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Silver Streak Digest V1 #42


Silver Streak Digest     Sunday, January 18 2004     Volume 01 : Number 042




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Topics in Today's Digest:

Re: [SilverStreak] Electronic Jack
RE: [SilverStreak] Electronic Jack

----------------------------------------------------------------------

Date: Sat, 17 Jan 2004 08:59:19 -0600
From: waymark1@xxxxxxxxxx.com
Subject: Re: [SilverStreak] Electronic Jack

Joan,

When brushes are almost worn out, if they have a positive stop and will
not wear clear to the wire, they will damage the commutator by arcing. So
it's very important to change the brushes at the first hint of poor
contact. I have saved a couple of starter motors by changing the brushes
before you have to bang on the starter to get it to work.

If your power jack is the same as mine (Reese) it has a recirculating
ball nut on the jack screw, which makes it able to operate with a
relatively small motor and reduction gear. So easy, in fact, that it has
to have a brake that goes on when the motor is not running to keep it
from lowering. This is why no oil is to be poured into the jack - it can
make the brake slip and let the jack lower under the tongue load. Heavy
oils can make the slip (overload) clutch slip too soon, too.

If the motor just suddenly quit with no warning you might have a bad
switch. The switch on my Reese jack looks like a generic rocker type.

Worn out brushes typically cause intermittent or weak operation. Also
brush wear particles can build up in the commutator gaps, which short
circuits the adjacent segments one at a time, making the motor weaker and
weaker. Such particles can be gently scraped out with a hardwood
splinter. Be careful not to damage the commutator.

"However, carbon brushes are soft and easy to modify their size to fit." 
With a file, or grind them down on a piece of abrasive paper on a flat
surface. Just get new brushes a little larger than the originals and
grind them down to slip easily into the brush guides.

"There should be less than 10 ohm resistance from the motor housing to
the battery negative terminal."
This is all solid steel as the jack is "grounded" to the A-frame, to
which the battery negative cable is fastened. Any significant resistance
should be fixable by taking the jack off the A-frame (support the A-frame
with a jackstand or hitch it to a vehicle) and scraping and wire brushing
all the rust from the A-frame where the base of the jack attaches, and
from the mounting flange of the jack. The battery negative or ground
cable/strap attachment point is another place that corrosion can make for
poor contact, so it may need to be removed and wire brushed clean.

I've had hard-to-get and extremely expensive alternators and starters
rewound and repaired by a starter-generator shop with good results.

Al

On Fri, 16 Jan 2004 20:29:00 -0800 "WILLIAM SCHMID"
<5150-n-flipper@xxxxxxxxxx.com> writes:
> Joan,
> 
> The first item to check would be power to the motor either with a test
light or a meter. Then check the ground return to the battery, preferably
with a meter set to the ohms setting at 1 ohm scale. There should be less
than 10 ohm resistance from the motor housing to the battery negative
terminal.
> Depending on the level of mechanical and electrical adeptness you or a
friend may have, the most likely cause of a D.C. motor to fail is from
brushes wearing out. These brushes are usually not too difficult to
replace, finding a replacement brush set may pose some problem. However,
carbon brushes are soft and easy to modify their size to fit. The brushes
are located at on end of the motor and spring loaded to push them against
the commutator ring. 
> This is how the power from the battery gets to the windings of the
motor to make it turn.
> When the contact is broken due to the brushes wearing past their
useable length the power can no longer flow through the windings to
create the magnetism to turn the motor. Brushes are relatively cheap,
usually $3-$4.
> If you are not confident in performing these repairs look for a motor
repair shop in the yellow pages and ask about a repair. I'm sure it will
beat the cost of replacing the whole jack unit and you will still have
that retro jack!
> 
> Bill Scmid

------------------------------

Date: Sat, 17 Jan 2004 22:19:13 -0800
From: "Joan Mayeaux" <j.mayeaux@xxxxxxxxxx.net>
Subject: RE: [SilverStreak] Electronic Jack

Thanks so much to Ros, Al & Bill for being so generous with advice
concerning the jack that went out on us. We store the trailer about 60 miles
away from us so unfortunately the manual is not here. We're headed out to
get it tomorrow. I can't recall what brand of jack it is, but I know it is
not REESE. It's something else that just won't come to me right now... I
have a feeling that whatever the problem is, it is pretty serious because
when we tried to get it going it started smoking. We probably shouldn't have
tried a second time, but as luck would have it, it was 20 minutes before
checkout time at the campground and our truck was blocking traffic so we
were a bit panicked. I am going to suggest to my husband that we find a good
machine shop. If that doesn't work I may let my brother play with it after
reading the advice that I rec'd from you all. He's an electrical engineer so
he'll understand what has gone way over my head :)

I feel so fortunate to have stumbled on to such a wonderful resource and
such a nice group of people. 

Thanks once again to everyone that assisted me! 

Let me know if anyone needs copies of anything from the '79 user manual. The
original owner kept everything!! I'm going to attempt scanning it into a PDF
file so I may be able to email it. 

I'm not technically adept, but I am happy to return the favor.

Joan 

- -----Original Message-----
From: sslist-admin@xxxxxxxxxx.com [mailto:sslist-admin@xxxxxxxxxx.com]
On Behalf Of waymark1@xxxxxxxxxx.com
Sent: Saturday, January 17, 2004 6:59 AM
To: sslist@xxxxxxxxxx.com
Subject: Re: [SilverStreak] Electronic Jack

Joan,

When brushes are almost worn out, if they have a positive stop and will
not wear clear to the wire, they will damage the commutator by arcing. So
it's very important to change the brushes at the first hint of poor
contact. I have saved a couple of starter motors by changing the brushes
before you have to bang on the starter to get it to work.

If your power jack is the same as mine (Reese) it has a recirculating
ball nut on the jack screw, which makes it able to operate with a
relatively small motor and reduction gear. So easy, in fact, that it has
to have a brake that goes on when the motor is not running to keep it
from lowering. This is why no oil is to be poured into the jack - it can
make the brake slip and let the jack lower under the tongue load. Heavy
oils can make the slip (overload) clutch slip too soon, too.

If the motor just suddenly quit with no warning you might have a bad
switch. The switch on my Reese jack looks like a generic rocker type.

Worn out brushes typically cause intermittent or weak operation. Also
brush wear particles can build up in the commutator gaps, which short
circuits the adjacent segments one at a time, making the motor weaker and
weaker. Such particles can be gently scraped out with a hardwood
splinter. Be careful not to damage the commutator.

"However, carbon brushes are soft and easy to modify their size to fit." 
With a file, or grind them down on a piece of abrasive paper on a flat
surface. Just get new brushes a little larger than the originals and
grind them down to slip easily into the brush guides.

"There should be less than 10 ohm resistance from the motor housing to
the battery negative terminal."
This is all solid steel as the jack is "grounded" to the A-frame, to
which the battery negative cable is fastened. Any significant resistance
should be fixable by taking the jack off the A-frame (support the A-frame
with a jackstand or hitch it to a vehicle) and scraping and wire brushing
all the rust from the A-frame where the base of the jack attaches, and
from the mounting flange of the jack. The battery negative or ground
cable/strap attachment point is another place that corrosion can make for
poor contact, so it may need to be removed and wire brushed clean.

I've had hard-to-get and extremely expensive alternators and starters
rewound and repaired by a starter-generator shop with good results.

Al

On Fri, 16 Jan 2004 20:29:00 -0800 "WILLIAM SCHMID"
<5150-n-flipper@xxxxxxxxxx.com> writes:
> Joan,
> 
> The first item to check would be power to the motor either with a test
light or a meter. Then check the ground return to the battery, preferably
with a meter set to the ohms setting at 1 ohm scale. There should be less
than 10 ohm resistance from the motor housing to the battery negative
terminal.
> Depending on the level of mechanical and electrical adeptness you or a
friend may have, the most likely cause of a D.C. motor to fail is from
brushes wearing out. These brushes are usually not too difficult to
replace, finding a replacement brush set may pose some problem. However,
carbon brushes are soft and easy to modify their size to fit. The brushes
are located at on end of the motor and spring loaded to push them against
the commutator ring. 
> This is how the power from the battery gets to the windings of the
motor to make it turn.
> When the contact is broken due to the brushes wearing past their
useable length the power can no longer flow through the windings to
create the magnetism to turn the motor. Brushes are relatively cheap,
usually $3-$4.
> If you are not confident in performing these repairs look for a motor
repair shop in the yellow pages and ask about a repair. I'm sure it will
beat the cost of replacing the whole jack unit and you will still have
that retro jack!
> 
> Bill Scmid


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End of Silver Streak Digest V1 #42
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