The Stovebolt Site Forums The Shop Area The HiPo Shop I need some th350 education

I am trying to educate myself on the th350 that I have in my 46/7. Through google images I have identified the vacuum modulator just below the cooler outlet lines but I have yet to find the kickdown connection. I have looked at lots of pictures of th350's and have yet to find one exactly the same as mine. Am I missing something here? I would like to post a picture but I don't have one at this time. By the way this is all in pieces and not an operational truck, I will have to assemble everything. Dave

The kick down cable on a TH350 is next to the filler tube. Are you sure you have a TH350? A TH400 does not use a kick down cable.

Also, the modulator on a TH350 is mounted at the rear of the transmission, the TH400 has it on the passenger side below or close to the cooler lines.

Also, the TH350 pan is angled on the right rear rather than square. A TH400 pan is not square at all. And the vacuum modulator is below the cooler lines on the passenger side.

I will have to get the numbers, I don't know for sure what I have, but the vac mod.is below the cooler lines on the passenger side. Dave

If the pan has an oddball shape with a bulge on one side and the modulator is 2/3 of the way back on the passenger's side, it's a TH 400. 350's have a basically square pan with one corner nipped off. A TH 400 has an electric kickdown with a single wire connector going through the transmission housing just above and slightly to the rear of the shift linkage.

Pan #3 is a TH 350. #4 is a TH 400:
https://search.yahoo.com/search;_ylt=AqpwxKaHukfMZnszqduwQjqbvZx4?p=transmission+oil+pan+shapes&toggle=1&cop=mss&ei=UTF-8&fr=yfp-t-442&fp=1

Jerry

Square'ish with a chamfered corner TH350, shape of Texas TH400

Sure sounds like you have the TH400.

Bartomos, you hit the nail on the head on that one,
that's what I always called the TH400.
The 350 a square with one corner cut off.

The TH400 doesnt use a cable, it has a switch at the accelerator pedal.

I was just saying what already was said, basically. I just leaned it that way. Thanks.

Well, the jury is IN. According to all of the hints you gave me it has been identified as a th400. The guy I bought the truck from said the PO told him it was 350. With all this said how should it work for me, 46/7 on s10 frame with 350 sbc. Unless others say no, I'm still going with it. Dave

TH400.. most excellent. What ratio rear axle gear do you have and what diameter tires on the rear?

Not sure why that matters as it's still 1:1 in high gear whether it's a TH400 or TH350.

Dave,

The TH400 uses an electronic switch that basically operates a dump valve for the kickdown. They can be very hard to adjust and finicky, so many guys don't both hooking it up (me included).

The TH400 is actually a more stout transmission and there's no reason not to run it.

I think I have a rear ratio in the 370 range, not possitve on this, I did check but don't remember. It has 15" tires on it but will have to measure diameter. My 350 came out of a 1980 truck according to the numbers, it has a quadrajet on it. Dave

The 400 is a much tougher transmission than the 350, which is a good thing. You'll need a momentary-contact switch at the carburetor for a kickdown if you choose to run one. Otherwise, just drop the shift selector down one notch to D2 for a forced downshift. Downsides- - - -the 400 is considerably heavier than a 350, and it consumes a little more HP to keep the gears turning. On a vehicle the size of yours, the power loss won't be noticeable at all. The 4L80E is the overdrive version of a 400, but it needs a dedicated computer and a bunch of electronic inputs to make it work. Big $$$$$ for the privilege of having an overdrive!
Jerry

Thanks everyone for the inputs on this, I'm getting schooled on this. I appreciate the teachers for putting up with me! Dave

not to mess up anyones mind,noone ever mentions the turbo 375.looks identical to the turbo350.i had one in a 1972 impala.ckeck it out.

Dave stated in his first post:
I mentioned the ratio because now would be an ideal time for Dave to look at what rpm's his truck engine will be turning at cruising speed, in the event he wants or needs to make some proactive changes now (different rear gears or an overdrive transmission).

http://i645.photobucket.com/albums/...lculators/GearRatioChart_zps0c03ad74.jpg

http://i645.photobucket.com/albums/...alculators/GearRatioData_zps0ccd1738.jpg

Always good to know this up front, as opposed to being disappointed once the truck is all put together.

Hope this helps.

John

The wheel/tire diameter is about 27 1/2 "

Dave:

Here's engine rpm data based on your combination:

3.73 Rear End Gear Ratio
27.5 Effective Tire Diameter
1.0 Transmission High Gear Ratio

55 mph = 2500 RPM
60 mph = 2750 RPM
65 mph = 2950 RPM
70 mph = 3200 RPM
75 mph = 3400 RPM

Note that actual rpm's will be slightly higher due to torque converter slippage.

Or the TH350C which preceded the 700R4. I've got one in my '50,just haven't hooked up the lock-up function.

B&M do a kit to do away with the need for all the factory vacuum gubbins...

Here's Novak's article on the 400.

http://www.novak-adapt.com/knowledge/th400.htm

Not to hijack the thread, a TH375 is a TH400 transmission that has a TH350 type tailshaft(uses the TH350 size tailshaft).

I think we should be ok on the hijack situation Don,afaik Dave (Homer) has the info he needs and the thread title does ask for TH350 education.

I assume then that the TH375 was just a packaging excercise in order to get it to fit a particular vehicle?

Since we're on the topic of education, usually the truck TH400 had a U-joint on the front end of the driveshaft with a slip joint in the driveshaft, whereas the car version had a slip yoke on the transmission. MY TH400 is the BOP version (Buick Olds Pontiac bellhousing pattern), and has the slip yoke.