Getting more clearance under your TT - Fiberglass RV


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Old 08-29-2007, 02:28 AM   #1
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Name: Val
Trailer: 1988 Bigfoot Deluxe B19 19 ft / 2007 Nissan Frontier V6 NISMO 4x4
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Wanted to share a success story:

Our Bigfoot had such low clearance that we had a hard time backing it into our driveway... which has hardly any slope to it. After looking at photos of other Bigfoots whose owners had moved the leaf springs over the axle to gain clearance, I realized we needed more clearance under the axle itself as well, not just the trailer body. So, after reading some of the forum discussions, I decided to have the drop axles replaced with straight axles.

This is the original drop axle:

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This is the replacement straight axle:

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I asked about adding shocks and our axle guy said that, in his opinion, they are not worth the additional cost of installation because they don't get enough movement on this type of suspension to actually do much--that on a 4 x 4 truck, they are great, but on a trailer like this, they don't get much use because the leaf springs tend to absorb and equalize any movement before it affects the shocks. So, I opted to wait to see how it rides on rough roads without them.

Now I will have to take my Equalizer wdh into a shop to get the bolts loosened so that I can change the ball height to be level with the trailer's new height. I tried getting them loose with a wrench...HA, nothing doing... even standing on the wrench didn't budge the bolts (but that always makes a gal feel so svelte)!

Also, something that I hadn't expected: After the axle change, I tried raising the electric tongue jack footing to see how the trailer would sit on just its wheels (i.e. not supported by the tongue jack)... to my great surprise, as I raised the tongue jack, the tongue got lower and lower and lower... all four wheels remained on the ground, but the tongue was as low as it could get with the wood blocks still under the tongue jack footing. Before the axle change, I could raise the tongue jack footing all the way up and the trailer remained level, with the trailer tongue in the air, not on the ground. I called Axleman right away to ask why this was happening... apparently, he had noticed that the suspension equalizers had been overtightened and had loosened them just enough for them to work properly, so as to allow movement between the tandem axles as the trailer goes over bumps. Which means that now, the tongue weight actually rests on the tongue jack and will tilt the whole trailer tongue to the ground if not supported. Well, once he explained it, it made sense, but it sure looked weird after having gotten acclimated to how the trailer sat with the suspension overtightened!

Total cost to replace the axles was $386 USD, and the clearance is sooo much better! Notice how there is now 4" more clearance under the axle and the body both:

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Nifty nifty!
Val
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Old 08-29-2007, 08:15 AM   #2
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You did the right thing, Val!
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Old 08-29-2007, 10:29 AM   #3
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Thanks for the report, and the excellent illustrations!

I agree that to raise a drop-beam leaf-spring suspension, eliminating the drop is definitely the better way to go.

I believe - based on my own experience of adding shocks to a leaf-spring axle - that the axle guy is mistaken. Fortunately, it's easy to add them later, so it's not as if a big opportunity has been missed at this point. The additional work of doing it later is just eight more nuts (the ones on the U-bolts) to remove and replace (plus, of course, taking the wheels off again).

The thought that the equalizer links were frozen so tight that there was no equalization is scary. Every dip and hump in the road was significantly changing the load carried by the coupler, and thus on the hitch! It can also mean that one axle at a time was being momentarily overloaded.

As a techie (geeky?) side note, the fact that the tongue hung in the air means that the centre of mass (balance point) of the trailer is no further forward than the leading axle.
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Old 08-29-2007, 10:48 AM   #4
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Price and work sounds pretty good Val. Who did you use here in Phoenix, I may need an axle change this winter?
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Old 08-29-2007, 01:42 PM   #5
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I need to make a trip to Phoenix to take advantage of this pricing. Haven't priced it out here but I'd bet that I can't get my single axle done for as cheap as what you had your double axle done for!
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Old 08-29-2007, 02:36 PM   #6
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Greg, it was Ken of Ken's Mobile Trailer Repair and Maintenance, based out of Phoenix, tel. 623-561-2904. Tell him that you saw my post on the FGRV forum... I told him I was taking photos to share with the forum, but he isn't into computers at all, so I think he had no idea what I was talking about!

Quote:
I believe - based on my own experience of adding shocks to a leaf-spring axle - that the axle guy is mistaken. Fortunately, it's easy to add them later, so it's not as if a big opportunity has been missed at this point. The additional work of doing it later is just eight more nuts (the ones on the U-bolts) to remove and replace (plus, of course, taking the wheels off again).
I mentioned several times how many FGRV forum people had said that shocks made a big difference to the ride and inside trailer movement, but Ken was quite insistent that we try out the new axle set up first, though he seemed willing to put shocks on later if we decided we still wanted them. I think he mainly works on tandem axle trailers and larger, so I wonder if having tandem axles has anything to do with his strong opinion about the non-effectiveness of shocks on trailers? He went into a lot of detail about it and I thought it was very ethical that he didn't just slap them on and charge us for them if he didn't feel it was worth the expense (even if we end up disagreeing with him). The true test will be when we take the BF on some bumpy roads, which should be in about two weeks... we are going to the Rally that Gina is putting together in the San Bernadino Mtns, and I believe that there might be some unpaved roads up there for us to try. Brian, will you share more of what difference the addition of shocks made for you (and on what type of rig and suspension)? We do expect to take our TT on some rough unpaved roads, so definitely want to protect it (and contents) as much as possible.

Quote:
The thought that the equalizer links were frozen so tight that there was no equalization is scary. Every dip and hump in the road was significantly changing the load carried by the coupler, and thus on the hitch! It can also mean that one axle at a time was being momentarily overloaded.
Yeah, Ken said the same thing and that having it so tight could have caused an axle to break from being overloaded. I am all the more grateful that we drove it all the way from BC without incident... whew!

Quote:
As a techie (geeky?) side note, the fact that the tongue hung in the air means that the centre of mass (balance point) of the trailer is no further forward than the leading axle.
If I understand this techie language, you are saying that when the equalizer was frozen tight, the weight of the trailer was balanced over the forwardmost axle, but what exactly does that mean in terms of proper weight distribution ratios... why is it that 10% of the trailer weight should be on the tongue, rather than all the trailer weight sitting balanced on the two tandem axles? Inquiring still-newbies want to know!

Elaine, you should come to Phoenix in the winter and get your axle replaced! It's gorgeous here in winter... and Kayla knows all the best hiking spots in the nearby Superstition Mountains... we love AZ... in the winter!
Val
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Old 08-29-2007, 03:39 PM   #7
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Quote:
you should come to Phoenix in the winter and get your axle replaced! It's gorgeous here in winter... and Kayla knows all the best hiking spots in the nearby Superstition Mountains... we love AZ... in the winter!
Val
I visited Phoenix a couple years ago in March and found the weather very agreeable A nice change from here!
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Old 08-29-2007, 06:15 PM   #8
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Quote:
If I understand this techie language, you are saying that when the equalizer was frozen tight, the weight of the trailer was balanced over the forwardmost axle, but what exactly does that mean in terms of proper weight distribution ratios... why is it that 10% of the trailer weight should be on the tongue, rather than all the trailer weight sitting balanced on the two tandem axles? Inquiring still-newbies want to know!
You've got it! The weight was balanced somewhere between the two axles... if it were any further forward than the leading axle centre it would have tipped down on the tongue.

The distribution of load between axles and tongue is determined by the [b]relative distances to the centre of mass. For 10% tongue load, that centre would be 1/10 of the way forward from the middle of two (equalizing) axles to the tongue. That's only a foot or so, so that's going to be between the axles (which are two to three feet apart). No problem.

If the fraction of weight carried by the tongue is higher, the [b]balance point (centre of mass) might be forward of the leading axle so the tongue would tip down (with or without equalization) - still no problem.

With braking and acceleration, load shifts on and off the tongue (tongue/hitch weight goes up and down); with no tongue weight at rest, the trailer would be pushing up and down on the hitch, which is unpleasant if any part of the hitch system has any free play (and they do).

Since the tow vehicle must [b]control the trailer, it needs some [b]traction... and that comes in part from hitch weight. With no hitch weight, there had better be minimal force needed to control the trailer (which is the case for "full trailers", which have their own steering axle and a bar to guide them), but normal trailers need some significant sideways force to keep them under control. The load of carrying the hitch weight "sticks" the tug down better.

In an era when all tow vehicles had rear-wheel drive, hitch weight added [b]drive traction... but the opposite is now the case for many of us. My Sienna would have better pulling traction if my Boler had no hitch weight at all!

Finally, the tires of the trailer provide the sideways force to keep most of the mass of the trailer in line. If they are further from the hitch than the centre of mass (balance point) they have some [b]leverage advantage. Although my description of this last part is seriously over-simplified, it is a factor in trailer stability, and reason to keep the balance point ahead of the effective axle location (middle of a tandem pair).
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Old 08-29-2007, 06:43 PM   #9
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You da MAN, Brian!

Would the overly tight equalizer and resulting incorrectly balanced weight have anything to do with why the trailer was really "uncomfortable" to tow when I drove it to Camping World without the sway bars last week (had to take the sway bars off to back into the driveway as they were literally getting stuck on the concrete because of course, with how low the trailer was, they were nearly ground level). I was giving all the credit to the eqaulizer bar for how well the trailer had towed from BC (and, based on forum comments, it probably deserves a lot of that credit, but I am thinking now that the way the trailer was handling without the sway bar was probably much worse than it would be now that the weight balance and tongue weight is normalized).

Val
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Old 08-30-2007, 05:09 PM   #10
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I've seen quite a few tandem-axle trailers which are so far from level that even a working equalizer link couldn't keep them from having too much load on one axle; usually they are fifth-wheel and gooseneck rigs on trucks which are too tall for the trailer, so they are excessively loading their rear axle and driving hitch weight up, but those are trucks which can handle lots of hitch load.

With the equalizer frozen, any deviation from the right hitch height would change the hitch weight, and either to high or too low would not tow well. If applying weight distribution spring bars helped, maybe the hitch weight was too high (suggesting that the hitch might be too high).
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