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4L80e Pressure drop during 1-2 shift only


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I need to reach out to you guys to see if anyone else has ever experienced a pressure drop between the 1-2 shift on their 4L80e and found a solution. The first 80e I had built did the exact same thing until the 1-2 clutches cooked and now the new one I just put in last weekend is doing the same thing...HELP!!!

 

Yesterday I did a pressure test while driving and found 200psi @ part throttle with nice and firm shift + all other gears shift very nice. Only at wot does the pressure drop down to 180 during the 1-2 and goes back up to 200 for the 2-3 and 3-4 :crazy:

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Did you clear your TAP cells when you installed new trans? You ALWAYS, need to do that when you rebuild or replace a trans....

I had the trans installed, I didn't do it myself. Is this something that's done with the tune?

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I had the trans installed, I didn't do it myself. Is this something that's done with the tune?

No. TAP is Transmission adaptive pressure. I would think most shops would know about this but I would ask because if you don't you can burn a new trans up in no time! I have only done it with a Tech 2, not sure if you can do with other scan tools.....

 

 

Transmission Adaptive Functions

(Source: AllData)

The 4L60-E transmission utilizes a line pressure control system during upshifts to compensate for the normal wear of transmission components. By adjusting the line pressure, the PCM can maintain acceptable transmission shift times. This process is known as "adaptive learning" or "shift adapts" and is similar to the closed loop fuel control system used for the engine.

 

In order for the powertrain control module (PCM) to perform a "shift adapt," it must first identify if an upshift is acceptable to analyze. For example, upshifts that occur during cycling of the A/C compressor or under extreme throttle changes could cause the PCM to incorrectly adjust line pressure. When an upshift is initiated, a number of contingencies, such as throttle position, transmission temperature, and vehicle speed, are checked in order to determine if the actual shift time is valid to compare to a calibrated desired shift time. If all the contingencies are met during the entire shift, then the shift is considered valid and the adapt function may be utilized if necessary.

 

Once an adaptable shift is identified, the PCM compares the actual shift time to the desired shift time and calculates the difference between them. This difference is known as the shift error. The actual shift time is determined from the time that the PCM commands the shift to the start of the engine RPM drop initiated by the shift. If the actual shift time is longer than the calibrated desired shift time, a soft feel or slow engagement, then the PCM decreases current to the pressure control (PC) solenoid in order to increase line pressure for the next, same, upshift under identical conditions. If the actual shift time is shorter than the calibrated desired shift time, a firm engagement, then the PCM increases current to the PC solenoid in order to decrease line pressure for the next, same, upshift under identical conditions.

 

The purpose of the adapt function is to automatically compensate the shift quality for the various vehicle shift control systems. It is a continuous process that will help to maintain optimal shift quality throughout the life of the vehicle.

 

Clearing Transmission Adaptive Pressure (TAP)

Transmission adaptive pressure (TAP) information is displayed and may be reset using a scan tool.

 

The adapt function is a feature of the PCM that either adds or subtracts line pressure from a calibrated base line pressure in order to compensate for normal transmission wear. The TAP information is divided into 13 units, called cells. The cells are numbered 4 through 14. Each cell represents a given torque range. TAP cell 4 is the lowest adaptable torque range and TAP cell 14 is the highest adaptable torque range. It is normal for TAP cell values to display zero or negative numbers. This indicates that the PCM has adjusted line pressure at or below the calibrated base line pressure.

 

Updating TAP information is a learning function of the PCM designed to maintain acceptable shift times.

It is not recommended that TAP information be reset unless one of the following repairs has been made:

  • Transmission overhaul or replacement
  • Repair or replacement of an apply or release component, clutch, band, piston, servo
  • Repair or replacement of a component or assembly which directly affects line pressure

Resetting the TAP values using a scan tool will erase all learned values in all cells. As a result, the PCM will need to relearn TAP values. Transmission performance may be affected as new TAPs are learned. Learning can only take place when the PCM has determined that an acceptable shift has occurred. The PCM must also relearn TAP values if it is replaced.

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Thanks for that, great info. ...I never cleared the TAP cells when I swapped from the 60 to the 80 last year either. I'll be sure and do this before I drive it anymore to see if that's the culprit. Thanks again Matt.

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Is this why the truck sputtered a lil bit at like 4500-5500ish area ... if you get what I'm trying to say lol I heard in the videos 2nd gear toward high rpm it sputtered a slip second ...I hope you figure it out as I'm doing the 80 swap soon

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Is this why the truck sputtered a lil bit at like 4500-5500ish area ... if you get what I'm trying to say lol I heard in the videos 2nd gear toward high rpm it sputtered a slip second ...I hope you figure it out as I'm doing the 80 swap soon

That's the converter locking up your hearing AFTER the 1-2 shift (:42 into the vid)...that's normal. Listen to how the truck sort of "slides" into second gear at :40 when it should have been a crisp clean shift.

 

https://www.youtube.com/watch?v=cmvkEalYO1A

Edited by L8ERBRO (see edit history)
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That's the converter locking up your hearing AFTER the 1-2 shift (:42 into the vid)...that's normal. Listen to how the truck sort of "slides" into second gear at :40 when it should have been a crisp clean shift.

 

Ahhh yah now I hear the lil slip... I figured that's how you or zippy tuned it....and at :42 is exactly what I was talking about.... my circle d didn't skip a beat when it locked.. made it actually goes faster .....
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  • 2 weeks later...

Mystery solved - at my own expense of course! Chuck from FLT suggested the pre '97 80e but failed to tell me the dipstick was a different part number. Just came in today from Chevy - a special order.

20150328_180700.jpg

20150328_175651.jpg

Note the witness mark I made last weekend after pulling the pan and marking the correct fluid level on my old 80e dipstick

20150328_175641.jpg

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Sure doesn't sound like it is all your fault. I would think that the dipstick info is very critical and should have been given to you right at the start of the deal.

That's what I was thinking too....oh well. I've already bought a junkyard trans and a bunch of good parts so hopefully I will get her back on the road in a couple of weeks.

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