Re-gear good, vibrations bad

[97JadeTJ]

So I read until my eyes bleed and decided to make the move to regear my 97 tj 2.5l auto on 33’s from 3.73 to 4.88 and today was the day… Install went great, dialed in perfect, until the test drive… power was everything I hoped it would be! until I hit 50mph… vibrations! I thought I had read enough but somehow I missed all the posts about driveline vibrations after regear! Front driveshaft removed and no vibration so that’s a start… I installed a 2.5” suspension lift and a 1” body lift back in September and did not have any vibrations at that time… I guess tomorrow I will start dropping my skid plate 1/4“ at a time and see if that will help… any other suggestions appreciated!

 

[freedom_in_4low]

If the vibrations go away with no front driveshaft installed, I would start with adjusting the front pinion angle first if you have adjustable arms or cam bolts.

 

[bobthetj03]

Feel your pain brother. Try to get the front pinion a tick hight than the DS if you can. A MML could help too.

 

[97JadeTJ]

If the vibrations go away with no front driveshaft installed, I would start with adjusting the front pinion angle first if you have adjustable arms or cam bolts.

No adjustable arms or cam bolts…

 

[TheBoogieman]

Are your front u-joints good? Changing gear ratio doesn't change driveline angles. Maybe the extra power just made you notice what was already there.

 

[97JadeTJ]

Feel your pain brother. Try to get the front pinion a tick hight than the DS if you can. A MML could help too.

I don’t know how I missed all the problems you had with your regear… and things were going so great!… LOL

 

[97JadeTJ]

Are your front u-joints good? Changing gear ratio doesn't change driveline angles.

I’m going to change the front driveshaft u-joints today… it’s down, might as well rebuild it… then I’ll try with it again

 

[TheBoogieman]

I’m going to change the front driveshaft u-joints today… it’s down, might as well rebuild it… then I’ll try with it again

Post your results.

 

[freedom_in_4low]

Are your front u-joints good? Changing gear ratio doesn't change driveline angles. Maybe the extra power just made you notice what was already there.

I'm thinking either the pinion angle or as you point out, the u-joint(s), are far enough from ideal for him to feel at 30% higher speed, but weren't perceptible before.

 

[AMS417]

I'm thinking either the pinion angle or as you point out, the u-joint(s), are far enough from ideal for him to feel at 30% higher speed, but weren't perceptible before.

Same issues I had with the higher driveshaft RPM that came from a regear to 4.88 I found a bad u joint and that I needed a small adjustment to my pinion angle on both ends. Not that the regear changed my pinion angle, just highlighted an existing issue.

Hope the front shaft rebuild solves it for you.

 

[97JadeTJ]

So driveshaft rebuild didn’t solve the problem… I thought I had escaped the drivetrain vibrations people talk about when I raised it up 4“ and added the 33“ tires but in reality they were probably there I just didn’t realize it because the 2.5l and 3.73 gears combo couldn’t create enough rpm’s or torque to make them noticeable… to anybody on the fence about regearing get it done!… An attempt to remove the skid plate was met by 3 bolts that spun so an order of 6 nutserts and tool from black magic brakes was placed and I’ll wait till the weekend to drop the tranny… The vibes don’t hit till around 60 and the wife said it felt like a new jeep!

 

[Jerry Bransford]

A 4" suspension lift will definitely cause big drivetrain vibrations for the SWB TJ. They are normal with a 4" suspension lift. My strongest possible recommendation is to bite the bullet and install a SYE kit and double-cardan (aka CV) driveshaft which will then also require adjustable length aftermarket control arms for the TJ. Those are required since the DC driveshaft will require you elevate the rear axle's pinion angle up so it is the same as the driveshaft.

No you cannot adjust the rear axle's pinion angle to get rid of the vibes with the factory rear driveshaft. The reason its u-joints are vibrating is that the 4" suspension lift created too much of an angle for the front/rear driveshaft u-joints to work into without vibrating.

 

[Shane Malone]

I have a vibration that develops when going downhill fast 60km/hr it is not ecident any other time. Mmm except it does show on a hard brake. I replaced the discs and pads on the front and new shoes of rear balanced all wheels made a little difference but not fixed. Anyone have an idea. Wheel bearing? Uni joints? This problem started after a very rough ride. Oh yes 2006 TJ Golden Eagle.

 

[AndyG]

Won’t hurt to make sure the Double Cardan is in top shape and have the shaft balanced at the highest speed while it is out.

 

[Shane Malone]

Thanks. I will pull it out and check it.