Hydraulic clutch cylinder sizes?

[Davekmd]

folks, my apologies as I'm not trying to post multiple entries, but I think it's probably best I post one topic for each of the issues I'm having with my recent purchase (2003 SVC).

The clutch in the car is basically unworkable. The travel is extremely long (like starting at all the way at the top to pressing INTO the floor) to get complete disengagement. The pressure is EXTREMELY high, not stiff mind you, but a ridiculous amount of pressure required. The pressure is so high it appears to me the previous owner BOLTED the seats down against the rear compartment wall and then used 2" wooden blocks to actuate the clutch! (and brakes). That way it was like a recumbent bike. The back is against the rear compartment wall so the clutch could be pushed in.

I have a master clutch cylinder and a slave cylinder (Wilwood no less). the master clutch looks to be SVC ... The car has a steel bell housing / scatter shield of unknown brand. Tranny is Tremec T5. This combination isn't workable. I've read tons of posts about addressing hard/high pressure clutches and so want to see if this external arrangement can be made to work before moving to a hydraulic throw out bearing. (that seems to be the general consensus).

The motor I have is a mild 302 so it's not like I've got some HUGE big block making 600HP requiring a massive killer clutch.

1. What cylinder size are folks using for master clutch cylinder?
2. What cylinder size are folks using the slave clutch cylinder?
3. What pedal ratio are folks using?

Any suggestions are most appreciated.

thanks, DaveK from Maryland

[Clois Harlan]

I have built several Cobras and a couple Daytona Coupes and I used a 3/4" mastercylinder for each one. I also like the internal release bearing that McLeod sells. I have also used one of Tiltons that worked well. In my new Daytona Coupe I am building with a Coyote Engine and TKO 6060 6 speed trans I am using an original Ford release bearing and a 3/4" master cylinder.

IMO you may need to flush the brake fluid and re bleed your clutch and brake system. I probably needs it anyway.


Clois Harlan

[DanEC]

If you have high pedal pressure and excessive travel then you have problems - because to lessen the pressure you will need to go to a smaller diameter master cylinder that will lengthen the travel further. Or to lessen the travel you can go to a larger master cylinder which will increse the pedal pressure even more. That's the trade offs in a master cylinder/slave cylinder system. Maybe it's the pedal set up. Can you identify the pedal set up or take a picture and some dimensons of the arm dimensions and dimensions to the rod attachment points?

[jhv48]

Make sure the master and slave cylinders are matched.

I run a 7/8 master and slave. Plenty of travel and pressure is normal.

I tried a 1" master and slave, and the foot pressure increased exponentially.

[Davekmd]

I do not know what the size of the master clutch cylinder is. I'm assuming it's 'stock' Shell Valley Classic from 2003. I've contacted SVC to see if they can help me ascertain what the car originally came with. While I will flush the fluid I was pleasantly surprised to see all hydraulic fluids (brake and clutch) looked pretty clean...

It has a Wilwood slave cylinder. I don't know the size but Wilwood currently only offers one size (7/8"). Circa 2003? I don't know but I'm assuming it's 7/8". I have three master cylinders; one for the clutch and two for the brakes. (I'm assuming one master brake if for front and one is for rear).

The 302 motor has a steel bell housing / scatter shield with a stock looking clutch pivot arm. The slave pushes directly (very parallel) on the pivot arm.

I'm attaching pics. They aren't the best but access isn't exactly the best ...

Thanks, Dave K (Maryland)

[Davekmd]

Ops, I missed a pic. While I was taking pics yesterday of the brake/clutch master cylinder assembly I found that the main pivot bolt looks to be backed out about 1/2" I didn't have time to investigate but I wonder if this is causing major problems. I'll check tonight.

[DanEC]

Did you receive any information on the clutch itself?

[g8rnbft]

Dave - I tried to private message you a couple days ago but my sent file shows nothing. See if you can send me a private message that I can respond to with my phone number - or with your number so that we may talk. Last resort would be for one of us to post our email or phone number here - which I am not fond of.

Blair

[Tommy]

Originally Posted by DanEC

If you have high pedal pressure and excessive travel then you have problems - because to lessen the pressure you will need to go to a smaller diameter master cylinder that will lengthen the travel further. Or to lessen the travel you can go to a larger master cylinder which will increse the pedal pressure even more. That's the trade offs in a master cylinder/slave cylinder system. Maybe it's the pedal set up. Can you identify the pedal set up or take a picture and some dimensons of the arm dimensions and dimensions to the rod attachment points?

I agree!

[trularin]

This really gets down to a matter of levers and pressure.

From the pressure plate ( your first item ) to the pedal - I recommend some High School physics with a working diagram to determine how and why it is a "leg breaker".

I ended up with a 3/4" slave and 7/8" master - but that is useless as each car is different.

Perhaps you could draw some pictures with measurements so we might help.

Just a suggestion.

Tru

[Davekmd]

Folks, I'll try to see if I can determine (via the documentation I have) what the master cylinder size is and what pressure plate was installed. I have the standard pedal box offered by Shell Valley. I'll double check but I believe the pedal ratio is 6:1. The slave is a Wilwood. The car is 2003. I have no idea if the clutch slave Wilwood is original or newer. The current Wilwood catalog lists only a 7/8" dia slave. The bell housing is Lakewood with throw out arm. I have no idea for the pivot/leverage ratio is...

This seems to me to be a very standard arrangement for hydraulic clutch. I can tell you the rod alignments are all very good.

I was hoping that folks could relay the sizes of their master and slave if they know them. That would give me a starting point for reference as opposed trying to re-engineer/define a system. I've done my spreadsheets on cylinder bore sizes, piston area, foot force, pedal ratio, cylinder output pressure, master cylinder rod travel, slave cylinder rod travel, etc. If folks can say ' I have a X" master, Y" slave, stock SBF pressure plate and my system is extremely light/easy to use, I have a data point. Several data points get me a consensus.

Also if folks have experienced this problem and solved it, knowing what they specifically did to solve it would be more data.


Thanks again, Dave K.

[Brooklyn-427]

i had a similar problem and it turned out that the hyd feed hose from master - slave was the problem .

[DanEC]

When I assembled my ERA it used a 3/4 inch master and I think the slave is 3/4 inch also (not completely sure) and I used a McLeod diapragm clutch. It was a bit heavier that I was expecting but even worse, the clutch throw seemed very long - it used the entire pedal throw. I switched to a 7/8 inch master and accordingly the pedal effort increased a little but the throw was more shorter. After I broke in the clutch the throw lessened further to where I could probably go back to the 3/4 inch master without problem. Assuming you have a 3/4 inch master (the Tilton cylinders have the size embossed in the side of the casting) I would expect the clutch to be slightly heavy, but not nearly as much so as you are describing. Have you examined the pedal am closely to see if possibly there is more than one mounting point for the rod to the master cylinder? Making sure that the cylinder is aligned with the push rod as well as possible also will minimize pedal pressure due to eccentric loading.

[PeteF]

Make sure the fork arm is not bottoming out on the rear of the bell housing when the clutch is fully depressed. With the clutch fully depressed, you should be able to get a feeler gage between the fork and the rear of the bell housing window. I added a .080 shim under the fork fulcrum, which shifted the fork slightly forward. This gave me added room for full actuation and a lighter pedal.

[Davekmd]

Folks, thanks for the many suggestions and recommendations. I hope to get at the hydraulics/mechanicals this weekend and gather some facts. The slave IS a Wilwood Pull type but the Wilwood site lists the bore as 3/4" on one page and 7/8" on another page for the same part number. I figure the only way to tell is remove the darn thing a measure. I'll do the same for the clutch cylinder. I'll check for any interference and basically lubricate any moving parts.

I hope to post better news Monday!
Thanks again, Dave K.

[Brooklyn-427]

yeah strip it all out and start again id go for a 3/4 wilwood remote res master a new braided hyd feed hose and a girling style 7/8 slave .

[trularin]

Things you might want to consider:

The fork - are you using a full length fork or a shortened one? Full length takes more travel, but is easier on the leg.
hydraulic volume - so, after you know the slave has the travel to move the fork to disengage the clutch, what is the size of the bore and stroke? This is the volume of the cylinder.
Master cylinder - the volume here will match what is in the slave. So if they are the same bore, the travel is the same. This means the effort at the master cylinder is the same as at the slave. So, if you use a smaller bore the stroke is longer.
Pedal lever point - the pedal is a lever - the fulcrum the rod it swings on. A push rod close to the fulcrum has less travel but should be easier to push.

These might help you tune your system.

Good luck

Tru

[powrby4d]

I’ve got a new to me SVC where the clutch has exactly the same problem - travel is extreme needing to go all the way to the floor where the clutch disengages only at the bottom of the stroke. However foot pressure requires tremendous force the entire length of the stroke, and depressing the clutch pedal results in a twanging spring noise. The clutch pedal has an odd bellcrank type arrangement in the engine compartment instead of being directly connected to the master cylinder. The car is basically not drivable with this setup. I was wondering if anyone has discovered this problem with an SVC kit and how to solve it, because my first thought is that this setup appears to be far more complex than it should be. Any advice would be appreciated before I dig into what is going on with the clutch and whether this strange bell crank clutch setup is a SVC thing and whether it should be replaced with a much simpler direct connect between the clutch pedal and the master cylinder.

[t walgamuth]

Originally Posted by PeteF

Make sure the fork arm is not bottoming out on the rear of the bell housing when the clutch is fully depressed. With the clutch fully depressed, you should be able to get a feeler gage between the fork and the rear of the bell housing window. I added a .080 shim under the fork fulcrum, which shifted the fork slightly forward. This gave me added room for full actuation and a lighter pedal.

I think Pete is on the right track here. I have seen problems with the pivot before. Could be broken or worn through changing the leverage.

[strictlypersonl]

I'm going to repeat and emphasize Dan's post.

"If you have high pedal pressure and excessive travel then you have problems - because to lessen the pressure you will need to go to a smaller diameter master cylinder that will lengthen the travel further. Or to lessen the travel you can go to a larger master cylinder which will increase the pedal pressure even more. That's the trade offs in a master cylinder/slave cylinder system. Maybe it's the pedal set up. Can you identify the pedal set up or take a picture and some dimensions of the arm dimensions and dimensions to the rod attachment points?"