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1982-2000 C/K Truck & SUV Chassis & Drivetrain Discussion Forum for the 1982-2000 GM Pickup Trucks and SUVs, and their Transmissions & Drivetrains, cab, chassis, electrical systems and a lot more.

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  #1  
Old 06-02-2020, 10:06 PM
utah smitty utah smitty is offline
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Default "Heavy Duty" Clutch Slave Cylinder?

Hi All

I'm new here... found the site after I recently purchased a 1995 Chevy K2500 4x4 Ext Cab with 6.5 Turbo Diesel and NV4500 Manual Transmission.

This is a great forum! I've learned a lot just from lurking here for the last few weeks.

I really love the truck. The original owner was an older gentleman who used the truck to tow a 5 th Wheel trailer. It is in very good condition for a 25 year old truck. I'm the third owner of the truck. The PO was a kid with a family who sold it as he was getting strapped for cash.

I had to put tires on it and get seals put in the rear differential and front axles when I bought it, but still feel I got a good deal on a good truck.

Now however, I'm trying to solve a problem that seems to be common with the NV4500 transmission--hard shifting. When it gets warm it gets hard to shift, especially 1st gear... i have to physically force the gear lever. When I try to put it in reverse it often grinds the gears. (This year truck supposedly has synchro in Reverse.) Also, the clutch doesn't disengage until the pedal is only an inch or so off the floor.

I had my shop look at the clutch hydraulic system and they said it was fine. (They also said the transmission was fine). The person I bought it from said the transmission had been rebuilt about 20,000 miles ago (it has 137,000 miles on it now). If so they didn't bother to replace the throw out bearing as it's got a bit of a hum to it.

I thought the shifting problem might be due to whoever rebuilt the transmission not putting the right oil in it. I know the Syn-torq oil is no longer available without taking out a 2nd mortgage, so I bought a gallon of Redline synthetic 75W85 GL-4 oil off Amazon. The container says it's for the NV4500 so I'm hoping it will help. I took the PTO cover off the tranny so I could clean out any oil that didn't go out through the drain plug. There wasn't any metal particles, but there was a dark film on the inside of the tranmission... kind of what you see on an automatic tranny with some miles on it. I used high temp oil resistant RTV on the PTO cover, and buttoned it up last night. I wanted to wait 24 hours before putting the oil in.

While working on the transmission, I noticed that I could easily push the loose end of the slave cylinder . The bolts are tight, it's just the plastic housing deflecting. The thought occurred to me that, besides probably having air in the lines, the slave cylinder may be deflecting when I push in the clutch. It probably gets worse after the engine and exhaust system are warmed up and softened the plastic.

I looked for an alternative slave cylinder, and found an aluminum slave cylinder on several websites. It's the Rhino Pac S0461 Slave cylinder. The application says it's for a solid flywheel on the 6.5 diesel and that it "must Use Flywheel 167126". It also shows it fitting many other 1500/2500/2500 GM trucks incl the 5.7 HD, the 7.2? (old 454) etc.


It looks just like the plastic slave cylinder, but it's aluminum. Has anyone used this on a dual mass flywheel? Is there any reason it won't work on a DMF?


Sorry for the long post, I just wanted to give some background to show I tried to do my due diligence.


Thanks in advance for your help.


Regards,


Utah Smitty
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  #2  
Old 06-03-2020, 04:44 AM
DieselDavy DieselDavy is offline
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Welcome Smitty,
While there are a bunch of smart folks here that will probably be able to help you out, I'm not one of them! I've never owned a NV4500.
Looks like you picked up a really nice rig! Hopefully, someone will jump in here and hook you up soon.
Again welcome to The Diesel Page!
Dave
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  #3  
Old 06-03-2020, 01:22 PM
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a5150nut a5150nut is offline
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Welcome.


There is a bleed screw on the slave cylinder. I had a 94 same as yours. If for any reason you move the slave line remove the end from the top cylinder first. It has a small roll pin that holds it in. A small finish nail and channel locks work to get it out. I replaced my starter without removing clutch line and ended up cracking the bottom of the clutch master cylinder that Monday at work and had to drive thru San Jose CA at rush hour to get part and get to where I was staying to change it. No fun with out a clutch and starting in gear. Glad to hear someone is making a better slave cylinder for them.


If you need parts or advise on your trans, clutch, transfer case or differentials drivetrain.com out of Las Vegas was a tremendous help to me both parts and advise. even on the weekends.


Welcome to the group and enjoy your truck.
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  #4  
Old 06-03-2020, 01:36 PM
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Quote:
Originally Posted by a5150nut View Post
had to drive thru San Jose CA at rush hour to get part and get to where I was staying to change it. No fun with out a clutch and starting in gear.
OMG! I'm having flash backs.... Only it was Boston, then down the turnpike, through all the tolls, to Worcester 60 miles away...
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  #5  
Old 06-04-2020, 05:49 AM
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a5150nut a5150nut is offline
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Don't worry John it OK now.


But after that about the only time i used the clutch was for starting out. Got to where I could slip those gears up and down without a stinking clutch. Same in my 85 Cavalier, sons BMW, or anything else I get in with a stick.
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  #6  
Old 06-06-2020, 03:45 PM
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Another possibility with the clutch - the fork fatiguing. Here was mine twelve years ago:





A couple of us documented our issues with the clutch here: https://www.thedieselpageforums.com/...ad.php?t=31207


The subject of the plastic slave and line came up in that. At the time, I couldn't find any alternatives. I did a quick check of the Rhino Pac and I'm not sure...


This link - https://www.carid.com/rhinopac/exter...mpn-s0461.html - shows a picture of a metal cylinder, but the description says plastic.
Quote:
External Clutch Slave Cylinder by RhinoPacĀ®. Material: Plastic. Tube Fitting Location: End. Seal Type: O-Ring. Mount Type: Flange. Thread Size or Retainer Type: Roll Pin. more details on - https://www.carid.com/rhinopac/exter...mpn-s0461.html


On Amazon - https://www.amazon.com/Rhino-S0461-C.../dp/B000CPIE7Y - there is no written description and the picture is completely different and the material is inconclusive.


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Old 06-07-2020, 05:42 PM
utah smitty utah smitty is offline
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Thanks trbankii...


I found an aluminum slave cylinder brand EXEDY p/n SC889. Made in Taiwan. The picture makes it look like it's brass, but it's cast aluminum. It was $28 at Rock Auto.


I'm hoping this will solve the problem... I changed the tranny oil with Redline MT85 75W85 GL-4 synthetic gear lube. It helped slightly, but it still doesn't like to go in gear and grinds the reverse when it's hot.


I did notice that the free end of the plastic slave cylinder can be deflected with very slight pressure. I've noticed that the problem seems to be worst when I have to wait at a stop light. I'm theorizing that, since the cylinder is near the exhaust pipe that it gets hot when the truck is stopped since no air flow over it, and the plastic gets soft and flexes without pushing in the clutch all the way.


We'll see as soon as I get the new slave cylinder installed.


Thanks again for the post.


Smitty
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  #8  
Old 06-08-2020, 06:05 AM
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Bleed it well when you replace is. Just a tiny bit of air in it can cause havoc too.
And don't forget to take the upper end loose from the master clutch cylinder or you will replace it next. Takes very little pressure moving the line to crack the cylinder above.
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  #9  
Old 06-20-2020, 05:17 AM
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Quote:
Originally Posted by utah smitty View Post
I'm theorizing that, since the cylinder is near the exhaust pipe that it gets hot when the truck is stopped since no air flow over it, and the plastic gets soft and flexes without pushing in the clutch all the way.

The plastic right next to the exhaust has been a concern of mine as well. I'll be interested to hear how things work out for you. Does the Exedy use the stock plastic line as well? That has been a concern for me as well as (like a5150nut states) it is pretty fragile itself.
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Old 06-20-2020, 01:43 PM
utah smitty utah smitty is offline
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So, I finally got the slave cylinder, the master cylinder, and the hydraulic line all replaced in my truck... I had just got enough of the shop finished and straightened to let me use my lift.


I used a metal Exedy slave cylinder and braided steel hydraulic line from Rock Auto, and bought a metal Centric Master Cylinder from Amazon.

Everything went together well, and I bled the slave cylinder using the tried and true "push and hold the pedal, open the bleed screw, let bubbles out, close bleed screw, release pedal" method, plus pushing on the slave cylinder rod to force fluid, and bubbles, back up and out the master cylinder, plus using a vacuum pump on the top of the master cylinder.

I finally got a firm pedal, but the truck shifts even worse than it did before.

So, a couple questions...

The PO had put the slave cylinder rod with the large rounded end against the clutch pivot, and the small, stepped end into the slave cylinder. This is different than what I've seen in pictures, such as in trbankii's above, which shows the small end sticking out, and retained much like a gas shock.

Which way is correct?

I also noticed that the aluminum Centric master cylinder is about 3/4" shorter than the OEM plastic one... if the bore is larger, then it could still push enough fluid to disengage the clutch, though requiring more pressure. If it's the same diameter, then not as much fluid will be pushed out and the clutch may not disengage completely.


Finally, I'm wondering if I have one of the old style flywheels, and possibly the original ball stud and throwout bearing fork. The truck has about 135,000 miles on it, and the tranny was supposedly rebuilt at 115,000 miles, but I don't think it was done by a shop... the throwout bearing is starting to whine, and a lot of the clips that hold the hydraulic line, etc. away from the exhaust were not bolted back into place.


It's hard to get a picture of the flywheel without removing the tranny, but can anyone tell if this is the two piece or one piece flywheel?




Lastly, I bought some heat shielding that consists of a fiber type substance bonded to aluminum and placed it on the exhaust cross over pipe and the main pipe going to the rear of the truck in order to cut down on heat radiated to the transmission.


Anyway, your comments and suggestions are welcome and appreciated.


Smitty
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  #11  
Old 06-26-2020, 04:29 PM
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As I mentioned above, my main issue was that the fork pivot had broken out.





I'd see if I could look in toward that point to see the condition of yours. You might be able to stick a cellphone in to take a picture.


Like in the other picture I posted, I've only ever seen the "pointed" end going in to the fork, not the "balled" end like you describe with the PO.


I'd have expected that if the tranny was rebuilt that a new clutch and other components would have been put in when everything is out. However, I've seen way too many shops that only do the immediate problem - and then are more than willing to charge you for the next thing that fails - and the next - and the next...
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Old 06-27-2020, 07:15 AM
utah smitty utah smitty is offline
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Thanks trbankii--


I finally took it to a friend who works part time at a transmission shop. He pulled the tranny and found that the throw-out bearing was completely wasted... all the steel balls were gone. The pivot ball and fork were also worn out. So, it's like you said, some shops (and people) only do part of a job...


My friend did say that the flywheel is a one piece, so that's good. I ended up having him have the clutch disk rebuilt and lined with ceramic pads like used in heavier trucks. Since I bought this truck to tow my travel trailer, and also a 10,000 lb dump trailer, I want it to be reliable.


I should have the truck back Monday... I'll let you know how it all turned out.


Smitty
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Old 06-27-2020, 07:39 AM
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Sounds good. I bought my K2500 used and one of the early projects was going through the clutch. Pretty much everything (just like yours) was worn out.
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