7.25 to 8.25 Swap

dm330

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Please forgive me if this topic has been discussed to death, but I have an 8.24 rear end with 2.45 gears out of a late 70s Volare or Aspen coupe for my 88 Fifth Ave. I want to upgrade to 2.94 gears for better city performance, while keeping this an open diff, if possible. The issue I've run into at this point is finding an empty carrier case for this upgrade, so my question would be to those of you familiar with the 7.25 to 8.25 upgrade, can this upgrade be completed while keeping this diff open? I see universal empty carriers available and plenty of limited slip/posi, even a couple lockers available. I appreciate the advice and recommendations.

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picklesgarage

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does this one need a new carrier to change the gears? my understanding is the ring gear just bolts on. are there different size carriers for the 8.25?
 

dm330

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From what I've read online there's a carrier for 2.71 gears and up and another carrier for the the others, although I also read the 2.45s have their own carrier and no other gear ration will work. That said, by 2.71 and up, I'm assuming they're referring to the numerical value, rather than high or low ratio. Today I did find a carrier, but for 29 splines, rather than 27, and thinking maybe that's the route to go.
 

dm330

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Yes, and I believe all other 8.25s from 1997 on. I haven't looked much into those because it may be more work than necessary to apply to my car. For now, my main concern is finding a carrier that will work with this unit and 2.94 gearing and work from there.
 

BudW

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On the 8-1/4" differential, there is a break on gear ratios. The 2.2 and 2.4 ratio gears use one carrier and 2.7 and lower (higher number) use a different carrier. The pinion gear is so large diameter, they have to have the ring gear attaching flange so far from the pinion gear center-line on the 2.2/2.4 ratio gear sets.

With that said, the '68-96 use one axle spline (27) and the '97 and newer use a different axle spline (29). The "open" carriers are the same so a person can use 27-spline spider gears in a 29-spline case if needed. On limited slip carriers - you are out of luck on spline count.
The 8-1/4" differential was used in Dakotas, a lot of Jeeps and the lightest of duty full size pickups/vans

Now with that said, I WILL NOT re-install an open carrier on a differential overhaul on any friends/family/or even somewhat friendly folk - for, in a huge amount of cases, there is absolutely no advantage to using an open carrier.


Off subject some, there is also a carrier break on the 7-1/4" differential, as well - which has been made sense the early '60's. Some of them used limited slip carriers - but I don't think any made there way into FMJ's. It is very hard to find a limited slip carrier for a 7-1/4" differential.
BudW
 

dm330

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Thank you for that information Bud. That is very helpful.
 

Loy

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I'm still needing an entire assembly (8.25 housing and all) to swap my 2.71 to a 2.94 (1989 5th Ave). I want to find one that is already a 2.94. I don't want to do anything but swap the housing so if someone has a unit like this available please let me know. Thanks.
 

dm330

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On the 8-1/4" differential, there is a break on gear ratios. The 2.2 and 2.4 ratio gears use one carrier and 2.7 and lower (higher number) use a different carrier. The pinion gear is so large diameter, they have to have the ring gear attaching flange so far from the pinion gear center-line on the 2.2/2.4 ratio gear sets.

With that said, the '68-96 use one axle spline (27) and the '97 and newer use a different axle spline (29). The "open" carriers are the same so a person can use 27-spline spider gears in a 29-spline case if needed. On limited slip carriers - you are out of luck on spline count.
The 8-1/4" differential was used in Dakotas, a lot of Jeeps and the lightest of duty full size pickups/vans

Now with that said, I WILL NOT re-install an open carrier on a differential overhaul on any friends/family/or even somewhat friendly folk - for, in a huge amount of cases, there is absolutely no advantage to using an open carrier.


Off subject some, there is also a carrier break on the 7-1/4" differential, as well - which has been made sense the early '60's. Some of them used limited slip carriers - but I don't think any made there way into FMJ's. It is very hard to find a limited slip carrier for a 7-1/4" differential.
BudW
The limited slip was my preferred choice until I found nothing available, but I did come across your post in another thread for the Dana Spicer part number D/S75101X and sent out an email requesting whether or not this product is still on the market. I'll post an update as soon as I get a response. Now if this unit is still available and I can find axle shafts for this car, I should be set to place some orders.
 

Duke5A

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This is a lot of leg work. These axles aren't easy to find anymore. You'd be money and time ahead finding a Ford 8.8 from a 90's Mustang. Get the limited slip, 3.2 gears and disc brakes all in one. Take that and your old 7.25 to an axle shop and tell them put leaf spring pads on it at the same place as on the 7.25. I can't remember if it would need to be shortened or not.

You'll have to cut your driveshaft down too, but that would need to he done with an 8.25 anyways.
 

dm330

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Yes, I've found that out, but I also may have found axles shafts for this, so if those are still available I'm sure I'll be good to go. I've bookmarked everything I need to do this, just waiting on replies for availability before I spend any money, that way if they aren't available, I can look at other options. Some sites let you know if parts are unavailable and some let you know after you've ordered the part.
 
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