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| Safely Jack Your Bus First, never assume "all the air" is out of the system - there are one-way
valves, backup systems, etc - seems there's always a little air somewhere.
Second, I don't think anyone on this board (even professional mechanics) is
willing to take the liability of trying to explain via text where to block
the bus Sounds like a cop out, but I've even got different opinions from
two mechanics I respect highly. Since standard procedure in bus barns is to
use a pit, this topic isn't exactly 'by the book' to begin with.
That said, I will go out on a limb and share what little I have learned (and
still remember!) about the subject. I am NOT a mechanic or expert, so read
for information only and ask questions from the pros. And I will say right
up front that I am not aware of any clear diagram that shows all proper
blocking locations. And keep in mind that MCI's may differ from GMC's etc:
1) But do check your operator's manual AND the repair manual for what little
information they provide on "jack points". If you have an MC-9 there is an
almost legible photo or description in each manual which almost explains one
blocking point.
2) The wood blocks must be Hard Wood, at least 18" or in length - OK to
stack in alternating directions (like a cabin without an inside), and must
be placed on thick concrete. The bus weight concentrated on block points
can pile drive through asphalt (or so I'm told). Make sure the top of the
blocks contact an appropriate place (this is the tricky part).
3) One mechanic recommended jacking at bulkheads on body, but when
discussing this at length with another highly qualified mechanic I was told
that the body bulkheads would just collapse under localized point stress and
the blocking must be done under the chassis (rear bogies and axle attachment
points, etc).
4) Keep in mind what is "sprung" and "unsprung" weight (air springs). The
rear of the bus floats above an axle bogie which is pretty much in direct
connection with axles and tires. So unless the tires blow, the drive axle
itself shouldn't drop, except towards the rear as the engine comes down if
the air system blows. Front axle is similar - if the body if properly
blocked, you can actually crawl in around the front axle, but the key word
is "properly" and I was seldom comfortable there.
5) As I recall I used several piles of blocks at several points to cover
my bases. I usually used at LEAST 4 piles of heavy duty hardwood (borrowed
from a house mover friend of a friend) - the jack points and the chassis
attachment places for the trailing arms (I've forgotten what they are
called, but they run horizontally in line with the bus [front to back] keep
the axle bogey in line).
Also, if you look at the under side of the bus carefully, you will see
REALLY thick approx 4" square vertical tubes extending down from the
chassis - Two in the front, and at least two in the rear - one set is
visible between the drive wheels and the tags. I'm not 100% sure, but they
appear to support the upper end of the air bags and thus the weight of the
coach, so I made sure they were among the block sites. I almost didn't
have room to get in between the blocks sometimes, and I'm not very big!
Pine is NOT a hard wood and should not be used.
6) Remember that if you are doing any air valve work, removing an air valve
from pressurize line may be the last thing you do on this earth if the bus
settles quickly.
7) You can drain the three main tanks by using a stick with a hook on the
end and tugging gently on the pig's snout ring (for lack of a better term).
That doesn't guarantee air drainage behind check valves.
8) Never poke your head or chest between parts that could get closer
together if the air collapses - like between the wheels and chassis/body of
bus, or between the differential and the ground (when unblocked). Heard a
sickening story of a mechanic crushed that way while working on a motor home
a year or two ago when the bus settled and he could not wriggle out -
suffocated or crushed, I don't recall.
Some may not take this as seriously as they should, but it all boils down to
how much you like living. If in doubt, find someone else to pay to do this.
It's claustrophobic work to begin with, and the knowledge of certain death
if something settles is even more disturbing.
my two cents, and worth every penny! But don't sue me if you mess up.... I
never claimed to know everything....
Dell
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