hi guys just wondering what would be better 742 or 489 case?
I have an opportunity to get a 742 case sure grip (clutch style)
in working condition for $450. its got Richmond 4:10's in it. I'm still running
my stock 318 poly. Are the 4:10's gonna be too much?

thanks

________________________
1966 Coronet 440 318 poly

 

Their are many sites out there explaining this difference, the primary is the date of service and the pinion tapper. Here is a good site to look at: http://www.moparfins.com/repairs/8-3...opar_Rears.htm also lots of other sites out there.

As for strength - depends on which camp you fall under. In my mind, the 489 is stronger. However, with that said, 742's are very strong in themsleves and with a 318, you should never have a problem. I had a 742 in my 600HP GTX, no problems and imagine many others can vouch for the same. 489's are easier to get parts for and more common, but at what extreme. As for the clutch type, you can have it rebuilt, but unless you are throwing a lot of abuse at it, both are good.

Now gears - 4:10's are low - too low in my book unless you are doing something special or don't mind the inconvience when you travel distance. I have 3:91's in my Demon with 14" tires. Driving back and forth to Reno menas I do 65 max at about 3700 to 4K. Eats up the gas and dont do it in records time. Cool thing is, the little 318 in first sure throws a whopping on those folks not expecting it off the line.

Price - $450 is about average +/- 75 dollars. Dont dismiss the 741's either, for your application, not a bad choice. But gears and such are less common for the 741 than the other two. Also, check your drive line yoke, there are two sizes, small and large - a bit of additional cost ehn you are doing the swap. I would speculate yours has the small - but never know until you check.

Good luck

 

Thanks yea i'm not planning on driving it everyday, but fuel is expensive so i don't want to make it horribly bad, but want to have much better pickup and the main reason for the upgrade is that i have a 741 case small yoke open diff. So i really want a sure grip diff, how much do the ring and pinion go for? I wanted a 3.55 or 3.23 but hes selling his with a 4:10. Is the price fair for 450? Its in excellent condition and appears to have a brand new Richmond ring. will i have to change the driveshaft joint for the large yoke?

thanks again

________________________
1966 Coronet 440 318 poly

 

You can get a conversion U joint If you have a difference in U joint size.

 

66,
450 is an OK price. Not sure where you live, but I would check Craigs list. In my area people think they are gold. I paid about $550 for a 489 case with 3:23's, $250 for a 489 case with bad bushings and had my 741 rebuilt with that sure grip, so in the end, I probably paid that much. But I have seen them on Ebay and Craigslist for more and less. I know that is a very ambigous answer, but seems this is an item for supply and demand. And by the time you buy the gears just a sure-grip yunit for your 741, you will probably have the same amount into it. I still have my one leg 742 case for my 67 Belvedere.

My recommendation would to hold out for 3:55's - regardless of the sure-grip type or number. They all do the same thing and really dont think the 318 will break even the smallest of them, nor a 440 unless you have crazy power. Good luck and sorry for the rambling. Let us know how it works out.

 

I appreciate the rambling hahaha. So I don't need to change the driveshaft end piece for the larger yoke? You can swap the suregrip into any case? Where can I get that conversion u-joint?

thanks


________________________
1966 Coronet 440 318 poly

 

Mine is a 489 case in my Dart. All I can add is the aftermarket gears and such are easier to get than a 742.

 

Sweet rides bremereric! So does anyone know if i have to swap out the end of my driveshaft for the bigger yoke?


________________________
1966 Coronet 440 318 poly

 

Yoke - Like TVLynn posted, there is a conversion U-Joint. When I was at the Napa store, the parts guy was telling me they are common? Never used one, so don't know. I have always taken mine to the driveline guy (about $100 for balance and change).

 

Here is a good read:http://www.moparfins.com/repairs/8-3...opar_Rears.htm

And some dimensions:http://www.dennysdriveshaft.com/p494...pco_greas.html

 

Thanks Coronet 500, i was worried about that u-joint. So im all set then just got to pick her up, thanks guys

________________________
1966 Coronet 440 318 poly

 

Last questions, will my stock axles work with the sure grip unit even if my case was a 741 and installing the 742? Do i have to use synthetic gear oil?
thanks

________________________
1966 Coronet 440 318 poly

 

Yes your axles will work and no you dont need synthetic, just addative, buy it at any run of the mill parts store.

 

Sorry more questions as ive been reading stuff online. will going from 2.94 gears to 4.10 mess up my speedo?

thanks

________________________
1966 Coronet 440 318 poly

 

Sure will...changing the tire size will also effect it.

 

How can i make it work properly?


________________________
1966 Coronet 440 318 poly

 

Yes it will. If you look through these post you will find the parts for the transmission gear conversions. Tire overall diameter and gear size will be what you need to know. I just updated my Demon's gear and it took about 20 minutes max. Search the threads, you will find it or search my threads, I just asked not too long ago and somebody posted the link.

I am guessing its about a 43 organge --- This is a guess

CP

 

http://www.mymopar.com/speedometer.htm

 

Thank you so much bremereric! im just not sure where to find this part, and how long/ easy it is to replace?

thanks again

________________________
1966 Coronet 440 318 poly

 

I remember there is a 741, 742, and 489 case. They say the 741 is not good. And the difference between the 742 and 489 is that the 489 uses a "crush-sleeve", and the 742 uses shims to get the pinion depth correct. Strength is not an issue unless you are "crazy fast"! There is a crush-sleeve eliminator available for the 489. You cant go wrong with either.

 

Yea i just like the fact that i can rebuild the 742 as many times as i want, and that its period correct for my car. Can i use the sg carrier from the 742 and put it into my 741 with my 2.94 gear?

________________________
1966 Coronet 440 318 poly

 

Here's where to get a speedo gear. If you have a 489 case and need a crushless sleeve I got one at Mancini Racing..it comes with shims to set it up...this way if I ever break a yoke again all I have to do is drive the old one off and drive the new one on.

http://www.transmissioncenter.net/sp...FcpeTAodVRcD0g

 

So i finally got the new differential and its in amazing shape, no play in the yoke what so ever, rust free and the sure grip seems to be working great! Thanks for all the advice guys!


________________________
1966 Coronet 440 318 poly

 

OK - So what did you go with in the end??

 

Hi sorry about the late response, im still looking for a 3.55 gear set, and have been reading about the yoke, and that if both of my diff's have a coarse (10 spline) yoke i can swap them, correct? So then i wouldnt need that conversion u-joint.



________________________
1966 Coronet 440 318 poly

 

Seems to me there was something about the early clutch type sure grip needs some buttons on the end of the axels ?????