So I'm starting to regret the 3.90 rear

[mag162]

Swapped out the stock 2.76 open 741 case for a 489 Posi with richmond 3.90 gears.
Ita actually fun as hell but not really being able to get on and cruise on the highway is become a pain in the ***. I should have tracked down a 3.23 Center section.
Anyway I wanna swap out the gears to 3.23.
How difficult is this and should I just take it to a shop to be done correctly.

 

[70bigblockdodge]

Sucks getting passed by granny in a KIA huh.
They are not hard but require some specialty tools and a feel for it.

 

[CBODY67]

Everything's got a cost, one way or another. I suspect the initial increase in acceleration compared to the 2.76s was amazing to feel, BUT unless you move on up to an OD automatic w/ the 3.90s, hehe, then 3.23s and a '68 Road Runner-spec torque converter might be the next best thing.

CBODY67

 

[slappys garage]

I agree 3.23s are probably the best compromise unless your going to swap in an OD tranny. If you have a reputable shop nearby(no shipping)that can do the work, that’s probably best.

 

[67Monaco]

Swapped out the stock 2.76 open 741 case for a 489 Posi with richmond 3.90 gears.
Ita actually fun as hell but not really being able to get on and cruise on the highway is become a pain in the ***. I should have tracked down a 3.23 Center section.
Anyway I wanna swap out the gears to 3.23.
How difficult is this and should I just take it to a shop to be done correctly.

Just get taller rear tires. Like a 255/70-15. Near 29" it'll get ya closer to where you wanna be faster than a gear swap. Those tires with a 3.91 rear will get you an effective gear ratio of 3.39. Still be fun, but be able to cruise with a slightly raised rpm.

I'm running that tire with 3.23's and my effective ratio is 2.81. I'm on the hunt for 3.73's to get me where I want to be.

 

[mag162]

Mmmm something to think about

 

[Badvert65]

I like the 3.23 and the 3.55 sets for daily drivers.
My Fury still has the 3.91 gears that I drove with for years. 55-60 MPH @ 3000 RPM. Takes some getting used to.....

 

[commando1]

I found even a 3.55 too annoying after a short period. Feels like you're always in second gear.

 

[413]

I agree that 2.76 sucks for many reasons. Don’t think of it as setting your cruising RPM, it much more, it’s your torque multiplication, and 2.76 kills it. It’s like using a short wrench to break loose tight bolts, no power. To a degree anyway.

I’d suggest finding another third member instead of taking apart a good unit. That 3.9 will sell easily if you don’t want it.

This rear gear set up is best left to a pro, unless you want to invest in the right tools and equipment. Press, bearing pullers, pinion depth tool, dial indicator, spanner wrenches, etc.

 

[Snotty]

I agree that 2.76 sucks for many reasons. Don’t think of it as setting your cruising RPM, it much more, it’s your toque multiplication, and 2.76 kills it.

Don't know about that; I'm still running 2.76 gears and I can burn rubber all day.

Mag, I'm not surprised you don't like those 3.91s; that's a HUGE jump! If you find another 3.23 third member, they are not hard to change. Just make sure you are getting one for a C Body, as the U-joints are larger.

 

[70bigblockdodge]

Don't know about that; I'm still running 2.76 gears and I can burn rubber all day.View attachment 282373

Mag, I'm not surprised you don't like those 3.91s; that's a HUGE jump! If you find another 3.23 third member, they are not hard to change. Just make sure you are getting one for a C Body, as the U-joints are larger.

Just match to your u joint. A C body does not guarantee a large u joint. I have 3 sitting here with little joints and 741 case all from C bodies.

 

[mag162]

Yeah my original case was a 741 with the 2.76 gears and a small yoke. This one is a 489 with a small yoke. Guess I’m gonna start collecting center sections

 

[67Monaco]

Bring it down here I'll swap ya 3.23 chunk for 3.91 chunk.

 

[BIGBARNEYCARS]

Contact Murray Park in Tiffin, Ohio.(OUR RESIDENT C-BODY PARTZ PURVEYOR EXTRAORDINAIRE) Tell him what you have and what you want to have and talk Trade and $ with him. Bring your 391 to Carlisle and hook up with him in the swap area. he's been renting the same 6-8 spaces at the east end of ROW-B or ROW-C for the last 25-30 yearz ??? Might be ah WIN WIN? Otherz here will probably supply you with hiz e-address and or Phone#. I have both on one of hiz business card and it'z gone where my socks go when she putz 'um in the dryer, Jer

 

[413]

Don't know about that; I'm still running 2.76 gears and I can burn rubber all day.View attachment 282373

Mag, I'm not surprised you don't like those 3.91s; that's a HUGE jump! If you find another 3.23 third member, they are not hard to change. Just make sure you are getting one for a C Body, as the U-joints are larger.

Put in a different gear and tell us how much better the car is in many ways.

 

[Turboomni]

If I was just tooling around town ,stop and go I wouldn't mind a 3.55 but I want to go on the highway which I think is where a big C body shines. 3.23 for me and a stroked 440 ought get it done out of the hole.

 

[CBODY67]

Everybody's got their own sensitivities and orientations of what gear's best for what. Including engine sizes, too!

A mild cam (as the orig B-eng 252/.390 cam) will run out of breathing room far too quick with a 3.90 gear, or even a 3.55 gear, no matter what tire size is on the car. With a 2bbl, by 4Krpm, most of the available power is already used. If you want to cruise at 90mph, then a 2.76 and 8.55x14 (for reference) tire size will do that. Cruising at 90mph is right on top of the torque peak rpm, of a bit past, but still "up there". 28.66mph/1000rpm, by my calculations with that tire size.

With the later 256/260 "std cam" for '68 383 2bbl/4bbl/350 horse 440s, then the 3.23 and 8.45x15 tires make for about 25mph/1Krpm. 75mph is right at 3000rpm, which is right at the top of THAT cam's rated torque peak rpm.

Personally, I'm fine with a shorter-stroke 383 4bbl, or even a 400 HO 4bbl. Put SureGrip with them and tire smoke can be a rare situation, so why bother? Adjust the kickdown linkage for a bit higher part-throttle shift points. A few other tweaks, possibly. I like that feel of passing gear stringing out into the triple digits, which means "there's more left".

IF you want to tell everybody you've got "390 gears", that's fine. But if you have to use a significantly taller tire to make them effectively lower numerically, wouldn't 3.55s with a normal tire size be better? Which means the front end alignment will be easier to do, rather than having a bunch of negative caster due to "the rake" from the taller rear tire size?

But again, we all have our own tastes and sensitivities on these things. 383, highway gears, and a level-setting chassis with good tires and HD shocks make for a better long distance "road eating" machine, to me. It's bad enough having to pay the money it takes to fill that 24+ gallon gas tank, so streeeettching out the distance between fill-ups can be a good thing. Even when Gulf NoNOx or Phillips66 Flite-Fuel were 35cents/gallon.

Y'all enjoy!
CBODY67

 

[detmatt]

2.94 is where it’s at!

 

[jct]

Glad i'm building my car for the highway cruising

 

[BIGBARNEYCARS]

2.94 is where it’s at!

Yeah Matt but that 294 only came in the Impz. OH Sorry, You knew that, lol