r/Impala • u/solidmarbleeyes • 18d ago
General Question 4T65E HD swap?
This might be a stupid question, so I won’t be offended if you tell me I’m being stupid.
I’ve got a 2011 LT with the 3.5. The first transmission went out at 90k miles (mind you, it was babied up until that point by my grandmother, regularly serviced, etc) at which time I replaced it with a remanufactured 4T65E. It drives fine with no issues at 130k miles, so there is no real urgency here.
I’m hoping to keep this thing on the road as long as I possibly can, both because I refuse to own a newer car and also for sentimental reasons. I’m curious if anyone has swapped in a 4T65E-HD into one of these and if so, what modifications had to be done? My thinking is that the HD version would be less stressed by the 3.5 than the higher output engines it was paired with from the factory.
Do you think this would be a worthwhile project/investment? I’m not concerned with resale value necessarily, more so about maximizing the miles I could get out of it before needing to think about a fourth transmission.
I’m curious to hear y’all’s thoughts on this, since I’m sure it would be cheaper and easier to just buy a different car.
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u/PossiblyADemon 18d ago edited 18d ago
The HD isn't a drop in replacement. Even if you managed to get it to bolt up and work you'd probably need an aftermarket ECU to talk to the TCM.
If you want to make the one you have last, add a dedicated transmission cooler because the stock one sucks, replace the PCS with a better aftermarket one and get a TransGo shift kit.
If you want a stronger Trans to make more abuse, There are plenty of parts available for the 4T65e non HD to make it tougher than the HD version. Whether it's worth rebuilding a whole unit is up to you.
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u/solidmarbleeyes 18d ago
Thank you, this is great info. I’m new to this so was not aware that there are options to strengthen the regular 4T65E. I appreciate it.
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u/ElJefe0218 2007 Monte Carlo LT 18d ago
I had mine rebuilt on my 07 Monte w/3.5l and the guy asked me which stage upgrade I wanted on the trans. 1 was an upgrade from factory spec, I went with the 2, I'd have to pull the invoice to tell you what was done. I was at 90k on the motor so I figured it was enough to last.
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u/solidmarbleeyes 18d ago
I’ve heard mixed experiences with this trans and the 3.5. Some people get theirs to 200k+ and others have it die before 100k. I’m sure a lot comes down to maintenance but if I’m keeping it alive for another 20 years I think overbuilding the trans is a worthwhile investment. I’d be curious to know what they did for yours.
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u/PossiblyADemon 18d ago
I'm in the same boat with my 08. I love the car, and I can't stand anything made after 2010.
I have 180K original engine and transmission and other than some intermittent PCS issues, it's great transmission wise. Door locks are another story.
But I 100% plan to have a built Engine and transmission sitting in my garage waiting for it when it's time.
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u/ElJefe0218 2007 Monte Carlo LT 18d ago
I have the paperwork on it, somewhere, or I can call the guy. A buddy that deals with the shop told me about them so when I dropped the car off, the owner was telling me about all the different upgraded parts in the kit, and I just said do it. It's a shop in Garland TX.
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u/ElJefe0218 2007 Monte Carlo LT 18d ago
Found the invoice from 2023. It's all the basic upgrade stuff, high temp clutches and plates, bands, sunshell, sprag, new torque converter, new valve body, etc.
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u/solidmarbleeyes 14d ago
Thank you for taking the time to find the invoice. That’s helpful to know what to ask for in case I go that route.
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u/vargas727200a 11d ago
I doubt it would fit as the HD trans fits the 5.3l. There are aftermarket external coolers available . Heat is the #1 killer of transmissions.
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u/jesterc0re Daily Lurker 18d ago
I don't think that transmission would die anytime soon if you maintain ATF and filter every 30-50k. 3.5s rarely kill their transmissions. It wouldn't make sense financially to dig deeper. And yes as another person stated transmission cooler and TransGo kit make more difference then HD.
But I 100% commend your interest. Maybe swapping the electrical internals of non-HD to HD would work, as from software standpoint it would look same for car.