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Old 11-15-2020, 02:26 AM
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Location: Gilroy, CA
Cobra Make, Engine: SPF 2291, Whipple Blown & Injected 4.6
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Quote:
Originally Posted by twobjshelbys View Post
I don't get all the dissing of the TKO600. I still think it was one of the best, snappiest shifting transmissions I ever had. As good as the Ford GT.
It has to do with decades of Tremec and a large number of their resellers denying the existence of the 2-3 shift gate problem and pushing back on the buyer that the problem was related to something they were doing wrong — when in actual fact it was directly related to Tremec design decisions when the box was originally designed and built. When you couple this with a reticence to correct the design flaw with an engineering change order so follow on production would provide a better driving experience, it leaves a bitter taste for those who experienced the problem.

The 2-3 gear change or any other gear change in the transmission will be affected by bell housing alignment. There is no escaping that. It is interesting however, that if the misalignment is causing a 2-3 gear change problem, why doesn't the same misalignment cause a 1-2 or 3-4 or 4-5 gear change problem? The answer is obvious, the alignment while important is not the primary cause of the 2-3 shift problem.

The 2-3 shift problem is rooted in a 1960's synchronizer design style and technology (simple brass ring vs muti cone modern designs) in conjunction with a poorly designed 2-3 interlock timing built into the shift rails when they were manufactured. The two changes that Liberty makes to the transmission that correct the problem are the higher co-efficient of friction carbon fiber faced synchronizer rings and the replacement shift rails with modified interlock timing.

Many of us never experienced the reason for the availability of the TKO 600. It was the 2 piece countershaft of the TKO 500 that used a relatively small woodruff key to lock the front and rear halves of the countershaft together. That key would shear off in service when the car had a good grip on the ground and the engine had north of 450 ft/lbs of torque. Another buyer beware design oversight that Tremec never chose to fix in the TKO 500 product line but instead just left current owners out to dry — a business practice they would revisit all too often in the years to come. BTW the TKO 500 still uses that same woodruff key design today, not even a hardened steel square key, a woodruff key!

The Tremec fix for the TKO 500 countershaft problem, was a new transmission, the TKO 600 (is this starting to sound familiar), with a one piece countershaft (which was a good idea) that had the countershaft third gear and the mainshaft third gear offset by approximately 0.200" (not such a good idea) so the chips from the countershaft third gear machining operation had an escape path. The TKO 500 countershaft did not have the chip escape path problem during manufacturing because the shaft was a two piece shaft that split right next to third gear allowing an ample exodus path for the machining chips generated during manufacturing.

Here is a picture of the misalignment and the carnage that it generates when you hook up the tires and put (in this case) 480 ft/lbs of torque through the transmission.



Notice the mainsheet / countershaft third gear misalignment.

At the time this occurred, the reseller (who is no longer in business under the same name) had Tremec look at the transmission for warranty purposes. Tremec's position was the damage was caused by operator error — specifically a missed shift (of course! what else could it possibly be from). Tremec maintained that the transmission was forced into third gear, after the clutch was full engaged following the missed shift, causing the gear teeth on the mainsheet and countershaft to collide with each other, while the clutch was fully engaged, producing the damage!

The explanation sounds sort of plausible until you remember that these are constant mesh transmissions with all gears fully meshing at all times! Gear selection is accomplished through synchronizer engagement / disengagement not sliding one gear into engagement with the other. Tremec knew this all along, after all they did design and manufacture the transmission. This was obvious obfuscation and an attempt to sidestep responsibility for a poor design that resulted in component failure well below the transmission's advertised torque transmission capacity / capability.

The failure was 100% attributable to the reduced gear tooth face width contact that produced reduced torque transmission capacity. Coupling that with 480 ft'lbs of torque and a tire that is hooked up will produce the kind of damage you are looking at in the photo. The potential for this type of failure in a Cobra replica is mitigated because of both the light weight of the car and the fact that it is very hard to hook up one of these cars under full power in almost any gear, so the tires spin before the transmission can be fully loaded.

Tremec tried to stiff the guy and in the end would only provide him a replacement mainshaft third gear and a replacement countershaft but would not repair the transmission — he had to go elsewhere for the actual repairs or do it himself. In fairness it was not Tremec who provided the replacement parts. To their credit, it was the reseller, if I remember correctly.

This sort of customer service / treatment was / is an all too common after purchase experience, with Tremec. Simply stated the Tremec response would amount to, you are wrong and we are right, please go away now. Sometimes there was considerable emphasis on the 'go away now' portion of the messaging.

Additionally, in those days, another fairly common whoops was to have your TKO lockup in whatever gear you happened to park it in, with no ability to shift it at the next engine start. Over time they eventually minimized but did not eliminate the problem. While users were getting stuck wherever they parked the car and this problem occurred, Tremec consistently denied its existence and put the cause and cure back on the user.

These people are poster children for the kind of manufacturer you do not want to do business with if you have any alternatives.


Quote:
Originally Posted by ERA 626 View Post
I agree, I am being told (from a very reliable person who has installed hundreds of them) that 98% of the so called shifting issues is due to the bell housing not being dialed in properly. All these people here recommending to have liberty blueprint a brand new transmission? I would be really pissed off If I have to have a shop rebuild a brand new transmission. I would pull it out and send it back to tremec at that point, why pay liberty to fix a brand new transmission? makes no sense to me at all.
Bellhousing misalignment is certainly a contributor to it, but it is not the primary cause of it. The primary cause is the 2-3 shift rail interlock timing and the inadequate, small, 1960's style brass synchronizer rings.

If the bell housing alignment were the root cause of the problem, then the problem would exist for all gear changes. It does not. It only exists for the 2-3 gear change. That said, bell housing misalignment definitely will aggravate the problem but it will not cause the problem as is evidenced by it's lack of occurrence in all other gear changes.


Quote:
Originally Posted by patrickt View Post
Yep, my TKO-600 shifts as good or better than any transmission I've ever owned, including high-end German stuff. But it took an entire day to get the Lakewood bell housing dead on straight. A lot of mechanics would have put a half hour in to that little task and called it "good enough."
The appearance of the 2-3 shift problem is related to both the transmission internals (and yes bell housing alignment) along with how aggressively the driver's shifting skills allow him to change gears. Drivers who have the skill and manual dexterity to execute very rapid gear changes will definitely reach the limits of this transmission's speed shifting capabilities very quickly. The use of a mid-shift conversion with a Pro 5.0 (or similar quality shifter mechanism) can substantially improve the experience. In fact tight internal shift rail linkage from the rear shift well to the center shift well on the transmission is also a contributor to improving the shifting experience.

If you couple the midshift upgrade with the Liberty modifications, the transmission is actually a fairly good shifting transmission — admittedly not as good as a T-56. A T-56 however, is a modern, initially OEM targeted, transmission that later became available as an aftermarket transmission. It is the result of generations of both Detroit and Tremec spawned improvements. A Detroit manufacturer would reject a TKO600 synchronizer or gear misalignment problem out of hand for no other reason than the potential for adverse warranty service expense. The cost to warranty the bad design would outweigh the cost to properly redesign the transmission - or use a different transmission..

Some drivers will not push the TKO shifting mechanism hard enough to consistently (or perhaps ever) experience a hang up in the 2-3 shift gate and then of course, others will. The spectrum of user experiences will run the gamut of no problems to OH WOW! If someone does not experience the hang up in the 2-3 shift gate that is good on them and they will be a happy owner. As the owner becomes more proficient at speed shifting then the problem will have an increased probability of rearing it's ugly head.

The fix is eminently doable, Tremec just chose not to spend the money on the TKO 600 product line (just like they did with the older TKO 500 2 piece countershaft / woodruff key problem). Because the T-56 product line was doing so well and also so profitably, the TKO product became a distant memory. When it came to allocating resource for design improvements or engineering change orders, the TKO was sort of like the red haired step child in the family. Now there is an interest in redeveloping those markets. I wonder how much of that initiative is driven by EV technology where these sorts of transmissions (read T-56 OEM business) are going to be phased out in the coming years because of the EV conversion in Detroit.



Ed
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Last edited by eschaider; 11-17-2020 at 02:50 PM.. Reason: Fixed broken pic link
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