Transmission Question

[62_C20builder]

I have a '62 C-20 Chevy truck with a straight 6 and it has a 4 speed transmission. First gear is pretty much useless, but I want to keep the manual transmission. Any ideas how I can resolve the issue? Is it possible to change the gears in the transmission or the rear end? Lost here guys...please throw me a bone. Thanks!

[Captainfab]

That's the way the SM420 transmission is designed. First gear is not typically used for normal driving. It is meant to be used when pulling heavy loads or slow offroad driving. That said, to achieve what it sounds you are wanting, you will have to either change the differential gears, the complete differential or change to an OD trans. There are a few options for each and there are many threads on each of them. You will just need to decide which way appeals to you more.

The Eaton HO52 differential that is under your truck has does not have any new gears available and replacement parts such as bearings and seals can get expensive. Your differential likely has either 4.11 or 4.57 gears. If it were my truck, depending on the condition of the differential, I would consider changing to either a Dana 60 or a GM corporate 14 bolt. As for an OD trans there is the 3 speed with OD, the T5, and MY6/A833. There is also the NV3500 and NV4500, but those will not bolt up to your 235 engine.

[jtrichard]

you just drive it 2nd 3rd 4th dont use first .... the later 4 speed of the same design was L 1 2 3 so people did not try to start out in "first/low"

[luvbowties]

Possibly the simplest & quickest 'help' for your scenario would be taller tires. Doing the math & assuming a present differential gear of 4.11, if you moved from 28" tires to 32" tires, it would effectively change the final ratio 'seen' by the engine to a 3.60 (4.11 X 28/32 = 3.596; rounded = 3.60).
HTH,
Sam

[62_C20builder]

Thanks guys, I will look at all of these options. You guys rock!

[par4tom]

I did an NP 440 / MY6 transmission swap. Had the SM420 like you.

The new tranny is a dream with 4th gear in overdrive. First three gears are similar to a Turbo 350 tranny. You can find some information on this in some of the threads already posted here.

You should be able to find one with some effort and only be out about $400 to $600 bucks. Watch for the bellhousing bolt pattern too.

Tom

[mr andrerson]

I swapped mine out for the t-5 behind my 230 in front of the 411 rear and i couldnt be happier. the whole swap is laid out nicely here.

[Old Bleu]

+1 for the T5 behind the 230 in my '64.