Softening a heavy clutch pedal - Page 2

Rossba · #21 (**permalink**) 11-25-2015, 12:31 AM

I have a Patrol with a vacuum clutch master cylinder. I have to park it in neutral because I can't push the pedal down to restart it. The system works well.
I also have a XY that has a assistant spring on the pedal. With the first clutch in it I pulled it out as it was to light. Now with the new clutch I have put it back in as my leg would shake sitting at the lights.

Just something to think about.

DanEC · #22 (**permalink**) 11-25-2015, 06:04 AM

It would affect travel quite a bit. The area of a 3/4 cylinder is .4416 square inches. The area of a 5/8 cylinder is .3066 square inches - or 69.44% of the larger one. So basically for the same volume displacement of hydraulic fluid to the slave cylinder, the 5/8 inch cylinder will have to be stroked 1.44 times further that the smaller one. And then because of the multiplier effect of the clutch pedal arm ratio you have to push the pedal several times that.

For simplicity sake say you have a 3/4 inch slave cylinder and most have said you need at least .9 inches of slave movement to fully release the clutch. So a 3/4 inch master would have to stroke .9 inches also. With a 5/8 inch master you will have to stroke it 1.296 inches to displace the slave by .9 inches. A pedal ratio of 5:1 sticks in my mind for most clutch pedal set ups so that extra .396 inches MC movement would work out at 2 inches more travel at the pedal face.

stephen low · #23 (**permalink**) 01-29-2017, 02:12 AM

Finally finally finally I discovered and made time this arvo to give the clutch a go in terms of reducing the pedal pressure.

I used BGT in Dandenong as my source of info and parts and have to say all credit to their work and knowledge.

Two things happened when I first went to them with both the clutch master and slave in my hand.

The first was recognition that I'd flogged out the master due to poor alignment of the plunger off the pedal. This was improved, I doubt it can be fully fixed with this set up, by moving the attachment point 8mm up the clutch pedal.

This in itself achieved a good result softening the pedal and I've been driving the car for months like that without too many issues.

As well, BGT knew from experience that they could bore out and sleeve the slave to 1" and this was done to a new slave.

With the slaves swapped out today, my release point is now earlier in the pedal travel but the increased hydraulic leverage has now provided a very comfortable clutch pedal pressure.

The final test was to let the missus loose and she went for a drive around the block. Seems I earned my brownie points today as she is very pleased with the result.

The whole G-Force set up is pretty agricultural but it is working for the moment. But it now gives me time to think silly thoughts like replacing the whole lot down the track with a proprietary set up.

I'd say it was marginal between the pressure improvements from moving the master attachment point on the pedal over increasing slave size, but together the two improvements have resulted in a good pedal pressure.

Hope this helps others with the same quandary.

Cheers

Tommy · #24 (**permalink**) 01-29-2017, 07:49 AM

Regarding the worn master cylinder: I bought my Cobra used and soon discovered that misalignment of the clutch rod had applied side forces to the aluminum master cylinder and caused it to wear into a leaky oblong shape. When I tried to change the geometry of the clutch rod I discovered that the original builder had boxed himself into a corner and it could not be aligned completely. So, I replaced the leaky aluminum master cylinder with a similar one made of steel. I figured it would take a bit longer for it to wear out. More than ten years later it's still dry.

kyleb · #25 (**permalink**) 01-29-2017, 07:58 PM

I'm looking at this for my 66 fastback.
It may also work in your situation possibly.
Hydraulic Clutch Master - Modern Driveline

stephen low · #26 (**permalink**) 01-30-2017, 12:41 AM

Thanks guys, I'll remember the advice down the track if I need to revisit the set up.

Cheers

Modena · #27 (**permalink**) 01-30-2017, 01:22 AM

Quote:

Originally Posted by kyleb

I'm looking at this for my 66 fastback.
It may also work in your situation possibly.
Hydraulic Clutch Master - Modern Driveline

That's a very interesting setup, I have book-marked that for future possible use. Thanks for sharing.

David Hodgson · #28 (**permalink**) 01-30-2017, 01:18 PM

Novel idea however have a look at the angle of the cylinder push rod - quite pronounced. This would straighten up as the fulcrum arm will swing through an arc when pedal is depressed. Being shorter, the arc is tighter on the shorter fulcrum arm than what is produced on the pedal arm.

Fixes one issue - introduces another

kyleb · #29 (**permalink**) 01-30-2017, 01:57 PM

More often than not these things are a compromise therefore less than ideal.
There's a number of different options on this style of setup depending on where your pedal sits.
https://www.google.com.au/search?q=l...5kt2vtpA6lM%3A

hauss · #30 (**permalink**) 11-18-2018, 10:58 AM

Install a tilton or mclead sorry spelling my not be correct they fit directly over the output shaft so there is no flexing and are smooth as silk not a easy install some machining may be required to set the proper depth. I personally installed both in customers mustangs and have been very pleased,also just my opinion but I like the tilton better.