Constant whistle from justice on back rack

[justavillain]

I have a 50" justice on a back rack on my truck using the oem brackets and whelen brackets to attach it. But 50ish+ mph I get a whistle in the cab like a cracked window would make.


I flipped it from hanging over the cab to behind and it still does it. But due to the size I cannot get a gutter strap kit for it for my truck. I need a 52-54 didn't realize that till I bought this. So I may just sell it if you guys don't have a solution.


Recap 50" justice on a back rack with br lightbar bracket and whelen kit to attach. Constant whistle from 50ish mph.

 

[Zoe]

This is just what happens when you put things into the air stream.


There are some common things that can cause a whistle (as opposed to straight wind noise).


Generally whistles come from small cracks/separations. Places to look would be tiny gaps between brackets, separation between lenses, etc. You can try to tape or cover these gaps and hope to eliminate the problem (and some bars are known to have whistles compared to others, not sure about the justice).

 

[HILO]

Anyone else remember all the hell we went through with the singing MX7000, and it turned out to be the metal clips being bent wrong?


For the Justice, I would make sure the domes are secure, the cable is secure at the base. Although, having moved the bar, and still getting the same noise makes me think it is not the bar.

 

[justavillain]

When I flipped the bar I removed the brackets from the rack and laid it down in the bed and test drove no sound. Reapplied I reverse and noise was back.


I have since removed it and getting ready to sell it and just go with no warning lights and no sound at all. This thread was a way to save the system I have instead.


The domes are on tight, the weather Seals are all intact and in place, the cables are in conduit to the gromit and the gromit opening is siliconed shut. Also the opening In the truck was sealed shut also.


I know the sound kicks in at about 55mph and continues up to almost 80 on the highway. So I guess that's when the air stream over my truck changes.


Thanks for the ideas so far.

 

[billforbush]

Just a thought - the cable entrance opening and especially the unused opening on the other end? Perhaps sealing them up better. I'm doing a 50" Justice on my Sierra pickup and all I needed was slightly longer bolts for the straps and it fits like a champ. Good luck


Bill

 

[JohnMarcson]

Just teach it the words so it does not have to hum or whistle.


:hahano: sorry....could not resist

 

[Storm4200]

IMO, The backrack brackets mount the bar too high. I just mounted a 51" Valor using the same equipment, and I have zero whistle. i didnt clamp the brackets to the backrack like they wanted me to, instead, i drilled new holes and mounted the bar as tight to the roofline as possible. Not a peep.

 

[jhallgren22]

I have a Mini bar on a standard back rack mount on my truck with no issues. I do however notice that the airflow over the cab changed and now i get light snow buildup in a triangle under the middle of the bar down the rear window. Not sure if that will help you solve the problem or figure out where the whistle comes from.

 

[Carlos SpicyWeiner]

The rails under the bar can often be a source for said whistling. The SOS magnum was notorious for it until they started coming with a filler for it.

 

[kitn1mcc]

are you using mounting feet or the studs to hold the bar to the back rack may want to try the studs it will lower it down

 

[GPC]

I've got an edge mounted to a back rack and have no noise issues with it.

 

[Storm4200]

If you're using the mounting feet, try the stud mount.

 

[justavillain]

I am using the studs. When you use the plastic feet the brackets angle and the bar sits too high.


I have seen a few threads about off road light bars with fins causing issues.


I could look in to mounting it like storm did but how did you attach the bar to the brackets? I'm guessing socket cap screws right to the plate in the bars channels (I like the super low gap means I can still use the drive through car washes.)

 

[Jamey@NNE]

Only problem with getting it too low is as the truck flexes the cab will move so be careful with that. I know storm put rubber under the bar for this but it still is a threat to the paint and mounts.

 

[JohnMarcson]

The snow pack pattern is an interesting bit of info. If you have a way of making non-toxic smoke and a decent fan, you can look for unusual patterns in air flow. If you use wet pine wood or tires and a leaf blower it's a redneck wind tunnel.


Seriously though whistles on cars are caused by the same thing as whistles and whistling in general. Air being forced through a small space or over and edge. Usually the air being unequally split between similar openings or over a plane or edge. The air stream does not split in equally and bounces back and forth between the two possible routes and makes a string of pulses that radiate as sound waves. On a car this usually means the gap size between the bar and car as well as the angle and size of the mounts that run in that space. The roof gap is the space and the mounts ac as the edge/blade that unevenly splits the airflow. You can mess with the angle and height no make the whistle disappear from human hearing range or totally removed it. Note if dogs riding in the vehicle whimper and pee, try again.

 

[justavillain]

I knew it was/is caused by the gap. I'm going to try the post mount idea I can always put grommets in the rack.


By now I've taken the 1 seat out of my truck to many times for my liking.


For the dog I have a back seater who can tell me if it's in his range

 

[jhallgren22]

I knew it was/is caused by the gap. I'm going to try the post mount idea I can always put grommets in the rack.

By now I've taken the 1 seat out of my truck to many times for my liking.


For the dog I have a back seater who can tell me if it's in his range

You said your mount folds back? is it the Back Rack minibar mount that does that? Maybe its something to do with the hinge on it having some space for air?

 

[justavillain]

It is the full size brackets just flat sock bent at a 90 they don't fold back you can mount the L over the cab or flip it around and put the L on the other side of the uprights.