Finished TH-400 rebuild... pics

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Ryan B., Feb 25, 2002.

  1. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

    Jul 18, 2001
    Likes Received:
    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=> 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]

    ... 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=>
    MY 1972 K/5</a>
  2. mudrunner78

    mudrunner78 1/2 ton status

    Sep 7, 2001
    Likes Received:
    Rocksprings, TX
    I to want to start rebuilding my own trannys, what special tools were required for the th-400..and keep mw posted when you do the th-350 since I have a ton around the shop that I'd like to rebuild. Jesse

    78 K-10 383, TH-350, NP-203, Dana 70 front, GM 14bolt Rear, 4.56 gears(underconstruction) 78 k-5 stock and rusty
  3. Seventy4Blazer

    Seventy4Blazer 3/4 ton status

    Apr 21, 2001
    Likes Received:
    Escondido, CA
    iv got one or 3 sitting around. i should do it myself, and some day when i get my garage in april, i am sure i will
    my buddy tried it, and it worked for a wehile, but then something went wrong. we dont know what yet. he has had a new one for a while now. but we keep forgeting to ask the guy who rebuilt it.

    take me drunk, i am home

Share This Page