NV5600 Clutch Not Disengaging

[Bafazane]

Hi Folks,

 

I want to preface this by saying I searched this site and many others without finding satisfactory answers.

 

The issue is that my clutch does not appear to be disengaging when I depress the pedal. The symptoms began yesterday with a sporadic increase in effort to get it into gear when shifting. Today, over the period of about an hour of mostly easy highway driving with a few of stops, the symptoms persisted and worsened until the clutch would no longer release and I had to start the truck in gear to get moving and float gears to shift to get the truck home. What was weird to me is that it was inconsistent in the behavior, mostly the clutch wouldn't disengage, but sometimes it seemed like it was releasing just fine. There is no new noise that I have identified.

 

I took care to ensure I was fully depressing the clutch, and always shift slowly (including double clutching into 3rd for a weak syncro). I can't see any obvious leaks in the hydraulic system (South Bend that I installed 4 years and 43,000 miles ago) and the reservoir is full. From reading it appears likely to be either the hydraulics or the pilot bearing. I'm going to pull the slave cylinder off to see if it's leaking there. How far should the rod extend from the slave when I depress the clutch pedal? Is there anything else to check on the hydraulics? Is there any way to troubleshoot the pilot bearing or whatever this may be if the hydraulics check out without removing the clutch and transmission?

[Tractorman]

What you haven't said:

 

How many miles on the truck?

You mention a South Bend hydraulic system 43,000 miles ago, but you didn't say anything about a new clutch.  How many miles on the clutch?

Is this the original clutch in the truck? 

 

For example, my original clutch made it to 297,000 miles.  The pilot bearing failed and finally spit itself out, but before it disintegrated, I had exactly the same symptoms as you are having.  For awhile I also had to float the gears to shift.

 

The hydraulics for the clutch could very well be your problem and there is a test procedure for this, but I don't recall the procedure.  I would think if it was a hydraulic failure that the symptoms would be consistent and slowly get worse, not what you were experiencing - "but sometimes it felt like it was releasing just fine".

 

- John

Edited February 9, 2020 by Tractorman

[dripley]

When my oe master cylinder failed it did so internally. No fluid loss, the internal seals failed. Took a couple months for to fail with warning sgns however. 

I dont of any way to check the pilot bearing without pulling tranny.

[Bafazane]

Thanks for the replies guys.

 

I just crossed 200,000 miles and as far as I know it's the original clutch.

 

I replaced the hydraulics because the original system failed on me. As far as I remember from that instance, the deterioration in shifting was a slower, steadier process than what I'm encountering now. But my memory isn't perfect...

 

When I get a chance to pull the slave off, I'll post what I find.

[Tractorman]

@Bafazane, I am betting on the pilot bearing.  You have had good life being that it is the original clutch.  When I took mine apart at 297,000 miles, the clutch assembly and the throw-out bearing were still in good condition - just at the end of their life.  The failed pilot bearing is what caused me to do the repair.

 

I highly recommend that you do a clutch job now.  When my pilot bearing failed, it significantly damaged the nose of the transmission input shaft. I elected not to replace the input shaft, but that may not necessarily have been a wise decision.  So far, at 38,000 miles later I have had no problems, but I know that I will be replacing my clutch next time around the 150,000 to 200,000  mile operating life and not wait for a failure to happen.

 

Also, I replaced my clutch and flywheel with stock  OEM Luk components.  I have RV275 injectors and a mild Smarty tune and I tow a fair amount.  The clutch is still very smooth and the transmission shifts well.

 

- John

[Bafazane]

I pulled the slave off and didn't find any weeping oil or anything that looked out of place. I had forgotten that the plunger extends itself as you remove it (hence those plastic tabs when installing a new slave), so I don't really see a way to measure the amount of extension you're getting by depressing the clutch pedal. If anybody has any ideas on testing functionality of the clutch hydraulics I'm all ears. Did I see something about using a steering wheel puller in place of the slave cylinder to determine if it's a hydraulic issue or not?

 

Also while outside with the truck, I started it up in neutral then depressed the clutch and slipped it into second no problem. I shifted back to neutral, the depressed the pedal again and couldn't get it into any gear. I tried pumping the clutch multiple times before holding the pedal down and noted no improvement in condition. The truck had been parked for approximately 7 hours.

[dripley]

1 hour ago, Tractorman said:

Also, I replaced my clutch and flywheel with stock  OEM Luk components.  I have RV275 injectors and a mild Smarty tune and I tow a fair amount.  The clutch is still very smooth and the transmission shifts well.

My OE clutch held up under adding a Banks tuner rated at 75 rwhp. I then later added RV275's. I towed my first trailer at 12k pounds and then my second at 15k pounds and never once slipped the clutc even on a 6% grade. Changed it out somewhere around 250k. I want that smooth clutch back. I loved it.

[Tractorman]

48 minutes ago, dripley said:

I want that smooth clutch back. I loved it.

 

I know what you mean.  I was tempted to put in a heavier duty clutch, but then decided against it for exactly the reasons you posted.  I am really glad I stayed with the stock clutch.

 

My wife and I moved from the Salem, Oregon area to Baker City located on the east side of the state this winter.  I made seven trips using the dump trailer to haul household and shop stuff.  I also made many trips last summer hauling my equipment back and forth.  I wasn't nearly as heavy as you were, but my gross combined weight averaged 15,000 to 18,500 lbs and I was pulling six 4,500 to 5,000 foot separate passes (6% grades) in each direction.  Climbing most of those passes I stayed in 6th gear until I had to slow for curves, then 5th gear for the rest of the pass.  The smooth, quiet clutch is worth keeping stock for what I do.

 

- John

 

 

[Dieselfuture]

11 hours ago, Bafazane said:

If anybody has any ideas on testing functionality of the clutch hydraulics I'm all ears.

Like you mentioned puller, if you could bolt it up instead of slave and adjust it to where you think clutch is disengaged try putting it in gear then start it, be clear of anything important incase it wants to go forward on you and be ready to shut it off. Or start it then try putting it in gear. I would think if pilot bearing is freezing up and keeps spinning the input shaft when clutch is disengaged it'll stand no chance against weight of the truck but to brake lose, maybe put it in 3rd gear so it'll take more force to break free if it's stuck, or if in first then it may want to start creeping forward. Should be able to do the same test with the slave back in the hole. 

These 5600 must have a known problem with 3rd gear synchros, mine also is hard to get in especially when cold, If I force it, it will grind. Been meaning to pull my transmission out ever since I got the truck, wanting to put an oversized pilot bedding. I believe one of the clutch companies offer one for this reason. 

[Bafazane]

I've got a new clutch and flywheel on the way, and will be dropping (or attempting to) the transmission tomorrow. Hoping for a straightforward parts replacement job. Tractorman, you mentioned the pilot bearing damaging the snout of the input shaft when it failed; what would you suggest is the damage threshold before you would without question replace the input shaft?

[Tractorman]

@Bafazane, I truly can't make a recommendation because I am taking a gamble with my own decision to not replace the transmission input shaft.  The pilot bearing was completely gone as in all of the needle bearings had left the area violently.  About one third of the pilot bearing area on the input shaft was badly damaged, enough so that only about two-thirds of the new pilot bearing would support the input shaft.

 

So, with that said, you will have to make your own decision based on the condition of your failure. 

Hopefully, you won't have the problem that I had.

 

- John

[Bafazane]

Yesterday was a long day and I'm about to head back out to the truck to keep putting stuff back together, but I wanted to post a quick note to say that @Tractorman was dead on (thanks!) and the pilot bearing had disintegrated. Luckily the input shaft was in pretty good shape (just needed a quick buff with 2000 grit) so was able to get the new clutch kit installed and the transmission bolted back up yesterday.

[Dieselfuture]

On 2/9/2020 at 2:00 PM, Bafazane said:

including double clutching into 3rd for a weak syncro

Let us know if 3rd gets better 

[Bafazane]

Well, everything is back together and I took the truck for a substantial test drive. What a difference the new clutch makes! The pedal is unbelievably light, engagement is smooth with no chatter. I might be sensing barely more rollover noise but if so, it's a very faint increase. I went with the South Bend OHD as I do plan on putting bigger injectors on soon and potentially going the Quad route for tuning at some point. I'm happy with that decision as it feels like a stock clutch, only with lighter pedal feel.

 

The pilot bearing needles had partially disintegrated but luckily the input shaft snout had only very minor scarring that I was able to smooth off with 2000 grit. The new ball bearing will be riding fully on the input shaft. I want to note as I think back on how I could have detected the issue sooner, there was a very slow, steady increase in vibration at idle with the clutch pedal out over the past months. It wasn't very noticeable at all, even at the end, but it's gone now so I feel confident the pilot bearing slowly self destructing was the cause. Something for others to watch out for I guess.

 

The clutch plate and the pilot bearing must have using the same clock because the friction surface was worn to just barely above the rivets. It was definitely time for a clutch!

 

The pressure plate was pretty worn but no bent or broken fingers and the release bearing was pretty haggard but not totally dead. It's nice to have a new one in there.

 

As always, I appreciate the help from all who contributed and thank you Mike for creating such a helpful forum!

 

 

Edited February 13, 2020 by Bafazane
Added images

[Tractorman]

Thanks for sharing the results of your repair.  Sounds like you have a smooth operating machine again.

 

I noticed some very hot spots on the flywheel in the photo.  The clutch had some abuse at some point during its life, but you must have been treating it well since you got over 200,000 miles out of it. 

 

Here are some tips for anyone to keep a smooth operating clutch for the life of the clutch: 

 

1.  NO throttle when engaging clutch to get vehicle in motion - apply throttle AFTER the clutch is fully engaged.  The high torque from the Cummins engine is more than adequate to get any load moving at idle.

 

2.  Second gear starts are okay with empty or lightly loaded truck.

 

3.  First gear starts should be used with heavier loads and / or  towing.  Second gear starts are okay if on slight downhill grades.

 

4.  Match engine rpm and road speed when upshifting and downshifting.

 

5.  Always shift to neutral for any extended periods idling at intersections (will increase the life of a pilot bearing).

 

If you do all of these things, the clutch really has it easy and very little heat will ever be generated.  Heat is the destroyer of clutches.

 

@Bafazane, thanks again for sharing your findings and the results of your repair.

- John

 

Edited February 13, 2020 by Tractorman

[Bafazane]

@Tractorman Yep, nice and smooth. Now on to the next projects...

 

Those are some good recommendations for keeping the clutch and transmission happy on these trucks and ones that I've followed since I've owned it. Not much sense beating on a truck I intend to keep for a long time.

 

I wish I knew more of the history of the truck but the dealer I bought it from (at 156,000 miles) didn't get any of it from the prior owner. All I know is that he was the original owner was local and had a fifth wheel hitch mounted. 

[Dieselfuture]

How's shifting to 3rd, did it improve any?

[Bafazane]

@Dieselfuture I have tried the shift into third a few times under different conditions and the crunchiness that made me start double clutching is still there. Would be excited if the new clutch fixed that too, but it doesn't appear so.

[Dieselfuture]

I had my hopes up, as mine is also a bit crunchy in 3rd. Been this way since I got the truck almost 10 years ago, some day I'll fix it, maybe, lots of maybes in my future. 

[Tractorman]

It is not unusual to start having problems with third gear on a five or  six speed transmission.  It shouldn't happen, buit is not unusual and is almost always caused by poor driving habits.  @Bafazaneand @Dieselfuture, the previous owners of your trucks likely caused the early symptoms of synchronizer failure in third gear.

 

A poor driving habit example in this case would be of a driver slowing for a right or left turn in which third gear would be a good selection to complete the turn.  Instead of matching engine rpm's to road speed when selecting third gear, the driver brakes, depresses the clutch pedal and lets the engine fall to idle.  While making the turn, the driver pushes the gear selector against the synchronizer until the transmission goes into third gear.  This effort forces the synchronizer to do all the work bringing the transmission input shaft up to speed to match the selected gear in the transmission. 

 

The correct method would be to use the throttle to control engine speed when the shift lever passes through neutral (foot off the clutch pedal) and bring the engine and transmission input shaft up to a matching speed before clutching and selecting the gear.  The results will be that the synchronizer will hardly have to do any work at all and will live a long life.

 

These poor shifting habits over time will take a toll on the synchronizer.  Once the synchronizer fails completely, the driver will be required to match road speeds with engine rpm's to make smooth, seamless shifts.

 

Think of it this way - anytime a transmission gear shift is not smooth, the synchronizer or the clutch will have to absorb all of the energy that made the shift not smooth. 

 

- John