741 vs 489 ?

[anlauto]

Okay.....I need a little edjumacation here.....

My customer's 70 Challenger has a basically stock 383, a Tremec 5 spd....and an 8 3/4. (stock axles)
I'm going to have him a 3:55 center chunk built with all new parts from Dr. Diff.

My question is: Is it a "waste of money" building a 741 case (which he already has) ? 

Should I bother hunting down and buying a 489 case to build ?

What really is the difference and will it matter ?

[nsmall]

http://www.doctordiff.com/blog/tech-info/rearend-pinion-comparison/


FINALLY, I may have helped Alan.   

[nsmall]

From what I know which isn't much Ive heard unless it's more than 500 horsepower....741 will work and it's an underrated case.

[Chryco Psycho]

I like the 742 best , the 489 is OK If & only if you eliminate the crush sleeve .
I have broken more diffs then anything , engines & trans no problem diffs all the time , having said that I have never sheared a pinion off & I believe a 741 will do fine behind the combo in front , but why spend the $$ twice build the best you can once

[Cuda Cody]

Keeping it pretty much stock, I bet it will be fine.  If I had my choice I like the 489 and the 742 best.  They are both very strong and proven to hold up well.

[RUNCHARGER]

The 741's are no problem especially with a stock 383. I guess if it needs new gears and bearings though that there are lots of 489's and 742's around.

[GY3R/T]

Why rebuild the smallest 8 3/4" offered.  1960's 741 are plentifull and have the smallest (weakest) pinion. I always frown when i see a 741 case in an E-body. Think about resale value also.   

[70/6chall]

Cody........... Pretty much everyone here knows of my SL6 powered '70 Challenger. Would you think that the 8 3/4, 742 case with 3:23 gear set even a one-legger up under my Dodge is a little overkill?
Well, at least I got the 11"x2 1/2" brakes out back, replacing the 10" on the 7 1/4 that was back there originally and a 2:76 gear set. Besides I thought $50. was a steal. Overkill........NAW!
Thanks,   Al

[Katfish]

http://www.doctordiff.com/blog/tech-info/rearend-pinion-comparison/


FINALLY, I may have helped Alan.   

Very interesting and Cass knows his stuff, no reason to change out the 741

[fc7cuda]

Go with the 489 case for 1970 car, large yoke too. 

[303 Mopar]

I always try to go more than less, even if he doesn't need it today you never know about the future.  And this is the perfect time since you're rebuilding it anyway.

[Shane Kelley]

Like some of the others I prefer the 742. But for that build I wouldn't be afraid to run the 741. It's not like he will be running slicks at the track with it. But if you got a 489 case for a decent price I would lean that way. Just use a crush sleeve eliminator if you do. 

[GrandpaKevin]

Probably not an issue with a Dr. Diff rebuilt unit but in the used 8 3/4 rear end market I would be more concerned about the type and condition of the differential inside the case.

I would take a Powr Lok clutch type or Eaton Trutrac differential in a 741 case over a cone type differential in a 489 or 742 case.

[LinceCuda]

I ran a 742 stock posi in my 70 RT Challenger drag car 4.88 gear ratio 600 HP never an issue. I spoiled it later with a 489 5.13  gear no issue's.  It comes down to 741 is a 1 3/8 pinion  742 is a 1 5/8 and 489 is a 1 3/4 pinion. Either the 42 or 89 would be the way I would go. My Cuda I am working on now has a broke 741 but it had what looks like way to much HP by looking at my 12.5 pistons. I picked up a nice 489 for $100. Just one mans opinion.

[crackedback]

Someone wrote an article years ago proclaiming hte 741 was "weak".

I'd build the 741 and be done with it.   I've run a lot more than 500hp through them and the pinion IS NOT the weak link in ANY 8.75 case.  It's one of the biggest red-herring, $ wasting things in the mopar community.