Building a stronger 6 speed hydramatic auto trans

[DevilSonic89]

This is what we have. The 6T30
140HP/129TQ as per gmpowertrain.com. Of course, those numbers reflect the output of 1.8, but its an idea.


Can it hold more???? And can this be mated with the 2010 ecotec 2.2 cobalt?? Im asking this because the 6T30 is just a smaller lighter version of the 6T40 and the similair version 6T45. The 6T40 was paired with the 1.8 cruze and the 2008 - 2010 Malibu 2.4 inline 4. The malibu had a stock hp of 165

 

[DevilSonic89]

..........

 

[ThatTmoGuy]

ZOMG! No responses in an hour must bump thread!!!!

just to put this out there, most people with the auto 1.8 are not looking at power mods, let alone enough power mods to need to upgrade the trans.

 

[DevilSonic89]

ZOMG! No responses in an hour must bump thread!!!!

just to put this out there, most people with the auto 1.8 are not looking at power mods, let alone enough power mods to need to upgrade the trans.

thats y i put it in ur guys thread. cuz i think im the only one thats this crazy lol

 

[sx sonic]

We don't want your 2 pedal contraption in OUR thread ;p

Wait a bit and You'll get some good responses with time. Is this trans used in any other platforms? (I think Cruze is different). If so you might find some good stuff browseing thru another forum. Preloader found a lot of good stuff about the manual trans from the european Vauxhall forums where the M32 had been out longer.

Also, have there been any auto trans failures on the forum? DP blew his trans with NOS but I'm not sure if there's been any other failures. If there are some that failed then you could get a guage on the weak points that need beefing up.

 

[vento]

My final goal has been ~160hp from the 1.8. Not too worried about it grenading. But a limited slip diff setup would be nice, I know they made them for some automatic J-bodies back in the day.

 

[OD3X1]

Chances are upgraded clutch packs are all that's needed. If you get real serious about power and want to use nitrous a torque converter with an anti-balloon plate might be needed. GM autos typically have stout enough main shafts to handle most of what can be thrown at them.

 

[Maddmatts]

GM's auto's have traditionally been underrated. BNR's Cruze test-mule is pushing ~40% more than the 6T40 was rated for without any immediate issues.

 

[american_tuner]

As being an automatic car myself, I am interested in your finds.

 

[TN1.4T]

So, has anyone decided how much power and torque the stock 6t40 can hold reliably? I've been looking, but can't seem to find an answer.

 

[Sneakerfix]

Only way to actually find out is to push it.

 

[Blue Moon Sonic]

Yeah that is definitely true. Just make sure to have a spare just in case.

 

[ChrisJ]

So, has anyone decided how much power and torque the stock 6t40 can hold reliably? I've been looking, but can't seem to find an answer.

Yeah, a long time ago.

As per GM :

Maximum Engine power ( hp/kW ) 180 hp ( 134 kW )
Maximum engine torque: 177 lb-ft (240 Nm)


That's how much power a 6T40 can handle reliably without concern. Anything outside of those figures could shorten the life of the transmission.

 

[Blue Moon Sonic]

If you guys can get the 6t45 transmission in the 1.8, there is a shop in Indiana that can rebuild them and make them stronger. I'd ask zbencur about it since he has the most details on it.

 

[ChrisJ]

Squeeze an 8L90 in it and call it a day.

 

[MyLonewolf25]

Squeeze an 8L90 in it and call it a day.

Yes but would it even fit?
Either way
Short ratio that thing
Awesome rally/autocross/drag trans

 

[Tesseract_Indeed]

So my 6t40 Transmission has been slipping, shifting very abruptly in pseudo-manual mode and overall acting very strange. I checked under the car and sure enough, the transmission is leaking fluid from the driver's side. I drive it in pseudo-manual 99% of the time because I like the control and connection with the car. Because the transmission is leaking, I think that it is just low on transmission fluid and that is what is causing issues, so replacing any broken seals and draining and refilling the trans should fix it. Just thought I would see other people's opinion as well.

I bought my 1.4t LT sedan bone stock with about 139,000 miles on and have put another 15,000 in the last year and a half. (lots of driving). The only mods I have so far are snorkel delete, K&N hi-flow air filter, bypass the bypass, and zzp midpipe and cat-back exhaust. I also removed the front license plate mount and lower grill to get maximum airflow to the intercooler.

The transmission is rated for up to 180hp and 177 lb-ft torque (shoutout to ChrisJ above). Is there any way that I am pushing those limits as of now, to account for the slippage and abrupt shifting? I have never been to a dyno to see, as it is beyond my budget.

Here is an article I found that says the ECU might need to be re-flashed up to three times by a mechanic to get it to sort itself out. It also says that the magnetic solenoids in the transmission might tend to go bad and can be tested for conductivity and easily replaced. Thoughts?

Working on A 6T40 Transmission? You Will Want To Read This!

 

[Maddmatts]

I agree that fixing the leak will likely solve all of your shifting issues. If it's leaking from behind the torque convertor, the earlier 6T40's had input shaft seals that were known to leak and there's an updated seal for it.

You didn't list a tune with your mods so you're likely still pretty close to the original power output. The only mod doing anything for you is the downpipe and you're probably not seeing the full benefit of it without a tune.

The transmission's rating isn't a hard limit though. Automatics can usually hold far more before breaking anything. After passing that point, the biggest limiting factor is dealing with the added heat and reduction in long-term reliability.

The solenoids are only easily replaced with the transmission removed from the vehicle. There's not a lot of room between the valvebody and the radiator. Also, replacing the solenoids requires a value relearn procedure on the TCM that can only be done by someone with the right software.