8 3/4 Help and Opinions?

[Haney]

I need some 8 ¾ rear help. I currently have a '741 case, 3.91 SG rear in my 69 cuda. It is currently a pretty hot 340, 4-speed but will eventually be a 416 stroker when I can afford a few more parts… This is a street car with street tires.

I am in need of a new driveshaft and started measuring. While measuring for the driveshaft, I found that this rear has the 7260 pinion yoke. Since I only want to buy one driveshaft regardless of engine, I was wondering if I should upgrade the rear yoke to a 7290 or 1350 size pinion yoke. What do you think? I know the 741 is the "weakest" case due to pinion size but looking ahead in case I ever break and go to a 742/489 case, I think I would need the 7290/1350 pinion yoke. Or would you just leave it alone and order a shaft with 7260 joints?

BIG QUESTION: In changing the pinion yoke on the 741 case, do I have to worry about messing up my pinion depth or can I just unbolt and bolt a new one in? I think the '741 has a solid sleeve and not a crush sleeve. Is this right?

I would appreciate any information and help. I would like to order my new shaft in the next couple of days….

Thanks,

 

[fishy68]

I'm in the same boat as you Haney. Mine also has the 7260's and I'm thinking about upgrading to 7290's. With your 340 and 4 spd and street tires it's not quite as much concern but if you go up to that stroker I'd sure be affraid those 7260's wouldn't survive long. As far as I know no 8-3/4 came from the factory with a solid sleeve. Those were aftermarket only but someone could have put one in yours. That being the case if it don't have it you take the risk of messing up the pinion depth by swapping the yoke.

 

[dusterdon]

First, I've seen a few fast cars with the small u joint. But they were automatics. You can change the companion flange without any problem.
Go ahead and change it now. Use either the big joint or the 1350. both will work. If you are going to buy a new driveshaft, buy an aluminum one. They will be a little more cash (but not that much), but there'll be a performance increase due to less rotating mass. good luck.

don

 

[Duster346]

At the minimum, I'd upgrade to the chrysler 7290 joint. Hopefully you don't plan on racing the car with slicks--even with the 1350 joint, 4 speeds are brutal on 8 3/4" rears!

I upgrade most of my customer's to a new driveshaft with 1350 joints, or I atleast recommend it. Regardless if you go to the 7290 or 1350, spend the money and get a GOOD pinion yoke--one with u-bolts to retain the u-joint instead of the conventional u-joint straps. The straps are a very common failure point!

For what it's worth, I used an aluminum case 8 3/4" & 7290 joint in my old car with a transbrake. It left hard with a 1.38 best 60' time.

As far as the solid pinion spacer--it is an aftermarket part offered only for the 489 case to eliminate the crush sleeve (the pinion nut can back off, with the crush sleeve). The 741 and 742 cases use pinion bearing preload shims--and they have nothing to do with pinion depth. You can swap the pinion yoke without worry. Just remember to replace the pinion seal, torque the nut to specified torque, and use red locktite on the pinion nut threads.

Hope this helps some.

 

[fishy68]

As far as the solid pinion spacer--it is an aftermarket part offered only for the 489 case to eliminate the crush sleeve (the pinion nut can back off, with the crush sleeve). The 741 and 742 cases use pinion bearing preload shims--and they have nothing to do with pinion depth. You can swap the pinion yoke without worry. Just remember to replace the pinion seal, torque the nut to specified torque, and use red locktite on the pinion nut threads.

Hope this helps some.

Learn something new everyday.:thumrigh: Bout time you get in here once in awhile Chris!!:wave:

 

[Duster346]

Did you think I forgot about you guys? I usually lurk--you guy's to a pretty good job of answering the questions in this forum!

:wave: