Th400 wont shift into third gear

[1986c10]

Hey everybody, I picked up a mostly done project a couple months back but ive been busy with school and just got back to being able to work on it. Anyways, its a 1976 K20 with a mild 396. It has sat for seven plus years and just occasionally started and the owner knew little about it. I tried to drive it to asess what it needs and noticed that it wont shift into third gear. No tachometer currently but I got it to roughly 4000rpm and it wouldnt attempt to go into third. I checked fluid level and had to add four quarts of dex merc. Surprisingly that made no difference. Vacuum line is connected from dedicated intake vacuum source to the side of the trans and doesnt leak from a simply sucking on it from my mouth (insert joke here). I noticed today that the trans fluid lines that go above the header collector and to the radiator are dripping onto the collector. I havent dug into the cause of that. I'll try and figure that out today. Anything you guys can thing of that would cause me to have no third gear? Thanks! here is a pic of the project

[cableguy0]

Just sitting for that long could cause it. You could have worn/cracked lip seals not allowing enough pressure to build in the drum. It could be a stuck valve in the valve body. Many things could contribute. Its really hard to guess especially not knowing the history and with it having sat for so long. Hopefully clinebarger will come along soon and be able to throw something more specific at you.

[1986c10]

Thanks for the response, I had/have a gut feeling something weird happened from just sitting so long and leaking fluid. Would it be wise to just change the filter as a first step? It has reverse so I know that narrows which drum is not getting pressure. Ive never messed with automatic transmissions though so the internal workings are foreign to me.

[cableguy0]

1st and reverse are the same clutch pack. Losing high gear though is on its own. A fluid and filter change isn't your issue and probably wont help. The unit sitting for so long is the wild card. It could be as simple as a stuck valve OR it could be the unit needs rebuilt.

[clinebarger]

Are you sure it has a 1-2 shift? 4000 RPM in 2nd gear means you were "hookin'-it" pretty good. A 1:48 (2nd) to 1:00 (3rd) is not much of a ratio jump.

If your sure you have a 1-2 shift & shift timing is OK, And reverse is nice & strong....

Physically check for vacuum at the Modulator.

Remove the governor & make sure the governor valve & weights are moving freely.
A stuck 2-3 shift valve is also a possibility. As is a 2-3 Accumulator issue.

Pressure testing is an invaluable procedure on any Auto transmission! Use the chart bellow. Can also be used to check Modulator operation with a hand held vacuum pump. High vacuum equals low line pressure, Low vacuum equals high line pressure.

This could have been a pre-existing condition that the previous owner conveniently forgot about.

[clinebarger]

Originally Posted by cableguy0

1st and reverse are the same clutch pack. Losing high gear though is on its own. A fluid and filter change isn't your issue and probably wont help. The unit sitting for so long is the wild card. It could be as simple as a stuck valve OR it could be the unit needs rebuilt.

Manual Low & Reverse use the Lo/reverse Band, In Manual Low the Band just prevents the Low Roller Clutch from "Overrunning" giving "engine braking" in L1.

In Drive 3 or D2, 1st gear only has the Forwards applied & the Lo/Reverse Roller Clutch is holding, But can "overrun" the opposite direction (No engine braking)

In Reverse, Direct clutches & Lo/Reverse Band are applied.

[1986c10]

Okay I did some of your steps, not all but I figured Id give an update. Yes it will shift into second but when you keep steadily increasing speed/throttle the rpms keep going up and it will not get into third. Shift timing seemed good for the 1-2 shift as well. Vacuum is at 12-15" and the modulator held 20" for 3 minutes with no decrease. I removed the governor cover but I cant remove the governor itself without removing the transfer case from the looks of it (linkage bracket is right in the way). I can however feel that the governor weights move freely although it feels like spring tension is very minimal or non existent. The weights have no problem being collapsed in and staying there... Is this normal? Thanks for the help Clinebarger!

[clinebarger]

Can you take the bracket off & remove the Governor, You have to remove the Governor to check it.

[1986c10]

It looked to me like it was part of the case itself which doesnt make sense so i'll look at it a little further tomorrow to make sure. Now on the governor, should those weights have some tension? I would think so to "ramp" with speed. I felt basically no resistance. The governor gear seemed okay because the governor would rotate out like a distributor but I couldnt remove it all the way. Thanks for the help, I was hoping you would chime into this thread. You know your transmissions!

[clinebarger]

Originally Posted by 1986c10

Should those weights have some tension? I would think so to "ramp" with speed. I felt basically no resistance. The governor gear seemed okay because the governor would rotate out like a distributor but I couldnt remove it all the way. Thanks for the help, I was hoping you would chime into this thread. You know your transmissions!

The weights will not have spring tension on them.

When Line Pressure enters the Governor, The Governor valve strokes & forces the Inner & Outer Weights closed. This compresses both Governor springs.

The Governor Valve is in the center of the Governor....That's what you want to check. Hold the weights closed & make the Valve is moving all the way up & down.

Make sure the Governor Gear has a roll pin & is tight.

Check the head of the Governor, It should be tight.

Measure the Lands on the Governor stem, Should be .800"

[1986c10]

I ended up pulling the trans tunnel cover off and access was simple after that. Got the governor removed and everything seems good. The valve moves freely and the diameters were dead on at .800". The nylon head is in good condition and the pin is holding it snug.

[clinebarger]

Pressure test next, Line pressure stuck "High" can cause no high gear.

You can also remove the modulator & use a hand held vacuum pump & make sure in moves with Vacuum.

Make sure the Modulator Valve is free, (Behind the Vacuum Modulator)

Then on to dropping the Valve Body & checking for stuck valves.

Keep in mind.....You don't know if this unit EVER had high gear, Could have been a Builder error or similar problems that will not be found 'til the unit is torn down.

Another possibility is the Directs are about done....But can still hold in reverse because the higher Line Pressure & 100% greater holding power on the clutch pack.

[1986c10]

Could I do the steps besides the pressure test first? Only reason I ask is because I'll have to order a transmission pressure tester/gauge kit. I'd like to dig into it more the next few days as I have a lot of free time. If I must check pressures first, I will obviously be patient and wait though. Exactly, the whole thing truck was "loosely" put back together and I wouldnt be surprised if it was a trans that had been lying around of unknown condition. Thanks for the help.

[1986c10]

Modulator valve didnt move with the weak magnet i had. I lightly gripped the valve with needle nose pliers and it moved a quarter to half inch but does not come out completely of its bore. Normal?

[clinebarger]

The Valve should easily come out of the Case. Work the Valve out of the bore, Clean the Valve, Dip-it in clean ATF, Work it back it the bore.....Repeat 'til the Valve is free.

[1986c10]

Modulator valve is working good now, probably was before too. Pulled the valvebody off and noticed some rust on valves and two were pretty sticky. I disassembled the valve body and laid everything out in order. Should I polish the rusty valves, clean the valvebody and reassemble or replace parts? Also which specific parts would/could cause my issue so that I can pay special attention to them and the bores they go into. Thanks

[1986c10]

I got bored and cleaned everything off good, wet sanded the corrosion, cleaned everything off again and reassembled with atf. Everything moves smooth and freely now although, the two spools in the above picture had some pitting on them likely from sitting for so long with no fluid. Should I replace the whole valvebody? Or order atf & filter, gaskets and see how it operates?

[cableguy0]

If all of the valves are moving freely you MIGHT be ok. The only issue would be the rust in the valve body itself that could float free. Everything in the transmission uses fine machining to seal. Something smaller than a grain of sand will clog up the work. I personally would grab another valve body that was clean and start over. That way you can be sure things are ok and will remain ok. Cleaning a valve body is next to impossible when it comes to rust. The cost of buying another will be far cheaper than the time it takes to get everything spotless.

[clinebarger]

Originally Posted by 1986c10

I got bored and cleaned everything off good, wet sanded the corrosion, cleaned everything off again and reassembled with atf. Everything moves smooth and freely now although, the two spools in the above picture had some pitting on them likely from sitting for so long with no fluid. Should I replace the whole valvebody? Or order atf & filter, gaskets and see how it operates?

I would see how it works, I work during the day, So I don't have time to post.

Here is a Valve Body diagram for future reference if anyone needs it. The 2-3 shift valve is the one you were after.

First diagram....Early Model.
Second Diagram.....Late Model (Yours is a Late Model)

[clinebarger]

Late Model Valve Body

[cableguy0]

Way to make me look inadequate Clinebarger. LOL . Thanks for posting those diagrams. If you keep this up your going to expect a paycheck soon.

[1986c10]

Thanks guys for the response, thats my main concern as well cableguy. It's hard/impossible to clean everything. I did a good job at getting any visible debri but there is obviously more that cant be seen.

That diagram is perfect, i've been doing alot of google image searches and that is better than anything ive found. Im gonna weld a bung and drain plug on this pan (I made a mess when removing and would rather not again) and put it all back together and see what happens. If not, I was looking at this valvebody. Good or bad?
http://www.ebay.com/itm/TCI-Auto-Val...39afa7&vxp=mtr

Also I found this in my transmission pan,



You guys are the best, thanks so much for helping with my first auto trans venture.

[cableguy0]

Nothing wrong with that valve body and the shift kit is already installed. The thing in your picture is a filter/screen. Im not sure a th400 used one like that but it damn sure shouldn't be laying in the pan. Clinebarger will be able to tell you for sure. On the plus side its pretty clean.

Edit....Btw your welcome. Ask away. Every guy that asks answers the questions or probably another hundred. Lots wont ask for fear of being ridiculed like happens on other forums. That garbage doesn't fly here. Feel free to ask whatever and someone will answer.

[cableguy0]

Also your hands are entirely too clean. Fix it. The last time my hands looked like that I was probably 12.

[1986c10]

Exactly, it takes out the possibility of me screwing up the do it yourself shift kit. Maybe the screen is for the governor tube? Even though I dont thing they originally had one. Also, my trans filter was super loose, and the bolt and spacer were tight. Ive read of this happening to other people, should I space it out so that the filter is snug on reassembly? Haha, i'll have you know I cleaned my hands before I took the photo and got my phone greased up. The photo doesnt show the trans fluid in my hair!