The Stovebolt Site Forums The Shop Area General Truck Talk 3.38 question

My 55.1 3100 is stock and original--except the trans, which is a later wide ratio 4 speed. The engine is leaky and tired, and is in the process of getting a replacement 235. The diff is leaky and still at 3.90. I'm thinking of replacing the ring and pinion with the 3.38 PG to get some longer legs. Running original 16" wheels, BTW. I'm not likely to replace this trans for a good while yet.

Pros/cons of using this ring and pinion in truck as described?

Since you have a 3600, it should have the 4.56 rear gear, assuming it still has the original rearend in it. The 3.90 rear, as well as the 3.38 replacement gears, are for the 1/2 ton. They will not work with the 3/4 ton rearend.

Fumblefingers here mis-typed. My truck's a 3100. Sorry to create confusion. Makes a difference, huh.

Yup, big difference . The main concern I would have is that you will lose in town performance due to the higher gearing. As long as you have a strong running engine and a decent 1rst and 2nd gear, should be ok. I would also suggest that you not go too big wth the tires, as that will affect the overall final ratio. Bigger tires give the same effect as runing a higher gear, which requires more torque to get the load moving.

Pro. The greatest thing you can do for your truck.
Con. Price & labor for correct instalation.

I sprung for the 3.38 gears in my 59 gmc. IMHO the 3.38 gears are a poor compromise. Granted some gmc 1/2 ton trucks of the era had the economy 3.07 rear, which is a higer gear ratio, and the 6 cylinder 270 had no problem moving it around in town.

I personally feel a 5 speed transmission is a better compromise... you get all the benefits of the low gears, and even more economy in OD.

3.38 gears will work with an OD, but it is not a desireable setup. The stock 3.90 will work much better with an OD transmission and a 235.

If you're happy with the 4 speed and want more economy, go for it... just be aware that you won't have as much low end grunt, or as much economy as you could have with a OD transmission.

I,m sorry...
But maybe I lost something here...
A Briggs and Stratton lawn mower engine can Move a Ton with the right Gearing
I dont care if you got 27 foward speeds,with triple od,
Whatever the rear end gearing puts to the GROUND,as output,is what your gonna get.
All the overdrive is gonna do is LOWER the Engine R P M

I put them in mine. They are very nice. I would rather have got a newer 4 speed trans for towing. But Ill take what I cant get.

Is the newer 4 speed out of a late 50's truck with a low 1st gear or is it newer. If its a late 50's 4 speed then you can still run the gears. I have the factory 4 speed in my 59.

"All the overdrive is gonna do is LOWER the Engine R P M"

Yes an OD transmission will lower engine RPM at cruising speeds, but it will not make as much impact at lower speeds as changing the rear gears would.

My point... 3.38 gears can't work as hard as 3.90 gears for pulling loads. 3.90 gears with an OD are more economical than 3.38 gears, as the final gear ratio with a typical 27% OD is equal to about 2.85:1.

In mathematical terms, a 3.38 rears will reduce rpm by about 13.3% in every gear. This reduction of rpm in the lower gears is not desireable. A 3.90 rear with an OD transmission will not suffer much in the lower gears, but the 27% reduction in OD is very desireable.

Here's the disclaimer: If we are talking about the sm420 4 speed transmission being replaced by any OD transmission...there will be a loss of that granny gear. The first gear of the sm420 transmission is around 7:1. The only OD transmission I know that comes close to that low gear is the NV4500 with a typical 5.61:1 first gear (early gm versions boast a 6.34:1 first gear).

Thanks for the responses, folks. Really helps out a newbie, even if I AM a geezer who grew up with these machines and should know.

So if I opt for an OD tranny and keep the 3.90, what trans is the one to look for? And what other dominoes fall in this scenario--clutch, I expect, and lose the floor starter? Anything else?

The T-5 would be a good choice, if you want to keep a floor shift transmission. They're very plentiful, as they were used in S10s and Camaros through the '80s/'90s. You will be able to keep the stock floor starter and bellhousing. I beleive the stock clutch will work fine with it.

T5, A833, NV4500 are a few that can be made to work. There are others, so this is just a partial list. The t5 swap is probably the easiest. The A833 4 speed and NV4500 5 speed swaps require more machining. The NV4500 might be too much transmission for a 235, but it is by far the strongest of the 3 transmissions listed.

The A833 and NV4500 will work with the stock 10 spline 1 1/8 clutch disc. I believe the T5 uses a different spline pattern, but haven't done that swap yet.

An SM319 is a near bolt in but you'll need a column shifter. I did the swap in my burb and I love it.

I have a 3.38 R&P from Patrick in my ’41, running an original 4 spd. crash box with a granny gear. The engine is a sock ’54 car 235. I love the 3.38 and almost never use granny to help me start.

I have a T-5 in my 54/3100 with 2.73 nova rearend and get along fine in flat land Indiana. i have dual carbs also. but in more hilly country i have too use 4the gear and even 3rd. i get 12-13 mpg around town and average 20 on highway and usually get a high of around 23.