Hydraulic Clutch, let's try this again

[Dallas]

Brian,

If you need reliable and cheap vacuum, why not try a refrigerator compressor? Hooking it to a spare airtank with a regulator and a check valve would supply all the vacuum you would need.

A plus is that if you found a 12v compressor, like a Danfoss, you wouldn't need to run the inverter to operate it.

Just a thought to move the fabrication along a bit.

Dallas

[Brian Diehl]

Hey Dallas,
Good idea ... I'm going to ponder that for a bit ....
Thanks

[Stan]

I must be missing something if you are going to use air assisted hydraulic instead of going straight air. If there are control problems with straight air I think they will be amplified with air assisted hydraulic.

A brake treadle valve does have short travel on the actuator pin so suitable linkage has to be used to get good control but there are many bleeder type air pressure regulators that would be easier to control. On some, you screw in the adjustment about 2'" to go from zero to full pressure. On almost any regulator you can change the spring to get the maximum pressure you need for full travel of the slave. This would be easy with a air throttle control without the treadle and using a suitable lever to get longer travel for better control.

If you are only using the clutch for initial start with an autoshift, then it doesn't matter if it goes all the way to the clutch brake so you don't rally need that delicate part way down on the pedal.

[makemineatwostroke]

Brian,why not get you a hydro boost off a GM car or truck that way you do not have to have two different component's to work your clutch

[Brian Diehl]

Brian,why not get you a hydro boost off a GM car or truck that way you do not have to have two different component's to work your clutch

What is a hydro boost?

[makemineatwostroke]

Brian,we converted 5 MCIS for a charter co here in Houston that wanted better fuel mileage the process is simple you can mount the Hydro booster in any position you want mount the reservoir any place and run lines to the booster all you have to do is make sure you can get the pedal rod to it tap your power steering lines flow and return use a good slave Cly with a adjustment on it and you are good to go you can buy rebuilt units from auto parts stores like Napa or buy on from the wrecking yards they were on lots of GM trucks and wagons i called the shop to see if they had any drawings left around if they find some i Will post or email them to you

[gus]

Brian,

Unless you plan to use aircraft hydraulic fluid I would strongly suggest forgetting the hyd part. Auto hyd fluid attracts water like mad and will cause rust and leaking. This is even worse on a bus that is not used daily. There is nothing to be gained by adding the headaches of hydraulics into the clutch system.

I have a bunch of antique vehicles of all sizes, hyd brakes and stale gasoline are my two worst headaches. The ones with mechanical or air brakes never seem to have any problems.

[makemineatwostroke]

Brian,the power steering pump runs the system it has brake fluid from the unit to the clutch

[Sean]

Straight air operation, using a treadle valve, is traditionally considered a bad choice for clutch operation because it eliminates almost all feedback, thus preventing the operator from "feeling" the friction point of the clutch, generally considered an important control function.  This is why power-assisted mechanical or hydraulic linkages are generally used for this application.

Here is one after-market air-assist system that is a straight bolt-in:
http://www.hbindustries.us/air.htm

If you want to roll-your-own, air assisted clutches are common on heavy duty trucks, and you can probably find all the parts for a complete system at a truck salvage.

FWIW.

-Sean
http://ourodyssey.blogspot.com

[buswarrior]

Hello.

I am only able to contribute this bit.

I would want to keep the ability to access the clutch brake in an autoshift application.

The computer will only engage the gears within a certain rpm band, and it is very easy to have the bits and pieces spinning above that band.

You will wait and wait to start off, in a situation that you would prefer to go now, if you could only get the internals to slow their spin.

This from a guy who has to teach others how to run a sewer sucker truck with one in it, unionized environment, so you know who gets forced into sucking sewers...

Push the clutch in early coming to a stop, touch the throttle while sitting still, disengage the fast idle, all leave the tranny spinning inside too fast to engage a gear.

happy coaching!
buswarrior

[Stan]

Sean: Do you know what is inside that cylinder, in the clutch rod, in the ad you linked to? I assume the rod from the pedal is connected to a control valve of some sort with a big spring behind it that determines the amount of  pedal force required in order to get air to the assist cylinder.

BTW: I installed an air operated clutch using a modified brake valve and drove it about 50k miles without problem.

[rv_safetyman]

Hi Brian.  I use only the master cylinder and do not use any vacuum chamber.  I selected a version that has a screw on top that makes pressure bleeding easier.  However, I have not had to do any pressure bleeding since I abandoned the Volvo master cylinder.  Something in the system would not allow normal bleeding processes including pulling a vacuum at the slave cylinder.

The vacuum chamber in a car obviously reduces the pedal pressure.  That is not an issue with an air brake chamber system.  Indeed, I have to be very careful not to apply full pressure as it over-pressures the hydraulic system.  I will put a pressure regulator in the system when I get done playing.  Right now, I have a large hydraulic pressure gage that I watch when I engage the clutch. 

Jim

[Sean]

Sean: Do you know what is inside that cylinder, in the clutch rod, in the ad you linked to? ...

Sorry, I don't.  Hey, I have an Allison 

That being said, generally, there is a standard process for proportionally adding power boost (whether vacuum or air) to a hydraulic system, whether that's a clutch, a hydraulic brake, or even power steering.  Here's a good explanation (from vacuum-assist brakes, but you can see the general idea):
http://auto.howstuffworks.com/power-brake.htm
(Just remember that vacuum assist is applied to one side of the diaphragm, while air assist would be applied to the other side.)

HTH.

-Sean
http://ourodyssey.blogspot.com

[Brian Diehl]

Hi Brian.  I use only the master cylinder and do not use any vacuum chamber.  I selected a version that has a screw on top that makes pressure bleeding easier.  However, I have not had to do any pressure bleeding since I abandoned the Volvo master cylinder.  Something in the system would not allow normal bleeding processes including pulling a vacuum at the slave cylinder.

The vacuum chamber in a car obviously reduces the pedal pressure.  That is not an issue with an air brake chamber system.  Indeed, I have to be very careful not to apply full pressure as it over-pressures the hydraulic system.  I will put a pressure regulator in the system when I get done playing.  Right now, I have a large hydraulic pressure gage that I watch when I engage the clutch. 

Jim

So, you are using a master cylinder, single I assume, without vacumn assist.  So, where does your air assist come in to play?  I'm having a hard time picturing the system given the information provided.

[rv_safetyman]

Hi Brian.  It thought I had a picture, but I can't seem to find it.

The master cylinder and the air brake chamber are mounted on a common fixture.  Right now I have that fixture on the floor beside the driver seat.  The air brake chamber rod center line and the master cylinder center line are the same.  I made a rod that threads on the air brake chamber rod (for adjustment) and that rod pushes on the piston of the master cylinder.  Pretty simple to fabricate.

Let me know if that makes it clear.  If not, I can try to take a picture, but it is pretty crowded in that area.

Jim