742 versus 489?

[BAFRAID]

Yesterday I found a complete eight three-quarter 742 rear end. I did some research On a Mopar site which gave a lot of the specifications of each rear end 741/742/489. It said the 742 case and unit is as strong or just as good as the 489. Basically it said the pinion shaft might be a tiny bit smaller however the bearings in the 742 are stronger than the 489. both were rated for high Weight and high horsepower. I know this may open a can of worms but I was just curious on what others opinions are?

 

[F4R/T]

None of them should worry you, I really think they are a lot tougher than you realize.. If your putting slicks on it, back brace it. I feel good with the 742 or 489, with an auto otherwise gear jamming probably should bite the bullet for a Dana 60.

 

[hunt2elk]

Dr Diff has a nice comparison sheet on his site if you haven't run across that. I for one like the 742 because you don't have to mess with the crush sleeve or eliminator.

 

[RemCharger]

Crush sleeve eliminators are cheap. Then its the same as setting up a 742.

 

[Jerry Hall]

Yesterday I found a complete eight three-quarter 742 rear end. I did some research On a Mopar site which gave a lot of the specifications of each rear end 741/742/489. It said the 742 case and unit is as strong or just as good as the 489. Basically it said the pinion shaft might be a tiny bit smaller however the bearings in the 742 are stronger than the 489. both were rated for high Weight and high horsepower. I know this may open a can of worms but I was just curious on what others opinions are?

As you all are probably aware I'm a 66-67 B body fan and the big V8's had the 742 8 3/4. My opinion is that the 10 spline pinion and yoke should be stronger than the I believe 29 spline 489 even though they are tapered. Ofcourse I'm not a mechanical engineer and don't know how to figure the stress that either can take. I will say that I had a shift kit in a car that over time beat the bearings out on a 489 gear. The 742 I replaced it with has taken the same beating and still seems fine.

 

[Cranky]

The first thing I do with the 89 is get rid of the crush sleeve but even the 41 is pretty tough. Besides how many people do you know that's broken the pinion shaft?

 

[68Moparmaniac]

Yesterday I found a complete eight three-quarter 742 rear end. I did some research On a Mopar site which gave a lot of the specifications of each rear end 741/742/489. It said the 742 case and unit is as strong or just as good as the 489. Basically it said the pinion shaft might be a tiny bit smaller however the bearings in the 742 are stronger than the 489. both were rated for high Weight and high horsepower. I know this may open a can of worms but I was just curious on what others opinions are?

If I recall the pinion bearing sizes are different, one is 1 3/4 (742) compared to 1 7/8 (489) respectively. Both were B & C body centers. 741 is A body stuff (1 3/8 bearing size)
Both will stand up to spirited abuse, so build what ya got and have at it.

 

[Darter6]

Like Cranky said they all are good. I have run 741's(and still do) in many cars both on the street and the track.
My 65 I ran a 741 for years even when it was a stick car. It takes allot of horsepower and sticky traction to break any of 'um
Like anything else,everything has a breaking point. What are you planning to throw in front of it ?

 

[BAFRAID]

Like Cranky said they all are good. I have run 741's(and still do) in many cars both on the street and the track.
My 65 I ran a 741 for years even when it was a stick car. It takes allot of horsepower and sticky traction to break any of 'um
Like anything else,everything has a breaking point. What are you planning to throw in front of it ?

Wanted to put it (the third member) in my 69 super bee with a mild 383 and 727.

 

[66383]

Got a 41 in my 383/727 Satellite and it's not stock and no problems burning street tires.

 

[w.Hudson]

I have ran them all. Heavy car with a trans brake. Several 4 speed cars. Lighter A bodies both auto and 4 speed. Big blocks and small blocks.

Broke spider gears and knocked the teeth off the ring gears.

Never broke a pinion shaft.

So, run what you have available to you. Build it and have fun.

 

[BAFRAID]

I appreciate everyone’s input and experience. I’ll run this one for now.

 

[Darter6]

You will be good to go.Mild 383/727 no problem.

 

[Challenger340]

As long as you aren't hitting it with a 4 Spd and good traction tires ? or Slicks on a Tranzbrake ? Shouldn't have a problem as far as I'm concerned.
I ran mid 10's on a 742 /Auto/High Stall with slicks for years at the track..... 1.5's 60 ft times on a foot launch..... and I was seeing splines twisting on the strange axles, but never had anything go south on the 742.

 

[dadsbee]

My original rear axle had the drivers wheel/axle moving in and out in '78/79 and instead of fixing stuff back then we just headed for the junk yard and traded "weight for weight" with Ma. I haven't broke the 741 we threw in back then from a '67 w/2.94's and clutch sure grip ...yet...

 

[33 IMP]

I prefer the clutch type suregrip,usually found in 742 case, compared to the cone style you would find in a 489.
But any suregrip can be installed in any case.
The only thing wrong with the 741 case is a lack of new gear ratios available. The 741 has a undeserved rep as being the weakest. If you look at the weakest point of the pinions for 741,742,and 489, they are all the same.
If you are happy with the ratio in the 8 3/4 you bought, run it!

 

[dvw]

Pinion shaft isnt what's I'll likely to break. If you use a 489 get a crush sleeve eliminator. Beyond that run it, 741, 742. Doesnt matter. If you make enough power to break it, then its time to upgrade to a Dana, modified 9", etc anyway. Only ever broke 1 8 3/4 pinion shaft. Turbo small block, 21 psi on drag radials using a transbrake@4000 leave rpm.
Doug

 

[Cranky]

Wanted to put it (the third member) in my 69 super bee with a mild 383 and 727.

Pinion shaft isnt what's I'll likely to break. If you use a 489 get a crush sleeve eliminator. Beyond that run it, 741, 742. Doesnt matter. If you make enough power to break it, then its time to upgrade to a Dana, modified 9", etc anyway. Only ever broke 1 8 3/4 pinion shaft. Turbo small block, 21 psi on drag radials using a transbrake@4000 leave rpm.
Doug

and it broke right around the front bearing area?

 

[Dipstick]

If I recall the pinion bearing sizes are different,

The 742 rear pinion bearing is larger than the 489 and will prevent pinion deflection better than the 489.

 

[dvw]

It broke right at the end of the yoke threads. So bearing diameter had no effect.
Doug