lost overdrive or maybe tc lockup?

Crazy Ex · February 23, 2013

on the way to and from work the last two days the expo seems to be slipping in and out of od. the problem is that i don't know if its losing od or tc lock up. i've read through many threads here and i'm even more confused as to which it could be. that being said, i had the trans flushed this morning (no filter) and on the way home i was at 3500rpm at 70-75 mph and if i drop into 3rd and back up to od there's no change in rpm's. this is also how it was acting the previous two days when it appeared to lose od. it shifts from 1-2 and from 2-3 just fine and the truck has less than 70,000 original miles on it. don't know where to start as the previous threads i've gone through have confused me more than they helped me :/

MrShorty · February 23, 2013

Because you can shift from D to OD without change, that suggests to me that the problem is at least loss of 4th gear, if not loss of both 4th gear and TCC lockup.

Chances are good that some of the previous posts you have read on this problem were mine, what parts are you finding confusing? In just about every case like this, I suggest that the first step is to check the wiring for the 3-4 shift/TCC lockup solenoids, so I would make the same suggestion here. The place to start is to determine if the problem is electrical or not.

Crazy Ex · February 23, 2013

i guess i'm confused on how to differentiate between lack of tcc lockup and loss of overdrive. also a bit confused as to where to start...i've read about band adjustment, pulling codes, dropping pans and valve bodies, hooking a multi-meter (to the solenoids i believe), changing fluid and filter and even throttle bodies, speed sensors, tps sensors and either map or maf sensors. needless to say i'm overwhelmed and a bit lost. mechanically i'm able to perform the work...it's just finding and even where to start finding the problem that has me lightheaded lol.

Crazy Ex · February 23, 2013

oh yeah, forgot to mention temp. sensor, as well as vacuum lines and the modulator as well lol! any opinion if it may be safe to drive like this while i'm figuring things out? 3500 rpm's is high but well out of the red zone and i drive a good 60 miles on the freeway daily.

MrShorty · February 23, 2013

i guess i'm confused on how to differentiate between lack of tcc lockup and loss of overdrive.

TCC can lockup in either 3rd or 4th gear, so testing the TCC lockup independent of 3-4 shift would involve a test in D. Hold a steady 50 mph, tap the brake pedal (just enough to "flip" the switch but not engage the brakes). If the TCC is engaged, it should unlock, the engine speed will go up 300-500 rpm, and then drop back as the TCC locks back up.

i've read about band adjustment, pulling codes, dropping pans and valve bodies, hooking a multi-meter (to the solenoids i believe), changing fluid and filter and even throttle bodies, speed sensors, tps sensors and either map or maf sensors. needless to say i'm overwhelmed and a bit lost. mechanically i'm able to perform the work...it's just finding and even where to start finding the problem that has me lightheaded lol.

Those things will come into play as you work your way down the diagnostic tree. Diagnosis is often about logically eliminating possibilities. As I noted before, the place I would start would be the electronics. Pulling codes is a good first step -- it is easy, quick, and will indicate if the computer can see a break in either the 3-4 shift solenoid or TCC lockup solenoid circuits. With that, I would get a wiring diagram and a multimeter and inspect the 3-4 shift solenoid/TCC lockup solenoid circuits. Make sure nothing has come unplugged or is loose.

Crazy Ex · February 23, 2013

Its crazy how many things can be wrong but as long as i don't need a rebuild I'll happily work through these other possibilities! I feel slightly confident that its not a major mechanical failure but in your opinion can i drive it? I'll keep you up to date on my findings. Thank you!

MrShorty · February 23, 2013

in your opinion can i drive it?

I believe that most "loss of 4th gear and/or lockup" situations, where the transmission otherwise operates as it should, it is ok to drive it--you are not going to cause other problems (other than the additional wear and tear of the engine running a little faster than it might like). I don't think I would drive it indefinitely like that, but until you can pin down the cause, I believe it will be ok in most cases.

Crazy Ex · February 24, 2013

update: i drove a good 20miles today at 50-55mph and i can verify that in fact i do have tc lock up. after i tap the brake the rpm's go up by 2-300 and then drop back down when the tc locks back in. also, i verified that i have tc lockup when the od id working and also when it is not working. that being said, i had od 99% of the time today and at 55mph i was at about 1900 rpm's and it would jump to 2500 rpm's when it slipped out of od. does the intermittent loss of od tell me anything?

MrShorty · February 24, 2013

Only that intermittents like that tend to be electrical rather than mechanical.

Crazy Ex · February 24, 2013

That was my thought too. I hope that's the case!

Mettler · March 14, 2013

Have you re adjusted the TV cable?

lost overdrive or maybe tc lockup?

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