Seriously bummed with this drivetrain setup right now :(

[SquareRoot]

Many of you know that I recently made some serious progress on my truck. A complete rebuild of the NV4500 and 205 T-case. Only the best parts available, meticulous attention to detail following the manual and everything visually inspected and measured with a micrometer.

Brand new driveshafts front and rear with 1350 series CV joints. Balanced, etc.

I got about 140 miles on the setup, mostly around town driving. Today was the second time I drove it to work and got out on the highway. Not impressed.

For starters, ONLY when shifting from 4th to OD, I can feel a noticeable imbalance in the clutch pedal. I don't know if the vibration is coming from the clutch or the other end and being transferred to the clutch. I installed a new pilot bearing and throw-out bearing. Clutch only has 3-4 thousand miles on it.

Also noticeable, is a serious vibration that starts at about 50 mph and feels more like the driveshaft. It's there when the drivetrain is load or unloaded but ESPECIALLLY harsh when I just let off the gas and it's kind of in that "coast" motion for a split second.

I'm stumped. I don't know where to begin. I'm really pissed due to the amount of work it is to take this all apart....again. Any suggestions on diagnosing with the easy stuff first?

 

[nvrenuf]

Make life easy - tell us a summary of the truck.

Your profile indicates an '85 K20, correct? If so then it should have hydraulic clutch pedal set up, I don't see how any drivetrain vibration could transfer back through the pedal unless it's directly related to the t/o bearing (like a bad brake rotor pulsation).

Lifted? I'm guessing it is since you have a rear CV joint. Did you turn the rear axle accordingly (shim / cut turn the perches)? Driveshaft chatter around the coasting state of throttle is usually related driveshaft angle.

 

[Bextreme04]

Put it up on jackstands and let it run in gear. Look underneath and see if you can see anything moving around like it shouldn't.

Check all of your driveshaft angles and the amount of spline engagement in the NP205. Do you have a SYE kit on the 205 or is it still a slip yoke? What are your driveshaft angles? Were you the one that switched form the Yukon locker to a posi because of the hard clunking you could feel/hear through the transmission?

 

[WebMonkey]

i think it's the CATs.



(just playin', i'm PRO non stinky exhaust)

hope it's something simple

 

[SquareRoot]

Make life easy - tell us a summary of the truck.

Your profile indicates an '85 K20, correct? If so then it should have hydraulic clutch pedal set up, I don't see how any drivetrain vibration could transfer back through the pedal unless it's directly related to the t/o bearing (like a bad brake rotor pulsation).

Lifted? I'm guessing it is since you have a rear CV joint. Did you turn the rear axle accordingly (shim / cut turn the perches)? Driveshaft chatter around the coasting state of throttle is usually related driveshaft angle.

Correct. Hydraulic Clutch. And the pulsation is an accurate description. 2" lift but that in itself didn't warrant the CV. I was starting from scratch so I opted for the CV since they run smoother and last longer than a single U-joint. Yes, I used 3 degree shims to point the pinion directly at the output shaft.

 

[SquareRoot]

Put it up on jackstands and let it run in gear. Look underneath and see if you can see anything moving around like it shouldn't.

Check all of your driveshaft angles and the amount of spline engagement in the NP205. Do you have a SYE kit on the 205 or is it still a slip yoke? What are your driveshaft angles? Were you the one that switched form the Yukon locker to a posi because of the hard clunking you could feel/hear through the transmission?

The 205 is a fixed yoke. The shafts were made based off the "center to face" actual measurements. New Yokes, slip shaft, everything. Yes, I hated the Detroit Locker and removed it for open gears for now.

 

[Redfish]

Is there any chance it is just a tire issue? Vibrations and weird harmonics can feel like they are coming from one area when they originate from somewhere else entirely.

 

[SirRobyn0]

@SquareRoot Vibrations are one of my least favorite things to try to chase down....

I've not been good about following everything you have done, but I'm just going to say that your line "a serious vibration that starts at about 50 mph and feels more like the driveshaft. It's there when the drivetrain is load or unloaded but ESPECIALLLY harsh when I just let off the gas and it's kind of in that "coast" motion for a split second." Especially harsh when you just let off the gas. My knee jerk reaction to that was rear differential. I'm not saying that's what it is, it was just my first thought.

What all did you have to do to relating to the transfer case? Drivelines obviously came out, where any lengths changed? Any chance the rear is out of phase? Any ability to tell if the vibration is come though the floor? behind you? ect. IDK I'm just throwing out what I can think of.

 

[SquareRoot]

Is there any chance it is just a tire issue? Vibrations and weird harmonics can feel like they are coming from one area when they originate from somewhere else entirely.

I'll say no because it wasn't there before I swapped out the trans, T-case and driveshafts. Tires were a constant and the truck wasn't driven during that time.

 

[SquareRoot]

@SquareRoot Vibrations are one of my least favorite things to try to chase down....

I've not been good about following everything you have done, but I'm just going to say that your line "a serious vibration that starts at about 50 mph and feels more like the driveshaft. It's there when the drivetrain is load or unloaded but ESPECIALLLY harsh when I just let off the gas and it's kind of in that "coast" motion for a split second." Especially harsh when you just let off the gas. My knee jerk reaction to that was rear differential. I'm not saying that's what it is, it was just my first thought.

What all did you have to do to relating to the transfer case? Drivelines obviously came out, where any lengths changed? Any chance the rear is out of phase? Any ability to tell if the vibration is come though the floor? behind you? ect. IDK I'm just throwing out what I can think of.

I removed the 208 tcase and installed a 205 fixed yoke tcase. Completely rebuilt. Both shafts changed length and both shafts are brand new. CV's on both.

 

[Snoots]

Just a shot in the dark; How long did the truck sit? Are there any divots in the sidewalls?

 

[SirRobyn0]

I removed the 208 tcase and installed a 205 fixed yoke tcase. Completely rebuilt. Both shafts changed length and both shafts are brand new. CV's on both.

Well I'm sure you'd know a tire vibration if you felt one so I'm throwing that out of my mind anyway. I wonder if the rear driveshaft is not balanced correctly.

 

[nvrenuf]

Disconnect the rear driveshaft and drive it, if the vibration goes away it’s either the shaft or rear differential.

As for the pulsating pedal the only thing I can think of is if the fingers on the pressure plate are uneven causing it to wobble against the t/o bearing.

 

[Craig Nedrow]

put an angle gauge on the back 1350 ujoint when it is up, and level. Now do the same for the front. The angle MUST BE THE SAME. Built lots of drivelines, the ujoints must be installed clocked, not 90 degrees off!! We had a 20' Mauser lathe we used to set the driveline on the lathe bed on the ujoints, then a three foot straight edge on each end, stand back and checked to see if the ujoints were perfect level with each other. Tach weld, back in the lathe, tap tap with a dead blow to get the least runout, weld up. Heat and water quench to straighten. Sounds like angles off, or driveline issues.

Driveline angles should be equal to or within 1° of each other to avoid vibration problems and reduced u-joint life. To measure joint angles, measure the slope of the pinion, transmission or transfer case, and the drive shaft. A good angle average for most is around 17-20 degrees, but there may also be 25-35 and 5-15's. Universal joint operating angles on each end of a driveshaft should always be equal within one degree of each other, and for vibration-free performance, universal joint operating angles should not be larger than three degrees.
Go Here: htthttps://spicerparts.com/calculators/driveline-operating-angle-calculatorps://spicerparts.com/calculators/driveline-operating-angle-calculator

 

[SquareRoot]

put an angle gauge on the back 1350 ujoint when it is up, and level. Now do the same for the front. The angle MUST BE THE SAME. Built lots of drivelines, the ujoints muct be installer clocked, not 90 degrees off!! We had a 20' Mauser lathe we used to set the driveline on the lathe bed on the ujoints, then a three foot straight edge on each end, stand back and checked to see if the ujoints were perfect level with each other. Tach weld, back in the lathe, tap tap with a dead blow to get the least runout, weld up. Heat and water quench to straighten. Sounds like angles off, or driveline issues.

Driveline angles should be equal to or within 1° of each other to avoid vibration problems and reduced u-joint life. To measure joint angles, measure the slope of the pinion, transmission or transfer case, and the drive shaft. A good angle average for most is around 17-20 degrees, but there may also be 25-35 and 5-15's. Universal joint operating angles on each end of a driveshaft should always be equal within one degree of each other, and for vibration-free performance, universal joint operating angles should not be larger than three degrees.
Go Here: htthttps://spicerparts.com/calculators/driveline-operating-angle-calculatorps://spicerparts.com/calculators/driveline-operating-angle-calculator

Good advice but I was under the impression that a CV should point directly at the output shaft? Driving home tonight I did some testing and can say the vibration is speed dependant NOT rpm dependent. That's good I think. Suggests a driveline issue versus a clutch. I also realized I can now just remove the rear shaft, put it in FWD high and drive it. That was a big benefit of doing the twin stick, fixed yoke setup.