I think the posi was only fitted with 4:11 and it wasn't all that much freeway friendly.

I think the powerglide came on 6cyl and 8cyl back then, plus the early 3-speed TH might have been available (you could Google to verify but its irrelevant to your plans so not going to myself). I feel like those were all with 3:36 in the third member. Great freeway, okay street bottom end.

There were some Buick gearsets back then that were in between 3:36 and 4:11 and actually fit. But today I would check speed shops for full kits.

 

Adding:
I just revisited these online. Age sux lol.

Look for a 3:55 it will add grunt that better matches the 200r4 output. There is a 3:70 but it might negate any overdrive ratio inside the 200r4. But it would be fun!

 

Thanks for your reply, i looked into the 3spd TH350 but i want the overdrive the 200R4 offers.

To clarify, my car did not come with the posi, it was added later by a previous owner who also swapped the motor for the 350 i ended up with now.

The 3:55 is what I had in mind if I go with the 200R4, just i'm having trouble finding any for sale at a reasonable price. The th350 are abundant and cheap, trying to think if there's a way I could use one with maybe a 3:36 and what the rpms would be at highway speeds in 3rd.. if I can manage 120kph and under 3k rpm I might do it.
But so far my calculations with a 205/75R15 give me 120kph at 3100rpm

Is cruising at 3-3.5K on the highway bad for the motor?

 

The '69 350ci sb motor won't care about 3100rpm it'll do it just fine. Use a full size modern radiator and a separate trans cooler.

Putting it into my lingo 120kph is ~75mph.
The 200R4 output in overdrive is 0.67 which is impressive. To get the actual highway rpm low as possible you need 3:36 rear end. You can leverage extra by going to 17" wheels.

But getting overdrive rpm down below 3000rpm you need to sacrifice the 4:11 and if calcs were run I think even 3:55 would miss the mark.

Your 350ci sb already has a 4bbl manifold, right? If you use a double-pumper 4v carb you can get hp back up for low end. But that sacrifices on the other end and will be a spendy gasoline bill at freeway speeds. It seems like you're gonna need to revise your vision. Settle on a reasonably affordable traveling vehicle. Or a street rod bar hopper.

Here's all gear ratios for 200R4 (aka 200-4R)

 

Just to add a little extra, the only Auto Trans available in '64 was the Powerglide. Also, you could get a Posi Rear in any of the available Ratios. I also agree with the 3.55 Ratio. I believe that would be a good choice with the OD Trans.

Also, stop by the other Impala site if you would like. We would like to hear more about your '64 over there:

Impalas.net

A forum community dedicated to Chevrolet Impala owners and enthusiasts. Come join the discussion about engine swaps, performance, modifications, classifieds, troubleshooting, maintenance, and more!

www.impalas.net

 

Are you working with a unilug 200R4 from a 305 Camaro/Firebird? Unless it's hardened internally one good stomp may shred the input clutch and break the low/reverse sprague. Speaking from experience with this one. Length is the same as the PG/T350 but the rear mount is further back just under the output shaft seal. Consider having it brought to the Buick GN spec before getting ambitious with the throttle.

 

I cant say specifically what car the 200R4 would be from, i'd be picking up one from a wrecker or off fb marketplace, and get a local transmission shop to rebuild it.

 

There were I think metal tags riveted on side with identifier, they usually survive. Also a savvy seller might recognize a clue like the rear mount being further back like @Brhatweed pointed out. Or maybe they have several units to compare.

 

The rear mount is located further back than the pg/350 on all the 200r4, not just some of them, so there's nothing to recognize, i think you've misunderstood.
The crossmember gets moved 6.5" back.
But I will look for a tag on the case when purchasing the core.

 

Okay. So that would leave only the metal tag. It had a code and I don't remember anything except we used it to find out what vehicle they came out of. Hope my old memory is correct lol. I'll do some looking.

Hope this is it.

 

Give me the trans tail code and I can look it up... have lots of experience with this transmission going back to when they were new. The 200R4 and it's older cousin the 200C are all unified cases meaning their is no tail housing, the 200R4 also uses a throttle valve cable not a vacuum modulator to control shift points & pressures and having a means of locking the torque converter in 4th is strongly recommended to keep from overheating even with an external cooler.

 

What can you tell me from looking at this?

 

Which kickdown cable did you use?

 

1981-1985 Oldsmobile/Buick/Cadillac RWD sedan with the 307 (VIN-Y) engine throttle valve cable will work with these.
Code OM was a diesel Olds spec 200R4 thru 1984

 

Hey guys, an update after 1 year.
I had the 200R4 tranny installed in the fall of 2024.
Being my 1st classic and also domestic car, I really did not know much about the car or how to identify the components, so I realized the hard way the seller lied about many things.
My car does not have a 350ci, it has a '87 camaro 305ci. It did not have a PG, someone along the way swapped in a TH350. My car also does not have a posi as i was told.
Anyways, here we are, my tranny is in, and i have purchased a '62 corvette posi diff which I will be installing next week. the diff came with 3.36 gears and someone on fb market place has some 3.55s i might pick up.
With the current set up my car got up to 150 km/h with relative ease on the highway. Check out the video of our cruise below.

Next week I am getting new power steering lines along with posi diff installed. I'm excited!

 

Have you checked out our sister site, Impalas.net? They're more focused on the older/vintage Impalas.