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Old 06-28-2010, 01:47 AM   #1 (permalink)
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Transfer Case drop.... reasons why its a no no?

So ive been runing a small transfer case drop kit on my truck (78 k5, tons, 4 inc lift, 35s) when it had the 700r4/208 combo and a 4 inc lift ......the rear shaft angle has always sucked and gave me bad vibes upon deceleration at higher speeds...granted i was running a homemade single cardan shaft but it was professionaly balanced ...i decided my rear pinion yoke was too low,which it was, so i got some 8 degree shims to shim it up, it looks better but then it vibed at lower speeds then before... so now that im doing my trans swap to a sm465/205 i want to rid the truck of these problems.... gonna go with double cardan joint and slip shaft at the pinion yoke, relocate leaf spring pads on axle tubes,.....but should i still use the transfer case lowering spacers? aside from eating ground clearence why else do they suck?
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Old 06-28-2010, 01:52 AM   #2 (permalink)
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they put more angle on the front dshaft and can cause other issues with shfters, fans and exhaust.
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Old 06-28-2010, 06:37 AM   #3 (permalink)
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transfer case drop HELPS front d/s angle on the short blazers. ive been runing a one inch for 6 years no..no problem.
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Old 06-28-2010, 07:13 AM   #4 (permalink)
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transfer case drop HELPS front d/s angle on the short blazers. ive been runing a one inch for 6 years no..no problem.
Only if you drop the motor as well. Unless you can bend the laws of physics.
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Old 06-28-2010, 07:22 AM   #5 (permalink)
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Only if you drop the motor as well. Unless you can bend the laws of physics.
all i know is i couldnt turn the front ds with it out, put it back in and it spins freely. ( i ground down the ears anyways). physics or not i have witnessed it work.
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Old 06-28-2010, 07:50 AM   #6 (permalink)
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Physics = how things work.

It may have helped your vibrations, but there is no way in hell it helped your front driveshaft angle. Not a chance. I don't feel like drawing it for you, but it's a simple fact. You are tilting the t-case, therein pointing the front output UPWARDS and not DOWNWARDS, while also pointing the rear output down toward the rear axle. Just think about it. There is no way it helps your front shaft angle.

I keep trying to find different ways to explain this, but all I keep typing are the same things over and over.

edit - to clarify: your front output will translate downward, but it will rotate upward.
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Old 06-28-2010, 07:54 AM   #7 (permalink)
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Quote:
Originally Posted by American View Post
Physics = how things work.

It may have helped your vibrations, but there is no way in hell it helped your front driveshaft angle. Not a chance. I don't feel like drawing it for you, but it's a simple fact. You are tilting the t-case backwards, which therein points the front output UPWARDS and not DOWNWARDS. Just think about it.
i totally agree with you on this as you can see the angle, but it worked for me is all im saying.
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Old 06-28-2010, 08:30 AM   #8 (permalink)
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Even double cardan drive shafts have limits to u-joint angles. To know whether you should use a transfer case drop depends on the facts: Mainly upper and lower joint angles, and the affect on the front shaft angle.
Google Tom Woods and drive shafts for detailed explanation of max angle before vibration is almost guaranteed. As I recall, if the total angle for the Cardan joint is =< 15*, the shaft will work, but with minor vibration (individual tolerance defines "minor") under certain circumstances, and u-joint life will be severely shortened.
Look here: http://www.4xshaft.com/techinfo.html
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Old 06-28-2010, 11:13 PM   #9 (permalink)
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i totally agree with you on this as you can see the angle, but it worked for me is all im saying.
i have a feeling you are a tall truck and talking about a rotation drop.

this is a mild truck and talking about a longitudinal drop.
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Old 06-28-2010, 11:37 PM   #10 (permalink)
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I just thought they were gay. Kinda like a 3" body lift. How you've got that big gap between the bed and the frame.
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Old 06-29-2010, 06:54 AM   #11 (permalink)
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Other than the things that have been mentioned, front ds angle, fan shroud and belly clearance issues, there could also be problems with distributor to firewall clearance. Also, you're adding stress on the motor mounts, they end up being the pivot point.

And it IS pretty gay.
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Old 06-29-2010, 10:18 AM   #12 (permalink)
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Quote:
Originally Posted by American View Post
Physics = how things work.

It may have helped your vibrations, but there is no way in hell it helped your front driveshaft angle. .
yess it can

how much more of an angle is created when you drop the t case an inch... vs how much angle is taken out of the drive shaft when lowing the front output an inch... it really depends on which hypotenuse is shorter, the shorter hypotenuse having the greater change in angle (from motor mount to t case mount, and the front output to pinion) im guessing the pinion to out put is shorter so yes it improves the angle.
no its not physics but it is basic geometry.
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Old 06-29-2010, 03:22 PM   #13 (permalink)
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g-wizz - maybe you should stop posting in transfercase drop threads too.


get rid of the t-case drop, it decreases ground clearance, and puts more stress on the frame. shim the rear end correctly, grind the stops on the front shaft and you'll be fine.
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Old 06-29-2010, 03:30 PM   #14 (permalink)
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I have my case dropped an inch, i also tho have an 8inch lift. The front shaft i had made to take the angle i have and it worked out real nice. The front axle was also angled to help. The rear is also turned up some to help with the angles. its been that way for years and never had a problem.
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Old 06-29-2010, 05:08 PM   #15 (permalink)
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Quote:
Originally Posted by g-wizz View Post
yess it can

how much more of an angle is created when you drop the t case an inch... vs how much angle is taken out of the drive shaft when lowing the front output an inch... it really depends on which hypotenuse is shorter, the shorter hypotenuse having the greater change in angle (from motor mount to t case mount, and the front output to pinion) im guessing the pinion to out put is shorter so yes it improves the angle.
no its not physics but it is basic geometry.
If your truck is lifted the driveline is going to be longer than distance between the mounts.
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Old 06-29-2010, 08:34 PM   #16 (permalink)
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Quote:
Originally Posted by g-wizz View Post
yess it can

how much more of an angle is created when you drop the t case an inch... vs how much angle is taken out of the drive shaft when lowing the front output an inch... it really depends on which hypotenuse is shorter, the shorter hypotenuse having the greater change in angle (from motor mount to t case mount, and the front output to pinion) im guessing the pinion to out put is shorter so yes it improves the angle.
no its not physics but it is basic geometry.
This would be correct IF the whole case was dropped straight down.
Since the case is bolted to the engine through the transmission,
and he's talking about a case lowering kit, not a case clocking kit,
the engine/trans/case combo is lowered only at case, increasing
the angle of front driveshaft, and flattening rear angle.
( unless, of course, he lowered the engine mounts too. )
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Old 06-29-2010, 11:41 PM   #17 (permalink)
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Quote:
Originally Posted by HAPPYJOHN View Post
This would be correct IF the whole case was dropped straight down.
Since the case is bolted to the engine through the transmission,
and he's talking about a case lowering kit, not a case clocking kit,
the engine/trans/case combo is lowered only at case, increasing
the angle of front driveshaft, and flattening rear angle.
( unless, of course, he lowered the engine mounts too. )
no it dosent matter, i get that the case twists... the actual amount it twists is negligible. the drive shaft is usually shorter than the length of the front motor mount to the rear tranny mount so any change affects its (the drive shafts)angle greater than the the angle of the motor.
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Old 06-29-2010, 11:42 PM   #18 (permalink)
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Quote:
Originally Posted by YZEATER View Post
g-wizz - maybe you should stop posting in transfercase drop threads too.


get rid of the t-case drop, it decreases ground clearance, and puts more stress on the frame. shim the rear end correctly, grind the stops on the front shaft and you'll be fine.
im not saying its a good idea, it does help improve front d shaft angle tho.
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Old 06-29-2010, 11:45 PM   #19 (permalink)
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Originally Posted by Snowbird13 View Post
If your truck is lifted the driveline is going to be longer than distance between the mounts.
no. how lifted are we talking about dude. i mean of course if you got a 24" lift a 1" t case drop is not going to do shit... duh...
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Old 06-30-2010, 06:57 AM   #20 (permalink)
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Originally Posted by HAPPYJOHN View Post
This would be correct IF the whole case was dropped straight down.
Since the case is bolted to the engine through the transmission,
and he's talking about a case lowering kit, not a case clocking kit,
the engine/trans/case combo is lowered only at case, increasing
the angle of front driveshaft, and flattening rear angle.
( unless, of course, he lowered the engine mounts too. )
dude get off your high horse. listen to what g-wizz is saying, i know it uses big words but is totally accurate. because of the back and forth here i decided i'de check if for myself with a magnetic angle gage on the front transfer output (i'm doing some trans work this week so it was partially unbolted). here's the setup small block/sm645/205. i unbolted the transfer crossmember and dropped it down 1", because of the length of the pivot from the engine mounts to the transfer mounts the degree of change of the front output angling up was ONE DEGREE OR LESS. but the amount that it helped the front driveshaft angle a considerable argument can be made for getting the driveshaft front and rear more on line with each other if that is what someone must absolutely do to get something to work. but, it does stress the engine mounts, puts the fan closer the to shroud and may rub, if you're running HEI such as myself it puts the distributor VERY close to the cab and may hit when the frame flexes, may have to clearance the trans tunnel for the trans and transfer shifters, and finally decreases ground clearance. quit jacking off to front flange angle, we get it.
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Old 06-30-2010, 10:26 AM   #21 (permalink)
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No. I don't think you do get it. The only driveshaft angle it can "help" is the angle at the axle. If you think the front output angle is getting helped, you are wrong. If you measured it, I think you should go out and take that measurement again. Let me go and jerk off to that worsened output angle right now. E-badass.

Simple geometry? Yes. And the simple geometry proves both of you wrong. I hate to break it to you (g-wizz), but physics uses geometry. Geometry isn't something that often gets used by itself. So to tell somebody that something isn't physics, but rather is geometry, is kind of like saying "That's not a Super Duty, it's a truck." Not all geometry is physics, but lots of physics is just geometry. In this case, it is physics (also geometry). I'm just saying: correcting something that isn't wrong by stating a random factoid just speaks to your lack of credibility.

All BS aside, the t-case output will rotate upward, and translate downward. This downward translation is outdone by the rotation. It is simple kinematics. If you can prove me wrong I will concede immediately, but I seriously doubt you will be able to. If I have time, I will draw it up in Mathcad and see what I come up with. Shoot... maybe I'll be surprised to find a smaller angle. But all of my engineering intuition tells me the angle will be worsened.

PS - is it possible that some people are confusing a t-case DROP with a t-case CLOCK?
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Old 06-30-2010, 10:36 AM   #22 (permalink)
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Can somebody get a measurement of the motor mount to t-case output in a Chevy truck? I don't have one on hand, and I would like to clarify what I have said since I opened my big fat mouth.
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Old 06-30-2010, 02:10 PM   #23 (permalink)
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well, please check your shit before criticizing. the measurement on the engine to transfer mount is right at 36". now we can do alot of math and still arrive at the same answer as we arrived at this morning. the amount of change in attitude of the front output measured in degrees is equal to about 1 degree. i have attached two pics, the first shows a magnetic angle finder, the second shows a tape measure, showing how far up your A** your head is, physically cause we used physics to measure the kinetic energy required to place your head that far up there.
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Old 06-30-2010, 07:07 PM   #24 (permalink)
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Holy crap i didnt imagine this when i originally posted but good info ..... since i actually had the case drop installed i can say that it helped with my front d shaft angle some too i never liked how it looked but it was the cheapest and quickest way to get my truck running ..... now im saying eff that im doing it right this time around with the sm465 swap
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Old 06-30-2010, 09:06 PM   #25 (permalink)
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dude get off your high horse. listen to what g-wizz is saying, i know it uses big words but is totally accurate. because of the back and forth here i decided i'de check if for myself with a magnetic angle gage on the front transfer output (i'm doing some trans work this week so it was partially unbolted). here's the setup small block/sm645/205. i unbolted the transfer crossmember and dropped it down 1", because of the length of the pivot from the engine mounts to the transfer mounts the degree of change of the front output angling up was ONE DEGREE OR LESS. but the amount that it helped the front driveshaft angle a considerable argument can be made for getting the driveshaft front and rear more on line with each other if that is what someone must absolutely do to get something to work. but, it does stress the engine mounts, puts the fan closer the to shroud and may rub, if you're running HEI such as myself it puts the distributor VERY close to the cab and may hit when the frame flexes, may have to clearance the trans tunnel for the trans and transfer shifters, and finally decreases ground clearance. quit jacking off to front flange angle, we get it.
1. What part of my statement, ( which I stand by ) is on a high horse?

2. wtf is an sm645?



My point is that the case end angle is increased more than
the differential end angle is decreased. and on most lifted
vehicles, the split would be increased.

Since most of us don't use the front driveshaft at speed,
it's rather a moot point, BUT, that is not what was asked.
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