TH400 cooler line fittings

[pismorat]

I am doing the 383 to 454 swap on my truck and doing the TH350 to TH400 at the same time. The stock cooler lines on my truck don't thread right into my tranny, the TH400 fittings are too big. And if I switch over to the TH400 cooler lines, they are too big to thread into my radiator. What do I need to make this work?

 

[sweetk30]

as far as i know all gm stuff this era is all 5/16 line.

was your 400 missing the adaptors in the tranny case ?

and you can try swaping over the th350 adaptors to the th400 and go from there.

some of the later stuff went 3/8 but this is newer body style stuff.

 

[diesel4me]

It is rare,but some TH400's came with 3/8" tranny cooler lines,I had a '67 Catalina that had 3/8" tubing,it screwed my weekend plans up when the 5/16" lines I bought to fix it didn't fit!..

I dont think they make brass fittings to reduce 3/8" to 5/16",but they do have onse to step up 5/16" to 3/8" ,though they may be hard to find locally..I have cheated and brazed a 5/16" line inside of a 3/8" one before when it was sunday and no parts stores were open,and I had to go to work on Monday morning!..the 5/16" line fits perfectly inside the 3/8"...(as does 3/16" into 1/4",and 1/4" into 5/16"!)..

 

[pismorat]

OK, so I figured it out. The TH400 has the standard casting with straight thread going into it, but it had the 3/8" line as the output. I took the fittings out of my TH350 and they had the same male threads going into the housing, but a 5/16" line as the output. I put the TH350 fittings into my TH400 and the cooler lines I had fit right in and I am good to go. Thanks for the help!! Hopefully I'll have some pics of the 489ci BBC running soon...1 or 2 days???