Greetings: I thought I had this problem licked a few months ago, but it has reared its ugly head again. Once in a while, and now with increasing regularity, my clutch fluid seems to mysteriously dissappear. I do not have any leak spots on the garage floor, and no signs of fluid dripping or leaking anywhere. Yet, and especially when it sits facing uphill for a day or two, the clutch goes to the floor and I can not get it in or out of gear without brute force. I check the reservoir, open it, find that it's a tiny bit lower than last time, add some fluid, pump the pedal and then I'm on my way. Where could it be going? Possibly a tiny hole somewhere in the line which squirts it out over time? What should I first look for? Worse case scenario, what am I looking at for a professional repair job? (I just spent $580 on new rear brake cylinders)...:>( Thanks!
If you have a coaxial slave cylinder then most likely its filling the bottom of the bell housing with fluid. Pull the rubber access plug on the side of the bell housing and check with a mirror and flashlight. If nothing there then check inside the truck around the clutch pedal rod or carpet.
You say, "tiny bit lower," but is a tiny bit a teaspoon, tablespoon, few ounces?
Unless the level is below MIN on the reservoir, I see no reason to top it off -- given the symptoms you are having. (There are lots of reasons to top it off, but the symptom set you are having does not prompt me to fill the reservior.)
Your clutch is activated hydraulically, exactly the same as the brakes -- with a minor variance. The variance is, as you rest yoru foot on the brake pedal to hold your truck inm place, you apply pressure to the sustem. The clutch has massive springs inside that apply pressure to the system. The end result is the same, and I will describe it for you from the perspective of the brakes.
As the pressure on the pedal is maintained, the fluid inside the Master Cylinder is held up on two different fluid circuits. There is a piston passing between two different chambers in the MC, and o-rings attempting to keep the fluid separated -- the chambers are designed to regulate braking pressure on two sets of wheels, so if one set looses brake pressure, hopes are the other set will retain functionality long enough to stop. In any case, a faliure of the o-rings allows the piston to move because fluid on one side of the o-ring can pass to the other side, and the affect you feel is your foot sinking as you wait for the light to turn green. As your foot falls and brake pressure drops, the vehicle may begin to creep; you remedy this by pumping the brake pedal a few times to bring the pressure back up, which raises the pedal off the floor and you continue waiting for the light to change, and your foot sinks again.
On the clutch, the same forces are at work, except the pressure is applied by the massive springs in the clutch itself. The symptom set is a bit different because the pressure comes from a different place, but at the end of the day, you still need a new Clutch Master Cylinder. There is a piston connected to the clutch pedal, and it has an o-ring that seals it to the bore inside the MC. You could simply press the clutch pedal several times while the trans is in N, this will build hydraulic pressure in the clutch system, allowing eventual selection of the desired gear. You probably have difficulty selecting any gear, and more difficulty on the first or second gear selection after not selecting any new gear for a long time. You notice that 1st and R are most difficult to select because the gears moving due to the engine and the gears not moving due to the driveline are the most difficult to engage -- as you make a shift after the turck is already moving, the selection is less difficult because the parts are already moving, and if you make the gear change at the right moment the gearsw will be moving at the same speed and the change can be done without using the clutch at all.
BOTTOM LINE The Clutch Mater Cylinder has an internal leak -- failing o-ring -- that makes the pedal action ineffective until you pump the pedal several times. The fact that you have filled the reservior is coincidence.
If you sat at a Red Light in 1st gear and the clutch depressed the whole time, you would notice that the clutch engages at different points, in extreme cases the truck might creep on its own, but you probably uswe the brake at the same time and do not notice. Normally, thbe clutch should start to grab at about the half-way point, but you should notice it grab nearly at the floor on some occasions, and further up on others. If this happens, the clutch springs have caused the fluid to leak past the o-ring(s) and the clutch plate is beginning to approach the flywheel all by itself.
In both systems -- clutch and brake -- the fluid pushes on slave cylinders that actually activate the mechanism at the other end of the pipe. These slave cylinders can leak and give the same symptoms, except they will leak to the outside and you will see fluid coming out. You will also see a noticable drop in the fluid level in the respective reservior -- the fluid will drop from MAX to MIN or below, and this sort of drop is never characterized as "tiny bit lower."
Curious as to what kind of labor is involved in the replacement of the master? Thanks.
It is not all that difficult. It is kinda like replacing the brake master cylinder and wheel cylinders; if you have done this before, then you should be able to do your clutch master.
You will introduce air into the system, so you will have to bleed the fluid until the bubbles stop. The master cylinder will be REQUIRED to be bled on the bench before you install it. When you buy the new master, you will have to ask the parts guy for the bench bleeding kit -- an assortment of plastic fittings and a length of hose, cost is about $5.00.
The master is held on from the engine side of the firewall. It will have two or three bolts (I usually find 2), and a fitting that goes to the clutch slave cylinder. TIP, the open lines can be plugged with a golf tee to prevent leakage of fluid and the introduction of dirt. This is when air will be introduced, and you will bleed this later.
Take the new master to your work bench and connect the fittings and hose, route the hose from the fitting(s) into the reservior and secure with a clip. Fill the reservior with fluid and make sure the hose is submerged and remains submerged through out the installation from this point forward.
Use an appropriate tool -- long screwdriver or ratchet extension -- to depress the piston fully. Repeat as necessary until there are no more bubbles coming from the end of the hose that is submerged. Repeat a few more times just to be sure. (WHAT YOU ARE DOING -- the clutch pdeal dies not move the piston fully inside the cylinder, so there will always be air trappped inside causing a mushy feel to the pedal. The suitable tool you are using will depress the piston its full travel and force out all of the air that can get trapped inside the cylinder, giving a firm feel to the pedal. If you ever replace a Brake Master or Clutch Master, you have to Bench Bleed or live with less than optimum performance/feel.)
Leave the hose and fittings attached to the master, and set the master to the vehicle. Be careful to NOT spill any brake fluid, and if you manage to spill some, be sure to clean it completely. Brake fluid is corrosive -- this means it eats stuff. When the master is set in place and bolted up well, you can remove the hose and fitting, and connect the hard-pipe that goes to the slave cylinder that is either mounted inside or outside of the bell housing. This is the other time you will introduce air into the line, but bleeding the line is the next step.
Bleeding the line is last. Well, adjusting is last, if adjusting is needed or available, but bleeding is what you do now. This step takes two people. (Indeed, the whole job takes two people if you have never done it before, but one of you should have done it so you do not get into a blind-leading-the-bllind situation.)
Open the bleed screw on the slave. Depress AND HOLD the clutch pedal. Close the bleed screw. Release the clutch pedal. Repeat until the air bubbles come out, then stop coming out. MAKE SURE THE RESERVIOR DOES NOT EMPTY.
The job is not that difficult, but the description I gave ignores crap that might be in the way, and this crap can increase the difficulty level considerably. The pedal might be held to the MC piston by a clip or other device, and this can be a bitch to get off. When I did my master cylinder, the rod that was connected to the pedal fit into a cup on the cylinder, so the cylinder came off easily without having to look for and find the clip.
Thank you a ton, Jeff! This is my weekend project!
Get a friend to help. Try to get one that knows this stuff if you don' know it. It is easy, and this is a good project to learn on.
Be sure to do your test drive VERY slowly until you are sure the brakes work. If the brakes give you trouble, turn the motor off and leave the gear selector in 2nd. I'd be testing the brakes in 1st until I was sure they had minimal function or better.
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