Differential Gear Ratio Sure grip?

[Yeya93]

Thanks in advance! My 70 challenger project planning on going with a 440 and this is the rear end that it came with which seems to be 3.23 ratio. Is this a sure grip? Good enough for some highway driving but nice enough for the occasional peel out? What would y'all do? Keep it or go with something different?

[rftroy]

Not a Sure Grip.
Picture angles aren't the best for evaluating condition, but I believe I see signs of heavy corrosion on the differential case and possibly also the gear teeth.
Did you drive the car before you removed these gears?  Make any noise?
If you have a tight budget, have someone who knows gears look it over.  Otherwise, if you have money for a better setup, I wouldn't bother with this. 

Robert

[68bee]

Its not a sure-grip. 3.23 gears are good for every day driving and burnouts. I would keep it and add a sure grip unit to it

[Yeya93]

No, I never drove the car as the car was not driveable at the time I retrieved it. If this was your car, what setup would you recommend on purchasing? I can always save up to purchase a good setup.

[Rich G.]

If you're just going to cruise and enjoy the car 3:23 are perfect. If you want to beat someone off the line at every stop light then I'd change the gears. 3:55 are the highest I'd go without overdrive if you plan on doing any highways driving.

[kawahonda]

3.73 is also great on the highway as well (but max). 3200 RPM with 235/60/15 is not a bad RPM to cruise at for some decent highway jaunts @65. These are not necessarily cross country cars, nor freeway cars (definitely still not with 3.23)

3.55 doesn't have to be the limit when there's 3.73s available. Either go bigger, or stay smaller (3.23). Fussing with in-between (3.55) will leave you wanting more in either direction. If you have larger rear tires, then 3.73 is the clear answer over 3.55 for highway cruising but having some street-stomping power.

I speak for small blocks only. A 440 will have a lot more torque. But the rule of thumb is to never blow a bunch of money to gain only a 1-size increase (3.23 to 3.55). You won't feel it. Either go two sizes once you know what you want, or do nothing IMO.

[nsmall]

If you're just going to cruise and enjoy the car 3:23 are perfect. If you want to beat someone off the line at every stop light then I'd change the gears. 3:55 are the highest I'd go without overdrive if you plan on doing any highways driving.

I have a 340 though. So maybe a 440 with a 323 would still be fun.

[70Barracuda]

IMO put a Dana in it and forget about it,  GM wants their 12 bolt, ford 9inch, Mopar, we need the Dana, the biggest, baddest of em all.  Plus they look so darn good!

[Chryco Psycho]

there is a lot to be said for building a Dana 60 they don't cost more to build than a 8 3/4 really but you will not break a dana
Bad news is less gear ratio choices with Dana , there used to be a 3.23 available & I believe someone is still making them but I could not find them when I built my Dana , you also have 3.54, 3.73 & 4.10 .
Dr Diff can supply a new center section for the 8 3/4 or build you a Dana 60 , this is who I would suggest you deal with which ever way you decide to go .

[7212Mopar]

Decide on the engine build, camshaft, transmission choice first before picking your final drive ratio. Also think about the tire size you want to run. Let say you go with a 727 AT and then like add a Gearvendor overdrive or get a 4 speed AT, a 3.23, 3.55 or even 3.73 might not be the best choice. If you just stay with stock 3 speed AT or a 4 speed manual, you will need to figure out how much freeway driving you want to do. A 440 spinning at over 3k at 65 mph for an hour takes a lot of gas. Dana would be nice and cost some $, but if you only have a 375 HP 440, then many would agree a 8-3/4 is just fine. Definitely go with limited slip if you are getting a new one. Plan it out, do it once and will save you money. Yes, definitely talk to Dr. Diff when you are ready.

[Joegrapes]

I have mildly built 440 with an 8 3/8 and 3.91 sure grip but with 27" tall tires. Yeah the rpm is a little high on the highway compared to modern cars but I don't drive much on the highway. If I did I would put the 3.23 back in. A sure grip is a must for any performance car. There is one more part of the equation you need to add in before you decide on 8 3/4 or Dana. You age! LOL. When I was 19 drag on the street and doing burnouts was a lot more important that now at 66. I see no reason anymore building a nice car and then beating the crap out of it doing burnouts. But that's just my age talking. You will spend a lot of money rebuilding your car and I think the money could be better spent on other things than a Dana.

[usraptor]

I have a 440/512 stroker.  The is an original super trak car that came with a 4:10 Dana and 4-speed.  With the 4:10s it was like a coiled snake and would light the tires if I floored it while cruising in 1st , 2nd or even 3rd gear.  On the highway I was turing close to 3700 RPM at 65 MPH.  Since most of our car shows around here involved driving on the freeway to get to them, I bought a set of custom 3:23 gears that Dr Diff makes and had those installed last summer.  I can still lite the tires in 1st and 2nd and a little in 3rd on a wide open run.  However, it is so much more comfortable to drive now, especially on the freeway.  I still have plenty of power with the 3:23s and can still do a burnout whenever I want and don't regret the switch at all.   (FYI, I did keep the 4:10s in case I or a new owner ever want to switch back and no I do not want to sell them in case anybody is wondering) 

My original '70 Cuda had a 383 Magnum, 4-speed and 3:55 sure grip rear end.  I had no problem driving it on the freeway at 70 MPH and took it on several rod trips back in the day.  It didn't get very good gas mileage, about 12 MPG if I remember correctly, but it didn't overwind the engine.

Whatever, you decide, like others have said, talk to Dr. Diff first.

[jordan]

Decide what is the overall plan for the car.  A cruiser with an occasional burnout will not hurt the 8 3/4.  If you have tall sticky slicks on a prepped track and do 4K RPM lauches, then go with the Dana.  In my opinion, I would use what you have.  Put a Sure-grip in it or a Eaton Tru-Track, a set of bearings, and crush eliminator kit, and forget it.  The 3:23 is a very nice gear for driving on the road.  Drag racing is a different story.  Remember, the guys that tell you to run 3:73 or 4:10 gears should tell you the height of the tire because it all factors in.  A 30" tall drag tire will change the ratio just as much as a 27" tall tire for any given gear.  Have an idea of what rims and tires you want to run too. 

[gzig5]

Unless you plan on putting really sticky tires on it and launching at drag strip, the current rear end should do just fine.  A healthy 440 should be able to light up any street tire without risking breaking parts, and the 3.23 ratio with a Sure Grip will be easy to live with around town.  Now if you are all about performance and drag racing, that would be a different conversation.  There is a reason they put Dana's in the high performance cars that were going to the track.  I don't think you can get enough traction on the street to break an 8 3/4.

[Topcat]

there is a lot to be said for building a Dana 60 they don't cost more to build than a 8 3/4 really but you will not break a dana
Bad news is less gear ratio choices with Dana , there used to be a 3.23 available & I believe someone is still making them but I could not find them when I built my Dana , you also have 3.54, 3.73 & 4.10 .
Dr Diff can supply a new center section for the 8 3/4 or build you a Dana 60 , this is who I would suggest you deal with which ever way you decide to go .

Packing a Dana 60 is like Dirty Harry carrying a 44 Magnum.