Entrance Door Step

T

thomas j. dj dugan

New member
Aug 14, 2002
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My 1976 Edgemonte has a mechanism which if functioning would position the
step for use when the vehicle is parked and would retract the step for
travel. The mechanism appears to be a diaphragm controlled by vacuum. I
believe I have a complete maintenance and parts manual but can not find
any thing on this mechanism so it may not be original GMC. Any one have
knowledge about this unit, can it be rebuilt with new diaphragm etc.? If
so, does it function by the engine vacuum system? Would it be better to
provide a separate vacuum pump and motor. Maybe there is a better way to
go??? Thanks, Tom Dugan
 
>My 1976 Edgemonte has a mechanism which if functioning would position the
>step for use when the vehicle is parked and would retract the step for
>travel. The mechanism appears to be a diaphragm controlled by vacuum. I
>believe I have a complete maintenance and parts manual but can not find
>any thing on this mechanism so it may not be original GMC. Any one have
>knowledge about this unit, can it be rebuilt with new diaphragm etc.? If
>so, does it function by the engine vacuum system? Would it be better to
>provide a separate vacuum pump and motor. Maybe there is a better way to
>go??? Thanks, Tom Dugan
>
I haven't seen one of these for several years. I had one on a 1972
Dodge Travco motorhome that came from the factory with it. But on
the GMC, it is definitely an aftermarket add-on.

When you start the engine it would provide engine vacuum to the step
and it would retract. When you shut off the engine it had a check
valve that would keep vacuum to the step until the door opened. The
door had a simple vacuum valve that was "teed" into the system so
that when the door opened it would allow air to enter the system
("dump" the vacuum). That switch is similar to the vacuum switch
hooked up to the brake pedal for cruise control systems.

You can test the step by applying vacuum to the diaphram. If it
works then you probably have a cracked hose or loose connection.

I had another motorhome later that had an electric step but I always
felt that the vacuum one worked better.
--
Emery Stora
77 Kingsley
Santa Fe, NM
 
I apparently have the same automatic step that you have. Mine works and
I like it very much. It stays extended when the engine is off. With
the engine running and the transmission in drive it retracts. I have
the original invoice but have no idea about the repair possibilities. I
think Ken Henderson was looking into that a few months ago.

Richard Waters
1976 Palm Beach
Troy, MI
My GMC's Website: www.digitek-asi.com/gmc.html

-----Original Message-----
From: Thomas J. DJ Dugan [mailto:pilot67]
Sent: Friday, November 22, 2002 1:29 PM
To: gmcmotorhome
Subject: GMC: Entrance Door Step

My 1976 Edgemonte has a mechanism which if functioning would position
the
step for use when the vehicle is parked and would retract the step for
travel. The mechanism appears to be a diaphragm controlled by vacuum.
I
believe I have a complete maintenance and parts manual but can not find
any thing on this mechanism so it may not be original GMC. Any one have
knowledge about this unit, can it be rebuilt with new diaphragm etc.?
If
so, does it function by the engine vacuum system? Would it be better to
provide a separate vacuum pump and motor. Maybe there is a better way
to
go??? Thanks, Tom Dugan

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> I apparently have the same automatic step that you have. Mine works and
> I like it very much. It stays extended when the engine is off. With
> the engine running and the transmission in drive it retracts. I have
> the original invoice but have no idea about the repair possibilities. I
> think Ken Henderson was looking into that a few months ago.

Richard, I never could make contact with anyone. So yours is connected to
the shift lever somehow, huh? Is it an electrical connection or valve? I
just hooked mine up so that the step retracts if the engine's running.

Thomas, if direct vacuum on the cylinder shows it to be defective, you might
be able to use a cruise control or headlight door vacuum servo as a
replacement.

Ken Henderson
76 X-Birchaven
Colquitt, GA
 
I didn't install the step, consequently the details are vague.
Apparently the PO wired it in such a manner that when the gear selector
is in drive the solenoid valve that applies vacuum to the step actuator
is activated. The system works great I thought at first that they all
came that way.

I'll try to find out more about the guy that made the system.

Richard

-----Original Message-----
From: Ken Henderson [mailto:hend4800]
Sent: Friday, November 22, 2002 4:42 PM
To: gmcmotorhome
Subject: GMC: Re: RE: Entrance Door Step

> I apparently have the same automatic step that you have. Mine works
and
> I like it very much. It stays extended when the engine is off. With
> the engine running and the transmission in drive it retracts. I have
> the original invoice but have no idea about the repair possibilities.
I
> think Ken Henderson was looking into that a few months ago.

Richard, I never could make contact with anyone. So yours is connected
to
the shift lever somehow, huh? Is it an electrical connection or valve?
I
just hooked mine up so that the step retracts if the engine's running.

Thomas, if direct vacuum on the cylinder shows it to be defective, you
might
be able to use a cruise control or headlight door vacuum servo as a
replacement.

Ken Henderson
76 X-Birchaven
Colquitt, GA
 
Charles,

> I would like to compliment you on the step presentation...
Thanks for the appreciation.

> ...The only question I had after viewing the pictures
> and drawing is; are the 3/8 thick supports strong enough to
> hold 300 pounds. I figure that's about how much my 150 pound
> grandson will but on it when he jumps in and out of the coach.
I had qualms about that myself when I first saw it. I'm now up to 220# and,
while I don't do much jumping, I don't notice excessive deflection of the
step. However, if I built one, I might replace the main arm with 2" stock,
or, more likely, 1-1/2" channel with the flat side up. That would impart
significantly more stiffness. I might also use 3/8" plate for the mounting
brackets rather than 1/4". One should be very sure the welds holding the
pivots brackets to those plates are of excellent quality.

HTH,

Ken Henderson
76 X-Birchaven
Colquitt, GA
 
Jim,

> I have converted your pictures and sketch into an
> almost complete AutoCAD drawing. No dimensions on it
> yet.
That's great! I'm about to sign off before a week-long trip to Maryland
(brrrrr!) for my stepdad's 80th birthday. When I return, I'll be glad to
post your drawing on Webshots. My suggestion is that we let all this jell
into a complete viable project, consolidated there, then ask Billy or Gene
to post a design package for everyone's long-term reference.

> You mention making the pivot pins longer. The pins
> shown are stock clevis pins. The next size longer
> would be much too long. Either have to increase or
> decrease the pivot block thickness if you really think
> a washer is necessary between the block and arm.
There's really no necessity for a washer, particularly since the pin's
locked against rotation vs the arm.

> I had intended to do a structural analysis on the arms
> on completion of the drawing. It may be possible to
> change them from flats to a modified structural angle
> which would add a good bit of stiffness, if necessary.
Very good idea -- you've seen my reply to Charles W.

> I also am looking at using a "throw away" cylinder as
> the actuator. It only needs about 2 1/2" stroke and
> the compressor puts out more than addequate pressure
> to accomodate the step. It would also more or less
> lock it in the deployed and retracted positions.
I'm not familiar with that term, but any economical solution will be an
improvement over the unidentifiable one we've got. The biggest problem I
see with using air is the cost of the solenoid valves. Also, since there's
a choice between extending and retracting with pressure, I'd suggest retract
with pressure. Otherwise those with leaky air reservoirs will not be able
to extend until they've climbed in without the step -- Big Deal!! :-)

Keep up the good work! See y'all in a week or so.

Ken H.
 
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