Hard Shifting! 2500 Sierra

2500sierra · February 16, 2009

Truck info: 2000 Sierra 2500 4X4 4l80E and 4.10 gears. 265 75 16 tires about a 31 inch tire

Just got the truck about two weeks ago, when first started up from cold as long as i don't get on the gas too much i can go forever without hard shifts as long as i dont stay in OD too long. After being on the highway in OD for 7-15mins almost always shifts hard from that point on, after it starts shifting hard all the time i can turn off the truck for minimum of 10mins and it will completely cycle through this again. Its gettin kinda annoying and its probably not good on the rear end, u joints or anything behind the tranny.

My diagnosis: What i think might be wrong from reading on here and expierence. Is that my converter clutch is shot (i think this because i dont notice it locking up, and when brakes are applied while also on the gas i dont notice a sudden RPM spike) so as i read if the transmission senses your lockup not working or slipping it will tell the EPC soleniod to send MAX line pressure to the components, but i also know more line pressure=clutch plates engaging quicker therefore HARD! shifts.

I dont know too much about this so any info or suggestions on it are greatly appreciated. Sorry for the lengthy post, Thanks.

terryk · February 17, 2009

Truck info: 2000 Sierra 2500 4X4 4l80E and 4.10 gears. 265 75 16 tires about a 31 inch tire

Just got the truck about two weeks ago, when first started up from cold as long as i don't get on the gas too much i can go forever without hard shifts as long as i dont stay in OD too long. After being on the highway in OD for 7-15mins almost always shifts hard from that point on, after it starts shifting hard all the time i can turn off the truck for minimum of 10mins and it will completely cycle through this again. Its gettin kinda annoying and its probably not good on the rear end, u joints or anything behind the tranny.

My diagnosis: What i think might be wrong from reading on here and expierence. Is that my converter clutch is shot (i think this because i dont notice it locking up, and when brakes are applied while also on the gas i dont notice a sudden RPM spike) so as i read if the transmission senses your lockup not working or slipping it will tell the EPC soleniod to send MAX line pressure to the components, but i also know more line pressure=clutch plates engaging quicker therefore HARD! shifts.

I dont know too much about this so any info or suggestions on it are greatly appreciated. Sorry for the lengthy post, Thanks.

I just got the same truck about a month ago.

First, pressing the brake pedal on a 4L80E (at least on a 2000 6.0L 2500HD) doesn't release the TCC like most cars and trucks. I've read up on this, scanned it to check that the EBCM sees the brake press and finally got a conclusive answer that it doesn't work that way. It's an odd man out. Press all you want, it won't unlock. It will only unlock if you release the throttle (or back way, way off)

Mine initially would spit trans fluid out the vent. I couldn't figure out *when*, but it would. It would also do some hard 3-4 up shifts. I suspected I had the beginning of the well documented 2000 TCC problem. I had the fluid and filter changed (nothing bad in the old filter) and the fluid spitting stopped. There is a TSB about a leak in the pump doing this but again it stopped. Also, my trans temps never got over 150F. The tech was perplexed.

I have figured out that if:

1. I climb a moderate hill (6%);

2. Lay into the throttle enough to drop it from 4 down to 3 while keeping the TCC locked (it will normally stay locked on 3-4 up and 4-3 down shifts);

3. Then quickly let off the throttle enough to allow a 3-4 up shift but still with enough throttle to keep the TCC locked;

4. It will do a pretty harsh up shift. I can make it harder by doing this in tow/haul.

I think what I am experiencing is the beginning of what you are seeing. The TCC takes a lot of line pressure to keep it locked and when it does the 3-4 up shift the pressure is way too much and it's harsh. Pretty good thud.

The 2000 MY appears to have used a one-off converter that is prone to this problem. I suspect I will be putting one in sometime (about $1000 total for the TC and labor).

I only had a brake switch error in the PCM (which is due to me holding the throttle down while pressing the brake) and it cleared from history when I stopped trying to unlock it with the pedal.

Sounds like we have come to the same conclusion.....

If anyone can add to this I'd like to hear it. I've checked other forums and these exact symptoms come up and seem to be resolved with a new TC. Many people have a P1870 code set and the trans will stop shifting into 4th until you clear the code or cycle the key. I don't have that code yet. You might want to check yours.

2500sierra · February 17, 2009

hmm thanks for the info.

As I drive my truck more and more I almost have what makes it shift hard down to a science, extended periods of time doing 50+ MPH willl make it shift hard.

Going over half throttle can make it start to act up under any driving style city or highway.

Also in city driving getting it to kick down for 4 to 3 then back up will make it shift hard.

My tranny fluid is still pretty bright and smells good but in the sun you do see some silver metallic.

I also noticed that when its shifting normal i check the fluid and it is a little overfilled, but when i check it when its been shifting hard its about 1 1/2 inches over full and looks a little foamy.

The tranny never gets above 150 degrees.

I wish i knew of a way to rule out TPS sensor and VSS sensors as my problem, because i would like to replace those before a 1000$ TC.

Thanks for the help!

terryk · February 17, 2009

hmm thanks for the info.

As I drive my truck more and more I almost have what makes it shift hard down to a science, extended periods of time doing 50+ MPH willl make it shift hard.

Going over half throttle can make it start to act up under any driving style city or highway.

Also in city driving getting it to kick down for 4 to 3 then back up will make it shift hard.

My tranny fluid is still pretty bright and smells good but in the sun you do see some silver metallic.

I also noticed that when its shifting normal i check the fluid and it is a little overfilled, but when i check it when its been shifting hard its about 1 1/2 inches over full and looks a little foamy.

The tranny never gets above 150 degrees.

I wish i knew of a way to rule out TPS sensor and VSS sensors as my problem, because i would like to replace those before a 1000$ TC.

Thanks for the help!

Yeah, that takes a scanner. You might want to consider having the dealer or a trans shop you like do an evaluation. Either will have a scanner to check codes and rule out any sensors.

2500sierra · February 17, 2009

ok well at my tech school we have a 3,500$ snap on scanner so hopefully i can hook it up later this week sometime and get some info.

terryk · February 17, 2009

ok well at my tech school we have a 3,500$ snap on scanner so hopefully i can hook it up later this week sometime and get some info.

Let me know what you find. I love the truck other than this trans glitch.

2500sierra · February 18, 2009

one more question, I just bought the truck and dont have the money to change the TQ would there be any way to trick the transmission into thinking no components are slipping. Also i would like to know if i just kept my tranny in 3rd manually and drove all kinds of conditions and never had any harsh shifting that would confirm our theory. right?

terryk · March 24, 2009

Update: I had my torque converter replaced and it fix the harsh shift. If you have access to a Tech II scanner or HP Tuners VCM Scanner, you can easily check it. The problem is obvious.

Select torque converter slip and watch the slip RPM. Go for a drive and get up to 65-70 MPH and wait for the TC to lock in 4th. Slowly add throttle and watch the slip. With a bad torque converter the TC slip RPM will rise above 100 or 200 or more. The slip will increase with throttle. Of course if you go high enough it will unlock and/or downshift to third.

A good TC will hold < 20 RPM before the PCM unlocks it. Mine would go into the 200+ slip range just adding throttle. I also noticed the tach would rise but not the speed as I added throttle. Clear indication the TC was slipping.

Some important notes (about the 2000 4L80E). May or may no apply to others years.

1. The 2000 4L80E had a problem with torque converters slipping. This is a known problem. I have read that 2000 was unique but I also have read the 99-02 were the same TC. I am not sure what is true on that.

2. The TC apply pressure is normally maxed out by design. This means the PCM doesn't have any extra to try and keep the TC locked. When there is slip, it doesn't know if it's TC slip or clutches so it raises the line pressure and voila, you have harsh shifts until you power cycle the key.

3. You may or many not have a P1870 TCC slip error. Mine generally didn't, but if I really worked at it (keeping the slip high for a couple of minutes climbing long hills), it would eventually set the code. Not having the code doesn't mean the TCC isn't slipping.

4. Mine cost $1100 out the door to replace including a new GM TC, fluids and misc stuff. The bill was $1300 but I had some other little stuff done.

5. Pressing the brake pedal does not unlock the TC. This is normal. The worse you do is set a brake pedal error code (no SES).

plowking · March 27, 2009

My son-in-law had problems on his 2000 dually with his tc locking or unlocking. On his he found a sensor on his transmission,I think it was on the tailshaft,he had to remove and clean arond the sensor,it had rusted and raised enough so it wasn't reading properly. My 95 chevy wil only give me trouble above 65 mph,worse if towing. plowking

SCOTT WILLIAMS · October 5, 2009

Update: I had my torque converter replaced and it fix the harsh shift. If you have access to a Tech II scanner or HP Tuners VCM Scanner, you can easily check it. The problem is obvious.

Select torque converter slip and watch the slip RPM. Go for a drive and get up to 65-70 MPH and wait for the TC to lock in 4th. Slowly add throttle and watch the slip. With a bad torque converter the TC slip RPM will rise above 100 or 200 or more. The slip will increase with throttle. Of course if you go high enough it will unlock and/or downshift to third.

A good TC will hold < 20 RPM before the PCM unlocks it. Mine would go into the 200+ slip range just adding throttle. I also noticed the tach would rise but not the speed as I added throttle. Clear indication the TC was slipping.

Some important notes (about the 2000 4L80E). May or may no apply to others years.

1. The 2000 4L80E had a problem with torque converters slipping. This is a known problem. I have read that 2000 was unique but I also have read the 99-02 were the same TC. I am not sure what is true on that.

2. The TC apply pressure is normally maxed out by design. This means the PCM doesn't have any extra to try and keep the TC locked. When there is slip, it doesn't know if it's TC slip or clutches so it raises the line pressure and voila, you have harsh shifts until you power cycle the key.

3. You may or many not have a P1870 TCC slip error. Mine generally didn't, but if I really worked at it (keeping the slip high for a couple of minutes climbing long hills), it would eventually set the code. Not having the code doesn't mean the TCC isn't slipping.

4. Mine cost $1100 out the door to replace including a new GM TC, fluids and misc stuff. The bill was $1300 but I had some other little stuff done.

5. Pressing the brake pedal does not unlock the TC. This is normal. The worse you do is set a brake pedal error code (no SES).

I am having the same issues with my 2000 2500 silverado. I posted my questions a few hours ago. I was wondering if you replaced the tc with a GM unit or an aftermarket TC?

Thanks

Scott

BuckFeverZ · October 5, 2009

Update: I had my torque converter replaced and it fix the harsh shift. If you have access to a Tech II scanner or HP Tuners VCM Scanner, you can easily check it. The problem is obvious.

Select torque converter slip and watch the slip RPM. Go for a drive and get up to 65-70 MPH and wait for the TC to lock in 4th. Slowly add throttle and watch the slip. With a bad torque converter the TC slip RPM will rise above 100 or 200 or more. The slip will increase with throttle. Of course if you go high enough it will unlock and/or downshift to third.

A good TC will hold < 20 RPM before the PCM unlocks it. Mine would go into the 200+ slip range just adding throttle. I also noticed the tach would rise but not the speed as I added throttle. Clear indication the TC was slipping.

Some important notes (about the 2000 4L80E). May or may no apply to others years.

1. The 2000 4L80E had a problem with torque converters slipping. This is a known problem. I have read that 2000 was unique but I also have read the 99-02 were the same TC. I am not sure what is true on that.

2. The TC apply pressure is normally maxed out by design. This means the PCM doesn't have any extra to try and keep the TC locked. When there is slip, it doesn't know if it's TC slip or clutches so it raises the line pressure and voila, you have harsh shifts until you power cycle the key.

3. You may or many not have a P1870 TCC slip error. Mine generally didn't, but if I really worked at it (keeping the slip high for a couple of minutes climbing long hills), it would eventually set the code. Not having the code doesn't mean the TCC isn't slipping.

4. Mine cost $1100 out the door to replace including a new GM TC, fluids and misc stuff. The bill was $1300 but I had some other little stuff done.

5. Pressing the brake pedal does not unlock the TC. This is normal. The worse you do is set a brake pedal error code (no SES).

I am having the same issues with my 2000 2500 silverado. I posted my questions a few hours ago. I was wondering if you replaced the tc with a GM unit or an aftermarket TC?

Thanks

Scott

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