Deceleration Vibration

Zukey14

TJ Enthusiast
Joined
Dec 6, 2018
Messages
116
Location
Lambertville Michigan
My TJ has done this since I have had it. At first I thought it was the brakes but after replacing the rotors and pads in the front and the rear drums and shoes there was no change at all. Jeep rides smooth when accelerating at any speed but when coasting or not pressing on the gas pedal I get a strange grinding/vibration feeling that seems to come from all over. I feel it in the seat, dash, wheel, everywhere and its enough to make the change and my sunglasses shake in the console or spill a drink in the console. If I am in a parking lot and put the Jeep in drive and let it roll I feel it, if I turn the jeep off and roll I feel it, basically anytime I am going under 10mph I feel it unless I am pressing the gas. I have 31" Duratracs and most of the research I have seen points toward the tires but on my previous JK with duratracs I didn't feel anything like this. It doesn't effect performance and doesn't seem to be getting better or worse so I have just ignored it but I don't like not knowing what it is. It did it before the lift and after didn't seem to make any difference. Motor mounts look good, Transmission mount could be replaced, I went through the diffs and didn't find anything out of the ordinary, Brakes are all good, hubs don't make noise, Drive shafts are rusty but there is no play in the U joints, Engine runs smooth, trans shifts smooth, I'm not sure where else to look other than tires but these are less than a year old or maybe something binding in the TC. Any recommendations?
 
Balance may be off with the wheels. I would start by having the wheels balanced again and make sure that is correct. Could be a bad tire but that's probably pretty rare. I work at a motorcycle shop and we see this in bikes when weights fall off or weren't balanced properly to begin with.
 
I have Duratracs on my 13 JK. At low speeds you can feel each lug as the tires go around. My wife thought the engine was misfiring when she drove it.
 
Some duratracs are imported. I hate to assume, but I feel that an American made tire is usually truer than an import tire.
Check your balance, find a shop who knows how to roadforce and go through them.
These are Brazilian.

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Yes, and it was the same pinion angle as used with the Dana 44. Same control arms for all TJs which are used to set the pinion angle.

Do you happen to know the number?
I’m having vibs, and I’m looking to cut some metal and do a tcase drop myself this weekend to see if it cures mine.

Edit I want to check mine.
 
I never pay attention to or measure the actual pinion angle, my method is to just eyeball it which works fine once you have done it a few times. For the OE driveshaft, the correct pinion angle will be the same as the tcase output shaft angle. They must be parallel to each other.

How much suspension lift height are you trying to compensate for with the tcase drop?

2joint_angle.jpg
 
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Balance may be off with the wheels. I would start by having the wheels balanced again and make sure that is correct. Could be a bad tire but that's probably pretty rare. I work at a motorcycle shop and we see this in bikes when weights fall off or weren't balanced properly to begin with.

Had discount tire check them twice and each time they said that they were in balance, plus at highway speed there is no vibration only less than 10mph
 
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No one has messed with your rear axle's pinion angle, right? Too low of a pinion angle can cause vibrations that would go away when accelerating.


Both axles are stock 3.07 gearing :( I thought of the angle being the issue but its stock upper and lower control arms so I don't think its been messed with. When I did the 2" lift I did get some vibrations from that around 35-45 mph so I put a 1" drop on the TC skid until I can get a SYE kit. From what I understand with a 2" lift its hit and miss and I happen to be an unlucky one that has vibrations. But with the 1" drop they are completely gone which would tell me that the pinion angle is back to an acceptable place, correct?
 
I have Duratracs on my 13 JK. At low speeds you can feel each lug as the tires go around. My wife thought the engine was misfiring when she drove it.

The feeling of the lugs on the road sounds familiar from my 15 jk with duratracs. I could always feel that at low speed but this is something else. I can feel the lugs on the road with these even stronger but theres a vibration or shudder that comes along with it.
 
Ideally both u joints should see the same operating angle, but there is a limit to that angle. If both output shaft and pinon are parallel but the u joint operating angle is 15 degrees, that's too much for my jeep.
 
Ideally both u joints should see the same operating angle, but there is a limit to that angle. If both output shaft and pinon are parallel but the u joint operating angle is 15 degrees, that's too much for my jeep.
That's why a small tcase drop is done with shorter lifts and a SYE plus double-cardan driveshaft is recommended for 4" and taller suspension lifts where a SWB TJ is concerned.

Vibrations will always occur once a tall enough suspension lift is installed. How to cure those vibrations is is straight forward and easily done.
 
Definitely sounds like the Driveline.

Brazilian Duratracs, boy that is a whole lot of tires. A Brazilian.
 
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