T5 Transmission Swaps for Stovebolt 216, 235, and 261 Chevy Inline Six Engines
On of the most popular upgrades for Advance Design trucks, is the installation of a late-model 5-speed T5 transmission in place of the original 3 or 4 speed gearboxes.
Choose your T5
The Borg-Warner T5 transmission was widely used by various auto manufacturers over the years, but we are primarily interested in those used in the Chevy S10 trucks and Astro vans from the mid 80's. These particular gearboxes use the same bolt pattern as your Chevy Stovebolt engine, and have manual speedometer outputs capable of driving your original (or aftermarket) speedo.
The main thing to consider in choosing your T5 is gear ratios. If you are changing the gearing in your rear, you will want to keep that in mind. Use a calculator to find the best ratios for you, while taking engine RPMs, differential ratios, and tire size into consideration.
Please see our T5 Information Page for information on gear ratios and Borg-Warner part numbers.
T5 transmissions can be found at junkyards, but you may get find a better deal in the local classifieds or an online auction.
Get Ready
The Chevy T5 gearboxes will bolt right up to your Stovebolt, but you will need to do a little massaging to get everything to mesh. Firstly, you will need to find a clutch disc with the correct diameter and the right number of splines to fit the input shaft of your T5. Most T5's use a 27-spline input shaft, and you can buy clutch discs to fit this from most local auto parts stores (Napa, Advance, etc...). Measure your original clutch disc and try to find something of the same diameter.
The input shaft on your T5 will be slightly longer than the original transmission. Use a feeler gauge to precisely measure the difference. You can either trim the extra length off the end of the input shaft, or create a simple spacer to fit between the transmission and bellhousing.
Finally, remove the T5 bellhousing from the transmission (if you have it) and drill out the 13mm holes in the transmission with a 1/2" drillbit to allow the bellhousing bolts to fit.
A 1985 Borg-Warner T5 overdrive transmission bolted to bellhousing of a 261 Stovebolt
Install It
Your T5 should now bolt up to your Stovebolt bellhousing. You should be able to use the original throwout bearing, clutch fork, and pilot bearing with your T5. With the right preparation and a little luck, the whole thing will go together and you'll have a working clutch!
Finishing It Up
The T5 gearbox is a few inches longer than the original transmission, so you will need to make some modifications to the driveshaft. Many people choose to replace or upgrade the rear axle at the same time and getting a custom driveshaft built to fit, but you may be able to get your existing driveshaft shortened at a driveline shop. You will also need to find a slip yoke for your T5 if you don't already have one. This may also be a good time to eliminate the Torque Tube if you're interested.
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