TKO 600 transmission shifting problem

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This is my experience with the Tremec third gear shift problems you can find mentioned all over the Internet. This is one specific installation, and may not apply to every transmission. While a clutch problem could stop a transmission from shifting, that certainly was not the problem in my car. Read this carefully to see why I was sure I did not have a clutch or operator problem.

My experience conclusively shows a current production TKO-600, purchased new in 2009, still had a factory problem with the shift rail design and/or production. This was a fresh inventory transmission purchased in July of 2009, and this means the problem has not been 100% cured. Hopefully the information here will save weeks of work and hundreds or thousands of dollars hunting for the fix. I was so frustrated I was nearly ready to give up weekend racing or install an automatic transmission, all because of the TKO transmission shifting problem.

Why did I change transmissions, and why choose the TKO?

My original goal was a stock appearing but very fast street car. I chose the Mustang LX platform because it was fairly light, reasonably safe, and proven parts were readily available. I also raced several Mustang Fox Body cars in the 80's and early 90's. I always found them very reliable, and easy to make fast. (My 1983 GT Mustang small block was my fastest, running bottom 9's and high 8's in the 1/4 mile off the motor, and mid-8's and faster with nitrous.)

Tremec tko 600 shifing problem

While searching to find my perfect Cobra kit-car, I stumbled upon and purchased this clean Mustang '89 LX in early 2009.  I couldn't pass it up.

My Mustang LX coupe ran OK with GT40 parts, mid-to-low 13's in the 1/4 mile with standard tires and wheels. Further engine modifications included TFS twisted wedge heads, TFS intake, Vortech supercharger, 2003 Lightning MAF and injectors, and Motorsport "F" camshaft. These modifications  increased engine power into the 600 horsepower region. The car ran over 122 MPH in the 1/4 mile on Nitto radials with a 100,000 mile 302. (My eventual plan, when the engine fails, is to use a 9:1 compression 363 cubic inch "302" Dart block built to handle big boost. That project is underway right now.)

Naturally, even with the tired old small block, I ran into the expected T-5 transmission problems. After 30 or 40 successful runs, I hit third under full power and third gear failed. I needed to upgrade my 5-speed World Class with a stronger or more reliable transmission, but I did not want to lose street drivability in the process. I checked other transmissions but discarded them because of life or drivability concerns.

The best transmission swap choices appeared to be the T-45 6-speed, or a Tremec TKO-600 5-speed. I knew extra gear ranges would not be any advantage for my typical vehicle use. My car has plenty of power and is geared correctly for the 1/4 mile, extra over- or under-drive gearing was not necessary. Other advantages of the Tremec TKO 600 include it being lighter in weight and smaller as well as easier and less expensive to swap.  Other than the transmission itself I would only need a clutch disk, bell housing, transmission cross-member, driveshaft yoke, and shifter. This would give me a 600 lb/ft rated transmission, which in theory would be over 600 hp at 6000 RPM.

I used the following Summit Racing parts:

CMG-TCET5008 transmission assembly (chosen for good 2.87 first gear and 0.64 overdrive ratio)

FMS-M-5059A Cross Member

FMS-M-4841-A Yoke

FMS-M-7550-T302 clutch disc

QTI-RM-6065 Bell housing (chosen for best clearance)

HUU-5380197 Hurst 5.5 inch shifter stick (chosen for appearance and shortest length shifter, but now going obsolete)

The forward transmission gear ratios I picked were:

Gear Ratio Percent drop in ratio 4.10 rear end overall gear ratio Shifting engine RPM Driveshaft RPM at shift After shift engine RPM
first 2.87   11.77:1 6250 2178 x
second 1.89 34% 7.75:1 6250 3307 4116
third 1.28 32% 5.25:1 6250 4883 4233
fourth 1.00 22% 4.10:1 6250 6250 4883
fifth 0.64 36% 2.62:1 X X 4000

These ratios keep the engine in the "sweet area" between 4100 and 6250 RPM, almost perfect. The 2.87 first, as opposed to being up in the lower 3's for first gear like the T-5, would mean I'd have much more time after launch to grab 2nd. Wheel spin would not be so violent during the 1-2 shift.

Installation

Installation went smoothly. The old T-5 transmission and bell housing were removed, the new clutch disk and QuickTime bell housing were installed. The QuickTime I purchased was properly dimensioned, run out was measured to be well within Tremec spec with no special locating pins or adjustments. I particularly like the QuickTime because of the extra room around it compared to other more "cylindrical" SFI approved scatter shields. The transmission bolted in without a problem, the stock speedometer drive gear fit properly. The Motorsport transmission cross member was slid all the way back to allow transmission mount alignment and the mounting tubes at each end were welded in place.

The clutch was set to be sure it engaged about an inch below the top and fully disengaged well before reaching the floor. We did have to adjust the clutch pivot in the bell housing by about an inch or so to get proper clutch disengagement. A diaphragm clutch can "stick to the floor" at high RPM if it opens too far, and of course if a clutch  does not open (release) far enough the transmission will not shift or properly synchronize.

At this point I made an executive decision I later had to undo. Since the TKO transmission nearly touched the floor in the transmission tunnel, I initially did not shim the transmission mount.

Note: The transmission-mount surface on the TKO-600 is 0.8 inches closer to the output shaft centerline than an original T-5 transmission. This means the transmission mount requires a 0.8 inch shim (increases height of mount) to maintain original output shaft height and driveshaft angles. Otherwise the tail of the transmission will point downwards more than the stock transmission. In a Mustang Fox body, it is a probably a good idea to slightly raise the transmission tunnel near the block-off plates for the forward alternate shifter locations in the TKO. The edges of the TKO600 block off plates actually touch strengthening ribs in my car's transmission tunnel when the transmission is shimmed to stock driveshaft exit height.

 

The driveshaft height change is shown by comparing dimension "E" in the two drawings below:

TKO Tremec transmission shifting and  vibration problems

Tremec TKO shifting problem T-5 height

First Drive

One thing that jumped out at me was an almost total lack of gear whine in any forward gear. The TKO 600 was very quiet compared to the old T5 transmission. It was also a pleasure to have a reasonable 1st gear ratio instead of the T-5's nearly useless 3.35 first gear ratio.

The first problem noticed was a bad vibration at about 60 MPH (I have a 4.10 gear). My car never had that vibration with the T-5. This turned out to be a slightly out-of-balance driveshaft that became noticeable with the new u-joint angles. To correct angles it is necessary to restore stock exit height. The rear mount should be raised about 0.8 inches with a spacer. Unfortunately this put the transmission into the transmission tunnel roof, so we used a slightly shorter 0.5 inch spacer as a compromise. By readjusting the pinion angles and fiddling with the transmission mount spacer we were able to get a sum of zero degrees (the rear angle was the compliment of the front angle) with reasonable u-joint angles.

Once the driveshaft was replaced with a properly balanced steel shaft, the u-joint angles could be adjusted all over the place without noticeable vibration. The slightly out-of-balance drive shaft, not noticeable with stock angles, made the system much more critical for u-joint angles.

If I were doing the install over, I would hammer the transmission tunnel up slightly bear the highest points and just use a 0.7 inch shim. This would result in stock drive shaft exit height at the rear of the transmission without annoying floorboard contact.

First Trip to the Track

This is where disaster struck.

First, I'm very good at shifting transmissions. I grew up speed shifting some very difficult transmissions. My father owned mostly six cylinder stick shift cars. I started driving by rolling his cars down the driveway and going for secret midnight rides when I was 13. My first "personal" car was a Green $350 1956 Studebaker with a 275 hp 352 cu in Packard engine and 3 on the tree with overdrive. I later had old used manual transmission cars like a 409 Chevy, a 390 Ford, and so on. I could easily power shift my 301 cu in '56 Chevy despite the high RPM full race cam, and I set the D/S national record in a factory 4-speed Rambler. I could always shift transmissions where friends had problems, and virtually never missed a shift. I often was sought out to drive buddies cars in races, including a friend's 427 Impala SS during street races and another friend's aluminum head 69 Camaro. Both cars were difficult to keep straight, let alone power shift.

I was dumbfounded when, during my first pass with the new TKO, I missed 3rd gear like a driver weaned on a power glide. Making several more passes, I tried various shifting styles. Every time I tried to hit 3rd with the TKO-600 it was like slamming the shifter into a brick wall. It just would not go. I finally tried to hold the clutch longer than normal at only 5000 RPM and I pushed really hard. The transmission went back into 1st! I beat my car to death trying to shift this transmission into 3rd. In 40 years of racing, the Tremec 2 to 3 shift was the worse thing I ever remember. It was like trying to speed shift my tractors, or an old three-speed stick!

The Problem

One thing of note, I could easily power shift 1-2 or 3-4 and never miss. I could shift at 6800 RPM from 1 into 2, or from 3 into 4. Holding the clutch on the floor at 4000 RPM or so, I could pull the transmission from 5th to reverse without grinding gears. These are clear indications the clutch was fully disengaging. The car also had good clutch disk clearance and very good pedal feel, it fully disengaged around two inches from the floor.

I searched Internet for "2-3 shift problem TKO 600" and was amazed at the number of results describing similar problems. (I probably never would have bought the TKO 600 if I had searched first.) I wondered if this was a big $3500 mistake.

Tremec stated they were not aware of 2-3 shift problems and suggested I probably had a clutch problem. They provided the name of a shop in Florida, so I called that shop.

The shop owner was a helpful person with years of racing experience. He suggested changing my clutch disc, saying he was largely unsuccessful using  dual friction discs. He also said I should change the clutch adjuster, the fire wall was flexing, and other things.

I told him I didn't see how the clutch system could be bad because I could easily speed-shift 1-2, 3-4, and even 4-5! I could also pull the shift lever into reverse without a grind, even with a revved engine. To me, this is a very strong indication clutch disengagement is adequate. I said it seemed to be lockout problem inside the transmission. It did not feel like the transmission was even getting into the third gear gate.

He countered by saying the 2-3 shift would show a bad clutch even though other gears would shift because 3rd gear has the largest ratio drop. I knew that was not entirely accurate. 1-2 actually has the largest RPM mismatch during a shift.

He also said 3-4 shifts  "hardly needed a synchronizer" because fourth "was a 1:1 ratio". I knew that was not true because a synchronizer actually matches the input shaft speed to the selected gear speed. If the input shaft is spinning 6300 RPM, the synchronizer has to block the slider out of the desired gear ratio until the input shaft system and everything it drives matches the RPM of the transmission components tied to the output shaft. Then the slider falls through the gate formed by the synchronizer teeth and locks the shaft to the desired gear. A transmission needs a 4th gear synchronizer just as much as we need a synchronizer in any other "shift while moving" gear.

Furthermore, it is often possible to overpower the blocking caused by synchronizers by pulling or pushing very fast and hard, and I could not do that.

Someplace in all that conversation he also said he did some "internal mods" to shifting components in the transmission, and that made me suspect those "internal mods" might be the real fix for my transmission.

I'm not a big fan of changing a half dozen things hoping something fixes a problem for three reasons:

  1. We would not know what actually fixed the problem, so we would not learn the true source of a problem
  2. We could actually add new problems
  3. Throwing random parts at a problem wastes time and money

In the electronics industry, we call this "shot-gunning a system". I don't shotgun anything, let alone things that are full of new expensive parts.

Liberty's Gears

It was evident Tremec was not going to be helpful and I did not want to start changing clutch parts when there was no hint they were bad (they were all new) or they would not work.

My second call was to Paul at Liberty's Gears in Taylor, Michigan. I found Paul to be a professional and experienced with excellent knowledge of transmissions and mechanical systems. Paul did not act surprised to hear about a TKO 600 2-3 shifting problem. Paul said he worked on hundreds of TKO 600 transmissions that would not shift from 2nd to 3rd gear, and said my description of it being like "hitting a wall' was typical of a common shift rail system problem. His mechanical descriptions made perfect logical sense to me. He also claimed a nearly 100% success rate in curing the 2-3 shift problem.

I decided to let Liberty's Gear take a shot at the repair on my brand new transmission. I removed the top cover assembly and rear housing. I sent Paul everything related to moving the sliders in the transmission. I did not send gears or synchronizers.

In less than week Paul shipped my parts back.

After reassembling the transmission (took about one hour) and reinstalling the transmission (took about three hours) I pulled my car out onto a local test track. I wound the engine up in 2nd gear to about 6000, and pushed forward with a normal "palm shift" I use on more difficult spring loaded shifters. Using a very fast clutch in-and-out, the TKO 600 transmission went into 3rd gear flawlessly! This was the very first try with the Liberty's modified parts, and it was a flawless shift. This was the first time I could get the TKO transmission into 3rd under full power! I made about three more tries using various shifting techniques, including a "point and push" into 3rd. Every shift was flawless. Finally I ran a wide open throttle run from first, shifting at 6300. 1-2, 2-3, and 3-4 were all flawless very fast shifts. Since then I have driven the car several times, and never missed a shift.

I was totally blown away by the difference in shift feel. While it was not like a Hurst Competition Plus or even a standard T-5 with its single rail internal shift system, it actually felt like a pretty good shifting system. The brick wall "won't go in third with a sledge hammer" feel was gone.

Do Over

If I ever do this again, I will never install another TKO-600 without sending it to Liberty's Gears first. They delivered everything they promised. For a few hundred dollars they turned this unshiftable 2-3 transmission into something that worked. Had I listened to Tremec, I would have spent several hundred dollars or more wasting time and parts chasing and correcting "non-problems".

These days manufacturers seem to play a little game of "if some of these don't produce complaints we must not have a problem in any of them". The proof, however, is in the pudding. Without changing the clutch, clutch adjuster, clutch adjustment, or anything else..... the TKO-600 transmission now shifts 2-3 just fine. All it took was a few hundred dollars at Liberty's Gears to make the worse brand-new transmission I have ever shifted into something that is quite acceptable for racing or daily driving, and the problem was clearly all in the shift rail system.

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