I'd like to learn about retrofitting a hydraulic clutch into an 81 that currently has a mechanical linkage in order to install a 5 speed ZF. My truck has a 351, so the ZFs that will fit use a concentric slave, otherwise I would have just made the mechanical setup work. Can anyone point me at how I might retrofit the master cylinder into this setup?

I've searched extensively on this topic and found the following:
- ZF installs behind a 460, which the 460 ZF uses an external slave so converting it to use the mechanical linkage is straightforward.
- ZF installs in 83+ trucks that had a hydraulic clutch option, so a pile of junkyard parts later and a hole punched in the firewall you have your MC
- Other people who want to do this swap asking this question.

I'm leaning toward just getting the MC and building a solution from scratch, which I'm fairly good at, but I don't want to spend a ton of time analyzing and mocking up a solution if someone else has already done it and can share their experiences.

Thsanks!

 

Don't re-invent the wheel. Find a 86-down manual tranny truck, and get the complete pedal assembly out of it, along with the master cylinder, etc. Bolt it under the dash, and cut the hole for the master cylinder.

You didn't mention it, but I am assuming you have a 351m? If so, the 460 zf should fit, but I am not sure what clutch options you are going to have. In other words, I don't know for sure if the 460 clutch diaphragm will fit a 351m flywheel. There should be a combo that works, you just have to find it. You will definitely need the zf disc, since it has a oddball spline and shaft diameter compared to the 4 speeds that were an option for your truck.

 

Thanks, Dave. I actually went out and measured everything last night and the mechanical pedal assembly in the '81 is a lot closer to the hydraulic in my '90 than I'd thought. Punching and reinforcing the firewall will be a bit of a pain either way, but I think re-orienting the arm on the end of the mechanical pedal assembly to work with the hydraulic MC is all it will take as the radius is about the same.

On the tranny itself, I have a 351W, so I need the "small block" ZF, which as far as I can tell only ever had a concentric hydraulic slave. Good point on the 351M - I'd be off to the races with a 460 ZF if I had that!

On the clutch disk and input shaft, the ZF 5 speeds (the diesel, 460, and small block variants, don't know about the mysterious "UPS truck"-only model) all have an 1 1/16" 10 spline input which is compatible with most of the Ford truck three and four speeds used in the last few decades. The 11" clutch I put in my truck shortly before the 4 speed started popping out off gear 'should' work fine with the ZF, that part I have researched to death

Thanks! I'll update the thread when I'm done and let you all know what direction I went and how it worked out.

 

Something is not jiving here. My info says the zf is a 1 1/4-10 input shaft while the you are correct, the 4 speeds where 1 1/16-10.

 

I went from a np435 to zf on my truck, and was able to keep the clutch I had (11") no problem, as for the master cylinder, the spot where it goes is stamped out on trucks with auto trans, maybe you could find one at the junkyard and take measurements on where it goes. The spot where it goes is stamped out on trucks with auto trans also.

 

Unfortunately, there aren't any stamps on pre-1983 trucks.

From my 1981:

 

As opposed to the '85:

 

Sorry, I think I'm lost. Looked at a post from ctubutis showing a pic of an '81 and thought I was responding to that. Where'd it go? Wrong thread? Wrong planet?

Ok, time warp explains it. He DID post and I DID see it. Please disregard my confusion - although you'll probably see it again.

 

Your 85 doesn't look like what I'm expecting to see....

I know what he's referring to wrt the stamps, you can see where a hole is punched when a hydraulic clutch is installed.

I don't see such marks on yours, perhaps they're covered up by a firewall-strengthening reinforcement?

 

I don't see a reinforcement, or at least not an added plate. Can you circle the exact area?

 

Heres a picture of my 1982, is it that spot right next to the booster?

 

Could well be! It's in the right place.

I thought it was 1983+, maybe yours was built in late 82? Could also be I'm wrong, it wouldn't be the first time (and I'll be wrong again, just wait and see ).

 

On a similiar note, does anyone have a pic of the reinforcement plate that is sold to prevent the firewall from cracking around the clutch master? I have a couple pieces I got from the junkyard (one factory-appearing and one homemade) but I'm not sure if they are the proper piece.

 

yup, that's it. On the later trucks the holes were there, and a plate was bolted on.

 

This might help you:

https://www.ford-trucks.com/forums/7...in-issues.html