What causes hi-pitch noise on decel??

I havent had a chance to fully investigate this one BUT here's what I have gathered so far...
I was cruising at around 55mph, when I let off the gas and heard this soft but hi-pitched noise coming from the rear. Probably goes away by 50mph. And I can reproduce this sound readily!!
I definitely goes away w/ acceleration and DOES NOT go away when I put it in neutral and coast. It did not sound up w/ applying the brakes also.

Could this be driveshaft issues or bearings??

Thanks JTS

Do you have the 8.25 rear axle? This axle is notorious for loud gears, and gear noise is typical at 50 mph+. I used to have horrendous noise on decel with my 8.25, until I replaced it with a Currie axle. Although, the Currie has developed a very minor amount of the same noise, so I may just be cursed.

Nay

Dave,

I've encountered a similiar situation with my 8.25/29 spl after a recent regear to 4.56's. I have picked up what sounds like to be a "droan" which would mimic a driveline vibration, when I let off the accelerator at speeds over 50. Sometimes I can get the droan at lower speeds too, but not always. I removed the front driveshaft to elimate that as a source...droan is still there. Rear pinion angle is 2 degrees below driveshaft on SYE equiped setup. I have noticed an "ever so slight" amount of play at the pinion yoke, but it strikes me odd as I had new Timkin pinion bearings installed.

My point... does the horrendous noise you experienced with your 8.25 sound at all familiar to what I'm having? Could the slightly loose pinion yoke/bearing thing be the issue since it seems to mimic vibrations when I let off on the gas? It goes back to the shop on Wednesday, but I'd like to be sure I covered all my bases before it goes in.

Sorry to hi-jack the thread jtszymano, but perhaps our situations are similiar....

Ivan

Couple things:
What do you mean by play in the yoke and how did you test it??

Also, I had that drone when I had 3" all around. I never found out what it was BUT I will say that when I dropped to 1.5" all around the drone disappeared!

Heck on mine...the 4.88's, Power trax, suspension, tires, and body rattles get in harmony sometimes...those are real 4 x 4 sounds..

Dawg

"I'm not stuck..i'm soaking"

jtszymano said:

Couple things:
What do you mean by play in the yoke and how did you test it??

Also, I had that drone when I had 3" all around. I never found out what it was BUT I will say that when I dropped to 1.5" all around the drone disappeared!

Click to expand...

The play in the pinion yoke was tested by grabbing the yoke and moving it by hand in relationship to the diff (back & forth across the diff, as opposed to in & out of the pinion). It just feels like a "no so tight" bearing(s). My front D30 pinion yoke is solid...no play anywhere.

My lift has been constant all along before the regear. There was no droan then (or vibes) before the regearing. It only came after...

Ivan

Ivan,
How much movt are you talking about at the yoke! Im not sure how to describe it, but do you describe it in milimeters or what?

I think I have a little play there as well, but I want to compare to your experience...


In regards to the drone, I cant remember if the drone went away when I changed back to the 3.55. I wish I could help...but I really thinkthat it only went away when I dropped down to the lower lift...
Oh and hopefully Nay will chime in on the loud noise he had as well. I am curious to find out...

This all sounds consistent with the 8.25. I probably know more people with some noise in an 8.25 with 4.56 gears than I know people who have one that runs totally quiet. I even had mine completely rebuilt, and couldn't cure it, although ditching the 8.25 all together got rid of the noise.

Gear noise is typically found between 35-45 mph, then has a "quiet spot", and then from 50 or 55 on up you have the noise. Gear noise can occur on decel, accel, or coast. Mine was always a decel/coast noise, and would go away with even the slightest throttle. My gear wear patterns were always good. It a constant noise, not a driveline type issue which carries a vibe with the sound.

The 8.25 isn't a bad axle strengthwise, but it is known to scream like a banshee. I wouldn't put a dime into an 8.25 for this reason. The noise is the only reason I ever got rid of mine...just couldn't take it anymore.

For anybody wanting to run 33-35" tires, I cannot recommend a Currie high pinion 9" enough. I have 8" of lift and a 14 degree driveshaft angle, and it runs so smoothly that my beast is actually reasonably quiet. For $2,700 shipped to your door with a Detroit and disc brakes, this axle is a bargain. By the time you do gears, locker, alloy shafts, and disc brakes on an 8.25, you'll be at $2K and still have an 8.25...unless of course you can do the work yourself, in which case by a high pinion housing from Currie for $300 and do the work yourself...

Nay

Thanks guys, some stuff to think about...