Turbo 350 Transmission Not Shifting? A Complete Guide to Fix

Once the Hot Rodder forum used to be buzzing for Turbo 350 transmission not shifting issue. For example, while driving your car, the transmission goes through 1st gear, and then it starts acting up and stops shifting. That means the transmission is not turning out of first gear or it is not moving into 2nd or 3rd gear.

Basically, your Chevy Turbo 350 Trans fails to shift mainly due to the governor gear problems, vacuum line and modulator malfunction, and inadequate fluid level. Also, binding detent cable, stuck detent valve, unadjusted shifter, and many more reasons are responsible for it. 

Now, you will get to know the details of all these by going through this article. So keep reading!

Why Your Turbo 350 Transmission Not Shifting [Easy Troubleshooting Tips]

In this troubleshooting guide, logically, we will diagnose what factors are causing problems in transmission shifting. Also, we will explain the step-by-step process to solve them. So, let’s start with the following:

1. Governor Gear Issues

Before directly jumping into the discussion about the governor gear difficulties, first, you must know what it is and how it functions. And then, we will discuss the details issues of governor gear and their solutions. So, let’s dive into the subsequent discussion:

What Is A Governor Gear On A Transmission?

Hydraulically controlled transmissions like the Turbo 350 use a mechanical valve which is known as the governor valve. Proportional to the speed of your vehicle, the valve’s governor pressure changes. For example, when around 30 mph your car is running, in the governor circuit, there should be nearly 30 PSI. However, the governor valve’s primary driving force is the output shaft.

A Bad Transmission Governor TH350 Symptoms

Any problems with the governor gear or a malfunctioning governor cause the sudden loss of upshift; thus, your turbo 350 transmission not shifting to 3rd gear or first gear. For example, sometimes the governor doesn’t spin or does not upshift because the governor’s shaft’s plastic gear breaks. 

However, the noteworthy Turbo 350 transmission governor problems are:

  • Stuck governor
  • Stripped, worn out, or binding governor gear
  • Corroded governor or dirt build-up in it
  • Governor’s plunger and weights are not moving freely

Also, the teeth of the governor are crucial to functioning perfectly. The teeth can be chipped, bent up, missing, or odd-shaped, and any of these reasons are enough to make the governor defective. Again, another issue with the governor is that the little valve inside it is not moving.

However, whether the governor becomes stuck, stripped, or its gear is worn out, it will hinder your Turbo 350 transmission’s shifting.

How To Fix Governor Gear Issues?

The simple solution to the above trouble is if you find the governor is faulty, replace it. But before taking any action or replacing the governor, you need to check whether it is the culprit or not. Otherwise, the same hitch will persist, and the trans won’t shift even after replacing the governor.

  • So, the first task is to inspect the governor gear, and it’s effortless. Start the checking process by putting the little pan under the gear and removing the governor cover. Right now, pull the governor gear, and it will come out very quickly. Now verify whether easily and smoothly the governor moves in and out or not.
  • After removing it, check the gear’s teeth; they should be uniform and look good. Ensure that there are no missing, bent up, or chipped teeth. Also, make sure the governor’s plunger and weights are moving freely.
  • One essential thing is when you move the weights and have the governor out, you must ensure that the little valve in the center is moving. This is because the moving weight not necessarily indicates that the valve is also moving. 
  • Therefore you have to check and ensure the little valve is moving in and out with the weights. If you find the valve is not moving, take a small screwdriver to give the valve a nudge. Moreover, the valve will move easily and freely with a little ATF.
  • Afterward, inspect the governor for damage and ensure it is not corroded. Also, make sure it is completely clean. Again, you must ensure the governor isn’t binding. In case you find the governor is binding or damaged, you must replace it.  
  • Finally, we recommend you check the plastic gear on end and ensure it is perfect. Then straightened out the edges and cleaned up the cover. If, while straightening the edges, you end up with bent it up, you have to replace it.

After following all these solutions mentioned above and solving the governor gear hitches, quickly drive around. And hopefully, the transmission will start shifting.

2. Vacuum Line & Modulator Malfunction

Are you done with solving the governor gear issues but still, your Chevy Turbo 350 Transmission is not shifting? Well, if so, now we recommend you try shifting the transmission manually through the gears. If you successfully shift it manually, that indicates the vacuum problem to the modulator.

The automatic transmission’s crucial part is the vacuum modulator. Transmission gets a signal from the modulator about what kind of load it is facing. Also, the modulator allows the transmissions to react to the good shift points and line pressures. 

But unfortunately, the malfunctioning vacuum modulator or clog up vacuum line causes no vacuum signal at the tranny. So, ultimately, the transmission fails to shift. However, the signs of bad transmission vacuum modulator are:

  • Cracked or leak in the vacuum line or line’s poor condition
  • vacuum hose
  • Faulty vacuum modulator itself
  • The vacuum line is not hooked up or disconnected vacuum line
  • Loss of vacuum in a vacuum modulator
  • The modulator is severely out of adjustment.

How To Fix:

Solving the above problems are simple. 

First, start by checking the modulator and see if the vacuum hose is hooked to it. Also, verify whether the rubber hose is split or torn. If so, change it. However, you can deal with the hose in another way. 

Afterward, check the vacuum line and ensure it is in good condition. Also must inspect the vacuum hoses from one end to the other. If your vacuum line is all good, and there is no leak, but the transmission won’t shift out of the first gear, then we recommend you replace the vacuum module. 

However, before replacing the modulator, another important task is to adjust it.

How to Adjust Transmission Vacuum Modulator Turbo 350 

If you find the modulator is severely out of adjustment, then the transmission will not shift. Therefore, we strongly recommend you adjust your Turbo 350 modulator following the steps below:

  • Firstly separate the vacuum hose to adjust the transmission’s shift points.
  • Now clockwise, turn the modulator inside’s screw using a tiny flat-blade screwdriver. Turning the screw will firm up the shifts and raise the shift points.
  • Again if you need to soften the shifts, clockwise turn the screw counter to lower the shift points.

3. Low Fluid Level

Lack of enough fluid is another root cause of turbo 350 transmission not shifting to 3rd gear. Mainly the broken modulator valve, mechanical defect, and leaky seal cause a low transmission fluid level.

How To Fix:

Before pulling your Turbo 350 transmission out to fix it, we recommend you check the transmission fluid level. It’s crucial to find out the reason which causes low fluid levels and then fix them. When taking the governor cap off, watch out for the fluid’s condition and ensure there is plenty of fluid.

4. Detent Cable & Valve Malfunction

In WOT (Wide Open Throttle) position, the detent cable to the carb can stick, melt or break and it tells the transmission to have a wide-open engine. So the broken, damaged or stuck detent cable, and the stuck pass gear detent valve are the other culprits to blame for your turbo transmission’s not shifting up.

How To Fix:

Firstly check the detent cable for damage. Next, move forward to inspect whether the detent valve is stuck or not. After checking if you find the cord is damaged or broken, simply replace it with a new one. The same solution goes for the stuck detent valve also. Replace the bad one.

Detent Cable Checking Instructions

Checking the detent cable is simple and easy. First, start the process by disconnecting the cable at the carb and then pull on the cable. With no resistance, the cable should move at a little distance. Afterward, with some pressure, the cable moves some more. During moving, ensure there is a detent valve in the valve body.

Following the above process will tell you whether the cable is good or bad. If you experience pulling the cable is not easy, that means the cable is bad. Moreover, no moving cable signals that either the detent valve is disconnected or stuck or something like that.  

You can check the stuck detent valve in another way. For example, take out the governor gear and flog it as hard as it goes. After flogging, if the transmission shifts up, that means the governor has taken over, and the pass detent valve is stuck.

5. Unadjusted Shifter

Sometimes you may experience the transmission not shifting out of 1st gear to 2nd and 3rd, simply because of the unadjusted shifter. No matter where you put the shifter as reverse, neutral, or park, the Trans stays only in low gear and doesn’t shift to any other gear.

How To Fix:

The simple solution is to check the shifter and ensure it is adjusted correctly.

Still, Transmission Not Shifting? – Some More Reasons To Explain

We already mentioned the details causes and resolving ways of all those major issues which are responsible for stopping the transmission’s shifting. But along with the above factors, there are some more culprits to blame for this hitch, and those are:

  • Stuck 1-2 gear shift valve assembly
  • Incorrect valve body gaskets
  • The intermediate roller clutch is not holding or broken
  • Incorrectly installed sprag-type clutch
  • Improperly assembled intermediate clutch etc.

Sometimes you may experience odd situations, like the transmission is not shifting 2-3 but shifting to 1st and 2nd only. The potential causes responsible for hindering the Tran’s shifting from 2-3 gear are:

  • Control valve stuck at 2-3 shift
  • Damaged or missing sealing rings on the pump hub
  • Incorrectly installed, damaged, or leaked valve body gaskets
  • Missing or damaged direct clutch seals

Furthermore, sometimes you may also find that your Turbo 350 transmission is shifting from 1-3 and 3-1 gear but not shifting from 1-2. According to Chevy DIY,  possible reasons for this are:

  • Broken intermediate roller clutch
  • Backward installed clutch

Frequently Asked Questions (FAQs)

What are the symptoms of a bad transmission modulator?

The symptoms of a faulty transmission modulator include a whistling sound, late, early or hard shifting, exhaust producing white smoke, inadequate transmission fluid level, etc.

How many gears does a TH350 Transmission have?

The TH-350 transmission has a 3-speed gear with an automatic shift.
Yes! A vacuum leak causes the transmission shifting trouble by illuminating the engine light. When the leak becomes severe, it can even damage the transmission shifting.

Final Thought

Turbo 350 Transmission not shifting is really a frustrating situation for drivers. However, as we already discussed all those potential causes which hinder trans-shifting and their solutions, we hope this guide will help you.

If you face this same problem, first detect which culprit is causing it and then fix the hitch following our suggested approach. 

Now, for further queries on your Turbo 350 transmission, you can let us know. Soon you will get a reply from us.

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