Author Topic: 24 volt vacuum pumps  (Read 5065 times)

Offline gus

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Re: 24 volt vacuum pumps
« Reply #15 on: November 23, 2014, 06:11:57 PM »
Trucks don't have 40'+ runs for hyd lines.
Ash Flat, AR

Offline Larry B

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Re: 24 volt vacuum pumps
« Reply #16 on: December 05, 2014, 07:54:10 PM »
  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
1977 MCI-5B---
8V71- 4speed man

Offline digesterman

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Re: 24 volt vacuum pumps
« Reply #17 on: December 06, 2014, 04:52:07 AM »
Larry that was a darn good post, a better than "good reply".

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Offline bevans6

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Re: 24 volt vacuum pumps
« Reply #18 on: December 06, 2014, 04:58:14 AM »
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!

1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Allison MT-647
Tatamagouche, Nova Scotia