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Discussion Starter #1
1990 w250 on 35s and a cobbled suspension.

From zero to 65mph, smooth as glass. No shimmies and no shakes. As soon as I get past 65mph (as measured by GPS), I start getting a driveline vibration. This is in 2wd, hubs unlocked (and they do both unlock, you can spin the axle joints by hand). Its not a tire issue, this is a high speed vibration not a thump or shake (almost a buzz).

I have checked the ujoints, they all seem good and take grease. I've checked the driveshaft phasing, both joints appear to be aligned and there is minimal play in the slip spline.

Differential seems good, wheel bearings seem good...

Any thoughts?

The transmission had a batch of garbage in the pan when I drained it last weekend, but it vibrated before, and it seems ok and shifts good...transfercase seems tight and has oil.

It runs and drives great under 65mph...everything is smooth.

I don't think it's engine or torque converter because I can wind it up in the lower gears and it pulls smooth and hard.

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How bad are the vibes? It’s a 30 year old truck on larger that stock tires yes she’s gunna shimmy at high speed. You could look into changing out the kingpins because they can cause this. Systematically go through the entire suspension and replace anything with even the slightest slop in it.
 

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I'm currently trying to figure out a drive line noise as well. Have you tried bringing it up to over 65 then shutting the truck off and seeing if the noise and vibration persists....good way to eliminate the motor, and tranny to some degree.
 

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. Have you tried bringing it up to over 65 then shutting the truck off
It goes without saying..... be careful when you do this!!!! You will lose power steering and power brakes and make sure to not click the key all the way off or you will lock the steering wheel ;)
 

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Discussion Starter #5
How bad are the vibes? It’s a 30 year old truck on larger that stock tires yes she’s gunna shimmy at high speed. You could look into changing out the kingpins because they can cause this. Systematically go through the entire suspension and replace anything with even the slightest slop in it.
Feels like the driveshaft would come loose if pushed too far...is that severe enough?

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I'm currently trying to figure out a drive line noise as well. Have you tried bringing it up to over 65 then shutting the truck off and seeing if the noise and vibration persists....good way to eliminate the motor, and tranny to some degree.
That would require a late night drive, we have too much traffic around here to play around during the day.

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Discussion Starter #7
This isn't a wobble or a shake, it's definitely a driveline vibration...imagine a buzzing vibration.

I think I've checked all the basics, I have to pull the driveshaft and put a straight edge on it. That will verify the phasing and make sure it is straight?

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Sounds like a bad U-joint to me.
 

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Discussion Starter #9
Sounds like a bad U-joint to me.
I checked those early on (couple months back) and they were good (had the driveshaft out) and all took grease. I'll check them again when I pull the shaft this weekend...

That is what it feels like, but why only over 65mph?

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Check the yokes too I have had one come loose on me in the past

Also you say cobbled together suspension, how are your driveline angles?
 

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Discussion Starter #11
Check the yokes too I have had one come loose on me in the past



Also you say cobbled together suspension, how are your driveline angles?
I did check all the yokes before I put it on the road, the one on the transfer case was loose, I retorqued it (but no loc-tite). It was actually causing a leak between the shaft and yoke (down the splines). I can check that when I have the driveshaft off...

It has blocks, but only two inches. I wouldn't think that would have affected the pinion angles that drastically. Wouldn't that also make it vibrate at all speeds?

I'm thinking I may take it to a driveshaft shop and have it checked and balanced, and maybe just have the joints replaced just in case there is a pin bad or the PO knocked the weights off.

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I take it that you do not have 2 piece drive line? so no carrier bearing/bushing?
If that yoke was loose it is likely worn on the splines and may be out of center/balance because of that and wobbly just at tiny bit.
Also when drive line is dropped on rear check the pinion yoke for ANY play in and out or up and down. The only movement it should have is a slight rotation in minor gear slop, but nothing in the bearing. Same goes for any other bearings and u-joints. U-joints should have no play or tightness when rolling around by hand.
Having drive line balance checked is good idea after all else is cleared.
I would look very closely at that yoke that was loose.
 

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X2 on rear yoke being an issue ^^^^. If that yoke was loose for any period of time it very possibly is sloppy on the shaft. You may be able to replace just the yoke as it should be a softer material than the shaft so the wear would be on the yoke.... in theory.
 

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Discussion Starter #14
The yoke on the transfer case was only loose enough you could notice it...it still fit the splines good. Wasn't sloppy loose when I found it, I wouldn't have noticed it other than I was investigating that seeping seal. Does that make sense?

The drive shaft is a one piece, no carrier bearing. The spline has minimal play (I've seen a lot worse)...

I did check the differential when I had the shaft off (the ujoints are installed with the zerks pointing the wrong way), the pinion was tight.

Unfortunately this isn't something that just started. It came with the truck...

Will diagnose further this weekend...

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Also make sure the bores the U-joint cups sit in are good, I had a driveline shop redo my driveshafts with all new parts and had a vibration, turned out that a bore was so worn that the cup would spin and move in and out just a hair, I was the one who actually found it...driveline shop tried to claim i damaged it some how with only a day or two on the driveshafts, owner was an A-hole!
 

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Discussion Starter #16
I pulled the driveshaft tonight...

Before I pulled it, I went over everything...the yokes are tight, the ujoints are tight in the yokes, the ujoints are tight.

I laid it on the tailgate, the joints are in phase. I pulled it because they looked a spline off under the truck. The slip spline is tight, almost no wiggle...

And not for nothing, this looks like a replacement shaft, it's painted, has weights on it, nothing obviously wrong and no signs of a weight being knocked off.

So I can rule ujoints and yokes out, and almost the driveshaft because I can't assess if it's balanced correctly.

Oh, and it has polyurethane transmission mounts but I know the engine mounts are going bad (but not shot)...

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While you have the shaft out check the flange angles.
The engine mounts could be some of your problem.
Also check the rear spring bushes,U bolts tight and no sign of the axle having moved on the springs.
Do the shock absorbers appear OK? You may have a combination of small things that compound at speed to give you a vibration
 

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Discussion Starter #18
While you have the shaft out check the flange angles.

The engine mounts could be some of your problem.

Also check the rear spring bushes,U bolts tight and no sign of the axle having moved on the springs.

Do the shock absorbers appear OK? You may have a combination of small things that compound at speed to give you a vibration
Yeah, I'm kicking myself for not replacing the engine mounts when I did the oil pan gasket...was holding out for some polyurethane mounts, had new rubber sitting on the shelf, but decided to wait.

The rear ubolts are tight, I had those apart a month or so ago...the bushings may be an issue, I'm holding out for new springs. The shocks are new.

If it was pinion angle, wouldn't it be pronounced at all speeds?



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Discussion Starter #19
Ok, left early this morning, and even then the idiots were causing five car pileups...

The vibration is harmonic...if I wind it up to say 70mph (and it vibrates while doing this), leave off the throttle and coast; the vibration goes away. So it is either a harmonic resonation (i.e., bad drone) or something that only happens at high rpm under load...it will cause anything loose in the interior to rattle, it's that significant (in other words it's felt and well as heard).

Maybe it's just the natural loaded high rpm vibrations these engines have? I want to say I remember my 3rd gen had this to a lesser extent with the 100hp tune at WOT...but that was eight years ago since I had that truck.

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What do your tires look like, tread, wear and pressure? Pics, video of sound vibration?
 
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