2004 LeSabre/4T65 GM hard shift when hot

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Dec 7, 2012
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Dad has a 2004 LeSabre, your typical 4T 65E and a Series II 3.8. Beautiful car runs great and shifts great about 120 K on the clock. After you've been driving the car for a while, out of nowhere the car will start to shift very hard almost as if it is commanding full line pressure. When this happens in the shifts will actually make the tires chirp sometimes. If you throw the car in neutral turn the key off and restart the engine it'll drive and shift fine for another half hour or hour. I think I've vaguely remember seeing about this and the fix was some sort of Mr. shift kit or maybe a couple of new springs in parts of the valve body or there is a cover you removing in the trans and a couple of new springs go in. Years ago I remember reading something about the transmission computer detects a ever so slightly longer shift than what it calls for so it thinks there's an issue and goes into a limp mode and commands full line pressure. Maybe some of you experienced GM techs or other folks know exactly what this is? I don't think the trans is failing though because until this happens the thing shifts beautifully and gives no indication whatsoever of any issues. Fluid and filter has already been changed and the trans has been maintained very well.
 
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Joined
Sep 6, 2018
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Raleigh NC
Yes, this is fairly common, I've done it on my Grand Pa beater and it's been running for years with no issues. I believe it's caused by a combination of pump wear, actuator seal wear and accumulator piston wear causing slightly slow shifting and triggering full pressure, just as you say. I think it's mainly jamming accumulators that cause the adapt to max out and still be unable to consistently shift quickly enough. Put in the parts of the TransGo kit you can put in from the pan, and get and replace the accumulator pistons as well: the center bores wear oblong and allow them to cock. When reinstalling the accumulator body, make darned sure the metal tubes that go into it are inserted fully, in the correct position all the way along and secure so they can't work their way out. That would kill the transmission. Other than this possible pitfall it's an easy job.
 
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Oct 28, 2014
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On the road Midwest
I have 3 Lesabres. Nice cars. All of them have the Transgo shift kit which comes with very nice & clear instructions. While you're in there, spend an extra $10-12 and install sonnax part # 84532-01k differential lube tube retainer https://www.transmissionpartsdistri...Y5SSjYe844JzacFqQX3l-k8KDqBoCAIwQAvD_BwE I don't remember where I found the info, but the 6mm bolts on the accumulator housing that you'll need to undo to replace the springs (illustrated above) torque to 100 in. lbs....If you want to make FUTURE fluid changes much easier, put on a new ZZP aluminum pan with a magnetic drain plug. Make sure you check the (new) drain plug for tightness prior to putting fluid in. Mine was shipped just about finger tight. https://zzperformance.com/collections/3800/products/4t65e-aluminum-transmission-pan Feel free to PM me if you have any ??? (I've done this several times)
 

redhat

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Dec 7, 2012
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Just wanted to reply and say thanks for the info. Will be performing this on Dad's car come spring (it is cold and winter now in WNY). Thank you.
 
Joined
Jan 21, 2012
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No. California
I am glad I ran across this. I have my father's 2004 with 46,000 miles on the car. I always like preventative maintenance for preventing future possible problems especially in automatics. I will be doing this come summer on my Le Sabre.
 
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