Another vibration after re-gear thread

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AWayne

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Starting another vibe after re-gearing thread, because mine seems.. different.

Info on my shitbox:
4.0 / NV3550 / Dana 30+Dana 35.
33x12.50r15 STT Pro Coopers, 1.5" spacers, factory Ravine wheels.
Revolution Gear 4.88s, TrueTrac LSD rear /open front.
Tom Woods rear shaft. Factory front.
Rough Country SYE.
160k miles.
3" JKS springs.
Rough country x-flex control arms.
"ZJ" steering components.
Center frame repaired with RustBuster components.
Rough country single adjustable front track bar, rough country double adjustable rear.

Re-geared my turd less than 400 miles ago. Getting a "rumble strip" kind of vibration over 35 ish with clutch depressed. It is also present at higher speeds (50+ we'll say) with it in gear.
Over 50, under around 1/4 throttle (in gear) "blips" a vibration until it gains RPM/more throttle input. Much more severe with clutch in.

Had a Rough Craptry shaft and replaced it with a Tom Woods shaft which did improve the vibration by around 20%, we'll say.

Lift was installed last year before the regear, as well as tires. No vibes then. Pinion angle has not been messed with yet. Changing engine mounts tomorrow, but I'm doubting that will solve anything.

Any thoughts on what else to look for?
 
When you put your tires back on, did they go back in the same places?

I'd start by checking your tires.

-Mac
 
Have you removed one driveshaft or the other to narrow the vibrations to the front or rear?

What's your front castor angle? Toe setting? Do you have a drop pitman arm?

-Mac
 
macleanflood said:
Have you removed one driveshaft or the other to narrow the vibrations to the front or rear?

What's your front castor angle? Toe setting? Do you have a drop pitman arm?

-Mac
Click to expand...

Currently only have rear shaft in. Plan on pulling it, and putting front shaft in tomorrow to see if there's any difference.

I honestly can't remember what the castor was at. I've played with the toe and castor a few times since the lift, eyeballing it and measuring it, so I'm not 100% what it's set at. I'd have to check that as well.

No drop pitman arm.
 
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AWayne said:
Starting another vibe after re-gearing thread, because mine seems.. different.

Info on my shitbox:
4.0 / NV3550 / Dana 30+Dana 35.
33x12.50r15 STT Pro Coopers, 1.5" spacers, factory Ravine wheels.
Revolution Gear 4.88s, TrueTrac LSD rear /open front.
Tom Woods rear shaft. Factory front.
Rough Country SYE.
160k miles.
3" JKS springs.
Rough country x-flex control arms.
"ZJ" steering components.
Center frame repaired with RustBuster components.
Rough country single adjustable front track bar, rough country double adjustable rear.

Re-geared my turd less than 400 miles ago. Getting a "rumble strip" kind of vibration over 35 ish with clutch depressed. It is also present at higher speeds (50+ we'll say) with it in gear.
Over 50, under around 1/4 throttle (in gear) "blips" a vibration until it gains RPM/more throttle input. Much more severe with clutch in.

Had a Rough Craptry shaft and replaced it with a Tom Woods shaft which did improve the vibration by around 20%, we'll say.

Lift was installed last year before the regear, as well as tires. No vibes then. Pinion angle has not been messed with yet. Changing engine mounts tomorrow, but I'm doubting that will solve anything.

Any thoughts on what else to look for?
Click to expand...

So it goes away after more than 25% throttle?

Does it oscillate? Does it come and go as speed increases? Or is it continuous?
 
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JMT said:
So it goes away after more than 25% throttle?

Does it oscillate? Does it come and go as speed increases? Or is it continuous?
Click to expand...

If I am in gear, we'll say 4th. Going 40-45 with no throttle input, foot off the gas.. if I press the gas very lightly it vibrates like a dead misfire is another way to describe it I guess. Remove any throttle input and it's barely noticeable in gear. Or put your foot to the floor and it's goes away.


It doesn't feel like it oscillates. More of a low growl. Continues with speed, gets worse. For example, if I am going 40mph and depress the clutch it's like having a few phones vibrating in the seat. Depress the clutch at 70MPH and it's much more violent, like hitting a rumble strip on all 4 tires at that speed. I Have driven as fast as 70MPH and it was violent enough with clutch depressed I wasn't going to do that again.
 
Check pinion angle on both ends, pull on them and see what kind of play you get at output yokes, make sure splines feel tight. Curious what caster/pinion angle is in the front.

Who did gear work?
 
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AWayne said:
If I am in gear, we'll say 4th. Going 40-45 with no throttle input, foot off the gas.. if I press the gas very lightly it vibrates like a dead misfire is another way to describe it I guess. Remove any throttle input and it's barely noticeable in gear. Or put your foot to the floor and it's goes away.


It doesn't feel like it oscillates. More of a low growl. Continues with speed, gets worse. For example, if I am going 40mph and depress the clutch it's like having a few phones vibrating in the seat. Depress the clutch at 70MPH and it's much more violent, like hitting a rumble strip on all 4 tires at that speed. I Have driven as fast as 70MPH and it was violent enough with clutch depressed I wasn't going to do that again.
Click to expand...

Remove the front shaft. Get your pinion angles set in the rear. Start the rear at pinion 1* below shaft angle and move up or down from there if needed.

Move to the front and start pinion at 1* above shaft angle and move from there. Take note of your caster at each iteration. You’d like to have at least 6* caster with 33’s and more is better, but there’s a balance you have to find.
 
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JMT said:
Remove the front shaft. Get your pinion angles set in the rear. Start the rear at pinion 1* below shaft angle and move up or down from there if needed.

Move to the front and start pinion at 1* above shaft angle and move from there. Take note of your caster at each iteration. You’d like to have at least 6* caster with 33’s and more is better, but there’s a balance you have to find.
Click to expand...

Already got the front shaft out and it didn't make any difference. Believe my issue is going to be in the rear, so I'll drop the pinion angle a little lower and see how it does.

Would pinion angle still cause an issue like this, even though clutch is pressed/ engine at idle?
 
AWayne said:
Would pinion angle still cause an issue like this, even though clutch is pressed/ engine at idle?
Click to expand...

Yes, as the driveshafts are always spinning going down the road. clutch in/in neutral engine at idle eliminates an engine vibration as the cause.

at the rpms the driveshaft turns with 4.88s and higher gears at highway speed with 33" tires, they are very sensitive to pinion alignment, plus there tends to be some combination/cancelling between the front and rear driveshafts that produces a surging or cycling of the vibration experienced at speed.
 
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Replaced the passenger side engine mount (the easy one) and it seems to have made a little difference. I've discovered I need ball joints as well, so going to change those asap and adjust the pinion angle down more, as well as replace the driver side mount when I'm off work.
 
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Bearings are shot in front and rear. Full rebuild for both tomorrow. Hoping the axles/ R&P aren't shot. If they are, Jeep is going on marketplace.
 
Friends shop did the work. I used Redline gear oil instead of Revolution's GL6, so maybe that done it. Didn't know that was recommended, until this. Figured Redline would be good enough, but after some reading I suppose not.
 
AWayne said:
Friends shop did the work. I used Redline gear oil instead of Revolution's GL6, so maybe that done it. Didn't know that was recommended, until this. Figured Redline would be good enough, but after some reading I suppose not.
Click to expand...

While I agree conventional gear oil is the better choice, there is no reason a differential should fail with anything between 75w90 or 85w140, GL5 or GL6, conventional or not. Oil choice has little effect on bearings, more to do with the harsh environment of hypoid gears as they break in.
 
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JMT said:
Remove the front shaft. Get your pinion angles set in the rear. Start the rear at pinion 1* below shaft angle and move up or down from there if needed.

Move to the front and start pinion at 1* above shaft angle and move from there. Take note of your caster at each iteration. You’d like to have at least 6* caster with 33’s and more is better, but there’s a balance you have to find.
Click to expand...

Sorry for the hijack, but curious why you say to start 1 degree above the shaft in the front and 1 degree below in the rear?
 
AWayne said:
Friends shop did the work. I used Redline gear oil instead of Revolution's GL6, so maybe that done it. Didn't know that was recommended, until this. Figured Redline would be good enough, but after some reading I suppose not.
Click to expand...
highly doubtful

It's more likely installer error. My installer used Revolution gears, Revolution master install kit with Koyo bearings and filled with /recommended Valvoline synthetic blend. No issues years later.
 
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