Clutch Hydraulics, 1989 GMC C1500

[Renken2000Classic]

Having trouble with it...

New master cylinder several years ago. Shop said slave prob not far behind if you have to replace the master.

Son had been borrowing it, and it scrapped out several months ago - poor pedal pressure, hard to get out of gear.

I had it towed home and eventually got around to replacing the slave cylinder.

All seemed well for a while (few hundred miles). It acted weird after it sat for a few weeks but then smoothed out.

Now it's losing pressure or something like that in slow traffic, or extended maneuvering like for a tight parking spot. Still fine on the highway and so forth though.

I was going to try and re-bleed it today, and removed the inspection plug while he pushed the pedal, off and running, and it seemed to be moving (whatever it moves) good, and not bleeding down or whatever, so I left it alone in case I made it worse.

???

He's borrowing it again; it's all he's got to drive right now and I'm bummed about all of that.

 

[brodmann]

Is there a question here?

 

[Renken2000Classic]

I'm just venting. No, really, yes. Like, I don't know how to fix it. Could be I didn't bleed it right? Could be the master's bad now? Could be the bleeder on the slave/secondary isn't 100% sealed, and is letting air back in? (I opened and closed it about a hundred times trying to get it bled initially) Could be something else?

There's a master/primary cyl, a line, and a slave/secondary cyl. So it doesn't seem too complicated.

This truck's engine is worn out/needs rings at least, and I don't want to throw $300 at it having it fixed.

 

[flashback]

If you don't see any leaks at the slave then I would re-build the master, but be sure you are bleeding it properly first.

 

[matt167]

I had a 1995 K1500 and had to do the clutch slave cylinder. Bled it like a brake pedal.

Teach kid to drive without clutch. Only need it to get it into 1st

 

[Renken2000Classic]

He's got a line on a decently priced mechanic; I'm going to let that guy take a look at it if he's interested.

I bled it using a combination of pull a vacuum on the bleed screw, push clutch pedal in (assistant), crack bleed screw, close bleed screw, clutch pedal up, and repeat, while keeping M/C reservoir filled (assistant).

I did M/C and S/C on my Acura a few years ago, but didn't get the bleeding right or something. 2nd place I took it to, guy said "I know what it is", and added sealant to the threads on the bleeder screw. It's good but not perfect now. If I drive it aggressively (upper RPMs before shifting) the pedal gets weird sometimes. Perfectly driveable otherwise.

So my experience with this isn't breeding confidence, lol.

 

[flashback]

Your bleeding procedure is good as long as you open the valve first then depress petal, when petal hits floor then close valve.

 

[brodmann]

I usually get a piece of host that fits over the bleeder and stick it on the bleeder and the other end in a container of brake fluid. You loosen the bleeder and just pump the petal until it no longer creates bubbles in the container. With a long enough hose, you can do it solo! That's the best way I've found to bleed brakes and clutch systems. You'll need to buy a good bit of brake fluid, but pour it back in original container, and you can use it over and over again. With the master cylinder, I always "bench bleed" it before I mount it. That saves a lot of time. Lots of youtube videos on how to bench bleed.

 

[Bob_VT]

1989 truck....... I would seriously inspect the lines.

 

[Renken2000Classic]

Your bleeding procedure is good as long as you open the valve first then depress petal, when petal hits floor then close valve.

Took another crack at it yesterday, using this procedure. I was opening the bleeder after the pedal was on the floor before I think. So far so good...

 

[Renken2000Classic]

Took another crack at it yesterday, using this procedure. Before I was opening the bleeder after the pedal was on the floor, I think. So far so good...

 

[Renken2000Classic]

Based on what worked for my other car, I changed the master on this a few weeks ago (even though that was done at a shop a few years ago), and it's all better now.

It was driveable for a while after the last re-bleeding attempt, but my son recently said it was giving him trouble again, so I tried doing the master, and boom that was it. Sooo much easier than on the Acura too.

 

[Grub54891]

Any rubber lines going to it should be replaced also. Being that old, they collapse inside where it cant be seen.

 

[Scott06]

Based on what worked for my other car, I changed the master on this a few weeks ago (even though that was done at a shop a few years ago), and it's all better now.

It was driveable for a while after the last re-bleeding attempt, but my son recently said it was giving him trouble again, so I tried doing the master, and boom that was it. Sooo much easier than on the Acura too.

You rebled the master or replaced the master again? Only other thing that may be influencing it is if the pilot bearing. If they get worn they can drag a bit or a lot. I think of the time this issue shows up at slow speed or parking

 

[Renken2000Classic]

Replaced it. Still going good.

Didn't know if I would, but had to bleed it again; just cracked the fitting open down at the slave (no tubing or vacuum, etc. this time) had my other son push and hold the pedal, closed the port. Repeated several times. Got some good air burps.

There's a zerk on the trans that I've greased periodically. Don't know exactly what that's getting - throwout I think, but...