Seriously bummed with this drivetrain setup right now :(

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85K304SPD

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I usually, (mostly always) have to do everything at least twice. The first time to figure out what is important, and the second time to do everything right. Its usually easier the second time. It sounds like a good set up, just got to tune it. I learned alot about driveshafts from this thread. Thanks all.
 

SquareRoot

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Update: SquareRoot is an idiot!
Couple things discovered during troubleshooting. 1. @Craig Nedrow, it had nothing to do with driveshaft angle. Like the Tom Woods video states, the symptoms indicate an imbalance.
Mr. Stupid here pulled the slip joint shaft apart out of curiosity. A few weeks later after laying on the bench, I put it back together and installed it. Now I assumed it was balanced "in phase" so I put it back together with the joints lined up.
After discovering the vibration, I pulled the rear shaft and ran it in front wheel drive only. No vibration. Awesome! Not a clutch issue. So, I rotated the front part of the shaft 180 degrees and put it back together. Took it for a drive on a long smooth road. Hit 75 mph..... ZERO vibration. Lesson learned. Also a good time to mark the shafts for future reference.
Now about the angle. The rear pinion joint angle should be -2 degrees from zero. Spring wrap under load will bring it to zero. Mines not there yet but, within a few degrees. Since I don't have any vibration now, I'm not sure I'm going to go through the trouble to get it exact. Getting the angle correct involves some math and making adjustments on the vehicle to figure out what degree shims one needs. For the moment, all is good.
 

SquareRoot

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I want to add that there is a distinct difference between a drivetrain with an auto trans and a manual. I first noticed this with my former Detroit Locker. After swapping in a nv4500 in place of the th400, I had serious popping, banging issues thru the transmission when turning. It was unnoticeable with the slushbox but unlivable with the manual.

This current issue with an imbalanced driveshaft was similar. The imbalanced shaft transferred the vibration to the clutch pedal, making me think the clutch was the issue. Manual transmissions don't hide issues like the fluid coupling (torque converter) does in a slushbox. Just my observations.
 

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Glad it was a simple fix.
You and me both brother. I'm pretty sure the factory shaft had an index spline. If I recall, it's a wide or double spline that only allows the shafts to be indexed in one position. The aftermarket not so much.
 

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Also want to add that for 205 T-case users the lateral play on the output shaft is normal and there's no provision to set the output shaft bearing preload because it's a ball bearing. So when you can feel movement on the yoke it won't have any play under load due to the thrust pressure from the helical cut gears. Yup, I learned sumthing new.
 

Craig Nedrow

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Thanks Mike, aka square root, for sharing, and apologies if I steered you, wrong, but always like to learn. Now I know that CV's angles are different them reg u-joints. I've only had them on farm equipment, lets you turn sharp without rattling. Onward!
 

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I usually, (mostly always) have to do everything at least twice. The first time to figure out what is important, and the second time to do everything right. Its usually easier the second time. It sounds like a good set up, just got to tune it. I learned alot about driveshafts from this thread. Thanks all.
If it helps any, I feel better knowing I'm not the only one doing everything at least twice. Recently working on rear drum rebuilds, got one apart, realized my 11"x 2" replacements were the wrong size so I had to put it back together, get the 2 3/4" shoes and bigger drums, get them rebuilt and they didn't work. Because the wheel cylinder replacements were also 2".
 

TotalyHucked

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Glad you got it figured out. Chasing driveline vibrations can drive a person mad. I've had a phasing vibration in my truck ever since I put the 20s on it. Even getting the tires rebalanced only helped slightly, I think one of these cheap cast wheels has an imbalance in it. Go around a long sweeper on the interstate and it'll be gone and perfectly smooth for miles. Then after a while and a few more sweepers, it'll be back with a vengeance and can't comfortably maintain the same speed. I hate chasing vibrations lol
 

SquareRoot

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UPDATE: I think I jumped the gun and now I have to swallow my pride for thinking I had fixed the issue :(. Phasing the rear shaft as mentioned earlier eliminated the vibration in the clutch pedal 100% and reduced the vibration in the drivetrain considerably....but not all of it. There's still an issue. The vibration now starts at 60 mph and gets worse with speed. I removed the front shaft and drove it to work yesterday (60 miles) and it didn't change anything so I can rule the front shaft out. Last night I reinstalled the front shaft and once again removed the rear. Tonight I will take it for a drive and see if the issue is gone. I will be happy if it is as I'll know it's the rear shaft that's the issue.

After a bunch more research on Double Carden (CV) operating angles, I think I finally have a clear understanding on how to set them up. I'm about 90% sure that my pinion angle is wrong and that's my issue. I had read that the pinion should point directly at the tail-shaft so I determined I needed 3* shims to raise the pinion up. That wasn't exactly correct.

To understand this you have to completely ignore any thoughts on how to set the angle on a common Single U-Joint type shaft. Forget it! Since the CV has 2 opposing u-joints in the "head" they effectively cancel each other out. Whatever angle is created between the output shaft and driveline is split 50/50 between these two u-joints. It DOESN'T matter what the angle is as long as it doesn't exceed the capacity of the u-joints. Now, the driveshaft points directly at the pinion shaft. Since there is only one u-joint on the rear of the shaft, it has nothing to cancel out its operating angle so it MUST be exactly in line with the pinion to avoid vibration. No exception.

However, this is not the end of the story and where most people (me) go wrong. This is a static setting. When the vehicle is in motion, torque is being applied to the ring and pinion to overcome friction to keep the vehicle moving. This causes spring wrap which causes the pinion to rise, thus changing the static angle by several degrees (2-4 seems to be the consensus). To avoid vibration AT OPERATING SPEED this additional angle must be factored in the static setting.

In my case, I added 3* shims and got my pinion .5 degrees higher than my driveshaft slope at static. Close enough, I thought. So, I'm starting off .5 in the wrong direction and adding several degrees more in the wrong direction at speed. At 60 mph, I'm guessing my pinion angle is 3-5 degrees off. This makes sense because the angle (vibration) is not noticeable around town at slow speeds. Since I have a newly rebuilt trans and t-case with all new bearings and new balanced driveshafts, it doesn't seem logical worn parts could be an issue.

The tricky part of getting the pinion angle correct is that you have to install the driveline, measure the shaft slope and adjust the pinion angle 2-3 degrees lower. However, big note here, when you lower the pinion, you lower the end of the driveshaft, thus changing the slope. It's a feedback loop that can drive one crazy. I think the easiest way to do it is to loosen the axle U-Bolts and use a jack under the front of the diff and jack it up to rotate the diff while measuring the driveshaft slope and pinion angle until you hit that magic -2 degrees. Then determine what angle shims you need.

This weekend I'm going to remove the 3* shims and go back to the way it was. That may be all I need (+.5-3=-2.5), essentially what I started with. lol. Stay tuned.
 

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Update: Took the truck out for a drive tonight with the rear driveshaft removed. T case in 4 hi, front hubs locked in. Nice smooth road and I took it from zero to 80 mph several times. Smooth as a baby's arse. Sweet! That narrows it down to the output shaft on the T-case (unlikely as it's all new) or the rear driveshaft ( unlikely as it's all new). It's looking like the driveline/pinion angle is the suspect. Next step, pull the 3* shims and retest. If my suspicions are correct, @Craig Nedrow gets half the credit. Stay tuned.
 

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Update: Got the 3 degree shims out. I recently removed one leave from the spring pack so I decided to whack it and make a zero degrees shim out of it so I would maintain my level stance. 4 hours in the driveway in this 100+ heat bout to kill me! Taking a shower and few hours break before I wonder back out and reinstall the driveshaft. Stay tuned.
 

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TotalyHucked

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Yeah you can keep that. We were ~115* real feel yesterday but only 94ish today after those hellacious storms we had last night
 

SquareRoot

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UPDATE: Pulling the shims put the angle back to stock basically, -2.5 degrees. Unfortunately, that did nothing towards fixing the vibration. Trying to eliminate things, I am focused on the endplay on the output shaft. You can see that issue in the driveline forum under 205 connoisseurs. In the meantime, I'm gonna take the driveshaft back to the shop, explain things and have phasing and balance rechecked and marked this time.
 

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