Lila- 81 F100. Built for her, by her!

[ArdWrknTrk]

I think I mentioned the overcenter spring, above ^^^
Without full pedal return the reservoir port in the master cylinder will not open.

That's why arm position, pushrod adjustment and the condition of all the plastic bushings is so critical.

The arm was available as a replacement part from Ford.
Maybe Gary can post the #?

[ArdWrknTrk]

The two different 'at rest' orientations of the pedal arm are very apparent in the pictures.

The different shaft lengths are a bit disconcerting too.
When aligned on the left it appears simply swapping the hydraulic arm onto the mechanical shaft might put the pivot pin right up against the transmission tunnel.

I don't know if that's the case.
And I don't know if you'd need to flip the offset hydraulic arm around (with the pin pointing toward the door to get it in plane with the master cylinder pushrod, but these are things that need to be examined before cutting, drilling, welding or whatever 'fully committed' steps you take.

Maybe an appropriate torsion spring could slip over the shaft as it is inserted into the pedal support, in order to get the clutch pedal to return and have the master cylinder piston come fully to the rear?
The rubber bump stop should prevent the pedal from pulling the piston out.

Does your master cylinder have an adjustable pushrod?
... with wrench flats and a jamb nut*?

[Lila_the81Custom]

Gary,
I believe that I can get another splined arm and I know that the spring is for bringing the pedal back. The one on the 81' is on top and reverse from the 94', which I am sure is the difference in mechanical vs. hydraulic. The rod was way to short from 94' to 81'. Snaffu #4001 with this truck! My poor diesel mechanic husband is sick of telling me that there is a large difference between working on tractor trailers/buses and small/older resto projects!

Now just to figure out a solution. I have seen where the hydraulic master booster is placed on the clutch side instead of the brake side and it connects directly to the clutch pedal. I have also seen that there may very well be a master cylinder behind the clutch pedal. Ugh, nothing can just be simple can it!

All part of the adventure in my head!

[ArdWrknTrk]

Jaci,
Just go with the stock master in the stock location.
It will save you dozens of headaches going forward...

Yes, in a Z-bar clutch slack is taken up against any wear in the clutch or mechanism.
In a hydraulic setup the master cylinder has to retract all the way to open the piston to the reservoir.

With my external slave there is an internal spring that keeps the throwout fork & bearing against the pressure plate fingers.
It is far better for the bearing to be spinning with the shaft than to be accelerated from zero to 4000 and back every time you step on the clutch.

I'm not sure if the internal concentric slave of the Windsor bell Zf/M5R2 is the same, but Cory could confirm.

So, you're going to need to drill a large hole for the master, and two smaller ones for the studs.
This is best done with a uni-bit (step drill). You can get a cheap pair -$13.95- at Horrid Fate.
Be sure to deburr those holes when done!

[ArdWrknTrk]

Back to the pedal spring.

Look for a torsion spring similar to the ones used in a lawnmower to keep the bag chute closed when the bag's not attached.

Just go to the box store and look at displays.
Note the model number and go online to the manufacturer, ereplacementparts, repairclinic, or toolpartspro to see the exploded view and order the one you need.

Remove your existing spring and figure out how to use the torsion spring to hold the pedal against the rubber bumper.
(Note: the spring on either side of a mower will be wound the opposite way! 💡)

[Gary Lewis]

I agree with Jim - use factory parts.  I've put hydraulic clutch assemblies where mechanical ones where, put '95 masters and boosters in an '85, and was able in all cases to bolt it in.

[Rembrant]

ArdWrknTrk wrote

I'm not sure if the internal concentric slave of the Windsor bell Zf/M5R2 is the same, but Cory could confirm.

So, you're going to need to drill a large hole for the master, and two smaller ones for the studs.
This is best done with a uni-bit (step drill). You can get a cheap pair -$13.95- at Horrid Fate.
Be sure to deburr those holes when done!

Sorry, I'm no help with ZF5 stuff. I'm an M5R2 guy...lol. I know the slaves did change over the years, but I believe Jaci said that she took the whole hydraulic kit out of the '94, so she should be good to go. My '84 F150 was a factory hydraulic clutch truck, so the 5spd swap was very easy. I am now doing it in my 1980 (in a couple days) so I too have to drill the holes in the firewall like Jaci does. I bought a Bullnose hydraulic clutch pedal box/kit from a fellow member on here, so it should be a fairly easy install. I'll let you know later this week.

This 1980 was a manual trans truck (T18, I believe) and it was swapped to an automatic, and I'm now swapping it back to a manual.

[ArdWrknTrk]

I meant to say that I don't know if the concentric slave is spring loaded against the pressure plate fingers.

I know about the mounting screws changing.

[myrl883]

If'n it helps, the early timing cover will work with a reverse pump, and serpentine drive and a mechanical fuel pump are not mutually exclusive...

The P/S pump bracket can be mildly relieved to clear the fuel pump. The P/S pump fits closer to the block on a serpentine drive, so the clearance is tight, but they'll both fit.

Use an early timing cover with a mechanical fuel pump, and buy a water pump for a serpentine drive Mustang. That's how Ford made it work on the Mustang! Remember, they were carbureted, too.

My '81 has the original timing cover and fuel pump, a serpentine drive from a 1994ish F150 (with a G3 alternator and working ammeter) and a Mustang water pump. Everyone under the hood is happy!