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[Rox86]

Hello all,


So I've had my 86 Fifth Avenue for about 6 months now after buying it off its original owner. 60,000 miles and everything is in good shape.


I've been wanting to do some modifications to it, nothing too crazy. I want to swap out the 7.25" rear end for a 8.25" first. RockAuto Parts has a Dana 8.25" rear differential for a couple hundred bucks. Part number: DS73100 and DS73101
https://www.rockauto.com/catalog/x,carcode,1063493,parttype,2304


I've been reading on here that certain 8.25" rear ends from other M-bodies will be drop in replacements. Is this true for this Dana 8.25"? If so, is this worth it? If not, where else can I look since there is only one junk yard inside of an 90 minute drive from me?


Any advice here would be greatly appreciated!

[Dippy.org]

[DobaMark]

That Dana piece on RockAuto.com is just the locking portion of the differential.  You'd have to have gears and a carrier and an 8.25" axle housing with axle shafts to install it in.  Probably would cost well over $1k for all that plus the labor to put it together.  It's Dana's version of the Sure Grip differential the factory used.
You'd be much better off buying a complete 8.25" axle with decent gears and a Sure Grip in it even if it means you have to pay for shipping.

[Rox86]

That's a good point about it not being a complete kit. I've bought from RockAuto before and have liked their products.


Where would I begin looking for a complete kit? Not often do I see these cars on Craigslist or the junk yard around where I'm from. The few I have seen on Craigslist have been Fifth Avenues and don't have the 8.25". I'm tempted to make a run down to the junk yards in the Los Angeles area.

[The Cap]

First off....
Welcome aboard!

Just wondering why you want to swap the rear?

[DobaMark]

That's a good point about it not being a complete kit. I've bought from RockAuto before and have liked their products.


Where would I begin looking for a complete kit? Not often do I see these cars on Craigslist or the junk yard around where I'm from. The few I have seen on Craigslist have been Fifth Avenues and don't have the 8.25". I'm tempted to make a run down to the junk yards in the Los Angeles area.

You won't find a complete kit - no one sells anything like that for these cars.  You need to start with a complete axle from another car.  Then you can change gears or the differential (lotsa $$) if necessary

[DobaMark]

Go to www.car-part.com to search near you.  Look for "round cover" or "10 bolt cover" to find an 8.25" axle.  Then call and ask what gears (most will be 2.2, next common be 2.9 but some early cars had 2.7 or 3.2 gears) and if it has a Sure Grip.  I'd search a later mode car (like 1989 Dodge Diplomat) as well as earlier cars (1978 Dodge Aspen) to see what variety can be found.

[Rox86]

Thank you, I guess I should've mentioned I'm new here.


I've read a lot of stories about how poor and weak the stock 7.25" rear is on these cars. Also, I've read the rear end and gearing should be changed before doing anything else to the car performance wise. I plan on dual exhausting it and maybe upgrading the carb. An engine swap is too far in the future for now and the 318 I have now is running perfectly.


I realize I'm not going to be getting a whole lot of horsepower or performance out of this car, so I'm just sticking with small mods (exhaust, rear end, gears, rims, carb, maybe a nicer paint job.) A fun project, nothing too serious.

[Rox86]

Go to www.car-part.com to search near you.  Look for "round cover" or "10 bolt cover" to find an 8.25" axle.  Then call and ask what gears (most will be 2.2, next common be 2.9 but some early cars had 2.7 or 3.2 gears) and if it has a Sure Grip.  I'd search a later mode car (like 1989 Dodge Diplomat) as well as earlier cars (1978 Dodge Aspen) to see what variety can be found.

I looked it up for the Axel Shaft, round and 10-bolt cover. There is quite a few. I'm not exactly sure what I'm looking for and what else I would need besides the Axel Shaft. I'll admit I am very new to modifying cars, so my knowledge isn't perfect.

[DobaMark]

An axle shaft is only the internal part from the differential to the lug nut studs.  You need to look up "Axle Assy Rear" to get the complete rear axle.

[Rox86]

An axle shaft is only the internal part from the differential to the lug nut studs.  You need to look up "Axle Assy Rear" to get the complete rear axle.

Fancy that, the one junk yard within a 90 minute drive from me has an assembly off a '76 Volare. 10-bolt cover. Obviously I don't know the condition nor the gearing but I'll probably make a run over there this weekend.

[DobaMark]

In 1976 they offered ratios of 2.4, 2.7, 2.9 and 3.2.  Sure Grip optional.

[Rox86]

If it doesn't have the right gearing, could I look for aftermarket gears. Either the 2.94 or 3.23? If so, where would should I look?

[Mike]

yes, but any of those gears dobamark listed are better then what you'd have now. If the axle is in good shape you can just put it in your car and drive it for now and upgrade gears late.
Youd also need to the speedometer gear too.
do a search for 8.25 mopar gears and you should find some places to buy them.

[DobaMark]

When looking at changing gears, allow several hundred dollars for installation.  Also, it will cost much more to swap other gears into a rear axle with 2.2 or 2.4 gears because you have to swap more parts than those with 2.7 or higher gears.

[The Cap]

Just an additional two cents.
Yes....people tend to put down the 7 1/4" rear
But it depends on what you want to do with the car.
I've put nearly 40,000 miles on my 87 Fifth in the roughly five years I've had it without any issues whatsoever.

With the stock 2.2 gears....is it a slug off the lights?
Yep.....but it's a dream on the highway....gas mileage is pretty damn good too.

If you want to make this a semi performance car the rear would be the first thing I'd change.

If you want to change it simply as a reliability issue....I'd let her be.