489 vs. 741

-
I'd like to see the guys that have actually sheared a pinion off any 8 3/4 post their combos and when (roughly) it happened. I've never done it. Nobody I've known in 30+ years has told me they did it. ...And that's C bodies, nitroused big blocks on slicks, etc. I've seen axles twist, housings bend, driveshafts shear... I've never heard of a pinion shearing.

OP - The 273 stick cars had 7 1/4s in them and lived on the street and some track. I wouldn't sweat it.
 
With costs of a 742/489 rebuilt ready to go, if I had a 741 already I'd just buy a new sure-grip unit (if existing is an open) the ring and pinion, a rebuild kit, and a quality forged yoke, set it up myself and invest in quality u-joints, driveshaft, trans internals instead. Here's a good link to info on the 8-3/4, among others out there. www.mymopar.com/Mopar8_75RearEndGuide.htm
 
My 1970 383 RR, 4 speed, had 741 SG with 3.55 gears, I never had a problem in the ten years I had it and I drove that car like I stole it.
 
You guys make a good case for it.
Now if I was running mid 9’s........
LOL
 
I took a 741 in on trade one time. It had a broken pinion. the threads for the nut were snapped off the end of the pinion and were still inside the nut. I figure that they over tightened it. Other than that never seen a 741 with a problem.
 
The "weakness" of the 741 case is not the danger of "snapping off" the pinion, as we know all 8.75 pinions use the same diameter spline yoke, it's just the spline count and
u-joint size that varies. If they are going to snap off, that's where it'd happen, and as stated You just don't see that happening on any of the three varieties. The "weakness"
is in the size of the support bearing adjacent to the gear teeth to minimize deflection & keep the teeth engaged at the proper depth. If there is too much deflection the load
moves out towards the edge of the tooth where the strength weakens quickly, and it's an exponential fail as it moves to weaker & weaker contact points as the loads get
higher & higher until You see the teeth stripped of the pinion & part of the ring gear. 'Tis why the 9" Ford is very strong, lots of load support at the gear end of the pinion.
Also this is why proper bearing preload is so important. All this said, an A-body w/a smallblock, even stroked isn't going to fail a 741 case unless something's wrong.
 
I never broke a 8 3/4 yet and I hammer on them. 741,742,489. 5500 stall, and 4spd big blocks alway's slicks. Treaded tires are not allowed on the streets on a mopar where I come from . If its put together correct they hold up to anything . Spring wrap will destroy a pinion shaft real quick. pinion snubber or cal tracs. or a good stiff set of SS springs are a must.

The quick snap of the holeshot is when i see rears come apart. Once the wheels come down your clear for take off. Dragster's don't have springs and I have bought old front engines rails for parts with 8 3/4 rears in them . If the rear dosen't try and jerk the drive shaft out of the trans they take what ever you throw at them. Its the rear suspension or set up that kills a rear with slick's on a sticky track.

Did you ever notice cars not put together or set up correct that wheel hop usually have parts come out the bottom. Sometime's the whole rear.

 
Last edited:
You must log in or register to reply here.
-

Back
Top