Allison 5sp: RCLB Sled Pulling Setup HELP

[coker6365]

We are struggling with the LBZ bouncing severely. Any help or experience would be appreciated, I have only made 2 hooks in my life so rookie would be an understatement.

RCLB 6640lbs with driver
Torsion bars up front, no limiting, Rancho 9000's maxed out on 9
Rear track bars with a small amount of preload, Rancho 9000's on 9, suspension stops about 4-6" above normal ride height
Hitch height at 26" (or whatever the max allowed hitch height is)
305/50R20 Nitto 420 50psi rear 35psi front
We cannot hang weight or add weight, it must remain constant from the start of the event to finish.

The front is lifting to the point of airing out the front tires while hopping. We will be trying a different hitch configuration to bring it closer to the rear axle and reduce the leverage effect when the sled weight moves forward.

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[duramaxzak]

Definitely go to a roll pan and move the hitch forward. Also make front stops so you can set the ride height with the stops and crank torsion bars all the way down. I can send you some pictures of stops on FB.

What are you running for rear springs?

 

[coker6365]

Definitely go to a roll pan and move the hitch forward. Also make front stops so you can set the ride height with the stops and crank torsion bars all the way down. I can send you some pictures of stops on FB.

What are you running for rear springs?

Torsion bolts have been removed since 2013. Rear springs are stock full spring packs with overloads still in place. I think Josh may have a pic of the front stops from you, but shoot it to me if you get a chance. He sent a pic not long ago of a bracket with a bolt to adjust the settled height.

I have a roll pan sitting in the shop so we can definitely use that to bring the hitch forward.

 

[ikeG]

The bolts are out but are they stock keys?

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[duramaxzak]

Some double adjustable Viking shocks in the front and spring clamps in the rear to clamp
top springs to the bottom over lead spring would help stiffen the back up.

With out being able to add weight is not helping...

 

[ikeG]

What is the max weight in the class? If its 8k you definitely want to invest the effort to get it there.

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[clrussell]

The wheel and tire setup isn’t helping. We had issues with running rear bump Stops higher than ride height also.

Not saying this is your whole issue, just some things I’ve seen in the past

 

[clrussell]

What is the max weight in the class? If its 8k you definitely want to invest the effort to get it there.

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I’m thinking this is a three event run what you brung type thing. Truck can’t change between events?

 

[coker6365]

The bolts are out but are they stock keys?

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From what I can tell, they are stock keys.

 

[coker6365]

Some double adjustable Viking shocks in the front and spring clamps in the rear to clamp
top springs to the bottom over lead spring would help stiffen the back up.

With out being able to add weight is not helping...

We can certainly go back to spring clamps with the trac bars. We will eventually go to a coil over in the front, so the idea of wasting money on double adjustables now burns. But it may come to that as the Rancho's are lifting severely on the track as well.

 

[JoshH]

It helps when you don't chain the front down...

 

[coker6365]

What is the max weight in the class? If its 8k you definitely want to invest the effort to get it there.

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It is for the Diesel Power Challenge. Whatever weight we start the event with we have to end with, so no changing during the event. I would prefer not to add weight unless we just flat out cannot get it to work out as the lighter weight certainly helps in the other events along with longevity by not having to push the engine as hard.

 

[coker6365]

The wheel and tire setup isn’t helping. We had issues with running rear bump Stops higher than ride height also.

Not saying this is your whole issue, just some things I’ve seen in the past

We need to try lowing the rear and raising the hitch height to see if it helps the lift. Had a guy at the last sled pull say the same thing.

Wheel and tire setup will likely stay the same unless we swap to an all-terrain tire. Needs to be a well rounded tire as the drag strip is a tough event without a decent 60ft.

 

[coker6365]

It helps when you don't chain the front down...

It seemed like a good idea at first. :roflmao:

 

[duramaxzak]

It helps when you don't chain the front down...

Yes do NOT chain or strap the front down, that will definitely cause severe hoping.

 

[clrussell]

We need to try lowing the rear and raising the hitch height to see if it helps the lift. Had a guy at the last sled pull say the same thing.

Wheel and tire setup will likely stay the same unless we swap to an all-terrain tire. Needs to be a well rounded tire as the drag strip is a tough event without a decent 60ft.

Yeah I assumed you needed the tires for the rest of the event. If anything it should just blow them off. There’s just not much sidewalk to flex.

By lifting the rear you’re increasing leverage considerably.

The hitch won’t lift the front truck as much. Move it as far forward as allowed, then max hitch height. Using ride height with stops all but touching the axle.

 

[coker6365]

It definitely has no issues hitting 5300rpms in 4th on the street tune with these 420's. lol

So you are saying leave the bump stops just a hair off the axle and let the sled load it?

 

[ikeG]

So you put the rear travel stops in after raising the ride height 4-6"? If I'm reading right that's a big issue.
Also chaining/strapping the front down will put you in all the good fail vids...

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[coker6365]

The suspension stops in the rear were used to raise the rear about 4-6". Rear suspension was untouched aside from the stops.

We chained the front down on the very first hook ever. While it didn't cause a failure fortunately, it did make the cover page of the Diesel Power Magazine event issue.:rofl:Lesson learned for sure!

 

[duramaxzak]

Without being able to add weight, you may even want to try a 24" hitch height...