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Hydraulics likely cause of loose clutch pedal

| Friday, Oct. 26, 2012, 8:50 p.m.

Q It's been awhile since you helped me with my Toyota 4x4 truck starter. All has been going well with the new starter and the rest of the truck. A new problem just began this week. I went to start my truck, and the clutch pedal nearly went to the floor before I felt any resistance. I could get the truck into gear, both forward and reverse, and drive it without trouble or noise; it just felt strange to suddenly have so much free play in the clutch pedal before engaging each time.

The week before, the clutch pedal felt normal and shifting was not a problem — no grinding or difficulty getting it into gear. The pedal free play was normal, too. Then the sudden change in the pedal after not driving it for a week. So I checked the clutch cylinder fluid reservoir, and it was full. There are no leaks inside or outside the cylinder. I checked under the truck, and the slave cylinder looks dry. The line looks dry too.

Did my clutch suddenly go while sitting in my driveway? Or is it time to flush and replace the fluid and hope that will bring it back to normal? The truck has a lot of miles on it, and I don't know when the clutch was ever replaced. What else should I check before deciding whether a costly new clutch is needed? The truck is a 4x4 and I think it's beyond my skill set to do a clutch myself.

— Jen

A Great job, again, describing details and performing spot-on inspections — you'd make a super technician. Your truck, like most modern stick-shift vehicles, uses a hydraulic process to connect clutch pedal motion to the clutch mechanism within the transmission bell housing. As the pedal is depressed, a pushrod applies force to the clutch master cylinder, pushing a piston about 1 inch. Hydraulic force is applied, via fluid through a steel or plastic line, to the slave cylinder, which is bolted to the bell housing. The slave cylinder piston moves similarly, and a second pushrod applies force to the clutch fork. This process is infinitely smoother and usually less trouble than the cable or lever mechanisms used in the past.

Since your clutch releases OK, even with lots of pedal free play, and doesn't slip, it should be fine. A worn-out clutch typically releases (and may slip) near the top of pedal travel, or in the case of a warped disc or failed pressure plate, may not release completely, even when depressed fully, causing gear clash.

Your symptoms sure seem to point to a hydraulic issue, which should be fairly easy to fix. I'm thinking a layer of sludge in the bottom of the fluid reservoir may be preventing the master cylinder from receiving a fresh gulp of fluid, or the master cylinder may have begun to leak internally, back to the reservoir.

Does pedal free play decrease if you pump it repeatedly? This would further verify the fault as being hydraulic in nature. Did you look for leakage inside the truck, above and in front of the pedal? Many times, a faulty clutch master cylinder will leak inside the truck, rather than down the front of the firewall.

I'd try swabbing out the bottom of the reservoir and refilling fluid by bleeding the system.

Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at under-the-hood@earthlink.net; he cannot make personal replies

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