Trans not locking?

67ChevyRedneck · January 6, 2006

Hey all, I don't frequent here much, but I'm having an issue with my 2000 Z71 w/5.3L and hoping someone could help. The truck has 82K on it and I bought it with 67K. The last couple of days OD has been acting funny. The trans is not slipping, but after it shifts into 4th, it isn't locking like it should. It seems to do it in the morning when it's cold? It's never done this before. After is shifts into 4th the rpms stay about 2-300 higher than they should be, which is why I think it isn't locking. It's doing it randomly. The fluid looks clean and the level is good. Is it possible I just need a fluid/filter change? There are no messages in the message center. Could there still be an error code even if the message center doesn't flash anything? I'm kinda scared, I don't have 2K for a rebuild and it's my only ride. My 67's 700R4 went out last year and she's been sittin since.

redvett · January 6, 2006

Hey all, I don't frequent here much, but I'm having an issue with my 2000 Z71 w/5.3L and hoping someone could help. The truck has 82K on it and I bought it with 67K. The last couple of days OD has been acting funny. The trans is not slipping, but after it shifts into 4th, it isn't locking like it should. It seems to do it in the morning when it's cold? It's never done this before. After is shifts into 4th the rpms stay about 2-300 higher than they should be, which is why I think it isn't locking. It's doing it randomly. The fluid looks clean and the level is good. Is it possible I just need a fluid/filter change? There are no messages in the message center. Could there still be an error code even if the message center doesn't flash anything? I'm kinda scared, I don't have 2K for a rebuild and it's my only ride. My 67's 700R4 went out last year and she's been sittin since.

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Check your coolant level and temperature should be about 195deg. hot and TCC should lockup at about 151deg. Dont keep driving vehicle without fixing TCC it will burnup trans since there is no cooling of trans oil in 3rd & 4th gear.

67ChevyRedneck · January 6, 2006

I'm sorry, but I don't think I understand what your getting at? Do you mean coolant level as in radiator? The level is normal and the truck is running at the proper temperature. What does TCC stand for and how can I fix it? Torque converter....something? Why is the trans oil not cooled in 3rd and 4th gear. Once again, I'm sorry, but I'm new to this stuff and your post was kind of vague. Could you please elaborate?

Check your coolant level and temperature should be about 195deg. hot and TCC should lockup at about 151deg. Dont keep driving vehicle without fixing TCC it will burnup trans since there is no cooling of trans oil in 3rd & 4th gear.

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redvett · January 6, 2006

I'm sorry, but I don't think I understand what your getting at? Do you mean coolant level as in radiator? The level is normal and the truck is running at the proper temperature. What does TCC stand for and how can I fix it? Torque converter....something? Why is the trans oil not cooled in 3rd and 4th gear. Once again, I'm sorry, but I'm new to this stuff and your post was kind of vague. Could you please elaborate?

Check your coolant level and temperature should be about 195deg. hot and TCC should lockup at about 151deg. Dont keep driving vehicle without fixing TCC it will burnup trans since there is no cooling of trans oil in 3rd & 4th gear.

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Coolant in radiator & overflow tank must be correct no air in radiator.

TCC is Torque Converter Clutch.

Cooling oil when the converter is locked up uses energy (fuel economy) and transmission with aluminum case does not need that much cooling. The converter generates a huge amount of heat. Early cars 1947 and later with a fluid coupling and cast iron cases had no oil cooler since fluid coupling generated little heat.

Check the brake switch first PCM sends power to the brake switch and down to the trans. Assuming you dont have a SES light on it could be the switch.

Hope this helps.

67ChevyRedneck · January 6, 2006

I understand what your getting at now. I looked at what I believe to be my brake switch. They used to be a cylinder mounted on the pedal that had a button that was depressed, but the one on my truck is just a rod with some wires running to it connected to the pedal, how can I tell if it is bad or not??? Thanks for the help

redvett · January 6, 2006

I understand what your getting at now. I looked at what I believe to be my brake switch. They used to be a cylinder mounted on the pedal that had a button that was depressed, but the one on my truck is just a rod with some wires running to it connected to the pedal, how can I tell if it is bad or not??? Thanks for the help

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You will have to have access to a Tech2 or similar scanner and Heims Factory service manual since its quite complicated. the brake switch signal goes to the PCM and comes out and goes to the trans as 2 different signals TCC & PWM.

A Tech 2 can look and see if the brake switch or any other parameters and inputs are OK.

unkleJ · January 7, 2006

The characteristic that you are noticing may not be a problem. Your computer will not let the torque converter lock until the transmission oil temperature reaches ~75degs. Also, your trans will shift slightly different until the motor coolant temperature reaches ~175degs. The torque converter won’t lock below 42mph no matter what the coolant or trans temp is at.

If your torque converter doesn’t lock up when the truck is fully warm (which may take around 10-15 minutes depending how cold it is outside), than you may have a problem. Most likely the feeling that you are experiencing is normal.

I freaked out during the first winter with my truck when I noticed the same thing.

Jeff

redvett · January 7, 2006

In GMT 800 trucks TCC should occur at about 151deg. F. and no later than 195deg. You should be able to see tach drop at about 151deg on level road with steady throttle. It is a PWM program so as to not just lockup but instead progressively lock up so there is no lurch.

67ChevyRedneck · January 10, 2006

Update: Took the truck to GM over the weekend. I baffled them. They said they had never heard of anything like it. They put it on the computer during a test run (I rode along) and couldn't find anything wrong. And they DIDN'T CHARGE ME. Amazing, huh? Tranny flud did not smell or look burnt. I've been leaving it in third until the engine gets warm and it's been working properly. Funny thing is that it has been MUCH colder outside and it hadn't started this until last week. With that said I'm saving my pennies (haha) for a near future tranny swap....... I guess 82K and 6 years was long enough for a 4x4 tranny to last