Scamp Axle - Leading vs Trailing - Page 2 - Fiberglass RV


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Old 08-12-2013, 10:49 PM   #15
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Originally Posted by RogerDat View Post
I guess another question for Dexter would be is the common brake flange available for both 4 and 5 bolt hub configurations. Avoiding weird brake size would be important.
You don't need to ask Dexter - you can read their Application Guide, which shows all of their hardware.

All Torflex #9 axles use the same size brakes (7"). The only way to get a different size would be to go to a different series of axle, such as the #10, with up to 3500 pound capacity and 10" brakes. For each series of axle, there is a common or default bolt pattern, plus usually some alternatives. Typically, changing bolt pattern doesn't change anything else.

A #9 has a capacity of up to 2200 pounds, as already mentioned. If that's a lot more than the trailer weight, it can be built with shorter rubber rods giving it softer springing - and less capacity.
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Old 08-12-2013, 11:06 PM   #16
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Was told it the front floor dropped areas are in the way of a trailing arm.
Yes. The whole point of the original Boler chassis design - and a Scamp 13' is a Boler clone - is to be as low as possible, and that was accomplished by dropping the floor down below the frame in the middle. The axle can't go under that, since that would push the trailer back up, so the axle tube is behind the dropped section, with the arms reaching forward around it.

Switching to leading arm means putting the axle under the dropped section, on tall enough mounts to reach the frame. That raises the trailer and requires fabrication work, but you're raising it anyway and doing custom work anyway. I would see if I could get a trailing arm setup with a roughly zero or even up start angle to get about the same height without modifying the axle brackets or running the Torflex in a leading configuration. 22 degrees down seems like a lot for a configuration that works best with an up angle.
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Old 08-13-2013, 12:24 AM   #17
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That was my thought. 22* down on a leading arm axle with brakes seems scary to me.
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Old 08-13-2013, 12:52 AM   #18
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It seems like a better outcome would be to try to get a trailing arm setup even if it involves spacing the axle tube down from the frame to clear the dropped floor. Using a Flexiride axle in lieu of the Dexter would allow for ride height adjustment too. Leading arm @ 23 degrees down would act like a pole vaulter when the brakes are applied.
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Old 08-13-2013, 12:24 PM   #19
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When I touched base about making sure it was a 2200 lb. axle being ordered he told me since he was in Elkhart picking up a trailer to be worked on he had taken some pencil blue prints sketches to a different axle manufacturer Al-Ko.

Talked to someone he knows there. Was told they could manufacture axle as true leading arm and with brackets to match the install based on his sketches.

I know there is some internet debate over Al-Ko vs Dexter but there is also a pretty good chance the original axle is Al-Ko.

I also think there is much to be said for the idea of having an axle designed for leading arm install as opposed to turning a trailing arm around and making it fit by cutting off the "long" side of the bracket.

On posting the shop name and number he is going to talk it over with his brother. They really do not advertise or do much homeowner work, they primarily do commercial accounts that they have built up over generations of being in business. I was told to call back in a week to get an appointment to get axle measured, when I called it was another week before they could slip me in. I'm really only a customer because I bought a utility trailer they built.
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Old 08-13-2013, 12:52 PM   #20
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That was my thought. 22* down on a leading arm axle with brakes seems scary to me.
I'm not an expert but bearing down on the tires (side effect of trailer trying to pivot up) would increase traction up to the point where trailer tries to crow hop.

I know an old rule of thumb was 2/3 of the braking capacity was always supplied by the front wheels of a car or motorcylce because when stopping the weight shifts forward and bears down on those tires. Same as with a leading arm trailer axle. Rear wheel was losing weight (traction) during a stop which seems more like a trailing arm would act.

This behavior was one of the reasons for front disk and rear drum brakes being a common configuration in the past on motor vehicles, you got a lot more benefit from the disk brakes on the front than you did from putting them on the rear.

I don't know if one axle configuration may be much easier to control than the other or have a more sudden degradation of effectiveness and control. Sometimes the difference between working great and going south can be very abrupt, it is easier to react when there is more warning that you are getting closer to the limits of good operation.

What did the old Scamp 16's have? Leading or trailing? Brakes or no brakes? Angle might also be important if they had leading arm with brakes.

I think that was part of the reason for the suggestion of using the digital brake controller, to get that fine tuning that is a key to making that configuration "good".
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Old 08-13-2013, 03:09 PM   #21
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Roger, you raise some good points. I can't counter 'em, only tell you what & why I did it the way I did. I talked to an engineer at Dexter before finalizing my axle replacement (you're correct, my original axle was an Al-Ko, leading arm, no brakes). The engineer told me that they no longer built 'off the shelf' leading arm axles but had no objection to building a #9 axle in that configuration, with brakes, & it would work as well as trailing arm. I determined I wanted 22.5 degree down start angle, 7" electric brakes, & 5 on 4.5 hubs, as well as 'high In', side mount mounting bracket kit. The side mount kit adds 1/4", the 'high' mount bracket 1", & the portion of the old axle bracket I left welded to the trailer chassis another 1/4", giving me an added 1 1/2" plus whatever the 22.5 degree down start angle would add, depending on my tires (remember, I was sitting at better'n 10 degrees up & the radial automobile tires were occasionally contacting the underside of the wheel well on bumps).

I'd received an e-mail from Trent Fisher at Scamp stating that my original axle should have been a 22.5 degree down start angle. I found that very hard to believe as it was at that time sitting at better than 10 degrees up. Upon reviewing my pix of the old axle & using another forum member's procedure for determining original start angle I believe my old axle started at zero degrees (the square shaft that goes into the axle tube was welded into the torsion arm with opposing corners pretty well in line with the longitudinal axis of the arm).

I ordered the new axle from Dexter through Liberty Trailer in North Little Rock, AR, price $411 including the side mount kit & shipping to Liberty Trailer (I believe they get their stuff through Redneck Trailer Supply). My grandson took my trailer to his shop, set it up on blocks & jack stands, & we began the removal/installation shortly after noon by 'torching' off the old axle at the 'L' of its mounting bracket. After grinding the torch dross off the remainder of the old bracket we used a floor jack to raise the new axle into place (with the mounting kit attached), squared the end of the spindles with the center of the coupler (essentially the same position as the old axle), clamped it in place & 'tack' welded the mounting brackets to the remnant of the old brackets (had to cut & weld onto the trailer chassis 'spacers', from the brackets still attached to the old axle since the new side mount brackets were approx 1 1/4" longer in front than the old bracket remnant). We then unbolted the axle from the side mount kit, lowered it & welded the mounting kit in place. It was then a simple matter to raise the new axle, again square it to the coupler & bolt it to the side mounts. I'm not sure what your source meant by having to modify the mount to fit the drop floor in front?? We had no problem with the Dexter axle or mounts designed & mfg'd as a leading arm. If you take an axle mfg'd as trailing arm & switch the brake assemblies so you can mount it in a leading arm position you may possibly have a problem with the mounts?? If ordered from Dexter as a leading arm I'm pretty sure it'll fit if you've given them correct dimensions. We mounted the new wheels & tires & I was home before 5pm.

I've only towed my trailer a few miles since the axle swap (still working on my interior re-build) but have experienced NO difficulties. Of course I've not made any 'panic' stops but I don't expect any untoward trailer movement.

You'll note that the 'In' side mount brackets are designed so that the axle brackets fit 'inside' them. My measurements were close enough that it was a very snug fit for the axle brackets between the side mounts & the chassis on the 'curb side' of the trailer...

1st pic shows the axle mount from rear curb side. 2nd pic shows same side from forward of the axle. 3d pic shows street side rear & front. Welds are actually better than they look & I got good penetration without 'burning' the stock. Last pic is the old axle showing a better representation of the square shaft welded into the torsion arm, note one corner to corner axis is perpendicular to the arm's longitudinal axis...
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Old 08-13-2013, 08:34 PM   #22
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Harvey,
Thanks for taking the time to post those pictures and write up the process.

I think going off the Dexter catolog they only show trailing arm, the mounting bracket that is on that axle extends further one way than the other. Same as the original but in the opposite direction. Turning a trailing arm around puts the long side where it would run into the dropped section.

Looks like you and your grandson used the side mount bracket kit to successfully work around that. Being a commercial shop there may be a bit of reluctance to get that creative.

He was in Elkhart at Al-Ko plant on other business and took the sketch of my axle measurements with him. When he asked they said they could make it from that or if he wanted he could send them the old axle and they would copy it. I'm guessing if he had made direct contact with Dexter as you did they might well have offered a solution not in the catalog.

I think your old axle in that picture might possibly have a few more degrees of up angle than even mine. You know they could mount a plate behind the axle with marks showing axle true "age" based on what mark the arm lines up with. Ours would both be at or near the mark labeled "holy crap this is still on the road?".

It is good to hear that brakes on a leading arm at 22.5 degree down are not an out and out no-no. If it was I don't think Dexter and Al-Ko would both be willing to make them.

If he can get me a direct copy of the original at a good price I will be thrilled, and I bet it will make him more comfortable with installing it. As I told my wife even if it costs a bit more to get exact copy made not paying for custom install labor will offset that increase in the part cost. As long as the bottom line stays close to the same it's all good.
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Old 08-13-2013, 08:49 PM   #23
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Quote:
Originally Posted by RogerDat View Post
I know an old rule of thumb was 2/3 of the braking capacity was always supplied by the front wheels of a car or motorcylce because when stopping the weight shifts forward and bears down on those tires. Same as with a leading arm trailer axle. Rear wheel was losing weight (traction) during a stop which seems more like a trailing arm would act.
That's right for a vehicle with front and rear axles, but it has nothing to do with suspension geometry, and the trailer only has one axle (or a set of axles acting like one in the case of a tandem) - not front and rear axles.

The corresponding situation in a trailer is that during braking load (the vertical force) shifts forward to the hitch, and thus away from the axle... regardless of whether the axle is on leading arms, trailing arms, or leaf springs.

Weight doesn't actually shift (because weight is the force of gravity on a mass, and neither gravity nor the mass are changing): the front axle or hitch must carry more load and the rear less, to produce a torque (or moment, or force couple) which to resist the effect of the braking force being applied down at ground level instead of up at the centre of mass.
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Old 08-13-2013, 08:53 PM   #24
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... a different axle manufacturer Al-Ko.

Talked to someone he knows there. Was told they could manufacture axle as true leading arm and with brackets to match the install based on his sketches.
I don't think there will be anything specifically leading about the Al-Ko axle - they just have shorter standard brackets which will more likely fit, so a bracket modification might not be necessary. It might also have toe-in set to an angle desirable for leading arm use - that would be useful.

There are bracket options from various manufacturers which are not generally offered to the public and not shown in the catalog, to accommodate the specific needs of OEMs. The U-Haul travel trailers had an example of this, which causes difficulty for later replacement. A trailer manufacturer (even a small one) might have access to one of these options which might make the Scamp installation easier... great if there is and you have the contact.

Quote:
Originally Posted by RogerDat View Post
I know there is some internet debate over Al-Ko vs Dexter but there is also a pretty good chance the original axle is Al-Ko.
There is little functional difference between a Dexter Torflex and the standard North American Al-Ko rubber axle (the Al-Ko Euro products are different); I'm sure either will work fine. The Al-Ko six-sided outer tube and three-lobed inner tube are probably an advantage, but may not make a useful difference. Different brands may have different arm lengths (Flexiride, for instance, is much shorter than Torflex in this size range), which would affect mounting location.
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Old 08-13-2013, 09:09 PM   #25
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I think going off the Dexter catolog they only show trailing arm, the mounting bracket that is on that axle extends further one way than the other.
The leading axle should look exactly the same - just change the "direction of travel" arrow on the diagram (if it had one). The bracket is longer in one direction, not because the rear side should be longer, but because the bracket should be where the load is, and that's where the hub is.

Imagine a trying to balance a load on one point on the bracket. That point would be right over the centre of the hub... six inches from the middle of the cross tube. A sensible bracket for this type of suspension is much longer on the side toward the hub than the other, whether that direction is forward or rearward.

Al-Ko tends to make their brackets nearly symmetric, rather than longer on the side that should be longer. I think I know the reason, but it doesn't matter - the Torflex bracket is right the way it is, and shouldn't be any different if you turn the unit around.
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Old 08-13-2013, 09:39 PM   #26
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That's right for a vehicle with front and rear axles, but it has nothing to do with suspension geometry, and the trailer only has one axle (or a set of axles acting like one in the case of a tandem) - not front and rear axles.

The corresponding situation in a trailer is that during braking load (the vertical force) shifts forward to the hitch, and thus away from the axle... regardless of whether the axle is on leading arms, trailing arms, or leaf springs.....
I think the concern expressed by some is leading arm would have more tendancy to let the wheels act as something of a fulcrum during hard braking. Trailing arm less so. The greater the down angle the greater that tendancy.

My thinking is that the hitch and TV rear tires will take pretty much the same force no matter which axle type. Hitch acts like front wheels on a car when stopping, more force goes there than stays on the trailer (rear) wheels. Which is what it sounds like you are saying happens.

My guess (and it is just a guess) that under some braking conditions the leading arm by being angle in the direction of travel may have more traction, but at under extreme braking they may go squirrely in a different way, or at a slighty different point.

E.G leading arm might crow hop if locked up and trailing arm might skid.
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Old 08-13-2013, 09:59 PM   #27
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The leading axle should look exactly the same - just change the "direction of travel" arrow on the diagram (if it had one). The bracket is longer in one direction, not because the rear side should be longer, but because the bracket should be where the load is, and that's where the hub is.

Al-Ko tends to make their brackets nearly symmetric, rather than longer on the side that should be longer. I think I know the reason, but it doesn't matter - the Torflex bracket is right the way it is, and shouldn't be any different if you turn the unit around.
Look at the picture Harvey posted of the old axle, you can see it does not extend to the hub center, or anywhere close to it. Instead you can just spot the vertical welds where it attaches to the drop floor frame.

I'm guessing that being welded into the corner of the drop floor frame is what imparts the strength that would be associated with having the bracket longer in that direction and having the bracket run straight down the frame.

What your saying makes sense. What I said about having a bias toward sticking with what the original engineer came up with is what makes me willing to wait and see if Al-Ko will make the axle with that exact same bracket.

You also raise a good point on the toe-in.
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Old 08-16-2013, 08:47 PM   #28
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It seems that a trailing arm design would overcome bumps in the road better than a leading type, due to the direction of travel when compressing. You would think that when the tire strikes an obstacle in the road that it would be driven upward and backward if un-restrained. That would compress a trailing arm following fairly close to its travel arc which would go upward and backward. A leading arm would travel upward and forward during compression and the arm if set at around 23 degrees down would be nearly aiming straight at the oncoming path of the force. Since the arm doesn't telescope into itself to absorb the bump the trailer will just jump up over the obstacle instead of the suspension absorbing the hit which it is supposed to do. If the starting position of the axle was near 0 degrees (level) then the differences between leading and trailing link would I think be minimal. Just speculating about this.
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