Anyone add a Vacuum booster to 40 clutch master? (1 Viewer)

[bikersmurf]

I’ve discussed this idea on mud a couple times and never concluded it was possible.

Based on info in this 70 thread… Boosted vs unboosted clutch master cylinder. What’s the benefits? - https://forum.ih8mud.com/threads/boosted-vs-unboosted-clutch-master-cylinder-whats-the-benefits.1203228/
I believe a vacuum boosted clutch is lighter and potentially could have more slave travel if they’re in fact equipped with a 3/4” slave cylinder.

Now it had been suggested there Isn’t enough space to fit a clutch booster. I’d almost given up on the idea until I saw this photo in an add…

It appears to be a SA 40 series, and it has a vacuum boosted clutch slave.

Now some ask why?

In 2002, I was in an MVA while riding a motorcycle. The car saw me and pulled out in front of me anyway. Long story short, my left fibula was broken and the cartilage of that knee was also destroyed. It was described at that time as a knee of a 95 year old. Now, the same surgeon has said my right knee is worse.

The 80 series brake booster is great to reduce braking force for the right knee.

The left leg, however, needs to push a LUK clutch for a SBC. The SBC means I don’t have to shift often, but it still isn’t great for the left knee. Of course I could spend a large fortune and convert to automatic, but I hate automatics,

Thoughts? Comments? Anyone done it or seen it in person?

 

[Mark Jennings]

Have you ever thought about a ‘remote’ brake booster. Basically you can mount the booster anyplace and just run vacuum and hydraulics to it. These were used on like 50’s vintage Chevy 3 tons, etc… below is a picture I scabbed off E-bay….may make installation easier than trying to jam a booster on the firewall….and probably more than enough assist to help save your knees.

 

[bikersmurf]

Have you ever thought about a ‘remote’ brake booster. Basically you can mount the booster anyplace and just run vacuum and hydraulics to it. These were used on like 50’s vintage Chevy 3 tons, etc… below is a picture I scabbed off E-bay….may make installation easier than trying to jam a booster on the firewall….and probably more than enough assist to help save your knees.

View attachment 3570092

I’ve not considered a remote booster. From the picture, it looks like a couple holes to drill and then bolt on a 70 series booster. In the 70 series thread it was that simple to add a booster.

Offhand that would seem easier and less complicated than figuring out where to mount a remote booster and having an extra slave and master.

Now 70 series vacuum boosters have had some supply issues in the past (which was a bit discouraging), but I don’t know what the current status is.

 

[charliemeyer007]

Engine vacuum is just burnt valves waiting to happen IMHO. Do an electric vacuum pump by adding a small tank to the inlet side of an air compressor (plus you could have on board air) or a weak air conditioning compressor repurposed and with the electric clutch you could switch it off.

 

[scrapdaddy]

I thought about a 70 series master myself, but never acted on it, I'm in.

 

[bikersmurf]

I thought about a 70 series master myself, but never acted on it, I'm in.

I’ll have to see what I can turn up for parts…

 

[scrapdaddy]

I tried running an old single circuit brake master for a clutch master, in order to get a little more throw. It was so hard to push and really didn't work out right. I'll be watching if you come up with something.

 

[Mark W]

Engine vacuum is just burnt valves waiting to happen IMHO. Do an electric vacuum pump by adding a small tank to the inlet side of an air compressor (plus you could have on board air) or a weak air conditioning compressor repurposed and with the electric clutch you could switch it off.

Why would a booster for the clutch master be more problematic than the booster for the brakes? Am I missing something?

Mark...

 

[charliemeyer007]

I don't run a vacuum booster. 2 is twice the chance of a burnt valve.

 

[South Texas 97]

Why does the booster need to be on the pedal end? Could it be on the Clutch Slave Cylinder end? there seems to be more space on that side of the engine?

 

[bikersmurf]

Why does the booster need to be on the pedal end? Could it be on the Clutch Slave Cylinder end? there seems to be more space on that side of the engine?

Space looks pretty limited here for anything wide. I’ve considered a pneumatic cylinder as an assist… and I could see a pneumatic cylinder there, but not a 5” vacuum booster there.

Compaing this space to the same area in the green truck above leads me to believe the stock brackets wouldn’t clear the reinforcing rib. I don’t think it would be hard to fabricate a steel spacer to mount a vacuum booster though.
If a stock mount won’t work then I’m essentially looking for a small brake booster with a single circuit master that has a larger bore than a stock ‘74 clutch master.

Or do I just go back to the drawing board and use onboard air to run a pneumatic cylinder with a control valve pushed by the hydraulic slave. Just need a small, affordable, reliable, durable control valve. Unfortunately, in the real world, you only get 3 of those 4 options… if you’re lucky. With a regulator on the air pressure there’d be complete control of how much clutch feel there’d be.

 

[bikersmurf]

In a perfect world a two way control valve that could be mounted on the clutch pedal would be ideal. Perhaps even a small hole drilled through the pedal. Step on the clutch and it pushes out… lift your foot and it releases. If the air system fails, the clutch still works.

An air horn valve would almost work… but it’s only one way. I’d need a second to dump pressure when released.

 

[pb4ugo]

What slave and master cylinder are you currently running?

 

[bikersmurf]

What slave and master cylinder are you currently running?

1974 slave and master. It has had enough travel for the LUK clutch without going to a 1" Master. Some setups don't work with the LUK clutch, but this has been working since 1996 without any issues. I have had to replace the Master and slave a couple times in the last 28 years, but they still work great.

 

[bikersmurf]

The only other variable that seems to help is that I have a braided SS line that doesn't expand under pressure as rubber lines do.

 

[sogncab]

Dumb question, I have no clue if it's an option. My last pickup had a dual disk clutch. The pedal on that thing was lighter than my subaru.
I don't know if that was the source of the light pedal either. But it was shocking for a 1 ton. Especially when I was accustomed to a 1000ft/lb clutch I had in the pickup previous to that one.

No clue if it is even possible with what you've got

 

[bikersmurf]

Dumb question, I have no clueless if it's an option. My last pickup had a dual disk clutch. The pedal on that thing was lighter than my subaru.
I don't know if that was the source of the light pedal either. But it was shocking for a 1 ton. Especially when I was accustomed to a 1000ft/lb clutch I had in the pickup previous to that one.

No clue if it is even possible with what you've got

Options for clutches are quite limited. With a SBC conversion it’s usually a LUK low diaphragm 11” clutch or a Center Force Clutch for SBC conversions from @Downey. In ‘96 I used the LUK clutch and it’s still going strong.

Although other clutches could be made to work with enough money, space and throw out bearing travel is limited. So I’m not planning to reinvent the wheel… just improve on it.