Slipping Clutch

[graygun]

2003 F-150 4.2 5-speed: It doesn't seem to slip at all while moving away from a stop but always does from cruising speeds when pushing the gas pedal with slight,or higher,pressure. It seems it would slip under highest demand...accelerating from a stop.

It seems puzzling. I've replaced a few clutches many years back and they always seemed to slip the most under the greatest loads.

I know we have some experienced mechanics here. Can anyone offer help?

 

[Jeepnik]

Does you vehicle have a clutch master cylinder? I believe it should. Check the fluid level.

 

[Mobuck]

Unless you're pulling a load when "moving away from a stop", the lower gears put less strain on the clutch than when trying to speed up in fourth or fifth gear. Since you're already "slipping the clutch" when leaving a stop sign, you may not be noticing the clutch not fully engaging.

 

[Dave P.]

Unless you're pulling a load when "moving away from a stop", the lower gears put less strain on the clutch than when trying to speed up in fourth or fifth gear. Since you're already "slipping the clutch" when leaving a stop sign, you may not be noticing the clutch not fully engaging.

Mobuck has hit on the money.
End result is all the same....new clutch time.

 

[Dan in MI]

Your truck does have master cylinder for the clutch, but being a closed system where did the fluid go? The only answer beyond a leak is the slave cylinder. That would mean the clutch worn near, or to, the point of replacement.

 

[graygun]

Makes sense when your logic is not inverted,like mine apparently is regarding this.

 

[Wyandot Jim]

It is probably your clutch. If it slips when you try to accelerate from a stop in 2-3rd gear it is the clutch.
Hear is all you ever wanted to know about hyd. systems. It is for a Vette but probably about the same for all. I had to replace mine in my 96 Grand Sport Vette due to age.

A Simple Test

There's a fairly simple test to check out your clutch hydraulic system. The first step is to make sure that you've bled the hydraulic system and use GM hydraulic clutch fluid (P/M 12345347). When you're convinced that you've done a good job and all the air is out of the system you need to do the following things to check the master and slave cylinder for leak down, or internal leaks.

• Simulate being parked on an incline by placing jack stands under the front of the car for 12-24 hours. Raise the front at least 1 foot higher than the rear.
• Lower the car being careful not to depress the clutch
• With the clutch pedal to the floor start the vehicle.
• Try to put it into reverse when it first gets started.
• If you have difficulty getting into reverse there's a very good chance that the clutch master cylinder is not at 100%.

The following day you need to follow the same procedure but with the rear of your Corvette raised. This is the leak down test for the slave cylinder.

What happens is the hydraulic cylinders develop a leak and no pressure is available to actuate the clutch. The first thing you need to realize is that you can't rebuild these units. Even though there are rebuild kits available for both cylinders it simply isn't worth the effort.

When a master or slave cylinder goes bad it's because of wear in the bore. The anodizing wears out and leaves a rough spot in the bore. That spot accelerates the wear on the rubber O-ring. You can hone the cylinder out, but when you do that you'll enlarge the size of the bore. The O-ring seals only come in standard sizes. This means that after rebuilding the unit will fail again in a very short time because the seal will not be able to seal the enlarged bore.

 

[graygun]

I bought the truck 4 yrs ago and everything worked well with trans and clutch until recently : shifting,engaging,no noise or chatter. It just does the classic spinning/slipping upon demand in higher gears/speeds.

176K so it has done well for a long time

 

[graygun]

I see many sources for parts and the prices vary greatly. We have NAPA and Carquest in town but their prices are fairly high.

 

[96/44]

It is the clutch. Contrary to what you would think the load is much higher at a cruise when accelerating than from a stop. If I remember right the slave cylinder is part of the release bearing on that truck. Spend the money on a good clutch kit like a LUK. Buy once, cry once.

 

[graygun]

I'm securing parts. You're right about the bearing and slave cylinder.