Squarebody Transmission Fluid Capacities — TH350, TH400, 700R4 (1973-1987)

At-a-glance fluid capacities

For automatic and manual transmissions used in 1973-1987 Chevrolet/GMC Squarebody trucks:

These are factory rough capacities. Your specific truck may vary — different cooler line lengths, different dipstick tube routes, and aftermarket transmission cooler lines all change actual fill quantity slightly.

Identifying which transmission you have

Visual identification from underneath:

• TH350 — three-speed auto, 21.75" overall length, 6-bolt pan with rounded corners, "TH350" or "TH-350" sometimes cast into the bell housing.
• TH400 — heavier-duty three-speed auto, 24.4" overall length, 13-bolt pan (irregular shape, not rectangular), distinctly larger and heavier than TH350.
• 700R4 — four-speed auto with overdrive, 23.4" overall length, 16-bolt pan with one rounded corner. Visually similar to a TH350 in length but the pan shape gives it away.
• SM465 — granny-low four-speed manual, distinctive cast-iron case, side-mounted shifter, "Muncie" cast on side (yes, despite being a Saginaw GM transmission, the casting still says "Muncie" on some variants).

If you're unsure, the GM transmission tag (riveted to the case) will identify the trans by part number. Cross-reference against the GM Heritage Center service literature.

Filling procedure (automatics)

1. Park on level ground. Tilted ground gives a wrong reading.
2. Engine running, transmission in PARK (or NEUTRAL on some HD configurations).
3. Pull the dipstick, wipe, reinsert, pull again to read the level. The dipstick has two marks — "ADD" (cold) and "FULL" (hot). Verify the level on the appropriate mark for your engine temperature.
4. Add fluid through the dipstick tube in small increments (a quart at most). Wait 30 seconds between additions to allow the fluid to drain into the pan.
5. Cycle through gears (PARK → REVERSE → NEUTRAL → DRIVE → LOW) at idle to fill the torque converter and cooler lines, then return to PARK and re-check.

Common error: overfilling. ATF should be at or just below the FULL hot mark when the transmission is at operating temperature. Overfilling causes foaming, which causes erratic shifting and can damage the transmission.

Why Dexron III, not the modern Dexron VI

GM has updated Dexron specs multiple times. Modern Dexron VI is backwards-compatible in TH-series and 700R4 transmissions for general use, but the original specification for these transmissions is Dexron III (and Dexron II before that). Dexron VI is more synthetic and has slightly different friction modifiers — some old-school transmission rebuilders argue it changes shift feel in older transmissions.

For factory-stock TH350/TH400/700R4 in a Squarebody, Dexron III (or a Dexron III/Mercon dual-rated fluid) is the safest choice. If your transmission has been rebuilt with modern friction material, the rebuilder may specify Dexron VI — follow their spec.

Type F (Ford spec) is NOT compatible with GM transmissions. Don't use Type F in a TH350; the friction modifier difference causes harsh shifting and excessive clutch wear.

Manual transmission fluids

The SM465 uses 80W GL-4 gear oil (some sources spec 80W-90 GL-4 or even 90W; 80W or 80W-90 are both acceptable). Don't use GL-5 in the SM465 — GL-5 contains EP additives that attack the brass synchronizer rings.

The NV4500 (rare in Squarebody, factory in some 1986+ HD trucks) uses a manufacturer-specific fluid — check the NV4500 service literature. Some specify GL-4 only, others spec a specific NV4500 oil that's not GL-4 or GL-5. Don't substitute generically.

Transfer case fluids (4WD trucks)

All three Squarebody-era transfer cases (NP205, NP203, NP208) take Dexron III ATF, NOT gear oil. This is a common Squarebody fluid mistake — the front and rear differentials around the transfer case use 80W-90 gear oil, but the transfer case itself uses ATF. Putting gear oil into a transfer case ruins the planetary gear set within a few thousand miles of normal driving.

See our Bronco transfer case article for more on the gear-oil-vs-ATF issue — same logic applies to Squarebody.

When to deviate

Use the rebuilder's spec instead if your transmission has been:

• Rebuilt with modern friction material — may specify Dexron VI or aftermarket high-performance fluid
• Built with a manual valve body or shift kit — fluid spec doesn't change but service intervals shorten
• Converted to a different gear set — capacity may change

Common mistakes

1. Type F in a GM auto. Wrong friction modifier. Causes harsh shifting and accelerated clutch wear.
2. Gear oil in the transfer case. Ruins the planetary gear set.
3. GL-5 in the SM465. Attacks brass synchros over time.
4. Overfilling. Causes foaming and erratic shifts. Always check on level ground at operating temperature.
5. Not cycling through gears during a fill. Leaves fluid stuck in the torque converter, gives a false-low dipstick reading, leads to overfill.

A reminder on safety

These are research-derived starting capacities, not factory shop manual data for your specific truck. Always verify against the actual factory service manual for your specific year, transmission, and 4WD/2WD configuration. Transmission fluid errors are slow-failure modes — by the time a transmission is shifting badly because of wrong fluid, you've already done expensive damage.