Re: ****ing at high RPM
 

Thanks👋🏻

Re: Shifting at high RPM
 

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.

Re: Shifting at high RPM
 

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

Re: Shifting at high RPM
 

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.

Re: Shifting at high RPM
 

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.

Re: Shifting at high RPM
 

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?��

Re: Shifting at high RPM
 

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

Re: Shifting at high RPM
 

Let me try the new vacuum modulator and update you.

Re: Shifting at high RPM
 

Update

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

Re: Shifting at high RPM
 

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

Re: Shifting at high RPM
 

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.

Re: Shifting at high RPM
 

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

Re: Shifting at high RPM
 

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

Re: Shifting at high RPM
 

Agreed.

Re: Shifting at high RPM
 

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


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

Re: Shifting at high RPM
 

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.

Re: Shifting at high RPM
 

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

Re: Shifting at high RPM
 

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

Re: Shifting at high RPM
 

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

Re: Shifting at high RPM
 

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.

Re: Shifting at high RPM
 

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

Re: Shifting at high RPM
 

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

Re: Shifting at high RPM
 

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

Re: Shifting at high RPM
 

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/

Re: Shifting at high RPM
 

Pic not available