Clutch engaging weird

[Dave-T]

Howdy!

Due to a leaky master cylinder I replaced the master and slave on my 78 pickup (20R). I tried to get the adjustment on the master rod the same as the old unit. I also bled the system twice. What's happening now is the clutch is disengaging/engaging abruptly at the very bottom of the pedal travel, and even then not very smoothly.

So the next thing I will try is to bleed the system again, then play with the adjustments more. Any other recommendations? Please don't tell me the clutch itself is going out......

Thanks, Dave

 

[KLF]

How old IS the clutch?

I'm not as familiar with that series, but if it's the same as the next generation of trucks, then you should have about 10mm of "freeplay" at the pedal when the MC adjustment is correct.

 

[KliersLC]

That sounds like air in the system. Did you bench bleed the master?

 

[ms018kmf]

That sounds like air in the system. Did you bench bleed the master?

X2, bleeding bites. When I think all the air is out I give it 6 more tries to be sure. I think shops have the nicest equipment for bleeding if it's a real PITA.

Also was the truck not running for a couple weeks or more? I got a nasty layer of rust on my flywheel when I sat about 3 weeks. Mine was water related (abnormally bad) but rust may be on the flywheel just from humid air. Rusty flywheels grab and chatter like crazy.

 

[Dave-T]

That sounds like air in the system. Did you bench bleed the master?

I am not familiar with the procedure of bleeding a master cylinder, can you describe the process? The bleeding I did was through the slave cylinder with an assistant pumping and holding the clutch.

 

[Dave-T]

Also was the truck not running for a couple weeks or more? I got a nasty layer of rust on my flywheel when I sat about 3 weeks. Mine was water related (abnormally bad) but rust may be on the flywheel just from humid air. Rusty flywheels grab and chatter like crazy.

Interesting point. It was sitting in the snow and rain for over a month, so I may check on that.

 

[ms018kmf]

I had to adjust the master cylinder linkage to make things work. After driving again for a while (1500+ miles so far...) the chatter went away. I am pretty sure eating a bunch of rust off of the flywheel is not good for clutch longevity but I went for it. Eventually I expect I will need to re-adjust the linkage (really rusty flywheels should be re-surfaced ) If it was just down during snowy weather driving around could eat the rust off of it easily. Sort of like the rust you see on brake rotors.

 

[KliersLC]

Bench bleeding the master requires a couple of dummy plugs, but the short version is that it is just like bleeding on the truck but you engage it by hand and ensure all of the air is out.

 

[Dave-T]

Bench bleeding the master requires a couple of dummy plugs, but the short version is that it is just like bleeding on the truck but you engage it by hand and ensure all of the air is out.

I didn't do that, do you recommend that I pull the master and bleed it?

 

[ms018kmf]

It could be done on the truck, helps to have a second set of hands and eyes. If there were bubbles in the line they could have moved downstream. A lot of bleeding while it's installed could get the air out, just more work. All of my FSM stuff has them bleed it in the truck, not sure why. If you do a Google search on images for "bleeding master cylinder" it's the same thing minus one hose going back in the reservoir. I couldn't find a clutch master getting bleed.

 

[Cruiserdrew]

I don't know about mini trucks, but I've installed several FJ40/60 clutch masters and never had to bench bleed. I don't think that's going to be the problem. My guess is linkage adjustment, either at the pedal end, or possibly at the pushrod, if it's adjustable.

I do bench bleed brake masters, but even then, I'm not sure it's needed.