Hey everyone- no luck with the search on this so hoping you all could help. I am installing the mx4 on my 21 f150 and the tonneau rails appear to have 4 shims on each of the sides installed already out of the box. When reviewing the install guide, it doesn’t state whether the 21 model year requires these shims or not and honestly I can’t tell either way when I test fit the rails if it looks correct with the shims left in place or removed. Any insight is appreciated!

 

I installed the BAK mx4 on my truck right out of the box with no problems.

 

Ditto...

 

Installed mine yesterday with no issues.

 

I installed the G2 (same as MX4-different weight allowance) a few weeks ago and didn't need shims. The shims are to be used if the lip you are connecting to is flared in or out (at least on the backside), which they are not on a '21 F150. Hope that makes since.

 

Installed mine without shims as well.

 

I also had no issues with mine right out of the box, except for where to place the drain tubes. Any ideas?

 

Not to hi-jack the thread but there have been a number of innovative solutions for this. Personally I just let it drain into the bed and out.

 

The first time I had one installed was on my 2014. I only had a bed mat and the installer drilled holes in the rubber plugs at the head of the bed and inserted them snugly there. It worked fine. My 2017 and now my 2021 have drop in bed liners, so it makes it easy tucking them into the cutouts for the bed tow hooks.

 

Just make sure the flanges of the box are straight and vertical. That way you'll be sure the side rails fit flush and the seals do what they are supposed to do.