Bad Vibration.
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Elder User
Joined: May 2003
Posts: 575
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From: Orlando, FL
Bad Vibration.
So lately I have been experiencing vibration whiile driving. It started out in overdrive at around 1600 to 1900 rpms, so I figured it was 7 and 8 wire arcing and proceeded to replace the rotor, cap and spark plug wires. The plugs looked good so I just cleaned them with a wire brush and regapped them. Also added two bottle of fuel injector cleaner. Didn't work, now I am noticing that the vibration not only is in overdrive but also in 3rd between 1100 and 1900 rpms. It starts while accelerating and continues once I let off the gas until I slow down. This has lead me to believe that not only do I have a motor issue but also a driveline issue. When it does it in 3rd it feels like a bad u-joint, however it is not consistant throughout all speed ranges. One thing I have noticed is that although it is running like crap it is getting better gas milage? I also noticed today that the oil pressure guage (factory) is fluctuating while the motor is at constant speed, i.e. cruse is set, the pressure isn't doing that it is just the guage right? Any clues or ideas where to start looking?
Lead Driver
Joined: Sep 2002
Posts: 9,182
Likes: 12
From: Gateway to the West
First off, don't even bother trusting the OEM gauge. Its nothing but a varistor mounted in the block. Electronic components like this change resistance value as they age especially when exposed to the elements and extreme temperature changes.
Your description of the problem sounds all too familiar. I have one question that will more or less seal the deal on my response though. Does the vibration lessen or go away when the driveline is under load but get worse when coasting? I ask because everything else about the symptoms sound like a bad centering ball/spring assembly in the double cardon U-joint assembly (front U-joint of the rear shaft).
I drove around for two days with the rear shaft removed and the truck in 4 HI while I took my time doing the repair. Yes, I had a front-wheel-drive Bronco for two days.
Your description of the problem sounds all too familiar. I have one question that will more or less seal the deal on my response though. Does the vibration lessen or go away when the driveline is under load but get worse when coasting? I ask because everything else about the symptoms sound like a bad centering ball/spring assembly in the double cardon U-joint assembly (front U-joint of the rear shaft).
I drove around for two days with the rear shaft removed and the truck in 4 HI while I took my time doing the repair. Yes, I had a front-wheel-drive Bronco for two days.
Hotshot
Joined: Jul 2002
Posts: 14,285
Likes: 12
From: Bend,OR
I agree sounds like something in your rear driveshaft or possibly the tranny needs serviced.
if you want a replacement rear Drive shaft let me know. there is a guy on FSB.com that sells shafts for our broncos with an extra 1" of length for under $200 usually shipped.
if you want a replacement rear Drive shaft let me know. there is a guy on FSB.com that sells shafts for our broncos with an extra 1" of length for under $200 usually shipped.
Thread Starter
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Elder User
Joined: May 2003
Posts: 575
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From: Orlando, FL
Yes it lessens to an extent under load with the exception of being in overdrive. It does get slightly worse coasting but not throughout the whole range of speed.
Shouldn't be the tranny, just changed the fluid, filter and gasket two months ago due to a leaking gasket.
Shouldn't be the tranny, just changed the fluid, filter and gasket two months ago due to a leaking gasket.
Lead Driver
Joined: Sep 2002
Posts: 9,182
Likes: 12
From: Gateway to the West
Sounds even more like the double cardon U-joint. It will actually feel worst as road speed and engine speed (transmission output shaft speed) get closest but you are coasting. Basically when this happens there is NO pressure on the u-joint at all and if its weak it slops around because the shaft is still spinning. As the axle tries to push the shaft faster than the rest of the driveline will let it, the vibrations will decrease again because there is pressure on the u-joint again. Sounds crazy that the problem is most evident in "no load" situations but I spent two months trying to figure it out the first time I had one die on me. Yeah, I'm a slow learner but I LIKED my short yellow Big Bird Bus thank you very much!
Elder User
Joined: Jan 2005
Posts: 656
Likes: 1
From: Houston
Take it to a shop that will inspect for free. Tell them to check all your u-joints. If they find one they will be able to show it to you and how they know it is bad. Then make the dissision for them to change it or you change it. After they tell you how much it cost throw a fit and say you will change it your self.
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Elder User
Joined: May 2003
Posts: 575
Likes: 0
From: Orlando, FL
I'll skip the shop, although I doo like to throw fits in public and shout obscenities for no reason at nice people, figuring out if it is bad and changing it myself gives me something to do now that I work fewer hours than my wife.
