There are 5 different case numbers for the 8 3/4 housing....985, 657, 741, 742, and 489....the last 3 being the most common. The first 3 use the smallest diameter pinion shaft and their related bearings and seals. The 742 case uses the medium size pinion shaft, and the 489 the largest. The first 4 cases have a fixed spacer between the pinion bearings and allow you to swap flanges without having to worry about bearing preload. The 489 case uses a crush sleeve where you have to make sure the preload is the same if you swap flanges. That takes and inch/pound torque wrench to accomplish that along with the procedure involved to measure the existing preload. I've seen at least 6 different pinion flanges used depending on year and model of Mopar. Most are bolt and strap versions and are either for the 7620 (2 1/8") or the 7690 (2 5/8") u-joints. There are also U-bolt and velocity joint versions on C-bodies as well as some on trucks/vans. As I mentioned, you can swap them out for the ones you need once you determine case number and the number of splines on the pinion shaft. On the first 4 cases that's fairly easy (if you have an inpact gun). Zip off the nut and count them. The 489 can be converted to a fixed spacer these days, but, you have to reset up the pinion depth just as you would if you put in new gears. A recommended procedure if you want max performance or even if you change gears. It just makes life easier down the road should you need to pull the flange again for any reason. There are some side gear differences on the real early housings in the 50's, and also the oddball '65 B-body 6cyl. 3rd member. It's not an 8 3/4, it's actually an 8 1/4 3rd member. It looks very similar to an 8 3/4, but, it is different and not one for performance use even though it has an interesting 3.31 gear option. It might be fine for the highway or a grocery getter, but, it has lots of unique parts that might be a pain to find if needed. Another note I've run across is the real early 3rd member housings and pinion snubber holes. Some didn't have them drilled. Dealing with the different axle end play spacers usually isn't a big issue, but, sometimes it is when swapping '64 and older, with '65 and newer. Putting an older 3rd member into a '65 up housing with adjustable axle bearing retainers usually has enough adjustment on them to get them within specs, but, not always. Going the other way is more difficult with the need for various and sometimes lots of shims. Same goes with the sure grip versions. If you have a '66 Fury with a 741 case and a typical bolt and strap pinion flange, and you want to get another 3rd member, I'd stick with finding a '65-up 741, 742, or 489 with the gear and flange you want, and based on the horsepower you plan to have. The sure grip carriers can be swapped on any of those housings. Personally, I prefer the clutch type version as it's easier and cheaper to rebuild if worn out. There are some aftermarket ones too that are a good choice for drag racing. Oh, and your knock on the end play adjustment design, I think it's wonderful. One adjust to do the whole job, and it takes just a few minutes to do. Once set up and the new tapered roller bearings installed and properly greased, you can run that thing for hundreds of thousands of miles without a worry. They'll hold up to the most punishing side thrusts you'll see. Ball bear rear axles, well, just ask the FoMoCo owners how those hold up over that length of time and punishment. Chevy C-clip and bearings run right on the axle shaft? Please....The "green" bearings are a pretty good ball bearing though i have to admit, and one I would use of I couldn't get the end play within specs without major re-engineering.
Rear End Education please
- Thread starter 66furys
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Damn....I thought I was too wordy in some of my responses.....but you have taken the cake. And, it is all great, and I certainly appreciate it. Hard to find some of this all put together in one place....thanks.
just to correct a couple things in the long post #22 -- widths on the yokes should be 7260 - 3-1/4 and 7290 3-5/8 -- and PINION DEPTH does NOT change when going to a solid spacer on the 489 case ,,the solid spacer replaces the crush sleeve , you only have to set up the pinion bearing preload again 8-15 in/lbs used bearings 20-25 in/lbs new bearings.
I totally agree with your points on the thrust adjust and bearing strength on these designs.....but, but, but, I am not happy about having to pull axles to maintain these bearings.....and I have no clue on the old beast as to what the status of the apparatus is. I am used to the old chevy designs with outer seals and bearings pressed on, and no maintain. But, I do have a question on the internal thrust block. I have not found a manual with good description yet. And, on one uTube they talked about an outer puck falling out, and trying to replace with long magnet holder. Do you have a description or pic of these thrust blocks. I see that they move or slide, but will parts fall out during axle remove, or not. Thanks for education. I am not sure that my 383 will ever gen enough power to need the sure grip.....BUT, for the heavy beasty, might like a bit lower gear for spunky launch. Not 4.11, but maybe mid to low 3's. There is no more fun than acceleration (I grew up drag racing on streets every friday nite....couple years).
57fury440
Well-Known Member
You will not have any parts fall out. Once you coat the bearings with grease, they will be good for a long time.
So, being a slow student from the git go, I was still looking, since I want to get a new center section.....mine is the 741 and prob very high gear, and open. So, in my studies, I have gone thru the axle splines to make sure no problem, and then went back to the thrust block issue, since some show the three piece garbage falling out. And, today, looking at the manual, I FINALLY found that the open diff has a thrust block with slot for the spyder pin, and the sure grip has a spyder arrangement like a UJoint cross, and has the three piece crap that can come loose. So, IF I am correct, the open diff has a large thrust block that moves with axles, and the sure grip has a cross piece with the two buttons installed from each side, with the spring pin to hold them in place. And, it appears that some folks found it necessary to remove them to install the green bearings....in some cases. I suspect that if the new bearings which fit with the open thrust block, they would also fit with the sure grip buttons in place. There is a comment about the older green bearings. So, at this point, if I can find a sure grip, I will check the buttons to make sure they are tightly held by the pin. And, if I decide to go with the new bearing style, I would likely remove the pucks. I am not smart enough to know why both open and clutched rears do not use the same design spyders....maybe with the thrust block but not the stinkin pucks....more work on my part, and a trip to carlisle in store.
The measurements I gave for the U-joint size is the inside span from clip to clip. I found it a bit more accurate than the outside span which varied a bit depending on year.
The salvage yard has center sections. Cheaper than rebuilding and lower gear. But, how can I either be sure to get the newer pumpkin with the longer thrust block, or how can you measure it. Depth gauge on each side vs overall width?? thanks
Thanks again 413....your pictures are worth more than a thousand words. I found yet another paper on the chrysler center sections and have finally listened to all the notes above. I think I can decipher from the serial numbers and age, and now understand the difference in thrust blocks. Appreciate all the help, once again.
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