Chevy 5 Speed Transmission - C-10 Five-Speed Kit

It has only been a brief period of time since we added the blue and white '66 Chevrolet C-10 Fleetside to our collection of in-house project trucks. At first glance the stubby little pickup we dubbed "Farm Fresh" seems like it's in pretty rough shape. But beyond its cosmetic appearance, a closer inspection reveals that all the paint on the '66's original body panels is original, and a quick glance at the odometer reads slightly over 80,000 miles.

Based on how mechanically tight the truck performs, coupled with the fact that it still has a pair of original-equipment T-3 headlights in place, it's our guess the indicated mileage is correct. Another good general indication of originality was that the build sheet for "Farm Fresh" was still sandwiched between the seat springs and the foam underneath the seat. For any truck owner, discovering the build sheet still in place is a lucky break, to say the least. The details revealed are so specific that they even include all the information about the dealership that ordered the truck brand-new from the factory. Our '66 was built at the Fremont, California, plant for a dealer in Yucaipa, California, not far from where our friend Steve Bentley found it for sale in Southern California's high desert.

Originally, our '66 was equipped with a 292-inch six hooked to a compound-low four-speed transmission transmitting power into a set of 4.11:1 gears. Somewhere along the line the 292 was uprooted, with a stock two-barrel 327 plucked from a '70 El Camino dropped into its place, but the original tranny, with its "granny gear" and deep rearend gears, was left alone. In the great scheme of things, ordinarily our first steps toward increased performance for any classic truck would be to hop up the engine and worry about the transmission and rearend gears later.

But in a departure from our usual practice, we chose to upgrade the '66's transmission instead. This was mainly because of the high level of discomfort caused by the bone-shattering jolt to the shoulder with every missed shift due to the compound four-speed's naturally sloppy shifter's unwillingness to change gears at a decent clip. After asking our friends over at Super Chevy magazine if they had any good advice on how to improve on the '66's transmission, we contacted the folks at Classic Chevy 5-Speed in Carlsbad, California, and made some inquiries into the availability of a kit to fit a Chevy pickup. As it turned out, Classic Chevy 5-Speed was in the final stages of releasing a complete kit that will work for '67-72 C-10s, as well as '60-66 C-10s such as ours.

Of course, before we made the final decision to install one of Classic Chevy 5-Speed's kits based around the Tremec TKO five- or six-speed overdrive transmission, we did a little research into what the benefits would be. Right off the bat, with first gear at 3.27:1 on a TKO-500 or 2.87:1 for a TKO-600, the Tremec gearbox would launch our truck with a first-gear ratio twice as high as the compound four-speed's first gear, meaning we would actually have a useable first gear.

This would also be a good point in our story to mention that either the TKO-500 or the TKO-600 has a lower first gear than a Muncie or a BorgWarner four-speed close- or wide-ratio transmission, which in effect is like installing lower differential gears for a quicker launch.

The same holds true for a Tremec TKO versus an original equipment three-speed stick transmission. The second-gear ratios for the Tremec TKO-500 and TKO-600 are 1.98:1 and 1.89:1 respectively. Third gear comes in at 1.34:1 for the TKO-500 and 1.28:1 for the TKO-600, with both transmissions utilizing 1:1 for fourth gear. This brings us to where a conventional three- or four-speed transmission is stuck with whatever final-drive ratio might be installed in a vehicle, and where the Tremec TKO's fifth-gear overdrive ratio kicks in. With a reduction of .68 for the TKO-500 and .68 for the TKO-600 the Tremec, TKOs offer up to a 36 percent reduction in rpm while in fifth gear. What all this wonderful information means on paper is that any vehicle equipped with such a transmission should offer, in addition to higher cruising speeds and lower interior noise levels, a noticeable increase in gas mileage.

But as they say, the proof is in the pudding, so what did we find out when Classic Chevy 5-Speed's "GM" Jim Goodlad finished installing the Classic Chevy 5-Speed Elite kit into our '66? Well, for starters, we ended up choosing a TKO-600, which is rated to handle 600 lb-ft of torque, while the TKO-500 is rated at 500 lb-ft of torque. To say we were happy with the conversion to a Classic Chevy 5-Speed would be to put it very mildly. We just couldn't get the smile off of our face as we ran the '66 up through the gears. The TKO had the right gears at the right time, and no matter what speed we were at, the little stock 327 was punchy as all get-out. Not wanting to jump to any premature conclusions, with a smile still on our face we failed to show up for work the next day and continued to put miles on the truck. With the 4.11:1 rearend, the '66 ran out of gears at the end of the freeway on-ramp, but now we can scream up the ramp, shift to fifth gear, and cruise all day long with the big dogs.

It might sound kind of dumb, but we really had no idea that swapping out the stock transmission for a Tremec TKO would have made such a radical improvement to our C-10's performance. Not to make a pun, but it really transformed the truck into a hot rod. As far as an improvement in gas mileage is concerned, we have been having so much fun blowing the doors off of our friend's trucks that used to be able to beat the '66 that we haven't done any serious fuel-mileage loops yet, but offhand it looks like our "10 mpg no matter what" truck is hitting at least the 14-mpg mark on the highway. Naturally, since "Farm Fresh" is one of our ongoing projects, we'll get some solid mileage numbers to confirm our suspicions before we move on to the truck's next modifications.