Potential Causes for Sagging Leaf Spring on Passenger Side of 5th Wheel Trailer with Slideouts

Updated 09/23/2016 | Published 09/22/2016

Question:

2005 Mobile Suites 5th wheel. Tandem 7000 lb axles, Dexter 25 1/4 3500lb springs. This is a heavy trailer, 15 to 17,000 lbs loaded. Two years ago I noticed a bit of sag on the curb side. Curb side was an inch or two lower. I replaced the OE springs with Dexter 3500 lb same size springs. My theories being that the driver side springs did not know what was on the other side and the OEs had lasted nearly 10 years so the replacements would too. Wrong, Now the replacements are failing I guess. I have done a close visual inspection and see no other reason for the curb side to be low again. A close measurement of all four springs show the curb side with less lift at 4 spots I measured on each spring. I have not weighed individual wheels but the largest slide is right over the curb side wheels and my instincts tell me that side is heavier. So questions Should I insist on american made springs with american steel? can I get away with replacing the two on the curb side only? If I replace curb side only should I go up to a 4000lb spring? Or if I must replace all 4 should I go up to 4000 lb springs? Thank you

asked by: Stan Z

Expert Reply:

It is generally always best to replace trailer suspension components on both sides of a trailer. This can reduce the chance of tracking problems that can occur if the suspension characteristics are not symmetrical. If the springs on the curb side of your 5th wheel routinely wear/sag faster than those on the left side, and if this is where your largest slide is, then you may simply have a case of faster wear from that weight. Trailer loading naturally also affects wear and tear on the suspension.

Moving to higher-rated springs will provide a stiffer suspension but it will also tend to transmit more energy into the interior of the trailer where it can disturb its contents. You might provide your trailer VIN to the manufacturer and ask about the suitability of heavier springs. Changing springs will not increase the trailer's weight rating.

If your trailer is nose-high when it is hitched to your pickup then this will mean less of its total weight is resting on the hitch as pin weight; so this means more weight would be resting on the axles. 5th wheels and all other trailer types handle best when they are level with the road surface.

Note also that most roads are crowned, that is they are highest in the center and lower at the outside edges. If the trailer's stance is evaluated when it is sitting on a crowned road surface the passenger/curb side will indeed be lower.

Since you have made a thorough visual inspection of the trailer suspension you might have a trailer shop give it a look over if the above troubleshooting considerations do not apply.

expert reply by: Adam R