NEW AXLE - Fiberglass RV


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Old 03-12-2006, 11:12 PM   #1
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i just ordered a new straight axle for my amerigo it has a 4" drop axle and i am getting a straight axle has any on else done this go from drop to straight axle and did you see any real difference??? i am doing this do to i feel it sits to low and the tire rubs a little so if i raise it with the straigt axle i can put on a 14"tire with no rub...
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Old 03-13-2006, 05:43 AM   #2
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Dan,

The common terms are "positive" and "negative" angles for axles, or even more common "down" angle and "up" angle. I presume by "straight" you mean that you ordered a 0* angle axle, or one that has the pivot arms straight out from the axle, parallel with the ground?

Trailer frame height (off the ground) is directly related to the "up" or "down" orientation of the trailing arms on the axle as well as the axle bracket height and tire size. Without knowing what your stock axle's specifications were originally, it will be difficult to determine exactly how much increase in frame height you'll achieve. A 0* axle may show a negative (up) deflection when mounted on the trailer because of the weight of the trailer. A 10* positive (down) angle trailing arm may appear to be a 0* because of trailer weight. Your axle may have been a 0* from the factory and worn out, or it may have actually have had a negative deflection when new.

Torsion axles should exhibit about 3" of total travel when loaded (at least according to Dexter). Remember that tire width also increases with height and sidewall ratio. Make sure you have enough clearance inside your wheelwells to accomodate the additional width of a 14" tire.

Dexter also supplies a "high-lift" bracket that will give an additional inch in frame height. Some of our members have fabricated their own brackets to give additional height.

Roger
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Old 03-13-2006, 10:43 AM   #3
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I'm guessing that Roger is thinking that the Amerigo has a rubber torsion axle, but from Dan's description I think it has a beam axle on leaf springs, like my Boler B1700.

B1700 owners have changed from the stock 4" drop-beam axle (axle tube centre is 4" below the hub centres) to a straight (no drop) setup. If you must raise a trailer with a leaf-spring rigid axle, I believe that this is a much better method than the alternatives. At least a few FiberglassRV members have done this. My guess is that by the time you're done, it's probably as cheap to buy a whole straight axle assembly (with hubs and brakes) as to put existing hardware on a new tube with spindles.

Drop-beam axles routinely have the springs clamped under the the axle tube (spring-under), so as an alternative some people raise the trailer by changing to a spring-over configuration, which has about the same 4" effect with common axle tube diameters and spring pack thicknesses in the common 3500-lb capacity range. Unfortunately, the tube stays down there the same distance from the ground, which is not good for those who are looking for better clearance of objects on the ground (e.g. rocks).

There have been a few discussions of the pros and cons of raising a trailer, but I'm sure that 4" will make a significant difference in trailer dynamics. The way to get a more moderate rise would be a drop axle with less drop, but they don't seem to be commonly available in anything but 4" and maybe 3"; it doesn't seem to me like one inch would be worth an axle change.
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Old 03-13-2006, 07:26 PM   #4
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Quote:
I'm guessing that Roger is thinking that the Amerigo has a rubber torsion axle, but from Dan's description I think it has a [b]beam axle on leaf springs, like my Boler B1700.

B1700 owners have changed from the stock 4" drop-beam axle (axle tube centre is 4" below the hub centres) to a straight (no drop) setup. If you must raise a trailer with a leaf-spring rigid axle, I believe that this is a much better method than the alternatives. At least a few FiberglassRV members have done this. My guess is that by the time you're done, it's probably as cheap to buy a whole straight axle assembly (with hubs and brakes) as to put existing hardware on a new tube with spindles.

Drop-beam axles routinely have the springs clamped under the the axle tube (spring-under), so as an alternative some people raise the trailer by changing to a spring-over configuration, which has about the same 4" effect with common axle tube diameters and spring pack thicknesses in the common 3500-lb capacity range. Unfortunately, the tube stays down there the same distance from the ground, which is not good for those who are looking for better clearance of objects on the ground (e.g. rocks).

There have been a few discussions of the pros and cons of raising a trailer, but I'm sure that 4" will make a significant difference in trailer dynamics. The way to get a more moderate rise would be a drop axle with less drop, but they don't seem to be commonly available in anything but 4" and maybe 3"; it doesn't seem to me like one inch would be worth an axle change.
brian your right on the funny thing is we did all the measureing and by going with the straight axle over the 4" drop the trailer is only beig raised by 2 1/2 inches just perfect for the tires to fit in the wheel wells better ..
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Old 03-13-2006, 08:11 PM   #5
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Ah-ha! A straight axle vs. "drop" axle... ok... NOW I gotcha!

Well then, disregard everything I said past hello...

Roger
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Old 03-15-2006, 09:45 PM   #6
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I changed my 4" drop to a straight last fall on my Boler 1700. I was not willing to go to the expense of a total custom tube and the stock tubes were either 2" to narrow or 2" wider. After a bunch of measurments I found the wider worked just fine. Then when I was ready to order I discovered that the spring centers on a 3500 lb tube were to narrow and after they did some calculations they said I would be knocking about 750 lbs of the rating by sticking with the 50" centers of the existing frame. By adding 2" to each side of the frame I was able to get back into the acceptable spring center range. My brother has a metal shop in his business so he was able to fab four custom brackets which we welded on and mounted the new springs. If I didn't have the brackets I would have welded on 2" x 5" box tube to the sides of the frame. For the running gear I ended up ordering an entire set - axle, springs, hubs, e-brakes. I just couldn't verify the condition and proper fit of the old stuff to the new beam and it just wasn't an area I was willing to take risks.

After I had ordered and received everything from SouthwestWheel.com, Dexter finally returned my email from about a month earlier. They said a way around the spring center issue if you didn't want to mess with widening the frame would to go with a custom beam by using a 5000 lb rated tube and fiting it with 3500 lb spindles. It was pricey from them. I suppose it would have been a whole lot easier in terms of time. In the end I am happy with my decision and going wider with the springs while going up with the axle balances out any roll stability concerns. Now when we boondock on the logging roads we don't get caught up on the bumps and rocks.
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Old 03-17-2006, 09:32 PM   #7
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well the axle arived today including all mounting hardware the son and i will install in the morning etrailer part was great ordered 11:45 sunday night recived this am.
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Old 03-18-2006, 08:44 AM   #8
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Dan -- thanks for the site. Our Scamp is near the end as far as the torsion axles are concerned. It's one of the older ones with the light duty axles.

It also has a 4 inch drop coupler with a dinky 1-1/2 ball size. This combo would be OK for a small car type tow vehicle, but is a little ridiculous behind a full size Blazer.

Oh well! What's another project.
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Old 03-18-2006, 12:37 PM   #9
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Quote:
Drop-beam axles routinely have the springs clamped under the the axle tube ([b]spring-under), so as an alternative some people raise the trailer by changing to a [b]spring-over configuration, which has about the same 4" effect with common axle tube diameters and spring pack thicknesses in the common 3500-lb capacity range. Unfortunately, the tube stays down there the same distance from the ground, which is not good for those who are looking for better clearance of objects on the ground (e.g. rocks).
This was the situation I encountered with my Compact Junior. I speculate that it was configured that way to make the trailer lower, in combination with the drop roof section, in order to allow the trailer to be easily stored in a garage with a standard 7' high door. But I was always dragging the bumper in the gutters of driveway curb cuts. It's hitch height was something like 6" A good match for a Mexican Low-Rider...
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Old 03-18-2006, 07:30 PM   #10
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A somewhat related question for you folks who have replaced a worn torsion axle (on a 13' Scamp): what increase in overall height have you noticed? My admittedly worn-axled c. 1985 Scamp fits in my garage right now with a few inches to spare. Should I plan to expect that it will no longer fit in there (without removing wheels, etc.) after I replace the axle?
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Old 03-18-2006, 07:46 PM   #11
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...what increase in overall height... My admittedly worn-axled c. 1985 Scamp fits in my garage right now with a few inches to spare. Should I plan to expect that it will no longer fit in there (without removing wheels, etc.) after I replace the axle?
I have not replaced a rubber torsion axle, but I have read the manufacturer's material on their web sites. Precise values depend on the maker, but in general the arm (which connects the hub to the tube that goes across the frame) only moves about 35 degrees from no load to fully loaded. The arm is 5" to 6" long (depends on brand). If the worn axle's arms sit right down as if they are fully loaded, and the new one sits right up as if there is no load, that's only a couple of inches. The tables in the application guides on the websites (Dexter's is the most complete) give this full travel distance.

I doubt the trailer would rise "a few inches" with the replacement, unless you choose an axle with the arms set at a different angle than before. I'm sure Scamp can provide the stock angle for that vintage. If it were mine, I would determine what distance I wanted from hub centre to frame, then look at the charts to find the "starting angle" which would get me there when loaded.
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Old 03-18-2006, 08:08 PM   #12
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... the funny thing is we did all the measureing and by going with the straight axle over the 4" drop the trailer is only beig raised by 2 1/2 inches just perfect for the tires to fit in the wheel wells better ..
I don't understand how the 4" spindle-to-tube change makes only a 2.5" frame rise, so I must be missing something. Dan, are you also planning to change the springs or their mounting?

I clipped a bit of the illustration in Al-Ko's 3500 lb axle brochure and marked it up to show what I mean:


Name:   StraightAndDropAxles.JPG
Views: 124
Size:  4.3 KB

If the springs are in the same place (against the those pads under the axle tube) then the straight axle places the hub 4" lower relative to the frame, which means the frame and body are 4" higher off the ground (and 4" further above the tires).
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Old 03-18-2006, 09:48 PM   #13
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the original drop axle was mounted under the springs but the new straight axle will be mounted above the springs...
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Old 03-19-2006, 07:55 PM   #14
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the original drop axle was mounted under the springs but the new straight axle will be mounted above the springs...
I wondered if this might be your plan, but other B1700 owners (different trailer, same axle considerations) report that the change between spring-under and spring-over makes about the same 4" difference, so it seems that going from an spring-over drop axle (likely the result of a previous owner's mod) and spring-under straight axle (a better configuration in my opinon) will have about zero net effect on ride height.

The distance from the top of the top-mounted pad (lower surface of the spring pack) to the bottom of a bottom-mounted spring pack (includes the thickness of the springs) is about 4" with a typical 3500 lb axle and 4-leaf spring, which is why the height difference in the conversion is about 4". If the Amerigo has a lower-capacity axle, the tube would likely be smaller, and the leaf spring packs thinner - it's still hard to see the conversion lowering only 1.5" (4'' up due to the drop removal less 1.5" down from the spring mod would give 2.5" net height increase). Of course, if you change springs at the same time, the new springs could be more arched than the originals.

Dan, you already have this worked out, so I trust it will come out as you expect - I'm just trying to understand just how...
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