4T65 sluggish start, then a lurch and a bang

[The_Eric]

My friend/shopmate had an 2008 Grand Prix with a pile of miles. Once it's warmed, sometimes when leaving a stop sign it will be sluggish, as if it were in 2nd gear, then a harsh bang and it takes off and shifts through the gears normally. What is this and is it externally fixable (through the pan or side cover)?

It's had the Trans-go shift kit for the P1811 code (or at least the bits accessable through the pan installed, which fixed that issue, but this is new..

 

[Chris142]

Fluid level ok? If it is I would service it and put in a qt of trans-x. Stuff actually works sometimes.

 

[Astro14]

Start with new fluid at the proper level. Go from there.

 

[14Accent]

My mom's old '07 Impala started doing this exact thing around 150k, and last I saw it had 201k and was still doing the same thing. It didn't happen every time, maybe 1/10 once warm.

I drove the car for a while, and could always feel when it happened. As soon as I felt the "drag", I'd let off the throttle and wait for the bump down to first, then take off. Never an issue.

 

[Slick3914]

Start with new fluid at the proper level. Go from there.

Agreed, a pan drop and filter replacement would be a good idea.

 

[meep]

This to me feels like something is sticking. If it were me, I’d start like @Astro14 said with new fluid and filter. if no difference I would add a partial dose of lubeguard red, which IME has been helpful in helping sticky things move. Add the least amount needed to make the difference.

 

[The_Eric]

Fluid level is fine, filter was replaced with the shift kit which was not long ago. I've had a few 4T65s do this but their owners never cared enough to address it.

 

[clinebarger]

A worn actuator-feed-limit (AFL) Valve Bore can cause 2nd gear starts HOT., Then once RPM is raised, AFL pressure can come up just enough to shift the 1-2 shift valve & bang into 1st gear.

 

[The_Eric]

Who's kit do you recommend? To address the worn bore?

A worn actuator-feed-limit (AFL) Valve Bore can cause 2nd gear starts HOT., Then once RPM is raised, AFL pressure can come up just enough to shift the 1-2 shift valve & bang into 1st gear.

 

[ripcord]

A worn actuator-feed-limit (AFL) Valve Bore can cause 2nd gear starts HOT., Then once RPM is raised, AFL pressure can come up just enough to shift the 1-2 shift valve & bang into 1st gear.

My son was given Mamaw's Buick to drive when she gave up her keys, and the 4T65 in it would do this once in a while. It was pretty mild. I told my son he needed to baby it when starting from a stop or Bad Things would happen. Sure enough, a few months later he punched it from a stop a and blew it up. This was at the peak of the used car prices so I pulled the tranny and sure enough the pan was full of gear and spline fragments. I had my transmission guy tear into it. He said it, quote, "Looked like teenage driver in there," and recommended we find a different transmission to use as this one was all torn up and would need a ton of hard parts replaced.

 

[gregk24]

Years ago my parents owned a 2005 Chevy Uplander (minivan) with this transmission. It started this behavior around 120K and felt HORRIBLE when it happened. Jolted the whole car like you had been rear ended. The transmission ended up needing a rebuild but that did not solve the issue. The shop ended up installing a higher stall torque converter and after that it never happened again until 175K when they traded it.

 

[14Accent]

A worn actuator-feed-limit (AFL) Valve Bore can cause 2nd gear starts HOT., Then once RPM is raised, AFL pressure can come up just enough to shift the 1-2 shift valve & bang into 1st gear.

This is exactly what my mother's '07 Impala would do. Happened randomly for over 50k miles before I sold it, last I heard it was still doing it and still humming along just fine.

 

[clinebarger]

Who's kit do you recommend? To address the worn bore?

TransGo part# 4T65-AFL

 

[The_Eric]

Thank you much sir.

 

[DejaVue]

Yep, "they all do that." It was happening more and more (once every 200 miles?) on my 4T65 with 75k or so on it. New filter and fluid (and magnet) noticeably helped. Though it still happened once in a while, and not as bad. The old fluid looked rather good, by the way.

Some vehicles with that trans have a service bulletin from GM to add an extra magnet inside the trans pan. 2013+ or so vehicles apparently already have the two magnets instead of one.

 

[MalibuRam65]

My friend/shopmate had an 2008 Grand Prix with a pile of miles. Once it's warmed, sometimes when leaving a stop sign it will be sluggish, as if it were in 2nd gear, then a harsh bang and it takes off and shifts through the gears normally. What is this and is it externally fixable (through the pan or side cover)?

It's had the Trans-go shift kit for the P1811 code (or at least the bits accessable through the pan installed, which fixed that issue, but this is new..

take it to the dealership get that transmission service and whatever other services needed to bring that Grand Prix back to Factory Specs

 

[The_Eric]

take it to the dealership get that transmission service and whatever other services needed to bring that Grand Prix back to Factory Specs

I appreciate the thoughts, but that's not going to happen. We're a a small little repair shop, so generally speaking, capable enough of handling our own repairs. But to be honest, I'm not even sure if he wants to invest any kind of money in his "beater with a heater"... All I can do is suggest repairs and let him make his own decisions.

 

[Edited]

I have the same issue with my 08 Impala (110K mi) From my reading on the issue, there's a really good chance it's the PCS (Pressure Control Solenoid) which is known to go south on these transaxles. Apparently you need to remove a portion of the case to get to it as opposed to a pan drop while doing the filter or first portion of the shift improvement kit (accumator springs). I've done a filter/fluid change out and added an extra magnet to the pan - along with the spring kit in the accumulator. Plan to replace the PCS when I get a safe amount of downtime to tear into it. For now, I've just been easing into acceleration and letting off the brakes slowly after each stop. Haven't had many slams to report since getting comfortable with it.

 

[Slick3914]

Two bottles of Lubegard Red seems to have helped my 2000 Impala but I’m also pretty gentle with it on takeoff.

 

[CoachRoss07]

I have the same issue with my 08 Impala (110K mi) From my reading on the issue, there's a really good chance it's the PCS (Pressure Control Solenoid) which is known to go south on these transaxles. Apparently you need to remove a portion of the case to get to it as opposed to a pan drop while doing the filter or first portion of the shift improvement kit (accumator springs). I've done a filter/fluid change out and added an extra magnet to the pan - along with the spring kit in the accumulator. Plan to replace the PCS when I get a safe amount of downtime to tear into it. For now, I've just been easing into acceleration and letting off the brakes slowly after each stop. Haven't had many slams to report since getting comfortable with it.

This. 100% correct! PCS is definitely the cause of this. Located on driver side of transmission in Valve body. Engine Cratle will have to be dropped down to fix this issue. If one has a good code reader or TECH 2 you can watch the amperage on the sensor zero out when this happens. A simple engine restart and it's back to normal until the next spazz.

There are many many many TSBs on this issue back when. I've replaced many of them.