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Old 06-05-2014, 10:08 PM   #1
greywurm
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Fluid pouring out of TH350 when vacuum modulaor removed, hard time getting into 3rd

I'm debugging a late shifting issue with my 350 at. It has a hard time going into 3rd... Sometimes if I let off the gas for a second it will go into third by the time I give it some more gas, but sometimes it still stays into third. Last week, it started having issues staying in gear going uphill on the highway. Under heavier load it bounces back and forth between 2nd and third constantly every 3-5 seconds.

Anyways, I first figured vacuum leak or modulator, second would be kickdown cable (rubber insulation is slid up from the tranny about 3 inches exposing the inner cable). The rubber portions of the vacuum line appear to be ok, so I went to replace the modulator today. The moment I pulled it out, fluid started gushing out from the transmission. Is this normal or is the modulator valve shot?

I should note I just changed the gasket a couple days before I noticed the issues because the tranny leak looked to be coming from the pan, however it still leaks. So the fluid was changed at the same time and I used some transmission conditioner with the fluid, so I am tempted to also think that changed the fluid formula to something the tranny doesn't like.

I have only had the truck for a few weeks, so there could have been a problem beforehand that I hadnt noticed yet. Its a 71 fleetside with a 68 250 i6 on a th350.

Any insight, ideas, or discussion is appreciated. I can give more info if I left something out. Thanks!
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Old 06-05-2014, 11:58 PM   #2
kwmech
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Re: Fluid pouring out of TH350 when vacuum modulaor removed, hard time getting into 3

Fluid coming out of the vac mod hole is normal, but it shouldn't be "gushing out" . It will leak some, but not quarts. Maybe overfull? Take the cable off of the carb linkage and drive it. Cable is not needed for upshifting. Could possible have a stripped out nylon gear on the governor or the valve in the governor is stuck. 4 bolts (1/2'' socket) on the side of the case towards the rear, remove the bolts and pull out the governor. Report back
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Old 06-06-2014, 12:00 AM   #3
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Re: Fluid pouring out of TH350 when vacuum modulaor removed, hard time getting into 3

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Originally Posted by kwmech View Post
Fluid coming out of the vac mod hole is normal, but it shouldn't be "gushing out" . It will leak some, but not quarts. Maybe overfull? Take the cable off of the carb linkage and drive it. Cable is not needed for upshifting. Could possible have a stripped out nylon gear on the governor or the valve in the governor is stuck. 4 bolts (1/2'' socket) on the side of the case towards the rear, remove the bolts and pull out the governor. Report back
Thanks for the input. I will check this out tomorrow when I get a chance - working from home. Are you referring to the kickdown cable?
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Old 06-06-2014, 12:34 AM   #4
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Re: Fluid pouring out of TH350 when vacuum modulaor removed, hard time getting into 3

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Originally Posted by kwmech View Post
Fluid coming out of the vac mod hole is normal, but it shouldn't be "gushing out" . It will leak some, but not quarts. Maybe overfull? Take the cable off of the carb linkage and drive it. Cable is not needed for upshifting. Could possible have a stripped out nylon gear on the governor or the valve in the governor is stuck. 4 bolts (1/2'' socket) on the side of the case towards the rear, remove the bolts and pull out the governor. Report back
To add, fluid level is halfway between the add and fill lines when warm. I put about about 8 pints in it after I drained and changed the gasket.

I also had the governor on my list of suspects, but was leaning away from that for one reason or another. I don't recall why at this time.
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Old 06-06-2014, 07:55 AM   #5
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Re: Fluid pouring out of TH350 when vacuum modulaor removed, hard time getting into 3

My bet is on the governor.
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Old 06-06-2014, 10:35 AM   #6
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Re: Fluid pouring out of TH350 when vacuum modulaor removed, hard time getting into 3

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Originally Posted by greywurm View Post
Thanks for the input. I will check this out tomorrow when I get a chance - working from home. Are you referring to the kickdown cable?
Yes, disconnect the cable for now.
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Old 06-06-2014, 09:58 PM   #7
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Re: Fluid pouring out of TH350 when vacuum modulaor removed, hard time getting into 3

I got the governor pulled out. It appears OK to me. Gear looks fine. How do I check the valve?
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Old 06-07-2014, 10:11 AM   #8
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Re: Fluid pouring out of TH350 when vacuum modulaor removed, hard time getting into 3

I took a couple pics.
Upon further review, I can see some scoring around that hole near the gear on both sides, but it looks to me that is supposed to be there. Also there is minor wear on the gear, but really doesnt look bad to me at all.

http://imgur.com/a/V5h2X

Last edited by greywurm; 06-07-2014 at 10:19 AM.
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Old 06-07-2014, 12:37 PM   #9
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Re: Fluid pouring out of TH350 when vacuum modulaor removed, hard time getting into 3

Hold the assembly by the nylon gear in one hand. Now with the other, move the weights up and down by squeezing them gently together. Look at the valve in the center of the assembly and see if it is moving up and down freely. if it is the governor is good. If not you will have to take it apart and find out why it is binding up
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Old 06-07-2014, 01:02 PM   #10
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Re: Fluid pouring out of TH350 when vacuum modulaor removed, hard time getting into 3

Prob not the culprit but I had a big leak in my K5 when the TCS solenoid thing developed a crack - may be worth eyeballing that and if leaking just capping it off.
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Old 06-07-2014, 06:48 PM   #11
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Re: Fluid pouring out of TH350 when vacuum modulaor removed, hard time getting into 3

The marks to the side of the roll pin are where it was staked to keep the picture. From backing out.
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Old 06-11-2014, 12:53 PM   #12
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Re: Fluid pouring out of TH350 when vacuum modulaor removed, hard time getting into 3

Sorry guys for not getting back so soon. I got distracted trying to figure out an issue with the charging system having a voltage drop while the engine running. Still trying to figure that out, but I did get to make some headway on the tranny.

I ordered a new governor and swapped it out. The kickdown cable is disconnected. However it still wont shift into 3rd until I am going over 60 mph. Also, what I thought was odd is that when it is in 3rd, I was able to get her to shift down by flooring it 2 out of 3 times. The only time it didnt was when I was going uphill. But the kickdown cable is connected.

Am I misunderstanding the kickdown cable's purpose?

DeadHeadNM, I don't think my th350 has a TCS solenoid. But Im not sure - I havent had to do transmission work before.
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Old 06-11-2014, 06:49 PM   #13
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Re: Fluid pouring out of TH350 when vacuum modulaor removed, hard time getting into 3

Have you made any adjustments to the modulator? There is an allen head screw that can be accessed through the end of the nipple that the vacuum line attaches to. I believe turning this clockwise will push your shift points up in RPM, but make shifts much firmer. Perhaps it has been adjusted too far in (clockwise). Try backing it out and see how it affects your shift points. This is a quick check that will cost you nothing to do. Good luck.
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Old 06-12-2014, 12:42 AM   #14
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Re: Fluid pouring out of TH350 when vacuum modulaor removed, hard time getting into 3

The governor is not your problem. If it was the transmission would not upshift at all. The vacuum modulator or a cracked hose causing a vacuum leak going to it is what I would suspect. I had the same problem with a TH400, and this is what I was told. Turned out I had a brittle spot in the line and it was cracked, causing a slight vacuum leak. Replaced the line, problem solved.
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