DISLEXICDIME Posted October 13, 2010 Report Share Posted October 13, 2010 so i am going to go work on the 720 i bought. The previous previous owner lowered it and only left the large spring from the pack in the rear of the truck. Well guess what! The mono lief snapped. Now i have to go put a new set of lief's i picked up in the truck tomorrow. My buddy told me it is also eating carrier bearings. He said the previous owner raised the carrier bearing but it is still eating them so i am guessing the pinion angle must be off. Am I right? what is a good pinion angle for a 720 with 3 inch lowering blocks? I have not looked under the truck yet so i do not know if the guy who lowered it used flat or angled block's so i am going to take some 4degree shims i have with me. Can you use shims with lowering block's. it has ben a long time since i have messed with lowering a solid axle truck and my memory is a bit hazy. 1 Quote Link to comment
izzo Posted October 13, 2010 Report Share Posted October 13, 2010 i forgot you had that truck, pics :D 1 Quote Link to comment
DISLEXICDIME Posted October 13, 2010 Author Report Share Posted October 13, 2010 i have to get it to my house before i take pics! Quote Link to comment
datzenmike Posted October 13, 2010 Report Share Posted October 13, 2010 Angle at the hanger should equal angle at the diff. If you have ever had a drive shaft off and held the spline while turning the shaft you will know that it does not turn smoothly but in jerks that get stronger with the sharpness of the bend. This is because the U joint isn't turning in a circle but an ellipse, that's an oval for those that were high during math class. If you were to magically to look down the inside of the drive shaft at the U joint as it turns in an ellipse you would see that at the top and bottom of the bend it is tilted further or closer to you and has further to travel. In order to spin at the same speed it thus has to speed up and slow down when turning. When forced to turn at a steady speed on a vehicle this causes vibration. What to do? Have two U joints 180 out of phase so as one speeds up the other is slowing down and they.... cancel each other. To get the best canceling, both angles must be the same too. Measure the angle between the front drive shaft and the back one. For argument sake lets say it is 10 degrees. Now measure the back drive shaft and the pinion on the differential. If it is 10 degrees everything is fine. Here are two examples of proper drive shaft angles. If you have a single drive shaft then the tranny to DS angle must equal the DS to pinion angle. 1 Quote Link to comment
Pacific coast Datsun Posted October 13, 2010 Report Share Posted October 13, 2010 so i am going to go work on the 720 i bought. The previous previous owner lowered it and only left the large spring from the pack in the rear of the truck. Well guess what! The mono lief snapped. Now i have to go put a new set of lief's i picked up in the truck tomorrow. My buddy told me it is also eating carrier bearings. He said the previous owner raised the carrier bearing but it is still eating them so i am guessing the pinion angle must be off. Am I right? what is a good pinion angle for a 720 with 3 inch lowering blocks? I have not looked under the truck yet so i do not know if the guy who lowered it used flat or angled block's so i am going to take some 4degree shims i have with me. Can you use shims with lowering block's. it has ben a long time since i have messed with lowering a solid axle truck and my memory is a bit hazy. Im running 3 inch blocks w/ the middle leaf removed on my 85 720. I raised the carrier bearing 1 inch & have had NO issues at all. You can run angled blocks or wedge the shims UNDER the blocks. Either way Id still raise the carrier bearing to correct the driveshaft angle. 1 Quote Link to comment
datzenmike Posted October 13, 2010 Report Share Posted October 13, 2010 Angle at the hanger should equal angle at the diff. If you have ever had a drive shaft off and held the spline while turning the shaft you will know that it does not turn smoothly but in jerks that get stronger with the sharpness of the bend. This is because the U joint isn't turning in a circle but an ellipse, that's an oval for those that were high during math class. If you were to magically to look down the inside of the drive shaft at the U joint as it turns in an ellipse you would see that at the top and bottom of the bend it is tilted further or closer to you and has further to travel. In order to spin at the same speed it thus has to speed up and slow down when turning. When forced to turn at a steady speed on a vehicle this causes vibration. What to do? Have two U joints 180 out of phase so as one speeds up the other is slowing down and they.... cancel each other. To get the best canceling, both angles must be the same too. Measure the angle between the front drive shaft and the back one. For argument sake lets say it is 10 degrees. Now measure the back drive shaft and the pinion on the differential. If it is 10 degrees everything is fine. Here are two examples of proper drive shaft angles. If you have a single drive shaft then the tranny to DS angle must equal the DS to pinion angle. ..... or you could just guess at it. :lol: 1 Quote Link to comment
DISLEXICDIME Posted October 14, 2010 Author Report Share Posted October 14, 2010 ok so one more thing what do i use as a reference point to square the rear end back up? Do i just square it up with the lief spring mounts? here is a pic 1 Quote Link to comment
Pacific coast Datsun Posted October 15, 2010 Report Share Posted October 15, 2010 ok so one more thing what do i use as a reference point to square the rear end back up? Do i just square it up with the lief spring mounts? The top of the lowering block will have a raised "bump" thats round in shape. The "bump" slides into a hole thats on the leaf pad thats on the axle. Without a block the bolt that holds the leafs together is rounded...that slides into the same spot. That will line the axle up in terms of "front to back". 1 Quote Link to comment
Pacific coast Datsun Posted October 15, 2010 Report Share Posted October 15, 2010 ok so one more thing what do i use as a reference point to square the rear end back up? Do i just square it up with the lief spring mounts? The top of the lowering block will have a raised "bump" thats round in shape. The "bump" slides into a hole thats on the leaf pad thats on the axle.& the bottom of the block has a hole that slides over the rounded bolt that holds the leafs together. Without a block the bolt that holds the leafs together is rounded...that slides into the same spot. That will line the axle up in terms of "front to back". 1 Quote Link to comment
DISLEXICDIME Posted October 15, 2010 Author Report Share Posted October 15, 2010 thanks ! it rides so much better with a full lief pack. i don't under stand why they removed 2 Lief's in the first place. 1 Quote Link to comment
Pacific coast Datsun Posted October 15, 2010 Report Share Posted October 15, 2010 Usually leafs are removed for additional drop. As long as the overload leaf is left in the pack theres usually no issues other than you cant carry as much weight in the bed as before. 1 Quote Link to comment
DISLEXICDIME Posted October 15, 2010 Author Report Share Posted October 15, 2010 i know that :rolleyes: I am just trying to figure why they took 2 leifs out. It didnt raise the truck when i put them back in 1 Quote Link to comment
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