Sicklyscott

Hi -

I have a '65 Cutlass convertible that's been in my family for 30+ years. Around 2000 my father had a rebuilt and slightly warmed over 350 (forged pistons, Edlebrock performer rpm intake and cam, some cleaning up of the I / E ports) and TH350 trans put in. I have no idea realistically how much power this combo makes but it's a dog off the line. The car has the original rear end which I've read is something like a 2.8x ratio that worked ok with the 2 speed but leaves a lot to be desired with the TH350. After a frame-off "resto" I'm not looking into making the car quicker. I'm trying to plan out a 2004r swap and figure it might be the right time to also upgrade the gearing in the rear. Should I also be upgrading the entire rear end to something newer / beefier? I'm not sure I really care about posi / limited slip vs an open diff but I would like to have options for upgraded disc brakes (c5 setup perhaps) in the future. I would like to avoid buying new wheels for now.

Goals for the car is just to have a nice cruiser. I do not plan to race it but would like it to have a bite that matches the bark.

Teach me, fellas!

As she sits, today.

BangScreech4-4-2

Nice car.

A BOP 8.2 rear should be more than adequate for your purposes unless you're going racing.

Not sure how a 2.8 rear gear could have "worked OK" with a Jetaway but not a TH350 as the TH350 has a significantly lower first gear. Maybe you should measure wheel vs. driveshaft rotations to get an idea of what you actually have before you start randomly swapping gears and transmissions.

Optimizing the existing drum brake setup might be preferable to a disc swap for cruising purposes, at least in terms of cost/benefit.

Dream67Olds442

^^^This^^^ - With a TH350 your car should be considerably quicker off the line than with the original 2-speed Jetaway. Determining the exact type of rear end and carrier that is currently in your car will determine what you can easily swap in as far as other gears.

Sugar Bear

NICE ride...

X3, TH350 is a very reliable, strong transmission that will perform well. Follow up on the previous suggestions of tire diameter, gear ratio etc. Also try to learn what you can about the engine through casting, VIN derivative and heads. Also do a compression test.

I'd wait before jumping into the transmission swap. Any idea of the stall speed on the converter?

Rallye469

First I think you should figure out what rear you have.
On the passenger side axle tube, maybe 6” over from the differential there should be a 2 letter code.
Unless it’s been re-geared that will tell you the gear ratio.

There’s places to look up that code online or just post it here.
Great looking ‘65 btw!!!

joe_padavano

The standard axle in a 1965 Cutlass would have been 3.08:1. Optional ratios were 3.23 and 3.55. While 2.78 gears were available in the F85, they were not offered in the Cutlass that year. Of course, who knows what has been done to the car in the last nearly 60 years.

Sicklyscott

Thanks for the responses, I really appreciate it.

I didn't think you'd all question my trans choice so much but since it was brought up, there are a few things worth mentioning.
1. It leaks WAAAYY too much.
2. Before the restoration it made this weird sound when braking, sounded like the driveshaft was rubbing against the exhaust. We tried tracing it down but there was no way the exhaust was touching anything, inches of clearance, everywhere. Post restoration, when making a hard turn it now sounds like the flex plate is grinding against the floor boards but again, no sign of physical contact. I really do think something is wrong, internally. My thought was if you're going to pull it out to rebuilt it, might as just replace it with the 2004r. 4 gears have to be better than 3, no?

I used the term "woriked ok", loosely. Hard to compare because so many things changed between the Jetaway and TH350 change but, back in the 90's it felt quick (I was also in my teenage years, driving a Dodge K car to school every day).

Brakes have been optimized, already. Working as they should. I'd still like better stopping power on the highway.

Yes, it is faster but again, so many things were changed at the same time, I can't tell what part was trans and what part was a fresh motor. I did look for the stamping on the axle when the car was blown apart a few years ago, never found one. It does measure up like the stock housing and from a mechanical sense, much of it was original when my father got it in the 90's and he never changed the rear out.

No clue on the stall coverter. I'm going to assume its whatever OEM would be.

Engine is an early 70's block with #7 heads and 9:1 forged pistons. Heads were "cleaned up" but not extensively ported. Edlebrock Performer RPM intake and matching cam. Holley 750 cfm carb. W-31 style exhaust manifolds with 2.5" exhaust afterwards. I have all the paperwork on the motor work.

I'll look again this weekend.

Thanks for the info. I doubt the gearing was changed. It was owned by the original family to the mid-80's, older gentlemen who didn't really tinker with it. Passed hands to a college student who we happen to know, then to a mechanic's girlfriend who used it as her beach car, then my father. Car also doesn't have many options so I don't think it's anything but the standard.

Fun71

Interesting. I have never heard of 9:1 forged pistons for an Olds 350 engine.

joe_padavano

Obviously stock pistons were cast. You can get aftermarket low compression forged.

olds 307 and 403

Assuming the 6cc dish Speedpro forged pistons. You need a 2500 rpm stall minimum with that cam. The factory 1600 stall would be awful off the line. A 2004R with a 2500+ stall and 3.73 or 3.90 gears would be a great combo with that cam.

Fun71

Good call. That’s a bigger cam than in my engine (mine is 217/221) and I have a 2500 RPM converter.