th400 crack or casting?

[wage92]

Okay i just picked up this th400 and noticed that there may be a crack in it, but i cant tell if it is actually a crack or a casting mark. I searched some other sites and found out its pretty common for th400's to crack in this spot...What do you guys think?

 

[76zimmer]

from what I can see it looks like it could be the casting, but if it was going to crack that would probably be the area.
You could sand it down with some 150 to see if its just casting flash overlap, or if it goes deeper...if it does, grind it and Tig it!

 

[wage92]

okay will check that out. But having it tig'd will be strong enough?

 

[76zimmer]

What does the inside of the bellhousing look like?
You could mag it to find out if the crack is there or if its just the casting.

I'm sure a competent welder could handle the job, but it may be cheaper to find a used case.

 

[4X4HIGH]

That is from the casting.

 

[wage92]

it is a casting! pics are hard to see, but it dissappeared pretty quickly.

 

[Deuling]

run it!!

 

[wage92]

run it!!

after it gets painted

 

[4X4HIGH]

after it gets painted

DO NOT paint the transmission, they are made of aluminum for a reason.

 

[wage92]

to dissipate heat? or do you mean something else?

Ive seen lots of people paint trannys

 

[76zimmer]

GM had a service bulletin out in the early 80's to paint the case if there was a porosity problem, can't remember what type of paint it was though, some special GM number made by somebody else though.

Bare aluminum is a great heat conductor, but black works well too. And if you have a good cooler it don't really matter if you do or don't.

Deburring the case is a good idea to prevent stress risers which can lead to a crack, but it takes away a slight amount of cooling ability from the case...all those little risers are like heat sinks to get rid of the heat in the case.

 

[wage92]

sounds about right. Im aware that heat can be a problem with transmissions but ive seen plenty of people paint them, and it will have a good cooler so i think it will be fine.

 

[454Sub]

Yep, I sanded mine down and smoothed it, then painted it. So much easier to wash off, now that porous aluminum isnt sucking every bit of dirt up. Wont hurt it in the least.

 

[wage92]

what kind of paint did you use? just like oil based enamel or something special?

 

[76zimmer]

I just hit mine with satin black.

 

[4X4HIGH]

to dissipate heat? or do you mean something else?

Ive seen lots of people paint trannys

Yes, to dissipate heat. When you paint it it will now trap heat in. Black does help extrude heat BUT not painting it at all is best. They were NEVER painted from the factory for this reason and i'm talking EVERY manufacturer.

 

[boz42]

You may be correct I don't know.


IMO

1. My take would be they were not painted cause they don't rust, so that is an unnecessary to paint them & not painting saves money.

2. I have run a lot of painted & un-painted transmissions & even built some polished transmissions for customers. Before & after temperatures were never different.

3. Ford re-mans come from Ford painted grey.

4. If in a mud truck, paint would be a plus. As stated earlier it cleans up much easier. Mud all over the outside of a transmission case is no good.

 

[supermotard750]

I always wanted to polish a trans case, i think i have the patience for it an it would look pretty awesome

 

[boz42]

Lot of trouble for something you can barely see. Of course there are a lot of things like that on a rig.

 

[wage92]

well i have problems. i want to paint everything, i redid my chassis and painted every bolt.