I posted this on another forum but I figured I would post it here too, since the 87+ trucks are the ones that actually came with internal/concentric slaves.

I installed a small block ZF5 into my 1982 F100 and have gone through two slave cylinders from OReilly's. It has been a project, so the first one failed before I even drove the truck. The cylinder was installed for several months with fluid in it, and when I was about to move it for the first time I pushed in the clutch and the pedal went to the floor. I looked under and I had fluid dripping from the bell housing. The second one failed after a few months too, after doing nothing but moving it around a few times and a few trips to the gas station.

So what's the deal here, are the aftermarket parts really this unreliable or am I doing something wrong? My master cylinder is new, both slave cylinders were new (I removed the original because I was like, "if I don't replace this, it will go bad.."), and the pilot bearing is new. I used old (but sealed) containers of DOT3? brake fluid. I have the rod adjusted so that it is "neutral" when the pedal is not pressed (not pulling on the rod, and not pushing on it). The slaves were not leaking prior, they both failed in an instant rather than progressively getting worse.

Any knowledge/tips/anything? Any specific part that you guys have had luck with, or is third/fourth/fifth time the charm? I'm getting tired of pulling the transmission, and if I can't go a couple of months without replacing these things then there is no reason to keep the zf5 or truck.





Anyone have luck with these flimsier looking plastic ones?

 

Yeah some aftermarket parts are just plain JUNK!

When all else fails... replace it with a Motorcraft (Ford) part. You'll pay more, but for critical parts like this, more is less.

 

I think they use a DOT 5 fluid for the clutch cylinder. I'm not sure what the difference is, though.

 

Difference is...

DOT3, your basic brake fluid, made of whatever brake fluid is made of. Absorbs water and humidity real fast so don't leave it uncapped. Boils easily too.

DOT4, a little better than DOT3. Made of mostly the same stuff I think. Higher boiling point, and it don't soak up humidity/moisture as fast. Not sure if you can mix it with DOT3.

DOT5, the good stuff. Made of silicone, cannot/will not/do not mix with any other brake fluid. Won't absorb moisture and has the highest boiling point.

 

Did you happen to replace the clutch disk and pressure plate too, or is it the original one that was on the engine prior to the transmission swap? If not could it be a bad pressure plate that is damaging both new cylinders?

Also, can you tell where on the cylinder the fluid was leaking from?

When I replaced my slave cylinder, I used a genuine Ford/Motorcraft part. I went ahead and replaced the clutch assembly, TO bearing, flywheel, and rear main seal, at the same time. The only problem I had was trying to get the tranny to flush up with the motor.

 

The plastic one is for a later model truck and will need a matching master cylinder to go with it (different bore size). Everything I read says to spend the extra on a Motorcraft slave cylinder, as they will last the longest. I don't believe the problem you are having has anything to do with the pressure plate or the clutch itself.

 

The clutch and pressure plate are the only things that are not new, the T19 did have a failed throw-out bearing but the pressure plate didn't look bad. I don't know exactly where the fluid is coming from, but the entire cavity behind the cylinder was full of fluid when I removed the last one, including fluid leaking from the front.

I didn't know the bore size mattered. I just bought whatever would fit, I just checked and it is a 7/8th bore. I keep on reading around and it sounds like Motorcraft sells the same thing as everyone else.. a product with AP stamped on it. I thought I got lucky finding a LUK slave online, but I can clearly see the same logo stamped on the part.

 

References?

Yes the size matters greatly. If you are using the master cylinder from when you had a T19, then its too big for the concentric slave. You are overstroking the slave and making it leak. You have to use a master cylinder from the same vintage that the ZF5 came from. Best bet for you is to get a master, slave, and line all from the same year truck so you know sizes are matched.

The reason is the T19 used the external slave with pivot arm. It had a master bore size of 7/8". You need a master cylinder with a 45/64" bore size.

 

Hmm, I didn't know that. I thought everyone used the same internal slave when making these conversions (for a 1980-1986 truck), because the slot in the firewall doesn't even hold a 87+ slave correctly (it will be tilted a bit). But if that's my problem, it's nice to have found the solution. I just looked up the parts for a newer truck and it did say 45/64 on the master.

 

For which part of my statement?

Ford used a 7/8" bore master cylinder through '92, for everything - external slave, concentric slave, it doesn't matter. It changed in '93 to 45/64" (18mm) and there is a corresponding change to slave cylinders at the same time. This is going by parts store look-ups, both NAPA and RockAuto.com.

I re-used the original master cylinder (7/8" bore) with a new hydraulic line and a concentric slave cylinder (for an '88 model) when I swapped from a 4-speed (external slave) to a ZF (internal slave) in my '87 and the clutch works fine. I also re-used the original clutch and pressure plate.

What was the original clutch setup on the '82? Was it originally hydraulic or was it a mechanical linkage? If it was originally a mechanical linkage, it could be possible that the pedal travel is longer than the later models originally equipped with a hydraulic system, although I would think that would cause issues with the master cylinder before causing issues with the slave cylinder.

 

More info, thanks.

The truck was an automatic, but I got all the pedal assembly from a 1985 truck with a hydraulic clutch, so the linkage is correct. The slave cylinder was ordered for a 1987-1991 truck, and the master for 1983-1986. The ZF5 is from a 1988 F250.

 

I'm humbly corrected. Thanks for the info.

 

Okay, so I spent like an hour looking crap up and can confirm that the 7/8th bore master is okay with the metal slave. There was a change in master cylinders in 1988, but it was for a change in the firewall mount, not the bore size. They switched to 45/64 later. So my problem still remains, I found a website of a place that makes custom slave cylinders.. we will see if they actually get back to me. Either way I will probably replace the clutch/pressure plate next time since this will be the second go-around of getting hit by brake fluid.

 

I guess I'll just keep updating with info as I find it, because it always sucks when someone finds a thread like this that never came to a conclusion. This info shows that Ford made some changes with the plastic slaves but I can't find info whether the older metal slaves where upgraded or not. Also a bulletin about the upgraded LUK part. Maybe I will upgrade the slave and master since even the plastic slave was later used in the truck transmissions. I already ordered a new LUK clutch and pressure plate.

 

Hi everyone. I am looking to make a Zf5 speed swop on my 1985 F150 4X4 in the near future. The truck has a 351w T18 granny low 4 speed 4X4. looking @putting a ZF5 speed out of a 88-91 F250 4X4 with a 300 302 351w. I will be using the stock 85 master and the 88-91 clutch hose, 88-91 cross member, 88-91 front drive shaft with the 85 transfercase and shortening the 85 rear drive shaft. anyone know if the pilot bearing in the end of the crankshaft will have to be changed to a 88-91 pilot bearing or even what style it is??