tongue wt capacity limits?

[JAlford]

Just got back from last trip with RV, was forced to pull the Fox 5er with the '06 Megacab SRW as the '99 DRW was in the shop. Seemed to pull it fine on the way out, but found the springs over-extended by arrival. I weighed the rig upon departing, rear axle wt. 6140lbs, door listed axle wt rating 6600lbs.

Before return trip, bought elastometer overload springs rated to 8800lbs. On return trip, noticed that if pulling hard up grade, picked up a vibration similar to a clutch slipping. Question now is, could the spring be weakened dramatically enough to start axle wrap on harder pulling?



Truck - 06 Megacab - totally stock except for tires - 305/65R17 load E (BFG's)

Trailer - 04 Arctic Fox - 30ft

combined wt. - 20500lbs.



Has anyone else had this issue?

Jeff

 

[HBarlow]

I don't think so. Spring wrap occurs when severe torque loading is applied on starting a heavy load from rest. Pulling a steep grade at highway speed the truck and trailer are already moving at a steady speed so sudden additional torque is not being applied.

The vibration you feel must be something else. Could it be the torque converter in your 48RE? With all the power mods and heavy throttle application against a heavy load and steep grade you may have overloaded the tc.

 

[RVTRKN]

The 06 is stock with the 48re, his bombed truck is the 99 3500 with the NV4500.

 

[JAlford]

Could it be the torque converter in your 48RE? With all the power mods and heavy throttle application against a heavy load and steep grade you may have overloaded the tc.

HBarlow, that was the first suggestion from my mechanic. However, this truck, my '06 Megacab, has never had any power mods at all, totally stock since purchase new, so it would seem that overloaded is out. The other issue is that I am getting the same (or very similar) vibration in all gears, from dead stop. The entire rear driveshaft was rebuilt by a reputable heavy truck service only 3K miles ago.



The concern about the springs is that they did not hold the wt rating on the door stamp, and were damaged enough that the bottom flat spring (overload) is now curved downward on both ends significantly. When I arrived and realized that the truck was much lower in the rear than when I left home, you could see a reverse bend in the leaf stack, it was within 1/2" of touching the bump stops with just sitting in the driveway. I cannot find any cracks in the springs indicating that they broke, and both sides were identical in position.



I found a sheet in the owners manual that list the cargo capacity of this 3500 to be only 1298lbs, which is far below the axle rating (6600lbs minus the 3400 of the truck = 2200lbs capacity). Since I have never loaded the truck in the 6yrs I have owned it, I guess this never came up.



Jeff

 

[NIsaacs]

Before return trip, bought elastometer overload springs rated to 8800lbs. On return trip, noticed that if pulling hard up grade, picked up a vibration similar to a clutch slipping.

Jeff

I would guess it has something to do with the addition of the overloads since the issue was only on the return trip.



Nick

 

[AMink]

Check your u-joints. Maybe got a bad one in the axle rebuild? I had the same symptoms and thought it was my transmission. One joint was fried and replacement fixed the shudder.

 

[Road Dog]

The payload is based on the GVW and empty weight. You'll find that the two GAWR together exceed the GVW by quite a bit.

The measured weight is a static weight and bouncy roads can increase the the effective weight. Having said that, you shouldn't bend the springs or overload. You should get an opinion from a spring shop (where they build and repair spring packs). They would know a lot more than your mechanic. If the springs have softened I can see axle wrap and bad u-joint angles on even low loads.

 

[JAlford]

The payload is based on the GVW and empty weight. You'll find that the two GAWR together exceed the GVW by quite a bit.

The trucks GVW is 10,100 and the truck empty weight was 7650 when I bought it, which gives 2450lbs payload based on GVW. I have ask the local dealer to explain the 1298lbs cargo documentation, and they had no idea. They had never seen a similar document.

The measured weight is a static weight and bouncy roads can increase the the effective weight. Having said that, you shouldn't bend the springs or overload. You should get an opinion from a spring shop (where they build and repair spring packs). They would know a lot more than your mechanic. If the springs have softened I can see axle wrap and bad u-joint angles on even low loads.

I put overload springs (similar to air bags) on the truck to get it home. They are rated for 8800lbs, and did fine at supporting the truck. I got them from a spring shop, and he said they would hold the entire weight and act as the spring, and suggested that I might have the spring pack rebuilt when I got home, but he didn't think it was necessary since they were not broken, just bent.

Jeff

 

[JAlford]

Check your u-joints. Maybe got a bad one in the axle rebuild? I had the same symptoms and thought it was my transmission. One joint was fried and replacement fixed the shudder.

That is the next thing I will check. When I did an inspection on them before I came back, they seemed fine, no movement, but I didn't take the shaft apart. I was doing a full inspection to try and see what might have caused the springs to bend, never found anything. The truck has 125K on it now that I am back, was a 5K round trip. The rear shaft was just rebuilt, as I mentioned earlier. I could have gotten a bad joint though, will have the drivetrain shop that installed the joints and balanced the shaft take a look at it.

Jeff

 

[Wygate]

I vote bouncing while driving did the bending. Now I would re-check the U bolts and spring perches, if you had enough weight to bend the pack, good chance the spring perches are now bent a bit. This could allow a bit more wrap while on the gas pedal causing the vibration.
I have seen this with lifted trucks, lift blocks adding leverage and smashing the perch right to the axle housing.
Not a strong chance but real cheep to rule out...