New symptom- 4T65E

[JustN89]

Good afternoon folks. A new symptom has popped up with the 4T65E in my 2005 Impala that I'm hoping the collective genius on this board can help me with. Here's a little background on the transmission:

- Fluid changed at 109k miles
- Car purchased at 117k miles and within a few weeks after purchase, we began to notice the hard 2-3 shift commonly associated with the P1811- Max Adept, Long Shift transmission code.
- Fluid and Filter change with TransGo shift kit install at 119k(ish) miles. Process drained 7.5 quarts, filled up with MaxLife ATF and Lubegard Red
- Currently has 125k miles with no hard shifts during that time

The new symptom that popped up is that, from a standstill, the car has what I can only describe as a lurch with a single *thunk* feel and sound when accelerating at more than 2k RPM in first gear. I'm sorry for the poor description, but it's really hard to film and describe. Please note that the transmission is not shifting, and it only occurs when I accelerate at an engine speed of roughly 2k RPM. The problem is more consistent and noticeable when facing uphill at the stop.

I've checked fluid levels and condition and it checks out okay. I ran the transmission through the gears and observed the movement of the engine and outside of the shift into Reverse, the mounts are holding it rock solid (I do have a video of this that I can upload if needed). Also, a disclaimer, the dash doesn't have a tachometer. I use the Torque Pro app to read RPM on acceleration. If it would help, I will do my best to catch the issue on camera but the issue is more noticeably tactile than it is audible.

Thanks for the help!

 

[zvm77us]

contact Dave, the expert on everything 4t65e
http://www.tripleedgeperformance.com/Contact-Info.html

very nice person and a pleasure to guide you even if you don't purchase anything

 

[clinebarger]

From your description, It could be one of two things.........

1. The Input Clutch apply piston is worn, This will cause a intermittent neutral condition from a stop.....Revving the engine a bit will build enough pressure to seal the Input piston leak & the piston will slam into clutch pack & the car will take off.
*This is well documented issue with higher mileage 4T65E units, GM-Hydramatic was having issues with assembly line workers rolling the Inner Input Clutch Apply Piston Lip-Seal. To "correct" the assembly issue.....They started using shorter lips on the seals. Unfortunately this allows for little to no wear of the piston before problems with low pressure Input Clutch apply arise. Aftermarket seal kits come with long-lip seals like used in the previous 4T60/440-T4 units.

*I replace the apply piston as well, New OE ones are dirt cheap!!



2. It's taking off in 2nd gear intermittently, The most common cause for this is from low Actuator Feed Pressure from a worn Actuator Feed Limit Valve Bore OR debris in the valve bore is hanging up the valve.
*The AFL valve acts as a pressure regulator for the Shift Solenoids, If the valve sticks in a low feed state or is leaking bad enough......The Shift Solenoids will no longer be able to actuate the Shift Valves properly. The unit will default to 2nd gear 'til the AFL pressure comes back up.....Again revving the engine a bit will cause it to abruptly downshift back to 1st gear.

I guess the question is.....
Does it rev a bit then move?
Does it feel sluggish, "Thunk"....Then take off?

In the end, Doesn't really matter as BOTH should be corrected during an overhaul!

 

[SatinSilver]

If you're in DFW take it to clinebarger above to work on it for you if he's willing. You'll be in excellent hands. Send him a PM and go from there. At least that's what I'd do.

 

[Silverado12]

FWIW I had a 2004 Impala and heard before I bought it that the transmission needs frequent servicing. From what I heard, it's a good transmission but the car it goes in weighs more than the typical front wheel drive GM car. I would service the transmission every 25K miles. Disclaimer: all hearsay but seems accurate.

 

[JustN89]

Thanks for the replies everyone!

Originally Posted by clinebarger
From your description, It could be one of two things.........

1. The Input Clutch apply piston is worn, This will cause a intermittent neutral condition from a stop.....Revving the engine a bit will build enough pressure to seal the Input piston leak & the piston will slam into clutch pack & the car will take off.
*This is well documented issue with higher mileage 4T65E units, GM-Hydramatic was having issues with assembly line workers rolling the Inner Input Clutch Apply Piston Lip-Seal. To "correct" the assembly issue.....They started using shorter lips on the seals. Unfortunately this allows for little to no wear of the piston before problems with low pressure Input Clutch apply arise. Aftermarket seal kits come with long-lip seals like used in the previous 4T60/440-T4 units.

*I replace the apply piston as well, New OE ones are dirt cheap!!



2. It's taking off in 2nd gear intermittently, The most common cause for this is from low Actuator Feed Pressure from a worn Actuator Feed Limit Valve Bore OR debris in the valve bore is hanging up the valve.
*The AFL valve acts as a pressure regulator for the Shift Solenoids, If the valve sticks in a low feed state or is leaking bad enough......The Shift Solenoids will no longer be able to actuate the Shift Valves properly. The unit will default to 2nd gear 'til the AFL pressure comes back up.....Again revving the engine a bit will cause it to abruptly downshift back to 1st gear.

I guess the question is.....
Does it rev a bit then move?
Does it feel sluggish, "Thunk"....Then take off?

In the end, Doesn't really matter as BOTH should be corrected during an overhaul!


I would say that it only feels sluggish because, if I don't accelerate too fast, it doesn't do it so I take off rather slowly. If I take off even kind of normally, it responds fine but you get the thunk. There's no free rev before it takes off, thankfully. Thanks for the input!

 

[Trav]

Just going to throw this out for the heck of it, its probably not you problem but anyway...
Engine performance issues many times appear as transmission issues and clunks bangs and other such noises can be inboard cv joint related. these cars are known for thinning out the cv grease to almost oil at around 120K and even though the boot is still intact the joint is toast. MAF sensor issues are also common.

 

[clinebarger]

Originally Posted by JustN8


I would say that it only feels sluggish because, if I don't accelerate too fast, it doesn't do it so I take off rather slowly. If I take off even kind of normally, it responds fine but you get the thunk. There's no free rev before it takes off, thankfully. Thanks for the input!


You may want to look at the engine mounts a little closer, Also the lower control arm bushings as well. Your right at the mileage this stuff starts wear out/fail.
And the CV joints like Trav pointed out.

To eliminate the 2nd gear start as a possibility......Pull the shifter down into Manual 1st/D1, This will bypass the shift valve sequencing & lock it in low gear.
*Do the symptoms remain?

If the symptoms go away while taking off in D1.....Do a drain & fill & add some Lubegard Red (follow the instructions!). I don't normally recommend additives, BUT a sticky valve is an instance I recommend this product.

 

[JustN89]

Naturally, it's been two days since the last time this issue happened so I haven't been able to test it further. Next time the issue comes up, I'll try to accelerate from D1 and see if it happens. My last D&F (roughly 6k miles ago) included appropriately proportioned Lubegard Red, but I'll do another D&F and maybe that will help.