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Explain TC Lock Up To Me

M

mpljc

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Alabama
Wondering if someone could explain the torque converter lock and unlock process to me.

Here is what I understand so far.

In normal mode as opposed to tow/haul mode, the torque converter locks up in 5th gear around the 50 mph mark.

When transmission is cold, it does not lock up until it gets warmed up to a certain temperature. I think I can tell when it locks up the first time by watching the RPM's drop 200-300.

After the transmission has warmed up and I take off from a stop, I think I can feel it lock up as it gets to around 50 MPH. I think what I am feeling is probably normal.

In tow/haul mode, it locks and stays locked up 2nd gear and up.

Now, here are my series of questions with normal mode in mind.

1. Is it possible to feel the torque converter to lock up?
2. What does it feel like when it does lock up? Does it feel like a shift through a gear or what?
3. Is there a certain percentage of normal torque converter slippage when it locks up?
4. What would abnormal torque converter clutch slippage feel like and at what time and how often would you feel it?
5. Is it normal to feel it lock up?

I will probably have more questions based on any responses I get.

And yes, I keep my transmission fluid and spin on filter changed. Color and smell seem to be normal to me.

I don't think I have never really paid much attention to the truck when torque converter lock up happens. Now I think I am feeling it happen and have really honed in on it. I am afraid I'm trying to make a problem out of something when in reality I don't have a problem.

My truck is a daily driver. It is completely stock. I have never towed anything with it to amount to anything. I have not hauled anything of significant weight either - I have but not what I would consider true hauling.

Anyway, thanks in advance to the answers to any questions to help clarify the torque converter and clutch lock and unlock process and what it might would feel like in normal circumstances and when it is abnormal as in - you have lingering problems.

Thanks!
 
1. Yes, it feels like another shift and the engine sounds like it bogs down when it locks up. You'll also know it's locked because the engine speed will not increase independent of ground speed with more throttle. It feels like driving a stick because the engine is directly coupled to the transmission at that point.
2. See #1
3. Yes it slips when it locks; I'm not an expert, but I believe it uses a PWM signal to pulse the TC clutch on gradually to keep from banging your fillings out when it locks up.
4. Can't answer that, I've not experienced it. I assume you mean slipping because of a tune.
5. Yes, it's normal in the diesel to feel it. When you coast from about 55 down to below 45-50 you can feel it unlock also. The engine sounds like you let your foot off the throttle, goes down to idle and you feel the bump when it unlocks. Same thing in T/H and you coast down below 20. The bump you feel is the TCC unlocking.

Also, the TCC locks up when you go to WOT.


Also, welcome to TTS!
 
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Thanks for the welcome Saratoga.

Your answers help a lot!

Thanks for expounding on #5 - right on the money for what I notice with my truck.

I guess I have never really paid that much attention to it before. Then, one day, for some reason, I noticed it. Since then, I have honed in on it paying more attention to it. I was letting paranoia set in thinking - wow - great - is my TC starting to go south on me - how nice! Especially since I have never really towed or hauled anyting with my truck to give it any stress to tear up.

My truck is completely stock and has always been stock. I bought it used with about 2600 miles on it.

Under my normal acceleration, I can feel it lock up consistently right at if not on 50 MPH.

Now, if you throw the hammer down and really take off, will it lock up a little sooner say around 45 MPH instead of 50?
 
mpljc said:
Thanks for the welcome Saratoga.

Your answers help a lot!

Thanks for expounding on #5 - right on the money for what I notice with my truck.

I guess I have never really paid that much attention to it before. Then, one day, for some reason, I noticed it. Since then, I have honed in on it paying more attention to it. I was letting paranoia set in thinking - wow - great - is my TC starting to go south on me - how nice! Especially since I have never really towed or hauled anyting with my truck to give it any stress to tear up.

My truck is completely stock and has always been stock. I bought it used with about 2600 miles on it.

Under my normal acceleration, I can feel it lock up consistently right at if not on 50 MPH.

Now, if you throw the hammer down and really take off, will it lock up a little sooner say around 45 MPH instead of 50? not usually. it may feel quicker, but it is only because the parameters have been met quicker.
Click to expand...
you should feel the tcc lock up in a modded ally. it locks up and you can feel it. minimal pulse of the tcc solenoid and its on. it is very reassuring though when your towing because you feel the good positive lock up. any more questions just ask.
 
you'll feel it and it'll feel like an extra gear. As far as abnormal lock ups the only experiences I've had with abnormal TC stuff is either a failure to lock altogether or it'll "chatter" when it locks.
 
In second gear normal mode the TCM can lock the converter if the TCC slippage is less than a programmed amount. SO if you're running a big tune with a stock converter you won't see it lock in second.
 
stacks04 said:
big tune-stock converter=no lock up, big tune-good converter=no lockup. i am not sure how its supposed to work.
Click to expand...

It all depends upon the converter mostly. I'm running a medium tune with my PI ML and it locks up everytime spot on. People with the SUNCOAST seem to have more trouble with lock-up than those with the PI.
 
it locks in tow haul and in fifth like its supposed to. i guess it dont matter. i am not a wot driver:D. i am way to cheap to pay for fuel haha.
 
I tried WOT yesterday and mine did not lock until ~50ish just like normal. You might be onto something here Joe. I always thought the convertor was supposed to lock at WOT in 2nd gear regardless of T/H on or off. T/H she locks evrytime in 2nd, and blows the tires off if too much pedal is used):h
 
ferm that just sounds like the 2-3 shift to me. for my truck that shift happens around 28 mph. its hard to tell though from the video, but around 40 mph just sounds like a shift, i only say it because according to the tune i have it is not supposed to release even wot until 24 mph. yours releases as soon as you let off the throttle.
 
stacks04 said:
ferm that just sounds like the 2-3 shift to me. for my truck that shift happens around 28 mph. its hard to tell though from the video, but around 40 mph just sounds like a shift, i only say it because according to the tune i have it is not supposed to release even wot until 24 mph. yours releases as soon as you let off the throttle.
Click to expand...

I went back and looked at a log and pulled up a TCM tune in EFILIVE, and the torque converter actually locks during the 2-3 shift under WOT so that it is locked for 3rd gear. I thought that the 2-3 shift was just lock-up in 2nd as it isn't in 3rd that long and I've never stretched mine out hard enough for a WOT 4-5 shift.
 
All the TCM's command Lockup at WOT regardless of Normal or Tow/Haul. If it occurs as a gear change happens you will not feel it. It's the same for both 5 and 6 speeds in a Allison equipped GM pickup. Now if you get into changing the programming things can be made different.
 
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