'73 K20 bucking bronco

[FlockofGorillas]

Hi Everyone,

I have a 73 k20 long bed that is bucking hard at speeds above 55mph. The truck has a 4in suspension lift and is on 315/75/r16s (35x12.5s). The lift is 4inch tuff country EZ-Rides up front and the rear is stock springs with a shackle flip. The truck has new Tuff country sx8000 shocks all around. The only thing I haven't tried is getting new rear springs. The truck is a camper special and had a camper on it most its life, so the springs are pretty tired (they basically ride on the overloads sitting empty).

Does anyone have any idea what could be causing this, and if it is springs any suggestions on which springs to buy. I currently have the heavy duty 7 leaf (6/1) 52inch springs and am thinking about going down to the 6 leafs, but i tow around 6000lbs with this truck sometimes and don't want to go to soft. Thanks for the help in advance.

 

[hirschdalechevy]

I have a lifted 77 crew cab that I tow quite a bit with and I went with 56" custom, soft , deaver lift springs for the rear , no over loads. Then I put an air bag kit on for towing. I also went with rancho 9000 shocks set on 1 for unloaded use and turned them up for carrying a load as well as pumping up the air bags. There are way better shocks out nowadays so I might go a different route if I had to do over but my set up rides great.

 

[dvdswan]

Just to clarify. Are you saying the truck bounces really bad at speeds or the truck engine cuts out?

BTW, welcome to the site.

 

[RoryH19]

I noticed the same on my K5 when I installed a 3" Tuff country EZ lift, sprigs all the way around. I also have quad shocks up front and singles in the rear. Skyjacker black max.
Not sure how new your springs are but mine needed a little break-in time.

I would definitely change your rear springs if original.

I run 33x12.5R15

 

[FlockofGorillas]

Just to clarify. Are you saying the truck bounces really bad at speeds or the truck engine cuts out?

BTW, welcome to the site.

Thanks for the welcome.

the truck is bouncing real hard front to rear and not in a bouncy dead shock way, but more of a gocart with no suspension way. the engine is running fine.

 

[FlockofGorillas]

I have a lifted 77 crew cab that I tow quite a bit with and I went with 56" custom, soft , deaver lift springs for the rear , no over loads. Then I put an air bag kit on for towing. I also went with rancho 9000 shocks set on 1 for unloaded use and turned them up for carrying a load as well as pumping up the air bags. There are way better shocks out nowadays so I might go a different route if I had to do over but my set up rides great.

I thought about bags but with the shackle flip i would have to do something custom to fit them. Is yours stock height or lifted?

 

[Arkansas_V8]

Flat spotted tires.

 

[FlockofGorillas]

I noticed the same on my K5 when I installed a 3" Tuff country EZ lift, sprigs all the way around. I also have quad shocks up front and singles in the rear. Skyjacker black max.
Not sure how new your springs are but mine needed a little break-in time.

I would definitely change your rear springs if original.

I run 33x12.5R15

I've had the springs on for about 3 years old but probably about 500-1000miles on them only. How long did yours take to settle in?

 

[FlockofGorillas]

Flat spotted tires.

Tires are only about 2 years old and have never gone flat. They are BFG all terrains ko2s 315/75/r16 load range E. The truck sits in the shop alot probably only take it out every 2-4 weeks. You think they still could be flatspotted from sitting? how could I check for it?

 

[Arkansas_V8]

Having them balanced is the only way I know to find out.

My Suburban sat for a few months, tires did not go flat either and it did go away after a while.

It was enough to bounce me out of the seat. Lol, made for a fun ride. 37x13.5x17.

 

[Craig 85]

I had 4" EZ Rides in my prior truck. '79 K10 short bed with a 3/4 ton axle swap. It rode soft enough on the front that when I braked the front would squat and cause the steering wheel to rotate just a little. I had ORD's grease-able shackle kit and their sway bar disconnect kit. The rear was a the stock 5/1 52" springs with a 4" block. It was the best riding square I've had. The front did have a winch bumper and brush guard, but no winch.

My K30 has the 3" HD Tuff Country springs due to the big block. It has the same ORD parts. In the rear It has a 3" block. I had the 8/1 rear springs. I took one out when I rebuilt them. It's still pretty stiff, but rides better than a '77 K5 I had with a Skyjacker Soft ride 6" lift.

One thing I do with all of my trucks is run the front tires at 50-60 PSI (depending on the truck) and run the rears at 30 PSI. If I need to haul something, I air the rear up.

 

[FlockofGorillas]

Thanks Craig, maybe i will go with the 5/1 springs, also gonna have to try pumping up the front tires

 

[FlockofGorillas]

It was enough to bounce me out of the seat. Lol, made for a fun ride. 37x13.5x17.

Thats where I'm at right now. if i dont have a seatbelt on i might get launched lol. maybe i should go get the tires re-balanced.

 

[dvdswan]

Another silly question. I only ask because mine was doing the same thing but a short bed. Are the rear shocks long enough. PO on mine used stock shocks on the rear which left no down travel causing the truck to buck at 50+ mph.

So are the rear shocks long enough? Either pull them off and measure or jack up the rear and let the suspension hang to see if it droops.

I understand the shocks are new but are they the correct ones.

 

[FlockofGorillas]

Yeah, I've got plenty of shock travel.