2nd Gen Non-Engine/Transmission The great cab resonance mystery-- PLEASE HELP!

[Hohn]

Guys, I am completely stumped.



It all started when I decided to do the D25/bilstein install. Since the install, I have had a mysterious part-time cab resonance that I CANNOT find the source of! I have established only that it is linked to engine rpm only, so it's not a driveline (speed-dependent) vibration.



The spring/shock install went as normal as i could hope for. I ended up loosening the bottom trailing arms at the frame to gain enough droop to install the springs.



When i put the truck back together, I noticed there was a cab resonance that seemed mostly when I turned left, and seemed to go away when i turned right, even a little. Since I ruined my track bar doing the install, I attributed this resonance to the 1/4" or so of play in the track bar.



So I ordered and installed the DT track bar. No play whatsoever, yet the resonance is still there. It practically disappears when i make a right turn. It's VEry noticeable when I make a left turn. Going straight, it's usually there, I suspect because of the crown in the road acting like a left turn somewhat.



Track bar eliminated, I suspected a loose shock. Nada-- i cannot physically tighten the shock bolts any more.



I have also tightened (w/ a 1/2" breaker bar) the engine mounts (barely moved), the trailing arms (couldn't budge them, since I used an impact on those), and almost every nut or bolt I can find in the front end- tie rods, drag links, pitman arm, idler arm, you name it.



Still I have this mysterious resonance that sounds a lot like the shutdown shudder, only the whole cab resonates. You can feel it in the wheel and the shifter too.



I have a driveway with a slight incline and a big curb. When I approach it, the resonance stops as I make a right turn towards it. Then, when the truck starts swaying back and forth a couple times (from taking the bump at our driveway entrance) , I can hear the resonance start and stop as it transfers weight from side to side!! When i finally park, the resonance is really bad as it just sits there and idles.



I kinda suspected it might be the rear shocks (since I haven't checked those) but I did the rears first, and there was no resonance aferward. Not until I tore apart the front end did I get this resonance.



The Bilsteins that I have are the longer fronts (for the D25s) and tightening the upper mounts means tightening a 3/4" nut while holding the stud still with a 6mm Allen wrench. I can't tighten them down any farther!



The spring isolators are there on both sides above each spring.



As much as I LOVE the ride and look of the finished product, I am at the point where I wish I never touched the front end. Will I EVER get my smooth front end back?



Please help-- I feel like I have tried everything and don't know what to try next.



Justin

 

[HEMI®Dart]

How are your front axle u-Joints? They will make strange noises usually when turning one way.

 

[Boondocker]

maybe it's not the suspension

Justin,



It sounds like you have ruled out loose suspension and steering components. You didn't lose any tools in there, did you?



You have 2 clues - resonance tied to engine speed and initiated by left turns. In a way, it sounds like something is able to lean over and contact some part of the engine, engine connection or exhaust when leaning outboard on a left turn. Then when turning right, it lean back away from the source of the vibration.



I presume you had to remove the upper shock towers and air box (if you have one) for the shock install. It's very hard to tell if the bottom of the air cleaner box is secure as the rubber grommet lets it wiggle a bit anyway. Maybe the grommet isn't seated right and a bolt is contacting the fender.



Maybe, while the engine is running, you can jack up one side and then the other to simulate the sideways load of a turn. This might help you pinpoint the noise source from outside the cab.



Good luck,

Neil

 

[Dane]

What Neil said, maybe something is touching the engine or transmission? It's something you did during the mods, not necessarily the new parts. Could it be related to the track bar getting destroyed? I noticed when I installed my D25s that I had to be real carefull about letting the front axle droop far enough to get the new springs in, that I did not damage componants hooked to it. Did you remove the pitman arm? If not maybe you damaged the steering box shaft? Make it make the noise, block the wheels and crawl around under the truck till you find it.

 

[mediccummin]

air box

What air cleaner set up do you have. I know on my AFE the bottom of the box sits on the top of the shock itself, made a vibrating noise. I had to make a rubber bumper in between the two. Just a thought. Good luck... .....

 

[illflem]

Check that the adjustment coupling on the tie rod doesn't have it's large side facing forward. It can touch the steering stabilizer setting off weird vibrations.

New shocks may have changed the front end geometry causing parts that didn't rub before to now do so.

 

[willyslover]

when you jacked it up high on a corner ... did you dislodge a body spacer rubber. . maybe a spacer now has the bolt touching at the mount



check front area for a rubber problem with the radiator and CAC

 

[Hohn]

Thanks for the replies, fellas.



I have ruled out u-joints in my mind because it will resonate when idling and motionless. So if the noise is there with no u-joint movement, I don't believe they can cause it. I suppose it could still be a possible cause.



I have the stock aircleaner setup. I have also ruled that out as a source of the vibration-- the noise is still there with the airbox relocated and the engine running.



I DID lose a large socket when doing the install, so maybe it's hiding somewhere in a crevice and causing the problem. The sporadic nature of the resonance, and the linkage to the front being loaded or not on each side is what baffles me. How could a tool laying somewhere act this way?



I did not remove the shock towers during the install. I had enough droop to squeeze the coils in (barely).



Illflem, I will check that adjustment coupling. After I first started hunting down this resonance, I went through the front end and couldn't see anything close enough to touch. I will have to check again.



I beleive the steering box and it's connections are fine. There is almost NO play in the steering at all, and the connections at the pitman arm, the pitman shaft itself, and the all the tie rod ends are tight and free of play.



Last night when I pulled into the driveway and parked, the cab was resonating badly, so I got out and walked around the front, listening closely. You can feel the resonance in the springs and even the tires. The source of the lowest frequency sounds (which I believe to be causing the resonance) seem to be coming from the right front.

Because it's a low frequency, it's hard to pinpoint. It's like how you can hear a subwoofer but not know its location. Higher frequencies are much more directional.



I'll keep chewing on this.





Justin

 

[Jetson]

Take an old waterhose and cut off about 3' of it. Put it to your ear and put the other end near places you think might be causing the vibration. You'll hear it if you find it.

 

[Hohn]

Great tip! I will try that-- I have some heater hose laying around that should suffice.



Justin

 

[RustyJC]

Originally posted by Hohn

I DID lose a large socket when doing the install, so maybe it's hiding somewhere in a crevice and causing the problem. The sporadic nature of the resonance, and the linkage to the front being loaded or not on each side is what baffles me. How could a tool laying somewhere act this way?

Justin,



I'll betcha that sucker is wedged between the engine, bellhousing or transmission and the cab, probably down in the transmission tunnel area. Because the drivetrain and the cab are both rubber-mounted, they will tend to lean away from the direction of the turn - the suspended mass, CG and mount stiffness will, of course determine which moves the most. If it's the drivetrain, then the socket is probably on the right (passenger) side. If it's the cab, then the socket is likely on the left (driver) side.



Rusty

 

[Hohn]

So maybe I should just go offroading. . The sudden impacts might jar it loose?



Justin