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So, first, let me preface this post by explaining that I am not terribly knowledgeable when it comes to hydraulic clutch systems. My first car had a cable controlled clutch, my power wagon had a mechanical linkage controlled clutch. The only vehicles I've had that have had hydraulic Clutch systems never gave me any trouble.
When I bought my 1989 F250 a little over a year ago the clutch had quite a bit of travel before engaging, but still worked okay. Progressively over the last year, it has gotten worse until last weekend, it failed altogether. All the way to the floor and clutch won't engage.
I've already figured that the culprit is likely either the Master Cylinder, the Slave Cylinder or possibly just needing to be bled. Is there a reliable way to test what the problem is. I really don't want to get one part only to find out that the problem was with the other.
Have you looked up above the gas pedal to see if the plastic retaining clip is still attached to the master cylinder pushrod?
Another issue with these trucks is that the firewall can crack where the master cylinder is mounted.
The best way to check this is to open the hood and look at the master while someone else pushes on the clutch pedal.
Bleed it and see what you get. Beware that the master cylinder doesn't hold that much fluid, so if you pump it dry, you get to start all over... I've replaced two slaves over the years on my 94 f250. Never had a problem with the master.
Have you looked up above the gas pedal to see if the plastic retaining clip is still attached to the master cylinder pushrod?
Another issue with these trucks is that the firewall can crack where the master cylinder is mounted.
The best way to check this is to open the hood and look at the master while someone else pushes on the clutch pedal.
So you have the concentric slave cylinder mounted inside the bellhousing and being 4x4 you would need to pull the transfer case as well as the transmission to change it.
(These things are a real pita)
Have a look at where the pedal connects to the master cylinder and whether the master cylinder itself is moving
'80s trucks have a problem with rusting and cracking firewalls where the master is attached. As per the prior post, have someone look at the master while you work the pedal. Flexing etc could be part of your problem.