doojer

I've never seen a posted minimum. I've always been taught to keep up with the flow of traffic.

Anyways, I think the main point is to make sure your driveline is properly balanced.

chuck45

Well let's think outside the JK "box" for a minute here. The JK is the first Wrangler to go with Rzeppa driveshafts. And people certainly have lifted the dickens out of TJ's and other Jeeps over the years. And they have worse DS problems than JK's. So it's not just that we've not heard about a ton of these failures on JK's but also not on other Jeeps.

Perhaps there was an issue with a flawed TC casting that contributed to the problem?

Was the DS greased regularly and recently? I'm running JE Reel 1350s front and rear and I can tell you that with my skids it's damn near impossible to grease the front CV. In fact I just got a pair of 1350's that have std grease nipples in one of the caps which I should be able to easily get to, even with the skids. The needle fittings in the yoke are damn near impossible to get to (with skids). I'm going to drop the skids, pull the driveshaft and install the new u-joints. And while it's down I will have it balanced.

FWIW I drive 75 all the time as that is out speed limit. I've had no problems.

chuck45

I don't believe you are correct here. All you really need to figure driveline rpm is your tire diameter, gear ratio and speed. The standard calc is done for 60 mph and then you apply a multiplier, such as 1.25 to get your speed at 75.

When you ask to get your shaft balanced at, say 75 mph, the tech doesn't ask about your transmission, engine rpm or TC ratio. None of it matters.

RedneckJeep

Yup, that's about it.

RedneckJeep

That's right. It doesn't make a rat's butt what the trans ratios or anything else is. You can throw all that out the window. All that stuff will effect is engine speed. All that matters is the FINAL drive ratio. I don't care what anything else is, if you got a 4:10, that driveshaft IS turnin 4.1 times to the axles' ONE. The only thing that CAN make a tad difference is whether you gotta manual or automatic, cause the torque converter ain't always locked up. Might even be a little difference when it IS locked up, I don't know for sure.

RedneckJeep

I'm in the 10% range too and mine is still stock.....sans a 2" bb. Mine has NEVER seen above 75.....In fact 70 is as fast as I've gone and that was by accident.

wvextremist

Ok if none of it matters explain to me how you could change the speed of the driveshaft without changing the tranny or the engine speed.

If engine is turning 2500rpm going through a stock transmission then no matter what you do in the axle the drive shaft speed is the same.

What you are changing is the speed of things passed what you change. In this case he has larger tires. If he changed nothing but the tires he would go faster for a given transmission gear and engine rpm than before because the circumference of the tire is larger, however he would loose torque. So he changed his diff gears so that with the given transmission gear and engine rpm he would be going the original stock speed. So again the only thing that he changed is what is happening in the axle

Drive shaft speed in this case was stock!!!

RedneckJeep

Really? What if you go from 3.73 rear gears to 4.10? The driveshaft speeds up.

wvextremist

No matter the axle gear ratio the drive shaft can't spin faster than the transmission!!!!

PERIOD

When you change Diff gears you are changing axle and tire speed for a given transmission gear and engine RPM

Think of your jeep on a lift. Ok, now you have a stock setup. Start jeep and select any gear and let it just spin freely with the engine idleing. Now imagine the same setup with different diff gears (higher or lower). Engine rpm is the same. Transmission is doing the same thing. DRIVESHAFT is doing the same thing. Now because you have changed the Diff gearing, the axles will be either faster or slower depending on the change you made to your gear ratio. Also your tires will be affected the same way.

Now you put the jeep on the road and you have the same effect. Only the tire and axle speed changes with Diff gear ratio changes!!!

chuck45

You really don't have a clue do you? Take the transmission, transfer case and engine out of the vehicle. Leave the damn things on the garage floor. Support the DS in a sling. Drag the vehicle down the street with a horse. The driveshaft will turn at a speed governed by (in addition to how fast the horse is) the gear ratio and tire OD. Driveshaft rpm doesn't give a damn whether it is being turned by the engine being redlined in 1st gear in 4 Lo or being drug down the road by a horse. It will turn at a speed governed by tire size and axle ratio AT A GIVEN SPEED. You can't change physics. The transmission and transfer case change the needed engine rpm at a given speed. Stop thinking of the engine, TC and trans as providing motive power and think purely in terms of DS rpm. DS RPM affects longevity, balance and smoothness.