Need a Transmission Guru

[Adam]

Today while I was driving for about 25 minutes, my torque converter would not lockup whatsoever. The truck was fully warmed up and I was at speeds ranging from 60-100km/h. I tried feathering the pedal, screwing with the overdrive switch, and setting the cruise control, but that didn't work. I was on a flat road so there was no need for it to be unlocked. It started working perfectly again after I left the store I was at.

I thought it was a random occurrence the first time it happened on a really cold winter day, and I attributed it to having a bypassed stock cooler and being -20 outside.

I know nothing about automatic transmissions. The fluid is at the correct, hot level, checked as per the instructions in the FSM. It is also pink and smelled fresh. All other gears work fine and it doesn't slip as far as I can tell.

Thanks in advance. I need my truck for work so any help would be greatly appreciated.

[Bow_Tied]

No guru here... I think that the TC L/U is disable during open loop mode. If there was something telling your computer that you weren't warmed up, such as a failing temp sensor or loose connection to it, that might do it. Just a WAG.

[Adam]

I will check that out. I wonder if the TC worn out? Is that even possible.

[Scotto]

This is all poop off the top of my tiny little brain:

The TC is supposed to kick in when the RPMs hit a level that can spin the fluid and then lock the tranny to the engine. When below a certain RPM, the tranny will slide. That's why guys brag about their 4500 TC, or whatever they have in their. Remember that your TC is basically two spinning fans pointing at each other.

Yours should lock in at about 1800 RPM.

So, if it's not locking up, and you don't have any weird and funky noises, the fluid level in the TC could be low. Or it's fuggered.

[studum]

Is there a solenoid that controls the lockup function that could be getting lazy?

If not it may be worth trying what you do with every other auto tranny problem on the planet. Do a fluid change, maybe a bottle of lucas and pray that it works. If not it's likely getting near to tear down time.

[Adam]

Scott, it does kick in at around 1800. I believe this is called the stall rpm. Like if you hold the brakes and give it gas it will go to 1800 and then force it to move.

I'm not sure but there probably is a solenoid, but the tranny passed all the "tests" in the FSM. I am going to do a fluid change tomorrow, it has been about 60,000 kms since it has been changed but it isn't dark.

[Scotto]

Tranny fluid won't go dark - unless it gets mixed with something dark. Engine oil goes dark b/c of the combustion going on. Trannys don't have combustion to deal with, so they tend to look fine, even when getting old and worn out.

[Simon]

Tranny fluid WILL go dark It burns. It turns brown. In most premature auto tranny failures, heat is the #1 cause. Either abuse, lack of maintenance or design flaw (clogging coolers etc) can be the root cause of the overheat.

IN your case, Adam, in no way would a failure at this point be considered "premature". I had my old Pathfinder do the same thing once, until I shut it off, and restarted, then it was fine again. I'd be inclined to believe it's an electrical problem.

[Adam]

Thanks for the replies. I am about to head out for the day so I'll see how it runs today. The fluid was brown when I bought the truck but I had it flushed at Mr. Lube, and then later on bigbird changed the filter and the fluid in the pan.

I agree about it being electrical since turning the truck off, and restarting it, cured the problem so it seems. I am going to try re-seating the connection to the TCU and make sure the plugs for the trans are hooked in correctly and sealed. Did you ever figure out what was wrong with yours?

I am just worried about it just not going into gear one day, as you know these transmissions like to fail without warning. And yeah, premature was about 100k ago .

[Simon]

No, mine only ever did it once. I assumed a bad ground or something caused it. Because it never happened again.

[fleurys]

no guru, just more input... Like simon said,,... I had a monte carlo that did the same thing... To make it go in overdrive, while driving, I would put in neutral, stop the engine, re-start, then put back in gear, and it would work. This trans 4l60 I beleive was completely controlled by sensors and selonoids etc... A <reboot> of the car would somehow fix it... Now mine did this from the getgo... so If yours was ok before and now does that, I tend to think like the others that it is electrical and not mechanical at all...

good luck.

[Adam]

Ok, so the other day I pulled all the plugs apart for the transmission and sprayed them down with contact cleaner. They looked good (Thank you Nissan for those waterproof gray plugs) so I plugged them all back in. Same with the Plug for the TCU. I also drained the fluid from the pan and refilled it. On Saturday I towed a load of scrap to cohen's (probably about 2500 lbs including trailer) and it performed flawlessly. Actually I find it shifts smoother when you are towing something.

I will have to wait and see if this helped at all. I am thinking about replacing those grounds that used to go from the body or frame to the exhaust manifolds. They are all broken off!