I've got a stock 64 Chevy 4 speed and the truck it might go in has a higher geared rear end - because it had an automatic. Do I need to swap to the orig 64 ratio to make this work? 3.73:1 I think it was... Sorry if it's not too board-friendly and thanks in advance for the insight. I wish I was posting pics of my Ford, but these days I'm doing good just to have this.
Assuming your title means the trans is a truck trans that would be a "granny" geared trans. Full throttle launch in first would get you across the intersection, maybe, before you had to shift to second. You use second in them like first in a regular trans. You'll also need a bellhousing with side motor mounts as the trans doesn't have a mount on it, it hangs off the motor.
Like phat rat said, truck four speeds have a low first and you will rarely, if ever use it, (first gear.) If its' a muncie or something similar I think you'll be alright. Good Luck, Seth
I had a stock Truck tranny behind a 615hp 350 and you were lucky to get 50 feet befor shifting i found the only thing that first (granny) was good for was burnning up a clutch
With 3.73 gears you should be fine. I have that same transmission in my Suburban with 3.08 gears. You won't win any drag races shifting that transmission regardless of your rear-end ratio and unless you are over-loading the truck you'll find it works well with those gears.
Can you give us more info about the truck it will go in? what engine, rearend gears, what year is it, etc.
You probably have the good old SM420 box. It'll go up the side of a house in 1st gear. I think I used my 1st gear a few times when I towed a boat or had 2 tons of scrap steel in the back. My truck either had a 5.14 or 5.38 rear, but a 3.73 should be fine. The stock 11" clutch is pretty good too. Bob
I think the question is kind of misunderstood judging by the answers. So the situation is you're putting a 4 speed in a truck with high gears, like 3.08-2.73. In this case you might almost end up with a useable first gear, but you'll have a hard time starting off in 2nd. You'll also have reduced highway RPMs With the 3.73 it's probably possible to take off in 2nd and save the short shift. I don't see any issues with the combination unless you're planning to work it like a 3/4 ton truck. Then it might be hard on engines constantly pulling a huge load with highway rear gears. good luck
I, also have been looking @ this. The "justification" for this is as a tow-rig for a sprintcar i've acquired. The necessity to be able to crawl along in the pits has me desiring granny, too! Am looking @ NV4500 w/ both a "granny" & OD, relative to the '3 on tree' i inherited.
It will work ok. a trick when shifting from granny to second is to double clutch other wise it will grind . OLdWolf
Had a 3/4 ton GMC that had a 454/4speed/3.73rear gear, loved the truck, hated that damned tranny, and I'm a stick shift kinda guy! Oh, it had a 12" clutch, uses the same flywheel as 11", and the truck transmissions have a larger bearing collar, so the truck bellhousing is nescessary with it.
The SM420 from a 64 truck is different than the SM465 from a 68-up truck...the early one doesn't use the big front bearing retainer.
Yeah you think that bad I have a 46 chevrolet 3/4 ton truck with a unsynchronized four speed which is the older brother to the sm420. You can slmost pull a house with the gear ratio in the rearend
I had one behind the original 283 in my '62 Suburban, with 3.55 gears out back. I pretended it was a 3 speed and drove it that way, starting in 2nd gear all the time. Zero problems. It was fine. I drive the truck daily, so I needed to make the decision to go with highway-type gears in the back (3.08, etc) and keep the Granny trans and actually use 1st gear while daily driving, or go with a 4spd OD and keep the rear gears. I kept the rear gears and went with the OD trans. I did the math in all the ratios, and the OD trans seemed better for the street with 3.55 gears than the steep granny 1st with 3.08. -Brad
I don't know, Brad...the SM420 has a 3.58 second gear ratio, so it seems to me you wouldn't have too much trouble getting going from a stop with 3.08s or even lower gears. First gear is still mostly useless unless you're really loaded or need to drive real slow.
Yeah Squirrel as I said above I have no trouble running an SM420 with 3.08 gears and I almost never use that granny first. Getting started isn't a problem. However it would be a bit quieter on the highway if I had an overdrive and I sometimes think about a tranny swap for just that reason.
I decided to go with the OD trans because it would be cheaper than buying a new Posi carrier, new gears, a rebuild kit, and having it installed by someone who knows what they're doing (That is NOT me...I know the mechanics of how to do it, but I didn't want a rear end that howls. I know a lot of guys "who can do it," but they also usually have howling gears.) So I had the OD trans rebuilt and dropped it in, got a new driveshaft made, and had the shifter rebuilt. Then the original rear end ate itself, and I had to buy a new housing, new gears, new Posi dif, new axles and bearings. And a new rebuild kit, and pay someone to instal it. Sometimes my truck makes it real hard to love it. -Brad
I'm also building a 65 chev truck with a 283 / granny 4 speed..We plan to tow a trailer..have no idea what the rear gear is, but hope to be able to make this work without going to more HP..454.. thanks for the info.. 1939fiat
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