Solving Transmission Problems
Checking Vacuum Modulators
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.
Checking Throttle Cables
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.
Torque Converter Problems
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.
15 thoughts on “Solving Transmission Problems”
Colin
January 8, 2024 at 11:43 pm
Hi Eric I have a 2011 dodge ram 1500 when u put it in reverse sometimes there is a delay , but if I move the shift bet more to park it will go in I checked transmission fluid it’s good I’m wondering if the transmission is on its way out or what it could be, sometimes u put it in drive it make a chirp noise mostly if u are putting some that is for the noise in drive but reverse does it most time but all day if u are towing a atv trailer.
Chad Samsel
May 16, 2023 at 4:59 pm
I am getting ready to put my modified 5speed to 6 speed transmission back together. I am concerned because I haven’t found any tips or tricks on aligning the shift forks when reinstalling the shift selector. Thanks.
Victoria Addington
April 18, 2022 at 10:50 am
Thank you for explaining that automatic transmissions present a reverse gear just like manual transmission does. My brother’s vehicle is acting up, and he thinks it’s because of the automatic transmission. I think he should let an expert see it and allow them to fix it.
https://www.wangaraautomatictransmission.com.au/
luis martinez
November 30, 2021 at 9:06 pm
I went to pull out my transmission dipstick in the transmission fluid shot out burning hot just wanted to know why did I do that if it’s not supposed to
William Blanks
November 3, 2021 at 8:34 pm
https://www.youtube.com/watch?v=NYSispke5Qg
Mike
June 26, 2021 at 6:54 pm
Eric – I live in the oven = Arizona and would like to hear your thoughts on whether or not adding a separate trans cooler is worth the extra $$$ ? The lines on my 1992 f150 go through the radiator. I’m considering adding a separate cooler with fan attached which will go in front of the radiator. Thoughts? Thanks.
Kristofer Van Wagner
May 6, 2021 at 1:03 am
I do appreciate that this post pointed out that it is important for us to have our transmission repaired by professionals. In doing so, we can prevent further damage. Assuming that I need to have my transmission repaired, I will look into hiring a certified professional.
Scott
February 11, 2021 at 4:19 pm
Can a transfer case off a 1988vjeep cherokee v8 work on a 1995 jeep cherokee?
luis martinez
November 30, 2021 at 9:08 pm
I went to pull out my transmission dipstick in the transmission fluid shot out burning hot just wanted to know why did I do that if it’s not supposed to
Desperate Mike
December 5, 2020 at 11:19 am
I have a 2004 Sentra specV with a transmission leak passenger side, I replace de oil seal twice with cv axle joint twice as well and still have a leak…opened up transmission and can’t find anything wrong…any idea what could be the problem?
Daniel
April 26, 2021 at 12:51 pm
The shaft itself on which the oil seal is installed has come off
StreetMechanic
November 3, 2020 at 1:30 pm
I have a 97 Honda accord 4 cylinder and I recently got code p0715 and I changed the sensor. After changing the sensor the code came back and i changed it again. Now my car is making a whirling sound and its still having the high rpm low speed issue in addition to the code p0715. What could be the issue? What am i missing?
Dave Smith
October 27, 2020 at 3:51 pm
consider replacing your transmission as a unit yourself if you find that you have an internal transmission problem you can’t fix. Especially with automatic transmissions, this would be a good course to follow. Another option to consider is removing your failed transmission and taking it to a shop that can rebuild it for you. At least you’ll be able to save on the removal and replacement of the transmission. (Drop-in a used) Be sure you find the correct transmission, the right fluid, and understand the TCU. Learn the Transmission that is installed. Re set the TCM/U that you have. re-check the rest of the modules that affect the computerized operation of the car, too. — Battery disconnect, low fluid, and pressure change can destroy a transmission that you have 30 to 90 day warranty for, if that. My A604 is non functional likely for this reason. Presented starter type problem, cranked after the computer reset third time, you go off.. and after it sat, same thing. You can go through replacing three and more sensors, and three on a transmission, and checking vacuum.. that might resolve a bigger problem later. Keep the fluid filled. Instead you might see white smoke billow from a relief opening after a hard clunk, then no gears will engage. That might be serviceable, or not. At 127 thousand miles, this car might get a drop-in, and be resold to a desperate person that needs a car. A car that might last longer, or not. “For Sale in Georgia”
Yaman
July 24, 2020 at 4:14 am
I have Honda 99 model 1500cc automatic transmission
1st and gear change normal while 3rd to 4th gear need 3300 rpm is it not normal or not,
Please also make a video on it,
My car is converted from manual to auto with four gear ,
From Pakistan
Please make a video I will understand properly after seeing video
Alejandro campusano
April 29, 2020 at 2:14 pm
Hola como saco una trasmisión automática de jeep gran cherokee 3.7 año 2005 como se sacan los pernos superiores ud podría ayudarme en eso