Farley`s Dodge Diplomat Forum

Forum Index => The Garage => Topic started by: Rox86 on January 30, 2015, 10:38:20

Title: '86 Fifth Avenue Read End question
Post by: Rox86 on January 30, 2015, 10:38:20
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!
Title: Re: '86 Fifth Avenue Read End question
Post by: DobaMark on January 30, 2015, 10:44:07
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.
Title: Re: '86 Fifth Avenue Read End question
Post by: Rox86 on January 30, 2015, 10:52:52
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.
Title: Re: '86 Fifth Avenue Read End question
Post by: Captain Caravelle on January 30, 2015, 10:59:25
First off....
Welcome aboard!

Just wondering why you want to swap the rear?
Title: Re: '86 Fifth Avenue Read End question
Post by: DobaMark on January 30, 2015, 11:07:15
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
Title: Re: '86 Fifth Avenue Read End question
Post by: DobaMark on January 30, 2015, 11:11:53
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.
Title: Re: '86 Fifth Avenue Read End question
Post by: Rox86 on January 30, 2015, 11:15:52
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.
Title: Re: '86 Fifth Avenue Read End question
Post by: Rox86 on January 30, 2015, 11:22:02
Go to www.car-part.com (http://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.
Title: Re: '86 Fifth Avenue Read End question
Post by: DobaMark on January 30, 2015, 11:25:37
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.
Title: Re: '86 Fifth Avenue Read End question
Post by: Rox86 on January 30, 2015, 11:31:49
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.
Title: Re: '86 Fifth Avenue Read End question
Post by: DobaMark on January 30, 2015, 12:10:12
In 1976 they offered ratios of 2.4, 2.7, 2.9 and 3.2.  Sure Grip optional.
Title: Re: '86 Fifth Avenue Read End question
Post by: Rox86 on January 30, 2015, 12:19:37
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?
Title: Re: '86 Fifth Avenue Read End question
Post by: Mike on January 30, 2015, 13:09:09
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.
Title: Re: '86 Fifth Avenue Read End question
Post by: DobaMark on January 30, 2015, 13:16:34
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.
Title: Re: '86 Fifth Avenue Read End question
Post by: Captain Caravelle on January 30, 2015, 13:30:46
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.
Title: Re: '86 Fifth Avenue Read End question
Post by: 270SE on January 30, 2015, 13:52:11
If you want to re-gear, you need at least a 2.7 or 2.9. The 2.2 and 2.4s will require the case swapped to gear 2.9 or steeper. It's possible to do and if buying open and then going LSD it's not as big a deal but if you're buying LSD off the bat or staying open- easier to just go 2.7+ out the gate.
Title: Re: '86 Fifth Avenue Read End question
Post by: 79dodge4ever on January 30, 2015, 14:25:55
the differential in the car will hold up just fine if you drive it like it is; a chrysler luxury car not a challenger, if you spin it; its gonna let go
Title: Re: '86 Fifth Avenue Read End question
Post by: fifthcrunch on January 30, 2015, 14:53:22
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.
Especially in California you have to exercise care in making performance modifications.  The axle swap would be ok, but they check emissions and equipment under the hood and in the exhaust.   So there might not be much you can do.  The axle swap, if you get the right gears would be a huge performance gain.
Title: Re: '86 Fifth Avenue Read End question
Post by: grinner357 on January 31, 2015, 22:32:30
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.
if you live in CA then i'm not sure you can do duel exhaust. fatter piping and drop the cats in the front for just a single, yes, as i will be doing that in the next few days, but unless it came factory with duelies then i'm not sure you can change it over. and headers are out, since there's no egr provisions. also, the ARB is anal about things being stock/factory original equivalent or being approved, and visuals can be fairly strict; even a simple carb/ignition swap can be an automatic fail and have to change it back if the inspector can tell its not a factory setup.
Title: Re: '86 Fifth Avenue Read End question
Post by: lsm360 on February 01, 2015, 03:12:08
Rox86; welcome, and I wonder if you were to call the yard with the 8.25 rear they might check for a tag on the diff cover that shows the ratio. May not be there after all these years. They can also figure it out for you if tag is gone. Maybe if you explain you are an hour and a half away. I really love 2.94 gears in my cars. I was fortunate enough they all came stock with 8.25 and 2.94 gears. Don't forget, you'd have to have driveshaft shortened too IIRC, but that's not a huge deal.