My wife'* car recently began not downshifting into first when she stops. Doesn't do it cold, just hot.

I've replaced the shift solenoids and both pressure sensors which didn't fix the downshifting issue but it really improved upshifting.

I have ordered the forward servo so gonna try that next... considering replacing the secondary pump as well...

Any suggestions? Thanks

It'* always been serviced every 30k.

I'll also add my wife drives 165 miles a day to work so it mostly all highway driving.

Welcome to the forums!
If you have not done so already, would highly recommend having the transmission scanned for any stored codes & see what presents itself code wise.
What transmission fluid has been used in serving? The latest is Dexron VI (6)
Ever cleaned the accumulator 1-2 and 2-3 bores?

Thanks!

No codes present in the system current or pending. I have always used Dextron III as that is what the owners manual calls for and religiously changed it every 30k.

This last service about 800 miles ago I let the parts guy talk me into Dex 6 as it said on the bottle it'* backwards compatible and that'* where my troubles began. 100 miles later it began acting up. I immediately drained the 6 and put 3 back in it. It continues acting up...

No I have not cleaned the accumulator. I guess I could drop it, clean it and replace the seals. I dunno. I just need to figure this out. Can't afford to replace the car nor a $1500 rebuild. It was perfect before the fluid swap, that'* what annoys me.

Thanks

I installed a transgo shift kit:

It is possible that the Dex 6 started cleaning too good and dirt blockages may have happened even in the valve body IDK, but using the 1000 grit emery cloth dipped in ATF, used in a circular motion on the inside of accumulator walls, may be worth a try.

I wonder what happens if she comes to a stop, puts the car in park, then back to Drive. Does that end up in 2nd or 1st?

It stays in neutral, or better put, does nothing. doesn't engage drive unless I feather the accelerator a little. once the rpm'* come up a little bit it bangs into first.

I've talked to several people who are in the industry and they all have said the 4T65E is one of the few transmissions that engages the "Forward band" in first gear only, which gives you first gear. Without that band engaging it will appear as if its in neutral and will do nothing, which is pretty much what it does..

Once it engages first it will shift the rest of the gears perfectly fine, it doesn't slip at all and functions normally once first engages... TCC and downshifting from 4th, 3rd work as they should. Most of the time if I make it downshift while in second it will downshift to first but you also have to consider the RPM'* are up and so is pump pressure.

It seems to me that at idle the pressure is to low to engage the forward servo which engages that forward band, which give me first gear. Either that or the forward servo seal is leaking..

I ordered a new forward servo, all AcDelco parts to replace it and see if its a bypassing/leaking issue with it. If thats not it I guess I'll try the secondary pump next.........

I dunno, I just gotta get it figured out. I was hoping there would be a GM tranny guy on here that could help me out..

thanks

Ouch.

Is this the Rendezvous? How many total miles are on it?

Pan drop is about 7 quarts and full capacity is 13.4 quarts so I'll call it 14 so the math is easy.

Looks like you're going to do by accident what I'd suggest next: drain/fill with some more Dexron 3. By my count you were about 50/50 Dexron 3 and 6 after the service where you moved to 6. Then you drained and filled with Dexron 3 which put you at 75/25 . Or perhaps the solenoids were replaced in an additional drop/fill so 87.5/12.5 . Dexron 6 would seem unlikely to be an issue by itself any more.

I agree with Soft Ride, changing to Dexron 6 may have broken something loose. Also could be something unrelated to Dexron 6 and just happened because of a fluid change or something. Fluid change equals air bubbles passing through things that are otherwise 100% immersed.

Either way, the symptoms I find interesting is that the transmission shifts better with new solenoids. Solenoids generally either work or not work, with potential for leaks to make them marginal. When they are marginal they usually present a problem no matter the fluid. From what I see here they weren't doing that before the Dexron 6. Maybe the old ones were gunked up or something? Or maybe a combination of that and Dexron 6 breaking some other junk loose.

Then there'* the part where otherwise it works just fine. That tells me that the pump is probably not the problem.

These together make me think that perhaps some junk is in a servo bore somewhere and the higher pump pressure of being above idle overcomes the junk one time.

How much clutch dust is in the pan when you service?

Kind of thinking out loud here, hope it helps.

Ok first and foremost, I appreciate any and all suggestions and help. I have beat myself up trying to figure it out myself hence my post here so "Thank you" for offering up any and all suggestions...

I am sure I am not the first one to experience this issue and working with you guys I just might be able to get it figured out for others to see to fix theirs. Who knows lol.

Yes, this is the Rendezvous.. These pics were taken a week ago after I detailed it for her.





You asked about the total mileage on the car.... keep in mind, my wife drives all highway to work and back....165 miles a day. So it'* all easy miles. Ready for this?? 254,000

In regards to the fluid... I have faithfully changed the fluid every 30K and the filter every other fluid change.... I have never found "Metal" in the pan and the amount of clutch mud on the magnet has always been way less then I see when I service my Super Duty tranny. The magnet is always pretty clean. The fluid is always bright red and clean...never smells burnt or anything like that. Again, this transmission has performed flawlessly for 254,000 miles and only became a problem after putting Dex 6 in it.

Now I will add that when I did the service 800 miles ago, the Dex 3 I removed was in excellent condition, my brother even commented that I was wasting money by changing it.... I filled it up with the Dex 6 that the parts guy recommended... 100 miles later it began acting up.... I drained the Dex 6 and it was very dirty...very dark red but did not smell burnt at all. (I think the Dex 6 did some major cleaning to become so dirty so quick.)
I refilled it with Dex 3...

I drove it to work for a week while it was acting up, putting about 150 miles on it and the Dex 3 was bright red, not dirty at all and still looked like fresh clean fluid.
I figured I'd try replacing the shift solenoids and pressure sensors figuring maybe one of them failed so I drained it again, dropped the cradle to gain access to the side cover and replaced all the solenoids.
Put it back together, refilled it again with new Dex 3 and I still have the issue.

In regards to the solenoids improving the shifting... The car does have allot of miles on it and over the years the shifting had become, lets say sluggish. The new solenoids cured that sluggish shifting.. After the new solenoids and pressure sensors the shifting was again crisp, like it was when the car was much newer...

But as for my issue, It works perfect cold, once it heats up is when I loose first gear. If I feather the accelerator, bang, it pops in first. Something is not right lol.

I am waiting for the new Forward Servo to arrive and I'll change that out and see if it makes any difference... I will buy a master rebuild kit and attempt to rebuild it myself if I have to but I really dont think it needs a rebuild, I strongly suspect like you guys are saying, it'* trash in something or something simple..
For the most part, transmissions usually give you lots of warning that there is a problem, they rarely just fail all of the sudden. They slip, or make weird noises for a while before they just fail so I dont feel it needs rebuilt....
I guess what I'm getting at is, this car has had an easy life, never towed anything, always been serviced on time and has spent most of its life on the interstate running 70 mph... It does have allot of miles on it but they are easy miles....

Its a great car so I am reluctant to give up on it and will keep trying to fix it.. Hopefully somebody very knowledgeable in the 4T65E will chime in and help an old man out here lol.

Wow looks great in pictures!

Sounds like you are doing what i would. By your description of dirty-looking Dexron 6 sounds like it did indeed break a bunch of junk loose.