Transfer case shattered by front drive line wobble
02-16-2009, 03:19 PM
#81
JK Enthusiast
Join Date: Jan 2007
Location: Beckley, WV
Posts: 112
Likes: 0
Received 0 Likes
on
0 Posts
Actual formula to explain all of this would look something like this:
Engine rpm= E
Transmission ratio = R
Drive shaft rpm = S
Diff ratio = D
Tire rpm = R
Tire circumference = C
Vehicle MPH = M
E x R = S
S / D = T
(T x C) / 88 = M ( you divide by 88 to go from fpm to mph)
Or
(((E x R) / D) x C) / 88 = mph
Engine rpm= E
Transmission ratio = R
Drive shaft rpm = S
Diff ratio = D
Tire rpm = R
Tire circumference = C
Vehicle MPH = M
E x R = S
S / D = T
(T x C) / 88 = M ( you divide by 88 to go from fpm to mph)
Or
(((E x R) / D) x C) / 88 = mph
Last edited by wvextremist; 02-16-2009 at 03:25 PM.
02-16-2009, 03:38 PM
#82
JK Enthusiast
Join Date: Jan 2007
Location: Beckley, WV
Posts: 112
Likes: 0
Received 0 Likes
on
0 Posts
Sorry divide by r
Ex
2500 rpm 6th gear 4.11gears and 32" tire would be
2500 / .84 / 4.11 x 8.37' / 88 = 68.8mph
If you change to 37's and 5.13's it would be
2500 / .84 / 5.13 x 9.6' / 88 = 63 mph
Now if you kept the mph the same and change the tires and diff gears it would be this:
65mph x .84 x 4.11 / 8.37 x 88 = 2359 rpm for 32's and 4.11
65 x .84 x 5.13 / 9.6 x 88 = 2567rpm for 37's and 5.13's
Ex
2500 rpm 6th gear 4.11gears and 32" tire would be
2500 / .84 / 4.11 x 8.37' / 88 = 68.8mph
If you change to 37's and 5.13's it would be
2500 / .84 / 5.13 x 9.6' / 88 = 63 mph
Now if you kept the mph the same and change the tires and diff gears it would be this:
65mph x .84 x 4.11 / 8.37 x 88 = 2359 rpm for 32's and 4.11
65 x .84 x 5.13 / 9.6 x 88 = 2567rpm for 37's and 5.13's
02-16-2009, 03:40 PM
#83
JK Enthusiast
Join Date: Jan 2007
Location: Beckley, WV
Posts: 112
Likes: 0
Received 0 Likes
on
0 Posts
So to say this another way engine speed and transmission ratio determine ds speed, diff gears and tire size determine what speed you go with any given ds speed.
02-16-2009, 08:05 PM
#84
JK Freak
Join Date: Jul 2007
Location: Orange County, CA
Posts: 753
Likes: 0
Received 0 Likes
on
0 Posts
Yeah!
What he said!
Anyway, driveline speed did NOT cause this problem. I don't even thing a wobble problem would cause it, but???
I still think the things was locked in 4 hi and going down the freeway at 80 mph on dry pavement.
What he said!
Anyway, driveline speed did NOT cause this problem. I don't even thing a wobble problem would cause it, but???
I still think the things was locked in 4 hi and going down the freeway at 80 mph on dry pavement.
02-16-2009, 09:46 PM
#85
JK Super Freak
Join Date: Sep 2007
Location: Oxnard, CA
Posts: 1,533
Likes: 0
Received 0 Likes
on
0 Posts
You sir, get a gold star. People just don't understand volumetric efficiency. It's all in how an engine makes power. If the normal operating RPM for an engine is below or above it's most efficient RPM, then it is less efficient than what it could be. Although this doesn't vary too greatly from engine to engine, it DOES with the JK engine, because it is a 60 degree design. Most people think of an engine as a traditional 90 degree engine......even if they do so subconsciencly. When you start changing the angle of the cylinder banks, traditional thinking doesn't work anymore.
Well you certainly got me stumped.
V60 or V90 bore & stroke being equal seems like they have the same volume to me, and if the torgue/HP curve are the same or similar then what is the diff? The op's DS failed from a balance problem which can easily destroy other components depending on what component is closest to the bad vibrations, it certainly didn't fail from "volumetric efficiancy". Your idea that a V90 would somehow make a difference I find intriguing. So how about an I8?
02-16-2009, 10:08 PM
#86
JK Super Freak
Join Date: May 2008
Location: Grand Junction, CO
Posts: 1,279
Likes: 0
Received 0 Likes
on
0 Posts
I developed a roughness after taking my JK on a rescue in what turned out to be rock buggy terrain. I put the Jeep up on 4 jackstands, put it in 4High, and had my wife run it up to about 30 mph. I could see substantial runout in the front DS. I dropped both off at the driveline shop, the front to get straightened and rebalanced and the rear to have the balance checked. The shop said if the front was any worse it would have had to be retubed and couldn't have been straightened. Perhaps something similar happened to the OP and the runout put a lot of strain on the ujoints and transfer case at freeway speeds and things came apart.
02-17-2009, 08:21 PM
#87
JK Freak
Join Date: Jul 2007
Location: Orange County, CA
Posts: 753
Likes: 0
Received 0 Likes
on
0 Posts
No it is not. My engine rpm with 4.10's and 35's was 2050; with 5.13's it went to 2600. My engine is in a better power band and my engine and tranny are turning more rom - but the DS is turning the same.
I can't find the formula that I had in hand that a DS shop uses to figure DS rpm for balancing at a given speed. But I guarantee it did not ask for input on rpm, transmission type or gears, or TC ratios. All it asked for, at an assumed speed of 60 mph, was tire OD and axle ratio.
I can't find the formula that I had in hand that a DS shop uses to figure DS rpm for balancing at a given speed. But I guarantee it did not ask for input on rpm, transmission type or gears, or TC ratios. All it asked for, at an assumed speed of 60 mph, was tire OD and axle ratio.
The engine (through the tranny and trans case) drives the DS, and if the RPMs are up the driveline speed stays the same?
If you change the gears in the TRANSFER CASE this would be true, but not the axle ratio. The engine RPM goes up, so does the DS speed and the gearing takes place AFTER the DS, but the larger tires reduces the DS speed back to "normal" levels.
I am not that educated as some on here are, so I know this is not rocket science.
02-17-2009, 09:23 PM
#88
JK Super Freak
Join Date: May 2008
Location: Grand Junction, CO
Posts: 1,279
Likes: 0
Received 0 Likes
on
0 Posts
Did you read what you wrote?
The engine (through the tranny and trans case) drives the DS, and if the RPMs are up the driveline speed stays the same?
If you change the gears in the TRANSFER CASE this would be true, but not the axle ratio. The engine RPM goes up, so does the DS speed and the gearing takes place AFTER the DS, but the larger tires reduces the DS speed back to "normal" levels.
I am not that educated as some on here are, so I know this is not rocket science.
The engine (through the tranny and trans case) drives the DS, and if the RPMs are up the driveline speed stays the same?
If you change the gears in the TRANSFER CASE this would be true, but not the axle ratio. The engine RPM goes up, so does the DS speed and the gearing takes place AFTER the DS, but the larger tires reduces the DS speed back to "normal" levels.
I am not that educated as some on here are, so I know this is not rocket science.
03-01-2009, 04:15 AM
#89
JK Newbie
Join Date: Jan 2009
Location: Little Rock, AR
Posts: 57
Likes: 0
Received 0 Likes
on
0 Posts
Props to dpoelstra and wvextremist !
I'm glad you guys got this lined out because as I read this thread,post after post, I just got more and more agitated. So many people read on here and look to this sight for answers but some chime in with no idea as to what they are talking about.
I'd also like to thank you for being so civil in your replys, good job guys. I hope people who need good info actually make it to page 9 on this post and I'm sorry to hear about your t-case exploding. Clearly a parts failure (u-joint maybe) or manufactured defect in the shaft itself
I'm glad you guys got this lined out because as I read this thread,post after post, I just got more and more agitated. So many people read on here and look to this sight for answers but some chime in with no idea as to what they are talking about.
I'd also like to thank you for being so civil in your replys, good job guys. I hope people who need good info actually make it to page 9 on this post and I'm sorry to hear about your t-case exploding. Clearly a parts failure (u-joint maybe) or manufactured defect in the shaft itself