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vibration help please

F-ingrob

F-ingrob

Wheres the mud
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ok so i changed my gears then a week later did a shackle flip then a week later i added a 7* shim to point the pinion to match the trans angle and yes i think i did the measurement correctly thats why i added a 7* shim but i could be wrong
so the problem is at 65 MPH plus i have a vibration at cruise speed and when i let off the gas peddle
it does not seem to vibrate much at all when under power
so here are some details
lift is 6"
35" tires
corp 14BFF
dana 44 front
87 K5 700r4/208 non slip yoke
i added the shims due to the pinion pointing up so much that the pinion and drive shaft were in the same plane and i could not afford a double cardon joint drive shaft at this point

so if you can please help
not sure if its the gears that i did wrong or if its still drive shaft angle being wrong
 
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define the vibration better, but I'm leaning towards a u-joint not liking the new angle its forced to work at. Bad gears usually howl at speed and/or clunk when you load/unload them so I think your fine there
 
So you're not running a cv right? Then the pinion should not be pointed at the t-case, it should be parallel with t-case

image.gif
 
No I do not have a CV shaft
And the vibration is @ 65MPH and high when i am at cruise speed and under deceleration
I shounds and feels like when you drift off the highway and hit the grooves they cut in the shoulder to alert you that you are drifting off the road
I have new ujoints in it also i put them in when i did the gears
 
skunked said:
Then why is your pinion pointed up?
Click to expand...

^This

For how you did it, you need a CV shaft. If you have a normal 2 joint shaft, the output of the tcase and the pinion should be parallel with each other (like the picture linked above).

Your two options are to either get a CV shaft on there, or shim the axle back down to mirror what the picture above shows. This is 99.9% where your vibs are coming from
 
Making the pinion match the transfer case angle only works to a point. U-joints vibrate by nature, the caps speed up and slow down as they do their thing and they vibrate. If you put the u-joints in plane (i.e. if your driveshaft was built correctly) and if you make the angles match, one u-joint will cancel the vibration from the other. The problem is that once the operating angle gets steep, you might be cancelling 95% of the vibration but the vibrations are so violant that the last 5% really shows up. I've seen reference to where Spicer says that matching the angles like that only works up to a few degrees of operating angle.

The deeper gears spin your driveshaft faster, so that amplifies the vibration.

You can try shimming what you have, but it's guess and check. The right way on paper (i.e. pinion matching the transfer case angle) isn't always best in the real world. Sometimes pointing the pinion up works better, even though the angles don't match that does reduce a lot of the operating angle at the diff and flattens out the driveshaft which helps the operating angle at the t-case. That method is guess and check, and you'll never get it to be vibration free but you might be able to make it better than it is.

The 100% solution is a CV type shaft.
 
Sacramento driveline and they'll ship if that's more convienent. High Angle driveline in paradise is another option.
 
Going through the same stuff on mine. The kicker is the complaint of the rumble when coasting. Exactly what I had. I might have made it 20 total miles when my shaft decided it needed to be somewhere else other than attached to the rear axle yoke. Caught it slowing down for a stop light. Limped to the side of the road and it was halfway out. My angles were close to 8 degrees off from front to back. Sucks, but at least I caught it before it chucked out and slammed my exhaust and floor like a maniac with a baseball bat.

CV shaft is going to be your fix. In which case you'll need to keep that pinion angle in line with the driveshaft. Close to what you have now. Unlike the picture above with a standard 2 joint shaft, most of the angles getting cancelled out happen at the CV and need little to no working angle at the axle. 1 degree to 0 degree.

Keep this in mind too, the pinion angle is not static. Meaning it moves under acceleration and deceleration. Under acceleration, the pinion is trying to climb up the ring gear so the natural tendency is for the pinion angle is to rise. On the opposite side, under deceleration the pinion goes down. Try and shoot for a happy medium so that the change under accel and decel won't take the working angles on the joints out of the range they are ok with.

With all the problems I'm having now, I was really surprised my 75 was ok with a similar shackle flip and didn't require any driveshaft alterations at all. But the big difference there was due to that truck having a fixed yoke 205 with the 12 bolt axle. That driveshaft was at least 5-6 inches longer than the one in my 91 with a 14b and 241 slip yoke t-case. Length is a good thing. Shorter shafts are more sensitive to angles and require more radical stuff to be done to correct it. Longer shafts flatten out those angles and are not as sensitive. Both still require no more than 2 degrees difference from one joint to the next, but the longer lenght spreads the angles out and don't require added CV's or slip yoke eliminators.

Comparing my 91 to Larry's 89 Polar Bear Burb we are running the same size wedge shim in the rear to correct but due to the length he didn't need to add the CV to his rear shaft like I need to.
 
F-ingrob said:
well i guess its going to be a cv shaft then
i found 2 places to get one
Tom Woods and
Driveshaft super store http://www.driveshaftsuperstore.com/Iextreme.htm
what you guys think
Click to expand...

I Called down to the driveshaft superstore to check on the prices a couple of weeks back in my search. DO NOT go by that website. They admitted over the phone the site is way out of date and while they can make a cv shaft for a Blazer the cost is right in line with Tom Woods or any of the other guys at about $500.00 plus shipping.
 
I just ordered a 1350 cv with a flange from tom woods earlier today, $440 shipped. Super nice guys that answered all my questions, if the shaft is as awesome as the customer service I'll be happy..
 
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