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6T70 6-speed auto; has anyone swapped one into 3800?

April Thompson

April Thompson

New member
Has anyone ever swapped in a 6T70 6-speed automatic gearbox into a Series II/III-powered car? I can't find out whether the bellhousing is compatible, or if there's a retrofit adapter kit. Any thoughts? (and I know about the weak pre-2009 gearboxes)
 


i would figure on wanting the 6t75/80

but yes it will bolt up to the GM 60* v6 "FWD" bellhousing bolt pattern just fine as long as your not using the ford trans case
 
Fivefingerdeathpunch said:
Would be a cool idea, but there is no way to control the transmisson.
Click to expand...

There is a way to control it though.
Buying a standalone trans controller.
They're out there for these units.

The 6T80 is a beast… Would probably hold up to a 500whp turbo setup pretty well.
Seeing as though its in a giant fwd Caddy with 450hp.
 
iirc the newer transaxles are direct solenoid control without all the low/high pressure spool/shuttle valves of the older 4t hydramatics

quite a different control architecture
 


iirc im not sure which trans it was but I thought Will from Overkill had done a 6 speed behind a 3800?

More gears would be nice esp for a daily driver!
 
But 3800s are 90* V6s; that's what I was curious about...
And the 75/80s sound more stout, so anyone doing a conversion would be better off than the 70's 313 hp/280 lb-ft limits!
 
Are both 3.8L & LS4 using the same bellhousing pattern? Because apparently the 6T70/5 should bolt up; I've been on the net a little more, and there are folks doing LS2/4 & 6T75 adaptations, as well as F40! One bloke put that combo in his Fiero! But I'm reading that as long as the Metric bolt pattern's there, it should​ work... though the starter for 5.3L might need an adapter...
 


I would NOT recommend a 6T70 6 speed transmission. I had one in my Saturn Aura with the 3.6L and I disliked it compared to the 4 speed. It seemed to want to shift at merging speeds, or any time I needed to move, and was not quick to shift. Also, Look up the 3-5-R Waveplate issue, which happens on a lot of them. I had it happen at 98k, but many people have had it happen as low as 25k on their cars.

One positive with it though, is that you could do paddle shift with it. While not as exciting as driving a manual, if you've never driven a manual before, I hear it can be fun to use.
 
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