So far I’ve blown an engine, and replaced it. Munched a transmission, and replaced it, installed new springs, shocks and bushing, and I’m ½ through setting up a re-routed exhaust system. Desmogged, and cleaned up the engine bay nicely.

- Through it all, I’ve also been chasing a strange little vibration. It’s enough to be noticeable, but doesn’t seem to be getting worse (or better for that matter. Inspecting the U-Joints, one was a tiny bit loose, and thinking that’s what my vibration is, I replace both rear U-Joints. Well, it still does it.

- The vibration ONLY happens between 20 and 25 mph. It does it in ANY gear, regardless of RPM. Engine load defiantly makes it more noticeable, when accelerating lightly it only makes a little vibes. If going up a hill, it’s noticeable. Stepping on the clutch to let the engine free, and the vibe stops. Again, this only happens between 20 and 25 mph. before and after that window, i can't really notice anything.

- Sooo… Anyone have any ideas here? This one is a mystery to me. New transmission, new u-joints … can’t figure what the heck the vibration could be coming from. Only thing i can think of at this point is that the drive shaft itself might be out of balance? - Hmmmm... strange...

Kindly.

Bat.

 

Tires or driveshaft are all I can think of.

 

Well, it has to be something engine driven. That leaves the motor itself; flywheel/clutch assembly; the tranny. Could also be a misfire. Sometimes misses can be a trick.

You can flat-out eliminate wheels as a cause if the truck doesn't do it with the engine disengaged. It's a good bet it's not the driveline either but I've been wrong before.

Feel it more in the seat or the wheel? Or just everywhere?

 

~ OK, well, I jacked up the rear end at the differential, lifting the tires off the ground. I blocked one tire, and spun the other thus rotating the drive shaft. I could see a slight wobble, so putting the dial caliper on was able to read 4-hundredths of an inch off. It should be 5-thousandths at most. $60 dollars later, and I have my driveline straightened and balanced.
- Having that work done reduced about 50% of my felt vibration. While talking to the technician about my problems and the symptoms, he mentioned "Pinion Angle or phasing the drive line, making sure the angle of the transmission yolk was the same as the angle of the differential yolk. The two should be parallel, the U-joints should each have the same angle at each end respectively.
- Soooo, looks like i need to measure the difference in angle, and then hunt down some properly degreed wedges in order to phase my drive shaft and correct the pinion angle. Hopefully it doesn't tear up any bearings in the process.... really wish I'd known about this when doing the rear suspension, I'd have corrected it off the bat when it was apart the first time.

- Thanks Enigma and Jimby for the responses. As for feeling it, mostly in the seeat, defiantly not related to RPM, so I've ruled out engine/trans, and those would change pitch based on engine speed. This vibration is 100% vehicle speed related, as the vibe only happens at one vehicle speed regardless of gear. Load does come in to play, and from I've read this is typical of having a mis-aligned pinion angle. Hopefully I can get it sorted quick.

Back to it.

 

I remember driving with lose wheels where the vibration would stop when I would put the clutch in and be worse when I accelerated, but I'm guessing you must have taken the wheels on and off at least once since the problem started.

 

LoL! I bet it made vibes, and Yes Gillesdetrail, I have had it apart a couple times now . I think it's been apart and back together twice in the last three months., this morning being the second time.
- So, up early, and all done before work at noon including a test drive. I've managed to reduce a majority of the vibration. It still does it, but not to an alarming amount. Just a little vibe right at 20 then gone. I know what I need to do to remove the rest as well.
- In my efforts to find and eliminate this odd vibration....

1) Replaced some f-ugly U-Joints


2) Had my drive shaft straightened.
+++ Picture Soon +++

3) Took my rear end apart (Again) to flip the wedges. This, of everything, helped the most. I'll need to measure and get the correct degree wedges, then I believe it will be smooth again...

(Before: Notice the pinion agle is bacwards - really not good)


(The wedge I flipped this morning)


(After: Notice the pinion angle is a bit better. Still not where it needs to be, but made a huge difference!).


- So, I'll have to do a bit more work, but at least she wont break anything now.

 

I believe you have your driveline "backwards". the slip yoke end should be at the t-case (unless mine has been wrong for the last 20 years). Could be part of the problem. Single piece driveline or is it the two piece longbed kind with the center carier thingy? A slight tilt up on the pinion is okay but yours looks pretty extreme in the pics, might be enough to cause oiling issues in the pinion bearing? Prolly not but it's a thought.

 

My slip yoke is at the t-case, too. But his driveline looks different from mine.

 

Interesting ... Manual i have is 1985, and shows it as you described (Slip yolk at T-Case). However, the slip yolk on mine was at the bottom/differential when i bought it, and thats how all the wear/fade outline's looked as well. I will have to see if it even bolts up the other way, as well as some research to see if they changed it after 1982.
- Also, my drive shaft does not have the center carrier, it's just got the two u-joints, and slip yolk.
---- Man, now i have to do more research - lol.

---- Anyone else with a 1982 4x4??? what way is your drive shaft??

 

Yes, the slip yoke goes up behind the T-case. I don't think it will do any harm mounted backwards, except the slip yoke will be subject to a bit more dirt, road grime and abuse?

 

I think only long beds have that carrier bearing in the middle of the rear driveline. Just one more reason I like short beds.