Lately my shift times are taking longer. For the last few years my 1-2 shift under WOT was about 300 milliseconds. Now it is at about 450 milliseconds. Tried replacing the filter and did not change anything.
For those of you with 3800SC with the 4t65hd tranny, what shift times are you seeing 1-2 and from 2-3.
Thanks!
------------------ 84/87 NB, 3800SC, E-85, VS Cam, 2.8 Pulley, 4T65E-HD, HP Tuners, AEM Wideband, Regal GS Gauges, S-10 Brake Booster. 1/4 mile -11.85 at 114mph
I have tuned numerous 3800 SC cars that had the 4T65-E HD transmission in them. My impression of bone stock 4T65-E HD transmissions that had moderate to high mileage already on them (by the time they showed up here) is they never seem to have crisp shifts at WOT, not even if you jack the shift pressures all the way up in the tune. Sometimes you can turn the pressures up high enough at part throttle to get it to shift nice there, but it still doesn't help at WOT because the pressure can only be turned up so far due to the limitations of the pressure control system.
Now something else that can play into this is if someone had turned off the torque management in the PCM tune. Torque Management retards ignition timing advance during the shifts to help the transmission live longer. This also has the added benefit of helping the transmission complete the shift quicker. If someone has turned off the torque management in your tune (or even reduced it any), this could be causing your transmission to wear out more quickly which would have the result of extending the shift times.
Another separate issue/possibility is someone could have set up the shift times in the PCM tune to be longer than 300ms. If they have done that, then the PCM may be trying to get that shift to take longer on its own and there may be nothing wrong with the trans. To determine this, one would need to look at the PCM tune and see what the current settings are.
If it turns out the tune is set up for 300ms shifts (or quicker) and the torque management settings are still stock, then there's a good chance your trans is either wearing out or there is a shift accumulator issue that requires repair to correct the problem.
-ryan
------------------ OVERKILL IS UNDERRATED Custom GM OBD1 & OBD2 Tuning | Engine Conversions & more | www.gmtuners.com
I have tuned numerous 3800 SC cars that had the 4T65-E HD transmission in them. My impression of bone stock 4T65-E HD transmissions that had moderate to high mileage already on them (by the time they showed up here) is they never seem to have crisp shifts at WOT, not even if you jack the shift pressures all the way up in the tune. Sometimes you can turn the pressures up high enough at part throttle to get it to shift nice there, but it still doesn't help at WOT because the pressure can only be turned up so far due to the limitations of the pressure control system.
Now something else that can play into this is if someone had turned off the torque management in the PCM tune. Torque Management retards ignition timing advance during the shifts to help the transmission live longer. This also has the added benefit of helping the transmission complete the shift quicker. If someone has turned off the torque management in your tune (or even reduced it any), this could be causing your transmission to wear out more quickly which would have the result of extending the shift times.
Another separate issue/possibility is someone could have set up the shift times in the PCM tune to be longer than 300ms. If they have done that, then the PCM may be trying to get that shift to take longer on its own and there may be nothing wrong with the trans. To determine this, one would need to look at the PCM tune and see what the current settings are.
If it turns out the tune is set up for 300ms shifts (or quicker) and the torque management settings are still stock, then there's a good chance your trans is either wearing out or there is a shift accumulator issue that requires repair to correct the problem.
-ryan
Thank you for taking the time to post. I had the tranny rebuilt about 2.5 years ago and if I recall correctly shift times were about .350 ms. I used HP Tuners to lightly tweak the tranny values (cant recall off the top of my head exactly what tables) but for the past couple years I noticed on my scan gauge that shift times were always around .285 or so at WOT. Now I am seeing 400 -450 ms. I beat the tar out of this tranny, so it would not surprise me if I have worn the clutches in the 1-2 pack. I change the filter yearly and look for signs of metal and excessive clutch material in the pan and have not found any. I will check over the weekend and see if there happens to be excessive material in the pan now. I have read that the tranny will start setting codes if the shift times are over .650ms or so (luckily I have not experienced any shifts over .485) which seems like a really long shift to me. Do you happen to know the shift time at WOT of a typical normal 4t65e HD with stock tuning?
[This message has been edited by DimeMachine (edited 09-10-2014).]
Don't think I have the ability to look at that with either HP Tuners or Aeromotive Scan Gauge.... I will do some looking this weekend. Thank You!
HP Tuners VCM Scanner DOES have the ability to display and log PCS actual current. You will have to set it up as a custom PID but it can be found in their software.
Stock is anywhere between 375ms and 275ms depending on gear and throttle position.
Can you bring up PCS actual current data on your scan gauge? What does it say the PCS ma (milliamp) actual current is at WOT?
Note: dropped the pan and changed filter today. As usual the bottom magnet shows minimal fine material and fluid looks good.
Right you are - logged the PID. the shift time was .475ms and at WOT the PCS current was at 600ma and the PCS current was at 234ma when the 1-2 shift originated and held at 059 ma during the shift. Did some more research and it seems like these numbers look appropriate. Added some additional torque reduction (timing retard) during shifts and have the shift time down to .400ms. This may simply be as case that I have been asking too much from this almost stock rebuild and need to reduce torque to the 1-2 shift to maintain a reasonable shift time and extend the life of the tranny. I would appreciate your houghts.
Thank you!
[This message has been edited by DimeMachine (edited 09-14-2014).]
Note: dropped the pan and changed filter today. As usual the bottom magnet shows minimal fine material and fluid looks good.
Right you are - logged the PID. the shift time was .475ms and at WOT the PCS current was at 600ma and the PCS current was at 234ma when the 1-2 shift originated and held at 059 ma during the shift. Did some more research and it seems like these numbers look appropriate. Added some additional torque reduction (timing retard) during shifts and have the shift time down to .400ms. This may simply be as case that I have been asking too much from this almost stock rebuild and need to reduce torque to the 1-2 shift to maintain a reasonable shift time and extend the life of the tranny. I would appreciate your houghts.
Thank you!
PCS (Pressure Control Solenoid) / aka: Force Motor / trans line pressure is calculated based on engine torque. Engine torque is calculated based on RPM and airflow.
Any time you are at WOT, I would expect to see the PCS commanded to below about 300ma depending on RPM, especially on your car. The fact that you said you saw PCS at 600ma for at least some period of time at WOT scares me. It should really never be this high at full throttle (unless the RPMs are really low and the engine isn't seeing a lot of boost). I have a concern that with PCS ma running this high at WOT, the transmission could have been slipping and wearing the clutches out or even burning them.
Let's back up a minute here. What final drive ratio do you have in your 4T65-E trans? 2.93 (3.29 diff and 37/33 chain sprockets) or 3.29 (3.29 diff and 35/35 chain sprockets)???
Is this thread relevant to my shearing a stock input shaft (expected), a 300 m input shaft that was shifting way harder than any automatic I've ever had, or the aermet 100 alloy shaft from GM racing? The GM racing shaft actually twisted before shearing. Built 4t65e hd behind a turbo ls4. Not trying to hijack the thread, just curious.
PCS (Pressure Control Solenoid) / aka: Force Motor / trans line pressure is calculated based on engine torque. Engine torque is calculated based on RPM and airflow.
Any time you are at WOT, I would expect to see the PCS commanded to below about 300ma depending on RPM, especially on your car. The fact that you said you saw PCS at 600ma for at least some period of time at WOT scares me. It should really never be this high at full throttle (unless the RPMs are really low and the engine isn't seeing a lot of boost). I have a concern that with PCS ma running this high at WOT, the transmission could have been slipping and wearing the clutches out or even burning them.
Let's back up a minute here. What final drive ratio do you have in your 4T65-E trans? 2.93 (3.29 diff and 37/33 chain sprockets) or 3.29 (3.29 diff and 35/35 chain sprockets)???
Darth, 2.93. I am absolutely positive that the tranny clutches are not slipping. My only concern is that I have noticed that over the past few months the 1-2 shift at wot in this 11 second fiero has increased from the 275ish ms to 450ms ish and I am trying to tune it so I do not destroy this tranny. I change filters yearly and just did this filter last weekend - not much clutch material in the pan and fluid looks & smells new. Maybe the 370hp is too much for it? Maybe I need to change the shift time tables or pressure table to decrease the ma at WOT? Maybe I need to change the torque management to add more in? If money were no object, a high performance rebuild might be in order.... Thoughts?
[This message has been edited by DimeMachine (edited 09-15-2014).]
Darth, 2.93. I am absolutely positive that the tranny clutches are not slipping. My only concern is that I have noticed that over the past few months the 1-2 shift at wot in this 11 second fiero has increased from the 275ish ms to 450ms ish and I am trying to tune it so I do not destroy this tranny. I change filters yearly and just did this filter last weekend - not much clutch material in the pan and fluid looks & smells new. Maybe the 370hp is too much for it? Maybe I need to change the shift time tables or pressure table to decrease the ma at WOT? Maybe I need to change the torque management to add more in? If money were no object, a high performance rebuild might be in order.... Thoughts?
Ok. I was just making sure you didn't have a 3.29 overall final drive ratio trans. Because if you did, that could explain why you were seeing the high PCS ma readings (tune related issue, but that's a topic for another discussion as it does not apply to you)...
At this point what I would suggest you do, if you want to get the shift times down, is make adjustments in the tune to decrease the amount of PCS current (ma) the PCM is commanding at WOT and possibly increase your torque management settings.
If you already have the shift times set where you want them but the transmission isn't getting there, setting them lower isn't going to help anything. The shift adapts in the PCM are probably already maxing out.
Ok. I was just making sure you didn't have a 3.29 overall final drive ratio trans. Because if you did, that could explain why you were seeing the high PCS ma readings (tune related issue, but that's a topic for another discussion as it does not apply to you)...
At this point what I would suggest you do, if you want to get the shift times down, is make adjustments in the tune to decrease the amount of PCS current (ma) the PCM is commanding at WOT and possibly increase your torque management settings.
If you already have the shift times set where you want them but the transmission isn't getting there, setting them lower isn't going to help anything. The shift adapts in the PCM are probably already maxing out.
Thanks for your thoughts. I will use this opportunity to research further & learn more about tweaking the shift pressure and perhaps the force motor tables and see if that helps and if required more torque management. If you think about it, the stress on the tranny while bringing the engine at WOT making around 370 hp down from 6100 rpm to down under 5000 rpm while shifting from 1-2 is a lot to ask of a basically stock tranny.
[This message has been edited by DimeMachine (edited 09-16-2014).]
The shift time readout is deceving. There are rules that it follows to determine when a shift is done... as far as the pcm is concerned it just has to turn on the 2nd gear solenoids and its done its job. The rest is looking for input shaft speeds and such that are coded in uncharted waters of the tcu code according to the disassembly im looking at now.
Bottom line is I wouldnt worry about it. I had shift times reading out crazy numbers on my stock trans but it ran great for many years.
The shift time readout is deceving. There are rules that it follows to determine when a shift is done... as far as the pcm is concerned it just has to turn on the 2nd gear solenoids and its done its job. The rest is looking for input shaft speeds and such that are coded in uncharted waters of the tcu code according to the disassembly im looking at now.
Bottom line is I wouldnt worry about it. I had shift times reading out crazy numbers on my stock trans but it ran great for many years.
I tend to be aware of my cars and I noticed a couple of shifts that seemed to take longer than normal. Upon scanning them I noticed the shift times were in the high 400ms range and I do recall a couple years ago when I was firming them up they were in the high 200ms range. I view the shifts as too hard = broken hard parts, too soft= worn out clutches. I am not exactly sure what just right is but in my mind it is between 300 and 400 ms. I believe GM thinks 600ms+ is too long as it is my understand the PCM will set an error code at over 600ms. I will do what I can to keep it below 450ms. Thanks Guys!
[This message has been edited by DimeMachine (edited 09-16-2014).]
