NV4500 gone rock-crusher - Synchros or the clutch?

[Jagged]

I just got back from a short trip to wally world. Everything went well, except for the drive back home. My transmission turned itself into a rock-crusher.

I'm driving a 98 C3500 with a 454 and NV4500. With the clutch in, I can hear a small whine from the tranny hump. If I try to put it into gear, RPMs drop on the motor. I pretty much had to RPM-match the gears in the transmission to get the damned thing to shift. Starting off, I normally start in 2nd as 1st is a granny gear, but that literally takes some fighting and grinding to get it in gear.

My first guess is I might have to adjust the clutch; my gut tells me it feels like the clutch isn't fully disengaging the tranny. Ideas?

 

[dyeager535]

This advice has worked once already, got clutch fluid?

 

[Jagged]

This advice has worked once already, got clutch fluid?

You know, I never even bothered to check. There is fluid in the reservoir; it could use a top-off, but it shouldn't make that much of a difference.

 

[dyeager535]

Yeah, as long as there is fluid in the reservoir, it's fine. I noticed mine was low the other day, no idea where it went, no leakage I've found (yet, it's all relatively new/low milage), and it worked fine, but I topped it off anyways. I hate leaks.

 

[Jagged]

Topped it off, no fix.

I think this is more of a clutch issue. Really feels like the clutch isn't disengaging all the way.

 

[dyeager535]

Only external thing I can think of to check other than fluid is to get under the truck and watch and see what happens as the pedal is depressed...

 

[Jagged]

Not too much to look at other than the lines going into the clutch itself

 

[Jagged]

Odd, but now everything is working fine

Might take a closer look at it when I rotate tires later this week.

 

[Russell]

You might have a master or slave cylinder going bad. I had a bad master on my 80 and it behaved similar, it would partially move the clutch fork, but not enough to release the clutch disk. I spent hours bleeding the thing until I finally got around to thinking that it wasn't possible for that system to have that much air in there unless it was leaking in somewhere.

I had no leaks coming out of my master, but it was letting air in on a bad seal. Replaced it, and voila, it worked perfectly!

 

[mosesburb]

You might have a master or slave cylinder going bad.

I would try this first too.

 

[lectric80]

This thing sat for a while, it is pretty common for the seals in the slave and/or master cylinder to lose their seal. Then it will allow the pressure to bleed off and not get enough pressure to completely disengage the clutch.

 

[cegusman]

Its dead send it to me.

 

[dyeager535]

This thing sat for a while, it is pretty common for the seals in the slave and/or master cylinder to lose their seal. Then it will allow the pressure to bleed off and not get enough pressure to completely disengage the clutch.

Based on the design (assuming similar to '85+ old body style) if the master cylinder piston seal fails, fluid will get back into the cab. Yes, there is another "boot" there, but there is NOTHING between the fluid and it leaking out but the seal on the master cylinder piston.

I had one go bad in short order (less than a year) from whatever parts store I got it from, sure enough, fluid leaking down from the MC on the inside of the cab. If I had the carpet/insulation in place I would probably have never seen the fluid leaking. It never resulted in problems with operation, but obviously would have over time.

You might be able to "pump up" the system, and then watch for movement with the clutch depressed, but it sounds like this is a hydraulic throwout bearing design, right? Which means you won't see the slave movement.