Rumble on decelleration?

LABMBA87 · Jun 21, 2007

'94 XJ 4.0 AW4 NP231 4.5" RE on 31.10.5.15's. When taking foot off the skinny pedal at 45+ when warm, there is a load rumbling vibration that is rotational under the driver seat and tunnel. I would assume it's in the drive-train, and I have it on a lift right now at work. There are NO loose U-joints and I can't see any visible signs or witness marks of much of anything?
I do have the Chrysler 8.25 and I have a funny feeling there is some backlash issue so I am pulling the rear diff cover.

Any other rec. while I have it in the air? T-case?
TIA
Scott:rattle:

Ben H · Jun 21, 2007

That rumble is a slight pinion vibe. A SYE is the fix.

LABMBA87 · Jun 21, 2007

Just pulled the diff cover and found what looks to me to be excessive backlash. I have the 8.25 in the rear and if I'm correct it's only supposed to be .008 and i have like .015-.020. hmmmm?? anyone think this is the prob? I don't have the money to regear, and this is my daily rig so......... Do I need to just let it blow up and then regear or do I need to fix it?
Thanks
Scott

old_man · Jun 21, 2007

Double check and make sure the pinion nut is tight. It can cause what you say. It will make the backlash open up over time and ultimately will fubar the gears and bearings. Don't ask me how I know.:jester:

LABMBA87 · Jun 21, 2007

Is the pinion nut inside the pumpkin or outside?

j99xj · Jun 21, 2007

Outside. But you have to remove the U joint to get to it.

LABMBA87 · Jun 21, 2007

Ok, not to undercut anyone, but with 3.75-4.25 inches of lift, why on eart should I need a SYE? If I tighten up that pinion nut, won't i blow up my crush sleeve and stuff? How can I make sure I have the 8.25 without taking the diff cover back off? Any and all ideas are helpful at this point?
Scott

LABMBA87 · Jun 21, 2007

I got 2 prices. USA standard gear set for 131.xx or US Gear for 224.xx?? Anybody used these?? Any one know about them? The master OverHaul kit for the 8.25 is 75.16.. Decent?

Ben H · Jun 21, 2007

LABMBA87 said:
Ok, not to undercut anyone, but with 3.75-4.25 inches of lift, why on eart should I need a SYE? If I tighten up that pinion nut, won't i blow up my crush sleeve and stuff? How can I make sure I have the 8.25 without taking the diff cover back off? Any and all ideas are helpful at this point?
Scott

I had the same rumble while letting off the gas, had it while I had about 4" of lift. Went to 7" of lift, added a SYE and now have no rumble, maybe just a coincidence.

A SYE at 4" of lift is not uncommon. Do the cheap stuff first, but once you realize that you need a SYE, you wont be undercutting nobody.

LABMBA87 · Jun 21, 2007

So, now this brings me to the nest question. Where can I get a Cheap(er) SYE for this turd?

Ben H · Jun 21, 2007

Performance offoad center.

http://www.performanceoffroadcenter.com/oscommerce/product_info.php?products_id=1133&osCsid=fdb0565e863f707943c1d679d6094e1c

You should be able to use a front drive shaft for the sye with your set up. But you'll have to measure.

Rumble on decelleration?

LABMBA87

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