Transfer case shattered by front drive line wobble
02-06-2009, 04:36 AM
#71
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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.
However we have been discussing the effect of the Gear Swap on the DS speed.
You can't spin the shaft faster than the tranny wants to go!!!
They are hard connected!
Is the tail shaft on the transmission spinning the same speed after a gear swap for the given speed? YES!
So in turn so is the DS
02-06-2009, 04:48 AM
#72
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After some more thought I think maybe I know where the controversy is coming from.
Let me restate my argument.
Take a stock vehicle, stock tires, stock drivetrain. Then, put bigger tires on it. Now you have lowered the needed rpm for a given speed as well as driveshaft speed, you have also lost power. Ok you are unsatisfied with performance, so you do a gear swap to get back to stock rpm for a given speed so that you can regain your lost performance. You have increased your engine speed back to stock, along with your DS speed.
So if you haven't read the whole thread, I was trying to say that the op who blew out his transfer case because of so called "excessive DS speed", in fact had nearly stock driveshaft speed and it wasn't a factor.
Now, that aside if you only change tires or only change diff gears then yes you will see affected driveline as well as engine rpm.
However most of us try to cancel out the changes that we make with tires to achieve stock performance!
If you change ratios for more bottom end torque for pulling power then yes you are going to see increased driveline speed.
Let me restate my argument.
Take a stock vehicle, stock tires, stock drivetrain. Then, put bigger tires on it. Now you have lowered the needed rpm for a given speed as well as driveshaft speed, you have also lost power. Ok you are unsatisfied with performance, so you do a gear swap to get back to stock rpm for a given speed so that you can regain your lost performance. You have increased your engine speed back to stock, along with your DS speed.
So if you haven't read the whole thread, I was trying to say that the op who blew out his transfer case because of so called "excessive DS speed", in fact had nearly stock driveshaft speed and it wasn't a factor.
Now, that aside if you only change tires or only change diff gears then yes you will see affected driveline as well as engine rpm.
However most of us try to cancel out the changes that we make with tires to achieve stock performance!
If you change ratios for more bottom end torque for pulling power then yes you are going to see increased driveline speed.
02-06-2009, 05:57 AM
#73
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After some more thought I think maybe I know where the controversy is coming from.
Let me restate my argument.
Take a stock vehicle, stock tires, stock drivetrain. Then, put bigger tires on it. Now you have lowered the needed rpm for a given speed as well as driveshaft speed, you have also lost power. Ok you are unsatisfied with performance, so you do a gear swap to get back to stock rpm for a given speed so that you can regain your lost performance. You have increased your engine speed back to stock, along with your DS speed.
So if you haven't read the whole thread, I was trying to say that the op who blew out his transfer case because of so called "excessive DS speed", in fact had nearly stock driveshaft speed and it wasn't a factor.
Now, that aside if you only change tires or only change diff gears then yes you will see affected driveline as well as engine rpm.
However most of us try to cancel out the changes that we make with tires to achieve stock performance!
If you change ratios for more bottom end torque for pulling power then yes you are going to see increased driveline speed.
Let me restate my argument.
Take a stock vehicle, stock tires, stock drivetrain. Then, put bigger tires on it. Now you have lowered the needed rpm for a given speed as well as driveshaft speed, you have also lost power. Ok you are unsatisfied with performance, so you do a gear swap to get back to stock rpm for a given speed so that you can regain your lost performance. You have increased your engine speed back to stock, along with your DS speed.
So if you haven't read the whole thread, I was trying to say that the op who blew out his transfer case because of so called "excessive DS speed", in fact had nearly stock driveshaft speed and it wasn't a factor.
Now, that aside if you only change tires or only change diff gears then yes you will see affected driveline as well as engine rpm.
However most of us try to cancel out the changes that we make with tires to achieve stock performance!
If you change ratios for more bottom end torque for pulling power then yes you are going to see increased driveline speed.
02-06-2009, 07:20 AM
#75
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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.
02-06-2009, 07:36 AM
#76
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The JK as delivered from the factory is spinning at too low an rpm at any speed to satisfy the CAFE standards and emmisions standards of the Federal Nazi's. The single best thing you can do for a JK is regear and let the 3.8 live a bit higher up the rpm ladder. And the dirty little secret is that you often get better gas mileage in addition to more power.
I'm going to drop my DS's this weekend to replace two of the inaccesable (due to skids) ujoints with ujoints with grease zerks in the caps and while down I'm going to have them balanced (for my own peace of mind). I stopped at the local DL shop to talk to the owner about it and the DS rpm and he said "No problem, we do driveshafts for race cars and desert racers all the time. We can balance it for 100 mph if you want".
As to the cause of the OP's problem - I don't know - but things looked pretty dry in the pic of the ujoint. I guarantee mine wouldn't look like that. Of course I use that yellow sticky nasty stuff that Jack at CTM recommends for his ujoints and everything else. But I kind of think that it had something to do with a flaw in the TC casting.
One question I did have fo the OP though. At the cost of the repair of the factory TC why was the decision made to go with a repair and not drop a few extra sheckles on an Atlas 4 speed?
02-06-2009, 03:49 PM
#77
JK Enthusiast
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.
So the Drive shaft wasn't spinning much faster, it had to be out of balance or something...
Go here: http://www.differentials.com/calc.html
Per Web site:
4.11, 75 MPH, (245/75 16) 30.47 inch = 2385 Engine RPM Auto/OD
5.13, 75 MPH, 37.00 inch = 2446 Engine RPM Auto/OD
Very close to stock non-rubi JK, only about about 60 RPM at the engine faster!
Both are sweet spot as a rough guide from web site.
Oh and if you want to know a lot of high-level info about drive lines, this is a good read:
http://trailer-bodybuilders.com/mag/...ery_shop_know/
Last edited by Foo; 02-06-2009 at 03:56 PM.
02-06-2009, 03:56 PM
#78
I don't know of ANYONE who had the thought of duplicating stock driveline speed in mind when choosing compenents. Why would they?
The JK as delivered from the factory is spinning at too low an rpm at any speed to satisfy the CAFE standards and emmisions standards of the Federal Nazi's. The single best thing you can do for a JK is regear and let the 3.8 live a bit higher up the rpm ladder. And the dirty little secret is that you often get better gas mileage in addition to more power.
I'm going to drop my DS's this weekend to replace two of the inaccesable (due to skids) ujoints with ujoints with grease zerks in the caps and while down I'm going to have them balanced (for my own peace of mind). I stopped at the local DL shop to talk to the owner about it and the DS rpm and he said "No problem, we do driveshafts for race cars and desert racers all the time. We can balance it for 100 mph if you want".
As to the cause of the OP's problem - I don't know - but things looked pretty dry in the pic of the ujoint. I guarantee mine wouldn't look like that. Of course I use that yellow sticky nasty stuff that Jack at CTM recommends for his ujoints and everything else. But I kind of think that it had something to do with a flaw in the TC casting.
One question I did have fo the OP though. At the cost of the repair of the factory TC why was the decision made to go with a repair and not drop a few extra sheckles on an Atlas 4 speed?
The JK as delivered from the factory is spinning at too low an rpm at any speed to satisfy the CAFE standards and emmisions standards of the Federal Nazi's. The single best thing you can do for a JK is regear and let the 3.8 live a bit higher up the rpm ladder. And the dirty little secret is that you often get better gas mileage in addition to more power.
I'm going to drop my DS's this weekend to replace two of the inaccesable (due to skids) ujoints with ujoints with grease zerks in the caps and while down I'm going to have them balanced (for my own peace of mind). I stopped at the local DL shop to talk to the owner about it and the DS rpm and he said "No problem, we do driveshafts for race cars and desert racers all the time. We can balance it for 100 mph if you want".
As to the cause of the OP's problem - I don't know - but things looked pretty dry in the pic of the ujoint. I guarantee mine wouldn't look like that. Of course I use that yellow sticky nasty stuff that Jack at CTM recommends for his ujoints and everything else. But I kind of think that it had something to do with a flaw in the TC casting.
One question I did have fo the OP though. At the cost of the repair of the factory TC why was the decision made to go with a repair and not drop a few extra sheckles on an Atlas 4 speed?
02-08-2009, 01:57 PM
#80
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I did not read every single post here, so sorry if this is redundant.
5.13s with 37 inch tires will have a very similar driveline speed as stock, so I am not sure why anyone would blame driveline speed.
Almost sounds like you were doing 80 mph down the highway locked in 4 hi.
Driveline speed did not cause this.
5.13s with 37 inch tires will have a very similar driveline speed as stock, so I am not sure why anyone would blame driveline speed.
Almost sounds like you were doing 80 mph down the highway locked in 4 hi.
Driveline speed did not cause this.