TH400 issues - Chevelle Tech
Transmission & Driveline Transmissions and Differentials

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post #1 of 33 (permalink) Old Jul 1st, 20, 9:37 PM Thread Starter
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TH400 issues

Just took my ss396 th400 our for a shakedown run after purchasing it last week. Give it full throttle and it ran like a bat out of hell! Then I lost all gears except for park. It won’t even go into reverse. I smelled the fluid, it seems fine, not burnt. Could it be the torque converter? The 396 is from a 69 Camaro. I’m not sure if the th400 is original.


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post #2 of 33 (permalink) Old Jul 1st, 20, 10:16 PM
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Re: TH400 issues

I have to ask. Did you check the fluid level with it in park and the engine running?
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post #3 of 33 (permalink) Old Jul 1st, 20, 11:08 PM
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Re: TH400 issues

Sounds like either shifter selector shaft came loose or manual valve link fell off...both are inside the pan....or it stripped the splines out of the input shaft/forward drum, broke the tip off the input shaft in the converters turbine spline....or you have a pump/pump drive problem.
With a transmission pressure gauge, you could test pressure in each gear.....it is doesn't change when manually selected into different gears either the manual valve isn't connected or the front pump has a problem that could be converter lug contact not good enough or drive lugs broke in the pump gear.

At a bare minimum without a gauge, you could unhook a trans cooler line, place it in a jug, and start the car and see if the pump is even moving fluid.

It was previously mentioned in the post above, check the fluid level for sure.....if good, and you can't get a pressure test, looks like you need to dive into the pan and it that shows nothing wrong you'll be pulling the unit for internal inspections.

Park is simply another neutral gate in the manual valve, combined with a shutter wheel and pawl on the output shaft to lock it in place.
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post #4 of 33 (permalink) Old Jul 1st, 20, 11:59 PM Thread Starter
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Re: TH400 issues

Quote:
Originally Posted by oldcutlass View Post
I have to ask. Did you check the fluid level with it in park and the engine running?


First gear was a bit slippy, so I added a quart and a half and it drove pretty nice without slipping to the gas station. About 2 miles from home I decided to floor it. Man! This 396 screams! The Elco looked like a speedboat! That’s when the transmission lost all gears.


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post #5 of 33 (permalink) Old Jul 2nd, 20, 12:00 AM Thread Starter
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Re: TH400 issues

Quote:
Originally Posted by Ericnova72 View Post
Sounds like either shifter selector shaft came loose or manual valve link fell off...both are inside the pan....or it stripped the splines out of the input shaft/forward drum, broke the tip off the input shaft in the converters turbine spline....or you have a pump/pump drive problem.

With a transmission pressure gauge, you could test pressure in each gear.....it is doesn't change when manually selected into different gears either the manual valve isn't connected or the front pump has a problem that could be converter lug contact not good enough or drive lugs broke in the pump gear.



At a bare minimum without a gauge, you could unhook a trans cooler line, place it in a jug, and start the car and see if the pump is even moving fluid.



It was previously mentioned in the post above, check the fluid level for sure.....if good, and you can't get a pressure test, looks like you need to dive into the pan and it that shows nothing wrong you'll be pulling the unit for internal inspections.



Park is simply another neutral gate in the manual valve, combined with a shutter wheel and pawl on the output shaft to lock it in place.


I’m going to open up the pan and check it out! I’m keeping my fingers crossed it’s a clogged filter and a bad converter. First I’m going to check the trans lines to see if any fluid is flowing.


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post #6 of 33 (permalink) Old Jul 2nd, 20, 2:55 PM
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Re: TH400 issues

In my experience, failed converters make lots of metal-crunching noises. Not convinced the converter is your problem.
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post #7 of 33 (permalink) Old Jul 2nd, 20, 3:32 PM Thread Starter
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Re: TH400 issues

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Originally Posted by Georgia69 View Post
In my experience, failed converters make lots of metal-crunching noises. Not convinced the converter is your problem.


I hear a whining noise when I put it in gear, that’s about it.


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post #8 of 33 (permalink) Old Jul 2nd, 20, 3:33 PM
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Re: TH400 issues

push/pull on the shift shaft where it enters trans, should be no movement. If it moves , the finishing nail that retains the shaft to the case is missing and the connecting link has come off.
Next likely is splines in convertor and/or the splines on input shaft are stripped
Iff you have to remove trans , make sure the stator splines(fixed spline on ft -part of pump) are blued-heat treated. If not, replace pump with hardened spline version. That spline would wear on the early units
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post #9 of 33 (permalink) Old Jul 2nd, 20, 4:21 PM
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Re: TH400 issues

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Originally Posted by 69Chvll View Post
I hear a whining noise when I put it in gear, that’s about it.


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I am by NO means a transmission guy, but I am wondering if your pump failed. Buy or borrow a transmission pressure gauge, do a search on where and how to check pressures - it's not at all difficult.

Unless you see something obvious and simple to correct when you pull the pan, I see no way around pulling the transmission for inspection and rebuild.
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post #10 of 33 (permalink) Old Jul 2nd, 20, 6:53 PM
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Re: TH400 issues

"Just took my ss396 th400 our for a shakedown run after purchasing it last week."

" I hear a whining noise when I put it in gear, that’s about it"

It sounds like you just bought the car. Was the tranny serviced? Rebuilt?

If you can feel the detent when manually shifting it the linkage is probably ok. The whining noise can be caused by a lot of things.

I would drop the pan and check the filter pick up tube first and go on from there. See what's in the base of the pan also.

Just my .02c worth

John
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post #11 of 33 (permalink) Old Jul 2nd, 20, 7:20 PM
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Re: TH400 issues

Check the fluid not running & running see if it drops.
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post #12 of 33 (permalink) Old Jul 2nd, 20, 7:22 PM
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Re: TH400 issues

It ain't a clogged filter!
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post #13 of 33 (permalink) Old Jul 2nd, 20, 8:50 PM Thread Starter
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Re: TH400 issues

Looking forward to wrenching and checking it out. Thanks guys!


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post #14 of 33 (permalink) Old Jul 3rd, 20, 6:09 PM Thread Starter
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Re: TH400 issues

Quote:
Originally Posted by paul bell View Post
It ain't a clogged filter!


I pulled the return line to the transmission from the radiator and it shot out a bunch of fluid, so I would guess the filter and the pump are ok. I’m going to put it on the lift and pull the pan next.


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post #15 of 33 (permalink) Old Jul 3rd, 20, 7:05 PM Thread Starter
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Re: TH400 issues

Quote:
Originally Posted by LTJOHN View Post
"Just took my ss396 th400 our for a shakedown run after purchasing it last week."



" I hear a whining noise when I put it in gear, that’s about it"



It sounds like you just bought the car. Was the tranny serviced? Rebuilt?



If you can feel the detent when manually shifting it the linkage is probably ok. The whining noise can be caused by a lot of things.



I would drop the pan and check the filter pick up tube first and go on from there. See what's in the base of the pan also.



Just my .02c worth



John


Pickup filter tube felt loose. I’m not sure what issues that would cause. I’m going to tighten it back up to see if that helps


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