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4t65e to 4t65e-hd swap

kc199

kc199

New member
I am replacing the engine in my 99 GT and thought I might as well do something with the transmission while it is easy to get to. Found a 4t65e-hd locally out of a wrecked GTP with only 82k miles. Would this be a direct replacement for the 4t65e? If not, want might I run into that is different?
 


The gearing is different... 2.93 iirc, so you'd have to get the PCM flashed for that I think. I could be wrong though.
 
just remove the passengers side axle, diff housing and diff.

Inspect diff for wear, if okay, install those three pieces on your car.

Other than that, the HD would be a downgrade. It has a lower final drive.
 
matt5112 said:
just remove the passengers side axle, diff housing and diff.

Inspect diff for wear, if okay, install those three pieces on your car.

Other than that, the HD would be a downgrade. It has a lower final drive.
Click to expand...

Might just go that way then. I have a local transmission shop that will go through the tranny and inspect it for $100. Definitely don't want to downgrade lol
 
Stock transmission aren't great no matter how to look at it.

Its just which one is less worn.

3.29's are the ideal gear ratio it seems.

And thats what your GT transmission comes with.

The differential's have the same gear ratio (3.29).

The transmission uses the chain to over or under drive the internals.

Thats why there are so many different potential combinations.

HD diff is better, but unless you can get it for really cheap, its difficult to suggest.

Namely because either diff does not take well to abuse.
 
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