Is this a typical transmission failure mode?

S

segxr7

Registered
Background info: '95 Mark, 80k miles, Mercon V & new MLPS at 72k miles.

I was driving to lunch today, and I noticed that the transmission seemed to be shifting slightly more softly than usual. It wasn't flaring or slipping, it just didn't have the usual slight "kick" between gears. I thought that perhaps my LMS chip had come loose and it reverted to stock programming.

On the way back to work, it "hung" in first gear for about a half-second before upshifting. Kinda like a sticking 1-2 accumulator, but the upshift was pretty soft. The next time I pulled out, I got on it a little (enough to shift around 3000 rpm normally) and it stayed at 4000 rpm in first gear for about 2 seconds without upshifting. I let off the gas, at which point it dropped to ~1000 rpm. When I hit the gas again, it revved a little and clunked into either 2nd or 3rd.

I gently drove to an Autozone to check the fluid level. It was about 1/8" below the "hot" mark. This was probably because the car wasn't 100% warmed up, but while I was there I bought a quart of Mercon V and poured about half of it in to bring it all the way up to the full line. At this point it couldn't hurt anything!

I decided to drive it the rest of the way back to work in 2nd since I was in low speed stop-and-go traffic. I shifted into '2' at a stoplight. When I took off it actually started in first before quickly shifting into 2nd, where it stayed the rest of the way.

Fortunately I live about a mile from work, so I limped it home in 2nd. On level roads and gentle acceleration, it felt fine. But on a steep hill, the engine was running at ~3500 rpm while the car was doing 20. :eek:

Basically, it feels like the transmission started out with slightly reduced pressure, then quickly lost more and more until it was barely able to move the car. This all happened over the course of 5 or 6 miles. There are no flashing O/D light, weird noises, or anything else.

I'm 99% certain that it's in need of a rebuild, but I'm wondering what could have caused it to do this.. It doesn't seem to be a typical 4R70W failure mode, from what I've read!
 
First off the 4R70W's don't really have a failure(failsafe) mode, the first sign of trouble is your first sign that you have issues.

Second....if it hasn't been rebuilt, you're about at the mileage for a rebuild....sorry. :(

My advise would be do smell the fluid on the dipstick, if it smells burnt, thats a bad sign. If it smells normal(which is most likely the case since you just changed it), than you might be ok.

Also, check the color of the fluid...is it RED or dark RED? Look at the sight glass in these two pictures, these are the before and after pics of my transmission flush. Compare from there.....

Before
PIC079.jpg


After
PIC083.jpg


If the fluid smells/looks burnt....its time for a "pan drop" as the next step. You need to pull the pan down and check for debris, a lot of metal particles in the pan and on the magnet, or any other obvious signs of failure.

If the fluid smells/looks ok, than it almost sounds like your TPS is failing. One way to test a bad TPS is to manually shift the car from 1st to second. My friends TPS failed at WOT or close to it, so the car would never shift from 1st to 2nd until about 5k rpms, and it would do so with a SLAM. If you manually shift the car from 1st to 2nd it would work flawless, but when you shifted it into 3rd(Drive) it would not shift out of 2nd because the TPS thinks you're giving it more gas than you really are.

A TPS failure can do crazy things to a transmission.....if it fails low, the pressure/shifting will be affected, if it fails high, the car will think you're accelerating hard/fast, when in reality you're driving normal.

A bad sign about how you described this is the fact that you have to let off the gas for it to shift.....not good.

So, anyways...theres a start. :D

If you do need to get it built....I highly recommend swapping to a 98 Valve body...it has a lot of updates already done to it to fix a lot of common failures and the pre-98 transmissions.
 
This is not how they ususally fail... But pre 98 transmissions are POS... they often times fail before 100k!

The most common failure is the loss of 3rd and 4th. Your problem sounds a bit odd to me. Can you manually shift through the gears? Put in first then 2nd then D?
 
Thank you very much for the info.. It provides a lot of food for thought.. The fluid is bright red and does not smell burned. Of course the problems developed quite suddenly, so I'm not so sure that means too much.

You brought up a VERY good point with the TPS.. From what I understand, they tend to develop a "dead spot" where they don't register any changes in throttle position. Here are a few more weird things that came to mind:

-Before the tranny started acting really bad, I was going up a hill and it was in 3rd gear with the converter locked at 20 mph. I know these cars like to do that, but I had to give it more throttle than usual to make it kick down. In fact it made the engine lug and vibrate, which hasn't happened before.

-As I was limping it along in 2nd, I was going through an intersection and saw an approaching car from the side that didn't look like it was going to stop for the red light. I instinctively tromped on the gas, then immediately thought that I probably just killed my transmission (still better than the car/me though! :) ). Instead it took off hard with no slippage at all. It even got some wheelspin when one of the tires hit a patch of rough pavement.

I'll try manually shifting it and see what happens. Do you know what would happen if I unplugged the TPS? Obviously it would affect drivability, but I wonder if the computer would use a baseline pressure or try to figure it out based on the MAF & engine RPM. If so, it'd be better than tricking the computer with bad data.

Thanks again for all the help.. I'll look into it more tomorrow, at this point I really don't have anything to lose!
 
Well I have some very promising news.. I just scanned the computer and got the exact problem I was hoping for: stored code 63, "TPS circuit below minimum voltage".

I just hope I can find one in stock so I don't have to wait until next Tuesday to find out!
 
Awesome dude.....clean fluid and normal smell is a good sign, hence the reason I elaborated on the TPS so much. Glad you got it figured out....almost. :D

Have fun changing that....pretty easy once you remove the TB.

Are you still 99% certain the trans is toast? :)
 
Way to go Jesse :D. Didn't sound like the trans was shot to me either. They usually dump the last two gears and start sliping...
 
Well, I replaced the TPS. The good news is that the engine feels more responsive, and the code went away. The bad news is that it didn't change the transmission behavior one bit. :( I disconnected the battery to reset the computer, took the LMS chip out, no improvement whatsoever.

I also considered the possibility that the replacement TPS was bad.. I tested that by disconnecting the MAF. I figured that if the computer didn't have an airflow signal *and* it didn't know what the throttle was doing, it would have major drivability problems. But aside from a slightly wavering idle and a check engine light, it ran great and was just as responsive.

To recap: If I accelerate in first gear, it'll just stay there without ever upshifting until I let my foot off the gas. When I do, it drops back down to idle (there is no engine braking), then it'll upshift when I hit the gas again. If I do a manual 1-2 shift, the upshift is delayed and mushy. Once it's in a gear, though, I can floor it and it'll break the tires loose without any slippage at all. It just won't upshift until I let up. I didn't get it up to speed enough to test 4th gear, but I know the first 3 work and it'll go into lockup in third as usual.

I really don't know what to make of it.. It would make more sense if I had been romping on it and driving on the highway, but it happened out of the blue as I was driving in low speed stop-and-go traffic. I guess I'm gonna have to limp it to a transmission shop and let them figure it out.
 
Weird.

I re-read the post and come away with the thought that it demonstrates low EPC pressure by your symptoms.

Scanning through the transmission diagnostics points to 3 things in addition to a TPS problem.

MAF - a faulty MAF signal will cause hi/lo EPC operation, incorrect shift schedules and converter clutch scheduling - very similar to a faulty TPS signal.

VSS - The Vehicle Speed Sensor in the transmission has an open circuit resulting in abnormal shift schedule.

IAT - Intake Air Temperature - may cause hi/lo EPC pressure resulting in harsh/soft shifts.

Have you checked for codes after removal of chip?
 
That does not sound good, but I wouldn't condemn the transmission just yet.

Have you checked the alignment on the MLPS since it was replaced? Maybe it came loose and is out of adjustment?

The thing that concerns me is that it won't shift until you let up on the gas.....

Also, you say this is kinda out of the blue. When you serviced the transmission 8k miles ago, how bad was the fluid? My concern here is we've had a handfull of cars come in with REALLY dirty fluid, and after a transmission fluid exhange the trans will fail after a few thousand miles. This is due to the fact that the clutches are original and the only thing keeping them from slipping is all the crud built up on them. The new ATF will have a high detergent concentration causing it to "clean" the transmission once you run it for a while, allowing all the built up material on the clutches to break free.

Now......this crud could have blocked up the valve body, or done other damage, but this is kind of a stretch because you say your fluid is still clean.

Regardless....if you're mechanically inclinded enough, get down there and check the MLPS alignment(In NEUTRAL), and if it looks good its time to pull the trans pan and see what kinda crap you got in there.
 
Just to jump in a bit here...

It sounds like you are describing a situation where 2nd does not engage with the transmission in drive. Do you notice that it goes from 1st to 3rd?

If so (and please others jump in here), the one-way clutch, which is common in pre-98's, could have failed.

I would like others to jump in on the possibility of the one-clutch failure...

Ron
 
Thanks for the help, everyone! And kudos to Double 97- it was the one-way clutch; it failed at all of 80k miles.. I had a hard time figuring out what it was doing at first because I just drove it around the neighborhood at 20-25 mph. On the way to the transmission shop when I was in 50 mph traffic, it became pretty obvious that I had lost 2nd gear.

I took it to a locally-owned garage that is not the cheapest place in town, but they have a very good reputation. The owner took it for a spin and diagnosed it as a failed OWC, and once they opened it up they decided to do a complete rebuild. They replaced everything, down to the valve body and torque converter. The total came to $2300.

Conveniently, my little sister went on vacation for 3 weeks and lent me her car while she was gone. Now it's not that I don't appreciate her letting me use her car; I am of course very grateful. But DAMN was it ever nice to get my car back after driving her Volkswagen Cabrio for the past 2 weeks!! :D

Anyway, I can't get over how much nicer the transmission feels. I don't know if it's because mine had been going bad for a long time, or the updated parts improved shift quality, or both.. It feels more responsive now. The shifts are smoother when I drive it gently, and crisper when I tromp on it. It no longer locks and unlocks the torque converter repeatedly at 20 mph. It basically feels like a normal, non-schizophrenic transmission now. :)

The only remaining issue is that I'm pretty sure the new parts-store-brand TPS I installed is bad.. There's no 2-1 kickdown past 20 mph, and the computer is reporting code 121- "TPS voltage above or below normal". I have a Motorcraft replacement on the way; if that doesn't fix it, I'll take it back to the shop and let them deal with it.
 
Congrats on getting it figured out! We tried all the simple stuff, but the internet can only point you in the right direction, haha.

Good you found a nice shop...$2300 is a pretty good deal.

Let me recommend something.....get a chip! If I had known how much improvement I'd have on my car, it would have been my first upgrade. You think your car shifts good now, get a chip and feel it come to life! It will change the shift schedule so you don't have to stomp on it to get it to kick down, and it will also change the lock-up schedule so the converter doesn't lock up at 30mph!
 
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