Tranny ID

[Tom Kochtanek]

Cleaned up a three speed (I assume Saginaw, but I didn't write the numbers down) I snagged out of a 1961 Impala that was converted from an automatic. I noted this "thing" stuck on the side of the transmission. Is this an overdrive unit? How do they work? Are these desirable?

Pics attached. Thanks for your insights!

TomK

 

[oldskydog]

Yep, Its an overdrive. Desirable if you want an overdrive but there's a reason they weren't offered in 348/409 powered cars as they weren't strong enough to take a high torque hit. Works good with SBC. You can hook it up electrically or with a mechanical only setup which gives you effectively 6 speeds. The only problem with that is you have to remember to disengage it or do a lot of downshifting.

 

[Tom Kochtanek]

Numbers

Thanks Cecil, that's what I thought. These might have been found behind a 250 horse 348?

Here's what I found on the various cases:

Main: 3744920 casting with "F202" date
Tail : R10K-1 and "G11"
Shift cover has "3741357" on it.

It's cast iron from head to tail.

Thanks!

TomK

 

[oldskydog]

Thanks Cecil, that's what I thought. These might have been found behind a 250 horse 348?

Here's what I found on the various cases:

Main: 3744920 casting with "F202" date
Tail : R10K-1 and "G11"
Shift cover has "3741357" on it.

It's cast iron from head to tail.

Thanks!

TomK

Tom,
It might be ok behind a mild 250hp as long as you don't dump it but Chevy never offered it on the 348. Yours looks to be a June 62 version which was pretty much the same as when it was first introduced in 55. The gear ratios are:
Locked Out Locked In
1st 2.94:1 2.058:1
2nd 1.68:1 1.176:1
3rd direct 0.700:1
Reverse 3.33:1

 

[Tom Kochtanek]

3 speed 348?

Cecil:

What standard shift three speed transmission did they use behind the 348 in 1961? My 1961 Belair was a factory 348 and she has "three-on-the-tree". Engine and tranny are long gone. Was that perhaps a BorgWarner three speed?

Cheers!
TomK

 

[Skip FIx]

My dad's old 58 Chevy wagon had a OD standard in it, pretty sure it was a 283.

 

[oldskydog]

Cecil:

What standard shift three speed transmission did they use behind the 348 in 1961? My 1961 Belair was a factory 348 and she has "three-on-the-tree". Engine and tranny are long gone. Was that perhaps a BorgWarner three speed?

Cheers!
TomK

Tom,
It was the same old Saginaw 3 spd that has been used in it's basic form since 55 which was a more modern version of the old Saginaw design that has been around since the 40's. There was a lo perf version which was intended for the 235 and 283 applications with 2.94 1st, 1.68 2nd, direct 3rd, and 3.33 rev.
The standard ratio trans for the 348, 409, and Corvette 283 engines had 2.47 1st, 1.53 2nd, direct 3rd, and 2.80 rev. The main cases allhad the same casting number 3743368, the pass car extention housing was 3741456 while the Corvette was 3787067 ( with shifter mounting bosses), and the side cover was 3741357 except Corvette which was 3731911. As far as I know the difference between the lo perf and standard ratio trans was in gear ratio only and not overall strength.

Those numbers were from Colvin's CBTN but I think he made a mistake. He shows the 3 spds all being the same overall length at 22.5 ". That was true for 55-57 but in 58 I'm pretty sure the pass car trans changed to the 17" shorty while the Corvette kept the long version. I have trans which I took out of a 61 Bel Air which is the shorty version and I believe it's correct for 58-64.

 

[1961BelAir427]

I was reading a little about these in HOT ROD DELUXE Sept.'08 Issue and it mentioned that these OD units will bolt to all the Saginaw 3 speeds. That you just replace the tailshaft. It went on to say that it was rumored that you can replace the tailshaft on a Saginaw 4 speed with this OD tailshaft, but that this wasn't confirmed by the author. Does anyone here know if this is the case???

 

[68-biscayne]

Try this link:

http://www.hotrodders.com/forum/saginaw-4speed-overdrive-conversion-pics-included-10824.html

Not sure if the era of the transmission is the same or not.
Kentt

 

[1961BelAir427]

Thank you. From reading that it looks like our OD units are Borg Warner manufactured, and the 65 and later ones are Saginaw OD units. Looks like the BW ones won't adapt to the Saginaw 4 speeds but the Saginaw OD unit will swap right on. Figures....I have two 61 3 spd with OD trannies, but have never even seen one for 65 and up.