Learn me clutch boosters

I've got a customer who's having trouble with arthritis, and it's becoming difficult for him to depress the clutch pedal in his LS3 Miata. I remembered that some LBCs had a remote booster in the brake lines, and searching for "clutch booster" reveals that some Nissan vehicles have a little vacuum booster built right into the clutch master cylinder. Cool!

Anyone have experience with these? I'm looking for something with a master cylinder size of approximately 7/8" and a boost ratio of 2 or 3:1. One that goes inline on the pressure line might also be useful for packaging.

Bookmarking this thread for later perusal.

My knees isn't what they used to be and they wasn't ever all that good to begin with.

How about a push button clutch - air over hydraulics?
Who needs knees when you've got a thumb?

oldtin wrote: How about a push button clutch - air over hydraulics? Who needs knees when you've got a thumb?

I think I saw something similar on here a long time ago, as I recall, the guy wanted a stick Miata and only had one leg.

3000GT/Stealth uses a vacuum boosted clutch.

It's on the clutch master cylinder so it likely won't fit a miata, assuming the master cylinder is as well hidden as most cars. I found picture of one from an International Truck as well, but it's even bigger!

I don't even know if the Miata is a push or pull release, but likely to require a remote mounted vacuum booster. If you can find a place to put it, you might be able to use the 3kGT via cable extender. Check the local hydraulic supply store. You may be able to attach a vacuum diaphragm to the slave cylinder that's controlled by a "spool valve" attached to the clutch pedal. The electrical push button setup would work as well, but you don't have direct control of clutch engagement speed.

Miata is a push release. Let's not pay too much attention to packaging at the moment, leave the playing field open. Any idea what the master cylinder diameter is on that 3000GT unit?

Hard to say, but here's a picture with it assembled with the master cylinder.

Here's an interesting forum discussion of doing this on an MR2: http://www.mr2oc.com/188-v6-mr2-forum/456318-lighter-clutch-via-vh44-booster.html

What kind of clutch does he currently have, is it something that could be remedied with just a softer clutch?

It looks like the 3000gt one may be able to be mounted behind the firewall of theres room, which could help packaging in the engine bay

Keith Tanner wrote: Any idea what the master cylinder diameter is on that 3000GT unit?

5/8 if you believe the catalogs the rock catalog

Europas came with a remote mounted vacuum assist brake booster. Kinda hard to come by today. The small MC drove the remote booster system, mounted by the engine. Most people take the whole thing off, go with a dual circuit MC and press harder.

They have hydraulic pump assisted brakes, what about converting some of those components to the clutch.

I think it was GM trucks that had the most hydro-boosted brakes.

http://www.brakeandfrontend.com/operation-diagnosis-and-repair-of-hydro-boost-power-assist-systems/

oldtin wrote: How about a push button clutch - air over hydraulics? Who needs knees when you've got a thumb?

That release speed is gonna suck for shifting...

Someone on here had a Miata with an "e-clutch" controlled by an xbox analog trigger (mounted to the shifter IIRC), that sounds like exactly the technology needed here, although you could use an e-throttle pedal as a new clutch pedal instead.

Opti wrote: What kind of clutch does he currently have, is it something that could be remedied with just a softer clutch? It looks like the 3000gt one may be able to be mounted behind the firewall of theres room, which could help packaging in the engine bay

Of course that's the obvious solution, but it's not really plausible. It's a stock LS7 clutch. You can't get much lighter and still hold up to the 6.2.

The remote mounted brake boosters are what got me started thinking about this. This is a $50k car, not a Challenge car so if we have to spend money we'll spend money. We don't need brake booster levels of assist, though. That's potentially a problem for the hydroboost units as well.

Right now, the owner is thinking about tweaking the master cylinder size. I think he's going to run out of pedal travel, but that's what he wants to try first.

Found it, it's oldtin's electro-pneumatic setup:

https://grassrootsmotorsports.com/forum/grm/mad-scientist-project/24014/page1/

I wonder how it worked out in the long run?

Another option: VW Autostick gearboxes had a vacuum-actuated clutch. On the bellhousing there's a big diaphragm that moves the lever (purple arrow). Hard stuff to find though.

https://en.wikipedia.org/wiki/Autostick

If you reduce the pressure to one of the hydroboosters, won't it reduce the amount of boost? You could just use a throttling valve inline with the booster. Do people do that with power steering racks?

RossD wrote: If you reduce the pressure to one of the hydroboosters, won't it reduce the amount of boost? You could just use a throttling valve inline with the booster. Do people do that with power steering racks?

I know people change/shim the relief valve to change PS pressure up or down, or sometimes change the pulley diameter to reduce pressure. AFAIK all electric PS pumps have no relief valve and the pressure is fully dependent on motor speed.

After looking around, I suspect a booster like the Boursin truck booster you posted would be the least complicated. You can keep the same pedal and master cylinder assembly, but feed it to the booster circuit. You can tune the pedal resistance with a return spring if needed. The boosted slave cylinder probably won't fit in the stock location due to its larger diameter. In that case, you'd need a bracket bolted to the stock location to move the booster back, along with an extended actuation pin. If you need a vacuum reservoir for the booster, you can put that anywhere you have room.

If the customer wants to try changing the ratio first, fitting a larger diameter slave cylinder may be easier than fitting a smaller diameter master cylinder. Either way, if the pedal runs out of travel, it may require moving the pivot point on the pedal (assuming the MC has more travel available), and that would likely put you back where you started on effort.

In reply to GameboyRMH:

That release speed is without any clutch spring pressure (around 250-300 lbs of pressure). Loaded up the return speed is similar to activation speed.

Changing to a smaller master is easy - the car is built with a Wilwood master, and we have our choice of a half dozen sizes. The two interesting ones give us a 13% change in both travel and effort, and a 26% change.

Moving the pivot point on the pedal is exactly the same as changing master/slave sizes. We've had to do that in the Westfield kits when they got their math wrong and changing the hydraulic sizes wasn't possible.