i have upgraded my slant six motor with dual webbers, an offy intake, dual headers, a 260 mech cam and ignition upgrades as well. i am pushing close to 200 hp now and i have a 904 tranny. i have a 77 volare with original rear end 7 1/4" with 2:76 gearing. i want to put 3:55 gearing in. do i have to change out my rearend or can the 3:55 gears be put inside the 7 1/4" differential? and will the 904 tranny suffice with this added motor power and torque? the engine has been totally rebuilt but the original tranny has 60,000 miles on it.

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'77 Volare..not much to look at but has it where it counts!

The 904 can easily take the power if it is in proper working order. The 7.25 cannot take abuse for extended periods of time. You should be able to find a 8.25 rear for a volare fairly easily. Parts like gear sets are much more common for the 8.25. With a sure grip the 8.25 can handle 350-400 hp while the 7.25 is always a question mark for how much it can take. Some have had 7.25 that held up to abuse but if you're spending money to set up a rear you should spend it to set up the stronger and more common rear. Make sure to get the driveshaft from a 8.25 equipped car at the same time. good luck

The trans will be fine. The 7-1/4" rear axle will probably break. Are you sure you want 3.55s? That's an awful lot of gear, and it'll scream and guzzle gas at speeds above 45mph. If you only ever drive in the city, 3.55s might be marginally appropriate.

Swapping ratios in the small rear axle will almost certainly wind up a waste of money, since if the unit doesn't disintegrate before you change to the more fragile 3.55 ratio, it is likely to do so afterwards. An 8-1/4" swap would be a very wise idea. An 8-1/4" with 3.21s and built sure-grip would be my choice in your situation, assuming you actually drive on public roads.

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

i drive this volare pratically every day not long distances but i want to take it to farmington so that is why i want to change the gear ratios. i don't know the first thing about finding an 8.25 rear end for my car or the gears. any help in procurement would be appreciated. i live in clemmons, north carolina and i will have to find a reliable person to do the work also.

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'77 Volare..not much to look at but has it where it counts!

Want to buy a 5.13 sure grip, 7 1/4?

Just kidding, it's not for sale, yet.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

www.car-part.com , searchable used auto parts nationwide. Search 1978 Volare rear axle assembly, next screen pick your option, then proceed.

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

I have to agree with Dan on this one. You'll be plenty happy with 3.21's, especialy going from 2.76's. When I put 3.23's in my 8.75 (another option for you) in my late '70 Fury (with a 400) from 2.76's, it was like extra HP was added. You could hardly tell the difference in RPM's on the freeway, and I only lost maybe 1 or 2 MPG.

I have to agree with Eric on this one, too.

3.55s are gonna make that car a dåmn nuisance except on the occasion you take it to the drag strip.

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

If you drive the highway a lot even 3.23 s can be a little low. I have 3.23s but have an overdrive trans for a final ratio of 2.23. Im not sure I could live with 3.55s even with the OD. If you never drive over 55mph go 3.55.

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

I have the 3.55 SG with the A-833OD and it works just fine for daily driving (final ratio 2.59 in OD). It gets better mileage than the A-833OD and 2.94's, and can get out of it's own way, it also gets the same mileage as my '74 with the 1 barrel and 3.21 wirh A-230 3 speed...Mileage will go down if you tend to 'bark the tires' at every stop light, and my rpms at 65 mph are about 22-2300 (+/- standard variance of the analog tach...which whines about as much as the '74 3.21- 1barrel special at 65 mph). When I did swap out the 3.21's for 2.76's due to a bad axle bearing my mileage only improved with a bigger exhaust pipe (1-2 mpg), and cruise was better, but my off the line took a lot of rev even with the 3.09 granny 1st gear...)



The easy swap is finding another Volare/Aspen with a 3.21 SG rear.
The real match up is trying to find the combination for the 'heavy' F body, the not so low ratio'd A-904, to keep the slant in it's powerband (it's "up there"), and to get it to motivate well in city travel, but 'cruise' at highway speeds...


-D.Idiot

"Been there swapped that a few times..."

i have another 77 volare with a supersix setup that is sitting in my mom's backyard...how do i tell what the rearend ratio is in it? is there some number under the hood or in the engine compartment that tells me?

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'77 Volare..not much to look at but has it where it counts!

if the other one is an auto too, then you probably have another 2.76...(if the cover is roundish and has 10 bolts on the rear side then you'll want that 8 1/4" )...do a search on here about "ratio checking"...


good luck,


-D.Idiot

My 79 D 100 had a slant with 3.55s and a 3 0n the tree. Didn't have any problems relating to revs too high (235 75 15's ) When the 8-1/4 blew up
I found an 8-3/4 from a 69 D 100 also a slant/3 on the tree truck, main difference was the 8-3/4 was a 3.91. Still got 22 MPG (highway), I then swapped to a 69, 318 that I rebuilt pretty stock except for an RV cam and a 4 bbl Edelbrock manifold and carb with an A833 OD, after the slant chipped a tooth on the CAM... went thru 2 new dist gears B4 I saw the damaged cam. At the time it was easier to swap. Looking back, it woulda been easier to fix the slant. Hindsight, you know.

Well, sure, but that's a truck, not a car.

Those 235/75-15s are a 29" diameter unit, which is way taller than you're likely to find under a car.

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

Yes Dan, I know that I was dealing with a truck. What I didn't know that 2357515's a 3.91 ratio and a 3 speed trans, the engine would run a different RPM at a given road speed , than it would in a CAR. Being a truck, I would, however, expect to have to have my foot in it a little farther to KEEP that RPM because of the added weight of the full frame,etc.