7.25 Rear - Differential Interchange

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PocketAces

PocketAces

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My experience with 7.25 rear ends is limited to a 1965 I worked on for my Dart. On that rear end,preload and backlash was adjusted using shims per the factory service manual.

Today I learned that there are 7.25 axles that use threaded adjusters to set preload and backlash.

1. Does anyone know when the changeover occurred?

2. Will a differential from a later rear with the threaded adjusters fit an earlier axle housing that is adjusted via shims?
 
Not sure but I will tell you that the 68 had the screw adjs..I pulled the diff from the 68 small bolt rear and installed it in the 75 big bolt 7 1/4 due to bad spider gears. Charrlie S is the 7 1/4 guy on this site.
 
Yes, it works. you can install a differential carrier from the pre-1973 axle to a post-1973 one. The bevel gear is also identical. the thru axles have 25 splines.
 
PocketAces said:
My experience with 7.25 rear ends is limited to a 1965 I worked on for my Dart. On that rear end,preload and backlash was adjusted using shims per the factory service manual.

Today I learned that there are 7.25 axles that use threaded adjusters to set preload and backlash.

1. Does anyone know when the changeover occurred?

2. Will a differential from a later rear with the threaded adjusters fit an earlier axle housing that is adjusted via shims?
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1: I don't know what year the changeover occurred. The first one I worked on was my 65 Valiant in about 1974, and it had adjusters. I think the rear was original to the car.. I have removed rears from later years (can't verify original) that had shims. I have a LBP 7 1/4 (1972 or later) in the shop right now that has adjusters.
2: yes, All center section parts will interchange with all "A" body 7 1/4 years (even the big bolt pattern rears). However everything outside of the center section, is different between LBP and SBP.
 
townsend said:
Threaded adjusters on 7 1/4 differentials began on January 31, 1972.
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Thanks. I never bothered to verify years. I just fixed or changed ratios on whatever came into the shop. It is totally possible the rears were replaced in the early cars with later units.
But that does seem strange to me. As that would mean there were only 2 years (73 and 74) of SBP 7 1/4 rears, and I have seen many more SBP threaded rears then LPB
 
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Charrlie_S said:
Thanks. I never bothered to verify years. I just fixed or changed ratios on whatever came into the shop. It is totally possible the rears were replaced in the early cars with later units.
But that does seem strange to me. As that would mean there were only 2 years (73 and 74) of SBP 7 1/4 rears, and I have seen many more SBP threaded rears then LPB
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I recently installed a pro-built 273 / 4-sp in my 64 (originally a slanty / auto. It still has the original small rear axle (7 1/4 ?) I need to change the rear axle ratio to a lower (numeric) ratio. What ratios are available? Currently it runs at over 3000 at 65 MPH. I have no plans to race CUDAVRT, just use it for rod runs and crusing. Any help is appreciated!
 
StrokerMcG said:
I recently installed a pro-built 273 / 4-sp in my 64 (originally a slanty / auto. It still has the original small rear axle (7 1/4 ?) I need to change the rear axle ratio to a lower (numeric) ratio. What ratios are available? Currently it runs at over 3000 at 65 MPH. I have no plans to race CUDAVRT, just use it for rod runs and crusing. Any help is appreciated!
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You should have 2.93's in there now, what diameter tire are You running? 2.76's are common as dirt in later models, but would only drop You to 2,826rpm's, maybe You have a hard-to-find set of 3.23's....in which case it would drop You to 2,563rpm's.
 
you looking for gears or to swap the entire rear end? just gears, 5th aves came with 2.24's in their 7 1/4's, that would put 70MPH right at 2050 RPM ignoring converter slip with a 215/70R14 tire (a skoash under 26"), more if your tire is shorter.... a 2.76 puts you a touch over 2500 RPM @70 with the 215/70R14. >3k@65 sounds like you have a 3.55's (or 3.23's with a really short (24" tall) tire)
 
Killer6 said:
You should have 2.93's in there now, what diameter tire are You running? 2.76's are common as dirt in later models, but would only drop You to 2,826rpm's, maybe You have a hard-to-find set of 3.23's....in which case it would drop You to 2,563rpm's.
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I'm sure that I currently have a 3.23. I raised the rear end off the floor with my floorjack, marked the wheel and the driveshaft. The driveshaft turned about 1.2 times for 3+ turns of the wheel. Tires are 205 / 60 R15 Goodyear which Tire Rack logs at 24.7 inch diameter. So it looks like a 2.93 is what I need along with a change of the speedometer gear in the transmission. Assuming I'm correct, where can I get a rebuilt replacement?
 
2.94's might be a little tough to find. I'm thinking 2.76's might be easier, probably look at newer (73-76) A bodies with autos and drum brakes if you're still small bolt pattern.
 
michiganpat said:
2.94's might be a little tough to find. I'm thinking 2.76's might be easier, probably look at newer (73-76) A bodies with autos and drum brakes if you're still small bolt pattern.
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Will the 2.76 directly bolt in the original carrier? I'm running '64 axles, and the wheels are dual bolt pattern. Drum brakes. The 273+ makes something north of 275 HP so there should be plenty of torque at 65 mph to haul CUDAVRT around. If all the above is correct, all I need now is a source. Thanks to all for your help!

Warren

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StrokerMcG said:
I'm sure that I currently have a 3.23. I raised the rear end off the floor with my floorjack, marked the wheel and the driveshaft. The driveshaft turned about 1.2 times for 3+ turns of the wheel. Tires are 205 / 60 R15 Goodyear which Tire Rack logs at 24.7 inch diameter. So it looks like a 2.93 is what I need along with a change of the speedometer gear in the transmission. Assuming I'm correct, where can I get a rebuilt replacement?
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2.94's from 3.23's will only take You down to 2,721rpm,..in contrast to 2,563rpm for the 2.76's.
I don't know if anybody is selling reman 7.25's, but they ain't hard to find with either 2.94's or 2.76's, common as dirt. Swap Your axles into a good one, get somebody to put seals in it if You don't do that. The gears will swap over unless they are real early units which have a different pinion spline/yoke. Anything '64 or newer should work, those 3.23's are not available new anywhere, there are Members looking for them, @TF360 .
If it's a SG diff., guess You'll be swapping gears, good luck!!!
 
I had 3, 2.76 geared 7-1/4s sitting here for more than a couple years from various F bodies. I couldnt give them away for $25. so they went to be melted down, probably are now part of a Kia in some form.... These were actually C clip axles... IDK when that changeover happened/
 
volaredon said:
I had 3, 2.76 geared 7-1/4s sitting here for more than a couple years from various F bodies. I couldnt give them away for $25. so they went to be melted down, probably are now part of a Kia in some form.... These were actually C clip axles... IDK when that changeover happened/
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my '76 duster's 7 1/4 isn't a C clip axle. problem with an F body rear if looking to swap the whole thing is its almost 3 1/2" wider than the A body (60.5 vs. 57.125") and the wrong bolt pattern if he wants to stay 5x4.

another option would be to look for an A833 OD, gear ratios are 3.09/1.67/1/.73. my duster OEM is an A833OD/3.23, and with the 215/70/14 rear tires, I'm running 2000 RPM @ 65MPH but some people complain about the wide ratio spread...
 
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