Holy Shift. TKO 600/TCET-4617 Review.

Is it worth dropping coin on a beefed up 5 speed with an aggressive 5th gear? Fuck yeah.

We were stuck. Always stuck. (In-between gears that is) We had a great time flogging Coupé de Whore around Sebring for a recent SVTOA weekend – but we’re tired of peddling the battle weary Tremec 3550. It just isn’t up to the task anymore. It won’t downshift from 4th to 3rd without a complicated dance in and out of the second gear shift-gate – and staying in 3rd gear on an up-shift was a crapshoot. Sometimes it held, but more often it would pop out. The over-revving and double clutching to regain a slipped gear entertained the corner workers in turns 10, 13 and 17. Good times.

We’ll probably throw a rebuild on our 3550 and keep it as a backup – but we really needed something that can take a punch from the over-bored stroker motor.

In This Corner: TKO 600 – TCET4617

We got the car with the older Tremec, and it’s the last major component to be replaced from the coupe we bought in 05. The backstretch of Sebring proved annoying with the 3550. A hot exit from 16 was promptly rewarded by an early redline in 4th gear, and a mediocre pull down the rest of the straight in our .68 5th gear. The TKO 600 gives us a semi-usable 1st gear – closer ratios between the gears of 2nd through 4th, and a mouth watering .82 5th.

Tremec TKO-600 Road Race: TCET-4617

1st – 2.87   |   2nd – 1.89    |   3rd – 1.28  |   4th – 1.00   |   5th – 0.82   |   R –2.56

The TKO 600 is a direct descendent of the Tremec 3550. It shares the original housing that has been used since 1993. Commonly referred to as a truck transmission – the Tremec lineage has often suffered a bad rap for being clunky and inconsistent. Some users complain of sloppy shifting, and hard to engage gears – others swear the trans is smooth as silk. Why the wide difference in opinion?

Walt Leaman from Promotion Performance Products knows why.  Excessive tolerance. Not the kind you need to get through an opening-night release of a crowded, teen-movie sequel at the megaplex. We’re talking production tolerance.

Apparently – Tremec allows tolerances in the preload for the main shaft, and finish on the shift lugs that should be tighter. It leads to inconsistent performance (and if you’re a drag racer – the shift key is all wrong too. Wally can explain everything.) Tremec has a warranty that will fix transmissions that suffer from this excess – but only after the transmission is removed from the car and sent back to Tremec. Wow. How’d you like to plunk down $2k for a gearbox that may need to be immediately removed and sent back to the factory for a few weeks so they could have ANOTHER stab at getting it right? Meh.

We’ve bought from Walt before – he knows his shit. You can’t always tell from his website, but Walt has a solution for every production-based transmission a gear head could want. After a brief conversation about our needs, Walt offered his solution to making certain we would be happy with our TKO 600.

TKO 600 Nuts and Bolts

Our Fox coupe already had the necessary bell housing, transmission mount, and driveshaft length conversion from the previous Tremec 3550 – We needed to get a new clutch disc (the TKO has a 26 spline input shaft versus the 10 spline on the older 3550) and driveshaft yoke (31 spline versus 26) to complete the TKO upgrade. But Walt advised against selling us a TKO off the shelf.

Walt recommended letting Promotion remove the mid plate and reshim the main shaft for tighter tolerances (0.010-0.015” is factory spec – Promotion prefers 0.005”) for $90 and polishing the shifter lugs for another $60. We also opted for the Promotion Powershifter (basically a private labeled Steeda Triax) installed with proper shift-stops adjusted for another $159. For an extra $30, Walt also convinced us to step up to a 1330 HD extra long 31-spline slip yoke. We already had a Spec II clutch scuffing against our Fidanza flywheel – but we opted to upgrade to the Spec II Plus disc to match up with the new 26-spline input shaft. Since Tremec has a lower-limit on the price a licensed dealer can sell down to ($1,975 for the TKO600 with the Road Race 5th gear) – you’ll find your best deals looking for a package price for everything.

Out the door? With 3 quarts of synchromesh, and 6% sales tax we were looking at $2,750. Used TKO 500/600’s are out there in the $1,800 – $2,200 range. Good deal? We’ll see. We’ll provide regular updates with each track session – and immediate updates if something breaks. Too bad our next track doesn’t have enough straightaway to enjoy the straight-hungry 5th.

UPDATE: Well several track weekends later our reaction is complete thumbs-up. The shifts are predictable and crisp. The gearing is perfect for the road courses in general, and Sebring specifically. The back straight at PBIR becomes a challenge of nerve – we can accelerate far harder than we can brake – thanks to the hungry gearing in 5th.

We’re not alone in our praise. From another reader:

I’ve been using a proshifted tko 600 from promotion for 5 years now without a problem running 9.20’s at 148 on a 3000 lbs car. quality is unmatched as far as I am concerned. Walt and wally are working with me now on a new clutch set up. their ability to help over the phone is second to none. I first had problems in 04 when i puschased the stock tko 600 and could never shift over 6500 rpm I called walt and he told me what the problem was right away. So I sent him my transmission and 5 seasons of shifting over 8000rpm are the end result. Rarely miss a shift and all the guys at the local track still can’t believe I’m driving a clutch assisted car. you can check out video’s on youtube search nos347stroker and my videos should show up. Don’t forget I’m only 331 cubic inch 300 shot

Comment by mark williams — January 5, 2010 @ 9:25 pm


Give Walt or Wally a shout over at Promotion and see how they can help you. Just don’t be in a hurry – Walt can talk your ear off. :)

EDITORS NOTE: This article originally appeared on another site – inertiasport.com – on June 7th, 2008. It is reprinted here with permission from the original author.