Rubbing/vibration after 03 Lightning JLP 4" drop shackle

fordification · #1 10-04-2009, 03:27 PM

This is a repeat of my pinion angle thread over at nloc, but I thought I'd try here too.

Basically to sum it up, I started with the 180 stock shim rotation (-1 pinion/+5 shaft), and since then, I've had a rubbing/vibration only at 20mph.
1) After that I've tried a 4 degree shim (+3 pinion/+4 shaft),
2) dropped down to the 3" with the 4 degree (which caused a acceleration vibration)
3) tried no shim with 3" setting
4) stock shim at stock location with thick end in front (which caused a deceleration vibration).

So I've felt the extreme positive and negative pinion angles to the point of causing a u-joint vibration, with increments in between, and none of them would effect the 20mph rubbing/vibration, which is telling me it's not u-joint related.

Also, the truck is mint, buying it with 2100 miles, now with 10k miles. Zero rubbing/vibration before the shackle install.

Only thing I can think of is either something tight at the trans output, meaning driveshaft length, or something went wrong lifting the truck up at different angles. I'm just about to re-install the stock shackle to see if everything is ok.

I really debated on whether to keep the truck stock because it's so mint. Even made a miles before modding thread, but decided to take the chance.

I know this should've been so simple, but any help would be great man!

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blackedoutV6 · #2 10-04-2009, 04:20 PM

a 4" drop shackle is a BIG drop shackle, and it obviously makes the leaf springs sit way different than stock (higher in the back)

maybe you would have better luck trying a set of drop leaf springs or a 2" Shackle/2" hanger combo

Patman03SprCrw · #3 10-06-2009, 10:25 AM

Well first off, the JLP 2/3/4 shackle isnt actually that, its 2" 2.5" or 3" settings, so keep that in mind.

secondly the general rule of thumb is you need 1-2* for every inch dropped that isnt evenly dropped front and rear of the leaf springs. So assuming you have 3" shackles, try a 4* shim with the fatter part in the rear.

Are you certain the shackle isnt hitting the underside of the bed?

fordification · #4 10-07-2009, 12:26 PM

Quote:

Originally Posted by Patman03SprCrw

Well first off, the JLP 2/3/4 shackle isnt actually that, its 2" 2.5" or 3" settings, so keep that in mind.

secondly the general rule of thumb is you need 1-2* for every inch dropped that isnt evenly dropped front and rear of the leaf springs. So assuming you have 3" shackles, try a 4* shim with the fatter part in the rear.

Are you certain the shackle isnt hitting the underside of the bed?

Thanks for the reply.

I mentioned in my original post trying the 4* shim at both the 4" and 3" setting.

And to clarify, it's a rotational rub, that's why I call it a rubbing/vibration. Not sure what else to call it. But it's definitely not touching the floor of the bed.

Patman03SprCrw · #5 10-10-2009, 07:04 PM

only other thing i can think of is checking the parking brake cable where it goes across the leaf spring. You may have gone low enough now that you need to relocate the cable to the under side of the leaf spring.

if that is the case, either you are pulling too much on the cable, and you are feeling the parking brake grabbing, or the cable has slide down the leaf spring some, and could actually be rubbing on the tire itself.