Th400/th350/th700-r4

[RadRod]

Gonna start by saying that I'm not entirely sure if this is the right board to post in about this so, apologies for that.

So I just finished (for the most part) building my '69 C10 and I've been driving it for a few weeks now.

Out of nowhere my trans decides to stop shifting and sound like a supercharger, so I read up on it and found that most peoples experience suggests its the filter that is responsible for that. So I went ahead and changed out the filter and found out that I have an early TH400 with a strange filter setup which ended up being a little challenge to find a new one.

Anyway, I threw it all back together and it worked for about 4 days and now its worse than it was before. It stopped engaging randomly at a stop light and I was stuck at the head of traffic, which was an insanely lame time... So I shut it off and sat there for a second trying to figure out if I should call a tow or somehow make the thing work, so I fired it back up and its like nothing ever happened. I drove it another few hundred feet and the same thing happened, it stopped engaging so I shut it off and it worked again after a few minutes. One more time just down the road from my house it happened so I tried it again and it worked and got me home.

So as it sits right now, it's just parked outside doing absolutely nothing and here's where my whole reason for the post comes in.

I'm wondering if I should get another TH400 and just drop it in, or if I should go with a TH350 or if I should go to a TH700 R4?

What are the pros and cons of each trans? Because as it is in my city there are a few used 350's, a few 400's and one 700.

Also how much work would it be to swap in a 700 compared to the 400 I currently have in there?

Thanks for any insight to follow, also sorry for the mega write up... Definitely got a little out of control in a few spots