Hydraulic Clutch, let's try this again

[Brian Diehl]

A little bit more information to avoid the idiot syndrome

Okay, I estimate it takes about 55 - 60 lbs of force to fully engage the clutch brake as compared to how hard it is for me to pickup a 45lb weight.  This is with me grabing the end of the clutch arm and pulling up using one hand placed at the end of the clutch arm.  The clutch arm is 12" long and travels close to 4" or slightly under to clutch brake engagement.  I have a 13" clutch pedal with a maximum of 7" of travel.  If I have a slave cylinder with only 1.4" of travel that means it needs to connect on the clutch arm at (12/4)*1.4=3.6".  The force required = 55*12/3.6=183 lbs.

The clutch is NOT an "Easy Clutch".  The force to move the clutch out increases with distance.

Now, I want a lighter clutch pedal using hydraulics.  Can all the experts help me out now or do I need to give more information?  I have no room beyond the clutch pedal once it hits 7" of travel.  Can I get it down to 15 lbs of clutch pedal effort?  Do I need to use standard master/slave setup and supplement with air?

Constructive comments only please

If I didn't provide enough details ask the questions you need to help me, please.

Thanks in advance for any helpful guidance you can provide.

[prevost82]

Hi Brian

I going to assume that the Master cylinder will have to be solid mount / what I mean be this is the Master can rotate as the clutch pedal rotates throw it's  arc. So a short connecting link will have to be use between the clutch and Master to take out the arc miss alignment

Do you have a 4in stroke slave? and if you do what size is the bore.

So lets use the slave cyl that you have Bore dia of .88 = .60123 sq in x 100 PSI will give you 60lbs force on the clutch lever. But it has to have a 4" stroke right?

So to move the slave cylinder 4 inches you need to move 2.40492 cu in of oil

The Master cylinder is 1.4 Bore = 1.5393 sq in x 1.4 in stroke = 2.15587 cu in of oil ... so thats NOT ok to move the slave 4 inches ..in would move it 3.58 in

The master in rough terms is 2 1/2 time the dia of the slave so the force in the Master cylinder will have to be 40 psi to get 100 psi @ the slave, so with the lever distance on the petal this will be less.

Hope that help now you have to figure out how much top free petal distance you want and then the distance from the fulcrum that will give you 2 inch + travel on the clutch petal.

Ron

[Sean]

OK, with the additional information, here is a different answer (but probably not what you want to hear):

Again, this is basic hydraulics.  An unpowered hydraulic system is a "simple" machine which can provide a force advantage at the expense of distance, or vice-versa.

Likewise, a lever, which is basically what both the clutch pedal and the clutch arm are, provides the same sort of mechanical advantage -- force at the expense of distance (travel).

No matter what size bore and stroke you have on either cylinder, or where on the lever-arms you attach them, it still comes down to moving one lever through 7" of travel to cause the other lever to move through 4" of travel.  If the lever arms were identical*, the best mechanical advantage you can achieve without the use of some kind of power booster would be roughly 4/7*(60lbs) or about 34 pounds of pedal force.

It doesn't matter whether you connect the two levers with a cable, push-rod, or hydraulic system.  Hydraulics alone won't help -- you still are applying a force through a distance.

In order to get the reduction you want, you will need to either increase the angle of travel of the pedal, or lengthen its lever-arm, or both.

Otherwise, you will need to provide an external source of assistance such as air pressure assist or hydraulic power assist.

HTH.  Really.

-Sean
http://ourodyssey.blogspot.com

*Since they are not identical, a closer figure is 12/13 of that number, or 31 pounds, without getting into detailed angular force calculations (the applied force is not always tangent to the travel, etc. and the math changes as the angles increase).  And somebody probably ought to check my math, because it's very late and I've had a long day.

[wrench]

  The clutch pedal travel is 13" at the foot pad, not at the master rod axis, (you can alway drill new hole) & the clutch arm travel(4") is where the slave will be  hook. You may need to find cylinder with specific stroke & bore.  Are you upgrading to a hydraulic from a mechanical system?
  It's amazing at how every one analyze mechanical, that allow to view all possibility. How about designing an adjustable system so it can be adjust according to your feeling : strong& agressive, easy & soft(for when she drive), & then all to american inventor for the winner!!

[Stan]

Brian: When you first broached this subject, I suggested that you use an air system. The hydraulic system only replaces the connection between the pedal and the clutch. With hydraulics, you can't reduce the pedal force required to push it unless you increase the travel of the pedal or add some kind of external power.

[edroelle]

Brian,

For your objective, as others have said, you need an air or hydraulic assist.  I think GMs had this available.

Ed Roelle
Flint, MI

[bus05eagle]

Brian,wasn't this transmission a option on MCI and Newells if so way not check with them just a thought they may have everthing you need or can help

[Brian Diehl]

I was pretty sure the answer would be "no free lunch".  So, thanks everyone for confirming what I thought I had calculated out.  I'm going to need to provided a boosted setup then in order to accomplish what I want.

I'm wondering if I should go air over hydraulic or if there are other "boosted" options that might work?

I don't think MCI ever offered the autoshift ... did Newell?  If so, does anyone have contact information for someone who might be in the "know"?

[Len Silva]

Brian,

My seat of the pants solution would be air over mechanical.  Lots of Eagles had air assist and the parts are probably laying around somewhere.  I sold one not long ago for $100.  If not, new is about $700.00.

Len

[kyle4501]

As has been said, to reduce required pedal effort (without replacing the clutch or something of the sort to reduce required force at the transmission end), you will need to add power to the system to supplement the driver's input.

My scenicruiser originally had an air clutch. IIRC, The clutch pedal was attached to a regulator which sent a signal to an aircylinder at the clutch - This was used with the twin 4-71's. There was a fluid coupling connecting both engines to the 2-spd clutch in front of the 3-spd transmission. Needless to say, these kept the mechanics busy.


When they were repowered in the early 60's with the 8V71, they replaced the air clutch with an air assist cable operated system (with a little less other stuff that would make Rube Goldberg proud). In this current system, there is a air valve in the clutch linkage that sends air pressure to an assist device closer to the transmission. This system is still on most scenics that still have the 4-spd transmission.

SO, to make a long story shorter, using air is the way the manufacturers ease the required clutch pedal pressure & has worked reliably for years.

YMMV

[luvrbus]

Brian Newell uses a ZF transmission but it has a clutch phone #888-363-9355 MCI does offer a type of auto shift in their 4500

[Stan]

Brian: I think you were going to experiment with an air system. Did you try it and what were the results?

[Brian Diehl]

Brian: I think you were going to experiment with an air system. Did you try it and what were the results?

Hi Stan,
I got out the brake valve and hooked it up to air and the air cylinder.  It applied air, but I didn't have a good setup to get full air application.  I also tested full air pressure directly to the cylinder.  My little cylinder just couldn't do the job.  It was attached to the arm at 8" instead of at the end as well.  I wanted to fully investigate all my options before I go buying more "stuff".  However, it is looking like I'll need an air assist anyway and may try a larger air cylinder before going to hydraulic.  Just trying to see what other ideas are out there as I know I haven't been exposed to all options and ways of doing things.
-Brian

[rv_safetyman]

Hi Brian.  We now have two thread going on this subject and I am getting a bit confused as to which one I need to reply to. So, Here is a paste of my reply to the other thread:

>>>>>>>>>>

Brian, as Luvrbus pointed out, I have been working on this issue for a while.  Indeed, I think you and I talked about this on the phone once or twice.

When I started, I used all Volvo truck parts.  I had to modify the clutch pedal leverage a bit to make it all fit under the Eagle dash.  It was a b*^$h to push.  Also, I could not get the reservoir to fit and made a stab (didn't work) at a remote unit.

So, I started over on the master cylinder side.  A member of the Eagle group had developed an air over hydraulic system that seemed to work great.  He used a regular car master cylinder and a air brake can to actuate the master cylinder.  I have been playing with that concept as well as a mechanical hand lever system (does not work well at the toll booths, duh Angry).  The hand system did work well, but was not the answer I was looking for.  I have tried to design all kinds of pure hydraulic linkage systems, but there is not much room in the front of the Eagle.

I will be installing the third master cylinder in the next week.  I have done all of the calculations, but it still came down to cut and try.

The one thing I did mention in a previous post was to be sure to use a two wire hydraulic hose for the run from the front to the back.  You do not need it for the pressure (less than 800 PSI with my present system), but you do need it to minimize the expansion of the long hose and the associated loss of control.

Have fun! Jim

>>>>

Now, with this new thread, comes some new thoughts.

I think mechanical linkeage is probably not worth trying if it was not in the bus to begin with (your case).  All the connections are just asking for trouble.  Some folks have suggested cable, but there are still things that wear out in that type of system.

We now have two votes that pure air will work.  I have heard some strong opinions (off line when I was working on my application) that pure air did not work for them (one had very bad results).

Pure hydraulic can be made to work, but we don't have much space for a good actuation system (pedal linkage, etc).

So, it it would appear that air over hydraulic or air assisted hydraulic may be your best answer.  I am going the air over hydraulic route as noted above (using brake treadle valve).  From a pedal pressure point of view, it is great.  I am still working on the control capability (too touchy).

I have a friend who has developed an air assisted hydraulic system.  He has a control switch on the foot pedal that activates an electric air valve that activates an assisting air cylinder on the clutch arm.  He sent me pictures, but we have not had a chance to talk about how effective it is.

Just more thoughts to confuse you

Jim

[Brian Diehl]

Thanks Jim,
I appreciate all your thoughts and details.  Yes, I fully remember our conversation about the different setups you've tried.  Thanks for the reminder.

I have talked to a friend who used air and hydraulic.  His system works great for him and his pictures showed a good setup.  My setup is a little bit different and before I went down a complete refabrication I've been exploring all options.  I like the idea of a boosted hydraulic setup .... but it appears the parts are not well known as no examples have been forth coming.  I thought of a master cylinder from a car, but don't know how to go about providing reliable (and relatively cheap) vacumn to the booster.


FYI:  Just use this thread as I've abandoned the prior thread for obvious reasons.