Date:         Wed, 22 Aug 2012 23:24:09 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: Brake Pedal Pulse Questions
Comments: To: neil n <musomuso@gmail.com>
In-Reply-To:  <CAB2Rwfgd=HO=kD=-wYi=UVFGGAYhqTzwCxLPJdt_UT1aThOn-A@mail.g
              mail.com>
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At 03:26 PM 8/22/2012, neil n wrote:
>Are you suggesting one ramp per vehicle corner,

Yes.

>  each providing room and level surface for a jack and jack stand?

Stand or wheel for sure.  Another for the jack would be a good idea as well.

>
>
>Like this?  image:
>https://lh3.googleusercontent.com/-zCqGzE1KbmI/UDUyJPKF0WI/AAAAAAAAF_U/cBj1mBmkZ-Q/s800/ramp.jpg

Yes, exactly.


>For what I need, 2 ramps should suffice for now. (work on one end of
>vehicle at a time)

Safer to have all four, though if the other end is chocked very
securely perhaps it would be all right.

But by getting all four support points (wheels or jack stands) on a
level surface, you've eliminated any forces tending to topple the
stands or otherwise move the vehicle horizontally, and you've ensured
that the center of load on the stand runs right down through the
middle and not off to one side where it would require less force to
topple it from the other side.

The jack has all the same considerations except that you're not
underneath at the time, so if it's practical to level it it's a very
good idea, and you have to stay conscious all the time of how the
force vector decomposes at a given angle.  If your driveway has a
constant slope you can easily make up two tables: for a given load,
how many pounds of force are exerted horizontally; and for a given
height of lift, how far does the load center move horizontally from
the midpoint of the (tilted) lifting/supporting device.

Example: 4000# Westy sitting on a 3* slope.  Force vector is 4000#
straight down, but the slope decomposes that into approximately 3995#
pressing against the driveway, and 210# trying to make it run off
down the hill.  And a jack or stand sitting on the slope would have
the effective center of load an inch to the side of center.  Six
degrees would give you  420# shoving you down the hill, and the
center of load two inches off the centerline of the stand.

Doesn't sound like all that much, but every little bit hurts.

Yours,
David