It’s easy to get caught up in the headlines of big horsepower and all of the glamour and glory that goes along with it. Supercharged and turbocharged engines making over 1,000 hp on pump gas are the hottest rage right now. Monster big-blocks and super fancy LS engines seem to be in every driveway across the land.
Naturally, a top-of-the-line TH400 or high-end exotic Overdrive transmission back one of these unbelievable powerplants, or maybe even one of those fancy six-speed manual transmissions has found its way into the trans tunnel. The modern era of high-performance has brought us to the brink of insanity. That insanity, unfortunately, is not available in every driveway no matter how the wealth is redistributed in this country. For most of us those combinations aren’t realistic and won’t be finding their way into any of our street cars anytime soon.
Odds are most readers employ a really nice big- or small-block built on a workingman’s budget. These real-world engine combinations don’t require a transmission with a royal pedigree. We are also willing to bet that a three-speed TH350 is more than capable of harnessing most popular packages. If you have to leave the exotic high-end stuff for the other side of the Super Chevy marketplace, give Performance Automatic a ring. The company is making it easy to swap the popular TH350 transmission into your Chevy with its Street Smart package.
The Street Smart TH350 Stage 1 (PN PA35101)—transmission only—shows a $1,387 retail price tag, but no one pays retail anymore. We’ve seen several mail-order companies advertise Stage 1 for around $1,100—a number that won’t break the bank. The Stage 1 TH350 is rated up to 450 hp. Those seeking something a little stronger can check out the Stage 2 version (PN PA35102) that holds 550 hp and retails for $1,500 with a real world street price of $1,175 from most vendors. Both transmissions come with a standard one-year warranty.
Performance Automatic also offers a complete package that includes a torque converter matched to your combination, transmission dipstick, and a universal transmission mount. The Stage 1 complete package (PA53103) is listed for $1,750 but the three vendors we looked up online had the Street Smart TH350 Stage 1 package listed for around $1,350. The Stage 2 Package (PA35104) bumped the price tag up to $1,790 from those same dealers. A lifetime warranty is included in the Stage 2 Package.
Backing up for a moment, the TH350 came into existence in the late ’60s as a replacement for the popular Powerglide. The biggest difference between the two, besides internal workings, is the TH350’s three forward speeds verse just two speeds of the Powerglide. The three-speed automatic transmission enjoyed a service life of nearly 20 years as it was stuffed behind small-blocks and V-6 engines in most rear-wheel drive cars and trucks through 1984. It is safe to say production numbers are in the millions. That makes the cores common and with some minor upgrades these transmissions have proven to be versatile in a wide-variety of applications.
“Our TH350 Street Smart package comes as Stage 1 or Stage 2 versions. We have customers running them in their street cars, street rods, pro-touring/autocross vehicles, and it sees a lot of street/strip uses,” comments Harvey Baker of Performance Automatic. He invited us down to Maryland to take an in-depth tour of one the company’s most popular products. We jumped at the chance to follow Performance Automatic’s Gerald Nusser as he cracked open a TH350 and rebuilt it into a high-performance automatic transmission.
The build up is what you’d expect as each part is cleaned and inspected with the major items being replaced with stronger and better parts. Nusser was barely into the teardown when we came across one of the most common problems—a broken accumulator spring. In some cases the cracked spring will hurt the bore or accumulator so each is inspected and repairs are made, if necessary. The front pump is pulled apart and inspected. Nusser says to pay particular attention to the wearable pieces of the front pump and replace anything that shows signs of wear marks. Every pump is outfitted with new seals and bearings regardless of its condition.
As Nusser tore deeper and deeper into the guts, he showed us more upgrades. All clutches are replaced with high-performance Raybestos brand clutches and the stock band is tossed in favor of a Kevlar one.
As for clutch count, Nusser tells us that the factory supplies either three or four clutches, depending on the year of the transmission. Performance Automatic installs five clutches for better holding strength in Stage 2 units. The direct piston has to be modified in order to fit the extra clutches. The factory piston is put on a lathe and Nusser removes some material for the extra clearance.
We asked what are some common problems with the TH350 and he shared some interesting facts. Surprisingly, the transmission doesn’t have too many issues, but there are some inherent design flaws when this transmission is used in high-performance applications. First on the list is the race that rests between the high-gear drum and the secondary drum.
“The intermediate/Second gear clutch pack race is an issue. The race will shatter or break. We add a hardened one to eliminate this problem,” comments Nusser. “The clutches hold up pretty well in these transmissions. You don’t see a lot of wear at high power levels. Of course, a good shift-kit and valve body helps too.”
Another area he cautioned can be a problem in a high horsepower application is the OEM sprags. Like the race, it is susceptible to cracking and shattering.
Performance Automatic recommends going to a TH400 or Powerglide for applications over 550 hp. But for most enthusiasts, the 550 hp rating of Stage 2 is more than adequate.
Follow along as Nusser shows us the guts and glory of a Performance Automatic TH350 Stage 2 transmission.