I am building a 1953 Olds hardtop .Picked up a 67 Toro 425 from 2Blue442 and will use a Turbo 400. The books say the stock wheelbase is 59'' front and back . Put in a 1974 N---(Omega) front clip for steering and disk brakes. Am now looking for the differential . I have researched the options and have concluded that a "little bit of knowledge" is a dangerous thing! A friend turned me loose in the "boneyard'' and it looks like I have these options:
1. An "O" type open 2.56 marked R2,book says from 68-69 Olds ,59" WB
2.A diff my friend "thinks" (in between beers) came out a 74 Cutlass , which would be a 60.7 " WB, open,marked 7 AAO 344
3.A diff my friend thinks is from the 74 N---,open, marked PA1007C(last symbol could be G or O),59"WB,leaf springs
4.A bare housing my buddy (after numerous beers) dug out which he was told is out of a 65 Ch------,12 bolt, axle marked CW 0405 B,housing marked 387574SN ,which would be a 58" WB
5. The stock 53 open diff ,leaf springs (is a posi made for these?)
SO, the question: which ,if any, of these should I build & use. I want a "posi" and am thinking of gears 3.23-3.42.Looks like will stick with leaf springs. Unfortunately, $ is a factor. THXZ for the advise

 

Sorry I can't help you there. Monzaz is the guy that knows everything about differentials. He could surely answer your questions.

 

That type "O" would probably fit the engine very well since it was designed for use with the torquey Oldsmobile V8s. Not sure how much trouble you would have adapting the coil spring setup to your '53 frame though.

 

If $$ are a consideration (and when are they not), I would consider keeping the original rear, at least for the time being. You can always change it later. Those old rear ends are pretty tough. If you are going to swap to a later 10 bolt or 12 bolt, I would consider one out of a Camaro or Nova since they had leaf springs. They will be lots of $$ though.

 

59" is your width of the over all axle.

The 'O' type 12 bolt is probably more like 60" and it will also be hard to find a reasonable priced posi and the gears are 3.42 3.91 ONLY and they are 300.00 a set. SO unless your really attached to that kind of rear and the look. Not a good choice...besides alot of cleaninmg to do since it has all the mounts for a 4 link rear.

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74 cutlass rear again is a 4 link and will have a lot of clean up work. the rear is pretty wide more like 61" -61.5 the axle shafts are 30 3/8" long and then there is the center cross pin another 3/4" BUT it would be a 8.5 and that is a good choice as far as cheap good posi units are available and gear selection in your range is also fairly easy to find in the yards.

Might work...???
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1974 open leaf spring 59" - PROBABLY a 1974 nova rear diff. No cleaning required saves a lot of time... PLUS were in the width you need and this again is probably a 8.5 rear which again has a great chance at being a VERY good candidate for your swap. Sounds like a winner but will continue...

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12 bolt chevy rear- Well this is a pretty good find. 3.31 gears already in the rear. Plus the strongest car rear GM built. The length is really the same as the 1974 nova 59.5" - axles are 29 5/8" each and then the center cross pin 3/4" again . comes out to about 59.75" BUT still very in the range you need.

posi units are available but not as cheap as the 8.5 would be and the 8.5 you can definitely find in any yard still today.

Soooo I would do the 1974 nova rear or the 12 bolt 65 rear. I would sure love to get that 65 12 bolt from you if your not going to use it. I would hate to see it get chopped up. Not too many housing that age not all mangled.

So. I hope I have help a little on the choices. Take care and you can always check out jdrace.com for rear differential ID and parts or whole rear diffs.

 

Thanks for the great advice. I plan to open up the Nova rear today - will let you know what I find. Will the 65 Chevelle 12 bolt fit in to my 64 Cutlass ? Thanks again guys !

 

THXZ again for your help .The 1974 N--- measured out as you said. We cut off the stock pads (it had a narrow single leaf) and it cleaned up pretty well. Has 3.08 gears. Would this be a big difference from 3.23 with the 425 ? Looking in catalogs for "posi" units -too many choices ! Any recommendations ? Is there such a thing as a complete rebuild kit or is it best to buy separate pieces? Will it harm the bearings to have the diff blasted to clean it up ? I appreciate your help . John

 

While attempting to become smarter tonite, I visited jdrace.com . The cover on the diff we are working on looks like the "10 bolt chevy 8.2'' ,not like the "10 bolt 8.5''. The number on the ring gear is 1GM3790628 12 37 267 . Hard to measure the gear to tell if it is 8.2 or 8.5 . Is there another way to tell the difference? If it is an 8.2, is it strong enough for the 425? Or should I go another direction ? Confused in California.