Lift

[Dws327]

I have a 85 k10 I am wanting to replace the factor leaf springs on. The truck has 35-12.5-15 tires. What would be the best size leaf Springs to go with?

 

[theblindchicken]

Unless you have really undersized 35's, a body lift, or trimmed the fenders a ton, you probably don't have factory springs.

Rule of thumb with 35's
Street only: 4" lift
Offroading: 6" lift

But running a 6"+ lift opens another can of worms in that you most likely need extended driveshafts, a lot of steering correction or crossover steering, as well as all new shocks and extended brake lines too. But most of that is needed with any lift.

 

[Dws327]

I had bought the truck with the 35s on it and the and it did rub some when you turned. I am doing a ground up restore on the truck. So I had already planned on replacing those items. Just wanting to make sure I do it right the first time.

 

[theblindchicken]

I had bought the truck with the 35s on it and the and it did rub some when you turned. I am doing a ground up restore on the truck. So I had already planned on replacing those items. Just wanting to make sure I do it right the first time.

Gotcha.

What are your plans for it besides the restoration? Street only, street with light offroading, etc?

Do you want it to never rub in any scenario or would a little rubbing not bother you? If you don't want rubbing, are you intent on keeping 35's? If so, how high of a lift are you willing to go? Backspacing and width of your rims is a pretty big factor when determining how much will rub on the fenders.

I'm currently sitting about 4-5" of lift running 35x12.5R15 BFG KO2's on a set of 15x10's with 4" BS. On the street, I pretty much only rub when it's a full turn and hitting a dip or steep driveway. Rear has no issues at all.

Offroad and flexing the suspension, I rub quite a bit.

 

[Dws327]

Most of the time will be just street but yes some light offroad. Planning on keeping the 35s for now they look almost new but once I have to replace them probably will goto 33s but not sure just yet.

This will be my first restore so I am learning as I go on some of this. I have had 4x4 but they were stock.

 

[theblindchicken]

Most of the time will be just street but yes some light offroad. Planning on keeping the 35s for now they look almost new but once I have to replace them probably will goto 33s but not sure just yet.

This will be my first restore so I am learning as I go on some of this. I have had 4x4 but they were stock.

Feel free to ask all the questions that you can come up with.

Hmm.... With a 4" lift, you may be able to get away with light rubbing on trails as long as you don't flex the front too much. The rear should be able to tuck up in the fenders without rubbing pretty well as long as the wheel backspacing isn't too low. Rubbing will mainly be located at the front and rear lips of the fenders. Could trim those back a little bit to the edge of the cab to help clearance.

4" is a perfect setup for 33's when offroading.

If you're intending to keep costs down, you could probably do a 4" lift, with an ez rate in the front (5" suspension front, 4" suspension rear) and then do a 1" body lift all the way around for a total of 6" front and 5" rear. I believe the 1" difference will also level out the look of the truck, but may be a little off on that one. Depends if you like the factory rake or not.

That would total you to a 6" lift in the front, 5" in the rear. You wouldn't have much issue with actually clearing your 35's. Then when and if you plan to drop down to 33's, you can remove the 1" body lift and ez rate and you'll be at the perfect height for 33's as well.


For the steering,

4" requires a drop pitman arm
6" requires a raised steering arm, cost between the two is roughly the same.


Driveline

4" is about the limit of stock driveshafts.
6" usually needs lengthened shafts, sometimes needs a transfer case drop if shortbed to help with yoke angles.

Axles
both will probably need angle shims to correct the yoke angle after lift to limit vibrations.

Shocks - Works hand in hand w/ spring rate
Will need a new set of shocks all the way around no matter the lift.
High dampening will make the truck stiff over little bumps, but smoother over speed bumps/dips.
Lower dampening will make the truck ride softer and sometimes "floaty" over smaller bumps, but will have large amounts of suspension travel on larger bumps.

Spring rates
Typically the larger the spring lift, the higher the spring rate.
The larger the spring rate, the stiffer the ride.
ex. 500 lbs/in rate vs 350 lbs/in rate.

If you threw 1000 lbs in the bed, the 500 lbs/in rate will only drop 1" whereas the 350 springs will drop almost 1.5"

How the spring rate also affects the ride is that a very stiff spring will act almost as if there is no suspension in that you feel every crack and bump of the road in your back. No spring travel = no shock dampening = Spine travel
A very soft shock will be like a cadillac. Won't carry much weight, but will drive down the road very comfortably.

This is why trucks ride very nicely with a bit of weight in the rear compared to an empty bed. The shocks and springs are actually moving and doing work.

New bushings in the shocks and shackles and ensuring everything is greased up will also help greatly for softening up the ride as well as helping all your parts last longer.

Hope all this helps.