3t40 transmission reliability

[seabass1858]

In the stock form with the stock motor, how long should my 3.1/3t40 last. I have 310k on it now and drive it every day and it shifts like it did when it had 88k on it when I got it. Everything is original except the interior needs tlc.

1990 GT 3.1/3t40 310K miles all original

[Money pit Beretta]

If those are miles and KM's the you are getting close to setting the standard. Mine was doing fine at 213k before I lost the car. That was a 90GT also!

[1988GTU]

310 is great for that combo! I wouldn't expect it to go upto 400k tho. Start planning to do some costly repairs or buying another DD.

[seabass1858]

The Firestone guy is amazed at the mileage when I take it in for its yearly collant flushes, tire balance /rotations and alignments. I use amsoil low viscosity synthetic atf and mobil1 full syn 10w-30 since 88k miles.

[Koots]

The Firestone guy is amazed at the mileage when I take it in for its yearly collant flushes, tire balance /rotations and alignments. I use amsoil low viscosity synthetic atf and mobil1 full syn 10w-30 since 88k miles.

That's why you're car is doing so well LOL

Most people go the entire life of their vehicle and not change the ATF filter. Then they wonder why the transmissions are crap, when it's probably got the showroom fluid in it and the differential(s).

I would look into rebuilding your transmission in the next few years, if you intend on staying with the automatic. A good, experienced rebuilder should be able to optimize the transmission and make it handle power better and last longer.

[seabass1858]

Ill do the rebuild, I have done it to plenty of autos right on my kitchen table C3, C6, TH350, E4OD. The only thing I dont do is tranny flush or coolant flush, alignments, tire mount and balance. and Firestone does the rest, I have lifetime balance, alignment and rotation on all 3 of my cars, 1983 silverado 10 305/ 700r4 340k (20MPG highway), 2002 jeep liberty lifted with 4.10s and 32s 45RFE (best crysler tranny IMO and 23MPG highway) 1990 chevy beretta 3.1 3t40 Daily driver for me because I get 31MPG AVG and drive 100miles plus a day. All three are taken care of but my aunt is driving my silverado now because she gave her mazda 3 to her son for his new family.

[keiffith]

Mine had 270k on it before it got low on fluid and I Burt out reverse, but 1-3 where still fine.

[seabass1858]

So it isnt like I have a freak of production so they are reliable with care is what I am understanding. I don't dog it at all but I will say is that the weapon-R intake helps fuel miliage a good bit I wouldnt have replaced it with a weapon r its just my original box broke and the dealer wanted 347$ for a new replacement and no junkyards have it.

[Koots]

I would also make sure that the TV cable is properly adjusted. I know it's the main killer of the 700R4 (4L60), because of the low line pressure and excess heat.

Sufficient line pressure/rise, auxiliary cooling and regular filter and oil changes are all these transmissions need to stay alive under most conditions. I'd look into a "shift kit" like the one from Transgo. I've got one, but I'm just trying to get the car street legal right now, so I can actually start driving it. Once it's dialed in, then I will change the fluid/filter and install the shift kit. It should help this old transmission last a few more years

[seabass1858]

I got a trans-go for my liberty and love it and do you think I can make 500k with that advise

[ifixalot]

This is nice to hear that trans can go a long time. I have had an issue with the one in my mini van. The clutch pack seals harden with age
and it'll take a full 20 seconds for the trans to go into drive after being shifted. I added some trans seal conditioner and it cured the problem.
So if you experience this delay to go onto gear, there is a bottle of fix for that.

[seabass1858]

it just boils down to care and maintenance from what I hear

[1990BerettaGTZ2.3L]

If it's the same tranny as what was in my 94 grand am quad 4 sohc car it was a 4 speed auto, and my 95 grand am quad 4 dohc car with 4 speed and my 95 z26 with the 3100 4 speed auto then yeah it's a tough almost bullet proof tranny at least mine were cause I didn't go a day with out beating my ga's and they never starting slipping or anything like they stayed brand new, and my z26 I did a bunch of burouts with didn't hurt it as far as I know shifted fine

[Koots]

If it's the same tranny as what was in my 94 grand am quad 4 sohc car it was a 4 speed auto, and my 95 grand am quad 4 dohc car with 4 speed and my 95 z26 with the 3100 4 speed auto then yeah it's a tough almost bullet proof tranny at least mine were cause I didn't go a day with out beating my ga's and they never starting slipping or anything like they stayed brand new, and my z26 I did a bunch of burouts with didn't hurt it as far as I know shifted fine

The 3T40 is a 3-Speed, it's the same transmission as the THM-125C, but with GM's new nomenclature:

3-How Many Gears It has
T-Transverse mounted
40-Meaningless value scale to represent it's TQ handling

40 is primarily for cars, 60 is for 1/2 ton trucks and big cars/small trucks, 80 is for the 3/4-1 Ton trucks. The newer 6-speed autos in the late model HD's is a 6L90E.

The 4T60E, which I believe you might have had, is a great transmission, but not bulletproof, I think they have a 250TQ limit rating, or something like that. Don't quote me on the last part though LOL

[Money pit Beretta]

edit.

One thing I had go bad on my 3T40 was the shift solenoids. There are electric and you can get to them easy(they are on the valve body). I lost 1st-2nd and 2nd-3rd. Had to rev it up and dump it into gear to get it home(I was stuck in 3rd). Lucky for me I only had to do that once.
My trans lasted 213k, that was when a guy ran a red light and kill my car.
Oh and I have a stock air filter box and the tube to the TB. But you are better off with a WAI anyway.