Undersized axles on Momentum 320G or just poor design?

[chikenstiker]

I wouldn't beat yourself up over the lug nuts - most of us probably would have missed them being overtightened?
You put a torque wrench on set the the right ft-lbs and it "clicks" so you assume they're tightened correctly - what are the chances you'd have caught an overtightened/stressed lug nut?
And in your case it would have been pretty difficult to stand there and watch every step the welder & techs did even if you're retired as most of them won't let you watch.

Nice part is you're sharing and it's going to stick with several of us and somewhere-sometime what you've shared will keep someone else from having a horrible experience.

Where are you measuring the axle dimensions from?
The engineer part of my brain is thinking the absolute true value needs to be derived from having the 5th wheel unhooked and level with relatively the same weight on both sides & axles, then attach a plumb bob to the 5th wheel pin to put a mark on the ground (could be front, center, or rear of the pin just as long as it's centered side to side), then use the plumb bob to put marks on the ground at the front & rear axle spring brackets and run a triangulation measurement. If my brain hasn't taken a wrong turn this should provide a pretty accurate way to verify alignement? Also have an idea on how the same thing could be done with a reflectorless survey instrument and a drive-over pit like at one of the oil change places that would be even more accurate!
Yes, I overthink things sometimes.....


As for the rest, I have my own issues with Grand Design having bought this 5th wheel just prior to Covid taking off and still have unresolved pre-delivery items 2 years later plus some added items.
It just doesn't seem possible to get decent product support anymore from anyone and it's very disappointing.
Will have to say I did by pure chance wind up in an RV park in the Benson, AZ area a little over a year ago where a GD factory tech was staying, we visited and I let him know about my issue with finding someone to walk me through the different systems as it was close to 2 months between my pre-delivery walk-through and when delivery actually happened due to Covid so I'd forgotten so many things. He was going to help me out but then had a rush call to an event where several people needed help, but when he heard I'd found a leaking water pump when cleaning out the garage area and finding water he made time to stop and help, replaced the pump in no time and was very personable and definitely knew his stuff.
I'd gladly pay that person a bit of money to walk through my 5th wheel and help me understand the systems better!!! (I've offered 3 separate GD dealership $$$ to do the same thing and been turned down each time)

Our post-Covid world is a far lesser place than it was prior to Covid.

I think you misunderstood me, none of the wheels were torqued, not overtightened. The lug nuts were ALL loose! I had to tighten every single one and a couple took 3 full turns to tighten and the wheel that almost fell off had 2 broke, 2 stripped from the wobbling wheel and only a thread or 2 max left on the last 4. Wheel was wobbling again as I pulled into the dealer!

Measurements are per LCI as to their specs.

Front of Frame to Middle Hanger Bolt Center Spec: 187 5/8"
Mine before "Fix": R 185" and L 185 5/8"
Mine After "Fix": 187 1/4" and 187 3/8"

Hangers center to center Spec: 30 1/2"
Mine before Fix: 3 were correct 1 was 30 7/8"
Mine after Fix: Front 30 7/8" Rear 31"

I also Plum bobbed the Pin and measured to each tire front as another data point and after fix it was ~1/4" off

[RoyB]

Holy cow that is scary. Glad you did not have a serious accident!!

An update on my situation, I bit the bullet and paid for the Morryde IS and disk brakes. They got me in way ahead of schedule (~2.5 month wait). The cost was not cheap (approx $9,300 with tax). However, the cost to get out of my current paid-off camper and purchasing a new one with 8K lb axles would had cost far more than $9K for the same horse and buggy axles. I will make a separate post about the whole procedure in a couple days.

In the interim though, I will share a little.
They recommend coming in loaded up. I had my (2) ATVs (700 Kodiak), half tank of fuel for generator, and approx 80 gallons of fresh water. No food since we didn't camp, approx 40% full black and gray tanks (front).

With 7K lb OEM axles/drums
Trailer axles: 14,760 lbs. As a side note, I could had added approx 200 lbs to that figure had the fuel tank been full and the ATVs been gassed up since they were only 1/4 full.
Pin weight: 2,300 lbs. 13.48% of entire trailer weight (this would had been quite a bit less if front tanks were empty)

With 8K lb IS axles/Disk brakes
Trailer axles: 15,560 lbs. They had to remove my spare tire and I put it in the back of my truck. So the IS setup added approx 850 lbs.
Pin weight: 2,480 lbs. 13.66% of entire trailer weight

They were able to add approximately 3-4" lift to the trailer and I was able to drop my goosebox a set of holes (2"). This increased my bed rail clearance all the way around and the trailer tows level now vs 3" down in the rear (which also added a tiny bit of pin weight).

Now some of these figures may be +/-. After the axles I weighed at the same scale but had burned approx 11 gallons of fuel. However, the spare tire did not fit under the camper with the new axles so I had the spare camper tire in my truck which should had accounted for the missing fuel weight. I also weighed with my wife in the truck and our bags for the trip. We used the toilet a couple times which moved maybe 4 gallons of water to the pin from the axles. I weighed the camper the first time before traveling, so some of the water could had sloshed out between the 200 mile round trip journey.

It appears the pin gained some weight from leveling out the camper and the hydro pump. However, it's still grossly under weight imo. It really teeter-totters at times. However, the trailer seemed to track straight, stop pretty good and most importantly, I am not overweight on my axles.

It should be noted that this is likely heavier than we would normally tow. We only carry that kind of water when boondocking with the ATVs. Even then, that's more water than we need for 4-5 days because we are limited by the gray tank. The real test of tracking will be when the trailer is empty as that is when I noticed the most sway. I could likely had gotten regular 8K axles + disks installed for significantly less, however I called a few shops and no one was interested in doing it. Even camper stores. In addition, I wanted the extra height which is not easily accomplished without welding in steel which would had raised the price more. My total clearance now is approximately 13'-6". The trailer only went up 1/4" when I took 1600 lbs of ATVs out of the garage, but I fully expect the suspension to settle a hair bit with some age on it which should bring it back to 13'-6" unloaded.

At the end of the day, I just bought another 4-5 years with this camper upgrade. Our situation may change in the next 4 years and we may purchase a different model. But for now, it's reassuring knowing that we won't be overloaded on the axles. We are over the technical trailer gross, but I understand the trailer gross does go up from the factory with 8K lb axles. Coupled with the response from GD that the frame does not change to increase the gross tells me that the figure is solely from the axle ratings.