Drivetrain Tech General discussion of drivetrain for the Ford Ranger.

Slave Cyl. Won't Bleed

  #1  
Old 01-29-2019
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Slave Cyl. Won't Bleed

Hey guys! So I just made a post over on the introductions forum, and now I'm here to talk about that ever so common bleeding clutch issue. So I was having real difficulty getting my truck into gear for a while already, (2008 Ranger 4.0 4x4) and I had done a bit of research and figured it would be the slave. So I dropped my trans, unbolted old SC, bolted new one in, and put trans back in. Went out and bought a new MC while I was at it, bench bled it, (pushing a screwdriver in and out till its rock solid), then installed it in the truck, then hooked up the line to the slave cylinder, opened the bleeder screw, and let it gravity bleed (about 4 reservoirs). Closed the bleed screw, cap on the reservoir, and whatdya know. Soft clutch 7/8th of the way down. Just a litttleee bit of engagement. So, I went out and bought a handheld vacuum pump, the kind to bleed brakes. First I tried vacuuming from the top ( the reservoir, sticking an end into the hole at the bottom of the reservoir) and it sucks out quite a few bubbles, but it seems to go on forever. Hours, literally. After that, I hooked up the vacuum pump to the bleed screw and pumped while someone was pouring into the reservoir. It sucks out a lot of mixed fluid and air. I've got my driver's side wheel off, so I can easily see my line going down from the reservoir to the master. Cant see any leaks there. Can also see the line from master to slave. Looks fine as well. (No visible leaks). Is there anywhere on the slave where air could be drawing in? Thanks for reading, I know it's a long post. Frustrated at this point.
 
  #2  
Old 01-29-2019
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Welcome to the forum

No, no air leaks unless new slave is bad, the pressure when you push down on the pedal is caused by the Pressure plate in bellhousing, not anything in the Master
The slave/throwout bearing should be touching the pressure plate after trans is reinstalled, in fact you are suppose to open the Bleeder valve on slave if when reinstall trans, so it can collapse a bit as it pushes against pressure plate.

If there is no pedal pressure then yes, maybe alot of air in the system, not a little, a little air just means when pedal is down to the floor the clutch disc is not Fully released, so hard to get into 1st when stopped, but you should have good pressure all the way down
 
  #3  
Old 01-29-2019
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Hey Ron, yes I took a picture of the bearing against the pressure plate, it looks like its right up against it! I got someone to press the clutch pedal as I watched, and it only moved about an eight of an inch, maybe a little more. I just took out my master again and bench bled the entire thing, it's hard as a rock when I try pushing it in, with the line to the slave disconnected. As soon as I connect the line to the slave, its soft almost all the way down, and then just about a quarter inch of good feeling pedal. I did notice however, when I was watching the slave move, some writing on my clutch that said something like " Before Install < " with an arrow pointed one way, and there's a groove, with a spring in it, and the spring is on the opposite side of the way the arrow is pointing. Any relevance?
 
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Old 01-29-2019
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Never noticed any arrows, but usually dark when I am under truck putting stuff together, lol

But I doubt that would matter

Have someone watch the reservoir as you push down on the pedal, fluid has to be going somewhere, and if it ain't going into the slave then it must be going into reservoir

The whole system is pretty simple, like brakes.

The master has a piston inside with a spring that holds it up towards pushrod, and two hoses connected
When piston is up all the way the reservoir hose opening is open to chamber behind the piston so fluid can flow down and into the space behind the piston, and all the way down to the slave if gravity bleeding.

When you press down on the piston it slides down and CUTS OFF that opening to the reservoir, so all the fluid behind the piston only has the hose to the slave to flow thru, reservoir hose is like a one way valve

As the fluid flows down that hose and into the slave it expands and pushes on the pressure plate fingers releasing pressure on the clutch disc

From your description there is only one of two things that can be happening, unless there is a big Leak, lol
1. piston in master is defective and fluid can flow around it so as you press down on the pedal piston is just moving THRU the fluid not pushing it down the hose to slave
2. one way valve isn't working and most of the fluid is flowing up into the reservoir

Can't see any other ways for what you describe can happen
 
  #5  
Old 01-29-2019
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Yeah I get what you're saying, makes sense to me. I'm almost leaning towards "big leak", simply because when I attach my vacuum pump to the bleed nipple on the slave, it seems to pull out endless amounts of air. However, I would assume if the slave was leaking, wouldn't there be fluid in the tranny somewhere?
 
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Old 01-30-2019
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Yes, it would pour out of the bellhousing

Very easy to see

Quick connect fittings are not "universal", which is why its often best to get slave and master as a set

But again if it was leaking at that fitting you should see signs of that
 
  #7  
Old 01-30-2019
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I just read a post on a forum somewhere, someone was experiencing very much the same thing as I am. Turns out the torque specs in his Haynes manual were far too low, so the clutch actually wasn't tight against the flywheel...I'll link it over just for kicks.

https://www.ford-trucks.com/forums/5...t-bleed-2.html
 
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Old 01-30-2019
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No, not your problem, clutch would slip, and this wouldn't have any effect on air or pedal travel, slave would actually be pushed in more if pressure plate wasn't as close to flywheel as it should be.

And, not for nothing, DIYer would have to be a first time novice(to everything mechanical) to not tighten pressure plate tight to flywheel, regardless of torque specs, so can't even get my head around that one, lol.
 
  #9  
Old 01-30-2019
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Oh no kidding, stoked that its not that, would be a PITA to take it all out again, although I'm starting to wonder if Ill have to tear it all out regardless. Im going to be reverse bleeding it in a bit here, see if that by some miracle makes a difference. I would assume gravity bleeding the slave would work just as well, but Im not expert. I'm 100% confident its not the master though, its still hard as a rock when I have the quick connect disconnected. Is there a reliable way to tell if either my Master cylinder, or slave cylinder, is defective, and if so, which one?
 
  #10  
Old 01-30-2019
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Just as a heads up, the slave has no valve in it, if you take off the Quick Connect hose the slave is open, the valve is in the quick connect fitting

So you could plug that opening and then apply vacuum to bleeder and it should hold pressure, if it doesn't then you have a leak in the slave unfortunately

If it holds pressure then problem is in the Master side of things
 
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Old 01-30-2019
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Beauty!!! Definitely going to do that, thanks for the tip!
 
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Old 01-30-2019
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Originally Posted by RonD View Post
Just as a heads up, the slave has no valve in it, if you take off the Quick Connect hose the slave is open, the valve is in the quick connect fitting

So you could plug that opening and then apply vacuum to bleeder and it should hold pressure, if it doesn't then you have a leak in the slave unfortunately

If it holds pressure then problem is in the Master side of things
Just tried this method, so I plugged the hole where the quick connect goes with a rubber cap that originally came with the slave. Hooked up my vacuum pump to the bleed screw (with the bleed screw open) and pumped till about 20psi. It lost about 1psi every second or so, maybe a bit quicker. Wouldn't hold pressure at all. So, I closed the bleed screw all the way. Hooked up the line again, pumped again. This time it lost pressure again, but slower. But still the same. Figured it HAD to be the slave. So, went and bought another new one, and first thing I did was try this method. Same thing happened. So, I figured what the hell, I'll try it on my old slave. Same thing. What are the odds of this happening on 3 slaves? Is there an area Im not blocking, let air in somewhere? Or does this procedure have to be done with fluid in the slave?
 
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Old 01-30-2019
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Originally Posted by NotoriousNick View Post
Is there an area I'm not blocking, let air in somewhere?
Probably where your vacuum pump hooks up to the bleeder screw.
 
  #14  
Old 01-30-2019
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Originally Posted by 2011Supercab View Post
Probably where your vacuum pump hooks up to the bleeder screw.
Ok, that I can see, but how about when I've got the bleeder all the way closed?
 
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