GM TH350 3-Speed Automatic · GM/Chevrolet/GMC/Cadillac/Buick · Expert rebuild service since 1987. Lifetime warranty. Free diagnostic.
1969–1986 Chevrolet Camaro, Nova, El Camino, Malibu; 1969–1986 GMC/Chevrolet trucks; 1969–1979 Pontiac Firebird; widely used across all GM divisions behind 250/305/350/400 small-block engines
| Configuration | 3-speed automatic, cast-iron case, non-lockup torque converter |
|---|---|
| Gear Ratios | 1st 2.52:1 · 2nd 1.52:1 · 3rd 1.00:1 · Rev 1.93:1 |
| Fluid Type | Dexron II or Dexron III ATF |
| Fluid Capacity | 9.0 qts total, 5.0 qts service refill |
The TH350 uses a vacuum modulator to control shift timing and line pressure. The modulator diaphragm leaks engine vacuum into the transmission fluid, causing it to burn and turning it dark/burnt. Failed modulator causes soft shifts and rapid clutch wear.
Symptoms: Blue smoke from exhaust (ATF burning in engine); soft early shifts; burnt ATF smell; clutch slip
The centrifugal governor controls shift speed. A stuck or worn governor causes shifts at wrong speeds — either early (light clutch load) or late (harsh shifts).
Symptoms: Upshifts at wrong speeds; harsh 2-3 upshift; no 2nd gear at moderate throttle
The intermediate clutch engages 2nd gear and is common wear item due to its frequent cycling in stop-and-go driving. Degraded Dexron II accelerates its wear.
Symptoms: Slipping in 2nd gear; no 2nd gear engagement; RPM flare on 1-2 upshift
Full disassembly. Modulator replaced. Governor cleaned and polished. All clutch packs — forward, intermediate, direct, and reverse — replaced with new Alto frictions and steels. Band replaced and adjusted. Valve body cleaned and rebuilt with new gaskets. Full Transtec soft parts kit. Converter flushed.
Dexron III ATF every 30,000 miles. Replace the vacuum modulator every 60,000 miles proactively — a failed modulator burns the entire fluid charge and destroys clutch packs. Check modulator at every service.
The modulator is the TH350's throttle position sensor — it reads engine vacuum to determine load and adjust shift timing. When the diaphragm ruptures, ATF is sucked into the intake manifold and burned, producing blue smoke. It's a cheap part (under $20) but causes expensive damage when neglected.
Yes — TransGo and B&M shift kits are bolt-in valve body upgrades that firm up shifts and raise line pressure. Highly recommended for performance applications. We install shift kits with every TH350 rebuild.
Square oil pan with 13 bolts. Cast iron case. Single kickdown cable connection on driver side. Smaller than the TH400.
Approximately 350 lb-ft stock. With a shift kit and upgraded clutch packs, handles 450+ hp reliably. Very popular in street performance builds.
$1,200–1,800 including a shift kit. 2-day turnaround.
Free diagnostic, written estimate, lifetime warranty. Chicago's TH350 rebuild specialists since 1987.
