Transmission gear versus 3.73 rear ratio

[mrdave03]

Hi All, I finally blew my 3 on the tree tranny. I think the upgraded 327 didnt like it much. I want to upgrade to possibly a floor shift 4 speed. Perhaps Saginaw. I was hoping to use the same one piece drive shaft. The rear is a 3.73. Any thoughts on trans first gear size? A friend has a Saginaw 4 speed with 3.11 first gear but that would make the truck dog on start if I'm not mistaken? Or anything else that would mate up to my drive shaft that will gear well with the 3.73 rear? The tranny in it was the old 58-64 3 speed with 4 bolt side cover. So it had the shorter tail piece. I prefer not to have to cut shaft. I'm not adverse to a direct replacement trans either but having trouble finding an exact match.

[HumphreyMurdoch]

I'm not 100% sure what will be the exact same length but I'd guess most of the 4 speeds will be the same length. I can say that a saginaw 4 speed will be the weakest of them and it'll hold up for a while but will eventually let go if you're doing hole shots and side stepping the clutch and whatnot.

[Lugnutz65]

Originally Posted by mrdave03

Hi All, I finally blew my 3 on the tree tranny. I think the upgraded 327 didnt like it much. I want to upgrade to possibly a floor shift 4 speed. Perhaps Saginaw. I was hoping to use the same one piece drive shaft. The rear is a 3.73. Any thoughts on trans first gear size? A friend has a Saginaw 4 speed with 3.11 first gear but that would make the truck dog on start if I'm not mistaken? Or anything else that would mate up to my drive shaft that will gear well with the 3.73 rear? The tranny in it was the old 58-64 3 speed with 4 bolt side cover. So it had the shorter tail piece. I prefer not to have to cut shaft. I'm not adverse to a direct replacement trans either but having trouble finding an exact match.

I believe the 1st gear in your 3 speed was 2.95. The 3.11 would feel almost identical. You should be able to pick up a used 3 speed like your original for less than $100. Changing to a 4 speed will not give you any more highway speed and the 4 speed Muncie T10 will be pretty pricey.

[TJ's Chevy]

If you get the C-10 Truck tranmission 4 speed muncie you should be fine...its the one with the super low 1st gear...basically the same gearing as a 3 speed, but it has a super low 1st. Pending on tire size 3.73's are a good rear end ratio for an OD trans. A Tremic 5 speed would be a good choice..but you would have to change your drive shaft length.

[kieth]

Changing to a t5 would be the nicest upgrade you could make, lowering your rpms cruising down the highway, shortening your driveline is not expensive and you will still retain the same driveshaft...... Since you have to change the transmission might as well gain drivability.....and fuel mileage. Kieth

[66Submarine]

3.11 Saginaw + 3.07 gears and a 350 makes a really nice overall go-anywhere driver; I personally like the trans a lot and would like to have another to put in something (my father effectively stole mine, lol). The 3.11 first gear makes the tall gearing fine starting off, and it's got a nice spread between the gears IMO.

Not as strong as the Muncie car trans or similar, but those also blew up/blow up when hammered on, and by now they have all been blown up and pieced back together a hundred times. If I just wanted something inexpensive to act stupid in and abuse I'd probably go TH400, or try a TKO if the money was there. Whether or not you'll blow up a Saginaw (or other manual trans) is up to you IMO; really abusive shifting and launches seem to blow them up just fine from what I've read (I don't really care to test the theory out on my stuff!). On the other hand, they are a much less expensive trans that drives very nice, and should (I would think) hold up a lot better than the little Muncie three speed. If you drive the truck daily, the Saginaw's deep(er) first makes a taller rear gear much nicer than some of the other four speeds, and for that reason I actually prefer it for a driver to the Muncie M-20 that it replaced (I said he effectively stole it, lol).

BTW TJ, FWIW the SM420 is actually slightly deeper in the other gears than the three speeds were. SM318 three speeds were 2.94-1.68-1:1, and SM420's are 7.06-3.58-1.71-1:1 (IIRC). So, 3rd in the SM420 is pretty much the same as 2nd in the three speed, but 2nd is actually about 20% deeper than 1st.

[par4tom]

I agree with Keith...I have a 3.73 rear end and with the SM420, the 1:1 4th gear was just not high enough to cruise down the highway.

I swapped the tranny for a older NP440 overdrive unit with .73 4th gear. What a difference...

I did have to shorten the drive shaft and have it rebalanced, was about $110 here in California. Well worth it.

Best of luck.
Tom

[66Submarine]

The NP440/MY6/A833 is an interesting trans; seems fairly hard to come by IME, though. (I've been on the look out for one for a while now.) Also, I think they were apparently noted for excessive mainshaft/countershaft wear or something IIRC? (In the OD version)

[LVPhotos]

Chart

[mrdave03]

Thanks for all the great input. I have a pretty good idea what it is I need now. Next is to find it. The friend sold the 4 speed Muncie on me.. grr... but another friend has a mid 60's 4 speed truck trans he wants to unload for $100.00 I need to see what it is all about. He say's its cherry inside and out but have to see if it was a Sag or what with the granny low. I think those mid 60's years truck trans had that low gear. I'm finding it hard to track down the original type 3 speed just seems they are getting rare unless someone finds one? I think it was called a SM-318 but it was a tiny box for sure. I dont beat on the truck at all its my cruise night/Sunday driver vehicle. When we pulled the trans apart it looked like the previous owner built it out of tired scraps.

[kieth]

Originally Posted by LVPhotos

Chart

cool chart but it leaves out a few things, like how much torque to the ground different engines have and the speed they operate at......that is why my spreadsheet is a little more complicated.....

One cannot only look at mph or rpms, you must also look at how much torque the truck will have (by ignoring torque you can end up with a truck that looks great on paper but falls on its face going down the road......Kieth

[Lugnutz65]

I'm not knocking the chart. It's clear and easy to understand.

One drawback is that it does not show any figures related to OD transmissions. I agree with Kieth. If all other things are equal, (same tires, same vehicle weight, same rear diff), it remains clear that a 383 stroker and a 230ci L6 will perform very differently at certain RPMs.

For instance, a 230ci L6 would not perform nearly as well with a 0.63 OD gear (maybe fall on it's face?) as compared to a 350ci with the same 0.63 OD gear. The RPMs would be the same for each engine, but the torque to the ground would be very different and very noticeable on hills.

Manufacturers know this and design each drivetrain with drivability in mind. Matters not if it's a Hot rod or daily driver, if it doesn't drive well, it ain't gonna be any fun.

[66Submarine]

The SM318's are very easy to find and shouldn't cost more than $100. Several on this board have given good ones away recently after swapping them out; I think I even saw one in NJ. SM420 truck Muncie 4-speeds will need the high-hump conversion parts and the correct driveshaft assembly, so it's not a direct swap. If you were fine with the SM318's ratios, shifting, etc. and aren't going to beat on it, I'd just plug one back in it's place.