Hot Rods ST400 Switch Pitch converter

I'd like to find a stock converter for mine. I had it in the Studebaker with my blown Hemi. The thing took an insane amount of abuse. It was a regular 400 ('69 case) that I converted to Switch Pitch. All this was ahead of a Gear Vendors overdrive. I only went to the S/P because I thought my big cam wouldn't play well with the low stall speed I wanted for land speed exploits. As it turned out, the big hemi could idle down to 700 RPM in low stall, so I've since pulled it and am going back to a conventional low stall converter 400. The S/P will live on in my next project, but I really don't need all the stall the high side has.

 

A couple of switches in the throttle linkage. Buick had the convertor go to high stall at idle. That kept the car from wanting to creep while stopped and made for a bit smoother idle. Once off idle the convertor went to low stall unless you went to about 3/4 throttle when it switched back to high stall. 400 transmissions without the switch pitch have something called a part throttle down shift. If you are in high gear and jump on the throttle, but not wide open, the drop in vacuum at the modulator will cause the transmission to downshift to second. That only happens below about 40 mph. With the switch pitch, the transmission won't downshift under these conditions but it will go to high stall if you get to about 3/4 throttle. It's a bit like a second gear downshift, but much smoother.

Both versions of the 400 will have a full throttle downshift. This is through a switch on the throttle linkage.

 

Yes, a switch activates the solenoid, which in turn, directs fluid to a small piston deal in the center of the stator, which then angles the fins...Big windows in the stator = low stall.. Steeper angle =high stall.
I don't know what the spot welds on the impeller are for. I don't recall any difference inside.
It's all done by the stator...Maybe an identifier?

 

maybe as a stiffener/strongback ,if the fins are hinged inside there....

 

Nope...Fins in the pump (impeller) don't move...except with the engine ;-)

 

It would appear that some switch pitch converters have a sort of cover over them.

This might have been an attempt to move air over the converter to reduce heat.

I have seen two ST300 torque converters with this shroud on them:

The spots where it was welded on were right where the "dots" are on the converters without the shroud.

I can only speculate, but the converter body may be set up for the shroud, but they simply stopped using it at some point.

 

I can't get as technical as some of you, but noted above someone mentioned a plug in the trans and an electric throttle switch as potential identity. We stuffed a 65 Cadillac 429 in a 38 Dodge pickup, it has that same deal on it. I was too young to know anything about that shit, I just know when we stomped it down it hauled ass! Seems to me those Caddy models were also BOP bolt patterns, but that gets into more cobweb laden memory. Maybe it helps, maybe not.

 

Cadillac, like buick nailheads, had their own bolt pattern through 66. The BOP began use in 64 on the mid size non-Chevy engines, it was like the Pontiac, but slightly different.

The air cooled shroud was used on some Powerglides...I didn't know they ever had it on an ST300. The Dacco number for the ST300 converter was B1. The number for the non-switch pitch 300 converter, also used in BOP TH350s, was B1A. The Chevy version (with pads instead of threaded lugs) is B35, which was used on the TH350 starting in 1969. The ST400 converter was B2, while the TH400 converter (3 lug) was B3.

I got to help unload the Dacco truck at the transmission shop in Tucson in 1982-3, so I got to know them a little bit.

 

The th400 switch pitch that I have came behind a 67 340 Buick. I used a chevrolet trans behind it, and threw the switch pitch in the shed where it still rest. The trans man that I knew (RIP Rod) showed me about them, said the easy way to tell on the th400 was the electric plug on the side of the trans would have two prongs one for the sp and the other for the kick down.

 

I have a 70 Cad TH400 in my 49 Buick. It is not a switch pitch, but has a 2 prong plug on the drivers side. One for the kick down, and I have been told the other is for some kind of pollution control system.

 

The double plug was used in the early 70s on cars with TCS (some kind of pollution control system). 1967 was the last year for switch pitch. The TH400 has a tag on the side that will tell you what year the transmission is. But since people swap parts, the only sure way to tell is to look at the input shaft and stator support.

 

I think the idea of a dual stall speed torque converter is the best idea since sliced bread. I don't understand why the aftermarket hasn't developed this idea and ran with it.

 

On some light cars, the convertors are air cooled. There is no trans cooler in the radiator. That's what the shroud is about. Most of the transmission heat is generated in the torque convertor.

 

the man could have told me wrong or i didn't listen real well. he did hand me a vega convertor that was supposed to be able to use in the th350 or th400 for a stall, but the input on my th400 trans was to big to fit, so i used a 350 convertor.

 

The Vega used powerglides as well as the TH350. If you try to use a Vega PG converter in a 350 or 400, it wont 'fit, because the input shafts on a PG are coarse, and 350 and 400 are fine.

But a TH350 converter from a Vega is a pretty small converter, and will give you more stall speed in a TH350 or 400, behind a V8. It's a really old trick...which drove up the price of Vega converters to where you're better off getting something from the aftermarket.

 

Most, if not all of the 3 speed Vega converters will slip right onto a 350 or 400 trans. It has a smaller bolt circle than the 400 converters.
Sometimes called the poor mans "stall" . A light duty, weak unit, as one would expect.Anything with some hp and weight will rip the cast, riveted in turbine hub out of it.
On top of that, everything inside is wrong for getting one to couple up in high gear.

 

The records from Hydramatic were never very detailed, nor were they fully digitized for storage at The Heritage Center. I was not ever able to get any good information about any transmission from them, other than what was already out in the wild.

I cannot find any reason for the bumps on the converter housing, and it would seem that nobody else has, either.

For those that are unaware, they are on the inner edge of the doughnut, and the outer edge of the doughnut.

This is the appearance of a ST400, and TH425 (FWD 66-67 Toronado) converter. I suspect that they are the same one.



This is what makes the ST400 different from at TH400 (plus the holes and passages in the case, as applicable, and previously described by Squirrel).


That's what leads me to believe that they were placed there for a feature that was never implemented.

 

if only we had a bigger lathe.....

 

I could program the CNC to part one in two, but at what cost?

I have not yet decided if I want to use my SP TH425, or the fixed-pitch one.

I have enough viable parts to build and run the SP one, but am wary of running what might be a "dead end" should I have a failure, especially in the field.

Either way, my setup has exactly one mission-critical bespoke part, and I made, and will carry a spare.

 

I don't know, but that's not a good place to be drilling holes and then plugging them ;-)

 

I've been running a variable pitch (the proper term) 400 for 30 years in my wife's pro-street Corvette. Mine has an 1800 low stall and 4500 high. It works flawlessly. We ran a 3500 fixed stall previously and didn't like the mushy, slipping feel on the street. This one is connected to the brake light switch so at a stop it is in high stall so it doesn't drag the engine speed down. Step off the brake and you can feel it switch to low stall as the converter "tightens up" and car picks up speed without extra throttle. The shifts are nice and crisp. I even figured a way to make it launch in high stall (for good launch)and automatically switch to low stall (for less slippage)about 100 feet down track. It's much more pleasant on the street than a typical high stall converter. I have been told that the car would probably E.T. better with a normal high stall converter because they are smaller and lighter, but the drive ability is worth more than a few tenths to us.

 

I did, a brand new 18x80 with 21" gap, 10 hp.
But I'm better now!

 

I started with these in my truck over 40 years ago, I put a toggle switch on the shifter. I've been driving with them so long (in several different cars), it's just an instinct to flip it into high stall as I come to a stop, then low stall after I take off. Or if I'm racing, I leave it in high stall.

There are a lot of ways to do it. The brake switch is a good one.

 

Does Bruce Roe still make his controller for Switch Pitches?

 

Searches go cold about 6-years-ago.

 

I am pretty sure I have one about 1.5 Hours North in Mexico, MO. I looked around last night and found 3 ST300 convertors that I'm not ready to part with, but I am pretty sure there is one or two ST400 convertors around here too, I just have to find them.

 

Are you referring to the two additional pump bolt holes or fluid passage holes?

 

I was referring to the fluid passage

 

I bought one off him, but it was probably 5 years ago. It works great.