I rebuilt my clutch master cylinder and everything went fairly smoothly until I went to engage the pedal. When I press in nothing happens, that is to say the pedal goes in but it doesn't engage the clutch. When looking at the slave and the clutch it looks like it is already partially engaged all the time. I bleed the system and topped off the fluid so I know it has fluid but cant figure out what is going on. When I start the truck i cant put it in gear. Any ideas? did I miss a step? Help?

 

We need a lot more info: what motor, year, tranny, clutch, master cylinder, why did you rebuild it, how did you rebuild it? What was it doing before you rebuilt it? Did you have any parts left over? (don't laugh, it's happens to the best of us). Did you bench bleed the MC before reinstalling it? Did you change anything else? Is there bubbling or swirling in fluid in the resevoir when you operate the pedal?
If I had to guess from your brief diescription of the problem I'd say either air in the line or the bore in the cylinder is too far gone or honed oversized so the piston is bypassing.
If the bore in a MC is pitted or scratched enough to require honing don't bother there is very little to no extra tollerance for an oversized bore, replace it if a new (not rebuilt) one is available or have it resleeved with a stainless steel sleeve.

 

Not sure if this is applicable, but a clutch master cylinder has NO residual check valve of any kind (its not supposed to) and therefore you cannot build up enough pressure, or actually, hold back on the fluid to force the air to the bleeder, the air just moves back and forth inside the line. It’s been awhile but clutch master cylinders have to be bench bleed with you finger acting as a stopper so that fluid is sucked into the piston bore.

 

292, 1958, 3 on the tree, single master (original), rebuilt because it was leaking into the cab. I had no parts left over and was happy because it was not leaking anymore when I put it back together. I have no idea if it is swirling or bubbling because I cant depress the pedal and see the master at the same time. I bleed the lines so I dont think that it has any air in it but like I said it looks like the slave is 3/4 or more engaged at all times and when I press the pedal nothing happens. The inside of the MC looked great, no pitting. If is was gone I would think that I would be getting a leak again but since that isnt happening I think that the rebuild worked. Any ideas, things I can try. I really dont want to buy new to find out that I just did something wrong when reinstalling and even more so have the same problem with a new unit. Thanks.

 

OldF1, can you give me a little more instruction on what you are talking about and how to do this and still hook it up to the line without getting brake fluid everywhere?

 

If the slave is not moving then nothing is pushing it, right?
In my experience it is virtually impossible to bleed a hydraulic clutch on the vehicle. (without a pressure bleeder) Because there is no residual check valve so when you close the bleeder with the petal down and then release (pull up) the pedal is does NOT suck brake fluid like a brake system does it just pulls the trapped air in the line back up the line (path of least resistance?) all day long. You have to get all the air out of the master cylinder first so that it has brake fluid (pressure) to force the rest of the air out.

OK, MC in the vise, full of fluid. Cap off. Push the piston forward to the end with a screwdriver (or whatever) before you release hold you finger/thumb/bum over the outside port tight, release the piston, it should suck brake fluid from the resivour, repeat, it will spray fluid so have a catch jar, repeat using your finger until no air comes out, just clear fluid, make sure MC stays full.

Put your finger over the hole and reinstall on truck, have helper pump the poop out of the pedal, hold it down, and you release the bleeder, so should get a tiny poof of a deer fart, this is the air starting to move, close bleeder, it might take many attempts to get all the air. Nothing to it, right?

 

Ok, I will try that but my other question is how do I get the slave to release? it is like 3/4 engaged right now?

 

If you don't have 3 or more hands you might want to find a brass plug or even a rubber stopper for the MC port so you can seal it off while reinstalling it. I can't imagine how the slave cylinder is holding the clutch partially depressed, as F1 says there is no residual pressure in the line. If the clutch is partially depressed, I'd suspect there is something seriously wrong with the clutch: torn lining, broken springs, broken/worn thru fingers or diaphram (depending on clutch type), pressure plate hanging up. If you remove line from MC does the clutch fully retract? If so, something is wrong with the master cylinder (piston, spring or seals backwards, pushrod too long???) that it's holding pressure in the line.

 

Can you explain why you think it's 3/4 engaged? Just visually estimating?

Loosen the bolts on the slave; see if there is pressure on the bolts (be careful!) Don't remove them, just loosen enough to see if there is pressure against them.

It's possible the clutch fork got out of position when you pulled the slave off, and isn't on its pivot.

 

If you didn’t change the clutch unit or repair the slave,............... it will fix itself.

 

I was assuming it was an intergrated hydraulic throwout bearing, rather than an external slave operating the fork. If it is external, you should be able to jam or lock the end of the fork so it can't move when the clutch pedal is depressed, allowing the line to be bled.

 

it is external slave and it just looks like it is engaged, I could be wrong but when I put my hand on it it wont move either direction. Well I should say it moves like a 1/4" toward the back of the truck but that is it. is this normal?

 

I'd then unbolt the slave from the engine and see what happens. If it still looks like it's partially engaged (if it is you should be able to slip the end of a screwdriver or a putty knife between the clutch disk and the pressure plate. DON'T get your fingers anywhere near the clutch just in case it actually is engaged and suddenly released, it could take the end of your finger off). If the pressure plate is tightly sandwiching the clutch disk between the pressure plate and flywheel and you can move the throwout bearing back towards the tranny at all, it is not engaged.

 

how much movement should I be getting out of the clutch/slave? it is now moving but only the smallest amount. is it that I just need to bleed it more? I did the bench bleed and then used a vac bleeder to bleed the lines and still only get a very small movement.

 

Ok, it works. I got my preggo wife out in the garage and did the bleeding the old fashion way and it still wouldnt work so I asked her to step on it while I was underneath to see if I could see what was wrong and she says that it is harder to step on. I am like "really" and get out from under the truck and sure enough it was and it worked. Not sure what happened in the minute that it didnt work and when it did but I am glad it works. Thanks for the help.