The Stovebolt Site Forums The Shop Area Driveline Gear Ratios

Cablemill, this question is best answered in the Driveline Forum so I will move it for you.

....but, I do know that the rear ratio could be a 3.90 (most likely) but I got lucky on a 59 and got a 3.38 gear. There is a way to rotate the tire one revolution while counting the revolutions of the driveshaft and divide.
....what tranny you planning with the 283? that would also help to know. A 700R4, for example, is a good one with overdrive. Just a tat bit more info and the guys can give you more insight than I can.
Post a picture when you can. I've always like the Apache's.

The transmission ratios are going to be the same, the differential ratios will depend partially on what transmission is in it, and partially on what option ratio was optioned for it. The engine option really does not come into play. 3.90 was the standard gear, with 3.70 as an economy option. 4.10 was generally used in trucks with overdrive, and the 3.38 was the Hydramatic differential ratio. There was also a 3.92 option, that one is for the rare Positraction axle, which is a Spicer 45. Note; The Spicer was the standard axle in the GMC, using either a 3.08 or 3.92 gear. The code for the axle will be stamped on the carrier face, on the passenger side of the carrier.
Personally, I would go with an overdrive transmission over swapping the rear end gear. Keep the lower gearing for in town use, but still have a good highway gear using the overdrive.

Thanks for the responses.

I plan to keep the original 3 speed manual transmission behind the 283. I spoke with a guy that owns a local salvage yard and he had a 59 1/2 ton in his yard that was an original 283 truck. He sold the motor and has recently sold the whole truck (what's left of it), but kept the transmission. I wasn't sure if there was a ratio difference in the transmissions or not. If there was, I was going to buy the trans that came out of his V8 truck. I am pretty sure my differential ratio is the 3.90. I don't know what the differential ratio of a V8 truck is. I'm trying to keep my truck as original as possible. I'm going with a 283 as it was an option. I wouldn't mind an automatic tranny, but I don't want to put a floor shift in to ruin it's original appearance of a column shifter.

Most likely, you have the 3.90. That was the most common ratio found in them, regardless of engine. If you go automatic, you do not need to go to a floor shifter, the column shifter can be adapted. Alternatively, the SM319 is an excellent option. It's basically the same transmission as the base 3 speed, except that it has a Borg-Warner R-10 overdrive unit in place of the tailshaft. It's a direct bolt in if it came from a truck, and one from a '55-'57 Passenger will also directly fit with a couple of alterations, mainly the shift cover and arms may require swapping from the original transmission, and the lower mount bolts go in opposite from Truck, so you have to use a bolt and nut setup. Works great with the 3.90 gear.

How do you "...keep my truck as original as possible." by changing engines?

By the way, there is a difference in where the radiator mounts on 6cylinder and 8 cylinder trucks. It will be too far forward for you fan to be effective. That is another problem you will need to address.

You indicated your 6 cylinder truck has a 3 speed transmission. If it works OK you will not gain anything by purchasing one from a V-8 truck as they are the same transmission, same ratios, same mounting. If it is priced right and you feel you need a backup, go for it. As Bill stated, the factory overdrive is a good choice for all around driving and considerably better for highway speeds. There is no reason to change the rear end with this set up.
Fred

@rfs56trk and Longbox55........Thanks for the info, I appreciate it. The overdrive is something I'll give thought too. How hard is a sm319 to find? I googled it and all I found were parts listings, no transmissions.

@Cletis.........As I stated, a 283 was an option for the truck, that's my reasoning for saying I wanted to keep it as original as possible. Granted, it won't be original after the engine swap, but it'll be closer than if I put a 350 in it. I've got a radiator shroud to put in it and if that don't do the job, I have fan spacers.

Overdrive transmissions are listed on ebay, craigslist and local sources. You absolutely don't know what you are getting though,
you can pay a lot for junk or a little for a good one. I rebuild several a year and have found lately that most are very needy after they are disassembled.
For the overdrive to operate as the factory intended you need a pull cable and the electrical components which include the solenoid, governor, relay, kick down switch & brackets, and the wire loom.
You can also place a want ad in the swap meet on this forum.
Fred

You'll loose the foot stomp start set up (6 cyl. bell housing won't bolt to a V/8), and you will need a different ignition switch, so you can energize the solenoid on the V/8 starter.

@ rfs55trk....Thanks for the education on the overdrive, it's very much appreciated. This endeavor I'm on with the engine swap has been a big learning experience. I keep learning things as this progresses and my wallet keeps feeling it.....Laffinn. I was at one of the local yards today and they had a chunck that came out of a driving '55 Car with a 370 gear. If it will bolt in, I'm going to get it. Any thoughts on that?

@55shaker......I have picked up a couple of V8 ignition switches (minus keys that cost 18 bucks per switch) from my local salvage yards, hopefully one will work. I'm going to find out either today or tomorrow. If not, I can go back to the setup that's in it now, a push button under the dash. The stomp starter was taken out some time ago and replaced with a later starter. The bellhousing issue is hopefully resolved. I knew the bell needed changed over a year ago, so I got one (for a truck). I found out last week the pilot bearing hole and my bearing plate weren't the same dimension. Seems I bought a housing for 68 and up, I needed a 67 and prior and a different P/N. $75.00, plus 25 for blasting, later, I have the right bell.

The differential 3rd member from that era car will not fit in a truck. You could swap the entire housing out but would require repositioning of the spring perches. The car also uses 5 lug wheels vs 6 lug for the truck. You will also need a V-8 flywheel, front mounts, and V-8 throttle linkage for the conversion. Nothing from the 235 interchanges with the exception of the clutch which depends on which flywheel you use.
Fred

I was looking at changing just the chunk with the ring and pinion, not the whole rear end housing, if it would bolt to the truck housing. The salvage yard has the chunk that was removed from the '55 car rear end. If that won't work, then my next step would be to find a whole rear end that is the same width as the original rear end with 373 or less ratio or locate an overdrive transmission.

I have the OEM V8 throttle linkage, OEM cross member mounts, front engine mounts, a 14" flywheel, 11" clutch and pressure plate.

No need to change the rearend, especially if you go with the overdrive. The stock 3.90 ratio works great with the overdrive. Plus, originally, the overdrive equipped cars and trucks used a 4.11 ratio, actually lower than the 3.70 (car) and 3.90 (truck) that was standard.

You would probably be money ahead just buying new 3.38 ring and pinion gears and using the transmission you have. Randy's ring and pinion is the cheapest that I could find. 1'st and reverse will be really fast though once you swap out the rear end. Kind of unhandy if you will be hauling wood or hay in the pasture but not bad on the road.

I don't know, you can pick up a decent SM319 for under $200, and maybe about another $100 give or take to set it up. You still get the benefits of a higher final drive (2.73 in overdrive) and the in town drivability of the lower ratio when not in overdrive. Plus, it also gives the ability to split gears, 2nd over (4.58:1) is a great hill climber gear and is also good for getting up to speed off the on ramps. It just really has much more flexability.

Bill..Do you have an extra SM319 laying around?

I have an extra one, but it's pretty much just a parts transmission. Main box was pretty well trashed (ran behind a dual 4bbl Power Pack 283 in a '57 Convertible). I got it mainly for the overdrive parts, had the blocker plate in mine go bad, and it damaged the adapter plate. Swapped both into the one in the truck, so the parts trans isn't really usable anymore.