Why do the swap if the car already has an 8 3/4 in it?
The answers:
- I recently changed jobs and the new work site is a "cross town shuffle", no freeway time.
- I recently picked-up a 3.31 ratio and wanted to give it a try.
- The unit is an early 60's 8 1/4 "drop-out", that fits right into the 8 3/4 housing already in the car!

So it's gear swap time... 2.94 pumpkin comes out and the 3.31 goes in.
Here are the two center sections, side-by-side, as you can see... the case is the same.



Note how the ring gear bolts to the carrier, fewer bolts that thread into a inner flange 'lip'... this keeps the ring gear thin, thinner then the 2.94's ring gear.



The carrier itself is pretty small but the spider and side gears are a decent size... way bigger then what you see in a 7 1/4. What makes this sweet is that the 30 spline 8 3/4 axle shafts plug right in.
This photo show how "hollow looking" the smaller parts look in that 741 case.



The good news... the unit is a good 15 lbs lighter then the 2.94 that came out.



My 63 FSM shows the 8 1/4 drop-out listed with the 8 3/4 service procedures. It lists the unit as "for 6 cylinder cars" and shows the 3.31 and a 2.93 ratio. I am amazed that Mopar would do a smaller gear size for the lower powered vehicles... was it done to reduce HP consumption or to save some $$$... it just does not make much sense. ( or cents as the case may be)

Anyway... I like this unit and the ratio, it works well for my around town driving. One other nice thing, this gear set is noise-free, not a sound out of it. No gear howl, no bearing noise... I can almost hear the gear oil splashing around inside but nothing else.
I need to beat on it a bit to see if the unit give me any trouble.
DD

Hey, now that's pretty cool! I had no idea the pre-'66(?) 8¼" centre chunk was a drop-in for the '66-up 8¾" housing, but in retrospect the 2.93 8¾" (so I thought) centre chunk I spent a long afternoon pulling out of a '64 Plymouth B-body years ago for installation into the 8¾" in my Valiant was actually an early 8¼"; it had the nut-retained brake drums and everything.

Early or late speedo pinions in the Dacuda?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

The Dacuda has the later speedo pinion set-up so it will be pretty easy to get it correct.
Funny... I had the speedo correct for a 3.23 ratio and then swapped to the 2.94 so I was running a few mph slow and went to a few mph fast, after this swap.
I will need to do some math to figure out what pinion will correct the error.
DD

That's cool. I learned something new today. Thanks Doc!

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Rob

I’m Mater
The Kentucky Poser

Hmmm; never heard of an 8-1/4 drop out rear end.

Cool!....another result of the inquiring mind.....

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Where do you find this stuff??? I am amazed I've never heard of the 8.25" dropout. Guess I'm not old enough...

Lou

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Home of Slant6-powered fun machines since 1988

Nicely done, but now I have to crawl under all my pre-66 B-bodies to see what I really have. Will a regular 8'3/4 chunk still fit in the early 8 1/4 housing? Or are they completely one-off?

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Hey... who you calling "old"...

Truthfully... I like the 8 3/4 and like to "collect" different ratios and styles.
I have known about the early 8 1/4 drop-out for many years and yes, you can simply remove one chuck and install the other.

The only thing to watch for is the center thrust block in the open ( "one legger") carriers. The early tapered / keyed w/ nut axle assembly used a thinner center thrust block (square tubing) instead of the wider, round thrust block, found in the later units but again, these parts swap with-out any problems.

I kick myself for scraping-out a number of the 8 1/4 units over the years, mostly because of "bigger is better" thinking. I was smart enough to save the cases, carriers and yokes, which were used for other 8 3/4 build-ups... so I was not that bad about scattering a few of these.

I need to do some more homework on the early 8 1/4, I really do not know much about them, like the years they were made, what they were used in... why Mopar did these to start with and if there was ever a posi or other ratios available.
DD

I pulled a 3.31 chunk out of a 65 Belvedere with a slant and column shift manual trans a few years ago. I was sure that it was an 8 3/4 but now . . . ? The car that I installed it into was sold.

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. . . there was good sport at his making.

I knew they existed and always thought they looked like an 8 3/4.. Good stuff doc!


Greg

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http://www.youtube.com/hyperpack

Is there any way to easily tell from the outside if you have an 8 1/4 or 8 3/4 chunk? Like you said, the cases are the same but there must be a way. Would there be a different # on the vin tag?

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I am under the thinking that if it is a 3.31 ratio, it is likely a 8 1/4 gear set.
I do not see a 3.31 listed for any year 8 3/4

One other thought is to remove the oil fill plug and look inside to view the smaller and symetrical ring gear carrier and / or the ends of the ring gear retaining bolts, positioned inside of the ring gear teeth.
DD

JEEEEEEEZZZZZZZZ!!! Never heard of this before!! I was thinking that with 3:91's behind my 833OD would be about 3:32 pr 3:31.

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'72 Duster 198 stock cam, 3:23's

93 D350 Cummins THD Maxfuel 35mpg parts to hit 400hp+ Suncoast Cat2 A518, converter DDP Stage III injectors 62/64 HX35, 3 piece manifold, 4" Diamond Eye, Gear Venders OD. Stage I street/tow PDD head on order.

3.91x.71=2.7761

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Joshua