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Discussion Starter #1
i have a 94 bronco 5.8l 4x4 manual hubs rebuilt motor tranny front and rear end. I have been having this vibration problem ever since i had the drive shaft replaced. i thought i was hearing a grinding noise but after getting more opinions and listening more closely its definetly a vibration. this loud vibration only happens between 20 and 30mph if i'm driving nicely but if i drive the truck like i stole it everything is fine. if i let off the gas while this is happening it will stop or if i stomp on it i will get no response until it downshifts making the vibration stop.???????? is my driveshaft just out of balance?
 

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i have a 94 bronco 5.8l 4x4 manual hubs rebuilt motor tranny front and rear end. I have been having this vibration problem ever since i had the drive shaft replaced. i thought i was hearing a grinding noise but after getting more opinions and listening more closely its definetly a vibration. this loud vibration only happens between 20 and 30mph if i'm driving nicely but if i drive the truck like i stole it everything is fine. if i let off the gas while this is happening it will stop or if i stomp on it i will get no response until it downshifts making the vibration stop.???????? is my driveshaft just out of balance?
That is exactly what my 95 did before the rear end blew up. Not that yours is bad necessairly, but I would focus on the rear end, rear driveshaft, and rear axle bearings.
 

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Discussion Starter #4
I just noticed last night that the rear end was leaking so i replaced the gasket today and filled with fluid its a little better now but it did the vibrating again tonight
 

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I would think if it just started after ya put the drive shaft in, something is messed up with it. (Not trying to be a smart ass.)

Ours had a pretty bad one in it. Was that damn velocity joint.
Only place that I could think of to take it couldn't do anything for it. Don't remember why.

I about fell out when the dealer told me the price of a new one. Seems like it was about $900. Found one at a junkyard for $75.
 

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One Cold North Dakotan
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This is what I mean by in phase:

Because of the changing speed of the drive shaft the two u-joints (one at each end of the drive shaft) must be in phase. Each one must speed up and slow down at exactly the same time as the other. This is something to consider if you ever take your drive shaft apart, or it falls apart on the trail because the slip spline is not long enough for your vehicle's needs. Care must be taken when putting the two pieces back together so that the u-joints are in phase. If they are not in phase it will create unnecessary driveline vibration.
 

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Discussion Starter #8
im gonna have it checked by a shop i know well tomorrow thank you but one more quick question does my rear end need the friction modifier?
 

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Driving Stuff Henry Built
-90 xlt, 351w, e4od, man 1356, 3.55, sag, warn hubs, 35s. -73, 400, np435, d20j twin, 35s
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94 should have flanges at the ends of the driveshaft. Have you rechecked the mounting bolts since it was installed? Sometimes they can loosen & cause vibration.
 

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Yup, I'm another that my '95 did the exect same before my rear end blew. :banghead

It vibrated real bad at the same speed yours is, past that it was alright, but slowing down it did the same. Didn't think much of it and drove it the next day, bad idea. Comin down the highway my ABS sensor went out so my speedomiter cut out, and a little later it was acting weird. I thought it was the tranny. It finally completely cut out and quit moving. a parked it and the next morning everything around the rear axle was covered in oil. My worm gear was ground down and the ring gear was ground down and broke into 4 pieces.

I was a dumbass for driving it and ended up paying for it, runs great now though.
 

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You don't need the friction modifier unless you have a limited slip in the rear end. The easiest thing to check right now would be to make sure the flange was tight to the rear yoke. If it is lose it will do this to.
 

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Discussion Starter #13
You don't need the friction modifier unless you have a limited slip in the rear end. The easiest thing to check right now would be to make sure the flange was tight to the rear yoke. If it is lose it will do this to.
i grabbed the drive shaft and shook it; it didnt move really how else do i check for loose components?
 

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Thanks 351w500
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I should of said this in my other post.
To really check the drive shaft, chalk a wheel on both sides put your T-case in neutral or your tranny if you have an auto T-case and then see if you get any movement in the drive shaft. Doing this will take all the pressure off the drive shaft.

You said you might have heard a grinding noise. This also could be a sign that the pinion bearing is going out to. If the bearing is starting to go out, the pinion and yoke will wobble making a the vibration. This might be the problem cause you said it was a little better after you put new oil in the rear.
 

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Discussion Starter #15
ok i put the transfer case in neutral and shook the driveline. there was no movement. i forgot to mention before this problem is on and off sometimes everyday sometimes not for a week. thanks for all the advice so far:beer
 

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Discussion Starter #16
thank you guys for all the help i fixed the bronco. the old cat had broken apart so i had it cut off made into a y pipe and had all my fluids changed now no more problems! man these broncos drive nice when there running good:thumbup
 

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Thanks 351w500
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The old cat was causing the vib?????????????????????????????
 
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