Doing homework on Auto to Manual conversion. '71 350-270

Looking to have an easy to mash clutch effort. (Knee issue)

Will definitely go hydraulic rather than stock mechanical Z-bar, etc.

Car will be street driven, with only the occasional 'standing start romp and row' (always in a legal environment obviously). But will not be raced/stripped.

I need recommendation or experiences on brands and levels for:

-"Easy effort" Clutch in actual clutch package
-Are there any hydraulic units that are better than others or do they all generally use and create about the same hydraulic force?

I know this is a bit subjective, but trying to do what I can to make sure I can still drive it when I'm done and some of these things can be brutes.

Thanks for your input.

 

It's a lot more clutch than you need, but the McLeod dual discs (RST line) have the lightest pedal of any clutch I've tried. It will hold a big block with no problem so you could call them up and see if they can make you one with even lighter springs.
I'd think you'd want to go with a hydraulic throw-out bearing rather than a fork & slave cylinder. Less points of friction = less effort.

 

Go and test drive a C6 Manual corvette. If you can tolerate this setup, then the Twin disc RST line will be similar. It won't be as light but its a big improvement over a single disc.
Now also note depending on the transmission you choose with a Twin disc you may get additional noises during idle in neutral gear (clutch out) or gear rattle in a RPM Range during acceleration. This is because twin disc are smaller and don't have any dampening springs in the clutch plates.

 

Good advice. My 2007 Z06 clutch is the lightest of effort compared to my C3's single disc Centerforce.

 

I am running a Hyd master and throw out-

Was looking for a way to lessen the effort required and ran across this design. This piece is for 60's Mustangs -but I am working on adapting it to my 71.

 

That's a pretty interesting setup. I suppose that by putting washers underneath the bottom pivot, you could even mount this on a non-flat firewall which I suspect would be the case in a C3.

 

Looks like that plate may even reinforce the firewall, a must have.
Wonder if thats why sometimes conversions can feel notchy.

 

Agree. Everyone seems to love putting hydraulic throwout bearings in but nothing wrong with a slave cylinder on the existing fork approach either.

http://www.moderndriveline.com/Techn...tch-system.htm

 

I'm not sure what principle is at work for this assembly but you can't get something for nothing in a pure mechanical system. If you give up some force for a lighter pedal, you need more pedal travel for the same movement at the PP fingers. Is that what's happening here?

 

There are tons of articles on the iweb on how master/slave cylinders work together, but in general, depending on the bore size ratio of the master vs the slave you double the amount of force applied by your foot to the fork. Many cars use a master/slave cylinder method of clutch engagement.

https://www.doityourself.com/stry/wh...w-does-it-work
https://www.carthrottle.com/post/how...ir-importance/
http://www.enginebasics.com/Engine%2...0Cylinder.html

 

Instead of that convoluted lever system you could just switch to a smaller bore master or larger bore slave.

But only if you have enough travel on the pedal, otherwise you won't disengage the clutch all the way even with the pedal on the floor.

 

I couldn't find an exact statement in your references, but in any hydraulic system you are trading force for distance as determined by the area of the pistons. I would think with this rig you are losing some ability to shift quickly.

 

I can't speak for the "rig" above but master/slave systems do shift fast. Mazda Miata's use a master/slave arrangement for the clutch and they are some of the fastest shifting cars around.

 

All I'm saying is that there are consequences in the quest for less pedal effort that were not otherwise mentioned. Wouldn't you be upset if you went to all the work of installing this rig and discovering that you had to push the pedal all the way to the floor and maybe even then not getting full clutch disengagement? Some very simple math should give you an inkling of what's being traded.

 

Absolutely true. Either buy an already engineered system or be prepared for some math (desired leg force, desired clutch pedal travel, fork ratio, amount travel needed to disengage clutch safely, etc) to determine optimum bore sizes if rolling your own.

 

Of what I have seen pretty much every aftermarket kit uses a 3/4" Bore Master. The Slave Cylinder - Piston is usually a specific size and off the shelf parts are not available to chance displacement. I think they sell 3/4" Masters because they know they will get enough throw at the Slave to cover just about any Clutch Combination and make sure that it disengages. When I did my set up, I found a 5/8" Bore Master had plenty of movement for my Spec Twin Disc. Less Peddle pressure = More travel at the Peddle.

 

I would think the main advantage to the hydraulic systems would be two-fold:

• able to change the leverage ratio much easier than a mechanical lever
• overall less friction - but a more minor point

All the leverage and bore size comments above are correct, you trade more pedal travel for less pedal force.

The other main spring in the system is the pressure plate. In my mind this would be the main area to reduce pedal effort: (I'd focus 90% of your energy here.) There is a huge variety here, and many people over-clutch a car. In terms of pedal effort high to low: (due to pressure plate leverage)

1. Three finger race clutches
2. Diaphragm clutches
3. Dual-disc

All clutches are rated in clamping load, not pedal effort All three of the above categories have a range of clamping loads, but the same clamping load force will have a lighter pedal as indicated above, due to the internal pressure plate design leverage.. If you have a stock 270 hp motor, search for the factory clamping load rating of a factory 10.5 " diaphragm clutch, and make sure you don't go any stiffer than that. Some one here may even now what that is. Going lighter in load than that would be risky.

That's when you could get into changing the leverage pedal ratio, but I would think a previously engineered system would be more than sufficient.

By doing the pedal ratio math you should be able to calculate the pedal force. If someone on here has a similar clutch they may even be able to measure the pedal force for you to confirm. (Hint you don't want my reading on a BB 3 finger clutch)

I also know of local clutch rebuilders who would be willing to put together a one-off custom setup if desired.

My 7500 rpm LT1 had a very light pedal with stock linkage, diaphragm clutch, stock load, and "finger weights" for extra grip at rpm.

 

There is another method to obtain a lighter clutch with a hydraulic pedal set-up - use a remote 'in-line' vacuum brake booster - possibly not the best technical method to achieve a 'light' pedal but it does give the option on using a master/slave combination that has a far shorter pedal 'throw'

 

That's what I am doing.

Right now I'm using the master that Wilwood recommended for my set-up. I mounted it parallel next to the brake master and reinforced the firewall.

Using the stock location on the pedal only gives me about 2/3's travel to the floor- before the master is at full travel. I made a little bracket for the pedal- to keep the angle correct on the master- I still was bottoming out before it came close to the floor.

I saw that design- had some brackets that BMW used for a remote brake master cylinder laying around and will try it out. Hoping to get full travel of the pedal and lessen the effort a bit. Will cost a lot less then going with twin discs.

TKO 500 - made a spacer to get the throwout just where it needs to be-



Clutch master on the firewall- ½" aluminum plate was used for the mount-


Current bracket on the pedal-


parts I have laying around to make it up -