Pulsing/droning vibration at highway speeds (3 Viewers)

[krispykritter]

What a pain in the ass. I went out and adjusted it all today and had fun with the whole relative angle thing - if I extend the lower links to twist the nose downward, it increases the angle at the diff, but also increases the angle at the transmission (of course, right? Pulling the nose of the diff down increases the angle of the prop shaft, and that changes the angle at the tcase!). I rotated the diff down slightly (made the lower links longer by 180 degrees), and ended up adjusting my rear ride height sensor to drop the rear about half an inch, and that left me with around .6 to .7 degree difference between the two angles (IE angle at Tcase is about 5.3 degrees and at rear diff it's about 4.6 degrees sitting still). I think the highway vibration is less now, but I need to drive farther than a couple miles to be sure, but it's definitely not gone.

The Tremec app I use doesn't like angles anywhere greater than 3 degrees for some reason.

As @abuck99 said, I probably should've gone for the upper arms vs the lower arms, but don't want to spend even more money right now. Hopefully I can get it good enough to hold me over for six months or so with this most recent change. Or work out that it's not the pinion angle that's the problem.

 

[abuck99]

Ive been through the same learning process- its frustrating for sure. At some point you get it close and live with it.

But recheck your measurements- those static numbers seem weird ( If youre on level ground) Your TC flange should be around 1 or 2 degrees down(nearly level) your TC angles wont change. Dont worry so much about propshaft slope at this point, just the relationship between the output flange and the diff flange. Remember this orientation is your benchmark: output flange / - - - / diff flange.

Working from stock arm lengths, if anything you’d prob want to adjust to point the diff UP not Down. That would require shortening lower arms. Problem is, theres usually not much available thread to do that. Fwiw when you add lift to the rear end (taller springs etc) it has the effect of rotating to diff downward- so any post lift adjustment should prob focus on adjustments that would point the diff up.

Stating again, from my trial and error I found it also takes much more lower arm adjustment to make any impact on diff rotation- vs adjusting uppers.

 

[krispykritter]

Yeah, the angles are weird because I was on a downward sloped driveway. I concentrated on the relative angles vs the absolute. I included the propshaft slope because that allows for the relative measurement to be made.

Glad you mentioned the weird angles, I'll re-measure in my garage tonight and see if they make more sense. I'll definitely try spinning the links shorter and seeing if that helps the problem.

 

[abuck99]

Another comment to measuring: its easy to get inaccurate measurement if you don't have an enough of and an absolutely flat surface on the flange to take your reading from, any little offset will affect the reading- that is if you are measuring with prop shaft still connected. I've tried taking measurements with iPhone level app before and it was very inconsistent (iphone has all sorts of round edges and wide base). I ended up with one of the HF digital gauges. it shows up & down, calibrate and hold- works very well. You can stick it on the flat edge of the flange and take your reading. Lay it on the ground under the drive line- to check to see if your garage floor is level, then zero it then take your readings on both flanges. Subtract the difference- then adjust pinion as needed.

 

[snowglobe]

I had noise at idle and in other conditions for many months .... The sound seemed everywhere, above and below.
One particularly windy day I guessed some part of the stock roof rack was loose; it was, I hand tightened it, and the noise is now gone.

 

[krispykritter]

Obviously not the best thing to use but all I have right now. Did this about five times to make sure it was close. Driveline vibe is mostly gone... Very subtle now, which is good enough for me. I'll eventually get the upper links to truly fix this (I hope) but it's at least 70% better now. Probably the best I'll get without a good clinometer and upper links.

Thanks for the help!

 

[ClassyJalopy]

I will join the ranks. My 98 LX has 256K miles on original prop shafts and CV half shafts. Had always been smooth runner. I used to have some flop in the rear end but new OEM RUCA and LUCAs took care of it.

This last weekend I ran about in an offroad park and at least once dropped the truck on the front underbelly pan. Right after that visit, I started getting pretty violent shaking at 55 to 68 mph at highway. It is smooth at 70 mph and above. Below 55 mph it feels slightly grainy but doesn't have the shaking vibration.

So far I have had the tire shop rebalance the tires (they were found to be slightly out of balance) but that didn't help at all. Also, the CV axle boots are not leaking or seeping.

Next step is to grease the prop shafts and see if that helps. I am a little afraid that it might be one of the prop shafts.

 

[krispykritter]

Sounds like you damaged something.

Sadly, my vibration is still there, and I'm fairly certain it's not a driveshaft thing. When I get the driveline angle wrong I feel a pretty constant high frequency vibration. What I feel is somewhat lower frequency and fades in and out.

I know it's something with the rear driveshaft or axle, since it goes away in front wheel drive only mode. Or maybe it's the missing frame weight. Argh.

 

[atnolan94]

I will join the ranks. My 98 LX has 256K miles on original prop shafts and CV half shafts. Had always been smooth runner. I used to have some flop in the rear end but new OEM RUCA and LUCAs took care of it.

This last weekend I ran about in an offroad park and at least once dropped the truck on the front underbelly pan. Right after that visit, I started getting pretty violent shaking at 55 to 68 mph at highway. It is smooth at 70 mph and above. Below 55 mph it feels slightly grainy but doesn't have the shaking vibration.

So far I have had the tire shop rebalance the tires (they were found to be slightly out of balance) but that didn't help at all. Also, the CV axle boots are not leaking or seeping.

Next step is to grease the prop shafts and see if that helps. I am a little afraid that it might be one of the prop shafts.

honestly you should be more afraid it’s your CVs at $500 a piece. You can drop your own prop shaft and have new U joints put in and a high speed balance for less than $100.

 

[ClassyJalopy]

honestly you should be more afraid it’s your CVs at $500 a piece. You can drop your own prop shaft and have new U joints put in and a high speed balance for less than $100.

Yes that is what I am afraid of too. I pumped fresh grease in the yokes and the U joints until the old nasty grease came out. There was a lot of mud in the old stuff

Went for a short test drive and noticed improvement in the vibration. There is still very noticeable vibration between 60 and 70 (it was between 55 and 70 before!). The vibration isn't as severe as it was before even in that range. Also, noticed that the driver side grease cap is missing (the one that goes over the hub flange). Would this mean my wheel bearings would have been exposed to the muddy waters?

Oh and by the way this made the whole greasing job a breeze.

 

[atnolan94]

Yes that is what I am afraid of too. I pumped fresh grease in the yokes and the U joints until the old nasty grease came out. There was a lot of mud in the old stuff

Went for a short test drive and noticed improvement in the vibration. There is still very noticeable vibration between 60 and 70 (it was between 55 and 70 before!). The vibration isn't as severe as it was before even in that range. Also, noticed that the driver side grease cap is missing (the one that goes over the hub flange). Would this mean my wheel bearings would have been exposed to the muddy waters?

Oh and by the way this made the whole greasing job a breeze.
View attachment 2190601

Ok so first of all I want that. I have dewalt cordless tools so I'm totally in for that.

Is the vibration in your seat? Pedals? Steering wheel? Does it come and go with throttle input or is it always doing it in that speed range?

 

[ClassyJalopy]

Ok so first of all I want that. I have dewalt cordless tools so I'm totally in for that.

Is the vibration in your seat? Pedals? Steering wheel? Does it come and go with throttle input or is it always doing it in that speed range?

Yeah I paid $80 for a used one on FB marketplace. Totally worth it.

Between 60 and 70 the whole truck shakes, the objects in rear view mirror become blurry due to the shake. Coins in the ashtray jingle, kids in the back seat complain and I lose all respect in the eyes of my love... you get the idea!

 

[atnolan94]

Yeah I paid $80 for a used one on FB marketplace. Totally worth it.

Between 60 and 70 the whole truck shakes, the objects in rear view mirror become blurry due to the shake. Coins in the ashtray jingle, kids in the back seat complain and I lose all respect in the eyes of my love... you get the idea!

Get under the truck with a pry bar and check your rear u joints. I had the same problem and that was my fix.

Could be 1,000 other things but lets start there. Mine were so bad I could move them by hand.

 

[ClassyJalopy]

Get under the truck with a pry bar and check your rear u joints. I had the same problem and that was my fix.

Could be 1,000 other things but lets start there. Mine were so bad I could move them by hand.

I grabbed the rear and front shafts with both hands (phrasing!) and tried to move them in every direction. The U joint have no give in them at all! Neither lateral nor rotational. The front shaft could be rotated a little (guessing abt 5 degrees) with both front wheels on the ground - but the whole shaft moved, there was no play in the U joints.

 

[atnolan94]

I grabbed the rear and front shafts with both hands (phrasing!) and tried to move them in every direction. The U joint have no give in them at all! Neither lateral nor rotational. The front shaft could be rotated a little (guessing abt 5 degrees) with both front wheels on the ground - but the whole shaft moved, there was no play in the U joints.

Rotation doesn't matter here, thats just backlash in the yoke. Use a pry bar on the u joints, even if there's play with a pry bar it can cause significant vibes. Next step would be CV's.

 

[uHu]

Don't forget the spindle bearings (supporting the CV). They're easy and fast to check.

 

[ClassyJalopy]

Don't forget the spindle bearings (supporting the CV). They're easy and fast to check.

How?

 

[ClassyJalopy]

Rotation doesn't matter here, thats just backlash in the yoke. Use a pry bar on the u joints, even if there's play with a pry bar it can cause significant vibes. Next step would be CV's.

I will try to get under the truck again this afternoon with a pry bar and see if I can get any movement out of the U joints. To minimize the downtime, I am thinking about getting brand new prop shafts and the two CV axles. And on my day off, just remove the prop shafts one by one until I find the culprit. Here's the best deal on the parts, I could find:

 

[atnolan94]

I will try to get under the truck again this afternoon with a pry bar and see if I can get any movement out of the U joints. To minimize the downtime, I am thinking about getting brand new prop shafts and the two CV axles. And on my day off, just remove the prop shafts one by one until I find the culprit. Here's the best deal on the parts, I could find:
View attachment 2191090

Getting new U joints pressed in is substantially cheaper than both of those driveshafts, IMO.

 

[ClassyJalopy]

Getting new U joints pressed in is substantially cheaper than both of those driveshafts, IMO.

Would any shop be able to do that or only a specialty shop? Would I need to take the shaft off and take it to them?