Solving Transmission Problems
In the days before electronic control, transmissions had mechanical components that helped tell the transmission when to shift gears. Sometimes these controls would fail and cause shifting problems. One of the main ones that comes to mind is the modulator. This is a device placed somewhere on the outside of the transmission and connected by a hose to engine intake vacuum. The engine’s intake vacuum is directly tied to engine load. The modulator takes this vacuum signal and helps tell the transmission when to shift based on engine load. If it fails, it can leak internally and cause the engine to draw in a bunch of transmission fluid. When this happens, you’ll notice a lot of white smoke out the tail pipe and low transmission fluid.
Transmission fluid also does a good job of cleaning out your engine, by the way. If you remove the vacuum line and you see transmission fluid in it, replace the modulator. Some modulators are adjustable. I won’t get into the adjustment here but consult your service manual for specifics on that.
Another manual control is the throttle valve. This is a valve that’s connected to the throttle so that the transmission knows how far you are into the throttle. The valve is connected to the throttle via a cable. The cable is often adjustable.
If it gets out of adjustment, it can cause shifting problems. Honestly, it’s not likely to come out of adjustment unless someone puts it out of adjustment, say if you’ve recently done work on the intake manifold or throttle body and you had to disconnect the cable. My point is, don’t start adjusting this cable unless you have reason to. It’s not likely to be out of adjustment, but if it is, it can cause a shifting problem. I don’t have a video on adjusting a transmission throttle cable, but you can use the info in this video as a starting point.
I think every email I get about an automatic transmission problem starts with, “My transmission is having a problem and I think it’s the torque converter.” The truth is, it’s not often the torque converter that’s at fault. I think I hear this because the operation of the torque converter is rarely understood and it seems like a mechanic-ey thing to say. I mean, “torque converter”: It does sound kind of manly. So to combat the ignorance I’ve made this video on how a torque converter operates and what’s inside it.
The torque converter is designed to take the place of a clutch assembly that a manual transmission uses. It also multiplies engine torque so you can take off from a dead stop easier. In addition to that, it also houses what is referred to as the TCC, or torque converter clutch. This is a clutch and works in the same way a manual transmission’s clutch works. It’s there to prevent slippage that normally occurs within the unit. At cruising speeds, the clutch locks up and allows full engine torque to be transferred to the transmission.
A problem with the TCC can cause a few things to happen. The first is poor fuel economy. If you notice a sudden drop in fuel economy, put the TCC on your list of suspects. It’s difficult to check, but as your vehicle is shifting through the gears, count the shifts. If you have a four-speed transmission, count up through the gears as it shifts. After the transmission shifts into fourth, you might feel another shift after that. This is likely your torque converter locking up. When it’s working properly it might feel like another shift at cruising speed. If you don’t feel this shift, there could be a problem with the torque converter or its controls.
Another issue might be that the torque converter clutch does not release and stays applied. If this happens, it’s just like leaving your vehicle in gear with your foot off the clutch when you come to a stop. It’s likely your engine will stall. If you notice that your engine runs fine except when you come to a complete stop, you could have a problem with the TCC staying applied. Consult your service manual for testing procedures.
If I Don’t Change My Automatic Transmission Fluid for a Long Time, Will the Transmission Fail When I Do?
Maybe. That’s really the best answer I can give here. It is true that if you don’t change your transmission fluid for some time and then you change it, your transmission might fail shortly after. I’m talking high mileages here, like more than 80K before this becomes an issue. The reason for this is your old fluid is thicker, and as a result helps seal all the stuff that’s worn out inside the transmission. Take that thick fluid away and put in new thinner fluid, and it slips past all the areas the old fluid was sealing. Once this happens, the transmission can no longer function as it used to.
Remember, everything about the automatic transmission is dependent on the pressures of the fluid within it. If there is a loss of pressure somewhere, you have a failure in that circuit. A pressure failure can equate to poor or no shifting. It could also mean harsh shifting depending on the situation. If you have a global pressure loss inside the transmission, the transmission might not function at all. So, if it’s been some time since you’ve changed the fluid and filter or you purchased a vehicle and you have no service history of when a fluid change was done, proceed with caution. Know that the good you’re trying to do could spell the end of the transmission. I can’t tell you if that’s going to be the case; you’ll just have to try it and see. Cross your fingers.