Decode of this rear end...

[dspaulding70]

Please see attached picture.  I purchased these 3.23 gears for my 8 3/4 rear end but not sure what year they came out of.  This was front a different source that the housing and axles.

[mikepmcs]

Made 1969-74
Is it a sure grip rear...cone or clutch???
I'm thinking we need more info please.
Is this your chunk you purchased or did you just purchase gears and are putting them in this case?

Swiped this from tech pages.

2881489 AKA "489":
The strongest of the 8 ¾ units. As with the 742 there are tons of replacement parts available as well as gear ratios. Gear ratios available beyond 3.23 are: 3.55, 3.91, 4.10, 4.30, 4.57, 4.86, 5.13 and 5.38. Almost all original sure grips, except 1969, found in this housing are the non rebuildable and less desirable cone type. Also with suregrips there is a bit of noise on the net as which are better. The clutch type are rebuildable and the best for racing. The cone type are not rebuildable but are perfectly acceptable for a street car. They last at least 40 - 50K with means many years of abuse with a weekend driver. If you need a SG for a car, can't find a clutch type to rebuild, are not a racer go buy a new one for $300 - 350. I would not buy a used cone SG though.
Info: 1 7/8 Pinion

NOTE: All cases, pinions, bearings, gears are not interchangeable between the three units but the sure grip units themselves are. There are two types of sure grips:

Dana Power Lok, 1962 - 1969 which are rebuildable (clutch packs)
Borg-Warner Spin Resistant, Late 1969 - 1974 which are not rebuildable (cone type)

An easy ticket to a cheap sure grip is to find a clutch unit in an orphan 741 case and remove it with the bearings (pressed on) and races and swap it into your better carrier (742 or 489). Most people don't think they are swappable so whine to the seller that it is a 741 SG and negotiate hard. Once the unit is out remove the old 741 ring gear, install yours from your better pumpkin, install a new clutch pack (rebuildable remember? Most are worn out after 30 years. Clutch kits are available from Mopar or Mancini and others) and then swap the whole mess it into your 742 or 489 case. The ring gear bolts are left hand threaded so remember this and don't break any as you may need them. Also if you go this route double check the gear mesh pattern to make sure it is set up ok.

v/r
Mike

[68charger440]

NOTE: All cases, pinions, bearings, gears are not interchangeable between the three units but the sure grip units themselves are. There are two types of sure grips:

Dana Power Lok, 1962 - 1969 which are rebuildable (clutch packs)
Borg-Warner Spin Resistant, Late 1969 - 1974 which are not rebuildable (cone type)

An easy ticket to a cheap sure grip is to find a clutch unit in an orphan 741 case and remove it with the bearings (pressed on) and races and swap it into your better carrier (742 or 489). Most people don't think they are swappable so whine to the seller that it is a 741 SG and negotiate hard. Once the unit is out remove the old 741 ring gear, install yours from your better pumpkin, install a new clutch pack (rebuildable remember? Most are worn out after 30 years. Clutch kits are available from Mopar or Mancini and others) and then swap the whole mess it into your 742 or 489 case. The ring gear bolts are left hand threaded so remember this and don't break any as you may need them. Also if you go this route double check the gear mesh pattern to make sure it is set up ok.

v/r
Mike

This is a real old thread, but it is exactly what I think I would like to do, and I have a few questions.
1. Why should you use the ring gear from the 742 carrier?  Is it better than the one from the 741?  My 742 is an open diff and had 2.76 gears and my 741 is a Dana Power lok and has 3.91 gears so that wouldn't work anyway, right?
2. Are the clutch rebuild kits easy to install?  I have never done one.
3. Is there a link to detailed rebuilding instructions that I missed in my search of the site?
4. If I just put in a clutch rebuild kit, will the rest of the setup such as the gear mesh be good to go if it is good currently, or will a new set of clutches change it to where the mesh will need to be reset?
5. So I will be using the bearings and races from the 741 and putting them in the 742 case.  Just double checking.
6. If I do this I will end up with the pinion from the 741, right?  If so then do I really gain anything by putting it in the 742 carrier?
Thanks for any input!

[Ghoste]

The ring gears are the same, it is the diameter of the input shaft of the pinion gear that changes.  There is a long held, and probably (possibly?) accurate notion about the strength of the different pinions based on the old Direct Connection manuals.  I've never seen a pinion shaft sheared but I have no doubt whatsoever its happened.  I would however be interested to know if it has ever happened on a street car?
The clutch pack ones are not hard to rebuild... depending on your individual ability.
If you tear your differential down, you should always make sure backlash is good upon reassembly.  That is just my opinion though.
If you tear it down, why not replace the bearings and races?
You can't use the 741 pinion in the 742 case.

[John_Kunkel]

I've never seen a pinion shaft sheared but I have no doubt whatsoever its happened.

It does happen but not very often.

[Ghoste]

That's so funny (to me) because I was going to add to the end of that bit that it would be a good question for John K. 

[Alaskan_TA]

not sure what year they came out of

The OE ring gears have a date stamped in the outer ring.

[cdr]

I've never seen a pinion shaft sheared but I have no doubt whatsoever its happened.

It does happen but not very often.

spring wrap that made the pinion angle very steep.

[68charger440]

Thanks guys for the input.  
So it sounds like I would have to buy a new pinion gear if I want to put the sure grip in the 742 case and keep 3.91 gears.  Is that correct?   I'm still not sure what I should do.  Would you guys suggest just rebuilding the 741 sure grip with a new set of clutches and bearings, and leaving it in the 741 carrier?
The motor is a mild 500" stroker now, but I may go with TF or CNC Stealth heads and the Crower hdp282 cam that Ron recommended, but I will never go all out on the motor.  I want it to be a real respectable but reliable street car.  Emphasis on the reliability over the power.