4.0L 6spd Clutch Slipping? Only in low gears and not reverse

I have a strange problem that I originally thought was the clutch. When driving in 1st, 2nd or 3rd and apply power, especially on bumpy dirt road, a rubbing sound comes from under the hood. At first I thought it was my bad carrier bearing on my driveshaft. Then I tried to dump the clutch in 1st on dirt and it would not spin, just rubbing noise. I instantly thought it was the clutch. I have 340'000kms on the truck and it's on it's original clutch. However, when I dump the clutch in reverse, it grabs and goes. The problem can still happen at highway speeds if in a lower gear it will slip. Higher gears it will not. I went it and bought a clutch and spent extra to have it shipped to me fast as my truck is for work. Now, since the clutch doesn't seem to slip in reverse (even tried in 4wd so it wouldn't spin) I am starting to wonder. When driving down a dirt road with pot holes, it would make the slipping/rubbing noise when hitting the bumps - which I assumed was just the driveline jaring and making the clutch slip a little. When I push the clutch in while hitting the bumps it goes away.....unless hitting hard and seems worse while turning left! What the heck? Clutch depressed and I can still make the noise, and doesn't slip in reverse? My 4wd, 2wd and 4 lo all work fine. When crawling out of my bear bait tonight it could barely pull itself in 4lo without slipping. I still think this is the clutch. It's not harse enough to be a transfer case chain, and everything in a manual transmission is direct drive after the clutch right? I did replace my shifter bushings the other day, transmission is all original. Why doesn't my clutch slip in reverse? Everything before the transmission is spinning the same direction. Why does it still make a noise when hitting bumps while clutch is depressed? Hoping it's still the clutch! New exedy clutch gets picked up tomorrow. Thanks to the insight.

 

Is it lower gears that make it slip or higher RPM? If your clutch is going the clutch should slip in any gear, but at about the same RPM in each gear. I'm not a mechanic, but I imagine it's because it takes a certain RPM for the engine to make enough power to over power the slipping clutch. In 6th gear and 1500 RPM, your clutch might have enough left to hang on.

I've only had 2 clutches ever go out on me, but they both acted the same.

Did you order a new flywheel too? I actually just had a clutch go out in my GT500 this summer. Ford screwed me on it and that's why I bought a new Tacoma instead of an F150 My flywheel was toast. When I replaced the clutch I went with a lighter weight flywheel too. If the flywheel on your 6-speed is as heavy as the one in my Tacoma, I would replace it with a lighter weight one if someone makes them.

 

Lower gears are way worse. I know on my motorbike it was top gears that slipped first and I agree should be the same rpm in any gear because of power coming from engine. I heard I can resurface flywheel.

 

Yes you can. But would also make since to replace the clutch while you're at it. I'm sure your flywheel is polished smooth right now

 

The only time I've ever replaced the flywheel when changing a clutch is when it's grooved. Otherwise just sending it to a machine shop to have it resurfaced will be just fine.

 

the way I usually test my clutch, first gear romp it up, then straight to 3rd or 4th and floor it, you will be able to tell if your clutch is in need of replacement lol

 

If it going to slip the higher the gear the more likely it is to slip. Isn't the early 2nd gen the ones that had engine mount issues? You may want to have a look at that.

 

Hey folks. We opened it up and the clutch surface was fine. The center of the clutch with the splines was broken. We assumed that what is what was wrong. Installed a new exedy clutch since and put it all back together and it is still slipping. So its not the clutch. Something is slipping in the transmission. BLAH! Feeling bummed. Not sure what could go bad in there that would make it slip like that. You would think it would be a harse grinding if a gear was slipping. So, shopping for another transmission, hoping to get this one out this week to see what is going on before pulling the trigger on another. Going to check the classified section. Sad day.

 

A manual transmission doesn't " Slip ". You are wasting time and money.

Here is the best advice I can give you:

Take the truck to someone that knows what they are doing and get it repaired.

 

My mechanic is the greatest in all of the land. We took it out for a test drive today, and got under it and put it under load and listened. Since the new clutch - nothing is slipping - wheels will now spin. However once the clutch is out something starts "slipping" again. Well with two guys we discovered that it is the fan hitting the shroud. All because the motor is settled down far in between the frame rails. Motor mount is tore out of the frame - or caved in. When I load the engine, it twists in the frame and fan hits. When I went in reverse it would torque the motor the other way. I guess this is a common issue. I called my dealer about it, they took my VIN and will call me in the morning - they are checking on a frame replacement. Nuts.

 

So actually nothing was ever slipping.

 

So actually as stated in the original post, I could dump the clutch in 1st gear on dirt and it would not spin. Clutch was broken by splines. So combination of two issues here.

 

For future reference, the clutch will slip in the higher gears and work its way down to lower gears as the clutch continues to wear (this is for a normal worn clutch disc - no failures due to something breaking).

In higher gears, there is a greater torque required from the engine to push the car forward than the lower gears, since the torque is multiplied more in lower gears.

However, it also has to do with the powerband of the engine. Usually the first gear you feel slipping is 3rd or 4th, because in 6th you typically are too low in the RPM range (unless you are going really, really fast).

The best way to check the clutch is to drive in the highest possible gear that will allow you to have the RPMs just below the peak torque output of the engine (for a stock V6 Taco, 4000RPM is peak, so start at like 3500), and then punch it. The engine speed should just slowly rise with the speed of the vehicle. If the engine RPM surges at any time, then your clutch is slipping.

 

Yep.