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Discussion Starter · #1 ·
I was out off-roading again last weekend and got her stuck pretty good. Not stuck in the mud, just the inadequate clearance angle cause by bumper to get hung up. I had to get a pull from another truck to get out. So between that and a huge hill climb, nothing out of the ordinary happened.

So since then (the camping weekend) I've gotten a hard vibration somewhere in the driveline when I hit 120km/hr. All is well until I hit that speed. I then wondered if it was 5th gear only that the vibration occured, so I brought the engine back up to the same RPM in all other gears. It also does it then ( at a certain RPM) in all gears and in neutral with or without the clutch in. The rumbling is not as bad in the lower gears but it gradually gets worse as I get into 4th and 5th (5th being the worst). I think that vehicular speed amplifies the vibration. I have had it up to about 135km/hr but the rumble didn't go away; be it uphill or downhill driving. It also didn't get any worse (so that's a good thing I guess), the vibration was just there.


I was wondering where I should be looking. I have a feeling that it is transmission related though. I have installed the following in the past year- new BFG A/T's, new clutch, all driveshaft u-joints (front and rear), all fluids, pro-comp shocks, new-used 3/4 ton rear leaf springs from a '97: summer 2001.

I also posted this in another forum and got the following ideas that aren't the problem:

-tires out of balance
-u-joints NFG
-driveshaft bent etc...
-pinion angle incorrect (now this one I haven't checked yet but I will get right on it)-- none of my u-bolts have changed position, the flats from the axle and the leaf springs match up perfectly)
-Busted Shocks (I'm also gonna check this one out)

Any and all replies are welcome and appreciated.

Thanks,
Steph.

'92 Ford F-150 4x4 Inline 6
(p.s. msg also posted in Ford Truck Enthusiasts site)
 

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You probably dinked your driveshaft. Jack up the rear of your truck and rotate the wheels while underneath and inspect the driveshaft while it spins for any sign of damage.

My best educated guess.:cool:
 

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if it does it at a certain engine speed its engine related ,,,,check for loose brackets,pulleys,harmonic balancer,even a bad plug or wire may cause it ....if it only happens at a certain vehicle speed then check drive line or tires also check for dirt inside the wheels hope that gives you someware to start looking
 

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if it does it at the same RPM regardless of vehicle speed it'll be driveshafts or axle related .... have you unlocked your front hubs? Due to the ford TTB design it is recomended BY FORD that you don't drive on the highway with your hubs locked in at speeds iver 80Km/h for more than 50Km. 9 out of 10 times the front shafts are improperly balanced as well ... or the slipshaft in your passenger front axle could be loose. if the hubs are auto's they may not be disengaging. If they are manuals and are unlocked look for deposits of mud on the driveline.
NOW if the Vibe happens at roughly 2200 rpm .... check your harmonic balancer, ford used a lot of different compounds in the later model sixes damper ... all of which had a tendancy to wear out prematurely. :confused2
 

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Rockfrog said:
if it does it at the same RPM regardless of vehicle speed it'll be driveshafts or axle related ....

I'm assuming you made a typo here Rockfrog? IF the vibration is at a certain VEHICLE speed then it is driveshaft or axel related as your driveshafts and axels are always rotating at the same speed in relation to your tires. But if it does it at a certain RPM (Engine speed) regardless of vehicle speed than it is something within the engine/transmision/x-case. Wether it be a motor mount, plug wire, H-balancer etc etc..... Thats what you meant right?
 

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At 120KPH? That's quite high. Are you sure it's your driveline? Does the sound/vibrations change under load? When you decelerate/accelerate does it change pitch/tone? Do you have a lot of torque play in your drivetrain? Does your slip yoke have a lot of play? Is it the front, or the rear? Pull out the front drive shaft, and run on the rear only if you are not sure.

I have a problem on my front end: slip yoke loose; and pinion angles, so my vibration occures at about 60Kph, phases out at about 80kph, and then it just seems to slow down, and everything heats up.

If you suspect it's your drivetrain, first find out what type of drive shaft you have. How many U-joints make it up. There are a couple of standard ones.

2 U-joints - don't know what they are called, but it's what you'll find on about 90% of vehicles.

3 U-joints - CV on at least one end, most likely the side where your transfer case is at. Quite common shaft type.

4 U-joints - CV on both ends.

OK. Now that you know what type it is: Remove it.

Go to your local Home Depot, and pick up a magnetic angle finder ($10). Find your front and rear pinion angle (vertical - few if any trucks still have to worry about lateral angles).

Install your drive shaft back in. And measure the angle of your shaft. Oh ya, check to see if it's straight first (rear/front on blocks, blocks on other end, remove the other shaft or lift both ends on blocks, drop it in 5th, and idle it - watch the saft, drop a pencil on it, and see if it bounces), and if you have hit it/scratched it - did it loose a balancing wieght? Look for odd impressions in the shaft that may look like broken weld beads.

If you have a 2 U-joint shaft, it's angles should be even between both ends. 3 U-joint shaft, the CV end should be within 1-2' the angle of the yoke on the CV end - the other, doesn't matter. 4 U-joint shaft - I'm not 100% certain, but it doesn't matter on either end. If you have one, check with someone else about the 4 U-joint unit, not 100% sure.

Check your yoke. You shouldn't have much play in it. And lastly, make damn sure you have grease or some kind of lubrication in it. A yoke which barely moves, under torque, will do a LOT of damage to your drive train if is expected to travel during a hard bump. You'll also have shifting problems, transfer case mount point, and engine mount point problems if it is seazed or unlubricated. Not to mention heat and wear.

Good luck! :)

axle.
 

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Discussion Starter · #9 ·
Thanks for all the replies, they are surely to help out in a way or another. I wasn't led to believe that it was my driveshaft at all cause like I said before, the vibration occured at the same rpm (nearing redline) in every gear. Oh ya, vibration seems to be comming from under my seat and make no metel on metal type noise. That also led me to belive that it wasn't the shafts.
All of my shafts are 'two u-joints'-- front and back.

-I have no lift or blocks on my rear axle, all stock. The new leafs I put in had a slightly ( and I say slightly) higher arch that's all; so it shouldn't really make that much difference.

-I was gonna put my shaft on the lathe next week and do some dialin' with the mag base. I'd check the u-joints for all you people that think that's the problem.

I'm gonna put 5 bucks on the harmonic balancer idea, 4-1 odds. If anybody is in, post back your sum.
 

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Discussion Starter · #10 ·
Well here's what I did: I changed the spark plugs. End of vibration. They were about 1.5 years old so I didn't really suspect them to be the problem but when I took them out, the electrodes were pretty rounded off. I also went back to Autolite brand plugs and they seem to be working very well in my Inline Six. Dig that.
 

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Stephan said:
It also does it then ( at a certain RPM) in all gears and in neutral with or without the clutch in.
This alone tells you that it was your engine. Nothing else nothing else would viberate while in neutral. :D
:rolleyes:
 
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