6T9 GTS
Well-Known Member
What is the difference between the 472 and 489 8 3/4 cases?
8 3/4 Cases
- Thread starter 6T9 GTS
- Start date
-
green67cuda
Well-Known Member
the 742 case uses a 1 3/4" pinion, and the 489 uses a 1 7/8 pinion. the bearing at the gear on the pinion is larger on the 489, and as such, so is the race and where it presses into in the case. The carrier side bearing bores are the same, so you can use a 741/741 carrier (i.e. clutch type sure grip) in a 489 case, as long as you use 741-case bearings/races. and the 489 sure-grip (cone-type) in the 741/742 case with 489 bearings/races.
Guitar Jones
aka Angry Johnny
741 = 1 3/8" straight pinion shaft - pinion bearing preload set with shims
742 = 1 3/4" straight pinion shaft - pinion bearing preload set with shims
489 = 1 7/8" taperd pinion shaft - pinion bearing preload set with a crush sleeve
All use the same carrier bearing size and carriers are interchangeable.
The aluminum MP case is a 742 based case. The 489 doesn't really offer any strength improvement over the 742 case but the shim set pinion bearing preload of the 742 case does allow you to remove the yoke without having to worry about replacing the crush sleeve. This setup also means you shouldn't have to worry about the pinion nut loosening up from the crush sleeve losing it's tension.
Parts availability for pinion seals is not as good for the 742 case though and there is a conversion available from Ratech I believe to convert the 489 case to a shim set up for pinion bearing preload.
So in summary if you have a 742 case I wouldn't worry about finding a 489 case and vise versa as most gear set ratios are readily available for each.
742 = 1 3/4" straight pinion shaft - pinion bearing preload set with shims
489 = 1 7/8" taperd pinion shaft - pinion bearing preload set with a crush sleeve
All use the same carrier bearing size and carriers are interchangeable.
The aluminum MP case is a 742 based case. The 489 doesn't really offer any strength improvement over the 742 case but the shim set pinion bearing preload of the 742 case does allow you to remove the yoke without having to worry about replacing the crush sleeve. This setup also means you shouldn't have to worry about the pinion nut loosening up from the crush sleeve losing it's tension.
Parts availability for pinion seals is not as good for the 742 case though and there is a conversion available from Ratech I believe to convert the 489 case to a shim set up for pinion bearing preload.
So in summary if you have a 742 case I wouldn't worry about finding a 489 case and vise versa as most gear set ratios are readily available for each.
Duster346
Chris Andrews
I usually build the 742 or the 489 for customers. But if I you do get a 489 casting make sure to replace the crush sleeve with a solid spacer from either Richmond, Randy's R&P etc; regardless if the vehicle is being used for the the street or strip. I have seen the pinion nut come loose, and it can cause some damaged.
Overall, I've always liked the 8 3/4 rear end. Its simple to work on, and the parts are readily available. Some of my customer cars are on the fence as far as how much power they're are making while still using an 8 3/4. With a heavy street car making some power you'd probably break it pretty good. You can get the billet caps and adjusters from MW, and put a back brace on it, but the weak link will always be the ring gear. Also, make sure you get your pinion depth correct, and you might also want to move the pinion into the ring gear a little bit more if your car is making some power. This will hopefully prevent the ring gear teeth from breaking.
My red b'cuda has a back braced 8 3/4 with the aluminum center from MP, and has been 1.38 60' off a transbrake launch, and low 10.0's at 130 mph. :shock:
Good luck with your 8 3/4 build!
Chris
Overall, I've always liked the 8 3/4 rear end. Its simple to work on, and the parts are readily available. Some of my customer cars are on the fence as far as how much power they're are making while still using an 8 3/4. With a heavy street car making some power you'd probably break it pretty good. You can get the billet caps and adjusters from MW, and put a back brace on it, but the weak link will always be the ring gear. Also, make sure you get your pinion depth correct, and you might also want to move the pinion into the ring gear a little bit more if your car is making some power. This will hopefully prevent the ring gear teeth from breaking.
My red b'cuda has a back braced 8 3/4 with the aluminum center from MP, and has been 1.38 60' off a transbrake launch, and low 10.0's at 130 mph. :shock:
Good luck with your 8 3/4 build!
Chris
-
