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Old 12-12-2021, 03:48 PM
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ZeGermanHam ZeGermanHam is offline
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Default TH400 case rib repair?

I picked up a freshly rebuilt TH400 for my '66 yesterday for a very good price. Only had around 500 miles put on it before the previous owner removed it in favor of an overdrive transmission.

When I got it home and looked things over more closely, I noticed that one of the ribs at the rear was cracked off. I'm thinking it's probably not a big deal for me since my car will mostly be a cruiser and I don't plan on spending much time at the drag strip. However, can this sort of defect be repaired? I don't have the piece that cracked off.



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Old 12-12-2021, 03:56 PM
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That is freshly rebuilt? You could clean that missing section real good with brake cleaner and fill it in with JB weld, the stuff that cures fast and file/sand it down.

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Old 12-12-2021, 04:10 PM
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I would use it as is, nobody will see the missing bit when mounted.

Is it an Olds/Buick switch-pitch ST400 or a 1970 and later TH400 (dual connections on the electrical connection)?

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Old 12-12-2021, 04:25 PM
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Smooth it out with a rattail file and some sandpaper to remove any stress risers that may cause it to crack.

I’m sure the chances of it cracking are slim but it can’t hurt to remove the sharp edges and the sharp dip in the fracture. The engineers added those stiffening ribs for a reason, so at least if it were mine I would spend a little time there just for peace of mind.

Adding JB Weld isn’t necessary nor would it add back any strength to that stiffening rib.

Run it.

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Old 12-12-2021, 04:46 PM
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Quote:
Originally Posted by SRR View Post
That is freshly rebuilt?
"Freshly" rebuilt in terms of mileage but not time since rebuild. The previous owner had it rebuilt about 10 years ago when he was finishing up a complete restoration of his GTO. Once his car was put back together, he took a 500 mile road trip in it, but discovered that a TH400 combined with 3.90 gears does not make for good fuel economy. So he had the TH400 removed and put a 200-4R in its place, and the TH400 has sat in his garage for the past decade with only 500 miles on it since rebuild.

Quote:
Originally Posted by Kenth View Post
I would use it as is, nobody will see the missing bit when mounted.

Is it an Olds/Buick switch-pitch ST400 or a 1970 and later TH400 (dual connections on the electrical connection)?
Tag on the side says "74-PD-8824", so I'm assuming it's a 1974. The kickdown solenoid has two prongs.

Quote:
Originally Posted by b-man View Post
Smooth it out with a rattail file and some sandpaper to remove any stress risers that may cause it to crack.

Run it.
Good idea.

Thanks everyone for confirming what I suspected, which is that although those ribs are there for a reason, it won't pose a problem in my street-driven application. That's good to know. I'm not concerned with appearance in this location, so it sounds like smoothing it out and running it is totally fine.

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Old 12-12-2021, 07:22 PM
Formulas Formulas is offline
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Some T-400s have a pressure switch in the valve body for spark control
So 2 prongs for them as well as switch pitch trans

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Old 12-13-2021, 03:32 AM
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Quote:
Originally Posted by b-man View Post
Smooth it out with a rattail file and some sandpaper to remove any stress risers that may cause it to crack.

I’m sure the chances of it cracking are slim but it can’t hurt to remove the sharp edges and the sharp dip in the fracture. The engineers added those stiffening ribs for a reason, so at least if it were mine I would spend a little time there just for peace of mind.

Adding JB Weld isn’t necessary nor would it add back any strength to that stiffening rib.

Run it.
Exactly. That small section missing isn't going to hurt anything.

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Old 12-13-2021, 09:18 AM
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Just sand/grind it smooth you'll be fine. Since it's OUT...remove the speedo plug and see what color drive gear it has....MUCH easier to replace NOW than after you install it.

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Old 12-13-2021, 12:15 PM
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Quote:
Originally Posted by 67Fbird View Post
Just sand/grind it smooth you'll be fine. Since it's OUT...remove the speedo plug and see what color drive gear it has....MUCH easier to replace NOW than after you install it.
That is a great idea, and an excellent reminder for me since the whole time I was driving the car with the previous trans before restoration began, the speedo was always way off. Now is my opportunity to finally have a speedo that reads correctly.

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Old 12-13-2021, 07:38 PM
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Run it as it is

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