Besides axles and mounts, there doesn't appear to be a solid road block to swapping in a 6t70 transmission from a 2010-2015 GM SUV. The only info I can't easily find are the spline counts for the input/output shafts and the bolt pattern on the 6t70 bellhousing. The 6t70 appears to have been designed around the high feature v6. So the question is, do the 3400 and 3800 engines share their bolt pattern with the high feature v6? Do they share output shaft spline counts?

 

The high feature v6 bolt pattern is different than the 3800 etc pattern. Id imagine one of the 6t transmisions had to have come with the 3800 style pattern at some point though as a lot of GM engines used that pattern.


I don't know anything about the 6t70, but why can't you just use axles from a 9G Impala with this trans? If they aren't a drop in, maybe its possible to build a hybrid axle like the 5th gens do using pieces of the old and new axle?

Mounts shouldn't be a big deal either as theyre fairly simple to make if no OEM one bolts up to both.


My big question is how youd get the electronics to work out. Do they have a standalone available that runs the 6t?

 

I'm still looking into the computer thing, the malibu and equinox these trans came in may have had separate Transmission Control Modules so maybe I can trick one of those. I'm also thinking the axles will be easy as I know of a custom driveline shop downtown. And worst case with the mounts is I make hybrid mounts using them from both cars. Thanks for the help, I'm kind of only spit balling right now, but when the trans eventually goes I'll pursue this route.

Edit: looking into the 9G impala it came with the 3.5 bolted to the 6T, so do the 3.5 and 3.4 share bolt patterns? Sorry I'm not great at figuring this stuff out.

 

IMO resolving that needs to be the #1 priority if you're actually serious. All of the mechanical stuff is 100% fixable with enough money - even bolt patterns can be adapted with a custom plate if needed. You can take mating parts to any respectable machine shop and they can make something work.

But the thing I've never seen pulled off is the control side of it. Obviously the factory pcm can't do it as its only able to run 2 solenoids / 4 speeds. Im not entirely sure your thought about using the donor car TCM works either as that has to communicate with the engine PCM to include a handful of data. I do not believe its just a wire up conversion to get them to talk as the old pcm doesn't have the necessary outputs.

It does look like some places offer an adapter - Zero Gravity claims theirs works with the 6t70 and only requires TPS and engine rpm inputs, but its not clear if you'd need a standalone controller on top of that or how it would work. Regardless its very expensive - almost $900 just for that.


Why the big desire for a 6 speed anyways? Just seems like it can potentially be extremely expensive for something with not much upside. Wouldn't take much to get to the price of a whole running driving 9G impala.

 

This is if the trans fails before the car is totaled, cause itll happen eventually. She's only got 70k so I've got awhile to figure out how to make it happen.
I want a 6 speed because why not honestly, it would be a cool way to make the car quicker, especially up the big hill climb outside of town.

 

IMO the why not depends on the cost. If you could cobble it together for not much more than the cost of a junkyard trans, it would be neat to have something a bit different. My guess is that isn't possible as it doesnt appear that anyone has ever done that swap with an engine running this pcm.

If you end up with $5k and tons of hours of labor between mechancial and electrical adapters and getting it working right, that makes for a pretty good why not, especially since the performance gains won't be anywhere near what that in power mods wouldve made through the 4 speed.

TBH I don't think the small performance gain will be anywhere near worth all the labor and cost of a pioneering effort like that.

If you really want more performance, it would be much more cost effective to spend that time on a L67 swap with some bolt ons or fabbing up a turbo for your 3400.

Regardless how steep that 1st gear gets, its never going to be all that quick with a NA 3400 turning it.

 

Fair point, get more HP first. Which is what the other thread I started is on, hopefully I can find info on the injector thing.