[THEGTOCHISM]

I am working on a 84 Grand GP . I replaced the 305 with a 350 engine. And disconnected all emission controls . The wire to the torque converter is now disconnected. I see no difference in performance or driving. car is not a hot rod. Do i need this wire connected? can/Should it be by passed by a switch?

[John62]

Places like jegs and summit make lock up kits for things like this, don't cost much. Your convertor/trans could overheat on longer rides if left unlocked over time. Without the ECM your Air Cond. will not work unless you bypass the relay to the compressor.

[THEGTOCHISM]

Originally Posted by John62

Places like jegs and summit make lock up kits for things like this, don't cost much. Your convertor/trans could overheat on longer rides if left unlocked over time. Without the ECM your Air Cond. will not work unless you bypass the relay to the compressor.

Thanks for the reply. I can't seem to find anything on a by pass for the 350 just the 200 and 700R transmissions. I cut/removed all the emission wires and it runs great after i added a new none computer controlled dist. Funny ac still works great. i didn't need to by pass it. I will check summit again.

[John62]

My understanding is you changed the motor from a 305 to a 350 but kept the 200r trans. That is the lock up kit I was thinking of. If you have a turbo 350 trans you are good unless you have a rare switch pitch trans.

[77 TRASHCAN]

Not sure about doing any damage, you are losing the lockup function. The engine is turning 300-350 more RPM's going down the highway, than it would if it were locked up.

I had a lockup TH350 in an older car. I ran a wire from a key on power source to a stoplight switch (has 4 terminals, standard motor part number SLS89, used on factory cruise control cars). The stoplight switch disengages the converter when the brake is on. Then ran power wire from other terminal of stoplight switch to a vacuum sensor switch under hood. I don't have a part number for it, but every GM vehicle with a lockup converter had one. It senses low vacuum in the engine (as in full throttle!). The vacuum switch will need a small vacuum hose run from it to a full time vacuum port on the intake or carb. The other wire coming out of the vacuum goes to the converter solenoid connection on the trans.
I do not know which terminal is the lockup solenoid...

This worked for me for years. I got rid of the car I had the engine and trans in, will have to experiment when I install this engine and trans in an old pickup.

[THEGTOCHISM]

thanks for the information on the torque converter lock up on the th 350 transmission

[Overkillphil]

I've run them with the lockup disconnected in some cars for years and never had an issue. The aggravating factor is the rear end gears. 2 series gears will prefer the lockup function to keep the heat down in the trans. 3 series-up should'nt be a problem unless you have tall tires out back.

[Bobalong]

You guys that have run the 350 transmission, I was told the drive shaft is a direct swap between the 350 and a 2004r in 70 GTO - A body. Does anybody know from experience if this is true ?

[Overkillphil]

Yes, I used a TH-350 driveshaft from a 70 LeMans Sport when I did the 200-4R swap in the 70 GTO.

[THEGTOCHISM]

Thanks overkill i have 245x60x15 tires in the rear so it should not be a problem. I may add a transmission cooler when i do the radiator swap

[Schurkey]

Originally Posted by John62

If you have a turbo 350 trans you are good unless you have a rare switch pitch trans.

So rare that there were zero made. The THM 400 had a switch-pitch converter on some pre-68 models. The THM 350 series had only a lockup converter on some models (THM 350C).





Failure to engage the converter clutch will increase cruise RPM, reduce cruise fuel economy, and increase trans temperature. If that sounds good to you, drive it that way.

I wouldn't.

[dataway]

My 68 GTO had a PX THM 400 with the typical kick-down switch. I took it off the pedal and wired it to a toggle on the dash .... which if my memories of my 17 year old life are correct ...it seems to change the stall on the converter .... is that a real thing??

[John62]

Originally Posted by dataway

My 68 GTO had a PX THM 400 with the typical kick-down switch. I took it off the pedal and wired it to a toggle on the dash .... which if my memories of my 17 year old life are correct ...it seems to change the stall on the converter .... is that a real thing??

You are correct, they made them on the t-400 and the 2-speed powerglide and so that is why I thought the original post was about that. I think some trucks got them to help pulling. They require a special matching convertor. Had a 2 speed in my first 65 GTO, lot of fun, like you i had a switch under the dash and when engaged I could take my foot off the brake and the car would not move. Then stomp on it and the motor would rev up and away you go, at least your tires did. I think it added about 1000 stall.

[dataway]

Don't mean to hyjack this thread .... I'm not the OP, I was just wondering if my memories are correct. The PX THM400 is pretty much the standard 68GTO auto, the switch just alters the pressure to the converter right? It's not actually a "switch pitch" is it? If it is ... I'd probably want to keep my original converter.

Again ... sorry to the OP, didn't want to redirect this thread.

[THEGTOCHISM]

Originally Posted by dataway

Don't mean to hyjack this thread .... I'm not the OP, I was just wondering if my memories are correct. The PX THM400 is pretty much the standard 68GTO auto, the switch just alters the pressure to the converter right? It's not actually a "switch pitch" is it? If it is ... I'd probably want to keep my original converter.

Again ... sorry to the OP, didn't want to redirect this thread.

not a problem. All information is valuable. a fella over at Monte Carlo sent me a drawing on how to connect it once the computer is by passed. Buts its only about 300-350 more rpm difference, And possibly a couple of gallons more gas per mile. . I'm going to leave it alone for now until warmer weather.

[Schurkey]

NO switch-pitch after '67 model year (i.e., '68 and later.) '65--'67 for those THM 400 that were equipped with switch pitch. Not all were. No switch pitch on the '64 THM 400, either.

NO switch-pitch on Potatoglide. There was a two-speed "300" trans, some of which had the switch-pitch converter.

YES, the stator angle actually changed on a switch-pitch converter, affecting the stall speed of the converter. The converter from a S-P "300" would slide right in place on a S-P 400, adding a bit of stall speed in both the high- and the low-stall positions.