I Swap the 4L60E Automatic for a Tremec Manual 5-Speed!
In the fall of 2022 I started noticing some new noises coming from the 4L60E transmission in my 1993 Chevy OBS pickup. The trans had been rebuilt within the past year, so I was not expecting this as the trans was performing very well. I took it to my mechanic and Paul confirmed that the noise was coming from the trans and that probably a bearing or bushing somewhere was worn out. This would necessitate pulling the trans and treating it down to find and fix the parts.
I weighed the costs and time to do this against another idea I had been kicking around – that of swapping the transmission out and replacing it with a 5-speed manual transmission. Where do I get that idea? It was featured on one of the truck shows I watch in my Motortrend+ subscription. It is a kit offered by American Powertrain which you can get details about here: https://americanpowertrain.com/shop/transmission-kits/88-98-chevy-gmc-c1500-trucks-obs-gmt400-5-and-6-speed-kit/ A couple of short videos about the kit are posted below.
I called American Powertrain and discussed the advantages/disadvantages of the 5-speed compared to the 6-speed. I decided to go ahead with the 5-speed swap because of the slightly higher overdrive ratio and ordered the kit on October 4, 2022. The kit was shipped a couple of weeks later with the bell housing back-ordered. We received the bell housing and all the parts in the kit by the end of October, and I schedule the weekend of November 13 with my mechanic Paul to start the project.
After all the parts and pieces arrived at my mechanic’s shop, we scheduled to begin the project on November 13, 2022. We followed the instructions, disconnected the automatic trans linkage, and then with the truck up on a hoist, removed all the rest of the automatic trans connections, wires, cooling lines, etc. After removing the driveshaft, we used a transmission jack to support and lift the back of the 4L60E. We then removed the transmission cross-member. Then we unbolted the bell housing bolts from the engine and pulled the trans back and then lowered it out of the way.
Next, we installed the flywheel and clutch assembly, then the bell housing. We test fit the trans several times to figure out how many spacers we needed for the clutch and to locate where to cut the hole in the floor for the shift lever. NOTE: This kit does not include a floor shift boot. I finally settled on a 14″ Hurst floor shifter for a Mustang, and a Hurst floor shift boot and mounting ring. I also added an 8 Ball knob instead of the white knob included in the kit.
In the process of the first day, we discovered a few problems. The rear transmission seal had been damaged during shipping. Also, when the clutch pedal assembly was put together at the manufacturer, someone had tightened down a bolt without clearing a fitting first, which caused the fitting to be dimpled. Also, when test-fitting the shifter lever, we discovered that it hit my dash in the forward position, and my console in the back position. So, an email and photos were sent to American Powertrain. American Powertrain responded within a day or so and shipped out the replacement parts.
American Powertrain did not tell me during the sales process that although the kit is complete, it requires you to measure for the driveshaft after the trans is installed, with the vehicle setting on the ground under normal operating conditions. We did this next, and then I filled out the driveshaft order form on the American Powertrain website. It is important to note that this process adds basically another week to the entire installation because it takes a couple of days for them to make the custom driveshaft, and ship it to you. You cannot do this swap in one weekend!
The Final Touches
The following weekend after Thanksgiving we were able to finish the project. The driveshaft fit perfectly. In my case, it was exactly the same length as the driveshaft I removed, meaning that my 4L60E was the same length as the TKX trans. The clutch pedal assembly also fit under the dash well. We had to move some wiring around, and hook up the backup light switch when in reverse. We were not sure that the hydraulic clutch line connecting the clutch with the slave cylinder was long enough, but finally figured out a way to drill a hole in the firewall that worked. It is very very close to not being long enough!
There were a number of parts included in the kit that I ended up not using. I decided against the reverse lockout feature since I would be the only driver, and I had never driven a manual vehicle with the feature before in my life. I didn’t see why I needed it now.
Also, the double-bend shift lever included in the kit did not work. I returned it and received a single-bend one that did.
First test drive with the 5-speed TKX transmission
I would say that this kit is a pretty good option for a way to change the transmission feel and performance of your OBS Chevy with the minimum of sourcing time and technical issues. American Powertrain has done a pretty good job of putting this kit together, and their instructions were pretty good. I’d say that their weakness is in customer service and communication. They did not make the entire process clear during the sales process, and I discovered major surprises during the process, rather than being informed at the outset.
They did come through with solutions to every problem, but it took extra time and communication was not always optimal. There were delays and gaps when I did not know what was happening or what to expect. So, if you choose to go with this kit, plan on spending extra time being proactive with American Powertrain.
But, it is very fun to drive!