Chevy Solid Front Axle Transmission Guide

Transmission Rundown

Feb. 01, 2005 By Shane Wager
Think of the part of your rig you worry about the most. Which of all those mechanical assemblies you're dragging over rocks, pulling though mud, bashing through snow, flying off dunes, or in my case, letting sit in the shop for eons, is most susceptible. I'll bet that it's either a toss up between your front axle and your transmission, especially if you're running an automatic.

Now, GM put some damn fine engines in these trucks so there's very little worries there. In fact, if one of those friendly Jeep wheelers, or one of those great Toyota guys want to throw a bigger engine in their rig without a lot of expense, it's going to be a small block Chevy most of the time, or at least a 4.3 V6. They probably have parts for your small block at the grocery store. Well not really, but you can get cheap t shirts there eh?

Moving to the back of the rig, your rear axle could be a bit small if you started with half ton, but throwing a 14bolt in the rear of any full size GM truck is entry level mechanics and pocket change finance. A Detroit is cheap and that low hanging lip is a cutting wheel away from being a non point. We're good to go here!

Then there's the transfer case department, not much to worry about here. Most cases are pretty tough (can you say NP205?) and those that are a little less so have a lower low range, to get your rig going as slow as it can go. A combo of 700R4 and NP241 is a low buck way to crawl, but that's another story.

Finally, everything else that's bolted onto your personal monument to wheeling is fairly user friendly and cheap. So, disregarding that 10 bolt front you keep blowing up on "a simple baby step obstacle, really" with tires that "aren't that big, thirty eight inches isn't big", you probably just need to keep an eye on that gearbox underneath your feet. That magical contraption that translates the harsh rising and falling argument of the engine into a sensible and smooth explanation of momentum. Hmm, wordy aren't I?

Anyway, I'm going to lay down a list of transmissions that GM threw in their trucks from the general time of 1969 to 1991. I may miss a few of those obscure ones, or I may not have all the info on an individual unit, and I apologize for that. But, I know you just love me too much for anger, so, one two three go!




The automatic used in straight axle trucks are mostly of three types. The TH350 and TH400 three speeds and the super controversial 700R4 (early 4L60E)

My personal experiences with automatics is pretty straightforward. I started with a swapped in 700R4 and ran it fine for a year or so. It didn't like light wheeling though and decided to leak quite a bit. Boo to that! I dragged the truck to a transmission shop and the owner, an avid wheeler himself, helped me find a TH400/NP205 combo and put it in. I wouldn't go back. 

Anyway here's a rundown of details.



The TH350. A basic, common, three speed.

  • Introduced in 1969, apparently as a successor to the powerglide
  • The TH350 is a fairly strong transmission, and from who I have talked to of off road message boards, holds up well in light and medium duty use.
  • In an unusual balance, the TH350 is fairly short for it's strength at 21.75" with no adapter.
  • The TH305 weighs in at about 120 pounds. Easily chuckable.
  • The TH350 pan is shaped like a square with the corner lopped off. It is held on with 13 bolts.
  • The TH350 case is cast aluminum
  • The TH350 is geared as follows: 1st - 2.52     2nd - 1.52     3rd - 1.00
  • The TH350 later was remodeled to the TH350-C, which uses an electronic lockup converter. It can be identified by an electronic plug on it's left side.
  •  As a general rule, the larger the engine your TH350 was behind, the stronger it will be built. Upgrading the weaker versions is generally cheap and easy.



The TH400. A monster of a three speed.

  • The TH400 is a strong transmission, and is what most GM wheelers aspire to run when they want to stay basic and automatic. The TH400 is said to suck the most power from your engine compared to other automatics. They are easily serviceable, and can be built like few others.
  • The TH400 measures 24.37" long
  • The TH400 weighs in at about 135 pounds. Amazing huh?
  • The TH400 pan is shaped like a mutated Texas. It is held on with 13 bolts.
  • The TH400 case is cast aluminum and fairly smooth.
  • The TH400 is geared like this: 1st - 2.48     2nd - 1.48     3rd - 1.00
  • The TH400 is rated at 451 foot pounds of input torque



700R4. Love/Hate/Loathe

  • The 700R4 is a sticking point. Some love it for it's low first gear and overdrive. Some hate it for it's weaknesses and apparent love of exploding.
  • The 700R4 measures 23.40" long
  • The 700R4 weighs in at about 155 pounds. 
  • The 700R4 pan is a square shape. It is held on with 16 bolts.
  • The 700R4 case is cast aluminum.
  • The 700R4 is geared: 1st - 3.06     2nd - 1.63     3rd - 1.00     4th - 0.70
  • Introduced in 1982, the early 700R4 had noticeable bugs, but by the late 80's, it had been reworked to negate these.

  • The earlier 700R4 can be upgraded with later stock parts, and all 700R4 transmissions can be greatly upgraded with aftermarket parts.

  • The 700R4 was renamed 4L60E in 1991.

  • Many 700R4's used in trucks have a thicker K case, as opposed to those 700R4s used in cars.

  • The 700R4 has 1/4" pipe fittings on the passenger side for running a transmission cooler. USE IT!

  • My super cool transmission shop man says: Every drop of 10 degrees adds 25K miles to it's life.



I don't have much experience with manual transmissions. Frankly, I'm a little sissy girl who can't drive stick. All I have is info.... poor me....


TH465. Hail to the king baby.

  • The SM465 is a heavy duty compound low manual used from 1968 to 1991

  • All gears in the SM465 are except reverse and first are synchronized

  • The SM465 has a case length of 12" and a case height of 18"

  • The case is cat iron and ribbed both horizontally and vertically

  • The SM465 is geared: 1st - 6.55     2nd - 3.58     3rd - 1.70     4th - 1.00

  • The SM465 weighs in at 175 pounds. HEAVY!

  • The SM465 has PTO ports on both sides

  • The early SM465 4WD output shaft was 10 spline and generally regarded as weaker than the later 32 spline version introduced in 1980

  • The SM465 has a top cover made of cast iron. Right on!


The Others


There are quite a few obscure manuals used in GM trucks from around 1969 to 1986.

These include:

  • SM318

  • SM326

  • SM330

  • T-89A

  • T-150

They seem to be fairly rare though, so usually, when it's a stick, it's an SM465.



An Old Argument

An old argument - Which is better, automatic or manual? I've gathered a few of the points for and against both.

  • Clutch can burn out
  • Shock loads to drivetrain if clutch slips
  • Loss of momentum in low traction areas
  • Extra work to operate
  • Stalling


PRO :   
  • On road driveability
  • Faster on easier trails
  • One less pedal to deal with
  • No stick to manipulate
  • Torque converter gearing multiplication
  • No loss of momentum during gear shifts in loose terrain
CON :   
  • Weaker overall
  • Needs external cooling system
  • Less compression baking
  • Generates more heat
  • Possibly less reliable
  • Can't be run on it's side long
  • Hard to brake in low range


PRO :   
  • More specific gear selection
  • Stronger overall
  • No need for cooling
  • Compound low gear in some models
  • Maximizes low power output of smaller engines
  • Push starting
  • Easy roll back
  • Compression braking on downhill

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