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Old 07-15-2019, 04:01 PM   #1
Dibdob62
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Need to drop the rear a little more ?

After fitting a 7"/5" drop kit with a notch kit and running 275/60/15 tyres on the rear and 255/60/15 tyres on the front I need to drop the rear 1 1/2" more.


I have looked at drop shackles and thought about fitting 255/60/15 tyres on the rear. What's your thoughts are there other ways ?

1977 GMC C15 short bed by the way
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Old 07-15-2019, 04:55 PM   #2
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Re: Need to drop the rear a little more ?

How many springs are in the rear?....could you possibly take a leaf out?
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Old 07-15-2019, 05:30 PM   #3
sweetk30
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Re: Need to drop the rear a little more ?

never going to haul heavy loads pull the bottom THICK overload leaf from each pack thats anywere from 3/4" to 7/8" thickness on average for them .

if you do make sure to clamp the leaf pack its under compression with the center pin holding them together .

tire swap info

255/60/15 = 27.05" tall
275/60/15 = 27.95" tall

half of this is the amount you will gain or loose on the ground . so you would only loose around 1/2" height of tire but might be skinny compared to the older fatter 275 tire .
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Old 07-16-2019, 09:37 AM   #4
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Re: Need to drop the rear a little more ?

Quote:
Originally Posted by sweetk30 View Post
never going to haul heavy loads pull the bottom THICK overload leaf from each pack thats anywere from 3/4" to 7/8" thickness on average for them .

if you do make sure to clamp the leaf pack its under compression with the center pin holding them together .

tire swap info

255/60/15 = 27.05" tall
275/60/15 = 27.95" tall

half of this is the amount you will gain or loose on the ground . so you would only loose around 1/2" height of tire but might be skinny compared to the older fatter 275 tire .

Forgot to mention I've flipped the axle, Will this still work ?
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Old 07-16-2019, 10:21 AM   #5
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Re: Need to drop the rear a little more ?

Shackles are easy enough but dialing in the exact 1.5" might be an issue (I believe they are either 1 or 2"). Word of caution though.... Installing shackles might also require notching the bed floor cross sill in the area directly above the shackle. The later trucks had the more common 52" length leafs which require the clearance. Earlier 56" HD leafs didn't require the clearance on my 74swb.

Once the rear is flipped, removing the HD overload leaf may not work. With the rear relocated on top of the springs, the overload acts as a lowering block of sorts. You could try removing it first & see what happens since you're only losing time vs. time + money.
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Old 07-16-2019, 12:38 PM   #6
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Re: Need to drop the rear a little more ?

flip kit = no extra drop removing the overload .

as said drop shackles can hit cross member in the box . my 2wd build i worked around it on the 52" springs via cutting / boxing / welding the section in with a chunk of exhaust tube for a super clean look .

marked out
cut out
exhaust pipe cut and halfed and set in
welded ends shut
drilled drain hole each side and old section on top to show what was removed
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Old 07-16-2019, 12:54 PM   #7
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Re: Need to drop the rear a little more ?

Are lift blocks available/legal over there? Plenty of companies make a 1.5" block
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Old 07-16-2019, 01:17 PM   #8
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Re: Need to drop the rear a little more ?

Quote:
Originally Posted by sweetk30 View Post
flip kit = no extra drop removing the overload .

as said drop shackles can hit cross member in the box . my 2wd build i worked around it on the 52" springs via cutting / boxing / welding the section in with a chunk of exhaust tube for a super clean look .

marked out
cut out
exhaust pipe cut and halfed and set in
welded ends shut
drilled drain hole each side and old section on top to show what was removed
Think this is the way to go Just had a look at mine and the cross member has already been cut plus I only have 4 leaf's in my spring pack.
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Old 07-16-2019, 01:18 PM   #9
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Re: Need to drop the rear a little more ?

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Are lift blocks available/legal over there? Plenty of companies make a 1.5" block
No and yes but I think the shackles are the way to go
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Old 07-17-2019, 08:28 AM   #10
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Re: Need to drop the rear a little more ?

the leaf removal will still work as it will less the load that the springs can handle...the vehicle weight will gain some drop
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Old 07-17-2019, 10:31 AM   #11
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Re: Need to drop the rear a little more ?

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the leaf removal will still work as it will less the load that the springs can handle...the vehicle weight will gain some drop
How so?

I was taught the over-load leaf does it's job when the other leafs are compressed enough to make contact @ each end of the over-load. Simply removing it should not impact the other leafs spring rate.

Removing other leafs within a spring pack can impact the spring rate & thus yield drop because they are in full contact w/one another regardless of compression amount. Removing one decreases the amount of weight the others can support.

What am I missing?
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Old 07-17-2019, 11:30 AM   #12
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Re: Need to drop the rear a little more ?

Quote:
Originally Posted by sweetk30 View Post
...I worked around it on the 52" springs via cutting / boxing / welding the section in with a chunk of exhaust tube for a super clean look.
Very nice job! I've been reluctant to simply notch mine, but may do it your way now that one of my buddies has a new shop with 12 ft ceiling.
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Old 07-17-2019, 01:07 PM   #13
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Re: Need to drop the rear a little more ?

i got ocd so it would drive me nuts knowing it was not correct under there .
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Old 07-17-2019, 01:18 PM   #14
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Re: Need to drop the rear a little more ?

I've just notched them in the past w/o boxing. Of course, boxing it in doesn't hurt but my thought is it wasn't beneficial.

The location notched is closer to the bed wall & behind the corner of the tub. That area isn't going to see the weight/forces the center of the floor would. They're not capped @ the ends so capping that local area isn't adding to the weight capacity since the strength is in the height of the channel.

The only reinforcement I've done is for the center (when it's notched for differential clearance). I will put in thicker pieces of angle parallel to the notched cross sill above the differential. They get spaced far enough away so they clear while providing support as close as possible to the notched area.

Although it's newer so not the exact same issues as a Square, I'll be doing my 99 CC SWB OBS bed in the near future & will get some pics since I know it will need it done.
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Old 07-19-2019, 10:12 AM   #15
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Re: Need to drop the rear a little more ?

your over load does have some effect all the way through the motion...

old 4wd tricks played here, we used to shorten the length of overload as well as flip them so the have more down ward arch before fully engaging.

its a freebie to pull it and see the difference.
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