Transmission life expectancy

Hello,
I have bought a '98 Riviera with a blown engine (ventilated block). I will be buying a junkyard engine for it. My concern is that the car has 220K miles and I'm wondering if I should put a lower mileage transmission at the same time, which wouldn't be a great deal more effort.
I know there are many variables and unknowns, but what are the chances that the transmission that is in the car now has some life left beyond its current 220K miles? All I know about it is that it was running when the engine threw a rod. ATF does not look bad.
Thanks.

My transmission was (carefully) rebuilt at 98000 miles, now has 323000 on it. Mostly highway.

Anything past 200K is a bit of a stretch in terms of trans life.  I've seen them go 300K without a rebuild, however, I'd try to get a lower mileage replacement or have a trusted shop rebuild it while everything is out.  Just makes sense while you're in there.

DEMonte1997 wrote:

Anything past 200K is a bit of a stretch in terms of trans life.  I've seen them go 300K without a rebuild, however, I'd try to get a lower mileage replacement or have a trusted shop rebuild it while everything is out.  Just makes sense while you're in there.

I am thinking the final drive in my transmission would be the weak link, at 98K it was replaced as part of the overhaul but I know that even in the 4T65 with the hardened gears/splines those things take a beating by a hooded executioner... That said, my transmission is not making any end-of-life grumblings. I change the fluid about every 45-50 K with Dexron 6 after about 150K miles. Last couple changes there has not been even appreciable clutch mud in the fluid in the pan. First change after the rebuild there was some, but it looked normal for a 50K maintenance change though. 50K is probably too early for a change, although with the highway driving I do, over time I think I kinda cook the fluid and the change is a good time to check and tweak the mechanical adjustments. I set things to factory specs more or less. All that said -- Dexron 6 does not cook anything like Dex 3 did. Dex 3 might as well have been used fast-food-restaurant cooking oil in comparison to what I see at a Dex 6 change.

My original lasted to 151k miles. I abused the car (daily driving, racing, towing) quite a bit back then. I changed the fluid a few times, about every 50k miles. It was rebuilt by AAMCO and reinstalled.

I removed the engine for rebuild at 246k miles, did not remove the transmission. I continued to abuse the car until around 260k miles; now I drive it fairly normally, not daily. Other than the TC lock-up clutch failing, the transmission has not given any signs that it might fail, now at 278k miles.

Things to consider:

Most parts on the Riviera will last ~150k miles, the engineered expected life of a '90s GM car. More mileage is possible with proper maintenance. There are exceptions, such as the 3800 engine, which should last 200-300k miles or more.

The 4T65E has gained a reputation for random failure. There is a chance it can go at anytime, or it could last another 50k miles. I wouldn't bet on it going much further than that.

You can remove/install the engine from the top. I found this to be quite easy compared to dropping the cradle, which is how AAMCO removed my trans. I don't know if the trans would come out the top side with the engine (may need to do them separately).

Much of the cost of rebuilding the trans is removal/installation. I believe it was around $1000 in labor back in 2007. If you have the means to remove it yourself, a rebuild at your mileage makes good sense, imo. If you do, I recommend replacing the TC clutch material. Also a good time to replace engine & transmission mounts.

Good luck. Let us know how it turns out.

Thank you guys.

I found an engine and trans with 89K miles that I will be transplanting into that car.

I've done a few TH400s but more modern transmissions seem a bit intimidating to me.

While you are in the mess a DIY shift kit is a nice mod. It has made my 230k trans a bit happier and crisper