Update 5/2/21 - Bounce and Porpoising - Especially Towing

[corvette744]

Without having looked it up - where do the airbags go with the leaf springs In back? Had previously considered on my 1/2 ton but those went inside the rear springs. Thanks for the input.

I have seen them mounted 2 diff ways either on top of your rear spring and into predrilled holes in your frame,or directly over your axle housing.

 

[George B]

I am no towing expert but I have been following this to learn. A few questions came to mind:

1. If towing with a half ton truck produced better results why look at adding more load capacity to a 3/4 ton?
2. Is the bounce due to excessive suspension travel or do you mean the ride is "harsh" and the rebound is faster than the 1/2 ton.
3. What if you don't use the load leveling hitch or reduce the tension on it?
4. What about tires and pressures compared between the 1/2 and 3/4 ton trucks? It's not apples to apples.

Just thinking...

 

[norcalboon]

I am no towing expert but I have been following this to learn. A few questions came to mind:

1. If towing with a half ton truck produced better results why look at adding more load capacity to a 3/4 ton?
2. Is the bounce due to excessive suspension travel or do you mean the ride is "harsh" and the rebound is faster than the 1/2 ton.
3. What if you don't use the load leveling hitch or reduce the tension on it?
4. What about tires and pressures compared between the 1/2 and 3/4 ton trucks? It's not apples to apples.

Just thinking...

Great questions George, happy to answer because I'm trying to get this figured out myself. I probably should have mentioned it's not a new trailer - I've towed it with my 1/2 tons over 7,000 miles the last 4 years with no issues other than under power with the 5.3L/3.42 combo on my previous 2005 - the 2012 Denali pulls it fine. I wanted to get this rig to last the next 10-15 years that my family will be camping until the kids are grown and not wear out the Denali because we love that vehicle too, but it's my wife's DD, and I just wanted my own

1. Not looking to add load capacity, added the Timbren's to try and soften the bounce, but it turns out they are too big so they may be contributing. Timbren is sending shorter versions at no cost (their support has been terrific BTW). Frankly I'm surprised that a vehicle with a 9400lb stock towing capacity needs anything to be honest, and the rear shocks are new. It was thoroughly inspected with significant maintenance performed at the GM dealer where I purchased it - and again when the water pump went out I had a different dealer inspect it and both did not note that the front shocks needed replacement, but I'm doing it since anyway the rears were shot. It only had 91K miles (now 93K).
2. Both right now, harsher I expected due to the stiffer suspension, but it's an uncomfortable ride and bumps in the road cause it to bounce a few times, and when loaded with the trailer it becomes worse - that when I get the porpoising effect.
3. I haven't tried pulling without WDH, but I've adjusted it to where it is BARELY distributing anything (likewise I've also tried cranking it up to distribute more up front). Hardly any difference in ride quality between those scenarios.
4. I did upsize the tires to 265/70/16 (vs. 245/70/16) and run General Grabber ATS load E inflated to 72 psi rear and 50 psi front. The Denali has Michelin 275/55/20 load D, the previous '05 had Cooper load E at 80 psi rear, forget the exact size. I'll reduce the rear more and see how that feels.

I'm surmising that my front shocks are bad and therefore do not dampen the rebound, and the longer than should be Timbren's are exacerbating that effect currently adding extra rebound in the rear. I saw someone post that they put Bilstein 4600 all around on their GMT 900 and it solved the same issue. So once the front shocks are in I'm hopeful that takes care of it. I mentioned the GM shock part number just to see if anyone else had poor performance from them - seems silly to replace brand new rear shocks that are made for this vehicle that's why I'm only doing the front right now.

Keep the idea flowing I really appreciate the input from everybody!

 

[fasteddy]

LOL....That 5.3/3.42 combo must have been crying it eyes out going up grades with a 28ft trailer.

Every tow vehicle needs needs to be tuned to the application.
Keep working on it....I'm sure you'll get there.
You should be towing in comfort, not getting bounced around.

One thing I do pay attention to is "loaded" weight centered OVER the trailer axles....as much as possible.
I don't know if that is a toy hauler or not.
Do you have a rock buggy, quads, motorcycles or heavy stuff in the back?

Since the 1500s towed it "in comfort" it sounds like you have a tow vehicle issue...So keep working on it.
Because that Yukon XL 2500 with 6.0 / 4.10 is a BadAss tow vehicle....and in the snow? OMG its a tractor especially with chains.
I am so missing mine now.

I don't know how much you paid for it, but out west here, clean 02-06 2500/6.0 subs with < 100K mileage are fetching like $15K-$20K.
I see contractors using them for their work trucks, just pop out the rear seats and you have a secured, enclosed long bed.

 

[norcalboon]

LOL....That 5.3/3.42 combo must have been crying it eyes out going up grades with a 28ft trailer.

Every tow vehicle needs needs to be tuned to the application.
Keep working on it....I'm sure you'll get there.
You should be towing in comfort, not getting bounced around.

One thing I do pay attention to is "loaded" weight centered OVER the trailer axles....as much as possible.
I don't know if that is a toy hauler or not.
Do you have a rock buggy, quads, motorcycles or heavy stuff in the back?

Since the 1500s towed it "in comfort" it sounds like you have a tow vehicle issue...So keep working on it.
Because that Yukon XL 2500 with 6.0 / 4.10 is a BadAss tow vehicle....and in the snow? OMG its a tractor especially with chains.
I am so missing mine now.

I don't know how much you paid for it, but out west here, clean 02-06 2500/6.0 subs with < 100K mileage are fetching like $15K-$20K.
I see contractors using them for their work trucks, just pop out the rear seats and you have a secured, enclosed long bed.

Appreciate it - my thoughts exactly and precisely why I bought it. Had been looking for about a year. Wanted something I can keep for the next couple decades. Wife approved The trailer is not a toy hauler, dry weight 5,500 and scale verified 6,420 loaded. Yes, the 5.3L did not like hills, but towed in flat lands just fine.

Paid $9K out the door from a SoCal dealer who took in on trade and was going to send it to auction, caught it before they did and worked out a deal. Also negotiated below maintenance for $3K and then about $2K for tires/tow mirrors/Timbrens/floor mats/fog lights, and a new water pump so I'm all in about $14K but expect minimal maintenance going forward. Almost all engine seals done, including new oil pan/gasket, valve cover gaskets, timing cover gasket, differential seal, new oil and transmission lines, new radiator and hoses/connections, new rear shocks, new cluster, new MAF, new windshield, new wiper blades, new exterior bulbs as needed, new driver side window switch, air filter, all fluids (brakes, transmission, coolant (obviously), power steering, differential), new airbag module and sensors.

Will do plugs and wires next but not in a hurry, runs great.

 

[avalonandl]

The airbags go on the axle with the help of a bracket right above the LeaF springs. I had good luck with them. Do you have something heavy on the front of the trailer?

 

[Bill 1960]

Timbren is essentially riding on a bump stop. Not what I’d associate with an improved ride. I don’t see any need, considering you’ve towed this with better results using 1500’s.

It sounds like you’ve been sampling different hitch settings, but it’s not best approached by trial and error.

Get the tongue weight right 12-15% (measured not estimated).
Set the hitch head so the trailer is level at tow vehicle loaded ride height.
Set the bars to maintain the same front suspension height on the tow vehicle when towing as it sits not towing (some vehicles will vary on this, go by what your manual says).

 

[livingez_123]

On thing you need to remember is the ½ tons use coil springs and the ¾ ton use leaf springs. They tow totally different. I pulled my Cadillac SRX4 on a u-haul trailer and my 99 ¾t rode great.
What kid of tire pressure are you running in the rear tires? 20in wheels or 17in? Does the trailer sway side to side at all? I would run an adjustable Rancho shock in the rear, that way you can change the rebound and air bags might help.

 

[fasteddy]

The airbags go on the axle with the help of a bracket right above the LeaF springs. I had good luck with them. Do you have something heavy on the front of the trailer? View attachment 277369

Look at that boat just dwarf that avalanche and not even sagging, even looks jacked up.
What's that weight like 7Klbs + and then a 2K trailer?
Nice drives.....


He's got a rock buggy in there, I betcha.

 

[avalonandl]

The boat and trailer weighed 10,800 and avalanche was rated for 12k. It was the 2500 w a 8.1 and 410 axls. Trailered well.