8 1/4 imperial/dakota rear questions.

[lastws6]

New to the world of mopar... and I have an 81 imp.. So that means an 81/4 open rear with 224 gears.. Something needs to be done about that. I *think* the guts from a dakota 81/4 can be used, and there a more than a few in local yards, but I'm sure there is a bunch I should learn.. It's where you fine folks come in.

First, will it work?

Second, did they put 321 gears with a sure grip in those trucks?

Third, Is there a way to tell the gears and if it's a sure grip from looking?

Fourth, if I find all that, what all do I need to get from the parts truck, from the parts store?

I'm on a budget (three daughters, single Dad)... so anything you can tell me about the cheapest way to do this would be a huge help.

Thanks. Dan

 

[Mr.Lopar]

More then likely it's a 7.25, and 8.25 guys won't fit

BUT, if it is a 8.25 , there should be a tag on one of the diff cover bolts, if not you can pull the cover amd look for the numbers stamped on the ring gear.

And the easiest way to check if ours a sure-grip is to jack it up and spin the tires, if they turn in the same direction, it's a sure-grip

 

[kkritsilas]

From what I can recall, the 7.25" differentials were only used on 6 cylinder cars. The Imperial, being a 318 V8 (fuel injected or 4 Barrel if converted over) would have an 8.25". Pretty sure that is true for the Cordoba and Mirada V8 cars, and probably for the F and M bodies as well. I don't think that very many of them were Sure-Grips, and most had very low gears (2.4s mostly, with a few 2.94s and/or 3.23s). Could easily be wrong, though.

Might want to review this previous thread:

http://www.forfmjbodiesonly.com/classicmopar/showthread.php?1653-Rearend-swap

Consensus seems to be that the 8.25" is stock, and that it is probably good for 400HP (without the use of slicks).

There are some people that can provide Sure-Grip equivalents for the 8.25" (ref. http://www.doctordiff.com/8-1-4-spicer-trac-lok-differential.html), but the gear ratio it can be applied to is from 2.76:1 to 4.56:1, so if the stock rear is a 2.4:1, it isn't going to be able to be used. If the car actually has a 2.94:1 or higher, and you aren't planning to apply more than 350 HP to it, it is a possibility; you will still need to factor in installation/setup.

Kostas

P.S. Would the rear axle ratio be called out in the build sheet, if that can be found? I don't think its on the fender tags.

 

[Mr.Lopar]

Nope, 7.25s were behind 318s and slants. Only thing I know 8.25s were in was the r/t Fs and cop cars

 

[My imp]

Imp is definitely 8.25" unless someone changed it. To my knowledge there was no sure-grip option. If memory serves (usually doesn't), the police package is your best bet on sure-grip. I had one with a 3.21 is what the #'s on the ring said. 8.75" had 3.23's.

 

[My imp]

Once again, I stand corrected. There were (4) 1981 Imperials delivered with the D91 sure grip axle according to the Imperial restorers club. Good luck with that!

 

[kkritsilas]

Easiest thing to do to determine the differential type is to look at the post by bremeric in this thread:

http://www.forfmjbodiesonly.com/classicmopar/showthread.php?414-8-25-10-bolt-Imposter

The way I am reading the diagram with the differentials, specifically in the 7 1/4" and 8 1/4" is that the 7 1/4" was used on all the slant 6s, and the small V8 A bodies (i.e. 273 V8 A Bodies). I read the caption near the 8 1/4" as that all F/M/Js with V8s (318s and the few 360s) got the 8 1/4", as did the A body cars from 72 on.

Either way, the easiest way to identify what you have is to use the diagram and check the differential cover, both for the quantity of bolts and the shape of the differential, and double check that against the axle tubes (tapered on 7 1/4" vs. straight on 8 1/4").

Kostas

 

[Mr.Lopar]

Almost all Ms.came with 7.25s (cops had the 8.25)
I could be wrong about the imps, but as far as I know for the most part all FMJs came with 7.25s except specially ordered/packaged cars and fleet cars

 

[Greg55_99]

In my humble opinion, the LEAST expensive way to beef up the rear to is track down an early Mopar B-body 8 3/4 rear. That's what I did anyway.

Greg

 

[lastws6]

Thanks all. To clear things up, my (and every other as far as I know) Imperial has the 8.25 rear. I just went to look again, Just to be sure... I even checked the diagram kkritsilas posted (thanks)in case i had my rear-o-meter out of whack and was dreaming when I had it up on the lift just after I bought it...

That being said. Can I use a 8 1/4 rear from a dakota for the gears and sure track, even if my car has 224 gears (like every imperial)?

I'll prob never be over 320 horse with this, no slicks, no 1/4 passes.. just want to add some grunt. The 224 is silly high.

 

[lastws6]

Oh.. My Imp? I didn't get one of the 4 cars without the open rear. I checked.

 

[kkritsilas]

lastW6:

If you want to use the entire rear end (I have no idea if it fits) see the dimensions here:

http://www.forfmjbodiesonly.com/classicmopar/showthread.php?494-Rear-Hub-to-Hub-dimensions

see the post by Holmes.

If you want to use the internal parts only, the 2.24:1 and 2.4:1 carriers are supposed to be different from the other gears available (2.73-3.55:1), so this gets more involved. Most of the sure-grip/sure-track limited slip units are made for the 2.73:1 and up carriers/gear sets. This is from reading around postings on various Mopar boards.

In all honesty, it would probably be the most economical to get that 66-70 B body 8 3/4" (preferrably with a Sure-Grip already in place) and be done with it. Just an opinion.

Kostas

 

[Shorty Thompson]

New to the world of mopar... and I have an 81 imp.. So that means an 81/4 open rear with 224 gears.. Something needs to be done about that. I *think* the guts from a dakota 81/4 can be used, and there a more than a few in local yards, but I'm sure there is a bunch I should learn.. It's where you fine folks come in.

First, will it work?

Second, did they put 321 gears with a sure grip in those trucks?

Third, Is there a way to tell the gears and if it's a sure grip from looking?

Fourth, if I find all that, what all do I need to get from the parts truck, from the parts store?

I'm on a budget (three daughters, single Dad)... so anything you can tell me about the cheapest way to do this would be a huge help.

Thanks. Dan

Where's home ? Anywhere near Illinois ?

 

[slant6billy]

Year Axle Type (A) (B) (C)
1963 - 1972 7 1/4" A-Body 53.200" 43.02" 10.09"
1973 - 1976 7 1/4" A-Body 51.400" 43.02" 10.09"
All 7 1/4" F/J/M-Body 54.340" 44.46" 10.09"
1973 - 1976 8 1/4" A-Body 51.400" 43.02" 11.69"
All 8 1/4" B/R-Body 57.800" 47.30" 11.69"
All 8 1/4" C-Body 59.200" 47.30" 11.69"
All 8 1/4" F/J/M-Body 54.340" 44.46" 11.69"
All 8 3/4" A-Body 51.400" 43.00" 12.35"
1962 - 1970 8 3/4" B-Body 55.000" 44.00" 12.35"
1971 - 1974 8 3/4" B-Body 57.800" 47.30" 12.35"
1971 - 1974 8 3/4" B-Body S.W. 59.200" 47.30" 12.35"
All 8 3/4" E-Body 56.500" 46.00" 12.35"
All 9 1/4" B/R-Body 57.800" 47.30" 11.69"
All 9 1/4" C-Body 59.200" 47.30" 11.69"
1966 - 1970 9 3/4" B-Body 54.936" 44.00" 13.47"
All 9 3/4" E-Body 56.500" 46.00" 13.47"

 

[slant6billy]

go 62-70 B body 8 3/4. 489 case is the less desired by other mopar folk, but good enough for our deal and more selection for sure grip. My luck got me a 8 3/4 with a 742 case. Diff parts are plenty and cheap. You won't kill the 8 3/4 ever. Ford 9 inchers are $$$$, but share the "drop out" center style design. If you are hell bent on the Dak rear- keep in mind the full size van used 8 1/4 in the 6 cylinder short wheel base. It is the larger lug patter 5 1/2, but you get bigger drums and can get the holes re drilled to 4 1/2. I tow with my van with an 8 1/4.... no issues. I just towed a 35 foot enclosed trailer. Again you should be able to get something to get it to do what you need.

 

[jasperjacko]

I've had 5 j-bodies with 318 engines. All had 8.25 open geared rearend. My current 8.25 has a 3.55 sure-grip and I may consider swapping for a 8.75 I have in the garage.

 

[Shorty Thompson]

View attachment 4622Year Axle Type (A) (B) (C)
1963 - 1972 7 1/4" A-Body 53.200" 43.02" 10.09"
1973 - 1976 7 1/4" A-Body 51.400" 43.02" 10.09"
All 7 1/4" F/J/M-Body 54.340" 44.46" 10.09"
1973 - 1976 8 1/4" A-Body 51.400" 43.02" 11.69"
All 8 1/4" B/R-Body 57.800" 47.30" 11.69"
All 8 1/4" C-Body 59.200" 47.30" 11.69"
All 8 1/4" F/J/M-Body 54.340" 44.46" 11.69"
All 8 3/4" A-Body 51.400" 43.00" 12.35"
1962 - 1970 8 3/4" B-Body 55.000" 44.00" 12.35"
1971 - 1974 8 3/4" B-Body 57.800" 47.30" 12.35"
1971 - 1974 8 3/4" B-Body S.W. 59.200" 47.30" 12.35"
All 8 3/4" E-Body 56.500" 46.00" 12.35"
All 9 1/4" B/R-Body 57.800" 47.30" 11.69"
All 9 1/4" C-Body 59.200" 47.30" 11.69"
1966 - 1970 9 3/4" B-Body 54.936" 44.00" 13.47"
All 9 3/4" E-Body 56.500" 46.00" 13.47"

2 real good reaons why I post " where do you live " . I got 1 I'm not gonna be using .

 

[kkritsilas]

Hi,

Just stuck my head below the rear of two of my three J Bodies. The 1980 Cordoba (318-4BBL) has an 8 1/4", and so does the 1981 Mirada CMX (318-4BBL). I don't know if either has a Sure-Grip, as getting the cars up to turn the wheels is a bit of a problem with the snow on the ground and the cold temperatures (I don't have a garage to work on stuff), nor can I check the axle ratio. The Blue Mirada (318-2BBL) is buried behind a number of vehicles, so I will need to wait until they get out of the way before I can check the rear end on that one.

Kostas

 

[lastws6]

jasperjacko, I have a customer for that rear you're swapping out.


Shorty, I live in PA, Eastern PA... a bit of a trip....

 

[kkritsilas]

As a further point of reference, I was poking around Allpar for some other information, and ran into this"

http://www.allpar.com/model/dodge-diplomat.html

Under the transmission section, it says:

"Available transmissions included the A230 3 speed (Slant Six only), the A833 4 speed overdrive (Slant Six and 318-2 only), and the A904 and A998/999 Torqueflite 3 speed automatics. These were coupled with either the Chrysler 7 1/4 inch rear axle (for Slant Six coupe and sedan, non-towing applications) or the Chrysler 8 1/4 axle for the wagon, heavy duty, and V8 versions. Axles were available in 2.45, 2.76, 2.94, and 3.23 to 1 ratios, depending upon transmission and engine. Sure-Grip limited slip axles were optional. Torqueflites got a lockup torque converter in 1978 for non-heavy duty engines. Police Package Diplomats with the 360 V8 were equipped with the virtually indestructible 727 transmission."

While just an Internet source, it seems pretty clear that V8 M body cars pretty much came with 8 1/4" across the board. It is more than likely to be true for the J bodies as well.

Kostas