Torqued Off: Troubleshooting Some of the Most Vexing Torque Converter Problems

We hear a lot of questions about torque converters.

That’s why we’ve spent a fair amount of time covering torque converters in the past. Our articles have included advice on how to choose a torque converter, the difference between flash and foot-brake stall speed, and lock-up versus non lock-up converters. We’ve even covered the basics of what you need to know when buying a torque converter: vehicle weight, engine displacement, camshaft powerband, intake manifold type, and more.

But what if you’ve already bought your torque converter, and it isn’t working or installing properly?

That’s the topic of this, our latest, post on converters. With help from the tech experts at Summit Racing, we’re going to help you troubleshoot some of the most common torque converter issues.

Problem: My vehicle experiences poor acceleration due to low stall.

Solution #1: Make sure the stall range properly matches the camshaft rpm range. Generally, the torque converter stall speed should be roughly 500 rpm higher than the starting rpm of the cam. If this isn’t the case in your situation, you’ll need a different stall speed converter or new camshaft that matches the current converter. To get a greater understanding of stall speed and the factors involved, watch this video.

Solution #2: Make sure your converter’s stall speed is the right match for your vehicle’s gear ratio. Your gear ratio helps determine how much energy it takes to move the vehicle. The numerically higher the gear ratio, the lower the flash stall. Typically, at least a 3.42 ratio is suggested with higher stall speeds so you may need to move to a different stall speed converter, depending on your application.

Solution #3: Consider the weight of your vehicle. The lighter the vehicle, the lower the stall speed will end up being–and vice versa. Again, consider switching to a converter with a different stall speed if you have a light vehicle.

Solution #4: Engine torque has a drastic effect on stall speed. For example, a torque converter will stall roughly 300-500 rpm higher behind a big block than a small block. That’s because engines that produce more low-end torque usually bump the stall speed up in the rpm range. Conversely, the same torque converter will stall at lower speed behind an engine making less low-end torque. Take a look at your engine and torque output and determine if you’ve got the right stall speed. According to B&M, the stall speed should be rated at about 500-750 rpm under your engine’s peak torque rpm. If you don’t know your exact peak torque rpm, be conservative. If you over-estimate your peak torque output, you’ll select a converter with too low of a stall speed.

Problem: My vehicle has too high of a stall and seems slower than it used to.

Solution #1: In most cases, the rules above apply in reverse for converters with too high of a stall. Go through solutions 1-4 and consider where your car or truck fits in with the parameters.

Problem: The converter is too tight against the flexplate.

Solution #1: Make sure the torque converter is fully seated on the input shaft of the transmission. In most cases, you’ll need to feel three clicks of engagement before it is properly seated. The first two clicks usually occur easily, and many people make the mistake of thinking the converter is fully seated at this point. However, there is a third “pump drive” click that must happen. If necessary, you may have to remove the transmission and re-install the torque converter to ensure proper engagement on the input shaft.

Problem: I can’t get the converter to engage on the input shaft.

Solution #1: Did you bolt the converter to the flexplate before installing the transmission? If so, you’ll need to re-install the transmission with the converter in place and then bolt the torque converter to the flexplate. The converter must be installed on the transmission before the tranny is installed into the vehicle!

Solution #2: Work the torque converter up and down on the input shaft, spinning it in the process. Often, smaller converters are harder to install because there is less room for the internal parts to move. This causes alignment problems with the input shaft, but a little patience usually pays off.

Problem: My torque converter went bad prematurely.

Solution #1: Start by looking at your vehicle’s gear ratio. If you choose a high stall converter to go with numerically low gears, the converter will overheat and fail. That’s because the torque converter likely never reached its stall point at cruising rpms. You’ll need to replace the converter and install a numerically higher gear set that will make the cruise rpm higher than the stall rating of the converter.

Solution #2: Make sure the torque converter was never installed on a transmission that failed. It is possible that debris from the failed transmission may have traveled through the converter and damaged it.

Solution #3: Install a transmission cooler with your new torque converter. For higher stall (2,500 rpm and above) converters, an external transmission cooler should be used to ensure proper fluid cooling.