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Finished TH-400 rebuild... pics

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by Ryan B., Feb 25, 2002.

  1. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

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    Well, I can now say that i am all done rebuilding the TH-400.
    This was the first automatic transmission that i have ever attempted to fix myself.
    (This is out of my '67 Camaro but the TH-350/NP205 in the blazer is next!)

    I was kind of waiting for an excuse to learn how to rebuild an automatic tranny and when mine burnt up it was time to learn... So I ordered B&M's master racing overhaul kit which comes with all the gaskets, seals, clutches, bands, etc. Unlike the Transkit i have heard... it did not come with any directions of any kind. I ordered a manual specific to the TH-400 through Jeg's. I also borrowed a couple of tools from a friend like the clutch hub compressor tool, a dial indicator, and an inch lbs torque wrench. (I have pic's of all this)

    I took (2 pages of pics!)<a target="_blank" href=http://communities.msn.com/Ryans1972Blazer/th400transmissionrebuild.msnw> PICTURES OF TH-400 REBUILD</a> &amp; of the whole process that are worth checking out i think.

    The tranny rebuild was very straight foreward and easy when you have a manual specific to that tranny... its just step by step directions you have to follow and you can't go wrong as long as you make sure everything is within spec and it goes back in the same way it came out. I used a big table and covered it with newspaper to lay all the parts out in the order they came out.

    I also had to go to a couple of different transmission shops to get a thrust washer to set the front input shaft endplay within spec.
    It was at .050" when i started as well as after i was done rebuilding it... (the endplay should not be affected.) I have 2 manuals that say the spec should be .007" to .019" for the endplay...
    One tranny shop (Aamco)[​IMG] said that would be too tight and at least .050" is what it should be at... another tranny shop (a good high performance tranny shop) said that .050" is too loose and sloppy and they like to set their race tranny's at about .015"
    My rear output endplay was at .015"
    and the front input endplay i shimmed from .050" to .022" and called it good.

    So after I got the tranny all rebuilt and back in, i came to find that i had no engine breaking in 2nd gear only... that is when I'd let off the gas the engine would not slow you down from the compression instead it would act like it was in neutral until you gave it some gas it would rev up and catch 2nd gear at the appropriate RPM's. It would accelerate and not decelerate becase of the engine only in 2nd.

    I had to drop the pan and the valve body to see what was going on.
    The worst part of dropping the valve body when the tranny is still in the vehicle was playing find the missing check ball.
    Where'd it go? is it in the drain pan? did it take off rolling? is it in the valve body?[​IMG]
    When the valve body drops out so do the plates which is the shift kit, and the front servo assembly will drop out. This is what i was needing to inspect to see why there was no engine breaking in 2nd gear...

    It turns out that when I installed the servo piston, i got it in there backwards of how it is supposed to be... amazingly it was easy to install it backwards like that. I must have not looked at the diagram really well on that part and realize which way the notches where supposed to be on the piston when installing it up or down.
    (Gimmie a break it's my first auto tranny rebuild!)[​IMG][​IMG][​IMG]

    I have pictures posted at that link above that show exactly what was wrong with having that servo piston installed backwards.
    And it would be possible to accidently get this wrong by just dropping the valve body out to install your own shift kit!
    So people who are installing your own shift kit pay attention to which way that piston goes or you'll be sorry![​IMG]

    Now that I found out what was wrong, I put it back together and man o man that tranny is SWEEET! I don't think a tranny shop could have done a better job rebuilding it than myself.[​IMG]
    "IF YOU WANT SOMETHING DONE RIGHT, YOU GOTTA DO IT YOURSELF!"

    ... So if a 19 year old kid can do it... so can you. [​IMG]

    [Real Men Don't Care About Gas Mileage Or Rapid Tire Wear!]<a target="_blank" href=http://coloradok5.com/gallery/albuo19>
    MY 1972 K/5</a>
    RyanB.
     
  2. 55Willy

    55Willy 3/4 ton status

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    How long did it take? My uncle use to do them for a living..he worked at a Chevy dealer, and Him and I did mine in 3 hours.



    <hr></blockquote>
    What do you mean, Where did I get it??...I <font color=blue>BUILT</font color=blue> the damn thing!!
     
  3. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

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    Well, from setting it on the table and starting, to taking it off the table ready to go back in, it was probally about 3 hours to rebuild it...
    The rebuilding, taking apart and putting back together went really fast, it was just waiting for a day or two running around to different tranny shops to find the right thickness thrust washer that took a while.
    Some guys didn't even know what i was talking about.. I was like how in the hell can you rebuild a transmission if you don't know what i'm talking about checking the endplay!?!?!?!?

    Seems like it took longer to get the tranny back in and lined up with the engine by myself than it did to rebuild the tranny. [​IMG][​IMG]

    [Real Men Don't Care About Gas Mileage Or Rapid Tire Wear!]<a target="_blank" href=http://coloradok5.com/gallery/albuo19>
    MY 1972 K/5</a>
    RyanB.
     
  4. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Dude, that's awesome! What a great feeling to do it yourself and have it work so well...... [​IMG]

    I know when the time comes, I'm gonna want you lookin' over my shoulder when I rebuild mine. Do you think a 4L80E would be similar to the TH400? I know they are supposed to be similar "strengthwise"....I just don't know what they look like once they're in a million pieces!!! [​IMG]

    Anyway congrats! I'm sure you saved a LOT of $$$ too!!!





    -Greg72

    '72 K5 Blazer - 427BB/TH350/NP205/6" Lift/35x12.50's
    <font color=blue>See it here: </font color=blue><a target="_blank" href=http://coloradok5.com/gallery/albun38>http://coloradok5.com/gallery/albun38</a>
     
  5. dogman

    dogman 1/2 ton status

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    Hooly$hit kid, is that what you where up to out in my garage.
    sorry, I couldn't lay on that cold ground and help you get that tranny in.
    When your out there in the middle of the night, all I can do is congratulate you on the perseverance to do it.
    good pics &amp; info

    finally old enough to know when to stay asleep!
    77 'K10 350 4sp &lt;cus I ordered it that way. @ 0miles
     
  6. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

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    Greg-
    As far as I know the TH-400 and TH-350 are very similar.
    They are the old school hydraulic fluid activated tranny's.
    The new age 4L60's and 4L80's are electronically selenoid actuated... if i'm not mistaken. That is... fluid pressure isn't responsible for shifting, electronic selenoids are.
    So they would be quite different.
    The clutch hub assemblys are all probally very similar in GM automatics, buy the valve body is more than likely where it is much different.
    To change the shift points or firmness in a TH350/ 400... you'd have to change the shift kit or governor. With a 4L60 or 4L80 all you gotta do is plug in a scan tool and hit a few buttons.

    I don't know exactly where and how the TH400 and 4L80 would be different / alike.... but I can say this:
    As long as you get a manual that is specific to that tranny... It should be all good! Just take that "can-do attitude" approach and anything is possible![​IMG]

    After I do that TH-350/NP205 I'll be a pro! heh[​IMG] I'm sure you'll let me know if you want a hand when the time comes.


    [Real Men Don't Care About Gas Mileage Or Rapid Tire Wear!]<a target="_blank" href=http://coloradok5.com/gallery/albuo19>
    MY 1972 K/5</a>
    RyanB.
     

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