Gearing change... rear end or transmission?

[Just Carbs]

No drum on the trans.

This car was born with a 727. The 833 was transplanted in.

Does your trans have a 2.66 or a 3.09 first gear? 2.66 I think.
From what I can gather the factory 4sp OD trans has a "3.09" first gear with a .73 overdrive 4th gear.
It would appear that the factory 4sp overdrive trans will cut the cruise rpm and still pull away from the stop light without burning up the clutch.

It can be found in these cars with the overdrive.

• 1975 to 1979 Valiant, Duster, Dart, Scamp, Swinger, Volare and Aspen (3.09:1 ratio first gear)
• 1975 to 1987 Dodge light-duty pickups and Dodge and Plymouth vans (3.09:1 ratio first gear)
• 1977 to 1979 Diplomat and LeBaron (3.09:1 ratio first gear)

 

[Polara_500_Jr]

Does your trans have a 2.66 or a 3.09 first gear? 2.66 I think.
From what I can gather the factory 4sp OD trans has a "3.09" first gear with a .73 overdrive 4th gear.
It would appear that the factory 4sp overdrive trans will cut the cruise rpm and still pull away from the stop light without burning up the clutch.

It can be found in these cars with the overdrive.

• 1975 to 1979 Valiant, Duster, Dart, Scamp, Swinger, Volare and Aspen (3.09:1 ratio first gear)
• 1975 to 1987 Dodge light-duty pickups and Dodge and Plymouth vans (3.09:1 ratio first gear)
• 1977 to 1979 Diplomat and LeBaron (3.09:1 ratio first gear)

I do not know.... unfortunately the trans was in the crate ready to be installed. Can't find any purchase information on it either.... Makes it so much more fun with the limited knowledge of where he got the parts.... or in some cases who they were sent to to rebuild, never did locate the carb he had on it.

 

[Polara_500_Jr]

So here's about the knowledge I have on this transmission.... So it was in that crate in the shop since at least 2011..... @HWYCRZR and I got it installed in the car in 2023, about 2 years after dad passed and left me with a basketcase.

 

[Polara_500_Jr]

So here's about the knowledge I have on this transmission.... So it was in that crate in the shop since at least 2011..... @HWYCRZR and I got it installed in the car in 2023, about 2 years after dad passed and left me with a basketcase.



View attachment 680200

He was worse at procrastinating than even I knew. I completed some of the window gaskets 2 weeks ago. He bought the parts, but always had better things to do than install them.....

 

[Ripinator]

It's a no brainer for me.
Swap in 27 to 28 inch tall tires.

I'm running 235-75X15 tires on my 66 300 with the 2.94 gear. Worked out great. I think those tires are at least 28 inches tall.

 

[Polara_500_Jr]

I'm running 235-75X15 tires on my 66 300 with the 2.94 gear. Worked out great. I think those tires are at least 28 inches tall.

I'll get that measurement tonight as well. I want to swap out the wheels....but not yet. Just not a fan of the Mopar Road wheels.

 

[Ripinator]

I'll get that measurement tonight as well. I want to swap out the wheels....but not yet. Just not a fan of the Mopar Road wheels.

Then go with Dodge Diplomat 15s and poverty caps. . . I'm running those wheels on my 66 with disc brake wheel covers

 

[Polara_500_Jr]

Then go with Dodge Diplomat 15s and poverty caps. . .

I really want to put a set of 17" Torq Thrust wheels on it. I know, I know.... we all have different opinions on wheels

 

[Ripinator]

I really want to put a set of 17" Torq Thrust wheels on it. I know, I know.... we all have different opinions on wheels

I like those wheels too. Torque Thrust Ds!

 

[Polara_500_Jr]

I like those wheels too. Torque Thrust Ds!

Technically I like these slightly better. very similar, but I like the sharp crease in the spokes rather than the curve... after all, a 65 slab side has very few curves but lots of sharp angles!

 

[Polara_500_Jr]

OK. Some numbers. Waaay better than I expected.
The recap of the basics, 383, 500ish miles on fresh rebuilt heads, with new hp manifolds and a new edelbrock 800 AVS2. Newly rebuilt a833 with a new performance clutch. Basic carb tuning by myself and @HWYCRZR. (tuning was simply idle/air circuits and then lighter springs.)

60mph=2600RPM
70mph=3000RPM
80mph=3400RPM

These are read from the analog tach in the console, that I think is pretty accurate, and the speeds are as indicated on the speedometer, which is 5-6 mph fast when compared to GPS.

Trip tonight was 99.6 miles, and burned 5.1 gallons of 91 ethanol free. This is at an average speed of 65-70.

19.5 miles per gallon. Much better than I had expected. Much better. I will keep quiet about gear changes now, and be quite happy with the performance to mileage I get. That said, when it's time for new tires (and wheels) I do plan to go maybe an inch larger.

But I'll listen, y'all almost overwhelmingly said leave it alone.... and while it feels high revving, maybe it's not as high as I thought. It's my first classic that can reach these speeds realistically. The 40 Ford is screaming at 50, and I am not pushing an 84 year old car on it's original engine very hard.

I also realized I need a cruise... I do terrible keeping a steady speed, but at least I tend to slow rather than accelerate, I can't afford a ticket in Minnesota.

 

[71Polara383]

Think of the mileage with an OD 4 speed though...

Id say besides changing tire size, maybe down the line swap in the later OD trans. Otherwise leave it be.

 

[Just Carbs]

The "engine" is most efficient at the max rated rpm point where it makes maximum torque with the engine AT FULL THROTTLE carb opening. Not at max torque rated rpm when at "part" throttle.

The car might "need" only 50 hp (arbitrary number) to go 70 mph. The engine may make 50 hp most efficiently at 2400 rpm with 1/4 throttle opening. So, your best mpg at 70 mph would be with the car geared for 2400 rpm at 70 mph. Or something like that.

Now, the car has all the arrow dynamics of a brick. And a bricks wind resistance increases at the square of the increase in speed. Or something like that.

So, best mpg will happen at about 50 mph turning the engine at about 1800 rpm. Or something like that.

But I would be impressed if you could hold your speed down to even 60 mph.

So, give it the "factory" 4sp overdrive for mpg, with the 3.09 first gear so the clutch survives.

My 75 dart 318 motor 2.96 rear gets 18 at 70 mpg.
My 87 Fifth Ave 318 motor 2.20 rear gets 24 at 70 mph. It has a lower first gear lockup convertor auto trans. Plenty of power, for me.

3000 is a lot of unnecessary rpm.

 

[mr gtx]

since it is a 4-speed i would not change gears. if anything go with an inch taller tire. your standard 4-speed is running about 200 or so less rpms than an automatic because of torque converter slip.

 

[Polara_500_Jr]

Think of the mileage with an OD 4 speed though...

Id say besides changing tire size, maybe down the line swap in the later OD trans. Otherwise leave it be.

Long term... definitely. When I can source an OD trans at a decent price I will jump on it.

 

[Just Carbs]

Long term... definitely. When I can source an OD trans at a decent price I will jump on it.

Might end up wanting a 3.55 rear to go with the od.

 

[Polara_500_Jr]

Might end up wanting a 3.55 rear to go with the od.

That is part of the joy of old cars. You can tweak things to be what you want and how you want them!! you never have to be "done" with one.

I can drive and enjoy my Polara as it is, while collecting parts for what I want to try. And if I don't like the OD Trans.... change to a 3.55. If I don't like that, change it back to how it is now.

And this site and all y'all are the best reference and sounding board I could have since my dad passed.... he would definitely disagree with my wheel choices though!

 

[live4theking]

That is part of the joy of old cars. You can tweak things to be what you want and how you want them!! you never have to be "done" with one.

I can drive and enjoy my Polara as it is, while collecting parts for what I want to try. And if I don't like the OD Trans.... change to a 3.55. If I don't like that, change it back to how it is now.

And this site and all y'all are the best reference and sounding board I could have since my dad passed.... he would definitely disagree with my wheel choices though!

He might not like your wheel choice, but I'm sure he'd be glad you're enjoying the car.

 

[Polara_500_Jr]

He might not like your wheel choice, but I'm sure he'd be glad you're enjoying the car.

Oh I definitely feel that, every time I take her for a drive, or research his posts on here!

 

[Nadir Point]

I put 2.76's in my New Yorker and would not recommend it, unless you're just driving cross-country. I checked the fuel mileage a couple times back when I was driving it regularly and it dropped at least 2 mpg from around 11 to 8-or 9 mpg at best after the gear swap. You're just heating up the environment with the torque converter getting it up to highway speed with those gears. Might be a little better with the stick.