Broken transmission - 1989 Reatta - LN3 3800

[turbokinetic]

Hey folks. I have a question and some pictured from an online friend. He has a 1989 Buick Reatta, which has a LN3 3800 and a 440T4 transmission.

The car had been driving nicely, and then one day the transmission started slipping. Owner found massive oil leakage, and topping up the transmission will allow it to drive, but it pours oil.

Upon investigation, he found the transmission case is broken at the final drive end. The end of the case is fully detached, as if it wanted to become a 4T65E with removable final drive cover!

The transmission still moves forward and reverse. The differential function smoothly, you can spin one wheel and the other smoothly spins the other way with car jacked up.

Car has no modifications and the owner is definitely not doing burnouts with it.

Has anyone seen this before? Any ideas what could have caused it?
Thanks,
David

[RJolly87]

Wow.

I know the 4T60 (which I believe is a tweak of the mentioned unit) supposedly didn't have the best of lubrication in the differential, so when one wheel would spin, it would wear the pin on the pinon gear, and eventually it could start backing out. When it backs out, it essentially starts cutting the casing in half around it, until it cuts all the way through, or gets thin enough that it breaks on its own.

There is no telling the actual cause until the tranny comes out and is taken apart. I also think the transmission will still work until the pin works it's way completely out, at which point power stops going to the wheels and the car drops where it sets, other concerns aside.

[MattStrike]

^^ +1, Roll pin that holds the differential pin in place either fell out, or broke, and allowed the diff pin to slide out and hit the case and wear through until it cracked. Common problem across 440t4, 4t60, and 4t65.

Unfortunately you will need a new case to fix that on the 440t4. I usually flatten the ends of the roll pin so it can't work it's way out when I rebuild the 4t65's.

[turbokinetic]

Thanks for the insight guys. I will forward this to the car's owner.
Sincerely,
David

[J Wikoff]

I had a diff pin back out. It would make a clicking when I turned from a stop. The rebuilder told me it almost wore through the case and he was amazed it didn't crack.

[Jrs3800]

Yup, diff pin walked out... sadly it's a solid case and doesn't have separate diff cover..