Rebuilt THM425 and Related Products for the GMC TZE


GMC Transmission Products Available from Manny’s Transmission

Transmission
Rebuilt THM425 Transmission
Rugged and Reliable - The Manny Tranny
Installed in the GMC MotorHome and TransMode, the Turbo-Hydramatic 425 was an automatic transmission developed and produced by General Motors from 1966 to 1978. The THM425 was originally developed for the Oldsmobile Toronado in 1966. The following year,(1967) the Cadillac Eldorado started using it. The transmission is totally rebuilt by Manny using new metal oil seals, new bearings, new spragues, new springs, new bushings, and new thrust washers, yielding a transmission that can be reliably utilized for another 100,000 miles or more.
The transmissions are rebuilt with Alto Red Eagle performance forward, intermediate and direct friction clutch discs and a 4L80-E wide high-energy front band. In addition, the overhaul implements the use of new paper, rubber, Viton sealing rings, fiber pan gasket and chain cover gasket, as well as a new canister filter, You’ll think your coach never had it so good with a transmission rebuilt by Manny.

The THM425 is also suitable for use in the following vehicles:
• 1971-1979 Cortez Motor Home
• 1966-1978 Oldsmobile Toronado
• 1967-1978 Cadillac Eldorado
• 1972-1978 Revcon Motorhome
• 1973-1978 GMC motorhome
Price - Please call or send an email to Manny


Switch Pitch
Properly Calibrated
The GMC automatic transmission used before the THM425 and THM400 units were fixed pitch transmissions. Basically, what was displayed on the console were just the designations of L and D. Downshifting from the higher gear to the next lower gear was mainly a function related to speed. The Switch-Pitch transmission was an innovative design. Unfortunately, it was discontinued before production of the TZE began due to a variety of factors.
However, when functioning properly the SP transmission can provide trouble free service and a significant performance increase. A properly calibrated switch pitch mechanism will control shift points based on acceleration, load, and RPM. The THM425 with SP had a torque converter with variable vane angle that was alterable between performance and economy. This gave 2.5 times torque multiplication, a 25% increase, and gave a bit better mileage in the economy mode. In a heavy vehicle this can provide a reduction of 0-60 mph time of up to 10%, and also give smoother shifts. As RPMs and output speed increases, torque is gradually reduced from 2:1 to 1:1, stretching the useful range of each gear.
Manny understands what is best for the TZE and for getting the kind of performance the motorhome deserves. Restore the advantages of SP to your motorhome with the bolt-on kit and supporting components. An electronic control has been added for maximum benefit.
Price - Please call or send an email to Manny

FinalDrives
3.21:1 Final Drive
The Ratio that Works
Originally, the GMC Motorhome was equipped with a 3.07:1 final drive using the same ratio as on the Oldmosbile Toronado. It was known to not be an optimum choice for the motorhome but using it reduced the GMC’s production cost. The original 3.07 assembly can be replaced with a complete 3.21 final drive assembly which will net an additional 5% torque multiplication. Additionally with our Power Drive installed in the transmission, the 3.21 ratio becomes 3.67 yielding a 20% improvement. This is an ideal ratio.
Our rebuilt unit comes with an aluminum cooling cover and an improved stub shaft with a stronger, new sealed bearing, and new style brackets.
Price - Please call or send an email to Manny

Power Drive - Installed or Kit
Hill-climbing Power
This is a great upgrade to the transmission that will really wake up your GMC. By changing the overall gear ratio, your engine is able to develop additional horse power. The gearing advantage contributes to an additional seventy foot pounds of torque (15%) to the front wheel drive. The transmission runs cooler because of lowered average torque converter slip. Those long grades on the interstates will not erode your speed and your GMC will feel like it has a new lease on life.
Installation of this sub-assembly is relatively simple, and the speedometer accuracy is not changed. Once the transmission is removed, this Power Drive can be installed in less than an hour. It may also be installed during a transmission rebuild.
Price - Please call or send an email to Manny