I have shelved, at this point, my work on an air operated clutch. Mostly because Bruce sent me detailed photo's of his hydraulic clutch installation that will work a whole lot better. It would need an electric vacuum pump to supply vacuum to the brake booster, so I was looking for 24 volt vacuum pumps. All I find is Alibaba pages and wholesalers in China. I figure every diesel truck and electric vehicle must have a pump, so they must be out there... Any leads?
Brian
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The old gmc's Cadilacs & mercedes diesels had them. 6.2 liter gm. New trucks do not that I know of my duramax is hydrolic & runs off power steering pump for brake boost.
The pump I used came from a Oxygen Concentrator, you can find them used. It will give a vacuum & or air pressure run on 110V AC from inverter, a lot less noise then DC ones.
Bruce
If you need a little accumulator/storage component for a extra capacity or to smooth things out, you can use one off a '99-'05 VW TDI Jetta, Golf, or Beetle. They're about the size of a baseball and have connections to fit usual sized vac hose.
Many Diesel cars and trucks used hydraulic brake boosters that worked off the power steering pump. If you have power steering, I would think it would be relatively easy to tap into the power steering lines to get booster pressure for the clutch assist. Good Luck, TomC
Thanks for the idea's guys. I have found many options for 12vdc units, and am now going to start to research the hydoboost idea. It's not like there isn't a perfectly good source of power steering pressure about 6" from where the boost unit is going to be. I want to run it "off the engine", which is a poor way of saying I want it to be fully contained and power by the prime mover engine, the 8V-71, without non-DOT approvable stuff in between, hence I would shy away from the 12v ( which is really the house battery system, even if I have an optional tap to charge that system from the engine) or the 120 vac from the inverter option.
I found nice chart that gives you the boost of a vacuum assist unit based on a nominal 23" of vacuum and the size of the boost unit. You can easily double the input pressure.
Brian
Here's a 24v one...
http://www.ebay.com/itm/THOMAS-Double-Diaphragm-Vacuum-Pump-24VDC-70060058-M42x40-new-/281368691704?pt=BI_Pumps&hash=item4182e183f8 (http://www.ebay.com/itm/THOMAS-Double-Diaphragm-Vacuum-Pump-24VDC-70060058-M42x40-new-/281368691704?pt=BI_Pumps&hash=item4182e183f8)
Steve
That's a nice looking unit. And the upside is that even if the motor is not running, you still have vacuum assisted brakes. The downside is electrical gremlins live everywhere!
Tapping into the power steering system may require a relief valve. Now if you use a ton of hydraulic pressure for your brake system, how much "power" will that take away from the steering system? Plus more connections/hoses to leak.
I seem to remember some heavy vehicles end up with very heavy steering when you have your foot hard on the brake and you are trying to turn the wheel while stationary. Also most hydro boost systems on heavy vehicles have an electric back up so that if a leak develops you still have brake assist.
If this is for a hydraulic clutch, why do you need a brake booster? Just a master cylinder and appropriately sized slave cylinder. Find assys off a medium duty truck. Volvo uses hydraulic clutches on their heavy duty models.
So far the math on volume leverage and pedal ratios says if I don't get a boost the pedal effort stays about the same as I have right now, mechaical like it is or hydraulic like a modern truck. Right now the pedal effort is about 65 lbs to push, straight down, and that is the problem for my knee. 65 lbs push doesn't seem like a lot, but another way to think of it is lifting half my body weight on that leg with my foot out in front of my body mass and my knee at right angles. It's hard! by changing the pedal to one that hangs down from the dash the push becomes more forward than straight down, and the boost will reduce the push to around 30 lbs.
With mechanical systems like this you get a certain amount of throw-out bearing movement from a certain amount of pedal movement. Changing the linkage from mechanical to hydraulic lets to play with leverages far more easily, but at the end of the day the only way to reduce the force is to increase the leverage. The throw-out bearing movement isn't going to change so the pedal movement would have to increase to reduce the pressure. The pedal throw is actually 7 to 8" now, and my knee sometimes hits the steering wheel, so there is no room for more movement.
I've designed a number of hydraulic clutch and brake systems for race cars from scratch, and I spent a fair amount of time looking for a free lunch on this one and haven't come up with one. The booster idea is pretty damn close to a free lunch, doubles the pressure with no increase in pedal movement. There's lots of other ways to reduce pedal effort inside the clutch itself, in the spring and finger design, and I have no doubt that the modern trucks take advantage of that newer technology.
Brian
Could also use a standard pump such as are fitted to 2000 model F350 diesel trucks and power it via a dedicated 24V to 12V converter. This would mean you would have the pump, pressure switch and accumulator all in one unit.
Freightliner trucks also use hydraulic clutch linkage.
Why would you use vacumn when you already have air pressure?
Vacumn systems are used only where there is no air press system available? A vac system is actually an air system anyway except it uses atmospheric pressure instead of an air tank.
They both push which is what you want.
The hyd part doesn't care what is pushing.
Quote from: chessie4905 on November 20, 2014, 11:09:28 AM
If this is for a hydraulic clutch, why do you need a brake booster? Just a master cylinder and appropriately sized slave cylinder. Find assys off a medium duty truck. Volvo uses hydraulic clutches on their heavy duty models.
Duh ... posting at work, while thinking of the jobs at hand don't mix.
Trucks don't have 40'+ runs for hyd lines.
Hello Brian--- I seldom post because I usually have more questions than good replies. Not tring to be smart but are you sure your air assist is working? I was having a similar problem to what you are describing --very hard clutch petal-- after a couple of days of checking book settings on clutch linkage settings and getting no less clutch petal pressure needed, I had the wife come and push clutch with engine running and aired up. she had to remain standing to do this, while I looked for binding linkage or something jamming up. I found the air assist cylinder only moved about 3/8" and then stopped extending. It had rusted up inside as you can see from the picture. (after sandblasting). I cleaned up inside hole where piston fits with boring bar on lathe and then made an oversized piston (1 1/2" pipe schedule 160) to fit new hole id. On a previous post I think I recall you mentioning doing machining, from that I going to assume you have a lathe. On the thought of air assists would a larger O.D. air assist be worth considering? Everything is there except the larger piston. A 1/2" larger would give you over 50% increase in assist force. (if I did math correct) Original piston is around 2"od. The only concern here might be the assist force too strong for clutch pressure plate springs and you might get clutch slippage on start moving. One could always tone down assist force with an air regulator. Hope I have not messed up your whole train of thought.
Larry B
Larry that was a darn good post, a better than "good reply".
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I rebuilt the air assist cylinder several years ago, and I gave it a good look-over when I changed the engine, along with the complete clutch mechanism. Going to a larger cylinder is an option I've considered. I do plan to pop it out and check it over as part of my clutch plan. I actually had a off-the-wall idea to feed the air assist cylinder from a small air tank with a check valve. It would air up to 120 psi as the bus airs up, and stay there so the cylinder always had maximum boost, instead of rising and falling between 120 psi and 95 psi with the air system.
What I actually plan to do is disconnect the whole mechanism from the actual throw out bearing arm so that I can move it freely through it's travel and examine all of the levers for correct geometry and action, make sure there is no binding, etc. Only then will I move on to modifications when/if that doesn't get me what I need. I actually suspect that simply changing the pedal from a "push down" motion to a more normal "push forward" will be enough, and that is pretty simple to do.
Thanks for your ideas, I appreciate them, and I agree, a darn good post!
Brian