Porpoising over bridges

[Mopar_Earl]

Originally Posted by rkymntsno

What owners manual? The truck? How is that gonna tell me exactly where to put the gain with this trailer? Maybe I'm missing something here but this is the second RV I've owned and both gains we're set by the RV dealership with the hitch.

Yep, in writing. It tells you how to set up the controller. Usually it's warm up the brakes and doing 20 mph full manual lever stops and adjusting the gain to provide the max braking power without wheel lockup. It's been that way for many years. Aftermarket as well. Also the manual will tell you about settings other than the gain too. You'd be surprised what the manuals tell you.

Gain usually isn't a set it and forget it setting either. Normally needs changed from empty to loaded. Road conditions. Snow vs dry. Heavy traffic, etc. Also as brakes wear and aren't kept adjusted the gain will need increased.


Earl

[Lowmiler]

Originally Posted by rkymntsno

Thanks for the info. I too notice the dark areas not just after bridges but all over the highway and try to prepare for them. Sometimes kicking off the cruise to slow down. The brake controller trick is something I will have to try. I already had to kick up the gain to 5.5. I left the dealership at PDI at 4.5, set by dealership. Just the few months we've had it, felt like the trailer was pushing us at stops so gradually increased to 5.0 then 5.5. I think it's where it needs to be now, not that this thread is about a brake controller, lol.

Ironically, assuming we’re talking about same dark spots, those are tire marks from trailers coming back down after being airborne, due to extreme porpoising (bordering on sharking!).

[rkymntsno]

Originally Posted by Mopar_Earl

Yep, in writing. It tells you how to set up the controller. Usually it's warm up the brakes and doing 20 mph full manual lever stops and adjusting the gain to provide the max braking power without wheel lockup. It's been that way for many years. Aftermarket as well. Also the manual will tell you about settings other than the gain too. You'd be surprised what the manuals tell you.

Gain usually isn't a set it and forget it setting either. Normally needs changed from empty to loaded. Road conditions. Snow vs dry. Heavy traffic, etc. Also as brakes wear and aren't kept adjusted the gain will need increased.


Earl

Ok, I understand all of that and that is how the controller was set up to begin with on both RVs. It's just this fifth wheel seemed to need adjustment on the controller.

[videoguy]

Originally Posted by jamaddox

I have this problem also and wanted to confirm the rancho adjustable helped. My 250 came with rancho shocks but I guess not the good kind

I switched from the factory Ranchos (too stiff) to the adjustable Ranchos on my last truck (Silverado 2500HD) after 1000 miles to be able to soften up the ride when unloaded. I too would turn the firmness on the rears all the way up when towing. Towed great! Traded that truck with 46,000 miles an they still performed like new so they seem reliable as well.

New truck in my sig came with the standard, non-Rancho shocks that seem a little soft when towing the new rig so I will be upgrading the rears on this truck to Rancho adjustables too!!

Highly recommend!

[Unclerico]

RE: Ionically, assuming we’re talking about same dark spots, those are tire marks from trailers coming back down after being airborne, due to extreme porpoising (bordering on sharking!).


This is the pavement stains that I look for, oil spots in center of travel lane.......(not sure how to rotate pic)

[Dargo]

Originally Posted by Mopar_Earl

Don't guess, set your gain the proper way as per the owners manual or aftermarket manual.





Earl

My gain is maxed and the trailer tires never lock up. I think it could use a little more but it is not too far. My trucks manual does not have any more settings that I have found yet.

[bstannard]

Videoguy,
We are pulling a 321RSTS with a 2017 Silverado 2500/DMax/Bilsteins and get along fine except for the porpiosing over bridges. We are contemplating a move to 3500 (even dually?) to help this. Did you see a big improvement when you moved up? SRW or DRW? What is your pin weight?
Thanks
Bill

[rkymntsno]

Originally Posted by Unclerico

RE: Ionically, assuming we’re talking about same dark spots, those are tire marks from trailers coming back down after being airborne, due to extreme porpoising (bordering on sharking!).


This is the pavement stains that I look for, oil spots in center of travel lane.......(not sure how to rotate pic)

Yes. Exactly what we're talking about. A very good indication of a dip and the darker the pavement, the more severe the dip.

[videoguy]

Originally Posted by bstannard

Videoguy,
We are pulling a 321RSTS with a 2017 Silverado 2500/DMax/Bilsteins and get along fine except for the porpiosing over bridges. We are contemplating a move to 3500 (even dually?) to help this. Did you see a big improvement when you moved up? SRW or DRW? What is your pin weight?
Thanks
Bill

We moved from a 28.5 RSTS/2500HD gas engine to the current combo so I don’t have experience towing the new rig with the 2500.

With the new setup the 321RSTS is around 2000lbs more total weight and I guesstimate our pin weight to be approx 2500lbs loaded. I have not weighed it but someone on the forum weighed their setup loaded and had around 2600lbs pin weight so I think I’m close. My 3500HD is SRW with a payload of 3513lbs. If I recall correctly, my 2500 payload with gas engine was 2700lbs and I believe it’s even less with the Duramax so you may be over payload. However, a lot of people pull this rig with a 2500 w/o issue.

As to the proposing, we do experience it with our current setup only occasionally and it never feels out of control and is caused by the bad roads/ bridges so don’t know that there is an ultimate fix. I will be upgrading my rear shock to the Rancho adjustables as they provide a lot of option for ride and they performed great for me in the past. Whenever towing with the previous combo, I would set them to max firmness and really felt the improved stability compared to the softer settings I used when unloaded.

[imjustdave]

Originally Posted by rkymntsno

Hello all. Back from our 2500 mile round trip to Pigeon Forge, TN and have a question about bouncing over bridges. I have the timbrens, a softer version they sent me after the first version seemed too rough. But I found on this trip some of the dips over bridges at the expansion joints almost caused us to bounce uncontrollably. I need advice on what causes this. Are my timbrens too soft now? Should I go with air bags? Speed is around 65 but swayed up to 70 at times when traffic allowed but still happened at various speeds. The softer timbrens do ride smoother but I don't recall this problem with the firmer timbrens. Advice/thoughts?

Why do you feel the need for timberline to start with? Doubt your truck needs them. And yes the I5 in Seattle and I90 over the pass suck bad with trailers, not sure any suspension setup can fix the harmonic motion of some of these areas at the speed limit.
Your long leaf springs in stock form should work well.

[John7349]

Originally Posted by Dargo

My gain is maxed and the trailer tires never lock up. I think it could use a little more but it is not too far. My trucks manual does not have any more settings that I have found yet.

DARGO


Do the brakes need adjustment? (Should be auto adjust).


Is it possible that oil seals blew out? Brake shoes bad, or both?
This happened to me. Factory seals bad and coated brakes with oil. Jayco ended up paying for it.

[Dargo]

Originally Posted by John7349

DARGO

Is it possible that oil seals blew out? Brake shoes bad, or both?
This happened to me. Factory seals bad and coated brakes with oil. Jayco ended up paying for it.

The only reason I think this may not be the case is because I could not lock the brakes on my old trailer with this new truck. Only drove it to the dealers to trade in. I thought maybe it was the old trailer but now two had the same thing with the truck being the variable.