One of the fastest ways to burn thru a classic car clutch is improper adjustment of the car’s clutch pedal. To work efficiently, the clutch needs the right amount of play in the linkage between the foot pedal and the clutch operating lever (also known as the release arm or fork). Anything less than the correct amount of free play (or clearance) will result in clutch slip because the pressure plate will be unable to exert its full pressure on the friction plate.
Failure to cure this fault will quickly lead to a burned-out friction plate, and possibly a ruined pressure plate. If, however, there is too much clearance in the clutch linkage, the car tends to creep forwards when in gear with the clutch pedal fully depressed. This is known as clutch drag, and it can cause difficulties in heavy traffic.
It is generally better, however, to have too much play in the clutch linkage than too little.
Why Should You Adjust Your Car Clutch Pedal?
If you own a vehicle with a manual transmission, chances are that you have replaced or at least thought about replacing your clutch. Usually, OEM clutches last a long time and do not require replacement before 50 to 60 thousand miles. That means many of those who replace their OEM clutches are looking for some action with aftermarket clutches.
So, after a careful selection process to find your aftermarket clutch, which is suitable for your vehicle, what comes next? Break in the clutch and you are good to go? Not really!
You have forgotten about a very important part of your manual transmission ecology, the car clutch pedal. After installing a new clutch, if it is an OEM clutch, sometimes it is not necessary to adjust the pedal, especially if the free play is fine. But in the case of an aftermarket clutch, you certainly need a pedal adjustment. Believe it or not, an ill-adjusted clutch pedal can go as far as destroying the thrust bearing of your crankshaft, causing engine failure.
How Does the Clutch Pedal Work?
Before explaining why you need to adjust the clutch pedal after installing a new clutch, we should first understand how the clutch pedal work.
Most newer vehicles with manual transmission use hydraulic clutch release. In a hydraulic release, when you put the pressure on the pedal, the pedal transfers the pressure to something called the master cylinder. There is a plunger in the master cylinder that is connected to the pedal. As you push the pedal, the plunger pushes the oil inside the master cylinder. The oil then travels through tubing and reaches another cylinder down the line, known as the slave cylinder. There is another plunger there which moves forward due to the incoming oil pressure. This, in turn, pushes the clutch fork and the release bearing associated with it. The release bearing pushes the center of the diaphragm spring and voila! your clutch is disengaged.
In a mechanical clutch release, the pressure is conveyed by a clutch cable sliding inside a flexible sheathing. The clutch cable is connected to the clutch pedal on one end and the release fork on the other.
Metrics for Clutch Pedal Adjustment - Pedal Height and Pedal Free Play
Before talking about pedal adjustment, let us talk about its two important parameters, the pedal height, and free play.
When you press the pedal, it goes down towards the floor, right? The pedal height is the travel distance between the pedal sit and the floor. This height determines how much travel you can put on the pedal to disengage the clutch. The height is adjustable and may need adjustment if you change anything down the line, such as the master cylinder, throw bearing, or the clutch itself.
Then we have pedal free play. It is the distance you can push down the pedal before feeling any resistance. In simple terms, it is the clearance before your clutch feels the pressure from your foot and starts to disengage. This is crucial for both your driving experience and clutch health.
Why Does Your Clutch Pedal Require Adjustment?
So now that we know the pedal mechanism and the important metrics, it is time to discuss why you need to adjust your car clutch pedal after purchasing a new clutch. It all boils down to the thickness of the friction plate and the clamping pressure of the pressure plate.
When you had your OEM clutch, the pedal height, free play, and clutch response, all were calibrated by the manufacturer to work properly.
When you install a new clutch in your vehicle, things change, things like clutch assembly dimension, friction plate thickness, and clamping pressure. For example, if it is an aftermarket clutch, it is bound to be thicker than your OEM clutch, and it will exert higher clamping pressure with a more robust pressure plate.
If you do not adjust the pedal, that means your pedal height is the same as before. When you will push the pedal down to the floor, the master cylinder will get the same actuation as before and in the end, the release fork will have the same travel. Since your new clutch has a new pressure plate with higher clamping pressure, the fork travel won’t be enough to fully disengage it. And here comes the infamous clutch slip. Whenever you will try to disengage and change gear, the clutch will be slipping, burning up the friction material. Slipping also puts rotational twists on the release bearing, causing it to seize and collapse eventually.
There is inconvenience regarding the friction disc too. Since it will be thicker than your worn-out OEM clutch, it will tend to bite sooner as you release the pedal. So, the moment you want to take your foot off the pedal, the clutch would want to bite, which can be pretty annoying for many people.
Then there is the issue of free play. Free play determines when your clutch starts disengaging after pushing the pedal. Some of us like the clutch to disengage immediately after depressing the pedal. But it is important to know that some amount, and more importantly, the correct amount of free play is essential for your clutch longevity.
When you install a new clutch, the changed dimension can change the free play available at the pedal. When there is less than ideal free play, the clutch will be right on point where disengagement begins, which means it will not have full clamping pressure on it and it will start slipping.
Also, without proper free play, the hydraulic oil cannot fully return to the master cylinder, meaning the rod of the master cylinder is not released all the way when your foot is off the pedal. This specifically happens when the parts are hot and expanded fully, or when you rest your foot on the pedal. Apart from wearing out the release bearing, the clutch fork, or the pivot, it can also cause leaks from the master and slave cylinders.
On the other hand, too much free play can cause clutch drag, making your car creep forward while changing gears, which can be troublesome in heavy traffic. Therefore adjusting your clutch pedal and achieving the correct amount of free play is very crucial.
My Clutch Release is Hydraulic, does it Mean Its Self-Adjusting?
Most new cars with manual transmission have hydraulic release instead of mechanical linkage. And some new models with hydraulic release also have self-adjusting mechanisms. That is why many assume that all hydraulic systems are self-adjusting. This is a quite common misconception.
Even if your vehicle has a self-adjusting pedal mechanism, it rarely works 100% and most often needs a bit of help in self-adjusting.
Self-Adjusting Clutch Adjustment
A self-adjusting clutch is supposed to adjust itself for the correct amount of free play, but sometimes this is not always the case. A self-adjusting pedal uses a hydraulic clutch pedal, which means it is typically easier to fix, no matter what the technician’s experience level is.
When the engine is running and you have the parking brake on, put your foot under the clutch pedal and lift it up toward yourself. This way, you can test and verify the results of your adjustment when you depress the clutch pedal and put the vehicle into gear. Next, check the distance that the clutch must move down before the gears can be changed.
Manual Clutch Adjustment
First, turn off the engine and engage the emergency brake. Position yourself so your head is partly underneath the dashboard, allowing you to see and access any adjustments that need to be made. Your vehicle will most likely have a clutch cable with a threaded rod. The rod will have a locknut and an adjuster nut to determine the amount of free play the clutch pedal has. Locate the nuts so you can adjust them by loosening both slightly. Pull up the clutch cable again so you can feel a point where the clutch fork engages.
Once you feel it engage, that is where you should adjust the clutch cable. Make sure you are keeping the pressure on the clutch cable, keeping it in the exact position as you tighten the locknut and adjuster nut.
Finally
The clutch is a critical component in the operation of manual transmission vehicles. The clutch allows the transmission to disengage from the engine, allowing the operator to change gears. To work correctly, the clutch needs the right amount of free play in the linkage between the foot pedal and the clutch operating lever. If the amount of free play or clearance is low, it results in a slipping clutch. When there is too much free play, the clutch may be dragging.
If you put a new clutch in your car, the clutch pedal needs an adjustment. Even a stock clutch will likely have to be adjusted. With an OEM clutch replacement, the new disc will have more thickness. With aftermarket clutches, the dimensions, and the pressure plate, both will be different, making it absolutely necessary to adjust the clutch pedal.
