Need a crash course on '65 ST300 Torque Converter Operation

Hi all, sorry if this has been covered already;
Been away for a while, but decided to get back into a Buick recently.
I've got a 1965 Buick Special with a 300/2sp (presumably the ST300).
From regular driving it seems like I have more gears than I know I do.

I need a quick crash course on this transmission.
- Does it in fact have a multi-pitched torque converter?
- If so, what are the approximate stall ratings?
- How does it operate? I don't have any switches like I would expect for the TH400 switch pitch option, so how does it actuate?

Hoping after this info I can work with it rather than fight against it. Thanks in advance!

 

Do you have a plunger switch attached to the throttle linkage under the breather? That's a sure giveaway.

The ST300 was an 11" (?) converter and had a higher stall since they were in lighter cars.

In operation, it should be high stall at lower throttle and kick to low stall at moderate throttle openings. It may also kick to high stall at full throttle but I can't remember. It has been a long time since I drove one with the factory setup.

 

I believe so. I can definitely feel the stall changes. That explains what that plunger is for.

So is it electronically operated? What triggers the stall change?

 

Good rugged transmission, low parasitic drag. Best explained as a two speed TH400, rather than a TH350 or Poweglide (although some internals will cross over like clutches and bands). the 64-67 had switch pitch converters, which is a neat set up and a lot of fun to drive.

 

There are two electrical switches in play. The plunger switch beside the carb energizes high stall around 3/4 throttle opening, it also controls detent (downshift).

The second switch is easy to miss, it's a microswitch at the other end of the throttle linkage arm near the firewall. This switch energizes high stall whenever the throttle is closed. The reasoning for this is that the variable pitch low stall is a bit lower than a typical non-vp converter, and having high stall at closed throttle at a stop smooths idle quality and prevents the car from tending to creep forward due to low stall.

The actual stall speed for the vp converters will depend on engine torque, but a good estimate is maybe 2000 rpm at high stall behind your small block, a bit looser than a typical non-vp converter. Higher yet with this small diameter converter behind a big block.

Here's some switch info from my '67 chassis manual for the ST300 trans.



Devon

 

Thanks for the detailed info Devon. It explains a few other behaviors I was concerned about like the no creep at idle but understand it better now.

It's a very nice peice. I was very confused when the car has such good manners at 40mph but when you step on it, it seems to kick down, rev to accelerate and then settles right down at 60mph again. The low stall feels very tight, almost like a lock up.

 

Sounds like all's well!

Devon

 

Let me expand on what Devon posted. If I'm sitting at a soptlight and my front wheels are touching the white line, I can take my foot off the brake without rolling forward. One of reason they did this is so less brake pedal pressure is required at stop lights. If I'm stopped with my foot off the gas pedal, I can rest my foot on the pedal enough to take the play out of the linkage but not enough to move the throttle plate, this clicks the micro switch putting the convertor into low stall, I can hear te engine bog almost like letting the clutch out on a standard trans. When it does this, it's working the way it should. Very few work the way they should because they get adjusted wrong or people put springs in the wrong place. The spring should be connected to a bracketthe firewall and to the top of the vertical linkage near the micro switch.