear with enough force.

    that is off the top of my head with distraction so there is bound to be errors
     
  5. RedDwarf

    RedDwarf 1/2 ton status

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    A fairly commmon misconception is that you cannot shift out of an unsynchronized gear while moving. Actually, you can. If you are on a steep hill, you can take off in granny and shift just like a regular 4speed.

    Like TX Mudder said though, it is difficult to shift into granny when moving. It helps sometimes if you double clutch, though usually it just grinds away
     
  6. pcorssmit

    pcorssmit 1/2 ton status

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    For some good pics and an article on this stuff, pick up the curent issue of Car Craft.

    Even with a syncro'd first, my NV4500 doesn't want to go in to first when moving more than 1-2 mph. No problem if you double clutch, though.

    Pete
     
  7. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Anybody what actually happens when "double clutching" as opposed to singel clutching. Is it just the fact you are giving the gears more "time" to mesh properly or is there something that happens differently inside when double clutching?
     
  8. m j

    m j 1/2 ton status

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    if you match the rpms of the 2 gears you dont have to use the clutch at all.
    double clutching is simply
    1. depress clutch to remove load on gears to allow shift into neutral
    2. release clutch to allow engine to be used to spin gear up to match output rpm
    3. once the 2 gear speeds are close enough depress clutch and shift into gear

    it is much easier to learn to drive without using the clutch
    double clutching means you cant 'power brake' unless you have 3 feet or are incredibly skilled heel and toe.
    able to modulate brake pedal and perfectly match rpm simultaniously
     
  9. morphed86k10

    morphed86k10 1/2 ton status

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    I'm with MJ on this one...no clutch at all is easier. And You can get a 465 to shift into first while moving very easily, you just have to rev the motor to match the speed of the gear. Anything below 10 miles an hour or so is pretty easy, just don't touch the clutch.
     
  10. m j

    m j 1/2 ton status

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    I guess I left out the important part
    double clutching is generally used in heavy truck "non syncro'd" trannies
    I cant see any reason to do it on a tranny with blocker rings
     
  11. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Thanks man!
     

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