I'm sorry I didn't do test drives between each change I did. That's cause I wasn't neccesarily working on fixing the 70 mph vibe.

Stock I had the "rrrrrrrr" vibe at around 70-75 mph.

Put H2 Hummer rims and 315 tires on.
I did take it for a test drive and drove my highway commute for a couple weeks.
Vibe still there and not really at a different speed.

Then I put my 5" exhaust on. Didn't really do a test run on the highway cause I don't run the route anymore.

A few days later I changed the lub in the diff's, adding the Mag-Hytec cover and had the speedo recalibrated from 400 to 601 revs per mile.

Been doing test runs all through the speeds and can honestly say... its smooth as glass now.

I have two exhaust hangers left that I haven't welded on yet. The exhaust is still partially welded (tacked) cause I wanted to drive it for a while to make sure it was positioned properly.

Hopefully doing the final welding and hanging won't bring the vibe back.

I think the exhaust was being an "instrument" that captured the harmonics of the Cummins at 70 mph and exacerbated it.

Somebody on another site mentioned that the hydroformed frame is creating the problem and that D/C is coming out with something that mounts to the frame.

 

I always thought it strange the mount on the tranny would hold the exhaust up, I have been told that mount is the problem.

 

Interesting to see how this turns out when you put the brackets back on. Please keep us informed.

 

My first 0-3 had the vibe problem. It always seemed to me to be a harmonics problem. But when I mentioned that to the service guy, I think he got stumped on the word "harmonic". My vibe problem got better with mileage, nearly was gone at 15K miles.

The current truck never had it. Luck of the draw.

An exhaust resonance would make perfect sense though. I did read somewhere that it was being caused by a power steering line.

Hope your fix works out.

 

If it was only the exhaust how do you explain the transfer case replacement repairing the few? And why wouldn't the vibration be there at 2000 rpm (OD off) and not 70 mph. I'm glad yours is fixed, and I have considered the exhaust myself but have dismissed it. Maybe DC will buy us all 5" exhaust systems

BTW, MyMaur I'm a current F-15 puke, man the things are getting old, we have A/B models built in '75. Maintenance nightmares.

 

The exhaust on my 02 Ford 4x4 FX had a harmonic weight hanging off of the exhaust system. There was another hanging under there to, don't remember where. Always wondered why.

Pete

 

That's a good question. I have no idea.

 

Conversely, if the transfer case is responsible for the vibe, why would changing the exhaust cure the problem for Hoot?

The answer might just be: two (or more) causes.

It's entirely possible that there are two or more causes for vibration at 70mph. It so happens (at least in my truck) that 70mph occurs at about 2000rpm. I have to say that I sense some vibe at 2000rpm even in lower gears. I blamed it on the CTD being a 6-banger (V8s often deliver their power more smoothly), but now I'm not so sure. Perhaps something taking place at 70mph exascerbates the 2000rpm problem to make it more offensive. It may be that some of us have one problem but not the other and some have both (or even more like the out of balance drive shafts) which could explain why some seem to be able to tolerate it and some want to lemon-law their trucks. Someone, I believe on the TDR board, proposed that there could be some cardboard pieces in the centers of the drive shafts that are moving around - meaning that they can never be balanced without cutting them open and removing the cardboard.

I think this problem may be more complex than we all think which could explain why it seems to be an open issue as far back as the 2003 models.

Neil

 

Hey, how about as far back as my 01 3500 ! ait has a slight vibe at 70 since I got it. I thought it was tires even after I changed tires ! 4 inch pipes, still got it at 70. Now I just drive it under or over 70 mph, lately over with the comp hooked up!

Hey Hey , my wifes volvo has the vibe at 68-70 and Ford owns Volvo so I wonder what that means!
STY

 

I still have not been able to detect any vibration since I did the exhaust, differential lube and had it reprogrammed for the 315's.

Tonight again I was trying to feel it at 65-70-75. Nothing. Smooth as glass.

There is no doubt it's gone and no way I could convince a dealership that it need a fix at this point.

 

Has anyone else changed their diff's lube,and noticed anything? That'd be nice if that was the fix....it'd sure be cheap,at least. Great news for you,hoot Mark.

 

That is what I was wondering as well. I'm curious to see if it was really the exhaust or axle lube, or tires, wheels etc. Who knows?

 

I've changed both the diff lubes and exhaust, but never had the vib's before or after.

 

My dad has had his diff fluids changed on his 03 QC SB 4x4, had the gears replaced, drive shafts checked and NO improvement. Says if DC cant get it fixed the duramax is looking awful good. Bought this one because of great service out of his '92. Now having regrets. I have told him about this site so maybe he is hanging around here somewhere...? Dealer says he is waiting on instructions from DC. He is not mad a dealer, just aggravated with the truck. Didn't realize he had the vibration for the first year, he had not had the truck on a highway at sustained speeds. It is a farm truck, usually on two lane roads where speeds above 55-60 are rare. Dad says it vibrates so bad it makes you nauseas if riding in it very long at highway speeds.

DuaneWKKC.

 

You guys aren't talking about the small vibs when the AC kicks in, are you?