I have to replace the slave cylinder on my 85 f150 np435.

Do I have to replace the line as well, or can it be reused? What is the best procedure to bleed the system after?

 

I don't think you have to replace the line. But I don't have much experience with that, so am not sure. On the other hand, I have a NOS line in my parts bin, so they must come off.

On bleeding it, that depends on what brand it is. My understanding is that the original slave cylinders don't have a bleeder valve. So, if you are replacing it, look for one with a bleeder valve. Then, fill the master and have someone push the pedal down while you go under and open the valve slightly until the flow stops and then close it. Do that several times until you aren't getting any more air, but make sure the master doesn't run out of fluid.

However, you can't get all of the air out that way. So, after you bleed it a few times take it for a drive and pump the clutch several times. In my case it took a 1 mile drive around the neighborhood to get all if the air out.

 

I haven't messed with them too much, but I believe there is a pin that you drive out to release the line. My slave has a bleeder, but it's not what you think it is. It's a small allen screw that is pretty much flush with the slave housing. Loosen the allen screw and it will bleed the slave.

I also had trouble after bleeding mine. The drive around the block fixed mine up also. After you bleed it as good as you can, you may still not have much clutch. But you can get the engine started in neutral, and then force the trans in 4th gear. Then quickly force it down the gears to 2nd if you can. If you need to get into reverse that can be more of a problem. Then when you finally get it going down the road, the clutch will get better and better as you use it.

 

The easiest and fastest way is to remove the slave, line and master from the truck.

Strap/fasten/mount the master to the top of a 6' ladder, attach a weight to the slave (now hanging by the floor) All you need to do is make sure the line has no "upward" facing kinks) now fill the master, with cap off, and open the bleed screw on the slave... now watch the fluid flow to the slave. keep an eye on the level in the master.
when the line is full, close the bleeder.

Now here's the next trick: lightly tap the slave and watch the air bubbles go up to the master. keep tapping and slowly tap up the line, repeat, repeat, repeat.

Now with air out, cap the master, take the system to the bench vise, mount the master in a bench vise with the master level, and the slave by the floor, and now SLOW pump the master, a few times.
When you can not compress the plunger more than, say 1/8" It's bled!
install whole-sealed system in truck.
Time needed,.... less that 10 minutes!

Look it up on you tube.
I tried for hours with my daughter when putting in the ZF-5, while it was in the truck,
But only 10 min (by my self) out of the truck....

 

If you have help you can have someone hold the old slave cylinder and drive the pin out with a nail. Install the slave cylinder and drive the pin in with a nail. Like what was said before have someone pump the pedal and there should be an Allen screw on the side of the slave cylinder and you can bleed it from there. I don't doubt that the guys on here put it in fourth and drove it and got the air out but I couldn't do that so I slammed it in first and drove it a few miles till I got all of the air out. I did basically have to slam it in every gear but after a mile it got a lot better. Two days ago I had to replace the master cylinder and that's what I did to get all the air out. I'm not exaggerating though you will have to slam it into gear at first it really sounds nasty at first but it will shift smoothly quickly after that.

 

Soooo much easier removing the whole system and replacing what is needed and replacing the whole system after its bled

 

With the system intact (line attached to master and slave) I find it quite difficult to get it installe dnad the line router correctly. Nearly impossible on my diesel and a PITA on my 460.

Either way, getting the last bits of air out is a pain. Bleed it a lot just like brakes. Pump a few times, hold, open valve, close before pedal hits floor, repeat. With valve closed and pedla released, slowly pushing in, holding, and releasing the slave pushrod (clutch fork) can help get air out, forcing it back to the master.

Also if you haven't already installed a firewall brace (originally made by Ford, no longer in production) get a firewall brace kit. The firewall cracks since it was designed when these trucks had mechanical z-bar clutch linkages and is not strong enough for a clustch master cylinder, resulting in cracking, flexing, and inability to fully release the clutch.
ford firewall page

 

To confirm, clutch master or slave replacement is just driving out the roll pin witha punch and replacing it after pushing the line into the new cylinder. There is a rubber seal/gasket/o-ring that goes in the cylinder port before inserting the line.

 

I did not put it in fourth and then drive it. I put it in fourth first because it's easier to force in 4th to stop the front half of the trans from turning. Once you get the trans stopped, then you quickly shift it to 3rd before the trans starts turning again, and if you can, quickly shift it to 2nd. I am doing all this still sitting in the driveway.

You should not have to force it hard once you get moving down the road. If you use what clutch you have, pull it out of gear, rev the engine a little bit while putting pressure on the shifter into the next gear, it should fall right in. Big trucks don't use synchronizers so this is how they always shift. If you just let your foot off the gas and try to shift it, it will go in hard.

 

I wasn't arguing or debating that you did it that way I was just stating what I did

 

Thanks for the info guys. I'll try to bleed it with the master in the truck, if it prooves to be difficult I will just pull the master and bleed it.