How loud is your MJ?

[Far McKon]

Hey

I have a bit of a beater MJ, and the sound level in it is driving me nuts.  I grabbed a free db meter and ran it in the truck. I am (honestly) trying to see if I have time for this as a project truck, or if I should just get rid of it.   For me, it's  un-drivable for multi-hour road trips since the noise is so bad.

 

My Sound Levels:

Idle, parked: 60 - 70db

Driving, 35-40mph:  78 - 85db

Driving, 40-50mph: 80 - 90db

Driving, 55-70mph: 85 - 95db

 

Any chance someone with a well-tuned, well maintained MJ run a DB meter and post back?  I'm trying to guess how much of a project to get it into OK shape.

 

[Sly_Jeeper]

Rotella diesel 10w-30 n a seafoam


Sent from my iPhone using Tapatalk

[Pete M]

you don't have to coat every single inch, but slapping some sound deadening material on the larger expanses of sheetmetal can help.   especially the roof.

 

is it exhaust noise?  bearing noise?  tire noise?  wind noise?

[Smokeyyank]

Jeep and quiet rarely go in the same sentence. I've had MJs,XJs, CJs and WJs. By far the best ride is in a WJ but it's also because it's made to be a better ride. A MJ was never really made to be a cushy smooth or quiet ride. To get it that way I'd say you'd need to add sound deadener to the inside. While not a massive undertaking it takes time and depending on the condition of the interior could lead down a rabbit hole. 

[scaleless]

My MJ is absolutely coated in Dynamat and Dynaliner and it is my quietest vehicle by far, despite running a Flowmaster 40. 

Then again, that may be the hearing damage from the other vehicles speaking

I'll slap a dB meter in there next time I'm driving it

[eaglescout526]

I recommend installing one of those hood insulators. Helps quiet it down a bit. 

[MiNi Beast]

Noise.. multi hour roadtrips... project truck... yeah its a jeep. 

[gogmorgo]

I feel you. Of my two MJs one is definitely louder than the other, and the louder one is the one with the flowmaster and aggressive tires. Other things it has that contribute to quietness are a 4.0 and 3.55 gears instead of the 2.5 and 4.10, so 70mph is about 2200rpm instead of 3500, plus it also has floors and carpet and jute instead of failing vinyl over gaping holes with the jute long since rotten away. The one with floors is also warmer in the winter… floors are very much underrated.
Around town the 2.5 is okay, but it didn’t really occur to me just how loud it was on the highway until I had a passenger the one time, and we had to shout to talk to each other. Up until that point I always kinda laughed to myself at people wasting money on adding sound deadening, but I definitely get it now.

But even my loud MJ beats the crap out of my Lada that’s spinning 5000rpm to do 65 mph and shouting down a burnt out 2” glass pack. I drove that 2000 miles back from Alabama in a couple days, and was so done by the end of the trip, even with earplugs, that I shoved it into the snow in my yard and didn’t even unpack it for a couple months.

[jeepmjga]

I've Noico'ed mine (floor, back panel, roof and doors) with one layer of 80 mil black and a layer of 150 mil red foam and its still a little loud for my taste, could be the Puegeot thats on its way out though.  We will see if it changes when I swap it out.  Putting the new headliner in there definitely made a HUGE difference.  Also its a 32 year old Jeep so I'll take what I can get 

[89 MJ]

I used Dynamat in mine. You could whisper a conversation at highway speeds. 

[ghetdjc320]

1 hour ago, 89 MJ said:

I used Dynamat in mine. You could whisper a conversation at highway speeds. 

Same here. Takes a lot of time to go over everything but mine is super quiet even with my magnaflow. 

[Minuit]

55 mph: 70 dBA

65 mph, behind a semi with very little noticeable wind noise: 71 dBA

80 mph in heavy headwinds: fluctuated but the highest number seen was 76 dBA

70 mph in moderate wind: 73.5 dBA

 

Here is the sound meter I use. https://www.amazon.com/BAFX-Products-Pressure-30-130dBA-Warranty/dp/B00ECCZWWI/ref=sr_1_4?dchild=1&keywords=sound+level+meter&qid=1627952977&sr=8-4

 

Do know that dBA gives less weight to low frequency sound than other filters, and phone apps are not to be trusted. My relatively inexpensive meter only measures in dBA so that's what I'm stuck with.

 

Like you, I found the noise in my truck extremely objectionable at speed, especially wind noise. Here's what I did/am doing.

 

Do this realizing that this is a Jeep, not a Lincoln, and that these trucks cut through the air with all of the grace of a free-falling brick. There are lots of protrusions and gaps for weatherstripping to fill, some of them quite large by modern standards. The truck is a unibody, and tire noise is directly coupled into the cab through the bare minimum of bushings.

 

First off, all of the door gaps need to be sealed, and all of the various weatherstripping needs to be checked. If your door seals aren't doing their job, there's going to be massive wind noise. For me, dealing with wind noise has been an ongoing problem. I still don't have it down to a level I'm happy with. But I'll freely admit that I'm a "continuous improvement" kind of guy who isn't happy with anything, ever - especially if it has to do with sound.

 

Take an honest assessment of what you want to do with the truck, and pick tires accordingly. Highway tires are a lot quieter than all-terrains, which are massively quieter than off-road tires. I switched my all-terrains out for a set of Michelin highway tires, which not only gave better on-road feel but reduced road noise.

 

Secondly, any panel that can vibrate and become a speaker needs a generous smattering of Dynamat or equivalent vibration damper. 100% coverage isn't needed, but don't be shy. The main goal here is to prevent panel resonance. I would advise against putting this stuff on the floor and outer door skin, or roll it on very carefully if you do. If the adhesive fails, it can trap water. These trucks have enough trouble with that already. I'm going to have to reskin my driver door eventually because of adhesive failure on the factory vibration damper in the doors.

 

In regards to the above, the single biggest contiguous panel on the truck is the roof. Stick a whole sheet of Dynamat right in the middle of the roof and you won't have to hear that awful tinny sound on the roof when it rains.

 

Ditch the jute padding under the factory carpet/vinyl because it holds water. You want nothing that holds water on the floor of your truck.

 

If you still aren't happy, and you probably won't be, the most effective thing you can do to block sound from entering the cab is to coat it in a high density, limp material. Mass-loaded vinyl of at least 1 lb/sq. ft. is ideal for this. You're essentially creating as air-tight a barrier with the stuff as you can from the glass down. You don't want it in direct contact with the metal of the truck, though. You'll want to de-couple it from the floor with closed cell foam, such as as 1/8" neoprene foam rubber. Neither of these materials are exactly easy to mold into a carpet underlayment for a vehicle as you might imagine. The mass loaded vinyl doesn't stretch and won't conform to compound curves, so you basically have to make a quilt of the stuff in the shape of the floor, doors, and cab rear. HH-66 vinyl cement is great at holding it together. Use heavy duty velcro to hold the quilt to the truck. This step is a huge pain in the @$$, but it will provide results. If you want an off-the-shelf solution, DynaPad comes to mind. Some of the products on the market didn't exist when I did this, so I don't have experience with them.

 

I'll have to dig through my build thread and find some pictures.

 

Still not gonna be a Lincoln, though. My other car is a 25 year old almost-Lincoln that even has a sunroof, and it has zero wind noise until 80 mph, and a non-objectionable level of road noise at all speeds even though I haven't done anything to it. Gets frustrating after everything I've done to the truck.

[Pete M]

"almost-Lincoln"   

[Parei_doll_ia]

Before I fixed the rust- very loud, mostly from where the windshield channel rusted on the bottom and bad floor repairs from the PO. After- pretty quiet, not as quiet as my VW but good for a Jeep. I have a Flowmaster delta 70 with a resonator in it that helps too. Take the carpet out and look for holes.

[Far McKon]

Folks; thanks for all of the awesome feedback.

`these trucks cut through the air with all of the grace of a free-falling brick. `

[fiatslug87]

5 minutes ago, Far McKon said:

these trucks cut through the air with all of the grace of a free-falling brick. `

Could be worse, my wife has an FJ Cruiser, now that's a brick! However, it does have much better sound insulation.

[DesertRat1991]

Whaat....!?  You're gonna have to speak louder! 

 

This 30y/o pickup truck ain't got A/C so all the windows stay open, all the time!

[ghetdjc320]

Yeah, MJs and XJs are much more refined in the aerodynamics and interior comforts than CJs, YJs and TJs. Now those are more akin to bricks. If you have a beater truck then it will be loud no matter what. I hate seeing beater MJ’s but hey, they help my resale value since they already have a foot in the grave. That being said, you can get the interior of an MJ very quiet depending on the effort and expense you are willing to put into it. 

[87MJTIM]

What?!?!?  I can't hear you.  I am driving my MJ.

[AZJeff]

I went and did some quick measurements on my MJ when I ran out to the hardware store this AM. 

 

Idle -- 48dbA

Driving at 45mph (smooth paved road) -- 69dbA'

 

I was unable to find a spot to go any faster than about 45-50, so what noise level there is a 65mph is to be determined.

 

Also, since this is S. AZ, I am running my A/C all the time.  The blower setting was at it's lowest level when I did my measurements, so fan noise was minimal.

 

My MJ has foil-coated closed-cell polyethylene foam on the floor under the carpet, and the floor is bedlined under that.   The foam is also glued to the roof.  The hood has self-adhesive foil on the inside to reflect the heat off the painted surface, but no insulation beyond that.

[silvertwinkiehobo]

"Free-falling brick." Yeah, that's an apt description. So, Joe's rig, you have tire, rear axle bearing and exhaust noise when the windows are open; all of those plus the electric fan when the windows are all closed and the A/C is blasting.

[pizzaman09]

Mine had dynamat and two layers of carpet, it was very quiet.  It was also running on Mastercraft passenger car tires, made for a pleasant drive from southern California to Northwest Pennsylvania.  When I find a replacement Comanche I plan to do a similar interior quieting setup.

 

[Far McKon]

yo @pizzaman09man,  Thanks for sharing that video, it gives me some hope for getting my guy quite enough. 

 

Just finished an 5 hour roadtrip, and it was brutal (like 87-95 db the whole way). I won't take the kids (8,14,15yo) in if the drive is more than like an hour. It's just too brutal on them.

 

I'm digging around the forums to read about dynamat. What is the deal with  double carpet? Just two layers of the same basic carpet stuff?

 

[89 MJ]

In my truck, I can hear the fuel pump over the engine at idle. 

[ghetdjc320]

A lot also has to do with the road finish. You’ll need to look at a real time analyzer to see what frequencies are actually in the cab. This will give you db levels of the different frequencies. Without knowing what frequencies you are dealing with, it’s hard to do anything more specific than just a shotgun approach. For instance, new bushings, shocks or coil isolators may really help in certain cases or “road” noise. Motor and transmission mounts can also really make a difference as can leaf spring bushings.