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Horrible grinding noise after Shackle flip (with pics)

stoney126

stoney126

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Hey all, I just got done putting the shackle flip on my blazer. Its a 84. Shackle flip is a 4"ord. Xfer case is a 208 connected to a 400 and my 6.2.

Besides my the awful drive line vibration( another problem for another time:D) A horrible grinding sound comes under partial throttle. It is only at a certain point on the throttle but gets louder as you gain speed.

If I keep my foot at that spot it keeps making the noise but if accelerate past it goes awya quick or if I let my foot off It briefly does as it goes by that spot. Now it didnt do it before I put the shackle flip on.

The trucks does have a pretty noticable rake to it. The rear went from 39 3/4 to 42 inches. Its got the original drive shaft which was pulled a bit out with the 4 inch springs but has gone back in with the shackle flip. Possible the driveshaft is contacing something inside?

Also is the rake of the truck messing with my driveline angle and Caster?
 
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How much slip is showing on the rear d-shaft going into the 208?

Is it a grind or more like a really loud humm? Maybe it's needle bearings screaming for their lives in the u-joints that are being blown up because of the bad d-line angles...

I had a weird noise at partial throttle, kind of like a whirling metal on metal noise and it turned out to be the dust shield that goes around the neck of the yoke on my 14ff... it was loose and spinning around with the d-shaft.

Maybe some pics could help give us some ideas.
 
I believe you are hearing the driveline vibes now because you have changed your pinion angle on your rearend.
The U-joints arent working at the same angle, therefore vibrate.
You can either shim it back to how it was or get a c/v driveline, c/v would probably be best.
 
The sound is metal on metal. LOl i feel better with a Hum:haha:Ill have to shim it I guess no dough for a new drive shaft. Ill check the measurement of the yoke. I have the axle on the middle hole of the perch. I may move the axle back 1 inch err hole to help the yoke and drive line angle.

Any thoughts to why it starts and ends at the same position of the throttle regardless of speed?

I dont think I have a dust shiled but Ill check

Also since the rake is pretty noticeable, will this have a negative effect on my drive line? will get pics tommorow
 
I say driveshaft vibe is setting up a harmonic vibrationinside the t-case and you are hearing things like the chain slapping around or a bearing type knock.

It only happens at a certain speed because that is where everything in the world is perfect for it to happen.

I had this in an old truck of mine and it was tough to find but went away as I shimmed the axle to get the pinion angle to work better. Fun thing with that truck was the right pinion angle produced transfer case noises with no driveshaft vibes, but when the transfer case was happy the pinion angle wasn't.
 
What tranny are you running? Mine is doing the exact same thing and I haven't been able to track it down. The drive line vibration is different for me - it's constant and happens right around 55 mph. The metal on metal scraping sound happens any time i'm going over 30 mph or so and is most noticeable in 3rd gear (4th for you non- "L" believers) or will be constant if the clutch is pushed in. I don't think it is a chain slapping or bearings, it's a pretty angry sound.

I also thought that was strange that it happens in exactly the same spot on the throttle even at different speeds.

I've been told that it's everything from the rear diff to the tranny and everything in between. I know for sure it's not the rear diff and it doesn't happen when the t-case is in neutral so I don't think it's the tranny. From what i've gathered it's either the t-case itself or the u-joints in the rear driveline.

The next thing I was going to try was pulling the rear driveline and going for a drive using just the front wheels to see if that solves anything.

FWIW, I've got 4" blocks in the back and my t-case is in the stock location so I wouldn't be surprised if the lift is the culprit...hopefully it's just exposing worn u-joints and not a bigger issue 'cause damn it's a god awful noise to hear while you're driving.
 
After you did the shackle flip did you check the diff oil? The added pinion angle may be starving the bearings for oil. Just a thought and easy to check.
 
obvious question, but check all your u-joints...pulling the rear d-shaft and drive in 4-hi w/the front wheels does seem like a good idea....it would rule out the trans or rearend...then it maybe easier to track down this noise.
 
Good tips guys, ill give it a go. The wierdest part is its at a certain point on the throttle. I can hear at 5mph but its faint and gets louder the more sped i have. Gonna check the oil, dfidnt think of that . Gonna pull the Drive shaft too. The Trans a is a turbo 400
 
That rear shaft is definately too short. Also the u-joint angle at the t-case is not the same as the pinion which will cause vibrations.
 
I have the exact same thing with mine, happens at about half throttle. Sounds horrible. I know in my case, the noise is coming from the tcase cause I cut a hole in the floor to clock the case. Drove it with the hole in the floor and its obviously coming from the tcase. However I'm not sure what causes it. My guess is its like miniwally said...
 
stoney126 said:
Should I go cv at the top then?
Click to expand...

I did a SYE on mine and bought a CV shaft from HAD. A CV shaft will do the trick BUT it wouldn't do it with a slip style shaft, SYE the t-case along with a CV shaft and be done.

I'll show you mine when you come pick up the bumper this week.
 
I got a 208 but wanted to go with a 241. I got one job tomorrow and ill find out if I got anymore this week.
 
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