741,742,489 whats the pro's and con's

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trudysduster

trudysduster

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I have only been back in the Mopar cars in the last few years in the rebuilding aspect so to speak and I like to make sure I have good stuff in the Duster and the Dart Sport. I am looking to change the center section in the Dart and would any of the 3 be a good choice for a street rearend. I have pretty much decided to go with a 3.55 gear, now just have to pick the case. I have a 489 case in the Duster and like it. I have a line on a 742 on ebay but do not want to make the wrong choice. should I stay away from the 742 or the 741 case or should I just wait for a 489 to come along.OR would I be smart to keep the 2.76 open case I have in there now and just have it built. put a new carrier and gears and all the stuff needed.
 
Well, considering your build discussed earlier, small block and a Comp XE268, any of the rear center sections will hold up very well and under abuse. The engine is not so powerful as to test the rear. Though reving it up to 6 grand in neutral and slapping it into drive will break something! Sooner or later...

The 741 is the least desired unit. I have had it in my '73 4spd Cuda for a long time (20+ years) without issue and the engine is well endowed. 11-1-360 w/Edelbrock top end and cams that operate in the 3-6K+ only.

The thing you want most is the bigger 7290 U joint size no matter the case number.
In the past, this wasn't always possible to do. Just check the availability of such parts. Doctor diff .com has a lot of parts to scan through.
These day, *I don't think* there's a problem.
 
no. it will not be a powerhouse. from what I have read today, stay with a 742 or 489 and I guess a clutch type would be better. right now the rearend and driveshaft has a small u joint in it but could go with a conversion u joint if a large yoke came on the center section. thanks Rob.
 
there all strong with the 742 and 489 slightly slightly stronger they say. Try to pick up a clutch type unit.
 
would this be a good one on ebay. auction # 321515497418. don't know how to post links.
 
741 seems to have the 'weakest' gear support also. plenty for the 742 and 489 with the 742 coming out on top, along with its shim pinion setup. 489 takes a crush sleeve, sort of a hassle.
 
I ran a 741 Sure Grip with 3:91 gears I found in a van at Pick Your Part for $35, so I had nothing to lose. It survived behind a 440 with 275/60-15 tires. It has the smallest pinion shaft, but a clutch posi. 742 is larger, and also clutch. Both of these cases have yokes you can change without disturbing the gears, so you can put a large yoke from the junkyard you find in a van or New Yorker onto your small yoke Sure Grip. The 489 has the largest pinion, but it's strength is that the shaft is tapered from the small end to the large end where the gear is. They are all the same size where the yoke attaches. The 489 case also only came with the cone type Sure Grip, although some clutches may have gotten through in the switch over, and you can't swap yokes without disturbing the setup, requiring the whole thing to be disassembled and a new crush sleeve installed. Here's a pic from Dr. Diff showing the pinions. See how they are all the same size at the end? The strength comes from the larger bearing allowing better support of the pinion gear. The 742 may even be weaker since that step creates a stress concentration point.

From left to right: 489, 741, 742.

rrdd01.jpg
 
I know the crush sleeve is a pain as I have dealt with it in my Duster, but if I get the right gear, yoke and the right setup the first time, I would not have to worry about changing anything. so what I am getting is 742 or 489 would be best for him. Being in a strictly street car.
 
what about rebuilding the 2.76 open that we have in it now. it is a 489 case. what would that be like.
 
A nice 3:55 s/g unit should be about $350 - $400 ish..

To change yours would need a

sure grip ---------------- $375 ish
gears --------------- ---- 175 ish
new brgs ----------------- 90 ish
spacer ------------------- 20 ish
labor ------------------- $ 150 ish and up

hope it helps
 
I figured that is what I could find one for and I hope someone comes up with one. I posted in the want section for a 3.55 suregrip. It would cost a lot more to build this one. ok, thanks for that info. Bill
 
IMO, The 8.75 case strength deal is the first or second biggest overblown fallacy in the mopar world.

Get a case with a sure grip, preferrably clutch style and gear set you want and run it.

People running street cars rarely if ever should be concerned with the case they install in a car. You got a car that weighs 3500# and runs 1.35 or better 60's, then start to worry and bypass a 8.75 altogether.
 
good point. but I wasn't so much worried about the case itself as what I have heard about whats in the case. some say that parts for the 741 is hard to find. most 489's that has not been changed has cone type and some say to stay away from a cone type so a 742 with clutches is best. really, I guess it is like a woman. if you have a good one and treat it right, its as good as gold....... but if you have a bad one and abuse it, you can be in deep .................... but thanks. I guess it is going to depend on the pocket book.
 
There's ZERO discernible difference between any of the three in cars as light as the A body. A 12 bolt Chevy has a 1 5/8 pinion diameter. The 741 has a 1 3/8. 1/8 difference on either side. I've been in and around Mopars for over 30 years and have YET to see any broken 741s. I have seen some broken 489s from crush sleeve failure. I say run what you have, whatever it is. Wouldn't hurt to get a crush sleeve eliminator for ease of assembly though.
 
yeah, that is what I did on my 489 case in the Duster. I am talking to a member here about building one for me and he is going to include a crush sleeve eliminator if I go that way. thanks for the input Rusty
 
well I learned something today then. I was pretty much set on a 489 but now I can at least broaden the horizons. thanks for all the info........... now, someone cut loose of one.LOL
 
3.55 are most common in PU Trucks in my experience. If you want to "broaden the horizons" consider 3.23's, they are easier to come by and are a good street gear.
 
There are plenty of them out there, just be patient.
I put together a 4.30 year ago and here is what it ran.
Completely functional 489 case with open 2.76 gears $110
New Richmond ring and pinion with install kit $325
Used cone sure-grip $150
New pinion yoke 10 spline $180 ouch was not expecting that.
A local shop that does nothing but rebuild rear ends, $100 to assemble / clean /check everything, and setup, plus he thru in a gallon of rear end oil.

So it cost me $865 with careful shopping for good used parts, I could have put any ratio in but this is just for a weekend toy.
 
trudysduster said:
well I learned something today then. I was pretty much set on a 489 but now I can at least broaden the horizons. thanks for all the info........... now, someone cut loose of one.LOL
Click to expand...

i see em on craigslist in my area all the time for 350-500. check the wrecking yards also. alot of the earlier vans, trucks, c-bodys got em.
 
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