Changed my tranny fluid, filter, and gasket today. Very pleased

[Mister-B]

First off, wanted to thank SSTim for letting me pick his brain before, during, and after this project. You really were a big help

Much to my surprise, I discovered I have the beefier TH400 transmission. Cool!

While I was at it, I bought a new transmission filter and gasket. I got it from Autozone for about $8. The box includes both the filter and the pan gasket. I went with Valvoline Max Life full synthetic, that includes seal and gasket conditioners to help prevent leaks. I also substituted one bottle of Lucas tranny fix, because I like how it worked in there before the drain.

There isn't a drain plug. You just have to losten some of the bolts, and it'll start draining (very slowly). I got tired of waiting, and just removed the pan, and then cleaned up the crime scene on the ground later.

I then cleaned the bottom of the pan out with clean paper shop towels, installed the new filter, and buttoned everything back up.

Fill it through the dipstick hole with a funnel. Put in a couple quarts, then do a half a quart at a time, checking the fluid with the engine running and taking care not to overfill by much

Boy, the truck runs great! Shifts well and runs awesome. I ran it hard on the second leg of my test drive, and it's definitely got some good power.

So, in the past few weeks, I've changed the differential fluid, engine oil and filter, and now the transmission. The old beast is happy with me, and I have a deeper appreciation for how well this rig is put together with the huge 3/4 ton rear diff and beefy TH400 transmission.
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[69GWC]

Might take a look at the brake fluid next, my 70 had what i would call chocolate pudding instead of fluid in the master cylinder..lol. never know how long its been since these things where changed.
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[Mister-B]

Originally Posted by 69GWC

Might take a look at the brake fluid next, my 70 had what i would call chocolate pudding instead of fluid in the master cylinder..lol. never know how long its been since these things where changed.
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Thanks. Yeah, I looked at it today. It's actually in pretty decent shape, but I need to top it off
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[Spartan]

Excellent info. Not to hijack but what determines which transmission was put in?
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[Mister-B]

Originally Posted by Spartan

Excellent info. Not to hijack but what determines which transmission was put in?
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The main way is by the shape of the pan. If its basically a square with a notch in one corner, it's the 350. If it looks like a picaso version of a map of Texas, it's the 400.
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[SS Tim]

There are lots of variables when it comes to transmissions and drivetrains.
The powerglide (M35) or turbo-hydramatics (M49) will be differentiated on the SPID.
But the SPID will NOT tell which turbo-hydramatic is installed.

Mister-B, Your welcome! Happy to be of help when I can. Glad everything worked out well for you.

[special-K]

Originally Posted by Spartan

Excellent info. Not to hijack but what determines which transmission was put in?
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Since at this point a transmission could be swapped,you go by the shape of the pan,the TH400 is also larger/deeper,and TH400 has electric kickdown (wire) and TH350 has cable hooked to carb

[Lee H]

Mr B, great work!

I think Spartan was asking what determined 350 VS 400 as it was going down the assembly line?
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[Mister-B]

Originally Posted by Lee H

Mr B, great work!

I think Spartan was asking what determined 350 VS 400 as it was going down the assembly line?
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Someone correct me if I'm wrong, but where the th400 is more beefy, I would think it would be less likely to go in a 1/2 ton. Less likely to go in a 1/2 ton short bed. Hell, maybe even less likely to go in a 1/2 ton, short bed step side, with a I6 engine.

Mine is a 3/4 ton long bed fleet side, with a 350 V8. A th400 just makes sense.

I guess the th400 could have been an option, or thrown in at different trim levels too. Tim can tell us more info
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[Spartan]

Thanks folks. I heard different ideas as to why 350 vs 400. Some said supply was determining factor. Others said optioned per customer request. Like Mister-B said heavier duty.
...and to keep things on track I just want to applaud mister-b for his contribution to this site. Doing all these how-to threads as he does them helps and doing them in an apt. Complex and not a fancy shop just adds to the "I can do it" factor.
Thanks
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[WadmalawJoe]

Great job A.J.!!

I to have a transmission question regarding the 400's. Mine has a vacuum line to it. I have not noticed an electric line to it , but I haven't really looked for one. My motor is out of a 72 chevelle though. Where the transmission came from I don't know. Is there a way to run numbers on them as well?
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[GASoline71]

No TH350's ever came behind a Big Block in any Chevrolet or GMC to my knowledge. The TH400 came out around the time the 396 did. So it could handle the TQ that the Big Blocks were putting out.

Whether a TH400 was available behind a Small Block I'm not sure. But a TH400 eats about 40 HP just to turn it over a TH350. So I am doubting they came behind Small Blocks from the factory. But I'm sure there is a truck somewhere that has a TH400 behind a Small Block from the factory.

Gary

[Critter]

Originally Posted by GASoline71

So I am doubting they came behind Small Blocks from the factory. But I'm sure there is a truck somewhere that has a TH400 behind a Small Block from the factory.

I know some late 70s/early 80's 1 tons with 350 engines had t400 trans behind them for what it's worth.

[Mister-B]

Originally Posted by Spartan

Thanks folks. I heard different ideas as to why 350 vs 400. Some said supply was determining factor. Others said optioned per customer request. Like Mister-B said heavier duty.
...and to keep things on track I just want to applaud mister-b for his contribution to this site. Doing all these how-to threads as he does them helps and doing them in an apt. Complex and not a fancy shop just adds to the "I can do it" factor.
Thanks
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Thanks Spartan! I appreciate that. With a lot of this stuff, I get help from others if need be, and then I combine what I learned from them with what I know and learned from the experience. Just passing it on. I also enjoy getting to know you guys, and have made some great friends on here
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[Mister-B]

Originally Posted by GASoline71

No TH350's ever came behind a Big Block in any Chevrolet or GMC to my knowledge. The TH400 came out around the time the 396 did. So it could handle the TQ that the Big Blocks were putting out.

Whether a TH400 was available behind a Small Block I'm not sure. But a TH400 eats about 40 HP just to turn it over a TH350. So I am doubting they came behind Small Blocks from the factory. But I'm sure there is a truck somewhere that has a TH400 behind a Small Block from the factory.

Gary

Well lol, I think that truck somewhere might be right here. I've got a small block V8 350, and a TH400 that appears to be stock, as per my build sheet that SSTim decoded for me. If you look in box 44 the trans code is CT. This crosses on a fallback chart as a TH400 non-big block application


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[Mister-B]

Originally Posted by WadmalawJoe

Great job A.J.!!

I to have a transmission question regarding the 400's. Mine has a vacuum line to it. I have not noticed an electric line to it , but I haven't really looked for one. My motor is out of a 72 chevelle though. Where the transmission came from I don't know. Is there a way to run numbers on them as well?
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Boy, good question. Hopefully SSTim can chime in here
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[SS Tim]

Wow there is a lot of guessing going on here.
Like I said earlier there were three possible automatic transmissions the two-speed powerglide the TH350 and the TH400.

From a truck standpoint the TH400 is the most desirable. That said the powerglide is the least desirable, two-speeds just are not enough for a loaded truck. While a powerglide/250 C20 was offered and sold it is a rather slugish truck.

The TH400 was the first trans. offered and the TH350 was phased into production as it was developed.

Probably the easiest way to break this down is first that hard and fast rules won't work. Second I don't have a magic chart giving the exact trans. for any given year truck, powertrain and option content. But we can generalize it a lot and for the the most part if you expect a TH350 and find a TH400 be happy.

They are not hard to tell apart. Pan shape is the first. The vacuum modulator location (front right on a TH400 and right rear on a TH350). The TH400 uses an electric kickdown switch (the connector is on the left side of the trans.) and The TH350 uses a cable control (on the right front of the trans. forward of the dipstick tube).

So lets try this,

Trucks that probably have TH400s
C30
Earlier (69 down) C20
Big Block C20
Big Block C10

Trucks that probably have TH350s
Other than Big Block C20
Other than Big Block C10

Trucks that are only going to be TH350 from the factory.
K10
K20

[GASoline71]

Originally Posted by Critter

I know some late 70s/early 80's 1 tons with 350 engines had t400 trans behind them for what it's worth.

Way cool... I figured there would be a few from the factory out there.

Originally Posted by Mister-B

Well lol, I think that truck somewhere might be right here. I've got a small block V8 350, and a TH400 that appears to be stock, as per my build sheet that SSTim decoded for me. If you look in box 44 the trans code is CT. This crosses on a fallback chart as a TH400 non-big block application

Thats cool as all get out.

Gary

[kcsa75]

Originally Posted by Mister-B

First off, wanted to thank SSTim for letting me pick his brain before, during, and after this project. You really were a big help

Much to my surprise, I discovered I have the beefier TH400 transmission. Cool!

While I was at it, I bought a new transmission filter and gasket. I got it from Autozone for about $8. The box includes both the filter and the pan gasket. I went with Valvoline Max Life full synthetic, that includes seal and gasket conditioners to help prevent leaks. I also substituted one bottle of Lucas tranny fix, because I like how it worked in there before the drain.

There isn't a drain plug. You just have to losten some of the bolts, and it'll start draining (very slowly). I got tired of waiting, and just removed the pan, and then cleaned up the crime scene on the ground later.

I then cleaned the bottom of the pan out with clean paper shop towels, installed the new filter, and buttoned everything back up.

Fill it through the dipstick hole with a funnel. Put in a couple quarts, then do a half a quart at a time, checking the fluid with the engine running and taking care not to overfill by much

Boy, the truck runs great! Shifts well and runs awesome. I ran it hard on the second leg of my test drive, and it's definitely got some good power.

So, in the past few weeks, I've changed the differential fluid, engine oil and filter, and now the transmission. The old beast is happy with me, and I have a deeper appreciation for how well this rig is put together with the huge 3/4 ton rear diff and beefy TH400 transmission.
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How much fluid total did you put back in your transmision?

[Mister-B]

Originally Posted by kcsa75

How much fluid total did you put back in your transmision?

It took 4 quarts of tranny fluid, plus one (I believe it was a 24 ounce) bottle of Lucas Tranny additive. It's sitting just barely over the full mark. Like I say, I added 2 quarts, then added the rest a half quart at a time until it was full
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[71 super]

The 67-68 could be optioned with either power glide or th400 . My 68 had base v8 with th400 in 1/2 ton . 69 would have been first years of m49 th350 or th400 confusion. It was based on heavy duty and or big block option. 67-68 3speed auto recieved th400 exclusively as itvwascthe ONLY three speed auto...
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[SS Tim]

You are correct and now I see the hole in my lists.
So this is probably more correct.

67-72 Trucks that probably have TH400s
C30
69 C20
Big Block C20
Big Block C10
67-68 C10-30

69-72 Trucks that probably have TH350s
70 up other than Big Block C20
69 up other than Big Block C10

Trucks that are only going to be TH350 from the factory.
69-72 K10
69-72 K20