Rebuilt THM425 Transmission
Rugged and Reliable - 
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 the upgrades GM used on the TH-400 in the late 70s and 80s on the Flatbed and Box trucks. 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, Installed in the GMC MotorHome and TransMode, 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

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

How to remove the transmission from the Motorhome
First thing I do is raise the front end so you have 18” clearance under the engine mount crossmember. Place two jacks under the frame, where the front clip attaches to the frame.
Unbolt the negative cable from the starting battery or turn the switch to off if there is one.
Drain the fluid, either by unbolting the bracket that holds the modulator in and remove it to drain into a large container or by unbolting the drain if there is one.
The starter comes out first; two 7/16-16 bolts for the starter, one nut for the positive lead and a small nut for the solenoid.
Next comes out the converter shield; three ¼-20 bolts.
Take out the bolts that hold the torque converter.  Rotate the flywheel by using a pry bar or large screw driver.
Move to the final drive side and remove the bolts to the tranny. There should be six 3/8-18 by 1-1/4 long, There is also one nut on the passenger side. If the tranny is original to this particular coach, that’s all the bolts/nut. If there is another nut/bolt on the passenger upper side, it’s a pain to take it out but it can be done with a curved box wrench.
Note: One of the bolts holds the fill tube. Once the bolt is removed, pull the fill tube straight up.
Disconnect the speedometer cable from the speed bullet. Remove the pin from the shifter bracket.
To the rear of the tranny, loosen the two bolts holding the tranny mounts. It takes a ¾ socket with an extension through the large holes in the cross member.
From inside, remove the six bolts around the bellhousing to the engine. Also unbolt the cooler lines using a flare wrench.
Now get a chain to hold the engine up, bolted to the back of the heads. Loop it high enough to clear the distributor/spark plug cables.
I use two comelongs, one to hold the engine and one to lower/raise the transmission on gentry over the hatch. A five foot long chain with two hooks around the transmission hooking up at the peep hole works for me.
After the gentry is in place with the comelongs holding the engine and tranny up, go below and unbolt the three 7/16 bolts in the back of the transmission.
Pry the tranny back from the engine and pry the final drive from the transmission and lower it down.