CUCV Transmission issue

[Beanerboy]

Afternoon guys, we are having some issues with the tranmissions in the CUCVs. We have few that have a really hard shift. We need to rev it to a pretty high RPM before it will shift. Me and my fellow mechanics have adjusted and replaced the vacuum control on the side of the injection pump. We have replaced all dry rotten vacuum hoses from the vacuum pump to the control on injector pump down to the Mod valve on the transmission. We've even replaced the mod valve. No matter what we've done, it is still shifting hard. My question is,l is there a way to test the Air emission pump on top at the back of the engine? I have searched the 10, 20 and 34 manuals for something about the vacuum pressures or the amout needed to properly shift gears. It explains how to change it but no way to test it. I am really hoping that we don't have to have it rebuilt. I have read about the trans oil pressures but nothing about vacuum pressures. I am looking for some insight about this matter.

 

[Barrman]

Just plug a vacuum gauge into it. It is real easy just plugging into the line at the throttle valve.

 

[Beanerboy]

Just plug a vacuum gauge into it. It is real easy just plugging into the line at the throttle valve.

That I understand but is there a range it needs to be in. I feel the vacuum when I put my finger over the holes but I’ve done that the ones with the issue and it varies from truck to truck, some stronger them others. I won’t have a vacuum gauge till tomorrow.

 

[Keith_J]

Adjusting the regulator is on page 3-176 of the -34 TM. The vacuum pump should draw at least 20 inches of mercury. That is about negative 12 PSI. Stronger vacuum than most engines at idle.

 

[Beanerboy]

Adjusting the regulator is on page 3-176 of the -34 TM. The vacuum pump should draw at least 20 inches of mercury. That is about negative 12 PSI. Stronger vacuum than most engines at idle.

Thank you!

 

[Barrman]

Sorry I didn't include the vacuum value.

Another trouble shooting method is to bypass the throttle valve and just go direct from the vacuum pump to the modulator on the transmission. It will shift so fast and smooth that you will be in 3rd gear at 25 mph and never feel a shift if you drive easy.

Have you by chance removed the governor from the transmission and made sure it is not a rusted clump of goo? It is under the circular cover held on with a wire like a master brake cylinder lid.

 

[Beanerboy]

Sorry I didn't include the vacuum value.

Another trouble shooting method is to bypass the throttle valve and just go direct from the vacuum pump to the modulator on the transmission. It will shift so fast and smooth that you will be in 3rd gear at 25 mph and never feel a shift if you drive easy.

Have you by chance removed the governor from the transmission and made sure it is not a rusted clump of goo? It is under the circular cover held on with a wire like a master brake cylinder lid.

No I have not done that yet. Our day just started and the light has just come out. I am going to do the vacuum test first after I fix the wiring on a different CUCV. While it was running the wiring started to smoke and the rubber coating was melted off. These things are turning out to be electrical nightmares. The trans fluid and filter have been changed a few weeks ago. Not sure if that would fix that issue of the goo being there.

 

[chevymike]

Yep, first step is definitely checking the vacuum pump is actually pulling vacuum. If not, nothing after that matters.

 

[Keith_J]

If it shifts the same with light accelerator pedal or mashed to the floor, it is most likely to be the injection pump mounted vacuum regulator.

 

[stevemcgee99]

I shifted late and barely into 3rd. Turns out the vacuum switch on the injection pump was all the way forward, which is later shifting. I put it in the middle (and replaced the fat vacuum pump hose and thinner hose to the switch) and now I shift into 2nd around 25mph and into 3rd around 45mph, easily.

 

[ezgn]

I shifted late and barely into 3rd. Turns out the vacuum switch on the injection pump was all the way forward, which is later shifting. I put it in the middle (and replaced the fat vacuum pump hose and thinner hose to the switch) and now I shift into 2nd around 25mph and into 3rd around 45mph, easily.

I adjust mine at 15 MPH and 35 MPH

 

[Keith_J]

I made the calibration tool..still have it somewhere in my empire of dirt.
The original valve on my 1031 was completely shot, late shifts as vacuum to the transmission was nothing.
Even improperly adjusted, the new valve was much better.

 

[Mad Texan]

I found the tool on EBay for less than $20 so I added it to my tool box