Bad clutch hydraulics?
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Senior User
Joined: Nov 2006
Posts: 418
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From: Quad Cities, IA
Bad clutch hydraulics?
I'm pretty sure I know the answer to this question, but I want a couple more people's oppinions on the matter.
My problem is, the clutch in my '89 F-250 (ZF 5 speed 460 engine) feels like it's not disengaging all the way when the truck is cold, but after I drive it for a while (for example an hour on the highway) it operates perfectly. Since most of my driving consists of about a mile each direction to and from work, it doesn't have the chance to get warmed up all the way very often. Cold engine = very little clutch pedal travel, warm engine = good pedal travel.
Since it seems to be a heat-related issue, I'm under the impression that the fluid in the lines ...expands... a bit when the truck is hot, allowing more pressure to be placed on the slave cylinder when pressing the pedal, thus allowing the clutch to fully disengage. On my old '63 Chevy, the brake system did something similar (but sort of reversed) where it would work well cold, but as the truck got hot, the brakes would "pump up", as in not release as far when you'd let off the pedal. It would get to the point where if you drove it too much, the brakes would stop releasing all together. On that issue, it was mostly due to bad routing of the brake lines. They were way too close to the exaust headers.
Things I've checked already:
Firewall near master cylinder is solid (no flex or visible cracking)
System DOES have fluid in it, filled to normal level in master cylinder
Slave cylinder is not loose or improperly positioned
No leaks found present in hydraulic system.
I'm hoping to attempt a hydraulic system bleed on this in the next couple days but have never done one on a clutch before. Hopefully I don't screw it up horribly, since this is currently the only truck I have that's legal to drive.
Any pointers or suggestions to other issues that might be causing this would be greatly appreciated.
My problem is, the clutch in my '89 F-250 (ZF 5 speed 460 engine) feels like it's not disengaging all the way when the truck is cold, but after I drive it for a while (for example an hour on the highway) it operates perfectly. Since most of my driving consists of about a mile each direction to and from work, it doesn't have the chance to get warmed up all the way very often. Cold engine = very little clutch pedal travel, warm engine = good pedal travel.
Since it seems to be a heat-related issue, I'm under the impression that the fluid in the lines ...expands... a bit when the truck is hot, allowing more pressure to be placed on the slave cylinder when pressing the pedal, thus allowing the clutch to fully disengage. On my old '63 Chevy, the brake system did something similar (but sort of reversed) where it would work well cold, but as the truck got hot, the brakes would "pump up", as in not release as far when you'd let off the pedal. It would get to the point where if you drove it too much, the brakes would stop releasing all together. On that issue, it was mostly due to bad routing of the brake lines. They were way too close to the exaust headers.
Things I've checked already:
Firewall near master cylinder is solid (no flex or visible cracking)
System DOES have fluid in it, filled to normal level in master cylinder
Slave cylinder is not loose or improperly positioned
No leaks found present in hydraulic system.
I'm hoping to attempt a hydraulic system bleed on this in the next couple days but have never done one on a clutch before. Hopefully I don't screw it up horribly, since this is currently the only truck I have that's legal to drive.
Any pointers or suggestions to other issues that might be causing this would be greatly appreciated.
Lead Driver
Joined: Dec 2002
Posts: 5,491
Likes: 16
From: Kuna ID
Changing the fluid is what I would do. Bleeding it is similar to bleeding brakes. You need an allen wrench to open the bleeder screw on the slave cylinder. It's on the top and kind of hard to see. Bring some rags or some kind of shield to deflect the fluid as it just sprays everywhere, usually on the exhaust. 
