Solving Transmission Problems
Manual transmissions, or, as they are sometimes called, standard transmissions, use an operator-activated clutch assembly and gear selector lever to change gears.
The operator is in complete control of the gear selected, and when that gear is selected. This is what makes a manual transmission manual. Manual transmissions are often considered less complicated than their automatic counterparts; I would agree with that. It’s much easier to repair a manual transmission than an automatic. Manual transmission issues can really be broken down into two parts: clutch problems and transmission problems. Finding out which one you have is the first step to your repair.
The clutch is the assembly that engages and disengages the manual transmission from the flywheel. The clutch assembly consists of three main parts: the clutch disc, the pressure plate, and the throwout bearing.
Configurations of the clutch assemblies might vary, but these are the three basic parts found in all clutch assemblies. If you have a problem with any of these three parts, I suggest replacing all three. In order to replace any of these parts, you often need to remove the transmission from the engine. That’s a lot of work, so it makes sense to replace all the wear parts while you’re in there. Most clutch replacement assemblies come in a kit that contains the above-mentioned parts and hopefully a clutch alignment tool. We’ll get into that in a little bit. It just makes sense to renew all the wear parts of a clutch if you’re servicing it.
Make no mistake; a clutch is a wear item. At some point you will need to replace it on any manual transmission. I’ve seen clutches last more than 100,000 miles and as few as 12,000 miles. It all depends on how you drive it. If you ride the clutch, meaning you hold the clutch halfway between applied and unapplied, for long periods of time, your clutch won’t last that long. It’s very similar to driving around with your brakes applied; in fact, the clutch disc is often made of a similar material to brake pads. The more it gets used, the more it can wear out. Here’s a video on driving a manual transmission.
Here’s a video about the basic parts of a clutch and how they operate.
You might notice that your engine just doesn’t have the power it used to. You might even notice that you have a surging or skipping in higher gears. You also might notice that the RPMs go way up when you shift into a new gear. These are signs that your clutch might be going out. A good test is to find an empty area in a parking lot somewhere. With the engine running and in a higher gear, like second or third, release the clutch with the brake applied. If the engine stalls, your clutch is likely good. If the engine keeps running then you might need a clutch. A worn clutch can also cause a distinctive smell. It’s difficult to describe other than it smells burned. If you find your clutch is worn, it should be replaced. Here’s a video on this procedure.
If you have the above symptoms, you might not have a bad clutch. Some clutches have mechanical linkage that needs to be adjusted periodically in order to maintain proper clutch operation. This linkage often involves either a cable or mechanical linkage.
With either type, you want to do the same thing: increase clutch pedal free play. When you depress the clutch pedal it’s supposed to disengage the engine from the transmission so that you can shift gears or bring the vehicle to a stop. When you release the clutch pedal, the pressure plate is supposed to apply enough pressure to the clutch so that it wedges in between the flywheel and pressure plate. This will transfer power from the engine to the transmission. If the pressure plate does not fully engage, the clutch will slip, and as a result it won’t be able to transfer the full power of the engine to the transmission. If you have a vehicle with an adjustable clutch, this could be the result of not enough free play in the clutch linkage. This produces a condition similar to what happens if you ride the clutch.
Each vehicle and manufacturer does this a little bit differently, and it would be impossible to cover all possibilities here. Consult your vehicle’s service manual for details on how to increase your clutch pedal free play, perform the adjustment, and then see if your clutch still slips. If it doesn’t, it’s a win and you can move on until you no longer have an adjustment. At that point, the clutch will have to be replaced and readjusted to have the proper free play. Here’s a video about adjusting a cable-operated clutch on a 1993 Acura Integra.
In addition to mechanical linkage, clutches can also be controlled by hydraulics. These systems use a master cylinder and slave cylinder to engage and disengage the clutch assembly.
The principal is the same as your brakes. When you apply your brake pedal, or in this case the clutch pedal, hydraulic pressure is forced out of the master cylinder into the slave cylinder, where it’s converted to mechanical motion. Hydraulic clutches are inherently self-adjusting, meaning they don’t require periodic adjustment in the same way mechanical linkage does. So if you have a hydraulic clutch setup, it’s not likely you’ll ever have to adjust it. If you do decide to adjust it, be sure to consult your service manual for the proper procedure. For the most part, leave hydraulic clutches alone when it comes to adjustments. The only time you should need to do an adjustment is when you install a new master cylinder. Once that initial adjustment is made, that’s pretty much all there is to it.