4T65E Harsh Shift (assuming shift pressure is too high)

[Matthew Jeschke]

I'm reaching out to those of you with experience building transmissions. I have a 2006 Buick Lucerne. Was my folks vehicle since new and always exhibited this behavior. Intermittently it will give a VERY harsh shift, like dumping the clutch in a manual transmission. The behavior is such that I'm now on my third set of motor mounts at 215k miles. I suspect the pressure regulator circuit has an issue because all shifts are harsh not just one. Unfortunately, I have to remove the driver side axel (in the least) to get the service pan off where the valve body is.

The car is at a point where I have to drop the service pan to change fluid / service the transmission. Any advice from the savvy transmission builders out there? Maybe my theory is wrong. Information I have is it's doing it in all gears, although TCC seems to operate normally (different circuit? I think...)

 

[RoadTrip]

I’m not a transmission rebuilder, but rather an owner of two of these transmissions in ‘05 Buicks.

This dreaded behavior eventually happens to all of these 4T60 & 4T65 transmissions.

You are correct in that it is a problem with the overall pressure circuit. GM only put one small magnet inside the transmission pan to catch shavings, which was overwhelmed by 100k miles.

The rest of the shavings were drawn to the electromagnetic field in the first solenoid they came to: the main line pressure solenoid.

The metal shavings jam the operation of the valve, not letting it close as far as it should and keeping the line pressure too high.

Even with the factory TSB of adding a second magnet, the damage to the solenoid is done.

Doing a pan drop, magnet cleaning, adding the second magnet and flushing the trans (yes flushing to get the torque convertor fluid changed) with new Dexron trans fluid will help.

A side note: If you need to take off hard from a stop, put the gear selector in L1 and there will be no thunk as you leave since this position engages an additional torque band.

Installing a shift kit will mask most of this annoying behavior. However, the real repair is replacing the damages main line pressure solenoid.

 

[strutaeng]

Good advice from @RoadTrip

I don't know anything about these transmissions, but just curious: Are the valve bodys and hydraulics similar to the 4L60e variants? My 99 Silverado 4L60e developed a "harsh" shifting with the infamous P1870(?) code. I believe it's related to the TCC valve wear on the valve body bore and a common issue. The ECU basically commands maximum line pressure when it detects the fluid pressure drop on that circuit, or something like that. The transmission was pretty high mileage when that happened though, maybe 225k?

IDK if @NickTransmissions works on these units?

 

[Matthew Jeschke]

@RoadTrip thanks, as I had thought, the pressure circuit has a fault. Great tip though... I'm going to service it, put in a new filter (used but good fluid from my truck) and will have a trans shop flush it. Maybe that'll take care of part of the issue.

I should mention it's done this since my parents gave me the vehicle with 100k miles on it. I think it did it to them too but they aren't good about noticing such things. The motor mounts were shredded from I am pretty sure harsh shifts, when I got the vehicle... there's a good chance it's been doing it since new. I digress though, if damage is done it's done. At some point I added copious amounts of Lucas Transmission fix which seemed to help the problem but still at random it will act up.

@strutaeng thanks! Yeah from what I'm told they are very similar. I have ATSG guides for both 4L60E and 4T65E and they look to share a lot of similar architecture. Although, I want to cry the valve body is SUPER hard to get at with trans in vehicle on 4T65E. Otherwise rebuilding the pressure circuit would be somewhat trivial.

 

[Matthew Jeschke]

I'm ordering the transmission pan magnet to add two more. Curious what type of glue they use to hold them to the pan?

 

[Matthew Jeschke]

I finally got around to dropping the pan. INSANE, I've never seen a pan so clean as that. The magnet had little of nothing on it. I'm actually impressed with this transmission. I'm at just shy of 220k miles and it looked soooo clean! I even went longer than I should have (100k miles?) between changing the fluid. Although the random shift clunks are annoying.

after brake clean and whipping the magnet. There was a little slime but not much...

For good measure I painted the outside of the pan.. and placed a second magnet... The original magnet wasn't glued or anything. It was just placed on inside the pan. So I did the same with the additional magnet, making sure it wasn't in a place that wouldn't impede the filter.

 

[Hunt4Gold]

Any luck? I have a 1999 Tahoe 4x4 with 114,000 original miles and had the P1870 code pop up. Checked the trans fluid, clean and red, no burnt smell. Went ahead and drained it, replaced the TCC solenoid, the two upshift and one down shift solenoids, installed the Sonnax pinless accumulator, changed the filter and filled with all new fluid. There was no debris at all in the pan when dropped. It worked fine for about a week but now getting the P1870 code again after it warms up. I've put a ton of work and parts into this thing but I'm burnt out and thinking of selling it if I can't get this code to stop popping up.

 

[Matthew Jeschke]

Any luck? I have a 1999 Tahoe 4x4 with 114,000 original miles and had the P1870 code pop up. Checked the trans fluid, clean and red, no burnt smell. Went ahead and drained it, replaced the TCC solenoid, the two upshift and one down shift solenoids, installed the Sonnax pinless accumulator, changed the filter and filled with all new fluid. There was no debris at all in the pan when dropped. It worked fine for about a week but now getting the P1870 code again after it warms up. I've put a ton of work and parts into this thing but I'm burnt out and thinking of selling it if I can't get this code to stop popping up.

This thread is about a 4T65E transmission... I think you have a 4L60E, I've actually a bit more experience with the 4L60E.

@NickTransmissions is a genius with them though so whatever he says takes precedence over my comments, should he chip in.

This code is triggered by excessive transmission slip. People typically focus on the torque converter clutch when they see this. I'm not sure if this vintage 4L60E can tell if it's clutch packs or a slipping TCC. I think that requires the input shaft sensor? I digress...

What size tire do you have and what's your rear end gear ratio (I assume 3.73?)? I run around 2000 RPM at 75MPH in locked up in 4th on the highway (I'm on 285/70/17 w/ 3.73 gears). Curious what you're seeing?

Also does your cluster have a transmission temperature gauge? Curious what temps you're seeing?

When you're experiencing harsh shifts...

How does 1st to 2nd feel? (1st and 2nd don't use the TCC)

2nd to 3rd?

3rd to 4th? (3rd and 4th can use the TCC)

I'm not sure if the transmission boosts line pressure to prevent slip in event of this code resulting in harder shifts... There's a lot going on here I don't have experience to know how it behaves in certain falures.

Long story short, I'd point my finger at the valve body, especially if your fluid is clean as you mentioned and there's no clutch material. If you've already replaced some solenoids then this isn't too much harder although you need to be very detail oriented (putting things back EXACTLY as they came apart). I'm not sure what a shop would charge to do it... I'd hope not too much as it's fairly straight forward on our trucks.

Some people block off the partial apply circuit when they install a new valve body. Transgo sells a kit for this (I disabled mine in my tune but think I still have that transgo kit in my garage). I also like the plastic checkballs from Sonnax as well. Some people modify the separator plate too.

@NickTransmissions is probably much more helpful than me when it comes to parts.

Factory triggers for P1870

 

[Hunt4Gold]

This thread is about a 4T65E transmission... I think you have a 4L60E, I've actually a bit more experience with the 4L60E.

@NickTransmissions is a genius with them though so whatever he says takes precedence over my comments, should he chip in.

This code is triggered by excessive transmission slip. People typically focus on the torque converter clutch when they see this. I'm not sure if this vintage 4L60E can tell if it's clutch packs or a slipping TCC. I think that requires the input shaft sensor? I digress...

What size tire do you have and what's your rear end gear ratio (I assume 3.73?)? I run around 2000 RPM at 75MPH in locked up in 4th on the highway (I'm on 285/70/17 w/ 3.73 gears). Curious what you're seeing?

Also does your cluster have a transmission temperature gauge? Curious what temps you're seeing?

When you're experiencing harsh shifts...

How does 1st to 2nd feel? (1st and 2nd don't use the TCC)

2nd to 3rd?

3rd to 4th? (3rd and 4th can use the TCC)

I'm not sure if the transmission boosts line pressure to prevent slip in event of this code resulting in harder shifts... There's a lot going on here I don't have experience to know how it behaves in certain falures.

Long story short, I'd point my finger at the valve body, especially if your fluid is clean as you mentioned and there's no clutch material. If you've already replaced some solenoids then this isn't too much harder although you need to be very detail oriented (putting things back EXACTLY as they came apart). I'm not sure what a shop would charge to do it... I'd hope not too much as it's fairly straight forward on our trucks.

Some people block off the partial apply circuit when they install a new valve body. Transgo sells a kit for this (I disabled mine in my tune but think I still have that transgo kit in my garage). I also like the plastic checkballs from Sonnax as well. Some people modify the separator plate too.

@NickTransmissions is probably much more helpful than me when it comes to parts.

Factory triggers for P1870
View attachment 481775

that gives me a little more to go on. it does have 3.73 gears and P265/70-17 tires although it was doing this with the factory wheels and factory tire sizes also. Not sure on the temps as it has no trans temp gauge and it didn't show that option on my code reader. I'm seriously thinking of trading it off or selling it outright as i no longer have the time or patience for this...

 

[Matthew Jeschke]

Yeah it gets frustrating that's for sure. Does it still drive okay? or does it act like it's slipping (ex. are you holding ~2000 RPM at 75MPH on the highway?)... If it's just shifting hard due to excess pressure drive it till the transmission goes out, which could be a while... My thread here is similar (same?) issue and it's been going like that for 120k miles.

What I do, is I lean into the gas and shift it by tipping the throttle in (say 30% ~ 40%) then releasing it (0%~10%). When I release the throttle it shifts (not under as much toque). Then I do it with the next gear. Once you get the hang of that it's quite easy. Although a little frustrating knowing the underlying issue hasn't been resolved.

Where are you located? I'm near Tucson Arizona. I actually have a spare 4L60E in my garage...