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Discussion Starter · #1 ·
i took my 86 dodge 4x4 318 to the garage to see if they could help me out. i have replaced the rear ujoints, check both my yoke nuts, took the front drive shaft out( because they dint have the joint to fit it) and it still vibrates. now, they checked the drivesahfts and they arent bent or lost wghts, replaced the vacum lines to the transfer and the cad. checked my torque and all the mounts. they said everything was o.k. and the problem was in the motor. the motor runs smooth, at idle it dont jerk around or rock. even when you rev it up it sounds good. what could it be? sunday i plan to check the balancer and the flex p[late. the guy at the shop said he really didnt know what it could be, but it needed a motor. and my steering box is shot which i already knew. how much would one cost from a jy? and he says one off of a chevy would fit form certain models. i would greatly apreciate your help guys, it aint looking good for the big dodge.
 

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Are your slip joints clocked properly, if there out of phase then you have a problem
 

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does it only do it when going down the road ?? has the trans been out ?? did you buy it used ??

It MAY have a 360 torque convertor on a 318 engine...that will give you a vibration too, and it will be hard to find if the people looking at it don't know that a 318 & 360 torque convertor are not the same. A 360 torque convertor has a counter weight on it that the 318 doesn't have or need. I had a 360 engine that had a 318 torque convertor on it and it had a vibration, but it was only when going down the road that you noticed it. It was rpm related, and it would make most people think it was a driveline problem. I thought it was the wrong convertor, and everyone else told me it was my driveshafts. I could not confirm it until I swapped the trans out...and dang, it had a 318 convertor on a 360 engine.

OR

The harmonic balancer may have come apart or moved so it is not working like it should anymore. it will have the same effect as above, but not as noticeable.
 

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Discussion Starter · #4 ·
ill check the torque converter tommorrow, that is a possibilaty.and as for the slipjoints, how do you check them?thanks for the replies. and to me it seems to only do it when your driving it. even when you let off the gas, but not as bad.
 

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Definitely look at the alignment of the slip joints, although since you had shop people looking at it they should have caught that...

Anyways, the crosses of the Ujoints have to be exactly lined up on the front and rear of the drive shaft. Sometimes when people slip the driveshaft apart at the splines, they don't mark it, and put it back together without checking to align the crosses. If it looks close, and you can't tell, tape (or have a friend hold) a piece of string on the end cap of the Tcase Ujoint, then pull the string straight down the driveshaft and hold it snug against the center of the end cap of the rear Ujoint. The string should lay straight down the centerline of the side of the driveshaft... If the string appears to "spiral", or be slightly diagonal in either direction, you are that far off from straight alignment.
 

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well most of the problems have been mentioned here, how bout checking your motor mounts while you are at it. maybe check the wheels and tires for balance and alignment as well

eric
 

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Yeah could be a bad tire, bad wheel some stole the wheel weights off it to break balls, but do like Smokey said with the slip joints and very very important with the slip yoke and the yoke welded into the shaft they must be in line with each other, in other words where the u-joint cap goes into the slip yoke (the piece that slides in and out on the shaft) it must MUST be in line with the cap that goes into the welded end yoke on the drive shaft at the other end, if it is off alittle or it is clocked with the u-joint in the t-case yoke you will have major vibrations.
 

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Hey I am not sure what all you have checked or all the info here but I had a very bad vibration in my 318 when I got done doing a timing chain and all it turned out to be was that alternator was a little set back.. (must have missed a spacer) and that caused one wicked vibration regardless what you were doing even idling.. so you can check that.. make sure all belts are perfectly aligned. Hope you find it.
 

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Oh yeah lots of mechanics F up clocking the d-shafts with slip yokes, so don't rule it out, and this did start after you replaced your u-joints ? right or wrong? if wrong please be specific in when it started if you touched something or it was something that started on it's own
 

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Good point Marty. ddman, We need some more complete information on how/when it started...
And, as RCM and ramwild have mentioned, a slipped harmonic balancer, or pulley/belt misalignment, can cause bad vibes.
 

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Discussion Starter · #11 ·
the truck had set in a junkyard for a few years before i got it, and it has vibbed ever since then i didnt replace the u joints untill i started trying to figure this out. as i said at idle or even revving the motor it dont seem to vibrate only when you drive, the tires are ok according to the garage no knots or broke belts. i ll check more on wed. and let you know
 

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Ok motors that have a problem vibrate all the time not when driving only, so it's safe to say it's not the motor if you don't feel a vibration, so check everything else 1st and then see if anything is out or off and start there, also tell alittle about the truck, what wheels and tires?, lifted not lifted?, pinion angles if it is lifted?, does it get worse when accellerating? oh and answer all the questions this is called process of elimination without it i might as well go play with myself
 

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Ok question do u go wheeling alot ? in mud ? cuz chunk of mud dried inside your rim will make it vibrate like hell as well .

Also inspect the Harmonic Balancer there is a rubber ring that ends to crack over time and will eventually break hte balancer . I think this problem is with in the engine maybe sloppy timing chain as well will do it too .
 

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If those wheels got rusty inside while it sat all that time, that'll cause some vibe, too. I've been down that shaky road once.
 

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I'm also having the same problem ddman. I had my u-joints replaced 2 weeks ago and it began to vibrate. I've already taken the truck back twice to the shop and they keep telling me its the ring and pinion. That my whole differential needs to be checked or replaced. My truck vibrates when driving and also when you let off the gas. It starts vibrating really bad around 35 mph. Also, on the driveshaft are the caps to the u-joints supposed to be flush with the driveshaft? Because the u-joint caps in the front is flush with the driveshaft and the rear u-joint caps stick out almost a 1/4 of an inch. To me I figured that was the problem, but they said that that was normal. I have changed the u-joints before and have never had a problem. I don't remember ever seeing the u-joints looking like that with one side sticking a little more out than the other. I have seen a lot of the postings and I'm going to try and check everyone elses responses. Thanks.
 

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CHECK YOUR SLIP JOINTS!!!!!!!!!!!!!!!!!!!

We really need a class on this
 

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I had a bad vibration in my TD for about 2 years that nobody could find. It only vibrated when driving. We went to replace the rear main and found that the flex-plate was broken. Put a new one in and problem solved.
 

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JayBear88 said:
I had a bad vibration in my TD for about 2 years that nobody could find. It only vibrated when driving. We went to replace the rear main and found that the flex-plate was broken. Put a new one in and problem solved.
That's different than getting a vibration after you change u-joints
 

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What about a bent rim? You could get a little vibration from a bad race in the rear. When you get you r front drive shaft back in, remove the rear and try it. See what happens.
 

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I'm also having the same problem ddman. I had my u-joints replaced 2 weeks ago and it began to vibrate. I've already taken the truck back twice to the shop and they keep telling me its the ring and pinion. That my whole differential needs to be checked or replaced. My truck vibrates when driving and also when you let off the gas. It starts vibrating really bad around 35 mph. Also, on the driveshaft are the caps to the u-joints supposed to be flush with the driveshaft? Because the u-joint caps in the front is flush with the driveshaft and the rear u-joint caps stick out almost a 1/4 of an inch. To me I figured that was the problem, but they said that that was normal. I have changed the u-joints before and have never had a problem. I don't remember ever seeing the u-joints looking like that with one side sticking a little more out than the other. I have seen a lot of the postings and I'm going to try and check everyone elses responses. Thanks.
Same thing here....had ujoints changed (should have done it myself damnit! I think people on this site know a lot more about older dodge drivetrains than any mechanic shop)....huge vibration at 65mph after the new ujoints. AND the ujoints they put in weren't flush anymore like the front ujoints (the new ujoints have already rusted after about 4 months...my old ones still look like steel, so they must have used some cheap ass ujoint.)....2 of the caps are flush and the other 2 stick out about 3/16". Now, they also said that my slip joint was off by about 2 teeth and they corrected it....I looked and the rear ujoints were lined up perfectly. Hell, I'm thinking about turning the rear drive shaft 2 teeth off in either direction to see what happens or try some good quality ujoints and do the work myself.....what's the best brand name of ujoint? for the 79 RC NP203 NP435
 
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