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

[norcalboon]

I picked up a 2005 Yukon XL 2500 with 6.0L and 4.10 rear axle and only 91K miles a few months ago to serve as the primary tow vehicle for my 6.5K travel trailer. It's been exactly what I wanted and we've had it out on 3 trips covering several hundred miles and it's performed great - except the ride quality is TERRIBLE. 6,420lb TT and 13,520lb Gross weights are scale verified.

It's bouncy while empty, and when towing the TT we get moderate porpoising. At first I chalked it up to the stiffer 3/4 ton suspension, but this is "time your sips of coffee, wife can't read while driving, lifts me off of my seat bumpy", so I can't believe it was designed to act like this. I've adjusted my WDH six ways to Sunday - moved my drop shank down, tried several different chain links to shift the load, and tried to add weight to the tongue - but nothing has changed the way it rides by a noticeable amount. The rear shocks were replaced when I bought it with GM P/N 25984613. I've added Timbren SES bump stops to the rear, which helped dampen some of the bounce but not nearly enough. Since the rears were shot I've also got Bilstein 4600 shocks for the front ready to install as my next attempted fix.

What else could cause this much bounce? Appreciate the feedback. Loaded tow, and rear left shock pics (with old bump stop) below for reference. I don't expect it to feel like our 2012 Denali, but I just can't believe this is the way it should handle.

 

[Cbncanada]

It could be the photo is a little deceiving but it looks like your trailer is a little nose down and the equalizer bars are not level. Try to raise the hitch one notch and ensure the bars are level to the ground when tight. The trailer should also be level to the ground. Do all of that with the trailer just sitting in place on the hitch ball with no load on the truck. Once that is done put the load on the truck and try it.

 

[exp500]

Usually bounce is more related to springs than shocks. Shocks stop multiples. Have you attenpted to change the trailer loading to increase hitch weight towards maximum? Too much weight aft makes porpoise worse, steering wierd if near limit aft too. I have always preferred about a 20 percent increase in rear spring Rate.
Good luck and report your progress.

 

[avalonandl]

Figure out your tounge weight and overall weight. If your overloaded on the tongue, you need to crank up the bars- more weight shifting by doing this.

If your underloaded thats worse....makes for sway.

 

[TxTaz]

+1 on tongue weight comment.
I use Bilstein 5100 with reservoirs on my tow rig. Works great with and without the trailer.
Taz

 

[fasteddy]

.....tongue weight
+ Air Bags will correct any sag and stiffen the rear suspension.
All Escalades since 2002 have had airbags, All premium subs and Tahoes and Yukons have air bags.
My sub has air bags, I tow 8K lbs and it rides fine.
And I HATE towing.
Air Bags makes a big difference when towing.
Just get manual air ones and pump it up when you tow.

Weight distribution is important I've heard.....I don't do that.
I just hook up and go....as I hate towing.

and yeah 5100s are way better than 4600s.
I don't know what PN 25984613 is....
You can also use 3/4 ton truck shocks.

....Airbags! Manual pump.

 

[corvette744]

.....tongue weight
+ Air Bags will correct any sag and stiffen the rear suspension.
All Escalades since 2002 have had airbags, All premium subs and Tahoes and Yukons have air bags.
My sub has air bags, I tow 8K lbs and it rides fine.
And I HATE towing.
Air Bags makes a big difference when towing.
Just get manual air ones and pump it up when you tow.

Weight distribution is important I've heard.....I don't do that.
I just hook up and go....as I hate towing.

and yeah 5100s are way better than 4600s.
I don't know what PN 25984613 is....
You can also use 3/4 ton truck shocks.

....Airbags! Manual pump.

Agree get air bags.

 

[swathdiver]

Time for a trip to the CAT scales. Weigh the Yukon on both scales, reweigh the whole setup on all three scales. I think it's $12.50 for the first weigh and an extra $2 for the reweigh now.

I believe you that do not have enough weight up front, on the hitch and the forward part of the trailer.

 

[norcalboon]

Time for a trip to the CAT scales. Weigh the Yukon on both scales, reweigh the whole setup on all three scales. I think it's $12.50 for the first weigh and an extra $2 for the reweigh now.

I believe you that do not have enough weight up front, on the hitch and the forward part of the trailer.

Appreciate your input James (and others) - it's been weighed at a scale which I included, 6,420 TT only 13,520 total Gross. Dry tongue weight is listed at 540lbs - and I have the storage in the front loaded with 2 cases of water dead center, and all of our gear so it is easily another 100lbs minimum for a total minimum tongue of 640lbs which is 10% - it's likely even more considering I have two deep cell batteries vs 1 and two 7.5 gal propane tanks up front and also have a 100lb german shepherd in the very back of the Yukon, so it's likely closer to 800lbs or 12%. Don't have much extra stored in the back/middle of the trailer to add weight there.


This is the 3rd Yukon XL I've used to tow this trailer and never had a bounce issue - granted the previous 2 were 1/2 tons but still I'd be surprised if it was just how the WDH is set up or how it's loaded - and as I mentioned I have already moved the shank up and down and adjusted my chain links to several different positions with no change in ride quality. It also rides rough empty with bounce over bumps (but no porpoising without the TT).

I contacted Timbren and they are sending shorter helper springs because the current almost touch when unloaded. I'll also replace my front shocks with the Bilstein 4600s (standard height) when I install those. I'll report back after that but was after any other possible causes which haven't been offered.

 

[norcalboon]

.....tongue weight
+ Air Bags will correct any sag and stiffen the rear suspension.
All Escalades since 2002 have had airbags, All premium subs and Tahoes and Yukons have air bags.
My sub has air bags, I tow 8K lbs and it rides fine.
And I HATE towing.
Air Bags makes a big difference when towing.
Just get manual air ones and pump it up when you tow.

Weight distribution is important I've heard.....I don't do that.
I just hook up and go....as I hate towing.

and yeah 5100s are way better than 4600s.
I don't know what PN 25984613 is....
You can also use 3/4 ton truck shocks.

....Airbags! Manual pump.

I'm stock ride height

B6 4600 Versus B8 5100 (bilsteinus.com)

 

[norcalboon]

It could be the photo is a little deceiving but it looks like your trailer is a little nose down and the equalizer bars are not level. Try to raise the hitch one notch and ensure the bars are level to the ground when tight. The trailer should also be level to the ground. Do all of that with the trailer just sitting in place on the hitch ball with no load on the truck. Once that is done put the load on the truck and try it.

different photo

 

[Sobro]

My WDH says you measure the height of the rear bumper unhitched but the truck loaded and then hitch up and measure the height again. Adjust the chains on the WDH bars until the bumper height is back to the previous measurement.


But it sounds like you've done similar and are still getting the same result, so you working on your suspension seems to be the solution.

 

[exp500]

Appreciate your input James (and others) - it's been weighed at a scale which I included, 6,420 TT only 13,520 total Gross. Dry tongue weight is listed at 540lbs - and I have the storage in the front loaded with 2 cases of water dead center, and all of our gear so it is easily another 100lbs minimum for a total minimum tongue of 640lbs which is 10% - it's likely even more considering I have two deep cell batteries vs 1 and two 7.5 gal propane tanks up front and also have a 100lb german shepherd in the very back of the Yukon, so it's likely closer to 800lbs or 12%. Don't have much extra stored in the back/middle of the trailer to add weight there.


This is the 3rd Yukon XL I've used to tow this trailer and never had a bounce issue - granted the previous 2 were 1/2 tons but still I'd be surprised if it was just how the WDH is set up or how it's loaded - and as I mentioned I have already moved the shank up and down and adjusted my chain links to several different positions with no change in ride quality. It also rides rough empty with bounce over bumps (but no porpoising without the TT).

I'm not sure your numbers are correct, Thats why it was asked in post8 I believe. You can scale the truck, get F/R weights empty. Attach TT and reweigh with 3 shown- TT , rear axle, front axle of truck. No calculating or guessing on weights using supposed dry weights. For instance carrying 100 gallons of water behind the rear axle. Thats 800# in a bad place. You could very well be correct, But me- I'd want 1200# + on the hitch to test, roughly 25 percent. And also know the distribution= How hard to crank the hitch Bars. 7100# for the truck sounds hi.

 

[fasteddy]

I'm stock ride height

B6 4600 Versus B8 5100 (bilsteinus.com)

So was I. But I still used 5100s....and airbags....they are cheap and I consider them a safety item.
Bouncing is a dampening issue-shock absorbers, meaning compression and rebound aren't working.
So you need shock absorbers front and back and I wouldn't tow a trailer that big w/o airbags....it'll stiffen up the back.
You want to pull the trailer, not have the trailer pull you.
IMO it becomes a safety issue. Bouncing mean weight is moving uncontrolled up and down and it can destabilize/move the vehicle and/or trailer off track.
Get off track on a mountain highway next to a drop and it becomes dangerous really fast.

I knew this guy some years back coming back from laguna seca over the mountains and it was raining.....the trailer pulled him over the cliff.
We had no idea how it happened. They didn't find him until the next day. I hate trailering. Always overbuild the tow vehicle. Be safe.


Check out my yukon! Looks familiar yes?
I miss that thing....the seats were so comfortable, nice and puffy.

 

[fasteddy]

And how long is your trailer? Overall.
In your pictures I have yet to see the end of it. lol

 

[corvette744]

Bag it................

 

[norcalboon]

And how long is your trailer? Overall.
In your pictures I have yet to see the end of it. lol

28ft Tongue to bumber

 

[norcalboon]

So was I. But I still used 5100s....and airbags....they are cheap and I consider them a safety item.
Bouncing is a dampening issue-shock absorbers, meaning compression and rebound aren't working.
So you need shock absorbers front and back and I wouldn't tow a trailer that big w/o airbags....it'll stiffen up the back.
You want to pull the trailer, not have the trailer pull you.
IMO it becomes a safety issue. Bouncing mean weight is moving uncontrolled up and down and it can destabilize/move the vehicle and/or trailer off track.
Get off track on a mountain highway next to a drop and it becomes dangerous really fast.

I knew this guy some years back coming back from laguna seca over the mountains and it was raining.....the trailer pulled him over the cliff.
We had no idea how it happened. They didn't find him until the next day. I hate trailering. Always overbuild the tow vehicle. Be safe.


Check out my yukon! Looks familiar yes?
I miss that thing....the seats were so comfortable, nice and puffy.

View attachment 277273

Understood, I’d be inclined to trust the manufacturer recommendation as they state there is no difference between the 2 besides length to accommodate higher rides. I towed it with my previous 1/2 ton Yukon XL without added suspension just fine. My wife’s Denali pulls it it fine (of course it has air ride shocks). Went to a 3/4 ton for the heavy duty components and really wanted the 4.10 rear end b/c the biggest issue I had with the previous 5.3 w/3.42 was bogging down up hills - never had a sway or bounce or sag problem. Towing power up hills is perfect with 6.0 and 4.10s just need to get rid of this bounce. Appreciate the feedback, may still look into air bags.

 

[norcalboon]

I'm not sure your numbers are correct, Thats why it was asked in post8 I believe. You can scale the truck, get F/R weights empty. Attach TT and reweigh with 3 shown- TT , rear axle, front axle of truck. No calculating or guessing on weights using supposed dry weights. For instance carrying 100 gallons of water behind the rear axle. Thats 800# in a bad place. You could very well be correct, But me- I'd want 1200# + on the hitch to test, roughly 25 percent. And also know the distribution= How hard to crank the hitch Bars. 7100# for the truck sounds hi.

To be comprehensive I plan to re-weigh and get axle weights this time. Note the total Gross of 13.5 was fully loaded and the trailer was unhitched and weighed separate. Thanks for the input I’ll keep providing updates until I get it figured out.

 

[norcalboon]

Bag it................

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.