TH400 variable stall - Pontiac GTO Forum
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post #1 of 7 (permalink) Old 08-23-2019, 07:14 AM Thread Starter
 
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TH400 variable stall

I have a couple of old "switch pitch" TH400 transmissions with torque converters. This is the old mid 60s "variable pitch" technology that I believe was pioneered by Buick but exploited by many muscle car enthusiasts in the 1970s and beyond. I have one unit that is working fine, and I need to have the other rebuilt. I have two questions.

1) Any feedback on Phoenix transmissions in Weatherford, Texas? They reportedly have experience with these units. Bear, this is real close to home for you, so maybe you know these folks and their work.

2) Any suggestions on who else is rebuilding and/or converting TH400 variable stall speed transmissions these days?

Yes, it is essentially a standard GM TH400 with some very unique components so a competent transmission shop "should" be able to rebuild one. However, if not done properly, it will not function correctly and the benefit of the variable stall would be lost. Parts and experienced builders are getting more rare, so I don't want to just drop it off with a local shop and hope that it is done right. I prefer someone who is familiar with the differences specific to these transmissions and torque converters.

Thanks in advance for any advice.
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post #2 of 7 (permalink) Old 08-26-2019, 03:18 PM Thread Starter
 
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I guess there is not much interest in these units anymore, but just in case someone else is searching at some time, I will post a reply to my own question. The variable pitch torque converter is a really great technology that I wish were still in production somewhere. GM just gave up on it around 1967

The folks at Phoenix Transmissions in Weatherford, Texas have been very responsive and seem to understand these units. The prices sound competitive and I plan to take my unit up that way when I get some spare time.

I will post updates as I go.
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post #3 of 7 (permalink) Old 08-26-2019, 06:09 PM
 
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Originally Posted by michaelfind View Post
I guess there is not much interest in these units anymore, but just in case someone else is searching at some time, I will post a reply to my own question. The variable pitch torque converter is a really great technology that I wish were still in production somewhere. GM just gave up on it around 1967

The folks at Phoenix Transmissions in Weatherford, Texas have been very responsive and seem to understand these units. The prices sound competitive and I plan to take my unit up that way when I get some spare time.

I will post updates as I go.

Keep us posted.

I looked into them years ago in the early 1980's as they seemed to be a little more popular - maybe just more promoted/advertised. Never knew anyone who had one. Problem was that there were not a lot of them to be had. I recall there was one trans specialist that used to advertise them in the magazines. But, it was also about cost and then you have to have the electrical components to make it work.

Today, in my opinion, really no use for them with the lower gear ratio's found in the overdrive transmissions and you still have the OD final ratio - and of course some have the lock-up converters for no slippage at the converter. Same with the 5/6 speeds if you go that route. Lower gearing and different OD ratio's to match the rear end gear so you can install 3.90-4.11 gears for blistering acceleration and drop it in OD and loaf on the highway at 70-80 MPH.

And, converter technology has change, so you can get a good high stall converter that will respond well when you stand on it, yet be "tight" enough that it slips very little so you aren't on the converter like "back in the day." Got a custom built "tight" 2,300 RPM stall converter for my brother's Mopar build - 904 type transmission. Does not slip much at all. The difference in RPM with my foot off the gas to gas applied in a normal manner was 200 RPM's while driving, yet nail it from a dead stop or anything below 2,300 RPM's and it flashes up to the 2,300 RPM's and smokes the tires. Technology has changed and has been an improvement to our hobby.

Keep in mind that you will also want to add a quality transmission cooler as the additional slippage of the converter will add a lot of heat. The factory tank on the radiator won't cut it and you will wind up burning up the transmission.

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post #4 of 7 (permalink) Old 08-27-2019, 01:31 PM Thread Starter
 
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Originally Posted by PontiacJim View Post
Keep us posted.

I looked into them years ago in the early 1980's as they seemed to be a little more popular - maybe just more promoted/advertised. Never knew anyone who had one. Problem was that there were not a lot of them to be had. I recall there was one trans specialist that used to advertise them in the magazines. But, it was also about cost and then you have to have the electrical components to make it work.

Today, in my opinion, really no use for them with the lower gear ratio's found in the overdrive transmissions and you still have the OD final ratio - and of course some have the lock-up converters for no slippage at the converter. Same with the 5/6 speeds if you go that route. Lower gearing and different OD ratio's to match the rear end gear so you can install 3.90-4.11 gears for blistering acceleration and drop it in OD and loaf on the highway at 70-80 MPH.

And, converter technology has change, so you can get a good high stall converter that will respond well when you stand on it, yet be "tight" enough that it slips very little so you aren't on the converter like "back in the day." Got a custom built "tight" 2,300 RPM stall converter for my brother's Mopar build - 904 type transmission. Does not slip much at all. The difference in RPM with my foot off the gas to gas applied in a normal manner was 200 RPM's while driving, yet nail it from a dead stop or anything below 2,300 RPM's and it flashes up to the 2,300 RPM's and smokes the tires. Technology has changed and has been an improvement to our hobby.

Keep in mind that you will also want to add a quality transmission cooler as the additional slippage of the converter will add a lot of heat. The factory tank on the radiator won't cut it and you will wind up burning up the transmission.

Thanks for the response Jim! Even if it was out of pity for my neglected question. I do appreciate your input. You are correct, things have changed and technology has advanced. I guess for a few reasons, I am stubbornly sticking with this technology.
1) I have two complete units I have hung onto over the years.
2) I'm already wired and set up for the switch pitch in my car. I feel like now that I'm no longer a broke teenager, maybe I can finish this car the way it "should have been done" back in the 80s when I started it.
and I think you will most appreciate this,
3) I like to make it work with period correct, factory type equipment. My 65 GTO is not at all original, but everything is some sort of 1960s - 70s Pontiac or GM piece that I have made work. My shifter is a Hurst dual gate out of a 67 GTO, the block is from a 70 GTO, the rear end from a 69 GTO, and then the transmission is likely out of some big Buick of the 60s. I guess when I wear out or break the remaining switch pitch stuff I have, I will have to convert to something newer.

Yes, I have been investigating the external coolers. I have been using an external cooler since I installed the first TH400 in this car in 1986 or 87. The same one is still there It is a fairly small tube-fin cooler and I plan to replace it. I'm considering a plate -fin, maybe even stacked plate, but I'm not sure the cost of the stacked plate is really worth it. I'm open to suggestions there as well.
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post #5 of 7 (permalink) Old 08-27-2019, 06:37 PM
 
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I'm on board with putting the TH400/switch pitch so "I can finish this car the way it "should have been done" back in the 80s when I started it."

And, I can appreciate what you are doing because........... I am doing my resto-mod on my '68 Lemans to mirror what I recall in the mid to late 1970's. Jacked up in the rear, big & littles, 12" wide tires hanging out the rear wheel wells, ladder bars, one piece tilt fiberglass nose with no hood, outside tach mounted in a chrome pod attached to the vented panel right in front of the driver. Just bought a Kraco bolt-on under the dash 8-track for looks, period correct Jensen speakers to mount in my doors (yep, going to cut holes in the new PUI white door panels), Grant steering wheel to fit onto my aftermarket tilt steering column.

I have the aluminum slots, but am not going to use them because the rears are only 8" wide where I need 10". So have another style I am wanting to use. I like the black 5-spoke American Racing wheels, but a little pricey - maybe at some point I will splurge.

Adding a vinyl top, 2-piece rear deck spoiler fabricated by cutting a Trans-Am rear spoiler in half, and plan on fashioning rear window louvers. Have a graphics package in mind as well.

I want a tunnel ram, and it looks like I am going to try my hand at fabricating one. I have an old Big Block chevy Edelbrock UR2 tunnel ran top that mounts 2 Dominators slightly sideways (I like that look of the carbs mounted a little canted for that "cool" factor). I plan on adapters to use 2 matching Q-Jets I have to keep it Pontiac, then form my tunnel ram tubes to the flat plate that bolts to the heads. The Wenzler tunnel ram looks too much like a Pro-stock tunnel ram of the 1980's - I want the Weiand look. Of course got my Doug's headers and plan on Zoomie style pipes coming out from under the car in front of the rear tires - I'll have exhaust cut-outs that'll direct the spent gases out those pipes, nice and loud.

So I have a look in mind and like you, I am no longer a broke teenager - or just flat out broke. My problem is too many projects and not enough time.

Believe it or not, being that broke kid, I used an AC Condensor I pulled from some car I had and mounted it in front of the radiator - just like factory. Then hooked my transmission lines to it. Lot's of surface area. They sell new pretty cheap, so might be something to consider versus a cooler specific for a transmission. Cut the fitting ends off and use a high pressure hose to connect your steel lines together. AC Condensors are pressurized right? So should hold up just fine. https://www.summitracing.com/parts/s...yABEgIIfPD_BwE

So go for it, but do keep us posted as I want to hear what your thoughts are on how the switch pitch works behind a Pontiac. I know the Buick guys used them and they made some impressive 1/4 mile runs with them.
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post #6 of 7 (permalink) Old 09-03-2019, 10:45 AM Thread Starter
 
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Originally Posted by PontiacJim View Post
I'm on board with putting the TH400/switch pitch so "I can finish this car the way it "should have been done" back in the 80s when I started it."

And, I can appreciate what you are doing because........... I am doing my resto-mod on my '68 Lemans to mirror what I recall in the mid to late 1970's. Jacked up in the rear, big & littles, 12" wide tires hanging out the rear wheel wells, ladder bars, one piece tilt fiberglass nose with no hood, outside tach mounted in a chrome pod attached to the vented panel right in front of the driver. Just bought a Kraco bolt-on under the dash 8-track for looks, period correct Jensen speakers to mount in my doors (yep, going to cut holes in the new PUI white door panels), Grant steering wheel to fit onto my aftermarket tilt steering column.

I have the aluminum slots, but am not going to use them because the rears are only 8" wide where I need 10". So have another style I am wanting to use. I like the black 5-spoke American Racing wheels, but a little pricey - maybe at some point I will splurge.

Adding a vinyl top, 2-piece rear deck spoiler fabricated by cutting a Trans-Am rear spoiler in half, and plan on fashioning rear window louvers. Have a graphics package in mind as well.

I want a tunnel ram, and it looks like I am going to try my hand at fabricating one. I have an old Big Block chevy Edelbrock UR2 tunnel ran top that mounts 2 Dominators slightly sideways (I like that look of the carbs mounted a little canted for that "cool" factor). I plan on adapters to use 2 matching Q-Jets I have to keep it Pontiac, then form my tunnel ram tubes to the flat plate that bolts to the heads. The Wenzler tunnel ram looks too much like a Pro-stock tunnel ram of the 1980's - I want the Weiand look. Of course got my Doug's headers and plan on Zoomie style pipes coming out from under the car in front of the rear tires - I'll have exhaust cut-outs that'll direct the spent gases out those pipes, nice and loud.

So I have a look in mind and like you, I am no longer a broke teenager - or just flat out broke. My problem is too many projects and not enough time.

Believe it or not, being that broke kid, I used an AC Condensor I pulled from some car I had and mounted it in front of the radiator - just like factory. Then hooked my transmission lines to it. Lot's of surface area. They sell new pretty cheap, so might be something to consider versus a cooler specific for a transmission. Cut the fitting ends off and use a high pressure hose to connect your steel lines together. AC Condensors are pressurized right? So should hold up just fine. https://www.summitracing.com/parts/s...yABEgIIfPD_BwE

So go for it, but do keep us posted as I want to hear what your thoughts are on how the switch pitch works behind a Pontiac. I know the Buick guys used them and they made some impressive 1/4 mile runs with them.
Thanks for the suggestion. I had never considered that. That would certainly be more surface area for cooling. Are the flow characteristics the same?
I like your description of the 70s theme build. Until a few years ago, I had some classic 8 track tapes you could have played in that tape player, some still in the original wrappers! Please be sure to post pictures as you make progress.
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post #7 of 7 (permalink) Old 09-03-2019, 12:10 PM
 
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Originally Posted by michaelfind View Post
Thanks for the suggestion. I had never considered that. That would certainly be more surface area for cooling. Are the flow characteristics the same?
I like your description of the 70s theme build. Until a few years ago, I had some classic 8 track tapes you could have played in that tape player, some still in the original wrappers! Please be sure to post pictures as you make progress.
I don't know what the flow characteristics are. Good question.

I would think it would be OK, but maybe get a size on the inlet/outlet tubing. Check with a radiator shop or even trans rebuilders. I don't know if the cooling line flow/pressure is part of the operating process of the transmission itself or if a restriction of the flow has any effect on the trans. I was just seeing it as a cooler at that size rather than pressure values of the unit.
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