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Vibration problem

K5Steve

K5Steve

1/2 ton status
Joined
Aug 10, 2005
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Location
Carson city, nv.
I have done a search but can't really find what I am looking for.My 88 K5 with a 4 inch lift has a vibration problem.It is when I am accelerating,It feels like all 4 wheels are eggs,and it does it when I am heading downhill and off the gas,if I give it light throttle then it goes away,full throttle and it comes back.It does this intermitenly,only sometimes.I know my rear shocks are shot and I am replacing them tomorrow.It supposedly has new u joints,but I'm not possitive.
 
Well I was told when I bought it 2 weeks ago that it had new u joints and it may need new shocks.I found that the rear shocks are so worn out that I can wiggle them up and down and side to side on their mounts (bushings are pretty much gone so I bought new shocks today and will install them tomorrow.I need to inspect the ujoints and driveshafts tomorrow.Do ya think the shocks could cause the vibes?
 
I just replaced the ujoints and the rear shocks and it is still there.I can be cruising at 60 mph and it will be fine then all of a sudden it'll start vibratinglike my wheels are out of balance for a few seconds then it'll go away.The reverse in the tranny is out so I'm thinking there may be more wrong with the tranny then just that.I may swap out the tranny mount for a energy suspension mount and see if that helps.
 
What are the driveshaft angles ?

Lifting a truck changes the geometry . Perhaps the previous owner never addressed the issue .

You can shim the axles on the springs ( bolt on ) .

Or rotate the spring perches ( welding )

Another option is to buy a CV rear driveshaft ( expensive , but bolt on ) .

I took the latter route . And just for an FYI , I still get some vibes , mostly from the voids in the tires , and just plain being an older rattly truck .

BTW , the tranny could go anytime , please don't be too far from home and alone .
 
It has what looks to me to be a 2 1/2 inch lift with blocks that are angled.It goes away when I put it in neutral and it goes away if I give it light throttle.If I let off all the way,it has vibes,if I give it too much gas,vibes.
 
If it always goes away in neutral the ujoints are bad or binding. Check the angles like posted above. Who knows, they might have put the angled blocks in backwards. Seen it before. Shims are the cheap/easy fix. Also, see if there are any contact areas around the ujoints (read mangled or shiny areas). That would indicate a severe angle problem, like I had. Look at the bolt heads also. If they have been gound down or the heads are deformed, that indicates contact.
 
After I replaced the u joints it seemed to go away but this morning on the way to work it seemed worse so I guess I'll check them again.
 
So what you are saying is that the problem goes away when you are not braking or accelerating . Shifting into neutral is basically doing the same thing. Everything is still spinning but not under load. Are your axle u-bolts tight? How about the leaf spring eye bushings? Seems a little like an axle wrap problem causing u-joint binding or misalignment. Might try pulling your rear driveshaft and running in front wheel drive to narrow it down. That would confirm a rear driveshaft/axle issue rather than a transmission / engine issue. Good luck.
 
If I am going down a hill in drive and I let off the gas,it will vibrate.If I give it a little gas,it's fine but from half to full throttle it vibrates.If I put it in neutral,it goes away and rides smooth.I want to get rid of the blocks and go with springs anyway.To me the ds angle looks abit too much so I may shim it.I pulled the ds out the other night and about 1/2 a qt. of tranny fluid dumpt out so I don't want to drive it like that.I am going to get a new tranny and re seal my t case.
 
#1. Go to sears and get a magnetic protractor (angle finder). ($10)
#2. On level ground measure the angle at the output of the t/case, driveshaft and pinion yoke. Ideally you want the difference between the t/case-driveshaft and driveshaft-pinion yoke to be 2degrees or less. (boiled down to the basics of driveline angles) Use the flat side of the yoke with the yoke rotated so flat spots are top and bottom (where you can see the end of the u-joint cup) to take your measurements at the t/case and pinion yokes. This way you have a reasonable flat surface to measure. Subtract the Smaller number from the larger and you have what's called the working angle for that joint. Both joints should be within 2 degrees.

More than 2 degrees and you will get a vibration that will wipe out u-joints, tcase output seal, output bushing or pinion seal/bearing or all. This is where the c/v shaft works since it adds a 3rd joint at the front to allow for more angularity without the vibes.

For example mine would eat the front u-joint on the rear shaft in about 5 months of light driving. No noticble vibration until the joint started to wear. Then it would vibrate at a specific speed and go away if I pushed in the clutch. This was with no lift except 2 cut off add-a-leaf's bolted to the spring by the center pin (PO installed). It rotated the pinion down in my case and made my problem more noticible. I ditched the home-brew zero rates when I did my lift (front springs/shackle flip). By removing the quasi-zero rates and installing the shackle flip, the pinion was rotated back up allowing the drivline angles to have less difference, thereby canceling each other out like they should.

Like others have said, you could fix it with wedges/shims. Or if you do ditch the blocks for a real spring lift, you might get some of the pinion angle back, but still might need shims. Cheapest thing you could to now is get the angle finder and measure to see just how far off you are. Eyeballing it don't cut it here when you are looking for 1-2 degree increments.
 
I think I found where the vibes are coming from,I got under the truck and wiggled the driveline and the ujoint was sliding around in the yoke at the diff. so I took the caps off and noticed there was a big groove where the old ujoint was hitting and sliding around.I am going to get the new caps tomorrow and will post any changes.Just so I know for sure,this groove isn't supposed to be there, right?Excuse the bad pic but you can see the groove in the middle of the cap.
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Well that didn't do it.It feels like the rear end.If I gun it from a stop it feels like the axle is twisting up,and when it shifts hard from 1st to 2nd,like either wheel is moving back or forward.I am going to replace the springs soon anyway,so we'll see if that works.I do have wheel hop,I can feel it when the tires break lose in astraight line or around a corner.
 
My driveline angles are 18* for the shaft,5*at the t case,and 9*at the pinion.I bought 4* shims for the rear.The blocks in the rear have the short end of the taper in the front.I just had my driveline balanced,new spicers,and new slip and pinion yokes so after shimming,hopefully it'll go away.
 
I found that the quality of the u-joint can impact vibration. I had a drive line problem that was significantly diminished when I changed to Spicer. I'm not endorseing Spicer directly, but I recommend only using quality parts. I also recommend that you check and re-torque your u-bolts that hold the springs to the differential to spec (I think 120 ft-pds.). Also, sometimes idiot DPOs will re-bolt their driveshafts to the ujoints 180 degrees out of phase when replacing joints, causing driveshaft imbalance. Try unbolting and rotating the shaft 180 degrees and rebolting (try both ends), if you haven't already.
 
I have spicers in it right now.I heard that with the slip yoke allyou do is slide it in and bolt up the rear.I posted about it a few days ago.The vibes are coming above 40 when I give it a lot of throttle or when I am off the gas completely.My t case is pointed down 5 *,my driveline angle is 18*,and the yoke is at 9*.I thought about dropping the t case as it would be easier.
 
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