Gearing change... rear end or transmission?

[Polara_500_Jr]

Here's my situation. I put dad's car back together, but now would like to lower RPM's on the highway. I know taller tires would help, but these are a little too new/nice to swap out yet.

It has a sure grip with 3.23's (pretty sure based on his comments on here). I could look for a .276 diff to swap in, but might miss that low end grunt.

It has a new a833 4 speed. How difficult would it be to change the gearing on just 4th gear? I can always run it up a little more in 3rd before shifting, but I like going for longer cruises, and in this neck of the frozen tundra most of the speed limits are a bit higher than where I'd like to run the revs.

 

[496 polara]

I would think an OD 833 would work. Or have someone swap fourth gear with one from an OD 833. I don't know enough about the specifics to say whether there would be any issues. On the flip side look for a good used 2.94 gearset.

 

[Ripinator]

Here's my situation. I put dad's car back together, but now would like to lower RPM's on the highway. I know taller tires would help, but these are a little too new/nice to swap out yet.

It has a sure grip with 3.23's (pretty sure based on his comments on here). I could look for a .276 diff to swap in, but might miss that low end grunt.

It has a new a833 4 speed. How difficult would it be to change the gearing on just 4th gear? I can always run it up a little more in 3rd before shifting, but I like going for longer cruises, and in this neck of the frozen tundra most of the speed limits are a bit higher than where I'd like to run the revs.

You might want to look at a 2.94 differential. I'm running one in my 66 300 convertible with a 440. Good grunt and very responsive when you hit it out at 40 mph or so.

 

[Boydsdodge]

You could get one of the truck 4 speeds or also used in some A bodies and I think in early volare. Chrysler used the A833 4 speed and made it a 3 speed with 4th being an overdrive.

https://www.motortrend.com/how-to/40618-a-833-manual-transmission-swap/

 

[Polara_500_Jr]

With mine being a 65, was there something particular, like one year only to make these less compatible?

 

[The_Eagles’_Nest]

Either a whole A833 OD should be swapped in or swap the ring and pinion. I have 3.23s in my Imperials and they all get 9mpg in town and 17mpg on the highway. That’s decent of a 5,000 lb car.

 

[Polara_500_Jr]

I was leaning toward the diff change as the easiest.

With the sure grip. do I just find a 2.96 for a 8 3/4 diff?

 

[The_Eagles’_Nest]

They have a 2.94. The 2.76 in a slant six is a dog, but even with a 360 it’s fast. I think the 2.94 would be a good compromise.

 

[Polara_500_Jr]

They have a 2.94. The 2.76 in a slant six is a dog, but even with a 360 it’s fast. I think the 2.94 would be a good compromise.

Would the 2.76 be too doggy behind a mildly built 383? I’m not big on racing it, just comfortable cruising

 

[Toolmanmike]

Here's my situation. I put dad's car back together, but now would like to lower RPM's on the highway. I know taller tires would help, but these are a little too new/nice to swap out yet.

It has a sure grip with 3.23's (pretty sure based on his comments on here). I could look for a .276 diff to swap in, but might miss that low end grunt.

It has a new a833 4 speed. How difficult would it be to change the gearing on just 4th gear? I can always run it up a little more in 3rd before shifting, but I like going for longer cruises, and in this neck of the frozen tundra most of the speed limits are a bit higher than where I'd like to run the revs.

4th gear swap. You don't.

 

[CBODY67]

Stay where you're at! The 3spd+OD 4spd was not designed for anything more than a LA motor, like 318, back then. Not as strong as it needs to be, for a B/RB motor.

The expense involved in getting another chunk for the rear end, in either gear ratio, could well be near $1K by the time it's all done, I suspect. That can buy LOTS of gas.

Add a better under-car exh system for better road mileage. Maybe even an AVS2 carb. with the better venturis.

The highway gear and manual trans can be fine once going, but more clutch-slipping to get it moving in town can be a real issue as to ultimate clutch life.

So, stay where you are. There's a reason Chrysler put 3.23s with manual transmissions.

CBODY67

 

[MONC440]

Stay where you're at! The 3spd+OD 4spd was not designed for anything more than a LA motor, like 318, back then. Not as strong as it needs to be, for a B/RB motor.

I’m not disagreeing with you what the OD 4spd was designed for but I had one behind a healthy 440 in a challenger with a Dana 60 with 4:10 gears and it held up to about 3 years of abuse from an 18 year old kid learning to speed shift. lol
FYI if you switch from the 4 speed to the 3 speed with OD the 3-4 shift lever is upside down compared to the non OD 4spd. Don’t know what kind of shift linkage you have but might require some rod alignment. In the OD trans 3rd gear is where 4th gear is in the non OD trans and 4th(OD) is where 3rd is in the non OD trans. My OD trans was an aluminum housing and I finally ended up braking the housing after to many bang shifts. I ended up putting all the guts from the OD trans into a cast housing from a regular 4spd

Below are the Non OD and OD linkages for comparison.

 

[MONC440]

How difficult would it be to change the gearing on just 4th gear?

If you are talking about putting a OD gear in place of the 4th gear on the main shaft that will not work. I believe you need to change the main shaft and the counter shaft in the trans in order to get OD.

 

[413]

4th gear in an 833 is 1 to 1. There is no gear to change, the trans connects the input shaft to the output shaft.

An overdrive 833 has 3rd gear 1 to 1. And 4th gear is overdrive.

To do this you need really an OD trans. Every gear is a different ratio and tooth counts. The case has a very large front bearing retainer bore and needs a different bellhousing to match it.

2.76 would really suck with a manual trans.

Find out what rear gear ratio you have and drop one step. So go from 3.23 to 2.94.

 

[rd92west]

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

 

[Polara_500_Jr]

Stay where you're at! The 3spd+OD 4spd was not designed for anything more than a LA motor, like 318, back then. Not as strong as it needs to be, for a B/RB motor.

The expense involved in getting another chunk for the rear end, in either gear ratio, could well be near $1K by the time it's all done, I suspect. That can buy LOTS of gas.

Add a better under-car exh system for better road mileage. Maybe even an AVS2 carb. with the better venturis.

The highway gear and manual trans can be fine once going, but more clutch-slipping to get it moving in town can be a real issue as to ultimate clutch life.

So, stay where you are. There's a reason Chrysler put 3.23s with manual transmissions.

CBODY67

It's already full dual exhaust, with the HP manifolds. And it has an 800 AVS2 carb on it already....

With 75 and 80 mph limits, I just wanted to get it below the 3200+ highway RPMs.

 

[CBODY67]

It's already full dual exhaust, with the HP manifolds. And it has an 800 AVS2 carb on it already....

With 75 and 80 mph limits, I just wanted to get it below the 3200+ highway RPMs.

Thanks for the information.

My '70 Monaco 383/330 car has P225/75R-15 tires and a 3.23 rear axle. That makes right at 25mph/1000 road speed. Which is fine at 75-80moh being on the engine's torque peak territory. Our '66 Newport with H78x14 tires and a 2.76 rear axle ratio is about 28mph/1000rpm, by comparison.

With the 3.23, you're NOT that far from your desired rpm levels. Only real advantage to the lower-number gear ratio might be fuel economy, but there's not a cost-effective justification for that. If needed, work on getting a more pleasant and a bit quieter exhaust tone at those cruising speeds.

Enjoy!
CBODY67

 

[Polara_500_Jr]

What's considered the ideal RPM for highway travel? I would have thought it would be lower is better. She's got plenty of snort in the low gears for how I drive, just wishing it was a bit better on the mileage, anywhere I want to take it is a decent trek from little old Fargo, ND

Maybe I need to dig around in the spare cars and parts.... Just see what's out there.
I have an hour drive each way this evening. I'll check the mileage, and the RPM's accurately at speed. Then I will have more accurate data to work from.

 

[Snotty]

I'd leave it like it is. You could put in 2.76 or 2.94 rear gears, but here's a reason they put the 3.23s with that 4 speed.

Your '65 should have the emergency brake as a drum on the back of your tailshaft. That would make swapping transmissions a real piece of work. Same for if you tried to put a GearVendors overdrive on it.

As I said, I'd leave it like it is.

 

[Polara_500_Jr]

No drum on the trans.

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