Rear axle: Welding on saddles at proper angle (due to lowering kit)

[OldBlueDually]

Gents, I want to be sure I am doing this the correct way before stuff is welded up. Sorry if this is a repeat of another thread.

Last night I removed the axle from my truck (76 GMC) to get ready for the drop kit. Now, when I weld on the new saddles to the axle, those saddles should sit at the same angle as the original saddles, is this correct?

Lowering it will make the 2nd driveshaft sit at a different angle, correct? However, the rear axle pinion yoke angle also needs to be the same, correct?

Here is how I plan to do this: on the floor I plan to have the yoke set at 0 degrees. I will see what angle that makes the stock saddles sit at. I will then tack into place my new saddles at that same angle on the opposite side of the axle. Do a test fit, then finish welding (then axle cleanup & paint).

Basically without so many words: All angles should stay the same, correct?

Is the above stupid, or am I on the right track? Thanks in advance!!

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[Rickf]

This sounds like a geometry problem. I am not an expert but you may need to also lower the center bearing to keep the 2nd driveshaft angle happy.

 

[C10MixMaster]

Gents, I want to be sure I am doing this the correct way before stuff is welded up. Sorry if this is a repeat of another thread.

Last night I removed the axle from my truck (76 GMC) to get ready for the drop kit. Now, when I weld on the new saddles to the axle, those saddles should sit at the same angle as the original saddles, is this correct?

Lowering it will make the 2nd driveshaft sit at a different angle, correct? However, the rear axle pinion yoke angle also needs to be the same, correct?

Here is how I plan to do this: on the floor I plan to have the yoke set at 0 degrees. I will see what angle that makes the stock saddles sit at. I will then tack into place my new saddles at that same angle on the opposite side of the axle. Do a test fit, then finish welding (then axle cleanup & paint).

Basically without so many words: All angles should stay the same, correct?

Is the above stupid, or am I on the right track? Thanks in advance!!

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If I read you right you are moving the axle from under the string to on top of it. If so yes keep the pads at the same angle. Unless the rear drive line as a double u joint/double cardan joint then things get a little more complicated

 

[Big Chip]

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I wouldn’t tack anything in until you get your angle right on the truck with it sitting on the ground (or all 4 corners up on blocks). The pinion angle will most definitely change going down 8” in the rear. Lowering the carrier bearing won't do what you need.

edit: I believe you’ll end up pushing the pinion down with the flip

 

[OldBlueDually]

C10Mix...this truck is a crew cab with the hanger bearing.....

Big Chip, if the pinion angle needs to change, if the axle is moving up 8 inches, would that mean the rear pinon angle would have to actually point down a bit to compensate for the driveshaft angle?

 

[Big Chip]

C10Mix...this truck is a crew cab with the hanger bearing.....

Big Chip, if the pinion angle needs to change, if the axle is moving up 8 inches, would that mean the rear pinon angle would have to actually point down a bit to compensate for the driveshaft angle?

Yes, down, my mistake there!

 

[C10MixMaster]

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I wouldn’t tack anything in until you get your angle right on the truck with it sitting on the ground (or all 4 corners up on blocks). The pinion angle will most definitely change going down 8” in the rear. Lowering the carrier beariywont do what you need.

edit: I believe you’ll end up pushing the pinion down with the flip.

As you raise or lower the differential , u joint angle 1 and 2 change equally making them cancel out . Doesn't matter how high or low, the pinion angle and the output shaft ( in this case the front drive shaft) should alway be the same angle in this type of drive line.

it is a good idea to tack it and measure the angle in the truck though.

 

[OldBlueDually]

As you raise or lower the differential , u joint angle 1 and 2 change equally making them cancel out . Doesn't matter how high or low, the pinion angle and the output shaft ( in this case the front drive shaft) should alway be the same angle in this type of drive line.

it is a good idea to tack it and measure the angle in the truck though.

I see what you are saying. Now see "if" I had been smart and thought of it, I should've done this before taking out the axle. So in my head, I think to myself "if I set my pinion at 0 degrees on my shop floor, I measure the angle of the axle saddles and mimic that on the other side"....but I was wrong once before

Will probably be a couple days before I get to this anyhow, they forgot to ship the axle saddles with the kit, so those are on the way. I still like to plan ahead however.

 

[Brett77]

I did my axle flip and yes you need to change the angle of the pinion to more line up with the driveline.

 

[Bennyt]

This is what I've learned over the years and what I believe to be correct.

I did what you are doing on my son's C10. I sat it on the table, set-up the new perches at the same angle as the old, welded the new on, cut the old off. This is for a one piece driveshaft where you want to keep the angle same as stock. If I changed the angle , it would cause a vibration as the transmission and pinion would be at two diff angles.

If you are using a 2 piece shaft, you'll need to lower the carrier bearing to maintain alignment. If you are switching to a one piece with a double CV, the pinion should aim up at the transmission at ride height under load.

Check Randy's Ring and Pinion, High Angle Driveline, Tom Woods shafts for more info...

If you are off a few degrees, you can always use shims to correct. The better shims are steel and bolt into the center pin of the leaf pack.

 

[OldBlueDually]

Thanks again for the info guys, I do have a 2 piece drive shaft with a carrier bearing.

Before I weld anything, I am putting it all together snug so I can adjust it. Once I drop the carrier bearing a little to compensate the angle and everything is good I will weld it all up. A little bit more work, but I want it to be correct.

I did put my inclinometer on the pinion and set it to 0 degrees. Rested it on each perch and it was reading 9 degrees. Then I cut off the perches after that. Now I have a base line at least. I will still do what I said above however.

 

[HankerCarl]

I would not mess with the carrier bearing. That extra joint is to help with long shafts and large angles at the end u-joints. If you are lowering the truck you are raising the axle and therefore making the u-joint angles smaller. Smaller angles are better. That means it is running straighter. Also I don’t think you should do the perches that way. The best thing for a driveshaft is to be as straight as possible. The pinion is not in the center (top to bottom)of the differential that could cause your angle to be off. The best way (in my opinion)is to set it up set it back on the ground measure and make adjustments from there. Again just my opinion

 

[eskimomann209]

It’s not so much the drop that’s the issue. Height ( to an extent) won’t affect the driveline. What affects the driveline is the height change rolling the pinion up or down. If your carrier is set at zero degrees you want to make your axle also at zero. If the carrier is down 2degrees point the pinion up 2. You also want to measure for operating angles ( each ujoint has an operation range). Better explanations can be found on google. but I think you should tack it up. Then bolt it in and drop weight on it. So you can see how much the axle rolls up.
on a 4 link you set the angles dead nuts. But for a leaf you can have the rear pinion a little lower to compensate for the axle rolling up under acceleration.


If you lower your carrier bearing and change its angle you must change the rear to match, that’s why people say leave the carrier and match the axle to the carrier. Else you’re chasing your tail.

 

[John Hickey]

Don't mess with the carrier bearing, the tail shaft of the trans and carrier are already set. 2-3 degrees down on the pinion is where you need to be in relation to the back side of the carrier. Raising or lowering the rear axle won't change the relationship between the pinion and carrier, only the degree of angle, but equal on both ends

 

[OldBlueDually]

I should really clarify what I did with the pinion at 0 degrees.

The axle is out of the truck on my shop floor. I blocked up the axle to get the pinion to 0 degrees.

Then I put the inclinometer on the spring perches and measured their angle, which read 9 degrees.

I only did the above so I could see what the perches were set at. I then cut off the perches.

The pinion seal leaks anyhow, so I have to replace it! The axle will not go in until this is done first.