8 3/4 diff

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gunmetal72

gunmetal72

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Hi all, I know there are allot of smart guys on here and hope someone can give me some info. I believe there are 2 different 8 3/4 differentials, large and small stem pinion. I would like to know how to tell the difference. I have 72 Duster with #'s matching 340 & 4 sp. gear ratio is 3:23. Not sure which one is in the car. Can someone tell me the difference?
Thanks..............Dale
 
A simple glance at the casting number on the drivers side of the center section will tell you!

741= 1 3/8" pinion shaft
742= 1 3/4" pinion shaft
489= 1 7/8" tapered pinion shaft

All are good, but I prefer the 742 case as it uses shims to set the pinion depth, unlike the 489 that uses a crush sleeve or the new upgrade hard spacer!
 
The 742 and 489 and 741 and every other diff use shims to set pinion depth..........


Let's lose the bs about crush collars being weak or the root of everyones broken diff.

THERE is no difference in strength between crush collars and shims for pinion PRE-LOAD.
.... only more time to get the pre-load perfect.
.
 
Supershafts said:
The 742 and 489 and 741 and every other diff use shims to set pinion depth..........


Let's lose the bs about crush collars being weak or the root of everyones broken diff.

THERE is no difference in strength between crush collars and shims for pinion PRE-LOAD.
.... only more time to get the pre-load perfect.
.
Click to expand...

^^^^^^^ Xs2
 
I had my yoke changed and the guy did not put in a new crush sleeve and I am told this should have been done. I have never gotten into a differential and not sure if I should have it done for me or not. I am always nervous about others working on my car as it seems there is always a problem after I get it back. So, some advise please?

Do I need to take the pinion completely out of the case or can it be replaced by just removing the yoke, seal and front bearing? I know he correct pre-load is critical. Also would it be a good idea to replace the pinion bearings at the same time? I never had a noise until after the yoke was replaced.
 
That there is the whole reason that I and cosgig (probably) prefer to stay away from crush sleeves. If you need to replace the pinion seal or remove the yoke for some reason, you have the chance of messing up the pinion depth. Changing the seal can be done without changing the pinion depth if you are careful, but often people aren't.

gunmetal72 - If you have the 489 case in your car (this doesn't apply to 741 or 742 cases!), and he changed the yoke without worrying about how far to crank it down, you likely have the pinion setting messed up. You will have to remove the entire pumpkin and take it to a good differential mechanic to get it re-built. When he rebuilds it, make sure he uses the hard spacer that replaces the crush sleeve so you can swap yokes again or fix a seal in the future without worry. Either that, or replace it with a used 742 or 741 gearset (probably cheaper - but you will need a different yoke).
 
You can NEVER effect the depth changing a end yoke.... NEVER

If the person changing the end yoke is knowledgeable of differentials then there is no problem changing the end yoke with a crush sleeve.

.What noise do you have and when is it happening ??
 
so Powerflite should have said some wrench turners can give U too much pinion bearings preload when replaceing pinion seal or yoke on a crush sleeve equipped diff. Cuz the problem is now the pinion nut tightening can not be done by the book, the wrench turner must get creative. and no matter how creative we get, down the road there is a greater chance of the nut loosening.
 
Supershafts said:
You can NEVER effect the depth changing a end yoke.... NEVER

If the person changing the end yoke is knowledgeable of differentials then there is no problem changing the end yoke with a crush sleeve.

.What noise do you have and when is it happening ??
Click to expand...

The noise a low growling sound, not very loud, but only does it over 30 mph. The noise was not there before the yoke was changed
 
I swapped 4.30's in a 489 carrier and when I tried to crush a new sleeve it would not move. I used a 1/2" breaker bar and a pipe extension with no success. I went to the shop in Kenwood, CA and talked to Joe a former Chrysler dealer master mechanic. He said take a big hammer, large pipe stub and hammer all around the OLD sleeve to extend it, so it can be reused. That was 30 yrs. ago and a spool added, and the pre-load is still at the "used pre-load" of 10 lbs?, turning the yoke nut, without a ring gear installed. So in a pinch, try the hammer tune up. Don't forget to use a nut with plastic lock, or 2, or lightly stake the stock nut at the stem edge with a point chisel.
 
..............He more than likely over torqued the pinion nut which then changed the pre load on the pinion bearings......used bearings do not want much pre-load ........if u want some help u can p/m me..........kim.....
 
Supershafts said:
You can NEVER effect the depth changing a end yoke.... NEVER

If the person changing the end yoke is knowledgeable of differentials then there is no problem changing the end yoke with a crush sleeve.

.What noise do you have and when is it happening ??
Click to expand...

Sooo, herein lies the problem!!! "IF" the person who did the work was knowledgeable.......you can't assume he was or the OP wouldn't be asking this question now would he???
 
aracer01 said:
I swapped 4.30's in a 489 carrier and when I tried to crush a new sleeve it would not move. I used a 1/2" breaker bar and a pipe extension with no success. I went to the shop in Kenwood, CA and talked to Joe a former Chrysler dealer master mechanic. He said take a big hammer, large pipe stub and hammer all around the OLD sleeve to extend it, so it can be reused. That was 30 yrs. ago and a spool added, and the pre-load is still at the "used pre-load" of 10 lbs?, turning the yoke nut, without a ring gear installed. So in a pinch, try the hammer tune up. Don't forget to use a nut with plastic lock, or 2, or lightly stake the stock nut at the stem edge with a point chisel.
Click to expand...

And you're telling someone who is obviously not a master chrysler technician to take a hammer, pipe and chisel to fix this problem?????..........
 
You betcha! I'm getting out some shade tree mechanical tech to the general public. Who really cares about some f'ed up, used gear; we only want to deposit in bank of mechanical knowledge. One may not have access to 280 ft/lb, air tool, or the solid spacer, in time to get to the track.
 
aracer01 said:
You betcha! I'm getting out some shade tree mechanical tech to the general public. Who really cares about some f'ed up, used gear; we only want to deposit in bank of mechanical knowledge. One may not have access to 280 ft/lb, air tool, or the solid spacer, in time to get to the track.
Click to expand...

Not going to the track, just want the noise gone, I don't think it is very good for he gears
 
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