Cuv

Do you have any updates?

tysmith747

The shop that originally did the work has thrown in the towel. I can tell they don't want to work on it anymore, and they didn't even entertain the idea that it could be something to do with the gear install they performed. They didn't even mention checking the wear patterns or anything else to do with the gears. I'm taking it to Unlimited Offroad in Fenton, Mi to see if they can id the problem. I drop it off in two days so I will give an update as soon as I hear something. The original shop did say that if someone found something wrong with the work they did that they would pay for it. We will see.

I watched the guy at the original shop remove and replace the front drive shaft a few times. All impact wrench and never torqued to specs. Just impact wrench untill it stops and it's good, right?

big dr

that shop needs to be boycotted!!

PRS

You have a 3.5" lift and now you're turning the drive shaft way faster. Make sure the pinion shaft is pointing directly at the drive shaft or less than 1 degree down.

jeeeep

not uncommon with 5:13 gears, Do you have adjustable control arms?
get your angle finder and see what your axle caster is, you'll have to make small adjustments to find a good balance between +4-6 degrees

Cuv

I'm not sure about the OP, but mine is def not front end related. The caster isn't affecting the rear drive line, and with stock drive shafts, from my understanding the pinion doesn't have to dialed in as it would with aftermarket drive shafts. But mine is dialed in, front and rear and still have the vibe. I also understand that with new gears everything is turning faster. Prior to the rear gears it was smooth at 75, the vibe is around 50. There wasn't that much change in gearing.

tysmith747

So I dropped it at Unlimited Offroad talk about a professional and great group of guys. They think they fixes the problem but the shop manager is driving it back and forth between his home and shop to make sure and to break on the NEWEST gears. Here the deal:

-Front and rear back spacing incorrect, somewhere around 2-3 I believe.
-rear pinion preload incorrect
-the original shop reused the old crush sleeves
-the original shop reused the old bearings
-the rear was so tight it heated up and basically made the rear ring and pinion unusable.
-the original shop never used any paint marker to check the gears after installing them.

W-T-F! Are you kinding me? Stay calm...

Unlimited Offroad recommended new bearings all around, new Yukon rear ring and pinion, and new pinion seals. They were able to adjust the front gears and reuse them. They say it is running smooth and I pick it up tomorrow. The original shop swears they will pay for it. We will see soon.

It's obvious to me that I got ripped off. I think the fist place just bolted the new stuff in (some of it anyway) and put the covers back on and hoped for the best.

Do not go to American Transmissions in Plymouth, MI!

If I have any other problems I'll update. I hope this helps someone out.

I'm having them check all my angles while they have it. That was good advice.

tysmith747

Correct me if im wro g here bu I'm not sure the shaft is turning much faster than stock. With the 35" tires and stock 3.73 ratio the drive shafts would have been turning slower than with the stock tires. So the new gears, depending on the ratio, would just bring the shaft back up close to the stock Rpm,s. the ratio of 31" tires to 35" tires is roughly 1.13, from 3.73 to 5.13 the ratio is about 1.38 so that leaves about .25 over stock. That means at 55 the shafts think they are at 69. Although that is faster it doesn't seem significant enough to cause a new vibration at 45mph.

Based on that math with 35" tires a 4.54 gear ratio would be equivalent to stock ratio. Does that sound right or am I way off? It's been a while since math class

Krynn

If you dig through the FAQ, you'll find a neat gearing chart that'll tell you what your expected engine RPM is at at 70 mph in top gear for a given tire size (as mounted, not as listed). If you want to see the drive shaft speed, just divide the engine RPM by 0.690 (the gear ratio of 4th gear in the 4-speed auto).

Anyway, it looks like 4.10 gears would get you the closest to your stock drive shaft speeds. That wouldn't equal to similar performance though, as heavier tires take a lot more force to turn. Since most 35" tires actually measure a lot closer to 34" when mounted, 4.88 is generally considered a good choice for people living in lower flater areas, and 5.13 for people living in the mountains.

Oh, just because it's late and I'm bored, I worked out the math. At 40 mph with your current setup, your drive shaft is spinning about the same as a stock setup at 50.279775185408178404187240759287 mph. Assuming that the actual tire sizes were measured at 35" and 32", that is.

DJCFHB

have the same pulsing vibration, have had the drivelines checked, bearings checked, backlash check. I used all new components with the install, still no answer to the problem. Hoping to have it corrected when i take my rig back to have o rings replaced in the lockers. Curious to see what the outcome is.