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

[71K20chevy]

The TH400 is the strongest of the three. I personally wouldn't go with a 700R4 unless you really wan the overdrive. TH350 is kind of in between. But if it were me, I'd just put a new 400 in and call it done.

[jocko]

TH400 and TH350 are both non-overdrive 3-speeds (1:1 3rd gear ratio).
700R4 in an o/d trans. If you drive on the highway, you will enjoy the roughly 30% drop in rpm at highway speeds - as well as the deeper 1st gear for greater acceleration in 1st.

All 3 transmissions are different lengths, so, only a TH400 replacement will avoid a driveshaft and, possibly, crossmember swap.

If you are interested in overdrive, which most are, then 700R4 (or a 2004R) is a great idea.

Also, don't quote me, but pretty sure the TH350 and TH400 use different kickdown mechanisms, etc.

Personally, I'm a big fan of a beefed up 2004R - but if it's just a drive-around-the-farm/city (not much highway time) then definitely go with the TH400 for ease of install and least overall cost/least required mods.

[71K20chevy]

Originally Posted by jocko

Also, don't quote me, but pretty sure the TH350 and TH400 use different kickdown mechanisms, etc.

Correct, 400 had an electric switch on the gas pedal if I recall, and 350 has one on the carb.

[RadRod]

To my knowledge the 350/400's are vaccuum kickdown and the 700 isn't.

I honestly don't care about the overdrive, the amount of work its seeming to require is a little much for something that I'm not dying without.

My truck is a '69 long fleet and it's a halfer

[Bigdav160]

Sounds like the converter went bad. What type of material was in the pan when you changed the filter? Powdered aluminum?

[MARKDTN]

Originally Posted by RadRod

To my knowledge the 350/400's are vaccuum kickdown and the 700 isn't.

I honestly don't care about the overdrive, the amount of work its seeming to require is a little much for something that I'm not dying without.

My truck is a '69 long fleet and it's a halfer

TH350 is a cable kickdown
TH400 is an electric kickdown
200R4/700R4 have a TV Cable that lets it know where the throttle is.

If you don't care about overdrive, another TH400 is the way to go.

[engineer_gregh]

I will add that the 700 might require swapping rear gears. I own one of each transmission type.
72 long bed/350 engine/3:08 rear end/700R/275x60x15 tacks ~2000 rpm at 65 mph
71 long bed/BB/turbo 400/same size tires and rear end tacks ~2400 rpm's at 65 MPH
71 short bed/307/turbo 350/same size tires and rear end no tack so i'm not sure of rpms but very comfortable at 65 mph on the interstate.

The 72 with the 700R tranny is the dog of the three, my least favorite.

[LockDoc]

-
If you have it on hand, try putting another half quart of transmission fluid in it and see what happens...

LockDoc

[jocko]

Originally Posted by engineer_gregh

I will add that the 700 might require swapping rear gears. I own one of each transmission type.
72 long bed/350 engine/3:08 rear end/700R/275x60x15 tacks ~2000 rpm at 65 mph
71 long bed/BB/turbo 400/same size tires and rear end tacks ~2400 rpm's at 65 MPH
71 short bed/307/turbo 350/same size tires and rear end no tack so i'm not sure of rpms but very comfortable at 65 mph on the interstate.

The 72 with the 700R tranny is the dog of the three, my least favorite.

TH350 and TH400 have same final drive ratio - so if your two different trucks with TH350 and TH400 have the same rear gears and tire size, they will also have the same rpm at 65 mph.