741 case question?

[bbcharger71]

Hey Guys, I'm new here, but i have searched through all of the threads trying to find my answer. I have a 71 charger that is an original 318 car with a 8 1/4 3.73 rear. I'm building a 400 big block for it. This motor has keith black pistons .030 over with 440 edelbrock performer heads, Torker intake, and .509 purpleshaft cam. I knew the 8 1/4 (even after beefing up) would not hold together with this motor. I lucked up and found a truck 8 3/4 rear that is the same length. All I have to do is flip the perches. It has a 741 case with 3.23 gears. My question is; will this cas hold up to that motor with just weekend cruising? Also, Is that a good gear for my motor combo? Oh I am going to run a TCI 727. Any info would be helpful. I know all of the specs on all three cases. I"m just not sure how mcuh it will handle.

 

[moparsteve636]

The 741 case should work fine just don't put slicks on it if you plan on doing any drag racing!

 

[Propwash]

I agree.....A 741 case will work fine, even with the 30 spline axles. Maybe upgrade to a 1350 series pinion yoke if it makes you feel better. Probably not needed though.

As far a gearing combo...Just a few more variables in that decision seeing they're all connected:

Tire height
Torque converter
Fuel delivery
Ect...ect....

Kind of off the hip here, but seeing you mentioned cruising and not knowing the other variables, i'd say the 3:23's would probably get you in the ball park of where you want to be.

 

[bbcharger71]

Thanks for the info. From my research on the cam, I think I'm going with something like a 3200 stall. I'm not sure on the tire height yet. I know I'm going to run at least 18 inch wheels (maybe 20's on the rear). I'm going to feel up the wheel well as much as poosible. I'm guessing maybe a 26" tire or so. As for fuel delivery, I'm going with a Holley 870cfm street avenger. They seem to be the most user friendly. Would you say I'm still on the right path?

 

[Propwash]

For cruising......3:23's still wouldn't be too bad. With a 26" tire, i'd be pretty weary of going much higher. As a comparison, 3:91's down at a typical highway speed would probably put you in the 3400-3600 RPM range (rough estimate).

Check out this little calculator from Richmond....Might be able to give you a ball park as well

http://www.richmondgear.com/101032.html

 

[Cranky]

The 741 case should work fine just don't put slicks on it if you plan on doing any drag racing!

I've run plenty of 741 rears and with slicks. What is it that breaks on them?

 

[67 B-body]

I've run plenty of 741 rears and with slicks. What is it that breaks on them?

AMEN!!!!!!
The bearing is a bit smaller, but who has actualy broken one because of it???
I think the choice is dictaded by band wagon jumpers! Dont get me wrong, the tougher the better, but lets look at the failure rate between any of the case types when putting them behind the same power / torque ratings. Maybe someone has had one fail "not as a result of poor rebuild or worn out" , and then replaced with a different type case and not have failure.
But I'm not aware of this ever happening.
Just my two cents.:bootyshake:

 

[racedodge]

i ran a 741 case 3.91 with 28" slicks for 3 years and it never broke. pinions are not the weak points on any 8 3/4 pig.. its the carrier caps or the ring gear itself.

741 gets a bad rap for no reason if you ask me.

 

[Cranky]

30 years ago some car magazine did a story on the 8 3/4 and compared the 3 units against each other and showed how large the pinion was on the 89 case and said "look at this over the others" and said it was the strongest of the 3 and that because gospel. The weakest point on all of them is the shoulder in front of the front bearing where the splines stop but I've never seen any of them fail right there.....and have heard of it happening only once.

 

[bbcharger71]

I kinda figured it would be just fine for my application. I just had a few doubts b/c of the 741 case having the same pinion diameter of a 7 1/4. Now knowing that the pinion isn't anything to worry about gives me more confidence to keep the case. I've also heard that the 741 pinion (eventhough the smallest) is still bigger than a Ford 9".

Do I need to do anything special to drop a limited slip in? I've looked up applications on some sites and they have limited slips for 489 cases,but in order use it in a 742 they require different bearings. What would I have to do to make one work in a 741?

 

[73rr]

With the auto trans I'd run the 8¼ until it broke. For a qualifier, I have a 79 PowerWagon with the 8¼ rear and it has over 250k miles on it...

.

 

[Meep-Meep]

Yes, the Ford 9" pinion bearings are pretty small but they also have that support bearing on the other side of the gear itself, which may compensate for the smaller bearings. However the 9" pro gears have larger pinion bearings then stock. The 741 has a smaller pinion than the 742 and the 489, but as mentioned here I've seen one run repeatedly in a nitrous application with slicks in a street car and nothing bad happened. That being said the 8.25" has the same bearings an the 742 8.75" (I believe). The 8.25" that I was working on didn't look like a terrible rear end and I wonder if it has a bad rap for no reason. I personally don't know anyone who has run one but see 10 bolt Chevy rears in hot street Chevys all the time. The newer Durangos offered with the 3.92 ratio all have 8.25" rears and they push around a pretty heavy piece of equipment, not to mention towing capacity. The big concern is impact resistance but maybe there is something one can do to keep the case from spreading. Putting in the proven 8.75" is the most economical way to go but I have to wonder if we should continue to overlook the 8.25" for some applications. The 9.25" might also be an alternative for performance use.

 

[Cranky]

I kinda figured it would be just fine for my application. I just had a few doubts b/c of the 741 case having the same pinion diameter of a 7 1/4. Now knowing that the pinion isn't anything to worry about gives me more confidence to keep the case. I've also heard that the 741 pinion (eventhough the smallest) is still bigger than a Ford 9".

Do I need to do anything special to drop a limited slip in? I've looked up applications on some sites and they have limited slips for 489 cases,but in order use it in a 742 they require different bearings. What would I have to do to make one work in a 741?

All three cases take the same OD bearing size. IIRC, the Dana Powr-Lok carrier takes a smaller bearing cone but this isn't really a problem as a different cup can be bought separately if needed. Timken bearings are not sold in matched sets...

 

[herschel]

i ran a 741 case 3.91 with 28" slicks for 3 years and it never broke. pinions are not the weak points on any 8 3/4 pig.. its the carrier caps or the ring gear itself.

741 gets a bad rap for no reason if you ask me.

I agree with you, I've ran them for years and only broke ring gears and cone s/gs.

 

[Cranky]

I agree with you, I've ran them for years and only broke ring gears and cone s/gs.

Never broke a cone SG unless it quit working and turned into a 'one wheel wonder' and then that would eat them up pretty fast...

 

[67 B-body]

So the conclusion here should be widely spoken and record set straight. Once again, it's the old band wagon theories that keep things going! Most people who would argue differantly rarely have experiance of failures, and sometimes have never even changed a set of gears themselves. I cant stand mindless opinions from people who have no real world experiance. I say use it, and I HIGHLY doubt you'll EVER hurt the thing!
This realy touches home with me because I just sold a 741 case to a guy putting together a road runner. Prior to the sale someone on here wanted to argue that it was worthless due to it being a 741??!! Obviously he fits into the affore mentioned class of people.
A bonus for you is that you'll basically have a "COMPLETE NEW" unit with zero miles for the same price as most of the overpriced used worn out units being sold as the "STRONGER" case and a gear ratio that you just settle with because its whats available.