Shifting at high RPM

[Captain J]

Originally Posted by Duck1

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

Thanks👋🏻

[Dead Parrot]

What is your idle vacuum reading? Also check at the hose going into the modulator.

If your vacuum is low, it will make the modulator act like you are really into the throttle and keep the trans from shifting.

Check the kickdown switch and make sure it isn't stuck on. If it is stuck, it is telling the trans you are at near WOT and will also keep it in lower gear.

[Captain J]

Originally Posted by Dead Parrot

What is your idle vacuum reading? Also check at the hose going into the modulator.
I don’t know the vacuum reading I don’t have the tools to do.
I checked the hose and it has vacuum.

If your vacuum is low, it will make the modulator act like you are really into the throttle and keep the trans from shifting. 👍🏻👍🏻👍🏻


Check the kickdown switch and make sure it isn't stuck on. If it is stuck, it is telling the trans you are at near WOT and will also keep it in lower gear.

The kick down switch is electrical, I checked the switch at it works.

[Dead Parrot]

Might consider adding a vacuum gauge to any parts order. They don't weigh much and shouldn't add a lot to a shipping charge. Many also include a 0~8 psi fuel pressure tester as well.

The kickdown switch check was a long shot but it doesn't require money to test.

[Shifty One]

Originally Posted by Captain J

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

Never had any problem, ever with a TH400, until I did. I tried ATP, Standard and RPM units. I found and old B & M unit, worked like a champ.

[Captain J]

Question to you all?
When removing the vacuum modulator, is it normal to see oil coming from the slot?
Or
When removing the valve body behind the modulator, is it normal to see oil coming from the slot?

Because
The first time I removed the modulator, nothing came out.
When I removed the valve, few drops came out, like 20-30 drops.��

Last night (my time +3 GMT, I managed to get new vacuum modulator, to replace the old one. The moment I pulled it out, oil came rushing down, socked me. I put the vacuum back. Then I swapped the old with the new, minimizing the quantity of oil loss.
Oil quantity lost was about a 1.5 ltr.������*����

The question:��������
Why no oil was lost when I removed the vacuum modulator and the valve body the first, while I lost a lot of oil when I removed the vacuum modulator ONLY the second time?
Where is all this oil coming from?

I didn’t test drive the truck yet, until I know what happened?��

[Captain J]

Originally Posted by Shifty One

Never had any problem, ever with a TH400, until I did. I tried ATP, Standard and RPM units. I found and old B & M unit, worked like a champ.

Yeah I know
I just bought one, with a red band (not sure of brand), let’s hope it works.

[Captain J]

Originally Posted by Dead Parrot

Might consider adding a vacuum gauge to any parts order. They don't weigh much and shouldn't add a lot to a shipping charge. Many also include a 0~8 psi fuel pressure tester as well.

The kickdown switch check was a long shot but it doesn't require money to test.

Let me try the new vacuum modulator and update you.

[Captain J]

Update

Installed new vacuum modulator,
Refilled trans oil to the correct level
Drove the truck,
No change, it will not shift ������

[cadillac_al]

If it was mine, and the trans was getting full vacuum, and a new vacuum modulator makes no difference, I would buy a Transgo shift reprogramming kit. When replacing the springs in the valve body valves I'll bet I would find a stuck valve even though I have never seen it happen before. Maybe it has a stuck or broken spring. I still think it will be something simple when you find it. just my .02

[Dead Parrot]

Don't think it was ever mentioned but does it do fine in reverse? And switch properly from reverse to drive and back? Its just not going from 1st to 2nd to 3rd?

In case you missed it, there is a sticky tread on the TH400 under the Engine and Drivetrain section. Might be helpful if you have to dig deeper.

[Captain J]

Originally Posted by cadillac_al

If it was mine, and the trans was getting full vacuum, and a new vacuum modulator makes no difference, I would buy a Transgo shift reprogramming kit. When replacing the springs in the valve body valves I'll bet I would find a stuck valve even though I have never seen it happen before. Maybe it has a stuck or broken spring. I still think it will be something simple when you find it. just my .02

We don’t have such kit, and no one knows how to do it.

[Captain J]

Originally Posted by Dead Parrot

Don't think it was ever mentioned but does it do fine in reverse? And switch properly from reverse to drive and back? Its just not going from 1st to 2nd to 3rd?

It shifts fine between all gears, P R N D 1 2. Only when driving it will not shift from 1st gear.

In case you missed it, there is a sticky tread on the TH400 under the Engine and Drivetrain section. Might be helpful if you have to dig deeper.

Don’t know that, do you have a picture to show it? I mean the sticky tread?

[Shifty One]

Originally Posted by cadillac_al

I still think it will be something simple when you find it. just my .02

Agreed.

[Captain J]

Originally Posted by Shifty One

Agreed.

Always the simple and obvious things get you
But what is?


I’m still waiting to know the reason of oil spillage?

[kwmech]

Oil level in the transmission while running is approximately at the oil pan gasket level. Vacuum Modulator is above the pan. If the truck sits for any amount of time the torque convertor will drain out some raising the level in the pan until you start the truck again. So to answer your question...it depends.

[Captain J]

Originally Posted by kwmech

Oil level in the transmission while running is approximately at the oil pan gasket level. Vacuum Modulator is above the pan. If the truck sits for any amount of time the torque convertor will drain out some raising the level in the pan until you start the truck again. So to answer your question...it depends.

It’s possible,
But still the issue isn’t resolved

[geezer#99]

Possibly it’s the detent switch that’s the culprit.
Says that in my motors manual.
Here’s a thread I found that might help.


http://67-72chevytrucks.com/vboard/s....php?p=7037666

[kwmech]

Originally Posted by Captain J

It’s possible,
But still the issue isn’t resolved

Yeah, I know. Kinda hard to diagnose over the internet without having hands on. We did hit the basics. I'm still thinking of a sticking valve in the valve body. The person to ask ---who is no longer here--- is clinebarger. He was really good on these maters

[Captain J]

Originally Posted by kwmech

Yeah, I know. Kinda hard to diagnose over the internet without having hands on. We did hit the basics. I'm still thinking of a sticking valve in the valve body. The person to ask ---who is no longer here--- is clinebarger. He was really good on these maters

Yeah I know, but you guys helped me a lot, I appreciate that
The question is when I replaced the vacuum modulator the second time and oil came pouring out, 1. Where this oil coming from, I mean what opening?
Why the valve didn’t come out?
I tried to drive in D1 and D2 to see if any changes, nothing.

[Captain J]

Originally Posted by geezer#99

Possibly it’s the detent switch that’s the culprit.
Says that in my motors manual.
Here’s a thread I found that might help.


http://67-72chevytrucks.com/vboard/s....php?p=7037666

I looked at your thread, but it’s beyond my expertise.

I asked one garage that says he is expert in transportations he said “ you need to replace your trans cuz your clutches are gone!!!!, but I’ve a used one to sell?”
How stupid he thinks!
If clutches are gone, trans will not shift, or it will slip.

So I’m searching for a solution.
Thanks for the info

[geezer#99]

Did you try to just unplug the connector on the detent switch and then test it?

[Captain J]

Originally Posted by geezer#99

Did you try to just unplug the connector on the detent switch and then test it?

No I didn’t not, I read the thread you sent, it involves some testing which I don’t know how, plus I’m not sure of the location (detent switch), and I don’t want to screw up

If it’s the kickdown switch by the gas paddle, that has a single wire connected to left side (driver side), yes I disconnect it, drove the truck, nothing it’ll not shift.

I appreciate your help

[geezer#99]

Bypass everything and unplug it on the transmission.
The switch is on the drivers side at the back.
Pic in here.


https://www.gm***************/thread...kickdown.1107/

[Captain J]

Originally Posted by geezer#99

Bypass everything and unplug it on the transmission.
The switch is on the drivers side at the back.
Pic in here.


https://www.gm***************/thread...kickdown.1107/

Pic not available