When I looked at my 2nd gen truck I noticed the factory did a good job of installing sound deadener. The factory actually did a good job in this one part of sound reduction. My passengers side floorpan had some minor rust. I figured that was because the cupthrower, err... cupholder had lost some drinks in the past. That water on the floor made the factory sound deadening loosen up. I pried that material off and installed some 3M sound deadening where the factory stuff had been. To me that was not really adding more deadener. It was replacing what had deteriorated.
My truck had lots of sound deadener from the factory. As far as I can tell every spot that needed sound deadening got it. That surprised me. There was deadening on the transmission hump, both front floor pans, under the club cab seat, and on all the sides. There was even sound deadening under the kick panels. I only really replaced one bad part of the factory sound deadening. I did not look at it as me adding more sound deadener material like the CLD's. I did not use the best possible panel deadener here. I used what I found cheap locally. It was needed for such a small area I did not worry about using the best material plus it was under $10 on clearance.
The one (and probably only) place the factory missed completely was the back wall. That I did put some spillguard 7/16" 8 lb carpet padding (underlayment) on. I put 2 layers of spillguard 7/16" 8 lb carpet padding under my trucks carpet. This should be easily found at most stores that sell carpeting for a house. I also added a little above the carpet on the firewall and around the steering column. The nice thing about spillguard carpet padding is it is waterproof. It should prevent your floors from rusting with your wet feet.
I can see that adding some under the plastic door panels would probably be a good idea.
After removing the carpet expect to find some rust. Remove the rust then use a good paint. I used POR-15 as it is a rust converting paint.
It looks like the cupholders did not hold the cup very well. I took out the factory sound deadening on this side because of rust and it was loose.
Now the rust is taken care of and the factory sound deadening has been replaced.
The drivers side was better.
Now it is good as it gets.
The factory actually did a good job of sound deadening on my truck. Those of you with a 1st gen may want to add soundproofing material in the areas my truck has it in.
I added some extra sound deadening on the transmission hump where the factory deadening was cut out for a 5 speed and transfer shifter as I have neither one.
Here we see sound deadening under the club cab rear seat.
It is time to add the sound absorbing material. It is called foam. I used 7/16" 8lb spillguard carpet padding (underlayment). After applying one layer I decided to add a second layer. You should be able to find this waterproof carpet padding at most house carpet stores nationwide. Try not to order it online as shipping is far to expensive on this heavy and bulky material.
Notice the studs for the seats sticking up. Be careful, they will rip your new foam if you are not very careful.
Use some glue (I used Roberts double sided carpet tape) to hold more foam up in the area above the carpeting on the firewall. I even added some scrap foam to fill in the hole the factory left in the sound deadening material here.
I wrapped a piece of foam around the steering column and added more on the firewall. The ford diesel guys say this is an important area to cover up for sound reduction. Maybe I should add a second layer of foam here.
This is the hardest part of the job. Making the foam fit the transmission hump tightly.
The foam did not want to lay down with 2 layers. The foam is bunched up.
I sectioned the foam to eliminate the bunching. Then I used aluminum tape to hold it together and hopefully remain waterproof.
Yes, I did put some foam behind the back seat on the back wall.
So far all I have done is 2 layers of foam under the carpet and one layer of foam on the firewall above the steering column on the drivers side.
This is what I used to show DB levels with.
The end results so far are 62-63 db at idle down from 85db at idle and greatly reduced noise on the road. My radio went from 28-32 down to 18-24. I could not hear the radio before on level 18. My grand marquis with the same exact radio usually is set at 18-22.
My 1999 grand marquis idles at around 50dba. 60dba with a -10 is as low as my sound level meter gets so it is hard to say for sure exactly how quiet it is. It is definitely quiet.
My truck now idles at 62-63dba
Driving down the road my Grand marquis will get up to about 63 db below 30mph with mild acceleration. It seems to get up to 66, perhaps 68db when getting around 50 mph. Yes, I am sure accelerating hard it would make more noise.
My truck now seems to be at 67-74dba while driving at 50 or less. It seems to be quieter when the torque converter is unlocked. This makes sense. I noticed that at higher rpm's the engine is quieter than at low rpm's. It may also have something to do with full engine power being applied compared to some power loss through the torque converter.
You can see without a doubt that my Grand Marquis is still quieter than my truck. However, driving down the road the grand marquis is not significantly quieter. The truck used to be much louder than my car would ever be unless perhaps the exhaust fell off completely.
1999 Grand marquis 50dba at idle 63-68dba on the road.
My now sound deadened 1997 dodge diesel truck 62-63dba at idle. 67-74dba on the road.
Perhaps adding more sound insulation to the doors and other panels would help the truck become even quieter.
I can still hear the diesel engine sound in my truck but it is not overpowering like it used to be.