I have a '95 Mark VIII with 80k miles. 2 months ago, the intermediate one-way clutch crapped out and I lost second gear. I took it to a local transmission shop that has a good reputation, has been around for a long time, and is a member of the Automatic Transmission Rebuilders' Association. They quoted $2300 for a rebuild, with a 12k-mile/1-yr warranty backed by ATRA. According to my invoice, the job included a "master rebuild kit", intermediate OWC, valve body, shift solenoids, and torque converter.
When I got it back, it shifted perfectly and felt great. However, the torque converter clutch hasn't worked right ever since. When I accelerate to 45 mph or so, it goes into lockup as usual. Then 5-10 seconds later, it unlocks for no apparent reason. It then stays unlocked until I come to a stop and go through the gears again. After 10 or so drive cycles, it eventually stops even attempting to lock the converter. At that point the PCM sets code 628 - "excessive torque converter clutch slippage". If I disconnect the battery to clear the memory, the whole cycle starts over again. I've tried it with O/D on and off, it does the same thing either way.
If I keep it at a steady 35 mph (just after it goes into 4th and locks the TC) and barely touch the gas, it'll stay locked up almost indefinitely. But as soon as I accelerate or go up the slightest hill, it unlocks and stays that way.
I took it back to the garage. The mechanic diagnosed it using a "Shaffer Shifter", which plugs into the harness and takes control of the transmission. He took me for a ride to demonstrate that it had no problems staying in lockup under manual control, and that there was no noticeable slippage.
Based on that, he said that it had to be something outside of the transmission. Which seemed like quite a coincidence, but you never know. Anyway, to make a VERY long story short, here's what has been done so far:
-PCM replaced with a OEM unit rebuilt by Cardone (same model #, same calibration code).
-The replacement PCM did the same thing but did not set any codes, so it was replaced. Didn't solve the problem, but it's back to setting code 628.
-Checked all wiring from the transmission harness to the PCM and tested the TCC solenoid.
-New Motorcraft TPS
-New Motorcraft output shaft speed sensor
...At this point, the shop began talking to a technician at ATRA. Based on his info, they went on to replace...
-Coolant temp sensor
...And after pretty much everything outside of the tranny was ruled out...
-TC bypass clutch control valve/sleeve
Not one of these things has made the slightest bit of difference. As of today, they're pretty much out of ideas and are waiting to hear back from the ATRA guy on what to do next.
On one hand, the shop has been reasonable. They aren't trying to BS me or weasel out of fixing it, they acknowledge there's a problem, and they haven't tried to charge me another dime for anything. They wouldn't cover the PCM/MAF/TPS, but they had no problems with me buying the parts and installing them myself. And they're still trying to fix it. So I really can't justify any nasty letters or lawsuit threats.
But then again, I paid them a lot of money to make my transmission work properly. I spent more time and money replacing parts based on their advice, without any resolution. It's been TWO MONTHS and counting, I still have a broken tranny, and I want my damn car back!!
So if anyone has any ideas or advice on what to do next, I would really appreciate it.