Why was the TH400 SWITCH PITCH discounted ?

Can anybody shed some light on this question?

I've heard from a guy that had this Torque converter in a 67 Skylark 400, it worked very well and added a lot of power to the Buick.

I have never heard of one, and I'm not sure, was this only build by Buick?
What was Buick's purpose of developing the switch pitch? Pro's & Con's.
VET (Navy)

 

And on that note... can a SP converter be used in a non SP trans or a SP trans / converter be used as a TH400 W/O the SP being operational?

 

They were available in BOP cars 65-7. Here's a primer on them.
http://www.buickperformanceclub.com/switchpitch.htm

 

The stator support splines and front shaft are "paired", so you need the correct one to match a SP or non-SP converter.

But all you actually need to do with a SP trans, is disconnect the wire on the side connector to disable the converter from going into high stall, and it will otherwise act like a typical -400 (the exception is the valve body differences that also affect 1-2/2-1 shift points.

If you "convert" a non-SP trans, you also need to have the small orifice cup plug installed in the front of the case. Install the vane solenoid and two terminal case connector, switch(es) to control or other method to actuate the feature. (I have the notes/drawings on a lot of this if you want them).

 

Thanks but was just playing with ideas. Going to remove the race TH 400 out of the RaSabre before I list it forsale and had a couple of SP trans / converters I was considering using .

 

ALL - I meant to say Discontinued......

Sounds like the TH400 switch Pitch Torque converter was a real performer.

Wonder why no one ever picked up where GM left off?
Too expensive to produce?
Better modern-day torque converters is my guess?

 

My bet on discontinuation was cost, as you mentioned.

I sure LOVE mine! Best of both worlds (high/low stall), even more fun when modified to give the converter's stator piston further travel for even more stall.

Devon

 

Maybe went away when the lock-up converter was starting to come out?

 

Maybe the ‘modern’ engine (400/430) didn’t need it, but the Nail did?
Patrick

 

I read somewhere that the main reason for the switch pitch was to reduce brake pedal pressure at red lights. If the front tires of my 65 Special are touching the white line at a red light I can take my foot off the brake. When apply light pressure to the throttle closing the micro-switch, I can hear the engine bog almost like letting a clutch out. If you want to get out of the hole fast: leave your foot off the throttle and floor it, it will stay in high stall for 1.5 seconds before it goes into low stall which will give you an nice launch. It is also possible to add a toggle switch the the linkage micro-switch so you can control stall. A good source for ST400s is 65 to 67 LeSabres that came with 300/340s, it's the same bell housing as a 455.

 

I think KB made a switch-pitch kit at one time.

 

Sure did. And if anyone comes across a Poston-modified VP converter, post here before buying it. You will have second thoughts after hearing about the mods they used, which may result in catastrophic failure of the converter and thus the transmission.

Devon

 

I would bet Buick ultimately realised it wasn't necessary with a three speed transmission. First was low enough.

 

Gas was cheap and the slightly better mpg and better performance with switch pitch wasn't worth it to GM given the extra cost to produce. Reliability was never an issue as far as I know......

 

I have a modified SP converter.. Is there any way to determine if it's a Poston from outside markings? Specifically how did they screw them up?

 

Thanks Larry, I'd better go make anothe cup of coffee, I've got some reading to do.

 

Two reasons from what I have heard, both covered already.

Cost.. Considerably higher than a fixed pitch unit.

Not needed anymore- One of the main reasons for the use of this converter is that as the power wars heated up in the 60's, the current big car engine of the time, the nailhead, required what for the factory, would be considered very long duration specs on the cam. This caused unacceptable rocking of the engine at idle, not something many Buick buyers of the time were interested in. The nose switch on the VP converter throttle switch put the converter in high stall when you stepped off the gas, which help soak up that camshaft lope. In 1967 the last series BBB engine debuted, which feature conventional wedge style cylinder heads, and the long duration cams were no longer desired, so the VP was phased out of production in that year.

And no, a VP converter requires a unique pump to be able to even mount the converter on the trans, so the entire package is required, regardless if of you use it or not.

JW