When GM started producing the C/K series of trucks in 1960, they were truly “built like a rock” – in most cases, a six-cylinder, two-barrel-carbureted rock. GM made constant improvements to the C/K line of trucks throughout each of the four generations, which basically ended in 1987. Larger engines and varied transmission offerings sought to give customers more choices when ordering their new utilitarian vehicle, but those options were still limited by the technology of the time. Now, however, you can install a five-speed manual transmission and enjoy what your dad couldn’t when the truck was new.
Upgraded Gearing Options
While many of these trucks are still serving their intended purpose, today’s owners of GM’s trucks are always searching for ways to help their trucks haul in more ways than one. One of the best bang-for-the-buck modifications that’ll transform any vehicle into an enjoyable highway cruiser is to install a five-speed transmission. Thankfully, for owners of two-wheel and some four-wheel drive, 1960 through 2007 trucks, Silver Sport Transmissions (SST) offers a variety of kits that’ll increase the durability of the drivetrain while lowering engine RPM and fuel consumption at highway speeds.
SST has several overdrive options including the five-speed TREMEC TKX, six-speed TREMEC Magnum, and the self-shifting SST A41 automatic transmission in comprehensive conversion kits for the entire line of Chevy and GMC C-series trucks.
Tremec is conservative in the torque ratings of the TKX and Magnum. These values are actually based on a 24-hour input at the rated torque. — Jeff Kauffman, Silver Sport Transmissions
In case you are wondering, the newest and most compact overdrive transmission offered by TREMEC, the TKX is rated for 600 lb-ft of torque. For those wanting even more torque capacity, the six-speed MAGNUM trans is rated up to 700 lb-ft and features two overdriven gears. The A41 four-speed automatic is based on the GM 4L60E transmission and comes in three performance stages rated from 450 to 650 lb-ft of torque.
Upgrading to More Gears
As you can see, our 1968 Chevy C10 CST has gone through a few upgrades already. The power brakes and A/C make driving the truck more comfortable, but the automatic transmission doesn’t deliver the joy of rowing your own gears. That is why the owner decided to install a five-speed transmission. Since SST was installing a TKX five-speed overdrive — which meant adding another pedal and going from a column selector to a floor-mounted shifter — we decided to follow along.
During the upgrade, the owner decided to use a hydraulic clutch system in lieu of trying to locate the outdated mechanical assembly. Of course, the swap requires a bell housing and clutch assembly, and SST offers everything in addition to the transmissions to complete the conversion.
Our TREMEC TKX transmission kit included a new pilot bearing, transmission crossmember, trans mount, and all the necessary hardware for the installation. The TKX transmission is available in either wide-ratio (3.27, 1.98, 1.34, 1.00, 0.72) or close-ratio (2.87, 1.89, 1.28, 1.00, 0.68 or 0.81) gearsets and is engineered to use either mechanical or electronic outputs for the speedometer. SST has a handy Speed Analyzer on its website to help you figure out which gear ratios will work best in your application.
SST started by removing the transmission, as well as the accompanying parts such as the starter, steering column, brake pedal, and shifter assembly. The SST kit comes with straightforward instructions to complete the conversion as well as templates for areas that will need trimming. Careful measuring will ensure that everything has enough clearance to operate correctly without interference once installed.
We installed the new pilot bearing, clutch assembly, and bell housing. Still, before we could install the transmission, it was imperative to properly check (and correct if necessary) the runout of the bellhousing to retain TREMEC’s warranty coverage. Click HERE for a quick way to check and correct bellhousing runout. There should also be at least 1/4-inch of clearance between the transmission and the underside of the vehicle once installed. This is to prevent contact noises and vibration while in operation.
A Transmission For All Generations
The flexibility of the TKX transmission allows SST to offer kits for each generation of trucks from 1960-1966, 1967-1972, 1973-1987, and 1988-1991 as well as a long list of other vehicles. The TKX transmission features three different shifter locations, and with a shifter upgrade, more than 25 different shifter configurations are possible. SST also offers a TREMEC TR-4050 transmission kit for conversion of 1967-1972 and 1973-1987 four-wheel drive K-series trucks.
The instructions sent with the SST kits are quite comprehensive and cover much more than we could in this small space, just take your time and go step by step. But, there are a few things to note as you’re finishing up the installation and are anxious to hit the open road. A key factor is making sure you have installed the proper amount of fluid in your transmission. Keep in mind that GM Synchromesh, Pennzoil DEXRON/MERCON ATF (non-synthetic), Valvoline Synchromesh, and Mobil 1 ATF are the only fluids approved by the manufacturer.
SST recommends the fluid be replaced after the first 500 to 1,000 miles of normal driving and states it is acceptable to use the less-expensive DEXRON/MERCON fluid for the break-in period and then replace it with one of the other approved fluids at the first change interval. After that, the fluid should be changed every 30,000 miles. Other considerations include checking for any leaks in either the transmission or the hydraulic clutch system during the initial shakedown runs. SST also recommends test driving the new transmission at low speeds and engine RPM, checking for any noises or vibrations as you go.
SST offers a vast number of components included in their kits and their in-house engineering department includes the very folks who design each kit. If you have any questions about how to install a five-speed transmission, a particular kit, or a process, their staff is ready and willing to help with the answers you need. Once your transmission is installed, it’ll be ready to give you many miles of smiles as you enjoy lower RPM and higher fuel efficiency in your Chevy C10 pickup.