4/6 lowering issues

Slowgoat60 · January 20, 2020

Hey everyone, I’m new to the page and also new to the lowered truck scene. I have a 2015 Silverado black rally 2 edition with factory 22’s. I recently installed the max track 4/6 kit. 2” drop spindles with 2” lowering springs and a flip kit in the rear. Everything went in pretty good for my first time with it being a truck. I’m used to my 05 gto. Had it aligned at a local shop and thought everything was good. Iv been noticing from a dead stop that there’s a slight shutter/vibration coming from the rear but goes away shortly after, normal driving, fast and slow. Also around 70, I can hear and feel almost like binding coming from the rear as well. Feel it and hear it most if I let off the gas and the faster I’m going and let off the louder it gets. Iv been trying to read and find my symptoms but can’t get a direct fit. Can someone help me so I can try to find a reputable shop to look into it. I don’t know if the angles are properly set or of the shaft is to long. Thanks in advance.

2015 rally 2

2005 gto 6.0

WHITESSTOWPIG · February 13, 2020

There is one problem that you are having for certain and another that you may or may not be having.The first problem is your pinion angle needs to be corrected now that the truck is lowered.They have phone apps you can use to measure its angle and shims to correct it.Every truck will be different so its not something you can guess at but to give you a rough idea of how off it can be on my RCSB that only has a 3/5 I had to put a 1/2" flat shim under the rear of the transmission and 3 degree angled wedge shims under the rear angle to correct the pinion angle.It can be severely off and causing all types of problems.The problem you may or may not be having is with the lowering kit itself.If the flip brackets do not shift the axle further back enough everything is going to bind down there.You need to look at the orginal engavement marks on the driveshaft at the transmission end and make sure its not being pushed passed that or your going to destroy the transmission.I would not drive the truck until you can check and correct everything IMO

00pooterSS · February 25, 2020

Just went through this with the max trac flip kit. My rear pinion angle was pretty far off. I ended up using the gold (thicker) supplied spacer on the transmission and the pinion angle was really off. It was at 5 degrees up.

I hate the idea of shims so I modified the flip kit buckets (brackets?) to allow the pinion to rotate downward. I trimmed the front tabs of the buckets (can't think of the proper name for them at this time) and then trimmed the half circle part of them to allow the pinion to not only rotate downward but to allow it to sit down in the bucket and make contact with the axle tube as designed. I had 5 degrees pinion angle upward, and transmission 5 degrees down when I started. I now have 0 degree pinion angle, 2 degree drive shaft angle upward toward trans and the trans angle is now at 4 degrees giving me a perfect 2 degrees at the front and rear u joint.

I the silver thin spacer on the trans first. It wasn't enough. I tired 2 degree spacers on the rear and they weren't enough.

However even when my truck was bone stock the pinion angle was too high and caused vibrations so things were all wrong to begin with anyway.

The best way to do all this would be put the gold shim under the trans and take the truck to a shop to have the leaf spring perches cut and relocated. I say that because if you look close you'll probably also notice it sits off center from left to right and you can have that corrected too all while not using shims. I did a lot of cutting and modifying things to center my rear end too. If you use shims you need to extend the leaf spring bolt length so that it reaches through the shim and into the flip kit bucket the rear end sits in. All these things are why it would be best, and would I would do next time, to just have the perches cut of and welded on in the right location.

Slowgoat60 · February 25, 2020

Hey, thanks guys for the responses. I did end up raising the truck up 1” in the rear and it made the binding and almost all vibrations go away and looks better in my opinion. I am taking it back to the shop for shims to be installed. Thanks again for your help. I will be letting the tech know what you guys said she he can take that info too!