Re-gear education please.

[SandDiesel]

Just learning about the car as it's a month old to me. Shopping for potential posi upgrades and deeper gears. As far as I can tell this is a stock 3.23 rear end in my 65 Belvedere II 4spd car, currently with a 383. I see references to 489 cases and others but don't know what I should be looking for in a 3rd member. Future plans are to stroke the 383 or a 400 block if I can find a deal on one and 3.91's are the steepest I probably want for a 98% street driven car but looking for insight from you guys.

 

[Meep-Meep]

742 or 489 cases have the largest pinion diameters and also larger bearings than the 741 case. Either of these will be a good platform to build from. 3.23's are hard to beat for 98% street driven, especially if you spend a lot of time on the highway. Anything lower than 3.55 tends to get uncomfortable at 70 MPH plus the car eats more gas.

 

[SandDiesel]

Thanks. Wasn't sure if both cases fit mine. Maybe just posi with the 3.23's then? Probably should make that last on the list, once I sort out the motor.

 

[dbowperson]

I would at least go to a 3.55, unless you do a lot of highway driving. I have 3.91s and love them, but I do at most about 40 miles each way on the highway to the furthest shows. Most of my driving is around town with short blasts on the highway. I have 29" tall tires (255/60-17s), and turn about 3K RPM at 70.

 

[racedodge]

fwiw.. i have never seen a pinion gear fail.. it is usually the case's main bearing caps that fail. totally matters on your HP/tq rating. I ran a 741 w/sure grip 3.91 case (which was used out of a 70 dodge truck) for 2 years drag racing and didnt have an issue. car was a 71 charger, 3800lbs, 450hp motor at the time.

 

[MarPar]

unless you do a lot of highway driving. I have 3.91s and love them

What he said...

It's great around town, with a pretty much stock 440, i can spin da tires @ 20 mph and it soooo much fun, but on the highway, it SUCKS. i would rather have something around a 3.73 or less (3.55's??) to get the best of both...it depends what you want to do w/her!!! :glasses10:

i'm not sure on the case #....one of 'em has a crush sleeve (that one you don't want???) i know mine has a 8 3/4" w/ a 3.91 gear (i never took the rear-end apart, but i spun the driveshaft and counted the revolutions on the tires and got about 4 spins)

BTW...POSI?????:eusa_hand: you're killin' me Diesel!!!! in MoPar land, it's a Sure-Grip!!! :tied up::icon_dwarf:

let us know how it goes!!!!

 

[72 Charger SE]

What he said...

It's great around town, with a pretty much stock 440, i can spin da tires @ 20 mph and it soooo much fun, but on the highway, it SUCKS. i would rather have something around a 3.73 or less (3.55's??) to get the best of both...it depends what you want to do w/her!!! :glasses10:

i'm not sure on the case #....one of 'em has a crush sleeve (that one you don't want???) i know mine has a 8 3/4" w/ a 3.91 gear (i never took the rear-end apart, but i spun the driveshaft and counted the revolutions on the tires and got about 4 spins)

BTW...POSI?????:eusa_hand: you're killin' me Diesel!!!! in MoPar land, it's a Sure-Grip!!! :tied up::icon_dwarf:

let us know how it goes!!!!

The 489 case has the crush sleeve, but there are kits out there to eliminate the crush sleeve. The 489 case is also the one with the largest pinion diameter, which means it is also probably the strongest. Not normally a problem for breakage from what I've heard. Usually other parts fail first.

 

[Cranky]

I've seen all kinds of carnage with rear ends but the one thing I've never seen was a broken pinion shaft. Heard of some but never had seen one. Some magazine many moons ago did a writeup on the different cases and said the 89 was the strongest because it had the biggest pinion bearing fit and the 41 had the smallest so therefore it was the weakest and everyone jumped on the band wagon. It worked for me because from then on, I was able to buy CHEAP gears with the 41's and sold all the 89's I could for much more. Yeah, I work on them and used to pick all the Pick and Pull yards around the Houston area that I could. The only draw back I see with the 41 is the small selection of gear ratios available.

 

[72 Charger SE]

Not just the magazines saying the 741 is weak, that is also actually written in the Mopar Performance Chassis Book. But I've never seen one break a pinion either.

 

[Redpolara]

The 489 has the largest pinion shaft diameter but the 742 has the largest rear pinion bearing of the three......true story.

 

[polkat]

The 741 pinion shaft may be small but it is actually a tad bigger then the popular Ford 9" pinion, and should hold up okay with most mild builds. The following site has good info on this, as well as other good articles on Mopar rears.

http://www.moparts.org/Tech/Archive/axle/1.html

 

[SandDiesel]

MarPar, bear with I'm new to Mopar terminology too. When doing parts searches on Craigs and ebay alot still say "posi". I stand corrected. Learn something new every day on here so keep the lashins comin'.

 

[MarPar]

MarPar, bear with I'm new to Mopar terminology too. When doing parts searches on Craigs and ebay alot still say "posi". I stand corrected. Learn something new every day on here so keep the lashins comin'.

LOL

i was just kiddin' around...stick with us, we'll teach you a whole bunch!!!

Posi (short for Posi-traction) is typically a Chebby (re:Chevy) term...

 

[Cranky]

Not just the magazines saying the 741 is weak, that is also actually written in the Mopar Performance Chassis Book. But I've never seen one break a pinion either.

It may be true that the 41 is the weakest of the 3 but it's still a strong unit none the less. I like the 42 the best and will use the 89 if I put a solid spacer in it but I'm also known to machine the cone type SureGrip and keep on trucking

 

[SandDiesel]

Just noticed this add says "8.75 P/L 30 SPLINE". Will that match mine?

 

[Cranky]

Just noticed this add says "8.75 P/L 30 SPLINE". Will that match mine?

Don't know about the really old 8 3/4 rears but all of the newer ones (60's and up) are all 30 spline axles.

 

[SandDiesel]

Just looked underneath while putting in my wheel studs and noticed I have the 741 case in mine. Original or not who knows.

Just to be clear, do all three cases fit the same housing without mods?

 

[Redpolara]

Yep, they all fit.

 

[Darter6]

Been racing 3600+ lbs b bodies with the 741 case and never broke one yet. Your results may vary and in some cases side effects may occur...............

 

[daredevil]

I would at least go to a 3.55, unless you do a lot of highway driving. I have 3.91s and love them, but I do at most about 40 miles each way on the highway to the furthest shows. Most of my driving is around town with short blasts on the highway. I have 29" tall tires (255/60-17s), and turn about 3K RPM at 70.

Dude I love your avatar. That dummy is funny as hell.