3rd member ques.

[440barracuda]

HI
i have 4 posi 3rd members.

1- 3.91 741 clutch posi
2-3.55 489 spring posi
3-3.23 489 spring posi
4-3.23 742 clutch posi

is the 742 3rd member as strong as the 489? is the clutch type posi unit better or worse than the spring type?

i would like to make 2 strong 3rd members and leave a back up one with the 3.23. what would you do? they will be switched out time to time depending if i want a different ratio.
how much would i be able to sell one for?

what would you do in this case. please help.

[VernMotor]

I myself like the 742 case best because it does not have a crush sleeve in it. the 489 does have a bigger size pinion in it but has crush sleeve in it. and if it been hit all with any HP it allready the preload on the pinion bearing is gone..too loose..now you can put a slim in the 489 case to replace the crush sleeve and be a good rear end. now the cone pos (spring pos) will not live ..might be junk allready.. the clutch pos are great for the steet. just need to look at them real good.. I myself would put the 3.91 in the 742 case with the best clutch pos together. trash the 741 case good for nothing.. pick the best other grear you want and put the other clutch pos with it in the 489 case and buy a crush sleeve slim kit for it.. IMO...every one got one LOL

[440barracuda]

so the spring type posi's might be junk? uh oh. well, i have 2 clutch types. could the spring be rebuilt and be used again?

i dont understand what might be wrong with the 489 case though. i am only 13. i seem to know alot about these mopars though.

[pishta]

13 years old and already messin with Mopars? You are going to be trouble...Anyway, the spring SURE GRIPS are good for the street, cruising and light duty stuff. The clutch pack diffs are a little more touchy around town. Yes, the spring diffs can be "rebuilt" if you wanna call it that, shaving the cones and installing heavy springs. I would put the biggest gear in the 489, shim it, and put the clutch pack in . Race with that. All the other ones can be built and sold. they are fetching a good price.

[ehostler]

Originally posted by VernMotor
I myself like the 742 case best because it does not have a crush sleeve in it. the 489 does have a bigger size pinion in it but has crush sleeve in it. and if it been hit all with any HP it allready the preload on the pinion bearing is gone..too loose..now you can put a slim in the 489 case to replace the crush sleeve and be a good rear end. now the cone pos (spring pos) will not live ..might be junk allready.. the clutch pos are great for the steet. just need to look at them real good.. I myself would put the 3.91 in the 742 case with the best clutch pos together. trash the 741 case good for nothing.. pick the best other grear you want and put the other clutch pos with it in the 489 case and buy a crush sleeve slim kit for it.. IMO...every one got one LOL

the pinion gear of the 489 tapers down to the same size as the pinion gear of the 742. That being the case, the 489 isn't much stronger than the 742.

You can NOT take the gears from the 741 and put them in the 742. the shaft fo the 741s pinion gear is smaller than that of the 742. The bearing wouldn't work and it would spill all of its oil through the nose.

741 gears will only work in a 741. 742 gears will only work in a 742. 489 gears will only work in a 489.

The 741 case has proven to be strong enough to withstand B-bodies with 650 hp. So, think again before saying that the 741 is crap. It may be the weakest of the three, but it is a rather strong unit.

Cone and clutch sure-grips are both pretty good. Once they begin to wear out, the cone unit will be weaker than the clutch unit.

Something else to think about... If you start swapping sure-grip units between rears, the rears will need to be setup up all over again. As the gers already have wear patterns in the, they will need to be set exact, other wise you'll rip the gears apart in no time.

[The Dartman]

A 741 pig is still stronger than a 12 bolt GM in its stock form, and is also much stronger than the Chrysler 8 1/4 rear.

I'd put the 741 with the 3.91 gears and the clutch type rear in the car. The next thing you do is to save the 489 with the 3.55's, and the 742 with the 3.23's and keep them both as spares. Then you take the spring 489 case with the 3.23 gears to a swap meet and put at least $200 on them. It is not worth the hassle to setup the 3.55's with the cone sure grip, when it is already setup and operational.

This way you have a cone type sure grip in a 742 to upgrade to a nice 4.10 or higher aftermarket gearset, as well as two nice spares to fall back on. The 741 has gotten a bad rap for the most part, especially for street use.

I have a spring type 3.91 in a 489 case, and a Richmond 4.30 with clutches in a 742 case that are my spares. You can never have enough rearend parts!!

Dartman

[VernMotor]

Well I was wrong stuck my foot in my mouth !
them guys are right you can not change the gears from one to other 741-742-489.... but the 741 case you can not buy no after markets gears for as far as I know ? that the big reason no one uses them.. them cone pos. I hurt them, with 400 hp motors..I got plies of that stuff. would not waste my time with one.. clutch ones will work good on the steet. still no good for every weekend drag racing..now anyone here taken a cone pos apart in the last 3-4 years that was anygood all of them I see are junk now..

[pishta]

Yo Vern, you on the juice or do you actually talk like that? Its like reading a Forrest Gump book!

[VernMotor]

Sorry just trying to help I will go back to just reading now.

[440barracuda]

randys ring and pinion sells the gears for all the rear ends.

ya, i am only 13 and i have helped out on building a 318, sold it, and i am working on a 440 for my 1968 barracuda. my dad works for Diamler Chrysler, so ever since i was younger we went to cars shows and stuff like that.

[littlecampbell]

Vern you had me worried again as I have the 741 with 3.55s and will be switching to 3.91s as posted in an earlier thread. Now whats all this about cone and clutch type sure-grips? Is this stamped on the carrier? Whats the difference between them and how do they work?......Lots of good info ehostler! My 741 pinion also tapers......Hey Vern thats a very nice lookin Coronet!

[ehostler]

There's alot of good info about the 8¾ at [url]http://www.autohobbydigest.com/8_75.html[/url

[The Dartman]

The worst that can happen with a cone type sure grip is that you will become a "one tire willy". My 3.91 (489) with cone type did this sporatically for one season, and then it went away and works perfect now.

There was an article in Mopar Muscle years ago about how to rebuild the cone type sure grip. It involved machining the cone surface and the inside surface, and replacing the springs with transmission and/or bed springs (yes, bed). Sounded pretty hokey to me, but I heard guys swear that they ended up with a tougher less slipping sure grip for very little money.

[dwc43]

Dartman you are wrong about the 8 1/4 rear. That rear was designed as a replacement for the 8 3/4,mainly due to the fact that it was cheaper to produce. These are two of the toughest rears I've ever used without any failures. I do prefere the 8 3/4 for oval track use due to the use of c clips in the 1/4 rear even though there is a fix for that one as well.

[The Dartman]

I'm sure we don't want to argue about the 8 1/4.... but... I broke one in a car that ran 14.75, under normal street driving. I believe a c clip broke and parts of differential went into every nook and cranny of the Richmond gearset. I also almost sent the tire and axle into the passenger side quarter panel. This was a rearend that was professionally setup to run in a J/SA stock class in the low 12's/ high 11's.

I will say that the 8 1/4 is as strong than a 12 bolt chevy, only because they share the same c clip design and are both limited by this when making large amounts of HP.

So, to say that an 8 1/4 is equal to an 8 3/4 in its stock form is what I believe is wrong.

I am not a big fan of the 8 1/4's also since Moser makes great, cheap axles to convert A bodies over to 4.5 bolt circles. But that's another thread(s)....