[ZLRob]

This has been a semi intermittent issue. At start up and immediate reverse the trans slips up to about 2k while moving back but not entirely engaged in gear it revs revs revs and then it finally feels like it catches and goes about like normal. This is happening in sub 50* temperatures. (About 42-48*F)

Moving forward, when at about 80-90* coolant temps when doing a quick shift up to 7th gear at about 35-40 mph and then going WOT, the trans just revs to about 3000 RPM for a a few seconds (maybe about 1-2 seconds) and then I can feel the positive engagement into 7th.

There's a reason why I'm doing these things and yes I'm aware that lugging the engine is not good, but nevertheless it is exposing issues that I have had for a while because I do remember reverse being an issue every once in a while when it was cold out.

Anyone had any experiences with something similar or have any insight? Transmission fluid got replaced 23K ago but it's been doing the reverse thing every so often even before any major modding, so I don't think this issue is new at all.

[KingLT1]

Sounds like potentially a VVE issue. Ime, it's best to give the setup what it wants and not always what looks best on your Histogram chart. Gen 5 stuff can be finicky. That being said if you are sure the VVE is tweaked the best it can be then I would start looking at mechanical issues with the valve body.

[ZLRob]

Originally Posted by KingLT1

Sounds like potentially a VVE issue. Ime, it's best to give the setup what it wants and not always what looks best on your Histogram chart. Gen 5 stuff can be finicky. That being said if you are sure the VVE is tweaked the best it can be then I would start looking at mechanical issues with the valve body.

I was afraid you would say valve body. I've never been a fan of transmission work because it's so messy and requires a big level of detail, even though I've done valve body upgrades myself in the past. Haha. Yeah, back when the car was really pretty stock with just a different lower pulley and a tune it would do it also, but mostly in reverse as I never attempted lugging it like I do now because VVE changes weren't needed.

I wonder if it would just be best to replace the valve body or if I should just do it the old fashion way and get as much data as I can and just live monitor it to see if a solenoid or something is bad and then target things that way. I think I remember reading something about warped valve bodies on the 10 speeds.

[djctoto]

If you already haven't done so you may want to check the fluid level first. Mine came to me overfilled and was shifting erratically. Not sure if this is your issue but it may be underfilled. The 10 speeds are known to be sensitive to fluid levels.

[JSH]

Originally Posted by ZLRob

This has been a semi intermittent issue. At start up and immediate reverse the trans slips up to about 2k while moving back but not entirely engaged in gear it revs revs revs and then it finally feels like it catches and goes about like normal. This is happening in sub 50* temperatures. (About 42-48*F)

.

No mine has never slipped. I always log every, drive and wait till the transmission fluid. has warmed up before asking anything of it.

[ZLRob]

Originally Posted by djctoto

If you already haven't done so you may want to check the fluid level first. Mine came to me overfilled and was shifting erratically. Not sure if this is your issue but it may be underfilled. The 10 speeds are known to be sensitive to fluid levels.

Checking level probably wouldn't be a bad idea. I thought the dealer I got it from did a trans service on it but when I called them to check they said they did not after all, so that's problematic within and of itself.

Originally Posted by JSH

No mine has never slipped. I always log every, drive and wait till the transmission fluid. has warmed up before asking anything of it.

This is going to sound odd but I have been experiencing it only when cold. I'm doing some density fueling tuning so I need the engine to be as cold as possible, I'm asking some unusual activity from the engine and transmission I know... Worse because I have to basically lug it in high gears at low speeds so I can get cold engine data at full fuel rail pressure.

Regardless, I ended up finding an anomaly recently that was affecting everything including shifting. I had a failing CMP sensor and it was throwing off everything including making the transmission hunt a ton. After replacement, I ran it and haven't really found anything worth note as far as slippage is concerned. May be coincidence, or maybe not, but I don't think a service would be too bad of an idea on the transmission. I'd really like to do a flush and switch over to full AMSoil signature ATF, but I'd probably be looking at a good solid $600 or so to do it considering the fluid is super expensive.. it might have to wait a bit until I can get the time to be able to do that.

[djctoto]

If you do a flush be sure to use the Amsoil ULV (ultra low viscosity) fluid. It is expensive but it does lower trans temps. To really get all the fluid changed out of the A10 torque converter it requires draining/filling/running the repeating the process so it can cost several hundred in fluid alone. If I read you signature correct you have a 2017 which comes with a steel pan. Mine is a 2019 and had a steel pan on it as well. Later models, not sure when they started but 2022 and later perhaps came with an aluminum pan which holds slightly more fluid. Not sure how much but more for sure. I bought an aluminum pan and had a drain bung and plug welded to the front and I also epoxied a heat sink to it to help dissipate heat. The factory procedure for filling to the right level is a royal PITA and the A10 is finicky about the level of fluid. If I had to do it all over I'd get the pan ready to install with the mods, with a new filter and gasket on hand. Then I'd carefully remove the old pan and filter and capture all the fluid to measure exactly how much came out. Then I'd also measure the difference in capacity between the pans. Now it'd be simple to install the new filter/gasket/pan and put in the same amount of fluid that came out plus the difference in pans. From here it will be a hell of a lot easier to drain and refill a few more times to flush out the old stuff.
Now that I've done mine I won't need to level the car, brake the trans to get it hot and remove the pan to change the fluid. I can now drain it and put the same amount back in and be done. You'll probably need 20 quarts to flush it completely.
I made a video which shows the pan with the mods I did to if you're interested.

[ZLRob]

Originally Posted by djctoto

If you do a flush be sure to use the Amsoil ULV (ultra low viscosity) fluid. It is expensive but it does lower trans temps. To really get all the fluid changed out of the A10 torque converter it requires draining/filling/running the repeating the process so it can cost several hundred in fluid alone. If I read you signature correct you have a 2017 which comes with a steel pan. Mine is a 2019 and had a steel pan on it as well. Later models, not sure when they started but 2022 and later perhaps came with an aluminum pan which holds slightly more fluid. Not sure how much but more for sure. I bought an aluminum pan and had a drain bung and plug welded to the front and I also epoxied a heat sink to it to help dissipate heat. The factory procedure for filling to the right level is a royal PITA and the A10 is finicky about the level of fluid. If I had to do it all over I'd get the pan ready to install with the mods, with a new filter and gasket on hand. Then I'd carefully remove the old pan and filter and capture all the fluid to measure exactly how much came out. Then I'd also measure the difference in capacity between the pans. Now it'd be simple to install the new filter/gasket/pan and put in the same amount of fluid that came out plus the difference in pans. From here it will be a hell of a lot easier to drain and refill a few more times to flush out the old stuff.
Now that I've done mine I won't need to level the car, brake the trans to get it hot and remove the pan to change the fluid. I can now drain it and put the same amount back in and be done. You'll probably need 20 quarts to flush it completely.
I made a video which shows the pan with the mods I did to if you're interested.

Yeah I haven't gotten the chance to check the fluid level yet unfortunately. I definitely need to especially given that from the factory the level may have been problematic and I don't know the history of that level or what color it's looking like right now. As of this moment I upped the line pressure in reverse and in 7th but I haven't gotten the chance to try out the revisions yet. Hopefully the tune just needed some tweaking, otherwise the next step will definitely be transmission fluid swap out and a filter as well. I should probably buy get to buying a filter to have it on hand for when I do need to get to doing a service.

[ZLRob]

Just figured I'd update this as service to others:

All of these issues I had? Resolved... What was it you ask? The transmission fluid being overfilled by the dealer at the time when they did the flush, at 9,100 miles (it has 51K now mind you), the fluid level was over by .3 quarts and that's ALL it took to make the tranny slip in 7th and lag full engagement into reverse when cold. It sounds stupid, but that's what the issue was.

Upon correcting fluid level, shifting quality improved, things were not as harsh engaging 7th gear slip is gone and the transmission seems infinitely happier now that things are correct. I'll be doing a service here soon, but as of right now, I'm very happy with the end result and the notable improvement in performance.

[radz28]

Excellent news, Rob! Like we already discussed - it's been EMPHASIZED to me that correct fluid level is essential for these things. I didn't think an over-fill, like you found, would have as profound effect as you experienced, but I guess it's not a surprise. Thanks for sharing, because this is quite helpful.

Regarding the OP's video: That's a great video and a lot of helpful information. Some comments that come to mind (take them or leave them):

• * Caution anyone looking for upgrades or improvements research their year and model. I'm not finding consistency with some of this stuff, so what we see for a '19 ight not work on a '21, for example
• My car (2020 ZL1 built in 07/19) has an aluminum pan
• My car's thermostat is in the valve body (attached). From my research, and I could be missing something, there is no other thermostat for the tranny in my car. The NGD it I'm installing eliminates the function of the OEM thermostat anyways.
• Make sure if you're replacing that OEM Cooler Line Manifold that there's a thermostat in there. My car's manifold has NO indication of a thermostat in this housing, so if your car has a similar set-up to mine, changing to that by-pass won't help much if the OEM one is still in the VB

[ZLRob]

Originally Posted by radz28

Excellent news, Rob! Like we already discussed - it's been EMPHASIZED to me that correct fluid level is essential for these things. I didn't think an over-fill, like you found, would have as profound effect as you experienced, but I guess it's not a surprise. Thanks for sharing, because this is quite helpful.

Regarding the OP's video: That's a great video and a lot of helpful information. Some comments that come to mind (take them or leave them):

• * Caution anyone looking for upgrades or improvements research their year and model. I'm not finding consistency with some of this stuff, so what we see for a '19 ight not work on a '21, for example
• My car (2020 ZL1 built in 07/19) has an aluminum pan
• My car's thermostat is in the valve body (attached). From my research, and I could be missing something, there is no other thermostat for the tranny in my car. The NGD it I'm installing eliminates the function of the OEM thermostat anyways.
• Make sure if you're replacing that OEM Cooler Line Manifold that there's a thermostat in there. My car's manifold has NO indication of a thermostat in this housing, so if your car has a similar set-up to mine, changing to that by-pass won't help much if the OEM one is still in the VB

You know speaking of the thermostat I really gotta wonder where they are located on 17's like my own. I wonder if they are still in the valve body or if they are in the cooler line or somewhere else entirely. GM went and changed so many things from year to year and have no indication of it apparently, which makes for really annoying and frustrating inspection, service, and repair procedures on these cars.

Also to anyone else reading this, you need to make sure you are at your cars exact operating temp (when your thermostat is set to open) before you pull the plug. For my own 17 it was set to 203 degrees F*. My temp to pull the plug was exactly within this specific range.

For others you may be able to pull it around the 170-180 mark as some of the later Z's ran a cooler thermostat.

It is worth noting that the overfill on mine was making the transmission run a full 4* hotter, because the moment I pulled the standpipe level plug my temp went from 203* to 199* immediately after. I checked these temps immediately after reinstalling the level plug and was surprised by just how much a difference this what otherwise would be considered trivial difference in level made.

[KingLT1]

Originally Posted by ZLRob

Just figured I'd update this as service to others:

All of these issues I had? Resolved... What was it you ask? The transmission fluid being overfilled by the dealer at the time when they did the flush, at 9,100 miles (it has 51K now mind you), the fluid level was over by .3 quarts and that's ALL it took to make the tranny slip in 7th and lag full engagement into reverse when cold. It sounds stupid, but that's what the issue was.

Upon correcting fluid level, shifting quality improved, things were not as harsh engaging 7th gear slip is gone and the transmission seems infinitely happier now that things are correct. I'll be doing a service here soon, but as of right now, I'm very happy with the end result and the notable improvement in performance.

I would never have thought that little amount of extra fluid would cause those issues.

An old trick with GM transmissions (at least older stuff like the 4l60) has been to slightly overfill them to remedy any kind of shift flare or slip...especially after installing a higher stall converter.

[JSH]

Originally Posted by ZLRob

You know speaking of the thermostat I really gotta wonder where they are located on 17's like my own. I wonder if they are still in the valve body or if they are in the cooler line or somewhere else entirely. GM went and changed so many things from year to year and have no indication of it apparently, which makes for really annoying and frustrating inspection, service, and repair procedures on these cars.

Also to anyone else reading this, you need to make sure you are at your cars exact operating temp (when your thermostat is set to open) before you pull the plug. For my own 17 it was set to 203 degrees F*. My temp to pull the plug was exactly within this specific range.

For others you may be able to pull it around the 170-180 mark as some of the later Z's ran a cooler thermostat.

It is worth noting that the overfill on mine was making the transmission run a full 4* hotter, because the moment I pulled the standpipe level plug my temp went from 203* to 199* immediately after. I checked these temps immediately after reinstalling the level plug and was surprised by just how much a difference this what otherwise would be considered trivial difference in level made.

Has your TCM been tuned? By way of example, mine has adjusted base pressure, Line pressure, Offset pressure, all adjusted for the setup, as well as TCC setup and shift times adjusted.

Does it slip mild throttle, wot only, partial, which gear? Was the level inspected?

[ZLRob]

Originally Posted by KingLT1

I would never have thought that little amount of extra fluid would cause those issues.

An old trick with GM transmissions (at least older stuff like the 4l60) has been to slightly overfill them to remedy any kind of shift flare or slip...especially after installing a higher stall converter.

Yeah since these 10 speeds don't need to be so tall in gearing due to having so many gears they get pissed off if they are under or overfilled even a little bit, when I called NGD they told me to inspect the fluid color and level before anything, but they never emphasized the level being exact like the way they had to RadZ28. I really didn't think it would be that big of a deal, but apparently it is.

Originally Posted by JSH

Has your TCM been tuned? By way of example, mine has adjusted base pressure, Line pressure, Offset pressure, all adjusted for the setup, as well as TCC setup and shift times adjusted.

Does it slip mild throttle, wot only, partial, which gear? Was the level inspected?

It was slipping at mild throttle like accelerating up to speed and wide open. Initially it was only slipping when really cold under wide open throttle in 7th but then eventually it started not liking it so much that those symptoms started emanating themselves in mild throttle when hot as well in 7th, but it was only ever in that gear and in reverse when cold.


TCM got tuned, as I finally decided to get it unlocked so I can get it tuned and is now adjusted in all of the areas that you highlighted in your examples. I think it's because 7th gear is 1:1 it expects to see precision in fluid level and values, especially since the transmission now sees more power in that gear than it has ever seen in stock form.