Last month, we ran a story ("One-Month Resto") about the trials and tribulations of building a '68 Chevrolet truck in 28 days. After all of the sleepless nights and overworked muscles trying to make the deadline, it was a worn-out TH400 transmission that kept the truck from being driven. We could have just rebuilt the 400, but the truck will be used as a daily driver and with gas prices going up, we wanted the fuel consumption to go down-an Overdrive transmission will do that for us. Since the truck is a classic, we didn't want to deal with a bunch wires or computers to make it work, and luckily, there is an option just like that.

California Performance Transmission (CPT) is run by Mr. Art Carr, a transmission guru with more than 40 years of experience under his belt. We told Art what we wanted for our '68: an Overdrive that can handle decent power, that is easy to install, and that has no computers. With a small chuckle, he said, "I got just what you need, my 2004R."

Originally, the 2004R came in the Buick Grand Nationals and is usually overlooked as a high-performance Overdrive because of strength issues. Because the 200 can shift into Fourth under full throttle and has good gear ratios compared to other Overdrives (see chart), Art decided to pack it with stronger internals. Depending on your project, you can pick the perfect tranny without over-spending because CPT offers these 2004Rs in many different power-handling tiers, from a mild 250hp to 800-plus ponies.

Additional features of the 200 that make it a good choice are the multiple bolt patterns for Buick, Olds, Cadillac, Pontiac, and of course, Chevrolet. It is the same length and uses the same yoke, gearshift, and cooler lines as a Powerglide or TH350. In fact, in a swap situation, all you have to do is move the trans crossmember, depending on what tailshaft you have. If you have a 400, then you will need a yoke, too. Shift points are controlled via a TV cable, and it has a non-lock-up converter, so no wires are needed to hook up. The factory torque converter has been replaced with a custom-built heavy-duty Super Torque version, featuring furnace-brazed turbine and impeller assemblies, Torrington bearings, a 4130 steel turbine hub, a heavy-duty stator with large sprag, a steel billet cover, and dual bolt patterns-and it has been balanced to 2 grams. All transmissions that CPT assembles are run on a dyno for a little piece of mind and backed by a 90-day unconditional and 2-year conditional warranty.

We drove down to CPT to watch the crew build our 200, before taking it back to the shop for the swap. We completed the job in a few hours with only one specialty tool, the transmission jack we borrowed from our friend, Bob, at Quality Automotive. We also used a lift because it makes taking pictures much easier, but it was not necessary. You can do this job on jackstands, but if you have a lift available for a few hours, use it. Once we had the trans in, the TV cable adjusted, and the fluid full, a testdrive was in order.

On the road, the improvement was almost instant-the truck moved! Besides that, the transmission worked perfectly. Under light throttle, it went through the gears almost seamlessly. Behavior during heavy throttle was a totally different story. Each gear featured a nice positive shift. We even got the tire to bark in Second. After the testdrive, we hopped on the freeway and drove back to CPT to have Art check our work. That extra gear is awesome and made cruising down the road enjoyable and thrifty in the gas-saving area. Once we got the OK from Art, it was time to go home-and the cruise home was not nearly as enjoyable as the ride out. The rear end of the truck started howling like a banshee and was getting worse with every mile. Unfortunately, the truck didn't make it to the shop; the rearend was toasted, so a ride on a tow truck got us home. We will address that issue soon, but for now, check out how easy the swap from the factory TH400 to the California Performance Transmission 2004R was.

Part One: What's Inside
Here are the goodies we got from CPT: a 2004R automatic Overdrive transmission, a 12-inch non-lock-up converter, TV cable, a dipstick, a yoke, and the proper brackets to hook up the TV cable to a Holley carb. This whole setup set us back almost two grand, and it was well worth the price. We didn't just get a refurbished assembly. We got a mildly built trans that can handle as much as 400 hp and shift into Fourth.

The Final Word
Upgrading our '68 pickup to an Overdrive transmission couldn't have been easier, unless we had someone else turn the wrenches. The 2004R from California Performance Transmission works great, shifting smoothly under light throttle and barking the tires under full throttle. Not only did we get a performance upgrade, but we also received one more gear for highway cruising.

Transmission lengths from bellhousing to tailshaft

POWERGLIDE
Short tailshaft 26
Long tailshaft 27
TH350
Short tailshaft 27
Long tailshaft 30
Extra-long tailshaft 34
TH400
Short tailshaft 27
Long tailshaft 34
Extra-long tailshaft 38
2004R
All 27
700R4 and 4L60
All, except Corvette 31
Corvette (1982-1996) 30

GEAR RATIO COMPARISONS
TRANSMISSION 1st 2nd 3rd 4th
Powerglide 1.76 1.00    
TH-2004R 2.74 1.57 1.00 0.67
TH-350 2.52 1.52 1.00  
TH-400 2.48 1.48 1.00  
TH-700R4 3.06 1.62 1.00 0.70

If you had 4.10 gears in your rearend, your final drive ratio would be:

TRANSMISSION
Powerglide 4.10
TH-2004R 2.75
TH-350 4.10
TH-400 4.10
TH-700R4 2.87

SOURCE
Drive Shaft Masters Co.
www.driveshaftmasters.com
California Performance Transmission
Huntington Beach
CA
800-278-2277
www.cpttransmission.com
Early Classics Enterprises
www.earlyclassic.com
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