1980 Dodge Diplomat question!

AJ/FormS

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Again, for your application, which automatic you install, makes as good as no never mind. This is because the power loss is not instantaneous through the tranny, but rather a percentage, as the rpms rise.And it is only somewhat linear.
For instance; if the absolute powerloss through the tranny was say 25hp at 6500 rpm, then at 5000 one might expect (5000/6500)x25=19.2hp loss. And at 3000 one might expect (3000/6500)x25 = 11.5hp loss. In reality this is just no so. Further more these are WOT numbers. At say 50% power application, one might expect 50% the power loss. So now the numbers are 9.6 and 5.7.
But here's the catch. The absolute loss through the tranny is directly related to the input power. If you are inputting 400hp. you might lose that 25. But if you are inputting 200,You will not also be losing 25.
So again for your application, I doubt you would notice a powerloss.
However, the mass of the rotating parts in the big 727 are considerably more. And that mass takes a wee bit more time to spin up. In a drag car, this is important on account of that car will suffer three accelerations and two decelerations during the course of the race.
Your car on the other hand will suffer only one acceleration, on account of first gear with 3.23s and 27" tires will hit the speed limit; 65 =6400 plus TC slip;say 6650.
So again, which tranny you use should probably be more related to what you have available, and what your chassis is already set-up for, and what you can afford.
Now for the wild card; there is available a 904 with ratios of 2.74-1.54-1.00 and a loc-up. This will give you a starter gear of 3.23x2.74=8.85 plus the momentary TC ratio. This will get you off-the-line quite a bit more briskly, than the 2.45 low in the standard box;about 12% better torque multiplication. The only downside is the rpm drop between shifts. But again at your power level, this is not a big deal. Another nice thing is the loc-up feature, which will eliminate the TC slip while cruising, and might be good for 1 or possibly 2 mpgs on straight point-to-point hiway useage.
These are the real reasons to opt for a 904variant.
Oh and it is a few pounds lighter. Plus the TC is usually lighter.

And if you are confused about some of this, consider that Chrysler put the 727 behind slanty's too, for HD use. In they often had reargears in the 2.xxs. If you had a 140hp slanty and you stuck a 25hp loss tranny behind it, you would turn an already sucked out combo into a total pig of a car.Ok, maybe sucked-out and pig-of-a-car, are a bit harsh.But after you drive your car with a 360 come back and tell me I was wrong,lol.
Anyhow, more ramblings from AJ, peace/out.
 

AJ/FormS

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The snout length difference between the 8.25 and the 8.75 is very little. I have successfully swapped them around with no driveshaft changes.It might be dependent on your ride-height, and the changes in ride-height during driving.
The only reason for you to swap the 8.75 in, is for ease of gear-ratio swaps. You might like 4.30s for summer and 2.76s for winter; at least I did,lol. It's about an hour to an hour and a half to swap it around, depending on if you have a hoist, or if you are trying to slide your,um,derriere, in and out from under the car,in your gravel driveway, and there is just barely room under there for your barrel chest, and the chunk laying on it,lol.Let's see now, how did that guy say to do this again? heehee. Hint;come in from the back, grab the chunk that is already laying there, hoist it over your face,then your throat, and finally your chest;then hang it on the studs. Say what? You tore the gasket? Choice words and start over.......:)
Hoist is waaaay better.
 
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SlantSixSullivan

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The snout length difference between the 8.25 and the 8.75 is very little. I have successfully swapped them around with no driveshaft changes.It might be dependent on your ride-height, and the changes in ride-height during driving.
The only reason for you to swap the 8.75 in, is for ease of gear-ratio swaps. You might like 4.30s for summer and 2.76s for winter; at least I did,lol. It's about an hour to an hour and a half to swap it around, depending on if you have a hoist, or if you are trying to slide your,um,derriere, in and out from under the car,in your gravel driveway, and there is just barely room under there for your barrel chest, and the chunk laying on it,lol.Let's see now, how did that guy say to do this again? heehee. Hint;come in from the back, grab the chunk that is already laying there, hoist it over your face,then your throat, and finally your chest;then hang it on the studs. Say what? You tore the gasket? Choice words and start over.......:)
Hoist is waaaay better.
I have a hoist, and a four post lift with available air tools. The swap is no problem! I do have an 8 3/4 available already, which is why I am considering using it rather than the 8 1/4. Free is good, usually. Now, if it requires more work than it's worth to install the 8 3/4 I will search for an 8 1/4 sure grip (which are easily found). It seems that in my neck of the woods, everyone's got Mopar parts. I know at least a dozen gearheads in town, and we swap parts regularly. Finding what I need should be easy.
 

AJ/FormS

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Naw, the 8.75 is kindof a bolt in deal. About the only thing that might be different is the location of the flex-hose mount and the method of attachment. Both easy to fix/change.
Unless the d/s yoke is different, which is still only a wee bit of a deal.
 

AJ/FormS

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Another reason to dump the 8.25 is if it has a gear ratio down in the low 2.xxs. These are hi-way friendly, but with your new combo, low gear(2.45) will be good to well past the speed-limit; say 75mph? You can probably measure your rate of acceleration with a sundial,at least until it gets wound up some!
 
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jamf

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Good looking ride. I saw that car on craigslist not long ago and was pondering it myself. Looks real clean.
 

LSM360

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I never gave the fab work a second thought.. being that the 8 3/4 is much different from an 8 1/4, I'd have to shorten the driveshaft. I will have to continue my search
You will still have to shorten driveshaft switching from 7.25 to 8.25. I see no reason to dump an entire rearend because of the gear ratio. Getting a used rearend you don't know the condition of the ring and pinion, and may need new R and P. If I could get my hands on a 8.75 for cheap, I'd want to for future project or to re-sell, but not for your project. If necessary I'd put a new R and P in the 8.25, like maybe 3.21. Maybe I am mistaken, but I did not think there was an 8.75 that was a bolt in to an M body. Spring perches, etc.
 
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BudW

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Header terms:
F – Flange to flange
P – Perch center to perch center
C – Center of U-joint to center of axle length
D – Drum to drum width
T – Track
(Note: green in column D and T is not a 100% accurate number).

header.JPG

FMJ possibilitys.JPG


FMJ bodies are 44.46” perch center to perch center (column “P”).

’65-70 B-bodies are 44” (0.23” difference per side). If using older shock plates, you can squeeze one into a FMJ without modification (except for possible driveshaft length) – but I would slot the shock plate holes out a little, at least.

’65-67 8¾” are a very close fit.
’68-69 and ’70 B-body 8¾” is somewhat close but wider (allows for a wider wheel – but gotta watch the offset).

BudW
 

8v-of-fury

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Has anyone ever tried DANA 35/44 axles from say a leaf-sprung Jeep Cherokee?

Curious, as these D35's are easier to get for me than an 8.25/8.75.. Being that anything pre 200 barely exists anymore.. let alone in a junkyard!
 

Remow2112

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8 3/4 is a pretty easy bolt if you are willing to swap to old style leaf springs with a pin instead of the rubber isolator hook up. The hard part is finding lower mounting plates to switch to B body style shocks.

Get a 360 with a 904 and you will have more fun and power then any /6.

I have done this in F and M bodies.

Dan...
 

BudW

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The DANA 35 and 44 are popular and easy to find parts for.

If you can’t find leaf-sprung diffs, then the coil-sprung diffs are still out there (just cut off unneeded attachments and weld on new perches).

They only thing I don’t have much data on is Jeep dimensions.

Being that anything pre 200 barely exists anymore.. let alone in a junkyard!
BTW, anything pre-2000 are getting hard to find, not counting anything pre-200 (hehe).
BudW
 

79beep

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cool car I almost bought it myself when it was for sale. Make sure you look at the drivers side rail under the firewall before you put a v8 in it.
 
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