Rebuild original st300 or swap....

Discussion in ''Da Nailhead' started by 1966buickgs, Feb 19, 2019.

  1. 1966buickgs

    1966buickgs 1966buickgs

    Trans has been leaking since day I got the car. Time for a complete rebuild or swap to another type of transmission with an adapter ring to bolt to the rebuilt 401 bored .80 over. Whats better 2 speed original switch pitch 66 or overdive 4L80e or 700R or something else? Let me know y'alls opinions on cost an what's better all around for a driver not a show car. Thank you
     
  2. gsgtx

    gsgtx Silver Level contributor

    what rear end gears do you have.
     
  3. 1966buickgs

    1966buickgs 1966buickgs

    3.08
     
  4. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    The 700R4 will team up to the 3.08 rear gear perfectly! You might want to make sure you have posi though because with the new trans the tire(s) will spin very easily.

    If you went to a 200R4 you would want at least a 3.23 rear gear with the 401 to be able to hit 4th gear by 45 mph, anything numerically smaller will pull the RPMs down to low to be able to be in forth gear @ 45 mph.

    The 4L80E would be very expensive(because of electronic controller needed) compared to the above 2 and wouldn't give as good of a 1st gear ratio not to mention the O/D ratio isn't as good plus it take more power to run this one than the other 2. But you could keep the 3.08 gear with this option and still be able to hit 4th gear by 45 mph.

    Definitely loose the st300 though for at least a st400 3 speed trans that will give better off the line performance for pulling out into traffic. The mentioned overdrive transmissions would be the best of both worlds though.

    I love my 700R4 that is in my '65 Impala behind the 383 sbc that is in it, 1st gear is like an empty freight train taking off!(better than a roller coaster ride!) My '65 has a 3.07 rear gear in it teamed with the 700R4 works great!(like having higher powered engine upgrade)
     
  5. Electra man

    Electra man Older and Slower

    4l80 or 700r will need an adapter plate as they are Chevy only. The 200r4 is a universal bolt pattern and can be built to handle some power. All the above will require drive shaft and trans mount mods.
     
  6. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    Is not a "universal" bolt pattern, it only has 2 different bolt patterns, BOP and Chevy. A 401 Nailhead does NOT have the BOP bolt pattern so ANY of the mentioned overdrive transmissions will need an adapter for it to bolt to the 401.

    The only trans that is a direct bolt on would be a ST400 from '65 or '66 from one of the bigger cars that came with one from the factory.
     
  7. Electra man

    Electra man Older and Slower

    What about the parking brake cable from the pedal. Wouldn't it have to be changed to the 400 tranny type?
     
  8. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    Parking brake pedal/cable is separate from trans. The only difference could be where or if a tensioner for the cable connects to the cross member if that needs to be moved or changed. If that's the case, fabrication skills will have to be tested to reconnect it.
     
  9. Bigpig455

    Bigpig455 Fastest of the slow....

    Or you could just reseal the ST-300? I really kind of like mine..?
     
  10. gs66

    gs66 Well-Known Member

    If you plan on long interstate trips the overdrive would be a nice feature. I had my 2 speed rebuilt and it’s never worked better. RPM’s weren’t that bad, even drove on Power Tour Long Hauls with the 2 speed.
     
  11. 1966buickgs

    1966buickgs 1966buickgs

    Torque converter broke but the trans was still shifting smooth just leaking from front & rear seal, modulator,dipstick,pan,selector switch an any other opening pretty much. A new variable pitch torque converter has been found by the transmission shop. My question is if I did go back with the st300 does this switch that's connected to the carburetor throttle linkage have to be connected? Cause it broke while removing the motor for rebuild. It's supposed to send a signal at a certain speed as the throttle opens to the variable pitch stators in the torque converter to lock up or open freely I think. Someone tell me if I have to have this connected? Thank you
     
  12. gsgtx

    gsgtx Silver Level contributor

    yes it does, it is also your kickdown switch for passing gear. there easy to find. unless your talking about the little micro switch by the firewall.
     
    Last edited: Feb 20, 2019
  13. 1966buickgs

    1966buickgs 1966buickgs

    Yes it is the micro switch by the fire wall that is broke. The kickdown switch is still intact. Don't know if it works either though. I have been driving the car with out it after the engine rebuild. So fuctionality wise I gotta have it? An without it no passing gear? Does that mean it will go faster with it working properly?
     
  14. GranSportSedan

    GranSportSedan Puppet dictator, wife has all power

    The little micro switch only engages High stall at idle. It isn't essential but it is nice to have if you don't have power brakes
     
  15. gsgtx

    gsgtx Silver Level contributor

    that is just for idle only, not kickdown or when your moving it does nothing , like gransportsedan said nice to have but wont hurt not to have it. you can find them out there.
     
  16. 1966buickgs

    1966buickgs 1966buickgs

    Let me know where I can find that micro switch if you come across 1. Thank you all for the help! I'm gonna have the original st300 rebuilt!
     
  17. gsgtx

    gsgtx Silver Level contributor

    someone on nailhead site posted about buyingedelbrock
    theres a thread about a micro switch from edelbrock photos too. if someone could find it
     
  18. gsgtx

    gsgtx Silver Level contributor

    its under thm 400 kickdown switch thread by john m he had it on secondary linkage you would need to put it on primary carb linkage.
     
    Last edited: Feb 20, 2019

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