Anyone replace the clutch master cylinder before?

[FastCougar]

I know it's fairly common place to see worn out/leaking slave cylinders (I still think this is an installation issue and not a parts issue). However, after bleeding the clutch for 3 minutes, I still have no pressure in the pedal. If I fill a bottle with a little brake fluid and then run a hose from the bleeder valve into the bottle, pumping the clutch sucks more fluid than it bleeds out. Sure sign that the master cylinder is shot (merely pushing/pulling fluid in/out vs. pushing fluild out only). I have to note that I bought the car with a "blown slave cylinder" ... turns out to have been misdiagnosed if I'm right. Oddly though, the master cylinder is nearly 1/3rd the price of the slave cylinder.

[wadespencer99]

Not sure how similiar the Cougar is to the Focus, but if you look on Focaljet or Focusfanatacs I'll bet you'll find a how-to as the ones in the Focus are known for failing.

[jrak123]

use a mighty vac to bleed the clutch Trevor, it's the only way to do it right. I have bled about 15 of them so far and the pedal always feels funny until the car is actually started and running.

[FastCougar]

Why is that ... vacuum pressure from the brake booster have an affect on the master cylinder filling you think?

[jrak123]

That shouldn't effect it really.. I have no idea why it happens, but that is what I have seen

[Blackcoog]

I have a few that just wouldn't bleed correctly. I even used a vacuum pump to try to bleed one, it worked but it took forever. Normally I keep the clutch line elevated as soon as I diconnect it so there is minimal fluid lost. Then minimal bleeding is needed.

[FastCougar]

Well, I'm going to stop by AutoZone on the way home and see if they have a Mighty Vac and will try bleeding again tonight. I already called my local dealer and had them order one, so if after starting the engine and rebleeding, the problem doesn't go away, I will pick it up Friday and replace it this weekend.

Which brings to this ... how do you diagnose a blown master? I disconnected the clutch line from the slave input and pumped the pedal and sure enough, fluid squired out. I then did the bottle test and it didn't get more full, but rather, less full. The slave was sucking fluid. I will keep at it!

Keep in mind, this car has sat without an engine/trans for a year now, thus why there would be massive amounts of air in the lines

[FastCougar]

99.9% sure it's the master cylinder. Here is what I did to diagnose the issue:

1) Purchased a MityVac and attached it to the bleeding nipple and opened the valve. I then applied 25 in Hg vac. It pulled a very small amount of fluid and then nothing but bubbles. It lost roughly 1 in of Hg vac every 30 seconds or so, indicating a leak.

2) Pumped up the vac again to 25 in Hg and then put my head into the foot well of the car to listen for a leak, couldn't hear any, so on I pressed.

3) Closed the slave cylinder bleeder valve and applied 25 in Hg vac and let it sit for 2-3 minutes ... no leaking, so I can now rule out the bleeder valve.

4) Disconnected the master cylinder line from the slave cylinder input nipple and opened the slave cylinder bleeder valve and tried to apply vacuum ... did nothing but suck air ... the slave cylinder can be ruled out ... if it can suck air, it should suck fluid.

5) Put a MityVac attachment into the master cylinder line (the one that attaches to the slave cylinder input line). I applied 25 in Hg vac and let it sit ... vacuum reading steadily dropped over 2-3 minutes. Definite leak in the line, but from where?

6) Put the MityVac canister on the end of the master cylinder line, got in the car and started to pump the clutch pedal ... heard a gurgeling sound. I got out expecting to see some fluid build-up in the canister, but there was nothing. So I tried it again, with the same results.

I have to conclude that it's the master cylinder. Anyone care to disagree???

[FastCougar]

I just thought of something ... keep in mind, I have never rebuilt a master cylinder, so I'm not certain of their machanical inards ... could an obscruction in the brake fluid line leading from the resivour to the master cylinder cause it do this? I would imagine so since the clutch pedal system must draw air on it's return travel right ??? I will find out anyways since the line must be pulled in order to replace the master cylinder. If I pull the line and see that it's obstructed, I will simply clean it out and reattach it ... if it's fixed at that point, I will return the unopened master cylinder.

[FastCougar]

Just did a search on Google ... found thid page: http://www.fourfold.org/RoverWeb/clutch.html

POSSIBLE MASTER CYLINDER FAILURES:

• Front seal fails, or pitting of cylinder wall. Fluid leaks back towards the reservoir instead of pumping out the outlet pipe. This will result in reduced or no slave piston movement. The effects may vary with a borderline seal. (rebuild or replace master cylinder)
• Air in system- master, line, or slave cylinder. Air compresses, resulting in reduced piston movement, as above, & soft pedal. (bleed system)
• Rear seal fails, fluid leaks out the back of the master cylinder body, possibly onto the drivers foot. (R/R master cylinder)
• Piston doesn't return completely due to crud or rough surface. Cylinder remains partially pressurized, and slave doesn't return, leaving clutch in intermediate state. This may leak back slowly. (R/R master cylinder)
• Blockage of inlet - shortage of fluid, reduced piston travel, mushy pedal. (R/R master cyl.)
• Blockage of outlet -Hard pedal &/or fluid blows back past front seal. (R/R master cylinder)