Bouncy Rear Springs. (1 Viewer)

[76 PTO]

I have a 76 FJ40 with a skyjacker 4" spring lift all around, as well as new bilstein 5125s. The springs are a few years old now and the rear bounces when kids are in the back wheeling. Now, I use this vehicle in the sand. It goes up steep sand dunes on the regular. When struggling on a hill it will start bouncing get traction and bounce again. The rear tires have rubbed in several areas. It seems the the rear springs are too soft. I was thinking of buying a add aleaf from Skyjacker. I was also thinking of flipping the rear springs to increase the wheel base for a better ride possibly. Anyone have issues with skyjackers being bouncy or too soft? Anyone add a leaf?

pic for context

 

[JackA]

Sounds like you need a traction bar.

 

[EWheeler]

I have a 76 FJ40 with a skyjacker 4" spring lift all around, as well as new bilstein 5125s. The springs are a few years old now and the rear bounces when kids are in the back wheeling. Now, I use this vehicle in the sand. It goes up steep sand dunes on the regular. When struggling on a hill it will start bouncing get traction and bounce again. The rear tires have rubbed in several areas. It seems the the rear springs are too soft. I was thinking of buying a add aleaf from Skyjacker. I was also thinking of flipping the rear springs to increase the wheel base for a better ride possibly. Anyone have issues with skyjackers being bouncy or too soft? Anyone add a leaf?

pic for contextView attachment 3366135

Great looking 40. I would follow jack's advise and work on a traction bar first. The bounciness you are experiencing is likely spring/axle wrap from the engine torque and load on your tires. A traction bar, if properly designed and built, keeps this spring deflection from happening, but may not necessarily ELIMINATE the bounce because the torque from the axle that was previously twisting your springs is transferred into a vertical load lifting the chassis. The traction bar will definitely save your pinion from snapping due to axle wrap, but you may also need better shocks to help control the rear suspension in conjunction with the traction bar. Springs are meant to be bouncy, bouncy is a good thing from a leaf spring. If it doesn't bounce, you are over sprung (too stiff). The shock's function is to control the bounce of the spring, you can go mild to wild with shocks. Off the shelf springs are a compromise for overall function, meant to work OK in all conditions. If you want to get a bit more advanced, you can buy rebuildable shocks and get the valving tuned to the use case of your vehicle.

All that being said, axle hop from a straight axle is likely going to be hard to eliminate completely unless you go to a linked rear suspension. Do some internet searches for rear suspension setups of Larry Minor sand Jeeps (most of them are setup with front a-arms and rear straight axles). Whipple Sand Jeeps also design and manufacture some really rad vehicles that would be worth reading up on.

 

[76 PTO]

Thanks for the advise. I was wondering about the axel wrap. I have never seen a spring under with a traction bar.

 

[jim land]

Open diff tend to bounce more in climbing, do you have a rear Locker ?

 

[EWheeler]

Thanks for the advise. I was wondering about the axel wrap. I have never seen a spring under with a traction bar.

Agree, SUA application typically do not need traction bars. It may not be axle wrap, it may just be the suspension loading and unloading in the sand. I spend more time in sand (not in my landcruisers) than anywhere else when I am playing, and you almost always see leaf sprung vehicles hopping under load when climbing. The vehicles that don't hop are linked......

I'm certain there is a solution for you, may take a bit more investigating as to the real cause of hop next time you're out.

 

[76 PTO]

Open diff tend to bounce more in climbing, do you have a rear Locker ?

yes locked rear

 

[76 PTO]

Agree, SUA application typically do not need traction bars. It may not be axle wrap, it may just be the suspension loading and unloading in the sand. I spend more time in sand (not in my landcruisers) than anywhere else when I am playing, and you almost always see leaf sprung vehicles hopping under load when climbing. The vehicles that don't hop are linked......

I'm certain there is a solution for you, may take a bit more investigating as to the real cause of hop next time you're out.

She will bounce in big waves of traction, bounce in the air, no traction and down in the sand again. It is enough for the tires to hit the quarters and inner fender wells. None of my friends CJ's do the same. a traction bar cant hurt but I feel that it is more than that.