Help identifying differential 65 Barracuda V8

[GHOST RUSTERS]

Hey FABO! Looking for some help in identifying the rear end on our 65 Barracuda/273 V8. I can’t seem to find a tag anywhere or any other numbers other than what’s pictured.

When I grabbed the flange I immediately noticed some “play” (i have not measured the backlash with a dial indicator yet, this was just a pre-inspection) as I turned the flange, minus the drag on the drums which are still on, there is noticeable play in the gears and I’m not sure where this puts me in the build of reviving my dads barracuda…

I am new and still learning what I don’t know.

As of right now, the plan is going from the standard 2 barrel to a 4 barrel manifold/carb, little bit larger cam, a904 cable auto trans is currently in the shop for inspection and possible rebuild, a 340 throttle bracket and the BPE kickdown cable kit… with all of that in mind and the condition/ potential or lack there of, with what looks to be the 7-1/4 diff… is it worth running and or rebuilding, oil it up and run it? Or considering the rest of the build, does this put me at a crossroads in needing to explore other options ???

There is a soft and final budget for the total build. With this being a crucial part of that build I understand and respect that quality isn’t cheap.

Not looking for anyone to hold my hand, only asking those with far more wisdom and experience than I on what to consider in making an educated decision… any and all feedback is greatly appreciated! Thank you!

(FWIW there was still oil in the diff after removing the cover and there was no metal in the bath or on the magnet. This car was parked for 20+ years)

 

[toolmanmike]

7 1/4" open carrier. If it isn't noisy and no metal in the lube,it may last forever. No need to hot rod that one. It's the smallest one Mopar makes.

 

[GHOST RUSTERS]

it does have a distinct “clunk” back and forth… no plans on hot rodding… just cruising, maybe spook a horse that wonders too close to the waters edge from time to time haha… but in reality a mild weekend driver. I have a video of the play and “clunk” if you care to see and or listen I certainly would appreciate your opinion…

 

[cosgig]

I believe that is a 7 1/4”, and there should be some stampings in the edge of the ring gear to identify the gear ratio. That being said, for all of your upcoming upgrades, you should strongly consider replacing the entire axle assembly with either an 8 3/4”, which would allow you to keep the small bolt pattern if you desire, or an 8 1/4” which will have the large bolt pattern. With the play present in the rear, regular driving will probably not harm it, but with your upgrades, I’m afraid that it will not last very long.

 

[GHOST RUSTERS]

I believe that is a 7 1/4”, and there should be some stampings in the edge of the ring gear to identify the gear ratio. That being said, for all of your upcoming upgrades, you should strongly consider replacing the entire axle assembly with either an 8 3/4”, which would allow you to keep the small bolt pattern if you desire, or an 8 1/4” which will have the large bolt pattern. With the play present in the rear, regular driving will probably not harm it, but with your upgrades, I’m afraid that it will not last very long.

I appreciate that perspective, thank you, and that’s exactly why I asked… I’m taking everything into consideration, im at a crossroads with deciding the future of the differential with the future upgrades in mind…

in exploring the two 8 diffs you mentioned, is there an adapter or anything that could be done to still allow me to run my dads wheels that were on the 7-1/4”? Not to be petty but they are sentimental to him and the story of the car but obviously not a priority over mechanical reliability…

I suppose this also changes my rear brake lines and brake needs… currently 10” drums all around and was just about to order a full replacement brake line kit soon… will this get me in trouble with the driveshaft as well? Will the 904 be able to handle all of this? thanks for the feedback!

 

[cosgig]

I appreciate that perspective, thank you, and that’s exactly why I asked… I’m taking everything into consideration, im at a crossroads with deciding the future of the differential with the future upgrades in mind…

in exploring the two 8 diffs you mentioned, is there an adapter or anything that could be done to still allow me to run my dads wheels that were on the 7-1/4”? Not to be petty but they are sentimental to him and the story of the car but obviously not a priority over mechanical reliability…

I suppose this also changes my rear brake lines and brake needs… currently 10” drums all around and was just about to order a full replacement brake line kit soon… will this get me in trouble with the driveshaft as well? Will the 904 be able to handle all of this? thanks for the feedback!

The 904 can handle anything you’re going to throw at it. Now, the 7 1/4” and 8 3/4” use the same size brakes, 1 3/4” wide shoes and a 10” diameter. The line set for the axle itself would be different, but you may not need that anyway. The drums will be the same, and all the hardware. The backing plates would swap over to an 8 3/4” from your axle, but a 7 1/4” backing plate is held on with 4 studs, the 8 3/4” has 5. You would just need to drill the 5th hole. All A body 8 3/4” axles came with the small bolt pattern, so unless the axles have been changed to an aftermarket axle with the large bolt pattern, you can use your existing rims. The driveshaft would have to be shortened with either axle I mentioned in my previous post.

If you just want to use the 7 1/4”, there are literally hundreds of them available that were removed for a differential upgrade, and they would be cheap, or most times free. You can surely find one that is in good condition that you could put right in place, but the fact remains that they are undersized for any spirited driving.

 

[GHOST RUSTERS]

The 904 can handle anything you’re going to throw at it. Now, the 7 1/4” and 8 3/4” use the same size brakes, 1 3/4” wide shoes and a 10” diameter. The line set for the axle itself would be different, but you may not need that anyway. The drums will be the same, and all the hardware. The backing plates would swap over to an 8 3/4” from your axle, but a 7 1/4” backing plate is held on with 4 studs, the 8 3/4” has 5. You would just need to drill the 5th hole. All A body 8 3/4” axles came with the small bolt pattern, so unless the axles have been changed to an aftermarket axle with the large bolt pattern, you can use your existing rims. The driveshaft would have to be shortened with either axle I mentioned in my previous post.

If you just want to use the 7 1/4”, there are literally hundreds of them available that were removed for a differential upgrade, and they would be cheap, or most times free. You can surely find one that is in good condition that you could put right in place, but the fact remains that they are undersized for any spirited driving.

With that in mind, and that there is little to no interest in “spirited driving” and that the existing 7-1/4 I have is already in place and complete… and it did run before sitting… would it hurt to give it a chance under gentle yet firm driving conditions with the build? Let it live its life and when and if it finally can’t take anymore… graduate into one of the 8s??? Like @toolmanmike said… maybe it’ll surprise us all and last forever? Or a week? Happy to know that there are options! Thank you!

 

[RustyRatRod]

7.25. The clunk is likely all the slop between the carrier internal gears. They weren't "real" tight from the factory. lol

 

[GHOST RUSTERS]

7.25. The clunk is likely all the slop between the carrier internal gears. They weren't "real" tight from the factory. lol

Well that’s a relief to hear… factory sloppiness haha maybe it’s a “dummy clunk” to help remind me to be gentle on the tall skinny peddle on the right haha… I’ll give it a healthy cleaning, some new lubricant (gear oil recommendations?) and put it back together and hope for the best. Anything else that you might recommend I address while in the diff neighborhood?

 

[GHOST RUSTERS]

I Got one of the drums off and here’s our first look inside… a little brake cleaner to assist the 8 legged residents to kindly move on…

 

[RustyRatRod]

Well that’s a relief to hear… factory sloppiness haha maybe it’s a “dummy clunk” to help remind me to be gentle on the tall skinny peddle on the right haha… I’ll give it a healthy cleaning, some new lubricant (gear oil recommendations?) and put it back together and hope for the best. Anything else that you might recommend I address while in the diff neighborhood?

You might also inspect the universal joints for play and I would also inspect the motor mounts and transmission mount, as these are other "clunk" producers when they go bad.

 

[GHOST RUSTERS]

Noted! I’ll be installing new u-joints, motor mounts and trans mounts. Thanks!

 

[Dana67Dart]

Or considering the rest of the build, does this put me at a crossroads in needing to explore other options

Clean it and run it while you look for a 8 3/4 or Ford 9" replacement.

My 7 1/4 was just retired after 350,000 miles it was behind a 273 2bbl.

 

[65 Cuda 340]

The original 7 1/4 rear in my 65 Barracuda Commando 273 4-speed lasted 90,000 miles and a lot of speed shifts. Even with a 4 barrel, you still only have 273 cubes (i.e., not a lot of torque). I'd just run the 7 1/4 for now. If it's in good shape it might outlast you. If not, well then you can replace it.

 

[GHOST RUSTERS]

Clean it and run it while you look for a 8 3/4 or Ford 9" replacement.

My 7 1/4 was just retired after 350,000 miles it was behind a 273 2bbl.

That’s impressive! And very reassuring… thanks for sharing!

 

[GHOST RUSTERS]

The original 7 1/4 rear in my 65 Barracuda Commando 273 4-speed lasted 90,000 miles and a lot of speed shifts. Even with a 4 barrel, you still only have 273 cubes (i.e., not a lot of torque). I'd just run the 7 1/4 for now. If it's in good shape it might outlast you. If not, well then you can replace it.

And that’s exactly what I’m hoping for… there really isn’t much more to do with it other than give it a fair chance… any recommendations for an ideal gear oil? Does this require any additional additives for the axle bearings or anything unique?

 

[RustyRatRod]

I don't think I'd shotgun replace all the things you mentioned. One thing at a time. That way, you can tell if one thing addresses your clunk.

 

[GHOST RUSTERS]

I don't think I'd shotgun replace all the things you mentioned. One thing at a time. That way, you can tell if one thing addresses your clunk.

That’s a good idea… I didn’t think of it that way… one leak at a time… good call!

 

[cosgig]

I agree with all of the above. I would first get it running, moving under its own power, and stopping safely. Those brakes might not need more than just the wheel cylinders, a new master, and a good bleed. Do everything you can that’s free, and buy just the stuff you need. I’m sure the fuel system will be a focus as well. I was speaking to the rear end situation because you asked about changing yours out, but the crowd is right on, don’t change it unless it’s bad, I’m sure it’ll make at least a few trips, and maybe many more.

Just be rest assured, spirited driving IS in your future!

 

[GHOST RUSTERS]

Mighty kind words that I’m gonna put on a post it and slap on the dash… “spirited driving” I love it! This has been a really good thread and I’m overly thankful for everyone’s perspective and two cents… once again the FABO has proven that there is nothing that CANT be done.

And yes you’re right, safety is my utmost priority with the build, plan so far is to replace all of the brake lines, distribution blocks, rubber hoses and go with a healthy dual master, I do agree with you on the brakes… they don’t look or feel awful… I cleaned them off and see no cracking or separating … how is that even possible after sitting for so long? Maybe that was the best thing for it in this case?

But I thought the same… wheel cylinders at the least. Fuel line is next and of course front end rubber. I need to take a step back and practice a little “if it ain’t broke, don’t fix it”

Thanks for yours and everyone’s help and encouragement here! Let’s all send out warm positive chi that the 7-1/4 diff is AT LEAST a 300k miler! Or… a few laps at with the family at Mopars in the Park *wink* or getting my dad to and from work for a while!

*NOTE** when I removed the diff cover… only about a half quart of oil came out… anything to worry about? Sitting for so long could it just have “evaporated” deteriorated? … or possibly ran low before being parked? I didn’t see any wet spots on the drums where it might have leaked through the axle bearings/seals? And the diff cover was dry… just another observation.

Still curious to anyone’s suggestion for a decent gear oil and if I’ll need any kind of additive?

Happy wrenching!

 

[GHOST RUSTERS]

Hey FABO, well I got some of the diff cleaned off and found some numbers. Looks to be 2.93 am I reading that correctly for the gear ratio? Just wanted to be sure in what I’ve got for a 7-1/4 rear end and what else these number might be able to tell me??? HELIX? Any feedback greatly appreciated! Thanks everyone! (How does it look in there?)

 

[65 Cuda 340]

Hey FABO, well I got some of the diff cleaned off and found some numbers. Looks to be 2.93 am I reading that correctly for the gear ratio? Just wanted to be sure in what I’ve got for a 7-1/4 rear end and what else these number might be able to tell me??? HELIX? Any feedback greatly appreciated! Thanks everyone! (How does it look in there?)

View attachment 1716299142

View attachment 1716299143

View attachment 1716299145

You are reading it correctly. Also, 2.93 would be the standard gear ratio for a 65 273 2-barrel automatic.

 

[GHOST RUSTERS]

You are reading it correctly. Also, 2.93 would be the standard gear ratio for a 65 273 2-barrel automatic.

View attachment 1716299153

Hey thank you for that! That explains a lot… follow up to my OP, will the 2.93 (vs the 3.23 the 4 barrels got) survive behind the modifications I am making to the engine? 4 barrel and a bit larger cam and possibly 235-60-14 tires in the rear?

 

[lkopaska]

It will be fine Kyle,
Same thing I'm running behind my commando in the valiant and what I ran in my barracuda.
Lon

 

[lkopaska]

Kyle
Any good GL4 or GL5 gear lube will work for that open diff no additive needed.