01/28/2026
Bringing a 1970 Chevrolet El Camino's THM 350 Transmission Back to Life
At Precision Gear Transmission CVT & Automotive, we have a passion for all transmissions, including those from beloved classic vehicles. This week, we had the pleasure of performing a full rebuild on a THM 350 transmission from a beautiful 1970 Chevrolet El Camino, ensuring it drives as smoothly as it looks.
What symptoms did we see?
The owner reported typical signs of a classic transmission showing its age: delayed engagements, soft shifts, and a general lack of crispness in gear changes. These symptoms pointed towards worn internal components and potentially compromised hydraulic integrity within the valve body.
How did we diagnose it?
Our diagnostic approach involved a thorough assessment of the transmission's performance before removal, noting shift points and responsiveness. Upon disassembly, we confirmed wear in the friction plates, the transmission band, and various bushings. The modulator, a key component for shift timing, also showed signs of degradation.
What was the solution?
This THM 350 received a comprehensive rebuild to our exacting standards. Our solution included:
A complete transmission overhaul kit, replacing all critical clutches and seals.
A new transmission band for improved engagement.
A new modulator for precise shift timing.
A full bushing kit to restore internal clearances.
A heavy-duty torque converter, enhancing durability and power transfer.
Crucially, to correct common factory flaws and significantly improve driveability, we installed a Transgo SK350 valve body kit. This upgrade optimizes hydraulic pressures, resulting in firmer, more consistent shifts and addressing inherent weaknesses in the original design.
The El Camino is now ready to cruise the Rio Grande Valley with a transmission that performs reliably and responsively, meeting modern expectations while respecting its classic heritage.
When should a driver bring their vehicle in?
If your classic car, or any vehicle with a THM 350, THM 400, or similar older automatic transmission, is exhibiting signs of wear like slipping, slow engagement, or poor shift quality, don't wait. Expert rebuilds can restore its performance and extend its life.
All our rebuilds are backed by a 1-Year / 12,000-Mile Warranty.
Visit us at 3106 S Alamo Rd, Edinburg, TX 78542, or call (956) 310-2167 to give your classic the transmission care it deserves.