Vibration from the rear when decellerating - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 04-16-2003, 10:33 AM
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Vibration from the rear when decellerating

Stock YJ.

On hwy, going some 60-70 mph, and then the car(s) in front of you slow down just a bit. Really just a bit. So you don't brake, there's no need to hit brakes. You just lift the gas-pedal-foot (right one, I presume) so the Jeep slows down, and then you go back normas as soon as everything else turns normal.
In the process, however, there's a vibration that comes from the back (ONLY from the back) when I lift my right foot slowly off the pedal. If I do it very quickly, the vibration comse, but is very very short. If I do it nice 'n easy, the vibration is a bit longer (about a second). If I use brakes to slow down, no matter how lightly (or heavily) I use them, there's no vibration. Also no vibration if I let go the gas pedal and press the clutch at the same time (i.e. I go "gearless") - no vibration.

I checked U-joints, but there's no play at them. Nada. Zip.



So I was thnking two things:
1. the vibration might have been there all the time, only I didn't notice it
2. the vibration could be normal. I let go of the gas, the engine starts to slow down but the rear wheels keep rolling, so at some point the wheels are rolling faster than the engine, so everything vibrates.

Could it be true, or is something gone bad?

Oh yeah, when I try that same gas-release thing in the city (30-40 mph) there is no vibrations whatsoever no matter what I do with gas/brakes/clutch.
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post #2 of (permalink) Old 04-16-2003, 12:34 PM
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Re: Vibration from the rear when decellerating

1. If it's selective speed...
2. The Slip Yoke?
3. The tires?
4. This is a wierd problem. [img]images/graemlins/confused.gif[/img]
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post #3 of (permalink) Old 04-16-2003, 12:48 PM
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Re: Vibration from the rear when decellerating

the only vibes i've ever had from the rear were either a worn out Ujoint or my R&P, which the R&P issue was right after some work on the rear [img]images/graemlins/chair.gif[/img]..... you haven't done anything envolving the R&P lately have you?
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post #4 of (permalink) Old 04-16-2003, 12:55 PM
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Re: Vibration from the rear when decellerating

No, no works at all. Only thing I did was to put some grease, when I layed my hands on the grease gun, on the slip yoke. There is a grease fitting, so I pushed some grease in.
But it doesn't sound like serious thing... I mean, testing by hand and everything is as it was before...as it ever was. And all I have to do when decellerating is to lightly (but really lightly) press the brake, and there'll be no vibes at all. Plus it happens only when going at hwy... I don't know...
I should be changing my O2 sensor next week, and then I'm at DC to change the cat converter - it's rattling like hell lately. So I'll aks them to check it out...
post #5 of (permalink) Old 04-16-2003, 01:00 PM
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Re: Vibration from the rear when decellerating

</font><blockquote><font class="small">In reply to:</font><hr />
DC to change the cat converter

[/ QUOTE ]1. These should be available aftermarket.
2. At about 1/3 the cost.</font><blockquote><font class="small">In reply to:</font><hr />
I mean, testing by hand and everything is as it was before

[/ QUOTE ]3. When you test by hand, it's a far cry from testing at highway speed.
4. Lots more centrifugal and other forces happening.
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post #6 of (permalink) Old 04-16-2003, 01:17 PM
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Re: Vibration from the rear when decellerating

I had that same thing about 2 yrs ago. i just let it go and it got worse and worse until i knew it was my r&amp;p then it locked up on me on the road before i could have it fixed. cost me a towing bill and new r&amp;p. i don't know what they can do in the early stages to fix it, if anything, but id check it out.
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post #7 of (permalink) Old 04-16-2003, 02:15 PM
 
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Re: Vibration from the rear when decellerating

Check the U-joints again very carefully. If they are greasable, grease 'em again. Lord knows how many vibrations are caused by U-joints that aren't bad, but on their way there.
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post #8 of (permalink) Old 04-17-2003, 07:36 AM
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Re: Vibration from the rear when decellerating

Yup, there are aftermarket even here [img]images/graemlins/crazy.gif[/img]
But, they cost almost the same (I mean, $500 vs $450). And a couple of friens who used aftermarkets on their cars (not Jeeps) tell me they last about half the time the original one does. I know they get pretty cheap in the States, but here it's still very expencive... Plus, all the aftermarkets available ghere don't include the guarantee (actually, they do, but only for 6 months). And if I order from the States, including shipping, customs, VAT - it gets the same price as the DC has. So why bother?
[img]images/graemlins/AR15firing.gif[/img] [img]images/graemlins/bs.gif[/img] [img]images/graemlins/cussing.gif[/img]
post #9 of (permalink) Old 04-17-2003, 07:45 AM
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Re: Vibration from the rear when decellerating

Don't know much about YJ's, but as long as your looking, check the rear pinion nut. It may be comming loose, if it gets too loose it will send that pinion into the carrier locking up your rear end. I had that happen when (just like you said) I let my right foot off the gas at hyw speed. The backlash sucked that puppy in, locked me up, and blew the pumpkin into pieces. Just a thought.
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post #10 of (permalink) Old 04-17-2003, 10:06 AM
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Re: Vibration from the rear when decellerating

And where is that nut located? Inside the pumpkin?
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