TREMEC TKX 5-Speed Manual Transmission

What are the differences? This article is to help you understand the basic differences in the TKO 5-speed and the new TKX that replaces it.

When Tremec designed the TKX they wanted a new design just for the aftermarket. In the past the aftermarket transmissions were based on OEM designs in house. These got tweaks or new tailhousing castings to offer more flexibility for aftermarket use. Tremec listened to customer input over the years and decided to offer a completely aftermarket design from the ground up.

But first let’s talk TKO

The TKO was a great transmission. Based on the TR-3550, it was an OEM design that was used in some 2wd truck applications. Later on, it was used for some OEM Ford Mustang Fox Body applications as well. Soon after it was known as one of the best upgrades you can do for your Fox Body car. It had a rated torque capacity up to 600 lbs/ft of torque, which is one of the reasons it sold so well over the years. It was versatile, with multiple shift positions, dual speedo outputs and it was available in Ford or GM bolt patterns. 26 spline input and 31 spline output for increased strength and capability. But it had one problem: it was square. This made it a tight fit into many muscle car applications. Here at American Powertrain we do what is called “case streamlining”. We machine down the top cover so it provides more clearance into cars such as Chevelles and Mustangs. One of the reasons the TKO was a boxy shape was that it was a “Topload” design, meaning the gears came in from the top. This made the case much taller and square to accommodate it.

The new 5-Speed

Tremec wanted to kept all the great features of the TKO but package it up in much more streamlined case. They made the shift from a topload design to an end-load design. The end-load design, similar to the super strong Magnum 6-speed, is significantly stronger and allows the case to be much smaller. The three-piece aluminum housing provides outstanding structural stiffness and includes main case, intermediate plate and rear extension. Gaskets at all flanges simplify assembly and eliminate fluid leaks. Improvements just didn’t stop with the case. All new wider, stronger gear sets made with special grade ASTM 4615 steel improve gear design. Shifting is improved through use of multi-cone synchronizers carried over from the Magnum 6-speed, and hybrid synchronizer rings made of sintered bronze and carbon. NVH (noise, vibration and harshness) have all been improved.

The new TKX 5-speed is an End-Load design. With the gears going in from the back.

All this means 600 lb.ft of torque capacity, and with the improved Magnum style syncro design means it can handle shifts at 7,500 RPM.

Check out all the specs and images below for more comparisons. Be sure to watch the TKX video at the end of the article.

More features of the TKX

  • Equipped with a high-performance short-throw billet aluminum shifter that isolates road noise while providing clean, crisp shifts.
  • Multiple shift locations for installation flexibility.
  • Robust design with internal three-rail shift system and steel shift forks.
  • Wide gear width increases gear life and torque capacity.
  • 26-spline input shaft with a 31-spline output shaft for added strength.
  • Built-in reverse light switch and cruise control safety switch.
  • Separate GM and Ford case patterns and input configurations. Integrated GM and Ford transmission mount patterns.

Some similarities with the TKO

  • Same length overall as the TKO. Can use any TKO crossmember and driveshaft.
  • Bellhousing bolt patterns are the same. GM version and Ford version. GM TKO/TKX share the GM Muncie bolt pattern. Ford versions share the Ford Toploader transmission bolt pattern.
  • Input shaft is 26-spline and bearing retainer design is the same. Can use any throwout bearing or hydraulic bearing for TKO or TKX.
  • 31-spline output same for TKO/TKX.

TKX features and dimensions

Gear Ratio Chart for TKX

Let’s look at some comparison shots of TKX and TKO

TKX on the left has a much smaller more streamlined case vs the TKO. Shifter positions are still the same with 3 possible locations. Overall length and mounting points are identical. This makes swapping from TKO to TKX a breeze.
TKX and TKO share the same input shaft size, bearing retainer size and bolt patterns. GM and Ford bolt patterns are available just like in the TKO.
TKX on the right has a more streamlined tailhousing. Gone is the old torque arm mount from the TKO. This helps with fitment for Corvette, A-body GM and Mopar. Note the neutral safety switch is now on the right for TKX.

26 thoughts on “TKO VS TKX

  1. I have a 76 TA originally with a close ratio Super T10. It has a modified 455 with with 400 RWHP and 425 lb ft of torque with 3.23 rear end gears. Which TKX gear set would you recommend for my car?

    1. What is the main use of your car ? Cruiser or once in awhile track?
      What rpm do you want to run at 70 mph? The TKX can handle your HP with no problem.

    2. If you run a wide ratio gear set it will work with that 3.23 gear. Personally I like the close ratio gear set with a 3.73-4.10 gear. This gives the best all around gearing for street driving and good acceleration. But still takes advantage of the .64 overdrive.

  2. I’m in the process of doing an LS swap on a 80 grand am , using a cammed 5.3 , 300-350 hp. I was thinking t56 , but a 5 speed may be enough. Using 373 rear set up as a street car / toy . Any recommendations would be appreciated, thank you

    1. TKX is plenty of trans for that set up. its good for 600hp easy. 3.73 gear with the .64 OD TKX will be a perfect set up. Call us at 931-646-4836 we have a full G-body kit for it.

  3. I am building a 1955 cameo pickup with a 383 stroker rated at 525 hp! I plan on running a 3:90 posi rear end. Can you please tell me would I be better off with a 5 or 6 speed manual tranny? The truck will have mostly city miles but dont want to be afraid of going 80 85 on the highway to shows? I want low gears 1 thru 4 and overdrive in 5 or 6 if you advise?

  4. I have a 1966 Backdraft 427 Cobra. Currently having the TKO 500 with American Power Train Shifter, I installed last winter. The 418 Ford engine is blue printed and has nearly 450 RWHP and torque. The TKO has never allowed me to shift above 5800rpm. My Howards camshaft is rated for 6400rpm while the Crank is a Howards forged steel with H beam 6.2 rods and Ross PIstons. Rear end is a 3.43 from the M-3 series BMW.

    What about the close ratio TCET17765? (ONE DAY A Year she does a few trips down the 1/8 mile, with no hard launches on the 17″ 315 radial tires.

    1. You can swap in the TKX with no mods since it has been set up for a TKO already. Its a pretty easy swap. You can reuse everything but the shifter assembly. TKX has a different bolt pattern. (shift handle is the same) but the base plate is different. But the out of the box shifter on the TKX will work.

  5. A new TKX 5 SPEED does not come equipped with a shifter assembly?
    How much will the shifter assembly cost?
    One last thing is “will the TKX 17765 with .68 final drive” work well with 3.43 rear gears?

    Thank you for the time you spent helping me

    1. They come with a shifter assembly stock from Tremec. They do not come with the shifter handle unless you order a full kit from us. We can also custom offset the shifter assembly based on your vehicle. What is your application? We put together full kits for all muscle cars and classic trucks. Yes that gear ratio will work great with that rear gear. You can go to this link and run the gear ratio calculator to see what RPM you will be at. You need to know your rear tire height as well.

  6. I have a 455 Oldsmobile with 360 hp@ 5000 rpm and 433 foot pounds of torque at 3300 rpm at the rear wheels. This was done with a Borg Warner 4 speed on a chassis dyno. Would you know what the parasitic horsepower losses are in 1st gear thru 5th gear? Do all gears have the same parasitic losses? And is there a difference in parasitic losses between the THO 600 and TKX? I am looking for an upgrade so I can cruise on the highway!
    Thanks in advance.

  7. I have the old Keisler RS400 in my ’67 Camaro. I’m running a Currie 9” 3:50 Posi with Continental Extreme Contact 275 x 40 x 18 in the Rear. I am strongly considering the new TKX and would like to know what improvements I can expect over the Keisler. The old Keisler has been a great 5 speed and done two long haul Hot Rod Power Tours. Why should I buy and install the TKX? Thanks!

    1. TKX is light years ahead in design over that old T-45 design that Shafi used. That RS400 was based a one type of factory trans. The TKX has Magnum syncros, greatly improved shifting and higher rpm capability.

  8. I have a legend LGT 7000 I Installed in my 1970 Chevelle replacing the factory 4 speed , every is great except in reverse it has terrible clutch shatter only in reverse, all forward gears are good. Starting off in first is smooth no chatter
    Is this something in the trans that is not right ? I understand Legend Transmissions are no longer in business
    Is American Powertrain able to diagnose this problem ?

    1. Sounds like a counter shaft issue maybe. As far as we know they are out of business. So the other issue is if its broken where do you get parts? We never sold those transmissions or have worked on them. New TKX is $2795 and can take 600lbs/ft of torque and comes with a two year warranty. You might find someone that would buy that Legend.

  9. I just finished installing a TKX kit in my 1965 Corvette. First thing, everything fit perfectly!
    I left the cross member alone, did not cut it out. My car is a factory A/C and power steering car. I you have access to a lift the instructions that come with the kit are great. I would recommend downloading and read them before you take on this project.
    If you are going to do this in your driveway or garage on jack stands it’s much easier to remove the engine and transmission as one unit and do the conversion on a stand. So much better to stand next to everything to measure the bellhousing and slide the trans into place. While I had it out I changed the spark plugs, exhaust gaskets and also installed a new water pump. The new trans is a longer than the old Muncie. If you have power steering remove the P.S. pump, it will be in the way as you lower the front of the motor.
    The entire shifter needs to come off, not just the handle. The bolts are easy to access through the shifter hole to re-install the shifter. Everything fit perfectly and went back together without an issue. I left the plug in the tail shaft and filled it with fluid while on the stand. Be careful when you remove the plug because some fluid will run out. No big deal, just a small mess to clean up. I have about 150 miles on it so far and can feel it breaking in and getting smoother every mile!! Shifts much smoother than day one. All is quite and smooth on the highway, 75 MPH @ 2200 RPM!!. I would highly recommend doing this conversion and the guys at American Powertrain are great to work with. I hope this helps someone.

  10. I have a 69 Firebird. 455 pushing around 550 hp and torque, 3:73 gears, and I’ll be running 15” Weld wheels while trying to keep the tire od size close to stock. After reading this, am I correct to think that the TKX close ratio would be a better fit than the TKO?

  11. curious about the shift mechanism inside. i had a 96 z28 and the t56 couldnt handle me banging the shifter, the trans wound up with at least 2″ of play in between gears, sloppy. so definitely hurt something. so my question is can this transmission handle smashing gears, shifting hard? my current setup is 406 78 nova with a super t10 with billet mid plate and hurst super shifter 3 and i know that will take my abuse but will later want a 5 gear instead.

    1. Well modern 5 and 6-speed are not designed to be “smash shifted”. They are full synchronized for everyday driving and longevity. They can handle a lot of power but if you want to shift it without the clutch you need a faceplated trans or stick with the old 4-speed.

      1. thats kinda what i thought, its not a clutchless shift i still use the clutch but i shift hard. well thanks for clarifying and yes there are some really good aftermarket 4 speed companies still around.

  12. I have a 1960 Chevy Biscayne 2 Door with a 350 sbc and a Saginaw 4 speed transmission. I would like to replace the Saginaw trans, with a Tremec TRX 5 speed. Other than the drive shaft and trans, mount what other major changes would be required? Thanks for your help.

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