In the early days of the automotive industry, manual-shift transmissions were the norm. Operating a clutch pedal and a shift lever peering up from the floorboard or mounted on the steering column was simply part of the process for venturing onto the road. As technology advanced, convenience equipment such as electric starters and automatic windshield wipers became available to consumers. It should come as no surprise that shiftless transmissions followed soon after.
Our custom-built Turbo 400 is being subjected to complete functionality testing on the in-house transmission dyno at GearStar Performance Transmissions’ Akron, Ohio-based facility. The trans is tested for functionality in all forward gear-selector positions as well as reverse. The test takes as much as 90 minutes to complete and the transmission remains under load for 50-60 minutes of that. It allows GearStar to verify torque converter stall speed, measure internal line pressure, and calibrate full-throttle upshift speed for the intended application before sending the completed transmission to the customer.
Designing and producing transmissions that shifted automatically was a challenging and costly endeavor for individual automakers. General Motors wisely created its Hydramatic Division in the '30s to develop high-quality automatic transmissions for its motor divisions. The first Hydramatic—an extra-cost option available in Cadillac and Oldsmobile models during the late '30s—used pressurized hydraulic fluid to couple each respective gear to the engine crankshaft, as opposed to the mechanical clutch assembly connected to the flywheel. Soon every GM Division was offering a Hydramatic-produced transmission in its vehicles.
HPP sent GearStar a well-used Turbo 400 from a ’68 Pontiac for a high-performance rebuild. The company starts each custom build by completely disassembling the transmission, and ours appeared to be all-original. It will be built to Level 4 specifications for our application using high-quality components.
Of all the different Hydramatics produced over the years, none may be as popular as the Turbo-Hydramatic 400 (THM-400 or Turbo 400). Introduced in '64 as a heavy-duty unit, Pontiac began using the Turbo 400 in '65 behind the 389s and 421s in the Big-Cars, as well as in '67 GTOs and Firebird 400s. It could be found behind many 400-to-455ci Pontiacs over the course of its production run.
Used extensively by all GM divisions, Hydramatic phased the Turbo 400 out of production during the late '80s. With literally millions of them produced in that time, hobbyists and racers of all GM makes still covet the over-engineered design, exploiting its strength and versatility with support from OE and aftermarket parts suppliers alike.
GearStar Performance Transmissions in Akron, Ohio, is one company that specializes in providing custom-built, high-performance automatic transmissions, and the Turbo 400 is among its popular offerings. Owner Zack Farah employs what he considers top-tier technicians and uses only the best domestically manufactured components to create four distinct levels, ranging from an improved stock replacement unit to a super version rated at 1,200 hp and 1,000 lb-ft. While basic rebuild techniques are readily available in any Pontiac service manual, we will instead have GearStar explain to us what improved components make its packages unique.
Choose Your Level
Level 1
Master Overhaul Kit with High Energy Frictions and All New Steel Plates
High Flow Filter
New Kickdown Solenoid
Adjustable Modulator
Transgo Shift Kit
New Front Band
New Torrington Bearings
Bushing Kit with Flanged No Walk-Out Case Bushing
Thrust Washer Kit
New Low-Reverse Spring & Roller
New Chrome Transmission Pan with Drain Plug
New Speedometer Drive Gear
New Speedometer Driven Gear
20,000 GVW Hayden Transmission Cooler
Converter: Heavy Duty
1,600 to 2,200 Stall Speed
Maximum Horsepower Capacity: 350
Maximum Torque Capacity: 325 lb-ft
Starting Price: $1,295
Level 2
Master Overhaul Kit with High-Energy Frictions and All-New Steel Plates
High-Flow Filter
New Kickdown Solenoid
Adjustable Modulator
Transgo Shift Kit
New Front Band
New Borg-Warner Low-Reverse Band
New Torrington Bearings
Bushing Kit with Flanged No-Walk-Out Case Bushing
Thrust Washer Kit
New Low-Reverse Spring & Roller
High-Capacity Direct Clutch Drum
Heavy-Duty Forward Clutch Hub
High-Volume High-Flow Pump Assembly with New Gears
New Chrome Transmission Pan with Drain Plug
New Speedometer Drive Gear
New Speedometer Driven Gear
20,000 GVW Hayden Transmission Cooler
Installation Kit
Converter: 12-in or 13-in Heavy-Duty High-Performance Furnace Brazed
Stall: 1,600-2,200
Maximum Horsepower Capacity: 450
Maximum Torque Capacity: 425 lb-ft
Starting Price: $1,495
Level 3
Master Overhaul Kit with Raybestos Stage 1 Racing Frictions and Hardened Kolene Steels
High-Flow Brass Filter
New Kickdown Solenoid
Adjustable Modulator
Transgo Re-Programming Shift Kit with Shift Command
New Front Band
New Borg-Warner Low-Reverse Band with Heavy-Duty Lugs
New Torrington Bearings
Bushing Kit with Flanged No-Walk-Out Case Bushing
Thrust Washer Kit
New Low-Reverse Spring & Roller
High-Capacity Direct 8-Clutch Drum with 34-Element Intermediate Sprag and Hardened Race
Heavy-Duty Forward Steel Clutch Hub
Extra-Capacity Intermediate Clutch Assembly
High-Volume High-Flow Pump Assembly with New Gears
New Extra-Capacity Cast-Aluminum Transmission Pan with Drain Plug
New Speedometer Drive Gear
New Speedometer Driven Gear
30,000 GVW Hayden Transmission Cooler
Installation Kit
Converter: 10-in Heavy-Duty Furnace-Brazed Flanged Hub with Billet Cover
Stall: 2,600-3,600
Maximum Horsepower Capacity: 600
Maximum Torque Capacity: 550 lb-ft
Starting Price: $2,195
Level 4
Master Overhaul Kit with Raybestos Generation II Racing Frictions and Hardened Kolene Steels
Transgo Re-Programming Shift Kit with Shift Command or Full Manual Forward Pattern
GearStar Full Race Shift Kit
High-Flow Brass Filter
New Kickdown Solenoid
Adjustable Modulator
New Kevlar Front Band
New Borg-Warner Low-Reverse Band with Heavy-Duty Lugs
New Torrington Bearings
Bushing Kit with Flanged No-Walk-Out Case Bushing
Thrust Washer Kit
New Low-Reverse Spring & Roller
High-Capacity Direct 9-Clutch Drum with 34-Element Intermediate Sprag and Hardened Race
High-Rev Spring Kit
Heavy-Duty Case Assembly
Extra-Capacity Intermediate Clutch Assembly
300M Billet Forward Clutch Hub
300M Main Shaft
300M Hardened Input Shaft and Reinforced Forward Drum Assembly
High-Volume High-Flow Pump Assembly with New Hardened Gears
New Extra-Capacity Cast-Aluminum Transmission Pan with Drain Plug
New Speedometer Drive Gear
New Speedometer Driven Gear
30,000 GVW Hayden Transmission Cooler
Converter: 10-in or 11-in Heavy-Duty Furnace-Brazed Flanged Hub with Billet Cover
Stall: 2,600-4,000
Maximum Horsepower Capacity: 1,200
Maximum Torque Capacity: 1,000 lb-ft
Starting Price: $4,495
GearStar charges $4,495 for a Turbo 400 fitted with its Level 4 package, which increases capacity to 1,200 hp and 1,000 lb-ft. Not every application requires such durability, however. Its Level 1 transmission package is rated at 350 hp and 325 lb-ft, and pricing begins at $1,295. Complete details and pricing of all its Level builds can be found here. We’re confident there’s one to fit your requirements.
