Stock linkage Z-bar modification

Bonnewagon

Bonnewagon

Geezer
Sep 18, 2009
6,066
2,235
113
Queens, NY
#1
It was a nice day yesterday so I made some final adjustments to my clutch linkage. I re-adjusted the spherical ball-end linkage so it better duplicated the stock upper push rod in length and position. Now I see better alignment with the pedal arm and Z-bar mounting points. But when I adjust the lower rod for good free play using the "gauge" hole, my pedal is on the floor at full dis-engagement. I even get some gear clash. If I get the pedal up off the floor, I don't have enough free play and I worry about the bearing riding the clutch fingers. I need better geometry in my linkage. The best place to get more push rod travel would be the clutch pedal arm by drilling a new hole farther away from the arm pivot, slightly below the stock location. But the thought of dropping the clutch/brake pedal assembly is so distasteful I won't even consider it. It would also move the rod lower and probably hit the firewall requiring making the hole bigger and then the boot may not fit. That leaves the Z-bar. The upper arm has a bend right where I would change the push rod mount so that is out. The lower end where the clutch fork push rod mounts is probably where the smallest increase in travel will result in the most travel at the throw-out bearing. Removing the Z-bar is a lot easier than the pedal hangers. My plan is actually something I read on another site where a guy made up a tab that he bolted to the Z-bar lower arm and then drilled a new hole on that for the push rod. There are two holes on the arm, one is a "gauge" hole and the other is the actual push rod mounting point. He bolted the tab on using both holes, and drilled a new hole at the end of the tab for the push rod. I like this idea because I can use different lengths of tab and mounting point holes to experiment with. This way I don't ruin the Z-bar by welding on something right away that may be wrong. I also know I need to not change the push rod angle too much or it will affect the fork. I know that increasing the length of the arm will result in more push rod travel but that will also increase pedal effort. But since I am using a diaphragm clutch that should not be objectionable. Once I get my needed travel, and the pedal effort is not bad, then I can weld the tab is place for good. Does this sound reasonable or is there a better way to get what I need?
 
fleming442

fleming442

Geezer
Dec 26, 2013
5,924
6,676
113
#2
I vote for drilling a new hole in the the pedal arm, but I would think revisiting the adjustments would be more prudent. Increase the length of the pedal to z-bar rod...
 
Bonnewagon

Bonnewagon

Geezer
Sep 18, 2009
6,066
2,235
113
Queens, NY
#3
I did that. Same affect as the lower rod- it does not affect the ratio. I can adjust but the sweet spot is so small and it leaves no room for error or wear. And getting the pedal arm off to drill some holes would be ideal- but what a nightmare job.
 
fleming442

fleming442

Geezer
Dec 26, 2013
5,924
6,676
113
#4
I was under the impression that the z-bar maintains the ratio. Lengthening the upper rod adjusts the pedal height, and the lower rod adjusts the fork throw. Altering the pedal attachment point will affect pedal effort, so keep that in mind (lower hole= more assist & vice versa).
 
Bonnewagon

Bonnewagon

Geezer
Sep 18, 2009
6,066
2,235
113
Queens, NY
#5
Actually there are three ratios- The pedal hanger from the push rod hole to the pivot point (hanger bolt). The Z-bar arms from the upper rod hole and the lower rod hole. The clutch fork from the push rod to the throw out bearing. All three ratios add up to the total mechanical advantage between the clutch pedal and the pressure plate. The rods themselves do not affect the ratios. There is a bump stop up on pedal hanger where the pedal arm stays when fully retracted by the return spring ( I added that for positive retractment) . I also added springs at the lower push rod/fork to retract it and between the fork and Z-bar to hold the push rod in place. Overkill? Yes. But when I release the pedal everything is retracted with no slack anywhere. So my 3/4" to 1" of free play at the pedal is perfect for proper air gap at the pressure plate. But at full disengagement the pedal is on the floor, sometimes clashing gears. I need more travel in my lower push rod without upsetting my geometry too much.
 
pagrunt

pagrunt

Comic Book Super Hero
Sep 14, 2014
3,645
4,089
113
Shelocta, Pa
#6
Would a longer lower rod work? Would be an easy way to test with a piece of all thread to see if a longer would be needed. Older A bodies have longer ones.
 
C

clean8485

Royal Smart Person
Dec 18, 2005
2,327
955
83
Ontario, Canada
#7
Sorry, but I'm a little late to this thread. What kind of linkage are you using? I purchased the linkage kit for my '80 Malibu from Speed Direct in Arizona, and intend to install those parts when I do my engine swap. Are these the parts that you're using? Any photos of your problem? Thanks.
 
Bonnewagon

Bonnewagon

Geezer
Sep 18, 2009
6,066
2,235
113
Queens, NY
#8
No, lengthening the rods only lets you tighten up on the gaps between the components. They do not affect the ratios. The reason you can push in a 3000lb clutch with 100 lbs pedal pressure is because the ratios of all the pieces multiply the force while increasing the pedal travel. An inch at the pedal is a fraction of that at the TOB. I need to increase my lower rod travel so I get full disengagement with less pedal travel. Fleming is correct that will increase pedal effort but I'm betting it won't be bad. That is why I intend on using the bolt-on tab to experiment. If it works I'll make it permanent. Clean8485- yes this is the Speed Direct spherical rod end linkage. Very nice, strong, and adjustable. The only problem is the SD upper rod is fairly straight while the stock rod looks like a demented pretzel. What I did was chuck the stock rod on my bench vise while I adjusted the SD rod to be as close as possible. If you get the long sides parallel and the rod ends to go onto the stock rod's pins- you are as good as you are going to get. I tried making adjustment on the car and it is impossible. Do it on the bench. It fit better and lined up nicely. The attachment points are what you want to mimic. Here is the stock rod you want to copy. You will see when you compare them what to do.
img_0972-jpg.108477
 
Last edited:
gnvair

gnvair

Master Mechanic
Sep 1, 2018
256
169
43
Southern New Jersey near Philly
#9
I have the Speed Direct kit on my car. I had to cut the left side lower stud off the power brake booster to get full travel on the pedal.
 
Bonnewagon

Bonnewagon

Geezer
Sep 18, 2009
6,066
2,235
113
Queens, NY
#10
I didn't. I looked like I was going to hit it but by closely following the stock rod I cleared it. The problem is that compound bend at the pedal arm. The SD rod is straight . But by matching the mounting points and keeping the rods ends in the same plane it worked.
 

Please support GBodyForum Sponsors

Classic Truck Consoles Dixie Restoration Depot Mike's Montes P-S-T Southside Machine Performance UMI Performance

contact [email protected] for info on becoming a sponsor

copyright ©2018 Ripp Technical Services, All Rights Reserved.