Pinion angle

[Yooper74]

I've got a 2.5" suspension lift that ended up sitting a bit higher than advertised. My pinion to driveshaft angle is currently 12 degrees. I'm thinking the suspension may settle a bit and I may add a pound or two with a rear seat and a full tank of gas so it may compress a bit.

I'm going to order some angle shims to straighten things out.

Any thought on what shims I should order? How steep?

 

[blubuckaroo]

Front or rear pinion angle?

 

[garberz]

I've got a 2.5" suspension lift that ended up sitting a bit higher than advertised. My pinion to driveshaft angle is currently 12 degrees. I'm thinking the suspension may settle a bit and I may add a pound or two with a rear seat and a full tank of gas so it may compress a bit.

I'm going to order some angle shims to straighten things out.

Any thought on what shims I should order? How steep?

What exactly are you measuring when you say, “pinion to driveshaft angle”? The drive shaft will have X*’s of angle at ride height. What is your pinion angle at ride height?

Mark

 

[Yooper74]

Rear

measuring the difference between the angle of the pinion and the angel of the driveshaft.

 

[armynavy17]

Just went through the same thing with my new lift. Should be corrected to 1-2 degrees down from the driveshaft.

Remember that a change in the angle of the pinion changes the angle of the driveshaft as well. It's not exact since changing the angle of the pinion changes the driveshaft length as well, but a way to approximate this additional change is to measure the distance from the center of the axle shaft to pinion and divide it by the distance from the pinion to the output shaft. Mine measured approx. 11"/35" for a ratio of .31. Thus for every 1 degree of change to the axle the driveshaft will change ~.31 degrees for a total change of ~1.31. Take the number of degrees you want to change, 10.5 in your case, and divide it by the total change per degree, 1.31, and you get an answer of an 8 degree shim.

Depending on how much you think the weight of the rear seat and a full tank of gas will change the pinion angle, you may want to go with 7 degree shims for a 9.2 degree change in pinion angle. Maybe put 100lbs or so of weight in the bed and measure the pinion angle again before ordering.

I placed an order from http://www.4crawler.com/4x4/ForSale/Shims.shtml and he said he's about 2 weeks out on manufacturing 2" shims.

 

[Yooper74]

Thanks. Great explanation. I'll do some measuring and get some shims ordered.

 

[fordguy]

Mine is currently sitting at 10 degrees i think. I am shortening a stock driveshaft to use while i build.

 

[armynavy17]

Remember that a change in the angle of the pinion changes the angle of the driveshaft as well. It's not exact since changing the angle of the pinion changes the driveshaft length as well, but a way to approximate this additional change is to measure the distance from the center of the axle shaft to pinion and divide it by the distance from the pinion to the output shaft. Mine measured approx. 11"/35" for a ratio of .31. Thus for every 1 degree of change to the axle the driveshaft will change ~.31 degrees for a total change of ~1.31. Take the number of degrees you want to change, 10.5 in your case, and divide it by the total change per degree, 1.31, and you get an answer of an 8 degree shim.

Just wanted to report back on my approximation calculations for future reference.

I ordered 5 degree shims and I measured the change in the angle of the pinion at 4.8 degrees. The angle of the driveshaft changed 1.6 degrees. Calculated out that is 1.33 degrees of pinion angle change per degree of shim, pretty close to the measured approximation 11"/35" = 1.31.

That 6.4 degrees of pinion angle change shortened my driveshaft by about 3/8" - 1/2", so if you're close to being able to use your old driveshaft, correct your pinion angle first with $25 shims before ordering a $$$$ new driveshaft.

Some additional info, I ordered 2" x 4.75" shims and they fit perfectly on the spring perch.

 

[DirtDonk]

Good info. Thanks.
I would have thought that the pinion change would have been more off of the shim angle though. That much difference in distance to centerline (shim on top of spring perch, axle centerline below, pinion centerline below that even) would have, I thought, made a bigger difference.
Sounds pretty precise though, so that makes both good data points to keep in the back of our heads. About 1 1/3 degrees difference.

But what is your reference to the " 11"/35" " mean? And if the change in pinion angle was LESS than the angle of the shim, how does that equal 1.33?

Just curious. I might be seeing it wrong.
Thanks again.

Paul

 

[armynavy17]

But what is your reference to the " 11"/35" " mean? And if the change in pinion angle was LESS than the angle of the shim, how does that equal 1.33?

The 11"/35" references my first post regarding approximating the additional change in pinion angle by measuring the distance from the center of the axle shaft and dividing it by the distance from the pinion to the output shaft.

That approximates the change in the angle of the driveshaft as a function of the change in the angle of the pinion. So by my approximation, 1 degree of change in the angle of the pinion results in 11/35 = .31 degrees of change in the angle of the driveshaft for a total change in pinion angle of 1.31 degrees (per degree of change in the angle of the pinion).

I skipped a step in my previous post showing 11/35 = 1.31. Angle of the pinion and angle of the driveshaft being referenced to horizontal (or vertical). Pinion angle being referenced to the driveshaft.

 

[71 CA Bronco]

The 11"/35" references my first post regarding approximating the additional change in pinion angle by measuring the distance from the center of the axle shaft and dividing it by the distance from the pinion to the output shaft.

That approximates the change in the angle of the driveshaft as a function of the change in the angle of the pinion. So by my approximation, 1 degree of change in the angle of the pinion results in 11/35 = .31 degrees of change in the angle of the driveshaft for a total change in pinion angle of 1.31 degrees (per degree of change in the angle of the pinion).

I skipped a step in my previous post showing 11/35 = 1.31. Angle of the pinion and angle of the driveshaft being referenced to horizontal (or vertical). Pinion angle being referenced to the driveshaft.

Thank you for this. It was a great help. I rotated my perches today. My first time doing this and if I hadn't read your post I would have rolled the pinion too high. I hadn't thought about the drive shaft angle correction.

I have an Atlas and 4R70W transmission. My pinion angle was way off after initial install. I measured 10.1 degrees difference from rear driveshaft and pinion yoke. It took me a bit to understand how you do this.

After figuring out what you were doing my measurements were 11"/29" = 0.379 drive shaft change per 1 degree of perch change. My goal was to be at 1 degree difference overall once finished. Based on this calculation I rotated the perches 6.52 (actually 6.6) degrees forward. Using your trick put me at 1.1 degrees final difference once the job was completed. Darn near perfect.

I think I owe you a beer.

 

[armynavy17]

Thank you for this. It was a great help. I rotated my perches today. My first time doing this and if I hadn't read your post I would have rolled the pinion too high. I hadn't thought about the drive shaft angle correction.

I have an Atlas and 4R70W transmission. My pinion angle was way off after initial install. I measured 10.1 degrees difference from rear driveshaft and pinion yoke. It took me a bit to understand how you do this.

After figuring out what you were doing my measurements were 11"/29" = 0.379 drive shaft change per 1 degree of perch change. My goal was to be at 1 degree difference overall once finished. Based on this calculation I rotated the perches 6.52 (actually 6.6) degrees forward. Using your trick put me at 1.1 degrees final difference once the job was completed. Darn near perfect.

I think I owe you a beer.

Beer is the gold standard of payment in my book, haha.

Glad it helped, I tend to drastically over think things. I don't just want to know that it works, I want to know WHY it works and HOW it does it. This usually results in me having useless information floating around in my head and projects taking twice as long. Sometimes though, the light flips on and the info is useful.

 

[71 CA Bronco]

I little bit better than perfect. ;D

Thanks again.

 

[garberz]

I little bit better than perfect. ;D

Thanks again.

Your pic looks like the pinion and the drive shaft are at the same angle. You want the pinion to be 1-3 degrees less angle than the drive shaft (pointed down), that helps the rear U-joint. A small difference keeps the needle bearings rotating around the trunion.

Mark

 

[BUCKWILD]

^^^ and you will get some spring wrap under load and that is when you get vibration. As spated 1-3* down is ideal

 

[71 CA Bronco]

^^^ and you will get some spring wrap under load and that is when you get vibration. As spated 1-3* down is ideal

The pic is deceiving. Its at 1.1 degrees difference. I was shooting for 1 degree. It came out very close to that.

 

[DirtDonk]

And that 1.1° has the pinion pointed below the driveshaft? Yeah, we've had trouble with that close angle and pictures before. In this case it looks like the pinion is pointed above the centerline of the driveshaft. Pics can be very misleading unless they're taken from just the right angle sometimes.

 

[71 CA Bronco]

Hi Paul,
Yes pinion is down 1.1 degree from driveshaft. I checked it again to make sure.

 

[DirtDonk]

Perfect. You should be good to go. Smooth sailing!

Paul

 

[68ford]

After my springs settled( high arch, 12in longer than eb springs) over the years, the pinion ended up about 1/2 to 1 degree "up" from the drive shaft. Im sure the angle goes up higher when under some load just driving normally.
Its been like that for roughly 20,000 miles. no issues or vibrations. I also have low gears and run 3500rpm down the freeway, which means the drive shaft is turning the same 3500 rpm.
if your within 2 degree in either direction i think you are fine.