Shifting at high RPM

[cadillac_al]

Is that modulator getting vacuum?

[Captain J]

Originally Posted by cadillac_al

Is that modulator getting vacuum?

Yes

[Captain J]

Originally Posted by kwmech

Back of the transmission right hand side is a steel cover plate with 4 bolts 1/2'' socket or wrench. Remove those 4 bolts. There will be a little bit of oil that comes out ---maybe a a cup at most. Pull the governor out --it should remove easily with a small twist--and look at the plastic gear. You can tell if it is in good condition or not. If it looks OK, you can move on to something else. If not...... Sometimes the rear bushing in the case will walk out and catch the nylon gear and strip it out. If the gear is stripped out, you'll need a new gear of course and pull the transmission out and gut it so you can locktite (green) and lightly stake a new bushing in. Then you can reassemble or rebuild at the same time. The governor controls shifting in the transmission and the vacuum modulator will fine tune it.

I did what you suggested, I posted pictures but couldn’t upload videos.
The gear is in good condition,

[Captain J]

Originally Posted by kwmech

The wire on the side has nothing to do with the transmission up shifting. That wire powers a small solenoid for kick down and only has power when really into the throttle. You don't have to be a mechanic to remove 4 short 5/16'' bolts and look at the governor. At the most you may damage the gasket when removing the cover. The gasket could be either a rubberized cork or a thickish paper.

EDIT: Another thing: when you get the governor out and the plastic gear looks OK, hold the governor by the gear with one hand vertically and flip the weights with the other and watch the small valve on the inside and see if it moves smoothly and does not stick. This can cause erratic shifting also.

Actually post up a pic of the governor when you get it out

Did what you suggested, initially the valve seems moving slowly but with repeated movement of the weights it did move, I noticed some scratches on the surfaces, in the pictures, cleaned it with brake cleaner.
I’m thinking of buying new governor and vacuum modulator, however I’m not sure what brand to buy. Any recommendations? 🤔
Note I live 5000 miles from USA, so I must make sure I buy the correct part.
Thanks 🫡👋🏻

[kwmech]

If it moves, there is no reason to waste money on another one. Cleaning it out was good. If anything buy a weight kit and an extra gear for it if you anticipate issues in the future. There had to have been a gasket on there, if there wasn't there would nave been a huge leak while driving. I'd pickup a couple of gaskets also. As to the shifting?? I don't know, if the valve was sticking somewhat and is now loose. I'd put the governor back in and try driving it and see what happens. If it still won't shift, there may be a sticking valve in the valve body under the vacuum modulator. See if you can pull it out with a magnet. What condition is the oil in....nice and clean?

[Captain J]

Originally Posted by kwmech

If it moves, there is no reason to waste money on another one. Cleaning it out was good. If anything buy a weight kit and an extra gear for it if you anticipate issues in the future. There had to have been a gasket on there, if there wasn't there would nave been a huge leak while driving. I'd pickup a couple of gaskets also. As to the shifting?? I don't know, if the valve was sticking somewhat and is now loose. I'd put the governor back in and try driving it and see what happens. If it still won't shift, there may be a sticking valve in the valve body under the vacuum modulator. See if you can pull it out with a magnet. What condition is the oil in....nice and clean?

Greetings
There was no leak at all prior to removing it, no gasket just silicon. Oil is new and clean.
I’ll put back, see if ok,
Regarding your suggestion of fishing the valve, how do I pull it out?

[Dead Parrot]

One possible thing that might cause a shifting issue is if the o-ring on the filter tube is damaged, worn, or missing.
Amazon link that shows the o-ring as part of a kit: https://www.amazon.com/ACDelco-TF231...2935891&sr=8-3

I noticed that some kits don't show the o-ring. It is needed or you won't get good fluid pickup and will have symptoms similar to low fluid levels. Including bad shifting.

#7 on the diagram shows where it goes. Another thing some folks miss is removing the old one if it sticks in the opening when you pull out the tube #14.

I would finish your check of the modulator and related stuff before pulling the pan. Pulling the pan probably means replacing the pan gasket + 4~7 quarts of ATF. No point in doing that until you know the problem isn't in the modulator you already have off.

[dmb]

the problem may stem from the silicone used to seal the gov cover. An automatic transmission is no place to use silicone. A small chunk of it will get in the governor and case it to stick.

[Captain J]

Originally Posted by dmb

the problem may stem from the silicone used to seal the gov cover. An automatic transmission is no place to use silicone. A small chunk of it will get in the governor and case it to stick.

I totally agree. However, This truck never had any issues with trans since I owned (2015), it parked for 3 months due to paint work. Otherwise all ok.

[Captain J]

Originally Posted by Dead Parrot

One possible thing that might cause a shifting issue is if the o-ring on the filter tube is damaged, worn, or missing.
Amazon link that shows the o-ring as part of a kit: https://www.amazon.com/ACDelco-TF231...2935891&sr=8-3

I noticed that some kits don't show the o-ring. It is needed or you won't get good fluid pickup and will have symptoms similar to low fluid levels. Including bad shifting.

#7 on the diagram shows where it goes. Another thing some folks miss is removing the old one if it sticks in the opening when you pull out the tube #14.

I would finish your check of the modulator and related stuff before pulling the pan. Pulling the pan probably means replacing the pan gasket + 4~7 quarts of ATF. No point in doing that until you know the problem isn't in the modulator you already have off.

You are correct,
This is not the issue, otherwise shifting problems will happen after the oil change.

[kwmech]

Originally Posted by dmb

the problem may stem from the silicone used to seal the gov cover. An automatic transmission is no place to use silicone. A small chunk of it will get in the governor and case it to stick.

This is a huge issue ^^^^. You may have already dis-lodged the culprit, but A small piece could have lodged itself anywhere in the valve body. Did you try to pull the valve out behind the vac modulator? It's about a 1/2'' in diameter and about 2-3'' long. Magnet will be useful

[kwmech]

[Quote]...... Another thing some folks miss is removing the old one if it sticks in the opening when you pull out the tube #14.

If the tube butts up against it ..yes. But you can actually double up the o rings if you have the deep pan to help retain the extension tube.

[Captain J]

Greetings to all,
Sorry for late response. I was sick (corona or flu) not sure.
Again, trans oil is new and clean, drove it less than 200km since last oil & filter change, all GM products. No silicone inside the governor housing. When replacing the old filter, I made sure the old o-ring is removed, the new o-ring was lubricated with trans oil, then it was fitted in the filter neck, then it was placed inside the housing. Truck drivers normally.

Update 12/23/2023 8:30pm my time.
I cleaned the governor tested the valve it works fine, made a gasket from gasket paper, put it back, added new oil to replace the spilled oil. Drove the truck, no change, it will not shift.
I’ll try to fish the valve body behind the vacuum modulator, and see.
Otherwise I’m out of ideas.

[dmb]

Originally Posted by kwmech

This is a huge issue ^^^^. You may have already dis-lodged the culprit, but A small piece could have lodged itself anywhere in the valve body. Did you try to pull the valve out behind the vac modulator? It's about a 1/2'' in diameter and about 2-3'' long. Magnet will be useful

He may have to pull the valve body Something is stuck somewhere, 400s just dont give problems as a rule

[kwmech]

Originally Posted by dmb

He may have to pull the valve body Something is stuck somewhere, 400s just dont give problems as a rule

I agree. I think he is going to see if the valve under the vac modulator is free first, that could be sticking in the case

[Captain J]

Originally Posted by kwmech

I agree. I think he is going to see if the valve under the vac modulator is free first, that could be sticking in the case

I’ll try to pull it out, is it easy to put it back🤔?

[Captain J]

Originally Posted by dmb

He may have to pull the valve body Something is stuck somewhere, 400s just dont give problems as a rule

I faced the same issue few years ago with my other truck, I found the vacuum hose was loose from the vacuum modulator, I reconnected it and shifting was fine.
My concern is how to return the valve body?

[kwmech]

Originally Posted by Captain J

I’ll try to pull it out, is it easy to put it back��?

It only goes in 1 way. It'll or should pull straight out with a magnet. Just a steel valve. Same as the governor valve it should slide in and out smoothly

[Captain J]

Originally Posted by kwmech

It only goes in 1 way. It'll or should pull straight out with a magnet. Just a steel valve. Same as the governor valve it should slide in and out smoothly

Aha, ok
What should I look 👀 for when I pull it out?🫡
Will it leak oil?
Because I put in 1.6L of trans oil yesterday to replace the oil that came out of governor area 🥱

[Captain J]

I managed to pull the valve out with a magnet as suggested, initially it did come out smoothly, I pushed it back with the magnet then out, I checked it, nothing noticeable, cleaned it then with the magnet I pushed in and out three times, it was very smooth.
Took the truck out for a drive, same issue will not shift. 🥱🥱🥱

I suspect that the vacuum modulator is the issue, but I’m no expert.😎

Someone said maybe the clutch’s are gone, but I’m no expert, that’s why I’m here.🤔🇶🇦🇶🇦

Out of ideas 🤒😏

[geezer#99]

Considering the rest of your truck collection do you possibly have a modulator you could borrow to see if it is indeed the modulator?

[Captain J]

I did consider that, however all my trucks are manual,
I’ll try to find someone that can lend me his modulator,
No parts available in my country for such trucks.
I have to buy it from the USA via eBay, SummitRacing, Rock Auto, Jets, and others, and hopefully they arrive un damaged, and they are the correct ones, after 4-6 weeks from ordering ��

[Shifty One]

FWIW, I've changed my TH400 modulator 4 times in 20k miles. The units you buy nowadays are not so good.

[Captain J]

Originally Posted by Shifty One

FWIW, I've changed my TH400 modulator 4 times in 20k miles. The units you buy nowadays are not so good.

I’ve never changed any of mine. Unfortunately most are made in China, and different brands, not knowing which ones will fit, and they sometimes don’t work

[Duck1]

Originally Posted by Captain J

I’m not sure if it’s TH400 or R700. When starting the truck it will automatically run as choke is on, then when I press the pedal rpm drops.
Oil level is good, oil clean, I’ll do this test.
However what’s this switch/solenoid that is located at the gas padel with 2 wires (red goes to fuse box 12v, the other goes to side of the trans)?

3/4 ton should have TH400, 1/2 ton should be 700-R4