rearend casings

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swinger1969

swinger1969

Repeat Mopar guy
Joined
May 2, 2015
Messages
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Location
Victoria, BC Canada
How can I tell which rearend casing I have in my 69 Swinger 340...741 or 742? I'm told it's on the VIN tag but can't decipher it . Do they both take the same crown & pinion ?
 
Crawl under the left side and get the numbers off the nose of the third member. After all these years there is no telling what’s in there.
 
Should be 741 but as said it could have any one of them. 741/742 are different but shim type. 489 is crush collar type.
 
741 small pinion.(Straight shaft)
742 Larger pinion (Straight shaft)
489 Large pinion (Tapered shaft) Most consider the strongest in 8 3/4 rearend.
 
Kendog 170 said:
741 small pinion.(Straight shaft)
742 Larger pinion (Straight shaft)
489 Large pinion (Tapered shaft) Most consider the strongest in 8 3/4 rearend.
Click to expand...
Well damn ! Just looked and the marking on the case says 2070741. That REALLY sucks because I have a set of 3:55's I was going to put in in place of the 3:23 and they're for the 489 case !
 
Not a bad thing The 3.55 for the 489 will sell fast. And 3.55 for the 741 were common. Those were found in pickups and vans.
 
S just to cofirm the case , on the drivers side of the case is the number 2070741.........that means for sure it's a 741 case , right ? I thought for sure it would be a 489 being a '69.
 
DoctorDiff said:
Very few A-bodies equipped with an 8.75" rear did not get a 741 casting.
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Before I sell off the new 3:55's , are the casings interchangable? Could I swap the 741 for a 489? Just wondering what my options are here - being up in Canada it would cost a LOT to send them back then reorder etc.
 
Yes you can buy a 489 case and bearing kit and use your gears. If your original 741 is a SG, you can use that SG in the 489 case.
 
Any case will bolt into you housing but each case takes its own gearset. Differentials will go into any case . Check the spline on your new gears to make sure you have the correct yoke when the time comes .
 
SGBARRACUDA said:
Yes you can buy a 489 case and bearing kit and use your gears. If your original 741 is a SG, you can use that SG in the 489 case.
Click to expand...
I really appreciate the help! When I bought the gears from Summit I bought the installation kit as well , so the bearings etc are there. I'm pretty sure the diff in it is a sure grip .
 
mbaird said:
Any case will bolt into you housing but each case takes its own gearset. Differentials will go into any case . Check the spline on your new gears to make sure you have the correct yoke when the time comes .
Click to expand...
I bought the C&P from Summit as well as the installation kit , so I guess I just need a 489 case. The yoke will be different because apparently the 741 has a tapered shaft and the 489 has a straight shaft.
 
There are basically four yokes. Fine spline or coarse, small u-joint or large. The yoke just needs to match your driveshaft u-joint and the spline on your r&p (or crown and pinion for you canadians). Yoke doesnt care what case, that area on 741,742, and 489 is all the same, if spline count is the same.
Of course, there are always billet yokes for 1350 joints, for race applications.
 
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