Resonance problem in cab

[cosmo]

I have a freshly rebuilt 351w and I'm running a dual exhaust with an h-pipe and 2 flowmaster mufflers. At idle to about 1500 RPM, I have an unbearable resonance (vibration) in the cab. Has anyone had this issue and solved it? I realize I should have used two slightly different sized mufflers, but since they are welded on now, I'm hoping there is another way to solve this

[Bill W]

Drone, i had the same thing when i had flowmasters. only way to fix it is ditch the bolwmasters and get something else. i went with glasspacks.

[f100jim]

Cosmo, mine will do it too sometimes. I think it's the back of the cab vibrating. Just for kicks take a piece of foam and stuff it between your cab and bed from the bottom and see if that stops it. If it does, you can pull the tank and put some insulation between the tank and back of cab.my

[65fordguy]

I have Thrush Welded.. almost like a flowmaster.. just more of a old school sound .. but same drone. The Vibrations in my truck were coming from the roof panels.. door skins.. back of the cab and the center hump...

My fix...

I wrapped the following products.. used both.. same results.

http://www.homedepot.com/Building-Mater ... ogId=10053

http://www.homedepot.com/Building-Mater ... ogId=10053

the stuff lays down great and looks good.. until someone slides a few rims across it.. as happened to the floor there... o well its gonna be covered up by the mat and carpet.



around my center hump... applied it in strips to the rear of the cab.. and put 2 strips on either side of the cab roof from front to back.. and then one going from left to right.. with about a 6 inch gap in the center. Applied 3 strips to the door skins. ( pull the access panel out and apply to the inside of the door skin)

You would not believe the difference it made.. and I didnt have carpet, headliner or any upholstery. . according to my iphone it was 28 decibels quiter.. in my book thats alot. plus the cab just sounds more solid.. not a hollow can.. especially when closing doors.. its a clink.. rather then a klangalanalanalangoooing .. you know what im talking about.


I also picked up a pre cut floor sound mat from LMC last year .. it fits down under the carpet... Havent installed it yet.. but cant imagine what it will be like with it , carpet, and headliner.

now, I had my exhaust dumped just pass the cab with the tips about 9 inches pass the rear of the cab.. yours may be a bit different.. but you should be able to get similar results.

[MadMaxetc]

You need to change the natural frequency of eather the Cab or the Exaust.

You could try different tips on the exahust or differant muflers.

You could also do some Dynamat or something like that to help with the cab.

[64shortie]

Two years ago I sounproofed (dampened) my entire cab with dynamat. I pulled everything out including the tank and layed it over the entire cab. Once that was done all those kind of problems went away. And, like 65fordguy said, The whole cab seems more snug and solid.

[Alan Mclennan]

I`d check the gap between the back of the cab and the brace the top of the tank fix`s to!, squirt some sikaflex in there! and do as shortie did.

[Brian Taylor]

both times I used Flowmasters I had the same droan with different vehicles. I have found with the slick the two rear corners make nice speakers for any under body sound, the doors are big drums too. And any loose braces need to be insulated.
I used the same Home Depot foil backed insulation throughout my truck and added jute backed insulation in the floor, rear of cab and the headliner (whenever I make one).
Mufflers are best installed to the rear of the system to not have it under the cab. Make sure to use good rubber insulators at any hanging point for the system too.

[Uncle Skip]

Just got back to Texas and saw this post.
Yea me.
Yes.
Insulate your cab.
But I think the answer is to install an H-pipe on your duals.
Goes a long way to help quiet down the exhaust.
I have Flowmaster 40's and I love the sound.
But I have the same problem at 55 mph that will be cured with the H-pipe crossover as soon as I get the truck running again.
U@ss

[64shortie]

Yes, the doors. That's the only part of my cab not dampened. Must do those soon.

[Phil]

H pipe in my Fairlane doesn't help.
Running Dynomax ultraflows under the car
I have 3" chrome tips with a rounded over end.

I may saw those off and see what happens
Or I may just try open hookers.

[cosmo]

When I painted the truck in 2008, I put that home-depot stuff in the cab. My floor and roof are completely covered with it. I only put a few strips behind the gas tank. (I should have put more I guess). I DID NOT put any in the doors or in the cab corners. I will do that ASAP. I may even put some under the bed. The exhaust tips dump down before the rear axle, but aft of the cab. I may be getting some "reflection waves" from the ground that are resonating the bed floor... When I solve it, I let you know what worked

[Sarg]

Here is a GREAT site to learn a bit more about this subject:

http://www.sounddeadenershowdown.com/cgi-bin/index.cgi[/url]

[jmf66]

The problem with the Home Depot foil backed insulation is that it's just not heavy enough to stop vibration. Dynamat is great, but expensive. I used B-Quiet ultimate in my Mustang whch worked great. I will use it again in my 66 F100 when I get the cab back on.