Common Fixes for a Transmission that Jerks or Hesitates

Transmission

Here are a few common reasons why your transmission may shift erratically, jerk or hesitate.

• Low fluid level
• Depleted fluid frictional properties
• Poor cold-temperature fluidity

Start with the easiest fix

There’s an old adage when troubleshooting: start with the least expensive and simplest fix. In this case, check the transmission fluid level first. Low fluid can prevent the transmission from shifting properly. It’s important to find out why the fluid is low and fix any problems. It could be a leaky seal or other mechanical defect. Otherwise, adding new fluid won’t ultimately solve the problem.

Worn fluid equals poor shift quality

Transmission fluid that has aged and lost some of its frictional properties can also lead to poor shift quality. When your vehicle’s computer tells the transmission to shift gears, hydraulic pressure (provided by the fluid) squeezes a series of plates together inside a clutch pack to connect the engine to the transmission output shaft and route power to the wheels. The fluid’s frictional properties play a vital role in ensuring the clutch plates bind together properly and gear shifts occur seamlessly.

Over time, the fluid’s frictional properties can degrade, leading to elongated, jerky or inconsistent shifts. In this case, it’s time for a fluid change.

How do you know for sure the fluid is worn? The only definite way to find out is to conduct used fluid analysis. However, fluid that smells burnt or appears dirty is likely due for a change. It’s best practice to change the fluid before the frictional properties are depleted and you experience poor shifting. Those poor shifts can cause the clutches to wear more rapidly and lead to bigger issues that need mechanical repairs.

Be aware of “adaptive” transmissions

One interesting note affects newer vehicles equipped with adaptive transmissions. These units “learn” your driving habits and the characteristics of the fluid to adjust shifts accordingly. As the fluid loses its frictional properties, the computer compensates and adjusts transmission performance.

If you’ve recently changed your fluid, the computer may still operate as if old fluid is installed, causing poor shift quality. In these cases, keep driving and eventually the computer will “relearn” your driving habits and the behavior of the new fluid and adjust accordingly. The problem was significant enough on some 2012-2013 Ford F-150s to cause Ford to issue a technical service bulletin (TSB 13-1-10).

What do “frictional properties” look like?

We know what good, crisp shifts feel like. Can we dive in even further and see what they look like?

We can, and they appear as a flat, boring line on a graph. The dark blue line represents the frictional properties of new AMSOIL Signature Series Synthetic Automatic Transmission Fluid. The light blue line shows the frictional properties of the same fluid after more than 180,000 miles in taxi cabs operating in the intense heat of Las Vegas

As you can see, the lines are extremely close, with no abrupt spikes or dips. This means, after 180,000 miles of severe service, the fluid continued to deliver crisp, confident shifts.

Granted, it’s not exciting to look at – unless you love driving and want to protect your transmission.

Cold weather can reduce shift quality

When the temperature drops, transmission fluids with poor cold-flow properties can thicken and cause elongated and hard shifts until the fluid has warmed up enough to flow properly. Switching to a high-quality synthetic transmission fluid will help. Synthetics don’t contain waxes, as conventional fluids do, meaning they remain fluid at lower temperatures for improved shifts during cold weather.

The best transmission fluid available won’t fix a broken transmission. But using high-quality synthetic fluid can help improve shift quality and maximize transmission life.

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Comments

  1. Starting with the least expensive fixes first is always best practice. You have no idea how many times I’ve wasted my own money when starting with something I “thought” was the problem then it ended up being something much cheaper.. Always start with the least expensive likely problems then move up from there.

  2. As many years as I have in the performance automotive and performance diesel business one glaring point isn’t made here…that point being once you allow fluid in an automatic to become low enough or dirty enough (pump starvation via dirty filter) it’s pretty much game over. It may work for a while after it top it up (if it’s low you have a problem anyway) or after you change it and the filter (again if it’s burnt or full of little black flakes enough to cause a performance issue) it’s toast! Automatic transmissions are among the most unforgiving pieces of automotive technology.
    Don’t ever think because it’s working ok again after you service or top it up that you have a reliable vehicle again…unfortunately you are on a timer now and how long it will last is a total guess!
    Proper and timely proactive maintenance, proper fluid for application, and COOLING are the keys to transmission longevity…not reactive maintenance.

    1. Hi Brad,

      Thanks for the advice. We agree with you – taking care of your transmission proactively beats fixing it after it starts shifting hard or fails altogether. We wrote about the importance of transmission maintenance in this post.

  3. Thank you for sharing this info! I found that the easiest way to test your transmission fluid to see if it needs changing is to take the dipstick and wipe it on a towel. If the fluid is a dark red or rusty brown, it’s time to change!

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