Which 6" lift kit to buy for a Cummins K3500 truck?

[RockinChevy]

I've searched and many say the Superlift and Skyjacker kits are the popular choice, yet others just add more leaves to their stock packs.

Well, I'm working on a budget to get a 6" lift to fit 35's for my crewcab, which will get a 5.9L Cummins swap sometime this fall. The truck has a 2" lift w/ 31's as it stands today.
I don't want to keep adding to my spring packs, I already have 6 up front and 13 in the rear. I'm aware the tallest pack I can buy for the rear is only 6".

My goal for this truck is to keep it a towrig, not necessarily meaning 100% street but somewhat 60/40 on/off road, such as sand washes and fire roads, no rocks so suspension flex is out of the question. And it must be capable of pulling 15-20k pounds safely so no lift blocks. I'm unsure at this point if shackle flips are safe, even if I use the 2.5" flip and 4" HD rear shackles. Not sure if this will be 6" in the rear anyway.

So, which 6" springs have the highest spring rate and how to make it a true 6" in the rear without blocks?

Thanks in advance

 

[nvrenuf]

On my 91 crew cab I used Rough Country front springs because they had the highest spring rate. I know you don't want a block but I used a rear block so I could keep the OE 1 ton springs. Knowing how generic off the shelf parts can be I was skeptical that rear lift springs would carry as much as the OE springs.

Fwiw, initially I also tried add-a-leaves in the rear (+ 4" block) and they broke within a month. Imo, there are just too many leaves in the OE set for the AAL to work properly.

 

[pseudomike]

I just put a Cummins in my K3500 SRW reg. cab. I only did 4", I went with Rancho (86206) front springs (for a higher spring rate) with DIY4x 5" shackles and their shackle hanger kit. This setup yielded a lift of about 2.5" over the stock HD replacement K3500 springs (4 leaf) with stock motor. In the rear I pulled 3 leafs out of the pack for a nicer ride (6 leafs + 1 overload left) and added an ORD 2.5" shackle flip and 6" DIY4x shackles. This yielded about 1-1.5" rake over the front for a nice stance. I am going to run bags for towing.

Thing to keep in mind is the 1 ton sits about an 1.5" higher than it's sister models from the factory...so a 4" lift spring is only going to raise the front about 2.5" and a 6" is only going to raise it about 4.5" I would go with a stiffer spring, rough country or rancho with that 1300 lbs Cummins up there. I would also upgrade the shackle hangers with larger bolts and diameter bushings. A 6" Rancho spring, 4" shackle flip, and a 5-6" rear shackle should get you about a 6" lift over 1/2-3/4 ton.

Mike

 

[thatK30guy]

On my 91 crew cab I used Rough Country front springs because they had the highest spring rate. I know you don't want a block but I used a rear block so I could keep the OE 1 ton springs. Knowing how generic off the shelf parts can be I was skeptical that rear lift springs would carry as much as the OE springs.

Fwiw, initially I also tried add-a-leaves in the rear (+ 4" block) and they broke within a month. Imo, there are just too many leaves in the OE set for the AAL to work properly.

John, did you use a long or short AAL in the rear pack? I'm asking because I'm debating whether to use the shorter leaf (somewhere around 28" long) and 4" blocks OR no AAL and 5.5" blocks.

The front springs I plan to install are discontinued Rancho 6" Mud Bogger springs. If you remember those, they have 9 leaves and a military wrap on the forward eyes. IIRC, the spring rate for these springs were somewhere around 675, so it will be good for the heavy hauling.

I just don't know what to do yet for the rear lift. I figured if I was using stiff Rancho 6" springs, I may as well use the shorter AAL and 4" blocks to stiffen up the rear springs a bit.

Oh yeah, rig is an '87 V30 dually which will see only towing, hauling, street and highway driving. No offroading, etc.

 

[nvrenuf]

The set up that brock was a 4" block and short aal's. I later removed them and went with a 5.5" block and no aal. Fwiw, the short aa' set up caused pretty good vibes, the 5.5" block almost eliminated the vibes totally (still had some above 65~70, iirc).

Those front springs sound sweet! That's quite a find there.

 

[thatK30guy]

I've already got the 5.5" blocks and will use them in the V30 now. I also plan to use a rear sway bar, too. Gonna be some loooooooooooooong u-bolts in the rear.

 

[nvrenuf]

Gonna be some loooooooooooooong u-bolts in the rear.

yessir

 

[muddermilitia]

A long time ago I bought a used set of 6" superlift springs from a guy at one of the 4x4 jamboree. I think he was a member here cant remember his name, anyways he swapped a cummins into his 1-ton crewcab and the front sat too low so he swapped the 6" springs for a set of 8" lift springs. I don't know what he did in the rear but with the weight of the cummins he was right around 6" lift in the front

 

[JDNobodi]

John, did you use a long or short AAL in the rear pack? I'm asking because I'm debating whether to use the shorter leaf (somewhere around 28" long) and 4" blocks OR no AAL and 5.5" blocks.

The front springs I plan to install are discontinued Rancho 6" Mud Bogger springs. If you remember those, they have 9 leaves and a military wrap on the forward eyes. IIRC, the spring rate for these springs were somewhere around 675, so it will be good for the heavy hauling.

I just don't know what to do yet for the rear lift. I figured if I was using stiff Rancho 6" springs, I may as well use the shorter AAL and 4" blocks to stiffen up the rear springs a bit.

Oh yeah, rig is an '87 V30 dually which will see only towing, hauling, street and highway driving. No offroading, etc.

How long ago did Rancho make those springs? In the early 90's when I lifted my 73 Jimmy, the highist lift Rancho offered at the time was 4".

 

[thatK30guy]

How long ago did Rancho make those springs? In the early 90's when I lifted my 73 Jimmy, the highist lift Rancho offered at the time was 4".

I still have my Rancho catalogs somewhere and the last one to list the MB springs in it was around '88 or '89. After that, they discontinued them.

I've searched high and low for another pair of these springs but with no luck. I will get pics of these springs up in a bit.

 

[thatK30guy]

Here are the pics of my Rancho #86207 springs:

 

[Zeus33rd]

Why not call up Deaver or one of the custom spring places and have a set made that you know will be right? It would certainly cost more, but worth the money in the long run.

 

[thatK30guy]

Few more...

 

[pseudomike]

The crew cab will sit a good inch and a half lower with the cummins depending what springs you get. Fairly simple equation...400lb/in springs x2 = 800lbs/in...now add 800-1200lbs (6-700 for the motor plus extra weight of the CC) to the front and you have a realized drop of 1-1.5 in. The rough country HD's, skyjacker, and warns run out in the 600-700lb/in range so your drop will be less. Rancho and procomp run out in the mid 500lb range. Tuff country's run in the high 300's to 400lb range with a larger arch.

 

[RockinChevy]

Thanks guys! I'll take your input into consideration, I'm still researching on the rear springs. Any other input is welcome.

 

[pseudomike]

I would stay away from blocks...especially over 4" tall!!!!! This creates a huge lever arm. I don't really care who says they have used them and they work. 6 years of engineering classes and if nothing else I can guarantee you that block will induce high levels of stress into your components with a very real chance of failure. I would put the blocks between the springs and the upper overloads if you are worried about losing them after the lift.

The best ride is going to be from a shackle flip...either home brewed or off the shelf. Springs with more arch will ride worse than springs with less arch. I would recommend the largest shackle flip you can get to obtain you're desired height. If you need more then the shackle flip will yield then think about springs with slightly more arch.

 

[thatK30guy]

I would stay away from blocks...especially over 4" tall!!!!! This creates a huge lever arm. I don't really care who says they have used them and they work. 6 years of engineering classes and if nothing else I can guarantee you that block will induce high levels of stress into your components with a very real chance of failure. I would put the blocks between the springs and the upper overloads if you are worried about losing them after the lift.

The best ride is going to be from a shackle flip...either home brewed or off the shelf. Springs with more arch will ride worse than springs with less arch. I would recommend the largest shackle flip you can get to obtain you're desired height. If you need more then the shackle flip will yield then think about springs with slightly more arch.

Take a look under any newer Dodge and Ford truck. They all have tall blocks. The Dodges have some around 5" or 6" tall. Something tells me if those new trucks can use tall blocks and not have any problems with them, their engineers know something we don't. Gotta remember there's a lot more diesel trucks on the road right now running these tall blocks and no one is trying to stop them from towing/hauling anything.

I'm not looking for the best ride characteristics either. So a shackle flip is out of the question, especially for towing.

 

[muddermilitia]

What about some dropped spring hangers? If properly built they should be fine and you can keep your stock springs

 

[nvrenuf]

Take a look under any newer Dodge and Ford truck. They all have tall blocks. The Dodges have some around 5" or 6" tall. Something tells me if those new trucks can use tall blocks and not have any problems with them, their engineers know something we don't. Gotta remember there's a lot more diesel trucks on the road right now running these tall blocks and no one is trying to stop them from towing/hauling anything.

I'm not looking for the best ride characteristics either. So a shackle flip is out of the question, especially for towing.

Yep, the bigger 5.5" blocks I used were OE Dodge blocks from a 1 ton 4x4 dually application.

 

[pseudomike]

Take a look under any newer Dodge and Ford truck. They all have tall blocks. The Dodges have some around 5" or 6" tall. Something tells me if those new trucks can use tall blocks and not have any problems with them, their engineers know something we don't. Gotta remember there's a lot more diesel trucks on the road right now running these tall blocks and no one is trying to stop them from towing/hauling anything.

I'm not looking for the best ride characteristics either. So a shackle flip is out of the question, especially for towing.

I am aware that there are some trucks that use them from the factory. Take note of where those companies are now. From an engineering perspective you are applying a much greater force to your u-bolts, axle tubes, and spring packs. Aside from wheel hop problems, you also run the risk of prematurely failing your leaf springs and or breaking/stretching u-bolts. If lift blocks are such a great idea then why are there a number of states that have explicitly made use of lift blocks illegal? I guess they wish to support spring manufacturers?

Many have used blocks with decent luck. I've personally seen more than one set fail. They are a method for lifting the vehicle but I would not recommend it. Just because GM, or Ford, or Dodge has stuck a set in the back of one of their trucks doesn't make it a good idea. If they were full of good ideas they would not be in the situation that they are in. Lift blocks are dangerous!!

On the shackle flip, I do not understand how a properly designed setup will alter your handling while towing. I know there are some guys that were running some early echobilt flips that claimed white knuckle experiences when towing. Compression shackles were used in the front of almost all make solid axle front trucks. If the geometry is correct (as close to 90 degrees as possible) the change in leverage on the leaf springs and thus loading should be negligible. The issue is when the shackle is not square and creates a lever arm. The less arch in the springs the less likely this is to occur. I have a friend that tows a 12K lb trailer and runs a shackle flip w/o problems.

If ride quality is of no concern then just run high arch springs. If you plan on towing huge loads a lift kit isn't the greatest idea anyhow. I would recommend bags for an tow rig, they make a world of difference. They would also alleviate the issues with the shackle flip.