ST300 Transmission Case

[campfamily]

Looking for suggestions on where to look for a replacement case for my ST300.....I'm thinking this is why my flex plate keeps cracking, at some time in the past, one of the mounting points on my existing transmission has been broken off, and somebody has re-welded it back in place.   Unless this was done perfectly, seems to me that now the transmission isn't lining up perfectly with the engine, which is putting strain on the flex plate and causing it to crack.  My plan is to find a replacement case that hasn't been damaged, and transfer my inners to that case.  Does this sound like a reasonable approach?  Do I need to be looking for anything specific for my GS, or will any ST300 case work?

By the way, I'm located in Southern California (Pasadena area).

Thanks in advance,

Keith

[nut465gs]

Hi Keith,

I looked in my 1965 Buick parts book to see what they had listed for ST300 transmission cases.
Group 4.103  Part # 1357668 ST300 trans case less Gran Sport
Group 4.103  Part # 1372869 ST300 trans case Gran Sport model

Looks like the NK ST300 transmission case is specific to the Gran Sport model. Too bad because I have a ST300 transmission (case) from a Special that I'd like to give away. I know that the NK transmission has a extra clutch plate. Maybe that accounts for the need for a specific case. (?)

John

[campfamily]

John - thanks for looking that up for me.  This might end up being harder than I thought.....

Keith

[Loren At 65GS]

The difference is in the shape of the case where it mates to the block. Small block verse big block. Also, the starter is on opposite sides and as John pointed out, the one extra plate in the forward clutch pack.
A '65 or '66 big block ST 300 from a GS are your options.

  Loren

[campfamily]

Thanks, guys.  I take it these are hard to find?  Kind of like the flex-plates?

Keith

[Loren At 65GS]

Keith,
 As production numbers go, automatics made up approximately two thirds of the total GS production in '65. Total production was 15,780 and 10,359 of that were automatics. I'd say you have better chances then some one looking for manual parts.
There were less GS models made in '66, at 13,816, and I would expect the majority of those also being automatics.
As for the flex plate, Russell Martin has new ones available.

  Loren

[campfamily]

I gave Russell a call a few weeks ago, he was the one who told me that if the alignment between the transmission and the engine was off, even by a little, the flexplate would go. In the time that I've had the car, I've never had a flexplate last more than 2000 miles.  I noticed the broken ear of the transmission case last week when I had the car up in the air, and this seems to be the logical culprit.

I have a used flexplate that I picked up on ebay a couple of years ago.  I'm considering loading the car up on a trailer and hauling it up to Russell to work on for me, his shop is about 350 miles north of me.  I really want to get this fixed once and for all, even if it costs a bit of money to do it.  Alternatively, I may just put a later model trans in it.  I'd really prefer not to do that, my car is mostly original, and I'd like to keep it that way if I can.

Keith

[WkillGS]

Mike in Nor Cal had a trans from the '66 GS he sold last year. Maybe it's still available.

I'd agree alignment is off somewhere, causing the flexplate to crack.
It could be alignment between the engine and trans (not concentric), or even a crank flange or converter mounts that are not perpendicular to the crank/trans centerline.

[Bigpig455]

Kieth - try schlepcar on this formum, he had a line on a ST300 core in Michigan:

http://65gs.com/board/index.php/topic,1686.0/topicseen.html

I just went through this too, it wasnt that hard to find a couple of candidates. I would up buulding a 66 tranny from Dr. Frankenbuick.


Very surprised how different the 65 and 66 tranny's are! Significant differences in the case, valve bodies, front pump, and low servo. I had my tranny guy build me the 66 case with the 65 internals, later he told me he'd wished I'd just have let him build the 66 tranny striaght up....of course he never told me what he was running across, he just kept going.

Also of note: we found that the competition AltoRed Eagle clutches and bands and Kolene steels from a powerglide will fit the ST300, and we increased the clutch pack from 5 clutches to 9.

Still waiting on the converter before it all goes back together..I'm a little sceptical but my guy swears it's all gonna work fantastic.....I'll let you know.