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Old 11-13-2013, 08:06 AM   #1
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Axle placement

When we purchased our camper, one question I had that was never answered to my satisfaction was - is it better to have axle placement over or under the springs. Since my camping time is limited due to the oncoming winter, I thought I would as the forum to see if anyone can tell me. Any thoughts?
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Old 11-13-2013, 11:34 AM   #2
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Many owners have had to flip the axles( from on top to under the springs) for ride height/ clearance issues, with minimal handling problems, bought on by the raising of the trailer's center of gravity.
Does the axle placement put extra strain on the springs , bushings and shackles; due to the added leverage of the side loading.
Good question, that would require long term study.
Maybe we can get a grant. Couple of million and we should be able to figure it out.
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Old 11-13-2013, 03:22 PM   #3
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If you can find the grant form, I will help fill it out....now who wants to do the hard part?
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Old 11-13-2013, 06:46 PM   #4
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Quote:
Originally Posted by Kdjay View Post
When we purchased our camper, one question I had that was never answered to my satisfaction was - is it better to have axle placement over or under the springs. Since my camping time is limited due to the oncoming winter, I thought I would as the forum to see if anyone can tell me. Any thoughts?
The only difference is center-of-gravity and ground-clearance, as far as the trailer is concerned. As Skip said, some must move the axles under the springs to obtain a level towing condition for their truck and trailer. Someone makes/sells a kit for this modification, as the axles must not be rotated.
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Old 11-13-2013, 09:28 PM   #5
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Look at the vertical distance from the center of the axle to the center of the spring shackle bolts on each setup. You will find that the axle under the springs has a much greater sideways leverage on the spring eyes. I would think that there may be more bushing wear and spring breakage as a result. Yes, my springs fatigued and broke.
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Old 11-13-2013, 09:38 PM   #6
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Look at the vertical distance from the center of the axle to the center of the spring shackle bolts on each setup. You will find that the axle under the springs has a much greater sideways leverage on the spring eyes. I would think that there may be more bushing wear and spring breakage as a result. Yes, my springs fatigued and broke.
You are correct. Plus more stress to frame where spring shackles ar mounted.
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Old 11-14-2013, 01:57 AM   #7
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Look at the vertical distance from the center of the axle to the center of the spring shackle bolts on each setup. You will find that the axle under the springs has a much greater sideways leverage on the spring eyes. I would think that there may be more bushing wear and spring breakage as a result. Yes, my springs fatigued and broke.
Depending on the rating of the axles (ie., axle tube diameter), you'd be increasing the leverage effect by around 3-4". That's a lot and can make a big difference in side to side movement of the suspension, especially if the TT has a weak frame design to start with. Also, some trailers have 4" high spring hangers and some have 6" tall ones (like ours) which adds another couple of inches of leverage.

Our unit has the axles under the springs and the plastic spring bushings were all completely worn from the day we took possession at the dealer. All it took was just over 2,000 miles of delivery from the plant to the dealer on the west coast. Anyone with the tall spring hangers and under-slung axles would be smart to check the bushings, even on a newer unit. In the case of Lynnmor's TT, which just happens to be the same model as ours, he ended up with broken springs. One thing you can do to help prevent this is to tie the bottom of the spring hangers together from one side of the trailer to the other. You can do it yourself or you can buy a kit for this. Installing brass bushings to replace the plastic ones would also be a good idea, which is what I'll be doing shortly using the Dexter EZ-Flex kit.

The photo below is our trailer coming out of a very tight spot in a campground. The side loading and increased leverage due to tall spring hangers and under-slung axles forces the axle tubes to bend and the frame to flex. This will happen while towing too and is not good for the tires or the frame & suspension. The worst thing that can ultimately happen is cracks and separated welds in the frame (ask Lynnmor).

If you see a TT with 3 entry steps, it's probably got the taller spring hangers and/or under-slung axles. I think the reason that manufacturers do this is simply so that there are no wheel wells protruding into the interior space to interfere with anything.

Asking a dealer technical questions on something like a frame and suspension is futile...

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Old 11-14-2013, 06:37 AM   #8
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Another thought does the axel have camber
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Old 11-14-2013, 06:55 AM   #9
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Okay. So now I am getting the kind of information I needed before my purchase. I will have my husband liking at the springs and bushings. Also, including a picture of something else I don't really understand....what is the purpose of the cantilever system? Is this a better design or does it just give me something else to keep an eye on?
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Old 11-14-2013, 07:51 AM   #10
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That is an equalizing link--it allows for movement of the wheels/axles forward/backward/upward/downward in relation to each other. There are more sophisticated ones with rubber inserts for cushioning and also air bags for cushioning.
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Old 11-14-2013, 08:27 AM   #11
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Gosh, I love this forum! Thank you
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Old 11-14-2013, 09:49 AM   #12
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That is an equalizing link--it allows for movement of the wheels/axles forward/backward/upward/downward in relation to each other. There are more sophisticated ones with rubber inserts for cushioning and also air bags for cushioning.
Joe

The one shown is a rubber cushion Equa-Flex system. This helps with the harsh ride a bit, however on mine it was installed so sloppy that the wheels could move about way too much.
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Old 11-14-2013, 10:25 AM   #13
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I fail to see any draw backs from having the springs on top of the springs. 99% of all 5th wheels have the springs on top. Never hear much about spring failure. IMO it's more about how well the springs, axles and frame are built. Is there enough payload reserve so the TT's not overloaded? Overloading either setup is far more destructive than having proper spring/axle combinations. Find a TT that has over 2000lbs in reserve payload capacity and either set up should be fine.
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Old 11-14-2013, 02:39 PM   #14
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I fail to see any draw backs from having the springs on top of the springs. 99% of all 5th wheels have the springs on top. Never hear much about spring failure. IMO it's more about how well the springs, axles and frame are built. Is there enough payload reserve so the TT's not overloaded? Overloading either setup is far more destructive than having proper spring/axle combinations. Find a TT that has over 2000lbs in reserve payload capacity and either set up should be fine.
Well, there's two of on this thread that have experienced this problem first hand and it's not because of overloading. The spring hangers in our TT swing from side to side and has caused the bottom flange of the I-beams to be bent and distorted. It would just be a matter of time before there are fatigue cracks. In our case, the tall spring hangers and under-slung axles along with the lack of any re-enforcement have greatly aggravated the problem. In fact, a government certified frame shop that looked at it said it was the worst frame design they've ever seen. I've seen the identical design on quite a few other makes and models of TTs now. You can be certain some owners will eventually have problems but will probably be after the warranty expires. From an engineering perspective, tall spring hangers along with under-slung axles is not great unless there is some re-enforcement.

I really doubt there are many TTs out there with over 2K lbs in actual reserve payload capacity. They're often built to a minimum standard to be lighter in weight and cost competitive. And in doing so, they generally just don't have much actual reserve carrying capacity. If they did that, they'd be pricing themselves out of the market.

Many of the 5th wheel frames I have looked at have stronger frames and have more re-enforcement of the suspension. The higher elevation of the FW hitch point would make the lateral forces and movement somewhat different. I don't think you can compare FW frames to the ones on TTs.
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