Differential Questions

[VTMopar]

I've been chatting on the side with 72 Cudaman  (who has been very helpful - Thanks!) re: adding Sure Grip to my Challenger Vert with a 489 case matched to a 440 6 pack (A/T) that is currently being re-built.  He suggested I contact Dr Diff, and I spoke with Cass today (he was very helpful).     He has his "own" posi unit for a 489 case that he sells... something like $400 and also offered an Eaton unit for an extra $150 or so.    Does anyone have any recommendations re: which might be best between these two?   

Also - I asked Cass about my gears.   He said I could keep what I have (currently I'm running 2.76 gears. )   However, I mentioned that my engine builder suggested I go with 3.23's (which I cannot find).   Cass indicated they are no longer being made for the 489 and suggested I be very careful about used ones.   He then inquired about my tires (I'm running 275x60 15's and he indicated that with those tires, I was very close to the 3.23 gear ratio.    He indicated my 2.76's are going to be pretty sluggish....   So -- now I'm lost - I follow that my tires are higher than stock - but can anyone help me understand how all this fits together and what makes sense?   

I plan on driving this (a lot) and -- like any red-blooded American -- I would like to have it both ways - great fuel efficiency and terrific acceleration    

Thanks
VT Mopar

[HP_Cuda]

Funny you should bring this up, I have some 3.23 gears for a 489 chunk.

PM me if you are interested.

3.23 gears are good all around posi gears but more folks like the 3.55 gears but you have to deal with higher rpms on the freeway. This is why I opted for 3.23 until I get that 5th gear.

Check this site out for gearing and tire combos:
http://vexer.com/automotive-tools/speed-rpm-calculator

[GranCuda1970]

3.23 gears would be your best bet. These guys should have em.

    http://www.usgear.com/aftermarket.php

[GranCuda1970]

Good price here for a entire 3:55 rearend.

http://www.ebay.com/itm/Mopar-3-55-suregrip-rear-end-for-E-body-Cuda-Barracuda-Challenger-355-rearend-/290826216922?pt=Vintage_Car_Truck_Parts_Accessories&hash=item43b697e5da&vxp=mtr

[GranCuda1970]

oooops 741 case!

[MEK-Dangerfield]

I have a 440 with a 489 with 3:23 suregrip gears on my car. The tires are smaller then your's(255X60X15). I have no problem lighting the tires up when pulling away from a stop light, but your bigger tires will make your car a tad slower off the line. The upside for you is better fuel economy on the highway.

I'm not making any recommendations, but I just wanted to point out how similar our cars were. But I can't see you being happy with those big tires and 2:76 gears.   

[VTMopar]

HP Cuda, I've been told to be careful with used gears...... Anyone have a different view?   

MEK ...  Sounds like very good advice.

Thanks,
Vt Mopar

[HP_Cuda]

I will post up a pic, they look pretty darn good to me!

B

[brads70]

With your rear tire size I'd go with a new  drop in 3:55 ratio from Cass.  I have 3:55 in my current Dana and had 3:55 in my old 8 3/4 As longs as you kept your foot out of it on the hwy it was ok.

[HP_Cuda]

That's my problem Brad, that dang skinny pedal on the right keeps calling out to me!!!

 

VT, if you want me to post picks of my 3.23 gears let me know and I'll put them up today!

B

[VTMopar]

HP Cuda - Sure - I'd  like to see them (you can email them to me also, if you'd prefer)....   Again, I'm just repeating what I've heard about using "used" gears in connection with an upgrade to a sure grip...

Thanks! 
VT Mopar

[msbaugh]

I just installed a 489 case in my car with 3.55 gears and 275-50-15 tires!! I had a 3.93 and it was killing me with my smaller tires.. needless to say the 3.55 change out was awesome.  I also have a 727 trans... go with the 3.55's you can cruise the highway and still romp it from light to light which is what makes these cars so fun in the first place.  3.23 isn't enough in my opinion, 3.55 is the perfect mix! 

[HP_Cuda]

Ok then tell him what rpms you are pulling at 70mph on the freeway then.

I like 3.55 gears and have them in another car but it drives me nuts because I'm right on the lower end of the power band and its like a rubber band just waiting to get stretched!!! Besides listening to the motor whine that high is not good for milage or your ears for any length of time.

B

[msbaugh]

Ok then tell him what rpms you are pulling at 70mph on the freeway then.

I like 3.55 gears and have them in another car but it drives me nuts because I'm right on the lower end of the power band and its like a rubber band just waiting to get stretched!!! Besides listening to the motor whine that high is not good for milage or your ears for any length of time.

B

I guess it's a matter of opinion, I went from 3.93 gears so after changing to the 3.55 it's great to me. Now the 3.93's yes they were awful, my top speed was 70 lol

[GranCuda1970]

I got 3.91's in mine and I Like the whine just not the gas mileage.