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-   -   Shurline scale accuracy? (https://www.airforums.com/forums/f238/shurline-scale-accuracy-89721.html)

dznf0g 04-09-2012 08:49 AM

Shurline scale accuracy?
 
Question for you folks with a Sherline tongue scale. Do you find that it "zeros in" on a reading? Or if you push and pull vertically on the tongue does it settle on different numbers.

It seems , with mine, I can get as much as 100# difference when "rocking" the tongue up and down, like the shaft is sticking in the bore.

Any ideas?

RickDavis 04-09-2012 08:53 AM

I have a tongue scale, brand unknown. Basically a hydraulic cylinder and a pressure gauge. It behaves as you mentioned. Very hard to get consistent repeat readings

slowmover 04-09-2012 10:04 AM

Perfect is not to the point. One must also deduct/add for distance from hitch ball center. It can be checked against the old bathroom scale "method", and checked again using the Ron Gratz Chart I've posted numerous times.

Another way of looking at it: What is the difference in TW percentage as a difference in readings?

A SHERLINE is a tool on my acquisitions list. But few of us can afford the type of tool to which is referred. Good enough is just that.

.

mojo 04-09-2012 10:56 AM

Well they say not to lift by or pull on the plunger. I have stood on and off mine to make sure it's moving freely before I weigh. And the tongue weight can vary by 200+lbs between the coupler and the jack stand. It has been a very useful tool for dialing in the tongue weight and packing the trailer with my Touareg.

RickDavis 04-09-2012 11:22 AM

Quote:

Originally Posted by mojo (Post 1131493)
Well they say not to lift by or pull on the plunger. I have stood on and off mine to make sure it's moving freely before I weigh. And the tongue weight can vary by 200+lbs between the coupler and the jack stand. It has been a very useful tool for dialing in the tongue weight and packing the trailer with my Touareg.

Just took a look and mine is Roadmaster, By Sherline. I find repeat measurements vary by 200 lbs or so.
I guess this is close enough as a % of trailer weight but not nearly good enough for watching effects from changes in loading etc

jimmickle 04-09-2012 11:27 AM

If anybody is interested, I have a like new sureline for sale as health issues have ended my travel years.

mojo 04-09-2012 12:17 PM

There are two different scales, 1000lb and 2000lb capacity. My 2000lb scale is fairly consistent but the measurements on the scale are in 50lb increments. It gets you close, but I do not have a 200lb sway in measurements at the same spot.

dznf0g 04-09-2012 03:03 PM

Quote:

Originally Posted by mojo (Post 1131544)
There are two different scales, 1000lb and 2000lb capacity. My 2000lb scale is fairly consistent but the measurements on the scale are in 50lb increments. It gets you close, but I do not have a 200lb sway in measurements at the same spot.

Hmmm, I wonder why some of us have this "stickiness" and you don't....any theory? I am aware of the "don't lift by the plunger" rule and am confident there is no air in the unit. Last year I even pulled the gauge and checked for air. (not hard to do, BTW). I wonder if fluid amount has anything to do with it...ie...plunger too high in bore and cocking?????

I have the 2000# scale as well.

boondockdad 04-09-2012 06:38 PM

I found if the trailer isn't *perfectly* level, I can get very disparate readings.

dznf0g 04-09-2012 10:15 PM

That's not what I'am talking about. Level, I mean. It's about varing readings at level.

ROBERT CROSS 04-10-2012 05:55 AM

I also use the 2000lb Surline.
I step on the tongue directly above the scale and compare reading with my known weight, note that it returns to previous reading. (usually with-in 50lbs), which I think is acceptable. The needle has always returned to zero with-in the brackets.

Bob
:wally:

Cracker 04-10-2012 04:01 PM

Quote:

Originally Posted by ROBERT CROSS (Post 1131900)
I also use the 2000lb Surline.
I step on the tongue directly above the scale and compare reading with my known weight, note that it returns to previous reading. (usually with-in 50lbs), which I think is acceptable. The needle has always returned to zero with-in the brackets.

Bob
:wally:

The only thing that comes to mind for me Bob is that the rounded top of the Sherline is designed to fit the contours of the female part of the coupler - i.e. - match the ball contour. If it's off center just a bit at the top, inside the coupler - or if the Sherline is not perfectly vertical - or if the trailer drifts slightly in any direction when you lower it onto the scale, it could cause a slight bind in the scale piston - which would probably not happen with a conventional mechanical scale or load cell. Also, the inside top of the coupler could be fairly loaded with trash, since the top of most balls are flat and not in contact with the female part of the coupler at the top - and that's exactly where the Sherline bears!Those factors could cause a variation in the reading as you rock the trailer. I've always just settled on an average reading! A simple swivel ball and bearing pad on top of the Sherline would probably eliminate most of the accuracy problem - but the additional machining would probably double its' cost.

ROBERT CROSS 04-11-2012 05:45 AM

"The only thing that comes to mind for me Bob is that the rounded top of the Sherline is designed to fit the contours of the female part of the coupler - i.e. - match the ball contour. If it's off center just a bit at the top, inside the coupler - or if the Sherline is not perfectly vertical - or if the trailer drifts slightly in any direction when you lower it onto the scale, it could cause a slight bind in the scale piston"

Cracker,

I've abandoned the use of the screw in extension since getting the Arrow.

The concave scale pad stays put very well, I lower the trailer on the scale using the tongue jack and compensate for the difference in the pivot point. It's also much easier keeping everything plumb.
The Shurline is most useful when a visit to the Cat's indicate a difference in loading, usually a lot lighter when not boondocking.

Bob

Cracker 04-11-2012 03:12 PM

One of the problems with using the Sherline at the ball is getting a proper height stack under the scale to support it. If you remove the extension and use the scale at the jack, what measurement point do you use to calculate the load at the ball with a dual or triple axle trailer - the center of the axle group???

ROBERT CROSS 04-11-2012 04:05 PM

Quote:

Originally Posted by Cracker (Post 1132584)
One of the problems with using the Sherline at the ball is getting a proper height stack under the scale to support it. If you remove the extension and use the scale at the jack, what measurement point do you use to calculate the load at the ball with a dual or triple axle trailer - the center of the axle group???

After we load the trailer,(full fresh,lpg,supplies), this Spring and before I re-install the Arrow I'll weigh it directly under the ball using the extension, then again at the jack, without, note the % difference and add whenever a tongue weight is needed during the Season.
FWIW..had brain farts two out of the five seasons we've had the Arrow and never weighed at the ball, wasn't really a problem as the TW still averaged between 1150 and 1225 at the jack post. Loaded heavy for dock'n.

Bob
:flowers:

dznf0g 04-12-2012 03:44 PM

Quote:

Originally Posted by ROBERT CROSS (Post 1132605)
After we load the trailer,(full fresh,lpg,supplies), this Spring and before I re-install the Arrow I'll weigh it directly under the ball using the extension, then again at the jack, without, note the % difference and add whenever a tongue weight is needed during the Season.
FWIW..had brain farts two out of the five seasons we've had the Arrow and never weighed at the ball, wasn't really a problem as the TW still averaged between 1150 and 1225 at the jack post. Loaded heavy for dock'n.

Bob
:flowers:

That would be a nice bit of info to have. Thanks, Bob.

Silver Goose 04-12-2012 04:15 PM

If you have a floor jack, set the Sherline on the cup of the floor jack then position it under the coupler and use the floor jack to lift the tongue just off the supporting post jack. Be sure the wheels are chocked. This should give you the weight on the ball with the trailer level.

ROBERT CROSS 04-12-2012 04:33 PM

Wish I could use the FJ, after the Arrow's on...I have to use the AS jack.
https://i40.tinypic.com/r01qip.jpg

Bob
:wally:

Cracker 04-13-2012 03:27 PM

Quote:

Originally Posted by Silver Goose (Post 1133030)
If you have a floor jack, set the Sherline on the cup of the floor jack then position it under the coupler and use the floor jack to lift the tongue just off the supporting post jack. Be sure the wheels are chocked. This should give you the weight on the ball with the trailer level.

That'll work! I'm still curious as to where the pivot point should be located to calculate the weight at the ball when measure at the jack - which, admitedly, is the easiest place to measure the weight??? If the trailer is dead level, and both axles are equal in capacity, I would use a point midway between the axles or, in the case of a 34', centered on the center axle. If "x" is the distance from the pivot point to the jack, "y" is the distance from the pivot point to the ball, "a" is the weight at the jack, and "b" is the weight at the ball, it follows that if "a" is known, b = (ax)/y. Conversely, if b is known a = (by)/x. One axle weaker than the other could throw the calculation off - but it would still be relatively close.

Phil&Sher 04-13-2012 03:55 PM

Quote:

Originally Posted by ROBERT CROSS (Post 1132605)
....... two out of the five seasons we've had the Arrow and never weighed at the ball, wasn't really a problem as the TW still averaged between 1150 and 1225 at the jack post. Loaded heavy for dock'n.

Bob
:flowers:

I plan to get a Sherline and weigh the entire dead weight that's being placed on my tow vehicle receiver by leaving the spear in the Hensley and using the tongue jack to adjust the spear to the same height as the bottom of the receiver. I'll place the Sherline under the upper part of the spear at what would be the midway point when it's in the vehicle receiver; then raise the hitch jack to place the load on the scale. Does this seem reasonable?

Phil


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