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4" drop complications?


solgroms

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4" is a long way to drop. Lowering the body over the rear end upsets the angle where the driveshaft meets the differential and to a smaller degree the driveshaft angles between the front and rear driveshafts at the carrier bearing.

 

Because a U joint does not turn in a circle, but an ellipse, it must speed up and slow down causing a vibration. By running two U joints one end is speeding up while the other is slowing down and this more or less cancels vibration, but, the angles must be close to the same. Angle in, must equal angle out.

 

You will have to measure these two angles and determine if tilting the differential up at the front will restore the balance. A shim can be slipped between the axle spring perch and the lowering block.

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It is caused by exceeding the maximum angle, rather than by mismatched angles.

 

The normal fix is to space the carrier bearing 1". This preserves all the angles while making the rear part of the driveshaft only drop 3".

 

Angled blocks will not solve the problem, unless you angle the engine/transmission, the carrier bearing, and the differential.

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Have to disagree.  Most put a 1 " spacer under the carrier bearing to raise it. Most drop block kits already have a 1 or 2 degree wedge shape for tilting the differential.

 

To bring my U joints back into agreement I placed a 1/8" shim at the rear of the block under the spring perch. This tilted the differential front down slightly and removed all the vibration. It is a one piece driveshaft.

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4 inches dont affect anything.

If you buy the blocks from summit they come with an angle on them. I have a total of maybe 5 1/2" drop daily driven no axle wrap or hop. Im no expert just saying. And yes with a lil load the chassis does sit on the axle but still isnt too bad.

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Glad you agree: if you angle the differential, the transmission should be angled to match. Just a different way of saying the same thing.

 

Pretty sure I would know if I was agreeing with you. :lol:

 

Both angles should be equal. If the rear one does not agree with the front one from lowering (or raising) it can be adjusted until it does. Tilting the front of the diff up (or down) one inch will make a big U joint angle change there but not as much of an angle change at the transmission 5 feet away.

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This is a trick that was taught to me by erich paul. 3 inch block and basicly de-arching the leafs with his trick.

 

20150107_152205.jpg

 

this is maxed out load chassis resting on axle

20140905_182533.jpg

 

this is another truck no blocks same trick as black truck but done wrong super bouncy and tons of wheel hop. With some some 6 degree shims i believe should fix the very light ujoint chatter.

 

IMG_20150405_131106.jpg

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or you can just replace leaf springs out with 720 4x4 leaf springs like I'm going to do on grimace521/my 620 kc's so that way I don't have to use 4" blocks and it is easier to adjust the rear drums

 brakes.

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No going lower is easier with a 1 piece than a 2 piece.  On a 2 piece you have to shim the rear end for the correct pinion angel and also have to shim the carrier bearing to to get the correct driveline angle.  One affects the other. 

 

One correct the pinion angle after lowering and the drive line angle is good.

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That is the difference Mr Tanker.  The 1 piece drive lines make it easier to go low.

 

Here is a good read if you are interested in technical aspects of drive lines.

 

http://www.4crawler.com/4x4/CheapTricks/Driveline-101.shtml

 

 

Easier. Not without complications. Any lowering will affect the drive line angles. Usually thewy vibrate after when they did not before. The fix is to get the two angles to agree again.

 

BTW any measuring of drive line angles has to be done with the vehicle sitting with wheels on the ground and you can have someone sitting in the driver's seat for ballast.

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