Transmission, clutch, or hydraulic actuator?

[RCourtney]

In addition to my other problems, I'm experiencing difficulty shifting gears with my NV3500 (5-speed manual) transmission. It shifts fine when cold, but gets increasingly worse as it warms up, to the point where it won't shift into reverse standing still (grinds) or into 4th or 5th gear when moving (almost impossible, tricky/difficult at best). I'm wondering how large a repair bill to expect - can anyone tell by these symptoms where the most likely source of my problem is? I've only had the truck about 6 months, it's got about 185K miles, shifted fine when I got it. Gear oil level recently checked OK (if I can trust the oil change place). Hydraulic slave and master seem OK but not sure if rod travel is adequate. No idea when clutch may have been changed last.

[RCourtney]

I guess no one out there has an NV3500. That must be why I didn't find any posts on it... OK, here's a related question - does anyone know if it's possible and a good idea to replace the NV3500 with the NV4500 if the cost to repair the 3500 is prohibitive?

[joed]

Are you sure you have a NV3500? I thought only the NV4500 came with the 6.5 (at least from the factory). You can check the code sheet in your glovebox. The code for the NV4500 should be MW3.

Anyway, I've got a 4500, and like it really well but have experienced similar clutch symptoms. In my case, it's usually only when towing (as tranny gets hotter). I think it's clutch related, specifically the hydraulic setup. (See the fairly recent post "Clutch Master Cylinder Failing?"). As others have said, I think the brake fluid in the system can actually boil, limiting action. I'm going to try flushing the old fluid out to see if that helps.

You might try that first, but it could just be a worn clutch not able to disengage completely anymore.

Joe.

[BuffaloGuy]

Rob,
It could be the clutch or it could be the fluid in the hydraulic system. Maybe someone put the wrong fliud in the case. These trannys are pretty particular about that.

It's always best to start simple/cheap and work up from there. I would:

1.Replace the fluid in your master and slave cylinder. You might have an air bubble or it might be low. (cheap) While there, check out the bolt that you can remove to observe the travel motion.

If that doesn't do it then:

2. Replace the tranny fluid with the GM stuff. It's not cheap. ($100) Chances are that your tranny is about due for new fluid anyway. It won't be a waste if your planning on keeping the truck.

If that doesn't do it then:

3. Pull the tranny and look the clutch over. Chances are that it's shot. Not cheap, probably $4-500 with labor. Maybe more depending on who's doing it.

These trannys will give a lot of miles before they need tore into so long as the haven't run low or someone put in the wrong fluid. Let us know how it goes.
Ken

[RCourtney]

Thanks for the feedback, Joe & Ken. Yes, it's definitely the NV3500 (MW3 in the glovebox, 1st gear "underdrive" for loads only). I'll check out the hydraulics first - hope that's all it is! Can you explain a little more about that bolt you're talking about, Ken? I looked at the system briefly already and didn't see any bolts to remove, and my Helms doesn't show anything...

[RCourtney]

Sorry, Joe, I just noticed you said the NV4500 was option code MW3 - my Helms manual says NV3500 - is that what you meant?

[BuffaloGuy]

Rob,
From memory... It's down on the bell housing right next to where the slave cylinder is. The slave is inside the bell housing and there is a bulge stamped in the steel to accommodate it. On the side of the bell housing there should be something that looks like a very fat bolt. That's it.
Ken

[JohnC]

As far as I know, no 6.5's came with other than the NV4500.

One thing that can make any trans hard to shift and is heat related is the pilot bearing.

[Hubert]

Mine did this too.

I have a 97 K2500 6.5 5spd. 104,000 miles. But some work was done to clutch at 60,000 miles by original owner.

My experience:
My truck 2 days ago did not want to go into rev without grinding. I had to shove it into another gear hard then rev. It shifted hard. I could play with rpm and feel it in ok.

I checked my clutch fluid level and it was maybe down 1 oz. My pedal felt fine same resistance as always but it didn't seem to disengage clutch so I bled the slave cylinder 4 or 5 times. Maybe used about 1 - 2 oz of dot 3. Lots of black dot 3 came out but I fiqure it was mostly clutch dust in bleeder nib ( but it was pretty crappy looking the last time same as first spurt). But it did the trick for now. Shifts fine and will go into rev after 1 sec with clutch in no grinding.

I asked a local mechanic and he said sometimes bleeding helps sometimes not. He said when you let the clutch out the slave, if going bad, will suck a little air. (maybe especially if you dump clutch or launch hard) After a while it sucks enough air not to want to push as far.

So then I tell him the bled fluid looked like crap and asked him should or can I drain and flush the system with fresh dot 3 since it looked so cruddy and he said he would nt' recommend it. Its hard to get a lot of air out of the system. He said just keep an eye on fluid level and wait for it to come back. Who knows when that will be.

By the way I think he said and its in the helms book the hydraulic clutch is self adjusting and it did get better after I drove it a while. So bleed it and drive it a day or so to see what happens. Maybe bleed it again a few times after you drive it. (thats actually what I did)

[Hubert]

Hey there is another post about a month old about clutch mastercylinder or slave cylinder going bad read it too.

At least someones recommends changing the clutch fluid every 3 years. I am going to do more reading/research. I'd never heard of that learn something new everyday.

[catmandoo]

johnc mentioned the pilot bearing,and these are known to fly apart or should i say disintegrate.if it's hanging up the input shaft will keep rotating at engine speed,causing the grinding going into gear,i lost a spring on my disc awhile back and when i took it apart there was almost nothing left of the bearing,and the new clutch came with both a bearing and a bushing.i went back in with the bearing but not the next time.i think its shot again already and it has about 35,000 since the clutch.

[RCourtney]

Thanks again everyone for the input. Hubert, check your post for my input. I'm gonna try bleeding first, then changing the fluid, last the clutch I guess. I've never changed a clutch before - I don't have access to a lift or special tools, have to borrow a garage if needed. Should I attempt it myself or take it in?

[RCourtney]

OK, here's the latest. I did a combination bleed/fluid change and it made quite a difference. I bled the old fluid out while filling the reservoir with Valvoline SynPower (synthetic). The label says it "Exceeds DOT 3 and DOT 4" standards and is "compatible with conventional brake fluids". Unorthodox technique, I guess - criticism is welcome! There did seem to be an air bubble in the slave, I heard a gasp when I did a pressure bleed. End result is that shifting is again consistently possible, but not as smooth as I'd expect - doesn't settle into gear nicely, needs a little finesse. Future may include clutch slave replacement if problem occurs again, probably clutch/transmission inspection & repair.

[joed]

Rob,

That's the clutch fluid I'm going to try - haven't had a chance to change it yet.

Has your actual transmission fluid been changed? I've changed mine a couple of times (try to do it every 50K or so), and have noticed better shifting afterwards. On the downside, the fluid is kind of $$$, (special GM fluid is required). I know GM says you never have to change it, but it does get dirty, especially if you do any towing.

Joe.

[Andy Chesek]

The option code MW3 is for the NV4500. I don't think an NV3500 would have a granny gear...

[sidedump]

It might be best to pull the trans and inspect the pilot bearing. If you continue to operate w/ a bad pilot bearing your input shaft will suffer and need to be replaced.

[radrecon69]

Now here is what I have found out about the Tranny oil first it calls for GL4 W75/90 you can't buy it I did find one Chevrolet dealer that had it in stock but it was $25.00 a quart WOW so I went online and order it, but they sent me the wrong oil so I went to my local Chevy dealer to find out if they could tell me what this oil was for but they couldn't (I know this is a long story but stick with me) even though it said it was for a manual transmission it wasn't for a NV4500 (still don't know what the oil is for) I was out about $75.00 so while I was there at the Chevy dealer I asked him if he had any in will he brings me a bottle 75W90 GL5 I asked them whats the difference was from Mobil 1 75W90 GL5 he tells nothing other then the GM smells like grape juice so they can tell that it has GM oil in it for warranty work so I said HUH and went and bought Mobil 1, now he should me the TSB or what they use and showed me where it had been changed a couple of years ago. So I have about 10000 mile since I changed and haven't had abit of trouble

Rick smile.gif

[Hubert]

Rob,

My Hydraulic clutch took a day or 2 to settle down after bleeding. And it shifted better. Mine is still shifting smooth and normal (its been about a week - knock on wood). I haven't changed the clutch fluid yet. I'm going to have to borrow a friends leg and do it the bleed method (before I pumped it by hand and wedged a 2x4 into the seat and did it by myself). I posted to another website too and at least another person recommended changing it too. So I'll do it but not sure when.

Just wondering when you bled it my helms shop manual for a ~ 97 year model ( but purchased in ~ 2003) suggested (to purge air) to pump the clutch about 20-25 something times fast, hold, then release pressure. I heard the swoosh and hydraulic noises as the clutch pushed the slave back. And the spurt of fluid kind of double spurted or surged like it had a little air in it or the slave was freeing itself up.

Post back with an update in a week or 2 if its cleared up and shifting smooth or not.

I am still driving with my fingers crossed and thinking that was too easy of a fix but counting my blessings. I am fearful that the bleeding kind of just allows the slave to readjust / realign to the input shaft / pilot bearing and its only a temporary fix. But if it aint broke don't fix it. I am not itching to spend the $1000 at the clutch shop unless I have to.

Hubert