Hi All,

Some time ago, the clutch pedal on my 1986 F250 6.9l V8 diesel 4x4 started losing pressure and then it wouldn't hold any pressure at all. When I checked under the truck, it appeared to be leaking from the slave cylinder. I tried replacing the hydraulic line which did not help and then I just replaced the slave cylinder. I was able to vacuum pressure bleed it and get all of the bubbles out of the line, however the clutch pedal did not hold any pressure. I then tried vacuum pressure bleeding while pressing the clutch pedal. It appears the pedal started to get a little bit stiffer, but then fluid started coming out of the slave cylinder again.

When I bought the truck a little more than four years ago, I did put in a new clutch master and slave cylinder.

I'm planning to put in another slave cylinder when the rain goes away, but I wanted to see if anyone had any recommendations.

I have no idea when the clutch was last changed and I have heard about issues with the clutch springs going bad. When I pressure bled the clutch system, I went up to about 25 psi. I did some research and some people say that may be too high and others say it is about normal.

I'm not sure what else it could be. It is my understanding that if the vacuum gauge holds pressure, then there are no air or fluid leaks. The only thing I could think of would be a seal or something that is not right in the slave cylinder.

Thanks,

h.ubk

 

Pretty odd to install a new slave and have it leak on you. Do you have a hex plug that some use as a bleeder on your slave? Did you use that hex plug in your vacuum pressure bleed? I'd check that hex plug as if it's not tight it will leak. I'm not familiar with a vacuum pressure bleed system. Usually it's one or the other. But for the stock master, line and slave with the roll pin connections a pressure bleed is not needed. For a new slave, remove the old one and disconnect it. Your reservoir should have fluid visible but keep the cap on tight before disconnecting the slave. Fill the new slave with fluid through the connection hole. Tip the slave fore and back and burp air between filling the hole. Fill till it seems full and tip it for and aft keeping the hole up. This will burp air out of the slave. Keep filling and burping till it's full. Then connect the full slave to the line and install the slave. Open up the reservoir and top it off. Then pump by hand the clutch pedal to purge air up the line. As there will be a small amount of air that gets in the end of the disconnected line. About a drop comes out when you disconnect the line. Keep pumping by hand till the pedal returns. Then climb in and pump by foot. Eventually you get pedal. Depending on how much air you let in could take about 15 minutes of pumping. When you have good enough pedal almost normal start and warm up the engine while you keep pumping. When the engine is warm shut it off and put the truck in first gear. Hold the clutch down and start in first gear. The truck may start to roll in first gear if you aren't disengaged. Drive around pumping the clutch in first gear until you can shift to second. In about 5 miles of driving and pumping the air should be purged and normal driving can commence. You don't have to drive. But you'll take longer and have to pump more. The driving, vibration helps air up the line. So it's quicker but you do have to contend with a rolling start. It's best if you have a little traveled back road to do that on.

 

Can you isolate the exact source of the leak? Is it leaking around the piston and pushrod? Or where the line attaches to the body? Wash down the area with brake cleaner if needed to get a good visual.

 

Bigblue, I had a NEW wheel cly leak just sitting in the garage as I was rebuilding the rest of my truck.
So new dose not mean good

If the slave went and both the slave & master were replaced at the same time I can see the master being bad now too.
Even more so if it will not build psi, master piston is bypassing fluid.
Dave ----

 

Dave, it's entirely possible for both the new slave and the existing master to be bad as you say. I think you start with getting the slave to be a non leaker. Even if the master is going out, should be good enough to prove the slave is leak free. If everything was working properly and then the leak sprung on the slave, I'd say start with the slave.

 

I'll add that if you do the rolling start a hilly, bumpy back road is best. You can't do that in the city with stop lights and traffic! Well you could but be ready to shut off the engine for a stop!

 

If your fluid is old you might want to purge your master and reservoir. Once you remove the slave and disconnect the line place a bucket under the line where you can see the fluid coming out of the line. Open the reservoir and the line will begin to flow. You'll see dirty fluid coming out, a flashlight is helpful to see the color change, but keep pouring in new fluid in the reservoir as the old fluid drains out. When you see new clear fluid coming out fill the reservoir one last blast and pop the diaphragm and cap back on. The drip will stop with the cap on snug. Now connect the line to the filled slave. Install the slave. If you have a helper you could crack the hex plug and have a helper depress the clutch pedal very slowly while you watch the hex plug and when the lil bit of air bubbles out the cracked plug and you see fluid without air close the hex plug. I usually don't have a helper. But it could save some pumping the clutch time if you can push the one bubble out the hex plug. Be sure to snug up the plug when done! Your helper can't let the pedal up while the hex plug is open. Probably one stroke of the pedal will do it. And maybe a partial pedal stroke is all you need. Best to control the pedal by hand rather than by foot for that quick purge.

 

It is leaking where the hydraulic line is connecting to the body of the slave cylinder.

h.ubk

 

So, the vacuum pressure bleed uses a vacuum line to connect to a tiny hole in the reservoir of the master cylinder. It sucks all of the bubbles out over a period of time.

I didn't use the hex plug in the slave cylinder, but I will double-check that it is tight.

h.ubk

 

There's a rubber donut that goes on the end of the line. You have to compress that in with one hand while pushing the roll pin with the other hand. I have used channel locks to push in the pin. Recently I had to replace the slave while away from home. I tapped the pin in with a small hammer. The pin has to be behind the flange on the line and the rubber donut in front. A new slave comes with a roll pin and a rubber donut. Always replace the rubber donut and pin. Do not reuse the old ones.

 

Okay. I think that is the lesser of the two evils when it comes to a leak.

Did the new slave cylinder come with a replacement seal? On mine, it was just a fat little O-ring. The original was more of a thick flat rubber washer.

To seal this connection, make sure the new seal is in good condition. If any doubt, replace it. If still no joy, I think you could compress the seal just a little bit extra by adding a thin washer.

For dealing with the roll pin, please see this recent thread. It's a long thread but I think you will find it worthwhile:

https://www.ford-trucks.com/forums/1...tch-fluid.html

Post #27 shows an inexpensive tool that will save you a LOT of grief, especially when working in tight quarters. I HIGHLY recommend this tool.

For bleeding the system, please see the first two videos in post #12. That's how I did mine, and it worked like a charm. I did it the hard way, with everything assembled on the workbench. I should say the bleeding was easy that way, but snaking the complete assembly in place on the vehicle was tricky. If I were to do it over, I'd assemble the pieces on the vehicle, but leave the slave cylinder hanging loose at first. I'd bleed it just like in the video, only on the vehicle instead of on the workbench. Then I'd install the slave cylinder to the bellhousing and be done.

 

I figured Karl would chime in about the special roll pin tool. You need one the right size to remove a pin. Pushing one in with one larger would work. The roll pins get weak too. I had one crush on me spitting out the hydraulic line at the master. By the way, how's your firewall? Do you have the reinforcement plate? The firewall cracking is a known issue that can affect proper clutch operation.

 

My firewall is in good shape. I doubt that is the problem. The brake fluid is brand new.

I ordered the pin removal tool and hopefully it should be in today. I am going to try again with a new pin from the hardware store.

I was playing around with sealing it on my old line and slave cylinder and it looks like the washer holds the seal and the pin is just to make sure the connection does not dislodge. It looks like the seal is the same on both sides. When I press the line in, I can feel it lock into place and if I try moving it back and forth it is solid. If the new pin doesn't produce results, I will try another slave cylinder.

Thanks for all the replies.

h.ubk

 

You won't notice if your firewall is cracking by looking at your clutch master. It might look completely normal. Watch the master while a helper depresses the clutch. Have the helper pump it a few times. If the master moves out more than 1/8" the firewall is likely cracked and it will progress over time. I'm on my second master and third slave but I have the original hydraulic line. It seems robust. The roll pins can fail and a partial fail will produce a leak. I had the roll pin in my master completely fail and the hydraulic line was spit out as the pedal went to the floor.

 

On my most recent slave replacement the metal clip that is held in place by the molding of the composite slave body became loose as the ridge holding it in place failed. Allowing the slave to rotate a bit on each depression. That rotation split the rubber donut seal and eventually the broken rubber donut was blown out past the washer element. So when I removed the slave there was no rubber donut in there!