Transmission safety is a subject that doesn’t come up as often as it should. With the insane amount of horsepower being made in real-deal street cars there are some major safety concerns that need to be addressed before the skinny pedal hits the floor. Obvious safety features like a five-point rollbar, five-point harnesses, and a driveshaft loop are necessary for cars running 11.49 and quicker in the quarter-mile, and that accounts for lots of street cars these days. We watched as a few vehicles get booted from the drag racing competition at this year’s Holley LS Fest due to safety concerns, even though some smaller tracks may turn a blind eye to certain tech inspection items. Safety items are typically intrusive and expensive, and they rarely improve your car’s performance. These are the reasons that transmission safety items are often overlooked in a high-horsepower street car application.
Manual transmission safety is fairly easy to attain, as it typically only requires a blow-proof bellhousing. In most cases, this doesn’t require any special fabrication or major modifications to your existing setup so it’s a no brainer if you have a car with a manual transmission. Our main focus in this article is automatic transmission components to keep you safe behind the wheel. A catastrophic transmission failure can result in major problems. This is especially a true when you’re using an original GM case. And while there isn’t a dedicated horsepower limit for any particular style of automatic transmission, some companies offer guidelines for customers.
When the subject of automatic transmission safety came up, we consulted with TCI Automotive. We planned to use a TCI TH350 “bracket race” transmission in a turbocharged, LS-powered Nova capable of 700 horsepower to the wheels. This level of power is pushing the limits of a TH350 transmission, so it’s better to be safe than sorry. We will be installing a new flexplate, a flexplate shield, and a transmission shield, all of which came from TCI Automotive and adhere to SFI specifications. The Nova will primarily be driven on the street, but with that amount of horsepower and a sticky tire on the back the car needs to abide by the safety standards set by NHRA and other sanctioning bodies.
When an automatic transmission lets go it can be quite explosive, so using the appropriate shields keeps you and your passengers safe. If you’re making more than 500 horsepower at the wheels and using an automatic transmission with slicks or drag radials don’t let money or installation time stand in the way of your safety! Check out the installation steps and the information here to become better informed about transmission safety on and off the track.
01. This is what the underside of your average street car looks like. This 1970 Chevy Nova is getting ready for a major drivetrain upgrade so it was a great time to include safety items.
02. As a part of our upgrade, we installed a TCI Automotive (TCI) TH350 “bracket race” transmission, which is full of high-performance parts including an HD drum and a reverse manual valvebody with trans brake. To keep the occupants safe, we’re also installing SFI-approved shielding and an SFI-approved flexplate.
03. SFI specifications are very important for safety items, such as this flexplate shield. This TCI unit complies with SFI 30.1 specifications. These items can sometimes be sourced from swap meets, but always be aware of the manufacture and recertification dates, clearly listed on the decal.
04. With the old transmission out of the way, we remove the six bolts and wiggle the flexplate off of the crankshaft flange. This is an original LS-style flexplate that has been modified to work with an old-style automatic transmission.
05. Take a closer look at the modifications necessary to make the LS engine adapt to an old-style transmission. The boltholes for the torque converter must be elongated to match up to the early-style converter. This is not something you want in a high-horsepower car.
06. The TCI flexplate (PN 399753) slides into place and it’s easy to see the difference in quality between the OEM piece and this purpose-built, SFI-approved flexplate. TCI flexplates are 0.035-inch thicker than stock.
07. In this case, we are using new OEM bolts and they are tightened to 74 ft-lb in a star sequence. ARP makes fasteners for this purpose but it’s important to note that aftermarket fasteners have different torque values than OEM specifications. ARP flexplate bolts for an LS engine torque to 85 ft-lb when using Ultra-Torque lubricant.
08. Moving onto the TCI Trans-Shield (PN 975000), we do a quick test-fit and figure out the appropriate mounting of the brackets and the shield itself. This piece meets SFI 4.1 specifications and works for TH350 transmissions. TCI builds the shield from 6061-T6 aluminum, which should protects the occupants in the event of a drum explosion.
09. The Trans-Shield kit comes with mounting hardware and brackets, but be aware that fitment varies and may require some modification. If the shield is modified it voids the SFI certification, but you may need to modify the brackets for precise fitment.
10. The brackets attach to the transmission pan rail using special spacers that keep the bracket from putting pressure on the edge of the transmission pan. These spacers are not needed on cast-aluminum pans. The shorter bracket bolts to the passenger side while the longer bracket goes on the driver side and shares boltholes with the shifter cable bracket.
11. As we were mocking up the fitment of the Trans-Shield, we noticed a clearance issue with the shifter cable bracket. We mark the bracket and cut it to fit.
12. After the shifter cable bracket was trimmed to fit we used a series of spacers and washers to keep the bracket off of the transmission pan edge. The two brackets are placed alongside the transmission pan and are held in place with a total of five bolts (two on the passenger side and three on the driver side).
13. The TCI Trans-Shield kit comes with two straps that bolt below the transmission pan. TCI makes the straps long so that it will clear extra deep transmission pans, but in our case, we need to shorten the straps to be closer to the pan.
14. After the straps are shortened to fit the standard-depth transmission pan we marked them to be drilled. TCI specifies a 3/8-inch bolthole, with at least 5/8-inch of metal above the hole.
15. A step drill bit is used to make quick work of the straps. Both straps are drilled, making a total of four holes.
16. Using the supplied hardware, we slide the flathead bolts through the countersunk holes in the shield as well as the steel straps that we shortened to fit. Then it’s a matter of installing and tightening the supplied nuts.
17. Two more nuts and bolts are tightened on the driver side of the transmission to button up the Trans-Shield install. Every transmission is different so your fitment may vary. Keep in mind that you cannot modify the actual shield during the installation process.
18. The TCI Flexplate Shield (PN 940000) has a much more straightforward installation. It attaches using the bellhousing bolts, and has a notch cut out for the transmission dipstick. This piece is made from steel and protects the occupants in the event of a flexplate failure.
19. One of the toughest parts of the Trans-Shield installation was raising the transmission into place. Most of the time, using a scattershield requires a bit of transmission tunnel modification. Sometimes it can be performed with a hammer while other times it may require more significant modification. Matched with a high-quality driveshaft loop, this car will be ready for serious dragstrip action.