1990 Nissan Truck Clutch Pedal Pressure Goes Up and Down Af

1990 NISSAN TRUCK
220,000 MILES • 4 CYL • 2WD • MANUAL
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WIRIKIDOR
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This is something that has gone on with my 1990 Nissan truck for two years now, and it always mysteriously fixes itself.

Sometimes the clutch pedal will be loose and have little pressure, and I have to pump the pedal to get enough pressure so I can put the truck in gear. Over a period of time, like 30 minutes to an hour it would loose pressure again and then I would pump it back up and it would be fine. It would do this for a few days, and them mysteriously stop for 4-6 months.

This time though it's been going on for a few days, and the time in between pumps so I can change gears is getting shorter, like 10 minutes. I've checked the fluid and it's full, and I cannot find any leaks.

I feel that it's time for me to fix whatever this is but I don't know where to start looking. The fact that it goes away for months and comes back is really confusing me.
Jan 27, 2010 at 9:23 AM
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KHLOW2008
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Hi wirikidor,

Thank you for the donation.

You do gave a peculiar problem and the most logical explanation is a faulty clutch master cylinder.

When hydraulic pressure drops without any loss of clutch fluids, the master cylinder is leaking pressure internally. When this occurs, it requires some pumpimg of the pedal to build up the pressure again.

Do the following test.

When clutch pedal pressure is available, fully depress the clutch pedal and hold for a few seconds with engine running. Try engaging the gears after intervals of 5 seconds without releasing the clutch pedal and if the egngagement becomes increasingly more difficult, it indicates and internal leak of the master cylinder and requires replacement.

When repairing the hydraulic system it is recommended to include the slave cylinder as well.
Jan 27, 2010 at 12:00 PM