Project Riviera TH400 Rebuild

Discussion in 'The "Juice Box"' started by 70rivme, May 30, 2020.

  1. 70rivme

    70rivme Well-Known Member

    Hey everyone, so I picked up a 400 trans out of a '69 Riv last week to rebuild and repurpose in my 1970 Riv. I have attached a pic of the tag from the '69 trans in case anyone knows how to decode it and it could contain any helpful details. With the help of a book and threads on this forum I have torn down the transmission in the past few days and ordered up parts. I picked up a stage 3 rebuild kit like the one @Luxus used for his rebuild, added the 34 element sprag, Transgo 400-1&2 shift kit, low roller clutch, Torrington bearing kit and thrust washer kit. I also ordered elsewhere, gapless spiralock intermediate sprag and clutch rings as well as a Sonnax heavy duty case bushing kit with the thrust bearing. If I am missing anything else that you could suggest please let me know.

    So, as I am slowly progressing through this transmission I have a few questions. By the way, I am pretty much new to trans rebuilding so thank you for bearing with me and answering my questions! First thing I encountered was that the vacuum modulator valve moves in the bore but does not want to come out of the case. Not sure how to proceed with this. Second thing I ran into is in the middle of all the teeth on the planetary gears there appears to be what I would call a notch. See picture. Is this normal for all of the planetary gears to have? Third is that the speedo gear on the output shaft is in good condition but it is steel. Is it preferred to have the plastic gear or is using the steel ok?

    Lastly, before I disassembled I measured input/output endplay. Input I got .043 and on the output side I could not get any movement. I know the front is a little too much but is it possible to have no endplay on the output side? During reassembly, at what point would you want to check input and output endplay and adjust?

    Thanks all
     

    Attached Files:

  2. Luxus

    Luxus Gold Level Contributor

    Hopefully some of the more knowledgeable trans guys will chime in but I'll give you my two cents. I don't recall my planetary gears looking like that, so I'm going to say it's not good and those gears should be replaced. The speedo gear being steel means it's original from the factory. People will say now is a good time to change it as it is easy to do as opposed as to when the trans is in the car. I left mine in.

    BT I believe means the trans was for a Riveria, though all the TH-400s are more or less the same. Mine was a BC. Those 5 numbers are the last part of the VIN of the car the trans came out of.

    When you reassemble is when you check the play. If it's not right, there are spacers/washers that can be changed to make it right.
     
    70rivme likes this.
  3. Stage2

    Stage2 "Heard about Pluto? That's messed up right?"

    If you don't already have one, get a copy of How to Rebuild and Modify GM Turbo 400 Transmissions. I'd never done an automatic transmission before, and this book made it actually easy. I've rebuilt dozens since then.
     
    Rossco and 70rivme like this.
  4. 70rivme

    70rivme Well-Known Member

    Appreciate the input Luxus!

    This exact book is what I am using for my guide. Seems pretty easy to follow. I don't see anywhere in the book about checking endplay on the output shaft, but there is always the chance that I missed it. Appreciate the input!
     
  5. Luxus

    Luxus Gold Level Contributor

    I forgot to mention, there are a couple of good YouTube videos on rebuilding the TH400. There is a link to a thread with a bunch of videos in my build thread posted by 1969RIVI. The book is good but it does gloss over a few things here and there.
     
    70rivme likes this.
  6. Luxus

    Luxus Gold Level Contributor

    70rivme likes this.
  7. BRUCE ROE

    BRUCE ROE Well-Known Member

    If your speedo is right on, the steel gear is fine and no doubt will far
    outlast a plastic one. But they are hard to change for speedo
    corrections, esp when the trans is assembled. I have done it, under
    the gear is a small hole to latch a plastic gear in place. Bruce Roe
     
    70rivme likes this.
  8. 70rivme

    70rivme Well-Known Member

    I happen to have another trans out of a 1970 Riviera but the case is cracked. So I'm goofing around with this one because I want to see if the planetary gears have the same notches in them. I just noticed that the valve body has 2 wires and a 2 blade terminal connector on the case where as the 1969 trans had 1 wire. Looking at my original 70 trans out of the car it also has the 2 blade terminal connector. Any ideas? Gonna move forward on disassembly, curious as to what I will find. Also the 70 trans with the broken case has the plastic speedo great on the output shaft.
     
  9. Luxus

    Luxus Gold Level Contributor

    Your talking about the downshift solenoid? It can have 1 or 2 blades. 1 is for the downshift. The second is for switch pitch control (which you dont have) or it is part of an emissions control system (which you can then just ignore).

    Bruce as far as speedo corrections go, wouldn't you do that with replacing the driven gear (the one connected to the speedo cable)?
     
  10. 70rivme

    70rivme Well-Known Member

    I was wondering about this. My Riv originally had a 2.78 differential in it, I ended up changing to a 3.08. It's not off a lot but I want to make sure I address this while I am assembling the trans.


    I will end up posting a picture of it later, but there is the downshift solenoid and the another electrical switch looking piece.
     
  11. 70rivme

    70rivme Well-Known Member

    Disassembled the 1970 trans with the cracked case and checked out the planetary gears. Yep, they are not supposed to look like my picture of the planetary gears from the 69 trans. I think my solution is I am going to move forward with installing the internals of the 70 trans into the 69 case. I spent some time today cleaning and degreasing the case I will be using and found a number sequence on the left side of the case right above the trans pan mounting flange. Curiosity got the best of me so I located the number sequence on the original trans out of my 70 Riv and it is a 9 digit sequence. The first digit in the sequence doesn't match my VIN, but the 8 characters following are the same as the last 8 digits of the VIN on my car. I didn't know they did this until today but does that sound correct that the last 8 out of 9 match?
     
  12. 70rivme

    70rivme Well-Known Member

    Picture of the 1970 valve body that I talked about a couple of posts ago. What is that other switch and would I just reassemble the trans and leave that wire off?
     
  13. Luxus

    Luxus Gold Level Contributor

    I'm not seeing a picture.
     
  14. 70rivme

    70rivme Well-Known Member

    Let's try that picture thing again.
     

    Attached Files:

  15. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    The other wire goes to an oil pressure sensor. It is part of the TCS, Transmission Controlled Spark system. The system shuts off vacuum advance in first and second gears, and turns it on in 3rd. The pressure switch is there so the system knows when the transmission shifts to 3rd. It's an emissions device. You can eliminate it.
     
    Lucy Fair and 70rivme like this.
  16. 70rivme

    70rivme Well-Known Member

    Appreciate the input Larry! I'll just remove the wire from the switch to the case connector.
     
  17. black70buick

    black70buick Well-Known Member

    Next will be the drive shaft if that stage 3 kit shifts hard. The second shaft with the rubber insulator can give way and melt. :)
     
    Lucy Fair likes this.
  18. 70rivme

    70rivme Well-Known Member

    Sounds like you speak from experience. Any suggestions on modifications that can help survive the extra oomph?
     
  19. 70rivme

    70rivme Well-Known Member

    The 69 case I am using did not come with a lower spacer ring in it. The 70 donor trans I am using for it's internals had a lower spacer ring in it. Is there a preference with this ring, can I just transfer it into the 69 case I am using or is there more to it? Is it beneficial to have one installed in the case?
     
    Last edited: Jun 3, 2020
  20. Luxus

    Luxus Gold Level Contributor

    That sounds right, the older ones didn't have that lowest ring in it. I can't remember the reason they put those in, but I know it's not a critical item. You can use it or not.
     

Share This Page