Will 741 Case Gears Fit a 489 Case?

[PurpleBeeper]

Like the title says, can you take gears out of a 741 8-3/4" rear end pumpkin & put them into a 489 pumpkin? I believe it's a 741 open pumpkin with 2.76 gears I'd like to put into a 489 posi pumpkin. thanks

 

[MoparLeo]

No. The 741 and 489 have different sized pinions. That is what makes them different. Here is a differential guide for you. Lots of good info. Hope you enjoy.
http://www.waywardgarage.com/tech/rearaxlemopar.html

 

[beanhead]

Wait for it......wait for it......

 

[PurpleBeeper]

Thanks gentlemen.... I will look for a 489 case with 2.76 gears. Speaking of which, were 2.76 gears available in a 489 pumpkin? What salvage yard vehicles should I be looking at? Newports/New Yorkers/etc? Thank You!

 

[beanhead]

Wait for it......wait for it......

Well I was just trying to be funny...I figured the "it's called a sure-grip!" police would come along any time lol

 

[beanhead]

Thanks gentlemen.... I will look for a 489 case with 2.76 gears. Speaking of which, were 2.76 gears available in a 489 pumpkin? What salvage yard vehicles should I be looking at? Newports/New Yorkers/etc? Thank You!

Yes the 'highway' gears could be found in the 489, it was the casting for the big-block cars 69-later. The 742 I have now was in a 68 polara..any of those c-bodies you mentioned would have had the 489 large-pinion/7290 ujoint setup as long as they were big-block cars. Which I believe most if not all were in late 60s/early 70s

 

[MoparLeo]

The 742 is a better choice for a sure-grip diff. Used rebuildable clutch type diff not the cone Auburn type.

 

[Cranky]

Why not just get a 'posi' and install it into the 741 case. The gears are already set up and all you have to do is set back lash once you bolt on the ring gear and reinstall it into the case. Are you afraid of breaking the 741 since all the dumb *** rags like Shot Rod and Car Crap says it's weak? How many have you seen broken?

 

[SublimeSixpack]

Thanks gentlemen.... I will look for a 489 case with 2.76 gears. Speaking of which, were 2.76 gears available in a 489 pumpkin? What salvage yard vehicles should I be looking at? Newports/New Yorkers/etc? Thank You!

Yes, 2.76 gears came in the 489 case. And some of them came with Sure-grip.

 

[PurpleBeeper]

Hey Mopart & Cranky....thanks, but I already have a 489 case with 3.55's & a posi in it. I just need a set of 2.76 gears that fit the 489 case until I can scrape together enough cash for an overdrive trans. (not going to happen anytime soon). The 3.91's I'm running now make the car un-drivable on the highway without an overdrive. I have VERY limited cash at the moment and I'm trying to stay cheap.

 

[Cranky]

Like the title says, can you take gears out of a 741 8-3/4" rear end pumpkin & put them into a 489 pumpkin? I believe it's a 741 open pumpkin with 2.76 gears I'd like to put into a 489 posi pumpkin. thanks

The way your post reads, I assumed you already have a 2.76 in a 41 case? If so, just swap the SG into the 41 and go. It would be a lot easier to install the SG into a unit that already has the pinion set to depth.

 

[MoparLeo]

Another way to go cheap is go with a taller tire for now.

 

[PurpleBeeper]

The way your post reads, I assumed you already have a 2.76 in a 41 case? If so, just swap the SG into the 41 and go. It would be a lot easier to install the SG into a unit that already has the pinion set to depth.

Actually, I have a 489 sure-grip with 3.55's in it (not in car now). I was considering buying a 741 open pumpkin with 2.76 gears to put the 2.76 gears into the 489 sure-grip pumpkin.

HOWEVER, now I find out that my plan won't work. (THANKS EVERYONE!). My new "plan B" is to see if I can find a 489 pumpkin in a salvage yard C-body. If it's already a sure-grip, I'll use it as-is. If it's an open pumpkin, I will swap the 2.76 gears out of it into my existing sure-grip 489 pumpkin.

Looking on-line, I haven't seen any 489 pumpkin 2.76 gears for sale. No surprise, all the aftermarket gears I've seen are 3.55's and up. Anyone have a set of 2.76's for sale?

My ultimate goal is to buy some 28" rear tires (replacing my current 26-1/2" tires - saves about 300 rpm) AND use the 2.76 gears to get my 70-80mph cruising rpm down to about 2500rpm (calculated) until I can (eventually) afford an overdrive Passon trans or a Gear Vendor unit. With no overdrive, 3.91's and 26-1/2" tires, my motor is 4000+ rpm on the highway....not good for long distance travel.

CRANKY - The more I think about it, the more sense your idea makes. I've never set up the "gear lash" in a rear end. I didn't realize that it's more of a function of shimming the pinion than anything else. So, just to be clear, are you saying that I could just
a) Gut the posi unit out of my 489/3.55 pumpkin
b) Gut the spider gears out of a 741 open pumpkin
c) Bolt the 2.76 ring gear out of the 741 pumpkin right onto my 489 posi unit.
d) Install the 489 posi/2.76 ring gear combo into the 741 pumpkin & my gear lash would already be OK because I never removed the 741 pinion gear????

 

[MoparLeo]

More links to file away for future reference:
http://www.bgsoflex.com/rpmmph.html
http://www.wallaceracing.com/tire-aspect-calc.php
http://www.hotrod.com/articles/scroungers-guide-buy-a-mopar-83-4-centersection/

 

[Cranky]

Actually, I have a 489 sure-grip with 3.55's in it (not in car now). I was considering buying a 741 open pumpkin with 2.76 gears to put the 2.76 gears into the 489 sure-grip pumpkin.

HOWEVER, now I find out that my plan won't work. (THANKS EVERYONE!). My new "plan B" is to see if I can find a 489 pumpkin in a salvage yard C-body. If it's already a sure-grip, I'll use it as-is. If it's an open pumpkin, I will swap the 2.76 gears out of it into my existing sure-grip 489 pumpkin.

Looking on-line, I haven't seen any 489 pumpkin 2.76 gears for sale. No surprise, all the aftermarket gears I've seen are 3.55's and up. Anyone have a set of 2.76's for sale?

My ultimate goal is to buy some 28" rear tires (replacing my current 26-1/2" tires - saves about 300 rpm) AND use the 2.76 gears to get my 70-80mph cruising rpm down to about 2500rpm (calculated) until I can (eventually) afford an overdrive Passon trans or a Gear Vendor unit. With no overdrive, 3.91's and 26-1/2" tires, my motor is 4000+ rpm on the highway....not good for long distance travel.

CRANKY - The more I think about it, the more sense your idea makes. I've never set up the "gear lash" in a rear end. I didn't realize that it's more of a function of shimming the pinion than anything else. So, just to be clear, are you saying that I could just
a) Gut the posi unit out of my 489/3.55 pumpkin
b) Gut the spider gears out of a 741 open pumpkin
c) Bolt the 2.76 ring gear out of the 741 pumpkin right onto my 489 posi unit.
d) Install the 489 posi/2.76 ring gear combo into the 741 pumpkin & my gear lash would already be OK because I never removed the 741 pinion gear????

The posi (SureGrip) doesn't care what it's riding in....41, 42 or an 89. Having to set pinion depth is more detailed than swapping out the carrier (the part the ring gear bolts to) which also houses the guts of the SureGrip. You don't have to deal with spider gears or none of that stuff. Just bolt the 2.76 ring gear onto the posi and bolt it in, set back lash and go.

 

[SlinktRR]

hey beeper I run 2.76 open with 28" tires, 2700 rpm at 80 mph. great for road trips but a dog on the bottom.

i am selling a 741 3.23 for 100 dollars obo if you are interested. 3.23 will get your revs down.

 

[MoparLeo]

489 pinion depth is set up with one time use crush sleeves. 742 are set up with shims. Just fully read the links I sent you. They will answer all of your differential questions, and for any one else who cares.

 

[pbiggs]

Thanks gentlemen.... I will look for a 489 case with 2.76 gears. Speaking of which, were 2.76 gears available in a 489 pumpkin? What salvage yard vehicles should I be looking at? Newports/New Yorkers/etc? Thank You!

I have a 489 case NOS 2881466 ring gear and pinion 2:76 ratio set for sale. $95.00

 

[Cranky]

489 pinion depth is set up with one time use crush sleeves. 742 are set up with shims.

Not correct. The crush sleeve is a quick way for the factory to set bearing preload. Pinion depth in the 89 is still set by the use of a shim just like it is for the others. The bearing preload uses shims in the 42 and the 41 cases......

 

[The Rebel]

Really great info here!