Rebuilding my TH400

Discussion in 'The "Juice Box"' started by 1969RIVI, Jun 9, 2019.

  1. 1969RIVI

    1969RIVI Well-Known Member

    So I'm about to start the removal process of my Th400 from my 69 Riv and this is my first removal and rebuild EVER! the first hurdle I see and need help with is the driveshaft yoke. Do I need to press out the U joint in order to drop the trans or can I unbolt everything, drop the trans and slide it forward so the yoke slips out?? Or unbolt the driveshaft from the rearend and pull in backwards out of the trans first? Unfortunately I don't have access to a hoist so I'm kicking it old school and doing all this on my back in the drive way, lucky me!:mad::(
     

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  2. Quick Buick

    Quick Buick Arlington Wa

  3. Bens99gtp

    Bens99gtp Well-Known Member

    A low lift that makes it nice when working old school. Bench pressing a th400 with converter into place isnt easy especially if you have to start the bolts by yourself........its a great way to rearrange some teeth though
     
    Quick Buick likes this.
  4. BennyK81

    BennyK81 Well-Known Member

    Get someone to help you or at least a jack like Quick Buick proposed.
     
    Quick Buick likes this.
  5. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    This is the lift I used when I R&R'd my converter and flexplate. I highly recommend it. I can't imagine trying to do that job without it, I put the front of the car on my ramps, and jack stands under the rear axle tubes. This jack slid under the car with room to spare, and the lift range was perfect. I could have rolled the transmission out completely from under the car, but all I needed to do was push it back and move it to the side to remove and replace the converter and flexplate. The tilt back and forth and side to side comes in real handy although it was difficult to turn those knobs with the weight of the transmission on the jack.


     
  6. hugger

    hugger Well-Known Member

    Bench pressing a th400, getting covered in Dex3 and smashing your fingers when it slides off your chest is a right of passage and unfortunately 100% required to be a car guy,..sorry no lift allowed this time
     
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  7. telriv

    telriv Well-Known Member

    Besides the bolts at the rear of the shaft on the diff. you will ALSO need to remove the two bolts holding the center support or the shaft WILL NOT come out. They have a 1/2" head on them. The rear diff. bolts have a 5/8ths. head. Use a 6 point socket to remove them as they can be REALLY tight IF they've never been off. Don't want to start a project by rounding off bolt heads that are difficult to remove with a 12 point socket.

    Tom T.
     
    Briz likes this.
  8. 1969RIVI

    1969RIVI Well-Known Member

    Thank you gentlemen for the words of wisdom and tricks of the trade. I did manage to get it out by myself and it sure wasn't easy! I'm sure I earned my right of passage today hugger because all three things you mentioned I accomplished lol I do have a nice low pro Jack Ben & Larry but no fancy trans craddle so I built one out of 2x4 and ply wood and ratchet strapped the trans to it and the Jack to help aid it down. I did what you said quick Buick and it worked nice......after I realized there were two more bolts like telriv mentioned. Now that the fun stuff is over time to dig into it and get it disassembled.
     

    Attached Files:

  9. 1969RIVI

    1969RIVI Well-Known Member

    Another thing I noticed while I was just laying about under a 3 ton car is that the flex plate on my engine doesn't look like any of the regular Buick ones I've seen on line??? When I unbolted the torque converter it almost sprung back/away from the flexplate like it should've been shimmed. Also it looks to have a pressed step down from factory to it which is weird and the ring gear is offset to one side. Is this normal for older flex plates? And I'm not sure if it's the age of it or the beer but it looked to be orange to me;), maybe when the P.O. did the engine swap and put the b&m gear in the trans he put a Chevy flexplate on? Maybe this is what is contributing to my flexplate wobble that I've mentioned in another post?
     

    Attached Files:

  10. telriv

    telriv Well-Known Member

    Yeah, in the 2nd. to last pic it looks backwards. Can a 400/430/455 flexplate be put on backwards????
     
  11. 1969RIVI

    1969RIVI Well-Known Member

    I'm not sure?? If it was to be flipped around the taper would make it further from the torque converter though?
     
  12. BRUCE ROE

    BRUCE ROE Well-Known Member

    My advice, build or buy the tools to get the job done right. I have never
    tried to service any trans (TH300 to TH425) by hand only. Bruce Roe
     
  13. hugger

    hugger Well-Known Member

    Psssh,...I got trapped under my GSX for 4hrs till my mom got home with my shirt wadded up around the creeper wheel and the the th400 on my chest,...just character building is all ha
     
    65Larkin, johnriv67 and 1969RIVI like this.
  14. 1969RIVI

    1969RIVI Well-Known Member

    If nobody noticed in a few of the pics there's a kiddy pool on my front lawn beside the car. I had my two girls (7&9) outside with me all day. The wife was at work. I gave my oldest my cell phone and one set of orders, if you don't hear daddy grunting or cusing for more than 5 minutes call 911 and whatever you do don't call your mother!!:p:D
     
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  15. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    As far as I know, the flexplate only goes on one way. The stock one has the weight facing the transmission as pictured so yours looks correct. You say the flexplate sprung away as you unbolted it? I’m wondering if the converter pilot was bottomed out in the crank and the converter bolts pulled the flexplate when tightened. That would not be good. There is supposed to be 1/8-3/16” clearance between the flexplate and the converter bolt pads. Use washers if it exceeds 3/16”.
     
    Briz likes this.
  16. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    When you unbolt the flexplate, see if any of the holes are egged out. That’s the only way it goes on wrong.
     
  17. Briz

    Briz Platinum Level Contributor

    Only goes on one way. If you flip it the holes will not line up. Also the crank bolt holes are indexed and will only go one way as well.
     
  18. 1969RIVI

    1969RIVI Well-Known Member

    When I unbolted the torque convert it didn't "spring away" quickly it just started to pull away slowly with each turn of the wrench on each bolt. It seemed to me that it shouldn't be that way that the bolts should just back out without the plate moving. After all the bolts were out I pushed the torque converter as far forward as I could to check the spacing between the flexplate and the torque converter pads and it looked to be a tad bigger than 3/16". It probably needed a washer to be corrected but somebody just snugged it up and called it good. Again, to me that flex plate looks wierd aren't all the BBB flex plates flat? This one has a step to it from factory you can see it in the pics.
     
  19. Bens99gtp

    Bens99gtp Well-Known Member

    All factory plate I've seen have that step. The aftermarket like the wheel, dont and without it they really need shimmed.

    Mine took so much that when I sent my converter back this time I had them weld them on so I could stop dealing with washer and be balanced
     
  20. 1969RIVI

    1969RIVI Well-Known Member

    Oh ok. If they bolted the torque converter to the flexplate without shimming it it probably warped it a bit and that explains why in my video that it flexes way too much when it is running correct?

     

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