97 4.0, auto, and 4x4. 4.5 inch lift TC drop

I just swapped in a 99 8.25 and I put on some chevy 1500 shackles they raised the rear about an inch. I wanted it to be a bit more level.

Anyway, I have a grinding that occurs when I hit the gas or let go of the gas It only happens for a few seconds and then stops.

I put in new ujoints and used the drive shaft from the 99 8.25. Every thing is tight nothing shakes and the ujoints are fully greased. What do you guys think.

here is a pic of the 8.25 installed and a side pic to show my driveshaft angle. thank you

 

Could there be an issue with the diff?

 

thats what I was thinking. Like there is some slack some where.

while I was working on it. The two spider gears that are held on by the center pin felt out. I put them back in, but there was no way to tell which one was on top or the bottom.

I just find it odd that it only happens when the diff gets or losses power.

 

That's when the forces reverse, though...

 

I have a similar drive line noise.
I pulled the open carrier and put an LSD carrier in my 8.25 last week and had no idea what backlash was. (it was a quick lesson) and mine would be OK in drive under power, but as soon as I let off the gas it made this god-awful "Whirrrrrrr" sound.

I'd lay money on it being backlash that needs set. There's supposed to be some sort of preload on the bearings to keep the ring and pinion in sync. If you had that all apart at all, you'll have to have the backlash reset.

 

Small update

I just put in a new TPS mine was original and I needed to change it anyway.

But it did get rid of most of the grinding no more grinding when I let off the gas quickly, or when I accelerate.

Now, it only grinds (not as bad much lower sound) when I'm just barely touching the pedal Like when u are about to let go but keep the smallest amount of pressure on it to cruse to a light.

but with the new TPS is seems like my RPMS went up a bit.

 

Old thread I know I have a fix/answer if you don't already have it

 

im having the same sound but i just put some slightly lifted springs on the back and some spacers on the front and this sound just started happening but i had the gears out of mine like 2 years ago and it seemed to be find a little knock when i let off the gas or got back on but no grinding any more help would e helpful

UplndVpr

 

Yet you dont post it??

WTH?

 

Well it was an old! Post I guessed everyone fixed it from what I gather its the u-joint at the axle had same problem till I changed it (did sye later on)
And the person who started the thread pmed me and let me know a hack and tap fixed his, it is the drive line angle and swaping u-joints helps but never fixes it the 8.25 has a longer pinion and match that with a auto and there's your problem...

 

Pinion angle?

 

Exactly my thoughts... its setup perfect for a SYE... but it doesn't have one.

It also looks like the OP's shackles go forward lol

 

so any help is it the rear end gears or the u joints

 

Do the joints bind or have play?

what is your driveline angle?

 

Installing longer shackles almost always gets your pinion angle set up for an SYE. Longer shackles require the use of shims to counter the pinion angle changed if you do not go with an SYE.

Shackles should just come with shims to correct the degree they will throw you off. Too many people install shackles and have vibes yet they don't understand why?