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1989 Ford F350 5.8 EFI. Manual.

Clutch pedal was very stiff and was only able to disengage the clutch at the bottom of its travel. Bled the system, and now the pedal falls to the floor; clutch remains engaged. Relevant info:

  • The reservoir is full.
  • Master cylinder has no leaks on cab side or firewall side, slave is IN the bell housing and I can't get a good angle to see it or take a picture.
  • Followed the entire hydraulic fluid line down to where it runs into the bell housing, no leaks.
  • The bleeder nipple was extremely tight and took a lot of force to initially crack. Afterwords, I noticed that the bleeder and hydraulic fluid line running into the housing were jiggling around. I hadn't checked if they were loose prior.

I am open to the possibility that we bled it incorrectly, we did: pedal down, crack bleeder and let fluid run out, close bleeder, pedal up. pump pedal between sets. repeat. The reservoir cap was off and we never let the fluid get too low. The bleeder didn't stick out far enough to get the hose and the wrench over it at the same time. While some air almost certainly got in, I don't suspect it was enough to make the pedal fall straight to the floor given its previous stiffness...

Could one of the hydraulic cylinders need replacement despite the apparent lack of a leak? Could the slave cylinder have gotten disconnected/damaged inside the housing as a result of the torque required to crack the bleeder? Did we bleed it wrong?

EDIT: Got a Mityvac and vacuum bled the lines, but the problem persists. A lot of very dark, sludgey "hydraulic fluid" (or possibly black coffee) was removed. Tranmission is getting dropped in the next few days for a new clutch, we're putting in new master/slave cylinders as well. After seeing the state of the fluid, I suspect one or both cylinders is fouled. I learned recently that if the internal seals fail, the piston can push past the fluid without actually moving any of it. So it can fail without an exterior leak. Will update again soon

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    I had similar trouble on my car. For me the adjustable fork where the master cylinder connects to the pedal assembly had to be perfectly centered, otherwise the master cylinder wouldn't utilize its full stroke, meaning it either never pushed the air down the clutch line, or retracted so far it pulled air back into the master. Eventually, after enough attempts and an entire $%&# weekend, I got the pedal adjusted just right, and bleeding took less than 5 minutes.
    – MooseLucifer
    Sep 15, 2016 at 17:52

3 Answers 3

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"While some air almost certainly got in, I don't suspect it was enough to make the pedal fall straight to the floor"

You should have no air at all in the system. This symptom is typical of air in the system. A lot of care needs to be taken when bleeding, "close enough" will not work.

Pick up a hand-powered vacuum pump off amazon or a local auto store for ~$20. It will make the job much easier.

The open valve-pump pedal-close valve method sometimes works, but is far from good.

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There are a couple different techniques you can use.

Similar to what you mentioned, connect a hose to the bleeder, submerge the end of the hose in brake fluid. Open the bleeder, push the pedal down, close the bleeder, release the pedal. The hose submerged in fluid acts as a 1 way check valve. Closing the bleeder before releasing the pedal ensures no air gets sucked back in from around the threads.

As Justin mentioned, you can use a vacuum bleeder. Use a hand vacuum pump with a jar to collect fluid. Connect the vacuum pump to the bleeder with a clear hose, apply vacuum, and open the bleeder slightly. Continue to pump to suck up fluid as long as you see bubbles. There is a possibility you will suck bubbles from around the threads, so you may want to apply some Teflon tape to the threads first. When you no longer see bubbles, close the bleeder and remove the vacuum pump.

Another bleeding method is pressure bleeding. In this method you apply a few psi of pressure to the master cylinder. You will need to either modify a master cylinder cap, or fab something that will hold pressure. Connect a line in a bottle, open the bleeder, apply pressure until you no longer see bubbles. Close the bleeder and release the pressure.

Finally, there is reverse bleeding. This method is good for when the slave cylinder is much lower than the master cylinder. Bubbles like to travel up, so if your trying to push the fluid downward to bleed, you may have a hard time getting all the bubbles out. In this method, you use pressure to push fluid from your slave cylinder to your master cylinder. I've done this with a sauce jar full of brake fluid, a line submerged in the fluid and a pump. Purge the line to get all the air out and connect it to your bleeder. Open the bleeder and apply pressure to the jar. It may not happen fast, but you will see the fluid in the master rise. After you've pushed a bit of fluid through, close the bleeder, and disconnect the line.

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After replacing the hydraulic lines as well as the master and slave cylinders, everything is working great. I confirmed the master cylinder was at least one of the problems. Testing it outside of the vehicle, the entire stroke of the cylinder couldn't move fluid at all. So yes, a hydraulic cylinder can go bad without having any external leakage.

The slave cylinder didn't appear to have any damage, but I didn't actually test to see if it was still functioning or not.

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