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Discussion Starter #1
Hey All, Been working on the clutch slave cylinder mounting for our 67 Nova project.

First off this is what I am working with, GMPP LS3 crate, T56 from Hurst Driveline and bought a mounting kit for the slave from American Powertrain. Also the car has a DSE front clip.

After reading the instructions from Hurst, the target pedal ratio is said to be 6:1. The info that came with the American Powertrain mounting kit states a range of 4:1 to 6:1. From what I have read elsewhere it sounds like 6:1 is closer to most stock hydraulic set ups. My question on ratios is what are the characteristics of less or more pedal ratio? I would assume more or less pedal effort. Interested in what ratio others are using and how it is working out.

Another tanget question regarding pedal ratio. That being the vertical placement of the slave cylinder mounting. What is the effect of raising or lowering the mounting? I can get the same ratio between pedal travel vs actual throw of the slave from different vertical positions in realtionship to the pedal mounting. Is it beneficial to have the pushrod pretty much level or to mount lower with an angle down? I ask this because I am having some issue with "packaging". There isn't much real estate between the firewall and the DSE inner fender. If I can mount higher I have more clearance. Fact here is that I cannot use the AP slave mounting as it adds too much depth to the engine side of the firewall, again limited space between the firewall and the DSE inner fender.

I am going to fab my own mount, just haven't decide where vertically that it will end up.
 

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doesn't the master bolt directly to the pedal assy? if so mounting the assembly i'd think would be where it fits and driver comfort.

pics of your components might help answer your questions...
 

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Discussion Starter #3
The clutch slave does not bolt to the pedal assembly. On other models (camaro, chevelle, etc.) there are brackets available that are sandwiched between the brake booster and the firewall. No brackets available for 1st gen II's. Closest "bolt in" available that I know of is the American powertrain set up which bolts the the firewall with it's own sandwich plates on the interior side and engine side. I didn't post pics because my questions are related to pedal ratio's not the hard parts of the mounting.
 

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FYI: The slave cylinder gets mounted to the transmission/bellhousing. It's the end of the system that actuates the throwout arm/bearing.

You're asking about the clutch master cylinder.

Greater the pedal ratio, the less pedal force input is required for a given output. However, that comes at the expense of fluid displacement. You'll need to determine how displacement you need at the master cylinder end to ensure that the slave fully dis-engages the clutch. You'd probably be OK at the 6:1, but be sure to double check.

Master cylinder mounting will be dependant upon your master cylinder. Which master cylinder are you using? OE F-Body style, Wilwood, Tilton, etc? What type of slave are you using? GM T56 hydraulic throwout bearing, aftermarket hydraulic throwout bearing, external aftermarket slave cylinder, etc? If you're using OE type stuff, then I'm guessing you're using the 4th Gen F-Body clutch master cylinder, which requires a different type of mounting than the Wilwood/Tilton styles due to its odd, angled mounting surface.

Either way, it doesn't really matter where you position the master cylinder, so long as the push-rod is not putting an undue side-load on the piston and won't bind during it's travel. Treat it the same way as you would a master cylinder for the brake system. Its function is identical.
 

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i believe the factory pedal ratio IS 6:1

he's using, i think, the Camaro style master which is an angular mount which will install in the plate area around the steering column. so far that i'm aware of there are quite a few guys BUILDING their cars with a hyd clutch set up but None that i know of with a tried & true, road tested system.

lots of guys can post pics of what they're building but none that are tested/true... yet...

here's a link showing proper way to calculate ratio...

http://www.mpbrakes.com/uploads/documents/pedalratiopdf.pdf
 

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Discussion Starter #6
Mike you are correct, I was using an incorrect term. I should have said master cylinder. Thanks for catching that!

The master cylinder I am using is a Tilton 3/4" bore unit that came with the trans from Hurst Driveline. The slave I am using is (I believe) an aftermarket hydraulic unit also supplied by Hurst Driveline.

At this point I am fairly pleased with what I have come up with so far. I am seeking validation before I set it in stone.

I am currently getting an actual measured ratio of 5.00:1. That is an actual pedal movement of 5.00" to 1" of pushrod movement at the master cylinder. This is obtained by using the the existing hole in the clutch pedal (per instructions from American Powertrain) which is 2.75" from the pivot point centerline. My pedal measures 13.875" from the pivot point to the pedal centerline whihc equates to a mathematical ratio of 5.045:1. The master is mounted on the same vertical centerline that the original mechanical clutch pushrod, also per the instructions from American Powertrain. Moving this point up or down affects the ratio but you would have to move it quite a bit to see a major change. (I moved it up 2" and only saw the measured ratio change to 5.25:1) The American Powertrain instructions give a range of 4:1 to 6:1 so I guess I am just obsessing over the 6:1 ratio that Hurst mentioned.....:eek:

So if you think I am on the right track let me know, if not let me know too..

Thanks for everyone's input!
 

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Discussion Starter #7
I believe I have the problem solved. I had a conversation with Phil @ DSE. Came to the conclusion that mounting to the outboard side of the brake master is the correct location. (this is where they mount on thier cars) Should be an easier job to mount there vs at a downward angle. I think the pedal feel will be more linear this way as well. And I can put the reservior right on the master cylinder. I am going to reinforce the firewall in this area with a 10ga. plate. Will post pics as I go.

Thanks for all the input!
 
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