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Old 10-31-2017, 07:56 PM   #1
Rufas
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Another Pinion Angle Question

I've been reading here about setting pinion angle. The general conscious seems to be that the transmission should have a down angle of 3 degree and the pinion angle should have an angle of 3 degrees up.

Of course not a perfect world. I have a transmission down angle of 5.5 degrees. I can set the pinion angle to 5.5 degrees up. But would it be better to shim the transmission to the desired 3 degree down and the corresponding pinion angle to 3 degrees up.

BTW this is a bagged truck, the driveshaft actually goes slightly up from the transmission when at my desired ride height.

This is a LWB using a single driveshaft with RideTech StrongArm rear suspension.

Setting everything to 3 degrees might help with the driveshaft clearance problems I am having.

Opinions or suggestions?

Thanks
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Old 11-01-2017, 06:45 AM   #2
PGSigns
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Re: Another Pinion Angle Question

Thing is with any measurement like the 3 degrees or your 5.5 is what it is measured against. Is your measurement with a level frame? Also the angle of the drive shaft in comparison to the trans is a needed measurement. If the engine is measured at 5.5 down and the drive shaft is 1.5 up that is 7 degrees and the U-joint will not like it for long. Then its time to look at the drive train and what can be done to help. Options are raising the trans in the back to help it but there are lots of things that can limit the rise. Another option that we used in trucks with a bunch of lift was CV joints in the front of the drive shafts. This may be the best option and allows you to run the angle in the front as needed and to point the pinion right at the back of the trans to get that u-joint angle to about 1 degree. This will drop it a good bit and lower the drive shaft in the cross member that seems to always be in the way.
Jimmy
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Old 11-01-2017, 11:40 AM   #3
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Re: Another Pinion Angle Question

Quote:
Originally Posted by PGSigns View Post
Thing is with any measurement like the 3 degrees or your 5.5 is what it is measured against. Is your measurement with a level frame? Also the angle of the drive shaft in comparison to the trans is a needed measurement. If the engine is measured at 5.5 down and the drive shaft is 1.5 up that is 7 degrees and the U-joint will not like it for long. Then its time to look at the drive train and what can be done to help. Options are raising the trans in the back to help it but there are lots of things that can limit the rise. Another option that we used in trucks with a bunch of lift was CV joints in the front of the drive shafts. This may be the best option and allows you to run the angle in the front as needed and to point the pinion right at the back of the trans to get that u-joint angle to about 1 degree. This will drop it a good bit and lower the drive shaft in the cross member that seems to always be in the way.
Jimmy
f the engine is measured at 5.5 down and the drive shaft is 1.5 up that is 7 degrees and the U-joint will not like it for long

So if I understand this. If my driveshaft slopes upward to the rear then even setting the pinion angle to 5.5 upward will not work? Is that correct? In other words the drive shaft can never slope up to the rear end?
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Old 11-01-2017, 12:12 PM   #4
Keith Seymore
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Re: Another Pinion Angle Question

The orientation of the frame is immaterial.

You are trying to establish the "u joint working angle", which is the relationship between the pinion centerline and the shaft (or the transmission centerline and the shaft).

The attached picture is pretty good but could use some explanation:

"Perfect - inline": this is true from a u joint acceleration/deceleration aspect, and would be ideal in theory but not in practice. The issue is twofold: 1) without any u joint working angle the rollers do not rotate inside the cup, causing them to "brinnell" a low spot in the cup and resulting in a disturbance, and 2) there is rear axle pinion nose windup during vehicle acceleration and deceleration, (and in trim height due to cargo loading/unloading) so the shaft doesn't really stay straight during vehicle use.

"Parallel; moderate strain/minimal vibration": This is ideal, with angles equal and opposite and less than 3-7 degrees. However, "strain" is not really the right word choice, as it is not a strain issue but the disturbance caused by the acceleration and deceleration of the u joints as they rotate. The equal and opposite characteristic allows the accel/decal to cancel out (while one is accelerating the other joint is decelerating the same amount) resulting in no disturbance and no vibration, and also provides some windage so that if the angles are set up like this statically then you come closer to the "inline" setting during vehicle use.

"No! High strain/bad vibration": again - it's not "strain" but accel/decal of the joint. Angles higher than 7 degrees are greater than what a single cardan joint can accommodate. Differing angles front and rear do not allow the accel/decal pairs to cancel each other out.

"Absolutely not! etc": the issue here is that the angles do not cancel each other out and are, in fact, additive. "Poor pinion vibration" has nothing to do with this.

I had a really nice write up on how to set this up, copied from an S10 service manual, but it got Photophucketed.


K
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Last edited by Keith Seymore; 11-01-2017 at 12:23 PM.
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Old 11-01-2017, 02:20 PM   #5
Rufas
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Re: Another Pinion Angle Question

Quote:
Originally Posted by Keith Seymore View Post
The orientation of the frame is immaterial.

You are trying to establish the "u joint working angle", which is the relationship between the pinion centerline and the shaft (or the transmission centerline and the shaft).

The attached picture is pretty good but could use some explanation:

"Perfect - inline": this is true from a u joint acceleration/deceleration aspect, and would be ideal in theory but not in practice. The issue is twofold: 1) without any u joint working angle the rollers do not rotate inside the cup, causing them to "brinnell" a low spot in the cup and resulting in a disturbance, and 2) there is rear axle pinion nose windup during vehicle acceleration and deceleration, (and in trim height due to cargo loading/unloading) so the shaft doesn't really stay straight during vehicle use.

"Parallel; moderate strain/minimal vibration": This is ideal, with angles equal and opposite and less than 3-7 degrees. However, "strain" is not really the right word choice, as it is not a strain issue but the disturbance caused by the acceleration and deceleration of the u joints as they rotate. The equal and opposite characteristic allows the accel/decal to cancel out (while one is accelerating the other joint is decelerating the same amount) resulting in no disturbance and no vibration, and also provides some windage so that if the angles are set up like this statically then you come closer to the "inline" setting during vehicle use.

"No! High strain/bad vibration": again - it's not "strain" but accel/decal of the joint. Angles higher than 7 degrees are greater than what a single cardan joint can accommodate. Differing angles front and rear do not allow the accel/decal pairs to cancel each other out.

"Absolutely not! etc": the issue here is that the angles do not cancel each other out and are, in fact, additive. "Poor pinion vibration" has nothing to do with this.

I had a really nice write up on how to set this up, copied from an S10 service manual, but it got Photophucketed.


K
So as long as my drive train maintains the 'parallel' in your drawings, then it does not mater if the the driveshaft is lower at the transmission then the pinion at the rearend.

As for the 7 degrees you mention I'm going to try to get the transmission set to 3 degrees downward and the pinion to 3 degrees upward.

Again I'm using the RideTech StrongArm suspension. This is not a leaf spring setup. So I think the the 'pinion walk upward' during acceleration is not as big of an issue as it is for leaf springs.

For those that have asked the frame is level for all these measurements.
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Old 11-01-2017, 08:01 PM   #6
Keith Seymore
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Re: Another Pinion Angle Question

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Originally Posted by Rufas View Post
So as long as my drive train maintains the 'parallel' in your drawings, then it does not mater if the the driveshaft is lower at the transmission then the pinion at the rearend.
That's a really odd configuration - but - yes, as long as the equal working angles are equal and opposite then the accelerations will cancel out.
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Old 11-01-2017, 08:17 PM   #7
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Re: Another Pinion Angle Question

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Originally Posted by Keith Seymore View Post
That's a really odd configuration - but - yes, as long as the equal working angles are equal and opposite then the accelerations will cancel out.
Thanks K for clearing this up. I was concerned because I've read a few post that seems to say this wouldn't work.

Not really that odd I guess. I'm running close to an 7 inch drop in the rear. Even a little more in the front. The pumpkin is really tucked up there.

This truck started life as a leaf springed 3/4 ton and now basically a 1/2 ton with trailing arms and bags. Fully slammed, the front engine cross member has less than 1/2 inch of ground clearance. But not really driveable like that.
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Last edited by Rufas; 11-01-2017 at 08:26 PM.
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Old 11-02-2017, 07:17 AM   #8
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Re: Another Pinion Angle Question

I would still look at the angle of the drive shaft and see what the working angle is once you move the rear of the trans up. Here is a little math to get the spacer thickness for the rear of the trans to move it up 2.5 degrees. measure from the center of the motor mount to the center of the trans mount and take that number time .017. The .017 is about 1 degree per inch. So for example the measurement is 46 inches you get 46X.017X2.5=1.955 for the spacer to get you to 3 degrees. You can use the same method to get the taper for shims for the trailing arms or to cut the tops of blocks to get you pinion angle adjusted.
Jimmy
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Old 11-02-2017, 02:52 PM   #9
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Re: Another Pinion Angle Question

Can you see the images in this link?

http://67-72chevytrucks.com/vboard/s...d.php?t=522180

I retrieved them from Photophucket and was just going to add them as attachments, but I can see them now.

K
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Old 11-02-2017, 08:11 PM   #10
Rufas
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Re: Another Pinion Angle Question

Quote:
Originally Posted by PGSigns View Post
I would still look at the angle of the drive shaft and see what the working angle is once you move the rear of the trans up. Here is a little math to get the spacer thickness for the rear of the trans to move it up 2.5 degrees. measure from the center of the motor mount to the center of the trans mount and take that number time .017. The .017 is about 1 degree per inch. So for example the measurement is 46 inches you get 46X.017X2.5=1.955 for the spacer to get you to 3 degrees. You can use the same method to get the taper for shims for the trailing arms or to cut the tops of blocks to get you pinion angle adjusted.
Jimmy
Jimmy
Great info .

Thanks
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Old 11-02-2017, 08:15 PM   #11
Rufas
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Re: Another Pinion Angle Question

Quote:
Originally Posted by Keith Seymore View Post
Can you see the images in this link?

http://67-72chevytrucks.com/vboard/s...d.php?t=522180

I retrieved them from Photophucket and was just going to add them as attachments, but I can see them now.

K
Wow! That's some light reading. It will take some time for me to digest all that.

Thanks
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