ZF5 Hard Clutch Problem Solved! Full Write-up post #20

[tailpipe]

I think it depends on which master you use as to where the hole needs to be. my master has the hose coming out of the front and not the bottom and the base does not rotate like the one in tailpipes pic. it is a solid piece of plastic. I used the speedo cable hole for mine and it is working perfect. seems to be the correct ratio. Even though mine is a M5OD application, I used the ZF internal slave and matching master cylinders. I got lucky though, I didn't know that there were 2 different bores and just ordered an internal slave for the truck I took the master off of and it all worked.

Crush, you bring up an interesting point here with the two styles of master cylinders. Silas is running the same style as you are (picture in my full write-up), so now I'm scratching my head again. Actually, now that I think about it, from what I have been reading most of the hard clutch issues are coming from the guys using the style of master cylinder that I have. I would be interested in hearing what the consensuses out there is.

 

[JSmall]

I think it depends on which master you use as to where the hole needs to be. my master has the hose coming out of the front and not the bottom and the base does not rotate like the one in tailpipes pic. it is a solid piece of plastic. I used the speedo cable hole for mine and it is working perfect. seems to be the correct ratio. Even though mine is a M5OD application, I used the ZF internal slave and matching master cylinders. I got lucky though, I didn't know that there were 2 different bores and just ordered an internal slave for the truck I took the master off of and it all worked.

I agree. This is the one I ended up using and it was a big improvement.

https://www.oreillyauto.com/detail/...m1279/4670645/1976/ford/bronco?q=CM1279&pos=0

 

[DEEPWOODS]

Mine is the Oreillys one jsmall listed above with tne bottom exit hose same part #cm1279 and it is very hard to mash and like on off

 

[tailpipe]

So I finally got to actually drive the Bronco today! After 13 years of running the 435 and five years of running the 435 with 4.88 gears this thing is a dream! I don't care what method you use, but please make sure your geometry and ratio is right for your hydraulic clutch set up. For us gear bangers (yes driving requires three pedals ya know!) the ZF-5 is absolutely the best upgrade you can do. Forget about the NV swaps that are super expensive and require adapters, get a SBF ZF and enjoy a low 1st gear, overdrive, and a four banger like clutch...now if I only had a place to wheel...help me out NOVA!

 

[Nevadasmith]

So here's a pic of the PDF I made the resolution isn't great but it complemens Tailpipes pictures, This has worked on 2 different trucks with different styles of master cylinders. If your clutch is fine leave it alone, if it's way hard try this mod! Hopefully it helps!

https://photos.app.goo.gl/qx7508PdAC1ejF293

 

[hankjr]

this is all great intel. i have follow up questions;

On the tab to attach the clutch push rod to, why move the pivot point 1 1/4" towards the firewall and not simply on the clutch pedal arm itself?

for those that have run this push rod angle for some time, any issues with the off-axis forces on the master creating binding? logic tells me that the piston in the master likes to be pushed along its central axis, not from an off angle.

i'm getting ready for final paint, but took some time yesterday to install pedal assy and master cyl and snap some pics of my (untested) set up. I will get those uploaded over the weekend likely

Hank

 

[Nevadasmith]

this is all great intel. i have follow up questions;

On the tab to attach the clutch push rod to, why move the pivot point 1 1/4" towards the firewall and not simply on the clutch pedal arm itself?

for those that have run this push rod angle for some time, any issues with the off-axis forces on the master creating binding? logic tells me that the piston in the master likes to be pushed along its central axis, not from an off angle.

i'm getting ready for final paint, but took some time yesterday to install pedal assy and master cyl and snap some pics of my (untested) set up. I will get those uploaded over the weekend likely

Hank

The only reason for the tab is to utilize the stock push rod length, you could just as easily extend the push rod. However by adding the tab and getting more upward sweep on the rod, you effectively increase the petal ratio at the end of travel. So you move the pettal further for the same distance of throw out travel which reduces the on / off tendency and the pressure to hold the pettal full in, like at a stop light. Similar to the quadrant clutch on mustangs.

The angles in the drawing are more than likely exaggerated, as I never measured pivot to fire wall distance I just picked a point for the drawing.

I'm running the origanal master from the donner truck (186K) and I have had my clutch in this configuration for over two years with no issues!

 

[hankjr]

The only reason for the tab is to utilize the stock push rod length, you could just as easily extend the push rod.

that makes sense, thanks

Hank

 

[DEEPWOODS]

I moved my MC like Tailpipe’s and Nevadasmith it is great now! I can push it with my hand now. It’s hard to believe that just moving it up closer to the pivot point made that much difference. Thanks again guys.

 

[hankjr]

So here are a couple of pics.

First is where the MC sits based on the Locofomoco plate that im using.



Second is looking towards pedal shaft, with a piece of threaded rod in the master showing alignment to master bore centerline.



the higher up the pedal shaft one attaches, the greater the mechanical advantage, and lesser pedal force. however, the stroke also goes downs, so depending on bore size, the clutch may be difficult to feather.

Like i've said, i have no data on pedal feel or response yet, but will post when i do. I have a couple of holes drilled in the pedal arm so i can adjust some if necessary.

Hank

 

[Slednut10]

* Note 1* For our two applications, I am running hydroboost brakes and Silas is running manual brakes. Unfortunately, I no longer have my power brake booster assembly to use to check fitment, so at this time we are unsure how these measurements will work with a stock brake booster. In order for this to be a viable option for all of us, we would like to know if it is possible to achieve these measurements with vacuum assisted brakes.

Here are some pics with a stock vacuum booster and my clutch m/c. Since mine has the hose coming out the front, there would be issues mounting the m/c higher unless you moved it further outboard. Mine is in the stock speedo hole.

 

[tailpipe]

I moved my MC like Tailpipe’s and Nevadasmith it is great now! I can push it with my hand now. It’s hard to believe that just moving it up closer to the pivot point made that much difference. Thanks again guys.

Awesome, and glad to hear it worked for you! Also, glad to have been able to help someone out, I know how frustrating this process can be. Enjoy!

 

[tailpipe]

Slednut10, thank you for the pictures and insight. Looking at your set-up I have reason to believe that the measurements used in the method discussed would most likely work with a 90° MC...anybody willing to confirm? Did you have any issues getting your system set up? Did you configure the set-up yourself or use "directions"? Are you happy with the "feel" of your clutch? I would like to know the details of the set-up just to confirm or deny some of our findings; pedal tab, push rod, pivot point, general geometry, etc.

 

[Big Slim]

Bringing up a somewhat old post but, looking at the geometry stated in your solution the length from the pivot is around 3.3”. So if we attach it to the pedal we need to mount it at 3.3” not 2 5/8 to equal the ratio.
Is this what works for everyone attaching directly to pedal? it doesn't get to the 6:1 or 5:1 ratio for hydraulic clutches. that would put it around 2.25".
My pic shows the width of the pedal (.8) around that distance since it tapers and the added tab (1.25) mentioned to get the hypotenuse distance.

 

[Nevadasmith]

I never checked the ratio , nor did I have a spec for it.
I simply modeled these dimensions off measurements I took from the doner truck. it has been so long since I have even thought about it, I don't remember the numbers exactly. But your sketch looks ruffly correct to me.
As far as pettel ratio goes I would think it would also depend on the ratio of bore diameter of master cylinder vs the throw out bearing and the amount of stroke need on each to fully disengage the clutch.
I figured ford had done all that math for me if I just replicated the distances of the 95 sbf zf5 pettel...
Good luck let us know how it works for you?
On a side note the overall pettel length is longer but Ford incorporated a massively stiff return spring that you don't use in the Early Bronco....the net result is actually a lighter pettel than the original f250 had.

 

[Nevadasmith]

I missed your question completely, sorry
So if you are doing a longer push rod and bolting directly to the pettel then yes you would want to be in the 3.13" range I would say looking at my setup that 3.25 - 3.500"
would work. But I have not tried that route, personally.

 

[Big Slim]

i see. so we have the pedal ratio i have researched that 6:1 is common design. but we also have the master/slave ratio. i have not been able to find any info on the equivalent bore size on the slave, so i cannot calculate that. I have measured the stroke on the 18mm diameter master cylinder is about 1.5". Do we need the whole stroke? maybe the master/slave ratio will make up for the lower pedal ratio with the smaller master.
I added more dimensions to my sketch and with the dimensions in your write up i am only showing about 1" of travel with what i measured on mine with 25 degree of swing. which coincidentally is close to using the 2.25 hole that is already in the pedal (also the 6:1 position). moving the point to 3.3 will get the full stroke of the master. though would need to move the mounting location of the master down for the push rod to go in straight. so by adding the tab you are able to keep the master mounted higher.

 

[73azbronco]

Excellent work, I would have gone ZF instead of NV if this info was out 10 years ago

 

[Big Slim]

so i got some info on the slave cylinder from Schaeffler (Luk) that the bore dia is 28.5mm and stroke is 35.8mm. with an 18mm master the slave would only move 10mm with a 25mm stroke (~ 1") and 15mm at full stroke (~1.5"). anyone know how much stroke is needed to disengage the clutch? i am hoping that the 10mm will work giving proper pedal ratio.