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Old 02-03-2009, 06:47 PM   #1
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Let's talk pinion angles

Ok, I'm learning about this phrase and what it actually means. I'm confused.

How do you adjust this "pinion angle?"
What determines the angle?
Is it an issue on an IRS car or only on SRA cars?

What would cause the angle to change?
- removing the rear end for gear install?
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Old 02-03-2009, 07:27 PM   #2
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Originally Posted by 0-60N3...View Post
Ok, I'm learning about this phrase and what it actually means. I'm confused.

How do you adjust this "pinion angle?"
What determines the angle?
Is it an issue on an IRS car or only on SRA cars?

What would cause the angle to change?
- removing the rear end for gear install?

PM Radio or Mike, they should be able to give you some information
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Old 02-03-2009, 07:40 PM   #3
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the pinion angle is one of 2 key angles, the other being the transmission angle. U-joints dont like a lot of angle for one. and if the angular difference between the trans to shaft, and shaft to diff joints is more than a few degrees, you get noise, vibration, and joint failure.

This does not apply to the GTO in stock form. one, we have and IRS, that doesnt move much. two, we have a 2 piece shaft, which by adding a middle joint increases the variability (althought the angles between joints on the same shaft must remain within the tolerance). And 3, we dont have a pinion u joint. What we have is a rag joint.

These angles matter most on SRA vehicles. They can be alltered by lowering or raising the vehicle, or by cargo loads. They can also change on a momentary basis during acceleration. This is called axle wrap. The pinion will move up, as an oposite reaction to the wheels moving down. What can I say, Newton knew his shit. Motor/trans movement can also change these angles, either thru torque rock, or mount bushing failure.

The closer you get to zero difference at static position (all 4 wheels on the ground, full vehicle weight), the more balanced the angles will remain under momentary dynamic conditions.

In SRA vehicles it is adjusted by changing link lengths on multi link suspension, and with wedged shims on leaf springs.

On an IRS like ours, youd first have to limit travel of the x-member the diff bolts to. There is some play there. Pedders subframe bushings and a HArrop cover will do that. to point the pinion more up, put shims under the Harrop-to-body bracket, or above the differential's back 2 dif-to-xmember bolts. to move it down, you shim the front two bolts.

These angles do matter on a 1 piece DS IRS car. as i said, the diff xmemeber does have play, as do the engine/trans mounts. You dont have as much issue as a SRA car, but it is still there. The chances of major noise and vibration are low, but joint life is still a factor.

also, you cant have a zero angle. the bearings in the ujoint must turn, or they will lock up. this is why old chryslers offset the engine to one side, and why GM engines slope to the rear. Ford cants some of theirs slightly. No i see people saying 'but you cant have a zero angle anyway, for the reasons you listed", and youre right. But thats momentary stuff. The car spends most of its time at the static position, be it idle in a driveway or parking lot, or cruisin downt he road. This is when the joint would seize. It would then fail during a momentary change. This is why its still important to check an IRS cars angles.

The exception is a 100% hard mount, like a c5/c6 vette. Those cars do not have a DS, they have a Torque tube. The diff is always in the same spot, and is infact directly connected to the engine. it does not move. This is how all IRS should be, IMO.
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Old 02-03-2009, 07:59 PM   #4
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Wow good info.

I have a stock driveshaft A4 GTO with IRS. Only upgrade is 3.91s and a built tranny. So would pinion angle not concern me?
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Old 02-03-2009, 08:44 PM   #5
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No, dont worry about it.
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Old 02-04-2009, 05:03 AM   #6
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Originally Posted by 0-60N3...View Post
Wow good info.

I have a stock driveshaft A4 GTO with IRS. Only upgrade is 3.91s and a built tranny. So would pinion angle not concern me?

the pinion angle will not efect you with a stock drive shaft becase of the 2 piece desighn.As long as you dont put in a 1 piece youll be fine.
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Old 02-04-2009, 05:09 AM   #7
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Awesome. Thanks guys.
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Old 02-04-2009, 05:23 AM   #8
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I wouldn’t worry about the angle with a one piece OR 2 piece shaft with a solid mounted IRS rear housing.
The angel is important in a solid rear axle because it changes when you launch the car. It doesn’t change much at all with an IRS rear.
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Old 02-04-2009, 06:08 AM   #9
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Originally Posted by Gforce1320...View Post
I wouldn’t worry about the angle with a one piece OR 2 piece shaft with a solid mounted IRS rear housing.
The angel is important in a solid rear axle because it changes when you launch the car. It doesn’t change much at all with an IRS rear.

I know we worry about angles
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Old 02-05-2009, 11:34 PM   #10
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Agreed. Pinion angle is a nonfactor on an IRS set up. Unless the mounting is bent or cracked, it never needs attention.

Even on an Fbody, the torque arm locks the tranny and the diff together in unison so the components maintain the correct angle. The problems start when using hi output motors. Then the torque arm cannot maintain the correct angle under heavy launch. That's why heavy duty torque arms, springs, control arms, and panhard rods are often used.

GTO wheelhop is a different issue usually caused by weak springs and other factors and not the pinion angle under launch.
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Old 02-06-2009, 05:04 AM   #11
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[QUOTE=rednari;5262833]Agreed. Pinion angle is a nonfactor on an IRS set up. Unless the mounting is bent or cracked, it never needs attention.

I hate to disagree, it is a nonfactor if its right from the start.If you take a car that was desighned for a 2 piece ds and then install a 1 piece youll see that pinion angle becomes a big factor
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Old 02-06-2009, 05:45 AM   #12
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it varies from car to car. i'm at 4 degrees down tailshaft and just over 3 up on pinion angle. this is kinda on the edge for a one piece.
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Old 02-06-2009, 10:04 PM   #13
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If the pinion angle is incorrect from the factory, then you do have a problem. If it can be corrected by adding spacers to tilt the diff, it is easy to correct. But if the unit must go up, then you are in trouble.

Also, a two piece shaft may need to have the center bearing shimmed down to bring the angle with tolerances if the angle is severe. But, I have never heard of a GTO having unacceptable pinion angle even with a one piece shaft. The diff mounting, again unless damaged, is set inline with the transmission. The only flex at launch being caused by the motor and tranny mounts.

While not impossible to occur on our cars, it is improbable and is a problem associated with standard axle cars under launch.
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Old 02-07-2009, 07:29 PM   #14
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Originally Posted by rednari...View Post
If the pinion angle is incorrect from the factory, then you do have a problem. If it can be corrected by adding spacers to tilt the diff, it is easy to correct. But if the unit must go up, then you are in trouble.

Also, a two piece shaft may need to have the center bearing shimmed down to bring the angle with tolerances if the angle is severe. But, I have never heard of a GTO having unacceptable pinion angle even with a one piece shaft. The diff mounting, again unless damaged, is set inline with the transmission. The only flex at launch being caused by the motor and tranny mounts.

While not impossible to occur on our cars, it is improbable and is a problem associated with standard axle cars under launch.

Not to disagree (because i generally agree with you), but i suspect that at least some of the NVH issues people have reported with various 1 piece shafts could be angle related. I dont know how many people have bothered to check that, or just attributed it to balance issues.

Assumption is the mother of all smurf ups. The only vehicle where the DS angles shouldnt be checked is one that doesnt have one.
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Old 02-08-2009, 03:13 AM   #15
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. The only vehicle where the DS angles shouldnt be checked is one that doesnt have one.[/QUOTE]

Great quote, can i use that on my website..lol.well put
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Old 02-08-2009, 04:34 AM   #16
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Originally Posted by Konnie the Goat...View Post
Not to disagree (because i generally agree with you), but i suspect that at least some of the NVH issues people have reported with various 1 piece shafts could be angle related. I dont know how many people have bothered to check that, or just attributed it to balance issues.

Assumption is the mother of all smurf ups. The only vehicle where the DS angles shouldnt be checked is one that doesnt have one.

I tend to agree and not being arguementive but I am convinced there are issues dealing with the movement of the shafts as the vehicle flexes, compresses, and does a hundred other things to extert external pressure on the drive train. I think you can see that most clearly in circumstances where undercarriage bolt heads etc contact the driveshaft. I've had that happen with the seat belt bolts you grind down on the single piece drive shaft installations as well as the passenger side muffler mount. Since the seat belt bolts and the muffler mount are fixed to the car, it is obvious that the driveshaft moves. This is true for the one and two piece driveshafts, I have had rubbing on both. However, I don't think the angle at the differential is that big of a deal since the differential is relatively stable. I found a worn transmission mainshaft, fixed it and that cured my vibration issues with the single piece drive shaft. Moral of that story is the flexing and changing angle in the only part of the Drivetrain that can flex most easily exert pressure directly on the output shaft of the transmission. Since the motor and transmission move and the differential doesn't its like having something stuck to the end of a baseball bat and swinging the bat trying to dislodge it. IMHO that explains some of the failures that resulted in broken tailshafts, bell housings, and even the rear of the motor. On the other hand I just saw a broken tailshaft on an A4 with an OEM DS. I personally believe that the Vettes have the tranny bolted to the rear and some movement in the IRS for that very reason. JMHO
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Old 02-08-2009, 07:09 AM   #17
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WRP, I think we need to mount cameras under some cars, and see whats moving. The DS does deflect from its static position under loads. And I agree the Vette uses a Torque tube and transaxle for drive train rigidity as well as weight balance.

I recall from my Harrop install just how much play exists in the x-member stock. That crappy diff-to-body bracket has too play. I really need to get the subframe bushings as well.

Couple that play with the Pedder's dealer's claims of cradle alignment issues front and rear, and you have the makings of out of whack DS angles.

Add to that 2QWK4ru's measured angles on a 1 piece (the first time ive seen any info on these cars), and his correct assesment that 1 degree is pushing it on a performance shaft, even an IRS.

I suspect the only reason we dont have more NVH issues is the ragjoint. Which is why we have one, to remove the NVH.

*for those non-tech types, NVH is the term used for Noise, Vibration, and Harshness in tech/shop manuals and training materials put out by OE's and similar bodies.

Non-Sponsor, if you want to use that line, go for it. Just make sure you credit me for it when doing so. My SN here or my real name is fine. You can even do it in fine print at the bottom of the page, and/or link the quote to this thread. Just so long as I get credit.


Rednari, the Torque arm has some effect on pinion angle on the F-body, but that still needs to be checked. I have some experience on this. A kid in my class last year has a V6 1996 camaro. He brought it in for NVH. Pinion seal was the first thing found. V6's pack a 2 piece DS stock. His carrier bearing was shot. and by shot I mean see thru. His trans-to-xmember mount was shot. And I mean see thru, after you lifted the tailshaft with a screw jack. The DS was deflecting up and hitting the floor under load. The fix was a 1 piece V8 DS off ebay, new trans mount, new pinion seal and new u-joints. We had to shim to the Trans to get the static angles under 1 degree variance. It was 3 degrees out to start. Now I know the Pinion seal was the last part to go, due to the angles being out of whack. Not sure if the carrier bearing or trans mount went first, but one took the other with it. Granted we had some broken parts, but the torque arm is not a magic solution to allow you to ignore angles.

There is another set of angle we havent eve discussed. Side angle. Refer to my first post in this thread, and you'll see I mention the mounting of various OE's to induce a proper amount of angle into the shaft. Now I realize that if the cradle in our cars was off too much, It would dog track, but that can be fixed in the alignment adjustment to a point, leaving the diff off line. The Side angles should also be checked in addition to the up and down weve been talking about. This is even more important on cars that lack the Harrop cover. I suspect from my Harrop install that My car might have this exact issue.
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Old 02-08-2009, 08:22 AM   #18
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Hope this isn't too dumb a question.....how do you measure these angles? I'm going to be going with a 1 piece DS in the future along with a complete rear pumpkin swap with my new gears & Harrop cover.

Seems like the concensus here is that it will probably be fine but I should check the angles just to be sure. Ok.....how?
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Old 02-08-2009, 09:00 AM   #19
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stock bushed cars will have play back there. i'm on noltecs and a harrop cover, mine is minimal.
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Old 02-08-2009, 09:32 AM   #20
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I have every Pedder's bushing you can have in the rear plus the tool to align the rear cradle.
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Old 02-08-2009, 10:21 AM   #21
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Hope this isn't too dumb a question.....how do you measure these angles? I'm going to be going with a 1 piece DS in the future along with a complete rear pumpkin swap with my new gears & Harrop cover.

Seems like the concensus here is that it will probably be fine but I should check the angles just to be sure. Ok.....how?

I would not recomend a 1 piece,might want to search on hear for the issues that the 1 piece imposes
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Old 02-08-2009, 10:30 AM   #22
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I would not recomend a 1 piece,might want to search on hear for the issues that the 1 piece imposes

I've seen all the trouble folks have had with the alum drive shafts. I'm opting for a carbon fiber 1 piece that Gforce 1320 is making and runs in his car.

Running 9's @ 140 makes me confident he can get that thing to work without the NVH issues other folks have had with the alum shafts.

If he wasn't 30 min or less away from me would make me more hesitant. But I'm sure he can help troubleshoot any problems I have. If it doesn't work, I'll just go back to the stocker.
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Old 02-08-2009, 12:36 PM   #23
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I would not recomend a 1 piece,might want to search on hear for the issues that the 1 piece imposes

Generally speaking, the weakness of a 1 pc DS are:
Lower critical RPM
and
Operating angle (and resulting NVH)

Both of which can be over come by design and installation. There is cost involved of course.

There are also dimensional considerations. A 1 pc of the same critical speed as a 2pc of the same material will be of a larger diameter.

While the 2pc design you sell is impressive, I'm still very much on the fence as to if ill be putting in a 1 pc or a 2 pc.
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Old 02-08-2009, 01:09 PM   #24
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one piece cf ftw. i just had one made with some special foam in tha tube to keep road noise down. when empty, there is some road noise to be heard. good luck on whatever u choose.
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Old 02-08-2009, 06:49 PM   #25
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Never had a problem with my one peice.. With 20k miles and over 100 track passes.. No vibration or other problems
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Old 02-08-2009, 07:21 PM   #26
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one piece cf ftw. i just had one made with some special foam in tha tube to keep road noise down. when empty, there is some road noise to be heard. good luck on whatever u choose.

i have built 2 replacement shafts for guys with carbon fiber 1 piece shafts,they got tired of the vibration. while you dont see as many im sure it has more t0 do with the limited number of cf shafts than the cf shaft being better
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Old 02-09-2009, 03:45 AM   #27
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im pretty sure they were from pst. mine is made at an aerospace company and is made better and balanced differently. ur right though, less cf ds out there.
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Old 02-09-2009, 09:54 AM   #28
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Wonder who had the vibrating c/f shafts.. all the vibration issues I've ever had were from the adapters and not the driveshaft.
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Old 02-09-2009, 10:59 AM   #29
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Wonder who had the vibrating c/f shafts.. all the vibration issues I've ever had were from the adapters and not the driveshaft.

chris i think its time for you to back up your statements, can you please list one person that has had a issue with a adapter plate.i will give you one guy that had a shaft made by me to replace a bad cf shaft.HEATH,now who had a bad plate with a vibration issue with a Non-Sponsor-Engineering shaft.thanks
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Old 02-09-2009, 11:02 AM   #30
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i never cared 4 my dss adapter. luckily i didn't really have vibes.
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