Slave cylinder problems

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

iamtherealJayy

Full Access Member
Joined
Nov 26, 2021
Posts
1,571
Reaction score
275
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
1987 Chevrolet V20 with an SM465 I believe, L123R gears, it’s got hydraulic clutch and I’ve replaced the slave cylinder twice in the last year and a half. Today after I changed my headlight dimmer switch and door jamb switches I had the truck in low just pulling back to where I usually park it since I had it closer to the house to vacuum it. Anyways, I couldn’t pull the truck out of low, it always grinds a little bit going into low and reverse but that’s because they aren’t synced? But why would I not be able to pull it back out of gear? I’ve had it happen a few times where I couldn’t put it in first, I’d be sitting at a stop in neutral and go to put it in first and it would drop down once but wouldn’t drop the second portion into the gear, kinda like it meshed once but didn’t fully go in. If I started letting out on the clutch pedal it would grind and throw it out of gear and I’d have to stick it back in first. Never happened a whole lot so never concerned too much. Big question is, is my slave cylinder going out again? I’ve replaced the slave twice, master once, and the line between them once. Why does my slave cylinder only last 6 months? The truck has got maybe 3200 miles on it in the year and a half I’ve drove it. I’ve never drove it more than maybe 15 miles in one direction.
 

bucket

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
28,956
Reaction score
23,465
Location
Usually not in Ohio
First Name
Andy
Truck Year
'77, '78, '79, '84, '88
Truck Model
K5 thru K30
Engine Size
350-454
Does the clutch start to engage as soon as you start letting the pedal off the floor?
 

iamtherealJayy

Full Access Member
Joined
Nov 26, 2021
Posts
1,571
Reaction score
275
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
It starts to bog down the engine yes, as far as I can tell the clutch system is bled as well as I can. The first time took me several hours to finally get some pedal but I’ve gotten a little better.
Edit: let me reword the big part, it engages pretty close to the floor, I wouldn’t say as soon as you let off but within an inch or so, that’s from completely down to the floor, I’d say within an inch it’s dropping the rpm and you have to give it throttle and start moving
 

bucket

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
28,956
Reaction score
23,465
Location
Usually not in Ohio
First Name
Andy
Truck Year
'77, '78, '79, '84, '88
Truck Model
K5 thru K30
Engine Size
350-454
Mine is the same way, but it is a boonrigged truck that was an auto to begin with. But, it has no trouble going into any gear or letting go of a gear. You're low pedal height may possibly be a separate issue and could be a simple fix, possibly a bent clutch fork.

Your shifting issue could possibly be a bad pilot bushing.

I'd start with having a helper operate the cluch while you lay under the truck and look at the slave cylinder throw and try peaking in around the clutch fork boot to see how far the clutch is releasing. That can be tedious trying to see, but a flashlight, mirror and/or a borescope will help.
 

iamtherealJayy

Full Access Member
Joined
Nov 26, 2021
Posts
1,571
Reaction score
275
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
The previous owner(my dad) replaced it as well when he had it and said the older fellow before him had it replaced several times as well. Are these slave cylinders just junk? The truck has around 94000 miles on it and it’s had atleast 6 slave cylinders that I know of. I had the clutch replaced last year and it now has around 2000-2500 miles on it. The previous clutch had around 92000. My pressure plate forks were destroyed. The clutch replacement is the only time I’ve had a shop do work on the truck. I’ve always done my own work but I had no way of pulling a transmission by myself. I know the clutch disc and pressure plate were replaced but do you think I might have got screwed and they could’ve left something wrong? I had to bleed my slave cylinder after the clutch job because it didn’t grab until top of pedal. I’ve never had this many problems out of a slave cylinder. It usually has no indication it’s going out, the second time I replaced it I drove to my girl friends house and I had to move my truck and I put it in reverse and couldn’t get it back out of gear and ended up having to shut the truck off and put it in low and start it in gear to get out of the road. Is what’s happening now a sign my slave is about to go out again?
 

bucket

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
28,956
Reaction score
23,465
Location
Usually not in Ohio
First Name
Andy
Truck Year
'77, '78, '79, '84, '88
Truck Model
K5 thru K30
Engine Size
350-454
It's had to say without crawling under and looking at it. If the slave cylinder is being over extended for whatever reason, they won't last long at all.
 

iamtherealJayy

Full Access Member
Joined
Nov 26, 2021
Posts
1,571
Reaction score
275
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
How can I tell if it’s extending farther than it should? And how could I fix that?
 

bucket

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
28,956
Reaction score
23,465
Location
Usually not in Ohio
First Name
Andy
Truck Year
'77, '78, '79, '84, '88
Truck Model
K5 thru K30
Engine Size
350-454
Hopefully someone here can measure the stroke of a known proper setup. The fix depends on what's causing it, if that's even the problem.
 

iamtherealJayy

Full Access Member
Joined
Nov 26, 2021
Posts
1,571
Reaction score
275
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
This may be an obvious thing but is it possible to “over bleed” a hydraulic system? Could there be too much fluid in it and it’s slightly out to begin with and when you press the pedal it extended regular amount plus what it’s already pushed because of excess fluid? Or is that something I came up with in my head? Just trying to come up with ideas, the truck over all isn’t bad but the things I’ve had problems with continue to give me problems. Example slave cylinder, had some problems with the battery but those are half user error of letting it go dead.
 

iamtherealJayy

Full Access Member
Joined
Nov 26, 2021
Posts
1,571
Reaction score
275
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
Since the truck hasn’t gotten any fixes with this issue I’ll try to provide a little more info. I’ll be sitting at a stop and press the clutch and try and put it in first and it will drop down once but won’t go completely into gear(meshes with synchronizes maybe?) if you start to let off the clutch it will grind a little and drop into gear. Or if you catch it and notice it didn’t go completely in than you can move back to neutral let off clutch press again and it’ll go in usually. Generally first gear is the only gear I get the problem with, L and R I use the 2nd gear to synchronize then it usually drops right in.
 

Redfish

Full Access Member
Joined
Nov 6, 2021
Posts
2,373
Reaction score
12,752
Location
Prairieville, LA
First Name
Andrew
Truck Year
1987
Truck Model
V1500
Engine Size
350/5.7
No, you cannot "overbleed". You can overfill the reservoir but you absolutely need pure fluid on the pressure side of the system. One thing that is VERY difficult is to actually bleed all the air out of the master cylinder. I was unable to do this with the master cylinder installed, I had to remove it and tilt it to get all of the air out. If you have air in the system you will not get a full stroke from the slave cylinder and it may not be completely disengaging the clutch no matter how far you push the pedal.

I am dealing with a lot of rain down here in Swampy Flatlandistan but if you need me to I can make an attempt to measure the stroke of the slave cylinder later this evening. I have no idea if this is even possible.

Honestly, I would unbolt the master cylinder, hold it level and pull the hose fitting out of the top. You will probably get some air out of it. Have some rags handy to catch any fluid that runs out. It sounds to me as though you still have some air in the system. That would account for the clutch engaging at the bottom of the stroke. Mine starts to engage about midway.

Of course I could be completely wrong here...
 

iamtherealJayy

Full Access Member
Joined
Nov 26, 2021
Posts
1,571
Reaction score
275
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
I’ve always heard with hydraulic clutches you want it to engage as close to the floor as possible, mines kinda iffy right now I noticed that day my brakes froze up that first gear I had the pedal about half way up and the truck wasn’t moving yet. The slave has been replaced twice, master once, and the line between them once(since I’ve had it). In my opinion the reservoir cap is annoying since the rubber cup makes it so no extra fluid can be in there during bleeding. To avoid having to remove the master cylinder could I lift the front/rear of the truck to make it sit level? I’m not looking at it right this second so I can’t tell how it’s sitting in there I believe the front would need lifted quite a bit.
 

Redfish

Full Access Member
Joined
Nov 6, 2021
Posts
2,373
Reaction score
12,752
Location
Prairieville, LA
First Name
Andrew
Truck Year
1987
Truck Model
V1500
Engine Size
350/5.7
You would have a lot of difficulty lifting the snout of that truck high enough to get that master cylinder level. That would be equivalent to a good power wheelie on a Suzuki Hayabusa. You may be able to just unbolt the master cylinder from the firewall but leave it connected to the pedal. I had my son hold the pedal down and I would partially actuate the cylinder myself by pushing the cylinder towards the pedal.

Regarding clutch engagement, you have more than one factor affecting it. If the clutch plates are worn the pedal would be closer to the top of its stroke before the clutch actually engaged and that would be A Bad Thing. On the other hand, if there is air in the hydraulic system you will not be getting the full stroke from the slave cylinder. If that is happening you may not be completely disengaging the clutch, that would also have it engaging closer to the floor.

You are going to be an Expert on these trucks by the time you get that thing working properly.
 

iamtherealJayy

Full Access Member
Joined
Nov 26, 2021
Posts
1,571
Reaction score
275
Location
Tennessee
First Name
Jacob
Truck Year
1987, 1978, 1976
Truck Model
V20, K10, K10
Engine Size
350, 350, 350
The clutch is newer, I didn’t mention it being replaced but I had it swapped about a year ago after the previous one self destructed. I’m not sure what all got replaced I had a shop do it since I had no way of doing it myself. I had to pay for a clutch kit and labor. Like $300 it wasn’t bad in my opinion. It has maybe 2000 miles on this clutch disc and pressure plate. I know those two pieces were replaced but I don’t know about the clutch fork, throw out bearing, pilot bearing, or anything else. I know after I had it swapped I had to bleed the slave again because I had no clutch pedal.
 

SquareRoot

Full Access Member
Joined
Mar 18, 2017
Posts
3,655
Reaction score
6,588
Location
Arizona
First Name
Mike
Truck Year
85
Truck Model
K20
Engine Size
350
I recently converted my 85 from auto to manual with factory hydraulic parts. Been daily driving it for over a year without any issues. The FIRST thing you should do is go to Napa and buy this bleeder tool. It makes bleeding the clutch (or brake) 100% fool-proof. I literally bleed my new clutch system in less than 5 minutes, by myself with perfect results.

My pedal does NOT engage close to the floor. If I push the pedal to the floor, my pressure plate diaphragm spring is over extended and I assume would be bad for the slave cylinder as well. From the "at rest" position, it might go down 2-3 inches max to fully disengage.

Out of curiosity, do you have a neutral safety switch installed and does it function?
 

Attachments

  • Bleeder.JPG
    Bleeder.JPG
    62.3 KB · Views: 115

Latest posts

Forum statistics

Threads
41,848
Posts
903,425
Members
33,362
Latest member
Dhatch84
Top