8 3/4 rear, what case?

[d fark]

Is the 489 case the best? or is it just the most plentiful? Is there any case to stay away from. Whenever I see one for sale the seller makes sure you know its a 489.

 

[HYRDGOON]

The 489 is considered to be the strongest of the three... Then someone will correct me if I'm wrong but I believe 741 is next then 742 as far as being sought after

 

[monaco66coupe]

489 is good,1 7/8 ring.
742 is good,1 3/4 ring
741 is good 1 3/8 ring
all are good,the 741 was in earlier B bodies, and later through all the A bodies. 742 is common thru 1968, 69' saw the 489, mostly B and C bodies, then E bodies. They are all tough units.

 

[Cranky]

Ring? It's the pinion sizes but how many 41's has anyone seen broken? Many moons ago the car rags took it upon themselves to compare the size of the pinion shaft and the 89 was the biggest at the bearing so it therefore must be the best. Also, if you look at the diameter of the splines and the shoulder just before the front bearing, you'll see that all of them are pretty much the same so if something is going to break, it's going to break there but the biggest killer of the 8 3/4 is the pinion gear trying to climb the ring gear on acceleration and shaving the ring gear. Yeah, Mom was trying to fix the deflection of the pinion by making the 89 bigger at the rear bearing but it didn't help much......the bearings are just too close to each other to handle big horsepower.

 

[monaco66coupe]

abv, I saw the pinion in my head, ring comes out.LoL I was trying to let him know they are all good units. My 67' 383 4 speed had the 741, and 68' GTS 383 has the 741 as well. people buying these units don't give the 741 enough credit.

 

[ZombiePopper]

Some,
would argue that the 742 is better than the 489...

 

[d fark]

sounds good guys, I'm trying to do my homework before the Indy Show the first of March. I would like to pick up a housing for my 73 as well. Thanks for taking the time to reply

 

[Garys1969RR]

To sum it up, just determine if you want a cone or clutch type posi unit. Then determine the gear ratio you want. Then buy the one that suits you, whether it be 741, 742, or 489. If you also limit your choice to 489 only, it may take awhile to find the ratio and type you want. I have found good 3.91 posi units on C List for $175 to $500. Good luck.

 

[monaco66coupe]

I like them both, and try to put the particular size in the correct year car. I not up much though on which of the two Limited slips are better, the cone type, or Clutch type?

 

[Garys1969RR]

I was lucky enough to buy a cone type, before I found out they were better in some ways. Works good in the 1/4 mile. My son has a clutch type in his 1970 Bee, and it works good on the street. Haven't had his to the track yet.

 

[monaco66coupe]

somebody said one is rebuildable,and one isn't? Which one is the Auburn? I'm asking because I have both types here, and don't know which is which.

 

[5.7 hemi]

Clutch is WAY BETTER! It can be rebuilt, and also if you stack the clutches different ways, you can ALMOST have a locker.

 

[monaco66coupe]

The clutch unit then is the better of the two. I'll look them over, may sell the cone type, as I don't need two of these units.

 

[Cranky]

Whenever I build an 89, I shitcan the crush sleeve and use a solid spacer and then it sets up like a 42 or a 41. The biggest drawback to the 41 is the selection of available gear ratios. A lot of people like the clutch unit because there are rebuild kits available for it....but, it also has the smaller spider gears and a very weak axle thrust pin. The cone unit is good but if it gets worn, people have a tendency to keep hammering it and that kills the cross pin making it spin in the differential case which ruins it all. If that hasn't happened, it can be machined and I do that sort of stuff. Also, it has the larger spiders and a no **** thrust pin that can't come out. If you want to get rid of the cone unit, let me know.

 

[emore]

If you live in NE Ohio i'll give you a 489 case. I live about 15 minutes east of Akron in Randolph, Bill

 

[mopar12372]

hmm my 63 tapered axle plymouth came with a 742 clutch type sure grip from the factory .

 

[monaco66coupe]

I wish cranky was closer, I would send him my 742 case from my 67' GTX and go through it. I can't trust anybody up here.

 

[roadrunnerh]

Although the 489 has a 1 7/8" pinion, it's tapered. The 742 is supposed to be the strongest because it has a 1 3/4" pinion that is straight, not tapered.
Personally, I wouldn't hesitate to use any of the three,
or even the earlier 8 3/4 carrier prior to the 741....

 

[d fark]

thanks to all. I feel more prepared now

 

[Cranky]

I wish cranky was closer, I would send him my 742 case from my 67' GTX and go through it. I can't trust anybody up here.

Sometimes it's worth it to ship things out to get rebuilt but the 8 3/4 chunks are about 80 lbs so they are not exactly cheap to ship. If you have one that's quiet running but needs the SureGrip worked on, then that's not hard to take apart and leave the pinion gear in place then replace the SG and set the backlash back to where it was. The pinion setting is the hardest part but the BL is fairly easy. Rear ends are not all that hard to do once you understand what's going on with them and with the internet, it's easier than ever but before the internet, there was plenty of books available in the library to look over.

- - - Updated - - -

Although the 489 has a 1 7/8" pinion, it's tapered. The 742 is supposed to be the strongest because it has a 1 3/4" pinion that is straight, not tapered.
Personally, I wouldn't hesitate to use any of the three,
or even the earlier 8 3/4 carrier prior to the 741....

I've seen more broken pinions at the front than ones broken at the back (just one) but most broken 8 3/4 rears I've seen had shaved ring gears.