Loweing c30 crew cab
 

Just purchased a 1979 Crew cab dually. (Pics soon)
Its mostly all original. Trying to keep it that way, just lowered with wheels. A nice driver.

I'd like to lower it as much as possible (and still be driveable) and use 22" milled semi wheels.

Western chassis has a 6/8 drop which is coils, spinfles, and a flip kit in the rear. This seems to be the way to go, unless anyone objects?
Only thing I've noticed is these drops seem a little nose-high.
Is there a way to raise the rear up a little if that is the case? Or, lower the front some more...I assume just cut out 1/2 a coil or so?

Can't wait to tear into it a bit! Thanks for any help.

Is there a specific dually section? Didn't see one so let me know if I missed it.

Re: Loweing c30 crew cab
 

3" spindles + 1-coil removed from the stock front springs = ~5" front drop.

For the rear, the flip kit = ~8" drop. Drop shackles & hangers yield 4" drop. You can do a flip-kit & use 'lift' shackles to gain an inch. This maintains the traditional 5/7 drop total. Even @ 7" of drop, the bed floor support above the differential will need to be tweaked for clearance & it's still likely the center housing will hit the floor (they are large).

Know going into it that the rear frame will be compromised w/bolt-in C-sections (significantly w/the Western Chassis units). A former board member that's a structural engineer did FEA calcs from the numbers I provided to him on the Western Chassis c-notches purchased/intended for my dually. The result was the rear rail would be approx 16% of the original rail strength using them. Boxing the inside increased that number (<10%). That's a bunch of stress @ the notch area given the pivot distance to each end of the springs.

I opted for full height step notch sections bolted & welded in + raised the floor.

Re: Loweing c30 crew cab
 

Dang, I didn’t realize a notch would compromise it so much. I do plan to carry/tow around some motorcycles so nothing huge but still…Is there a way to have a notched frame be strong and not have to move the bed floor?

Re: Loweing c30 crew cab
 

Whatever height that's removed from the bottom of the rail needs to be added to the top to stay @ what came from GM. There is a minimal amount you can go up under the floor (~1") by removing part of a bed support.

Lots of trucks out there w/c-notches. They might 'work just fine' but they definitely are not as strong as the uncut frame or one w/a step notch that has a full height rail.

The strength is in the height of the rail. However much the notch depth is relates to how much strength is removed. Yes, w/a bolt-in style notch the material thickness is doubled @ the notch area but the strength is in the height not the thickness.

I did the math on the notch depth:
Original rail height @ ~5"
C-notch depth @ ~3.75

3.75/5 = .75 or 3/4 of the rail height removed. My head told me @ most I'll be @ 25%. Then I figured the double thickness + boxing the inside would get me close to stock. It raised the number slightly. Then, add the distance to each spring end & the stress number got worse. I was shocked @ how much it would be compromised when someone who can actually calculate everything including the variables crunched the numbers. The math can be ignored but it doesn't lie.....

I still have those c-notches sitting on a shelf. Used step notch sections from Porterbuilt instead.

I learned all of this when I copied the Western Chassis lay-out & dimensions to build a similar home-built notches for my '64swb project. I actually re-worked my 64's set-up as well & tossed the dually's WC notches in the steel bin in favor of the step notches. Read more about it here: http://67-72chevytrucks.com/vboard/s...d.php?t=457037

Re: Loweing c30 crew cab
 

Im running the traditional 5/7 drop. Its a 3in drop spindle 2in drop spring in the front, and a flip kit in the rear. Pretty standard issue parts.

Regarding the notch, I agree with ^^. I wasn't willing to use a bolt in not I still use it to pull trailers etc. I used Low boy motorsports weld in under bed notch. Like stated above, you have to add material you cut out. His notch kit does that and it also adds enough material to box the c notch part.

I am also running his rear shock relocators. This allows you to use the factory shock. Makes for easier parts sourcing down the road.

TLDR: running a standard 5/7 drop with a weld in underbed notch. Wheels and tires are milled 22s.

Re: Loweing c30 crew cab
 

Now that I have lowboys 5/7 kit, notch, and milled 22s just like yours...my rear sits lower than the front. Was yours? Did you level it out?
I'm not positive on my options, but I think maybe helper bags?

Re: Loweing c30 crew cab
 

What does the 'lowboy 5/7 kit' consist of?

Re: Loweing c30 crew cab
 

A flip kit (Was told to remove the helper spring and spacer so I did that. Left the other leafs in.)
Front is spindles and springs.

The shocks arent bolted in yet but I don't think thatll raise it much if any...and the bed is off so theres another couple hundred pounds like would make it even worse.

Re: Loweing c30 crew cab
 

Like I stated, flip kits tend to yield 8" of drop on these things (height of the spring pack + pad + 1/2 the OD dimension of the axle tube = drop amount). Get some Bell Tech or Western Chassis 'lift' shackles. They'll help level it out.

I went through the same thing on my OBS (HD 3/4 ton leaf pack & the flip kit). It was ~8" of drop so I added the shorter lift shackles & nailed my desired 5/7 target.

Re: Loweing c30 crew cab
 

One option that I did not see mentioned. Which is cheap, but labor intensive.

Is to Z the rear frame, and then due a raised bed floor. This provides a level surface to load bikes, and is my favorite. From a visual perspective.

Re: Loweing c30 crew cab
 

Legal stuff is different up North. Can't just go choppin & welding w/o any worry of the DMV/inspections. How specific they are up that way?