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Let's talk pinion angles

12K views 55 replies 15 participants last post by  Konnie the Goat 
#1 ·
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?
 
#2 ·
PM Radio or Mike, they should be able to give you some information
 
#3 ·
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.
 
#10 ·
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.
 
#13 ·
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.
 
#14 ·
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 fuck ups. The only vehicle where the DS angles shouldnt be checked is one that doesnt have one.
 
#17 ·
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.

Hendrix, 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.
 
#18 ·
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?
 
#25 ·
Never had a problem with my one peice.. With 20k miles and over 100 track passes.. No vibration or other problems
 
#29 ·
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 hendrix-Engineering shaft.thanks
 
#32 ·
I know that I am bumping this from the dead, but I was wondering what someone would say that the optimum pinion angle would be... I have a vibration and am using a 1 piece aluminum d/s... its only above 75mph, but it is scary bad. I am trying to do some troubleshooting.
 
#36 ·
Huh. Same problem I'm fighting.

If someone offered me a good 2-piece that would work with my 4L80, I bet they'd make a sale.
 
#33 · (Edited)
The real issue i believe on these cars is the fact that the cradle can move. this would mean you would have to check the angle on 2 planes. there is a tool made to see it its straight left to right. as for the actual angle the simplest way would be to match the trans and the diff angles. in most stock or factory cars this is the safest way to go. Konnie had a very good post in the beginning of this thread. Read it.



p.s. with the Giubo joint you do wan about Zero so the "rag" joint does not push and pull on the 2 shafts
 
#34 ·
Konnie the Goat

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
Great post
 
#35 ·
I read that one, I was looking for someone who maybe had altered their pinion angle before and found that these cars liked -1degree best. I know how to find what the angle is, and how to adjust it, I was just hoping to not have to try the guess and check method over and over again to obtain the end results that I desire.
 
#37 ·
Im in the same boat, trying to figure out how to re-use stock driveshaft with 4L80 upgrade. I thinking about taking f-body driveshaft to shop and have them r&r it to fit gto
 
#38 ·
I am hoping that the pinion angle winds up being the issue so I do not have to get another driveshaft, I am willing to swap to a 2 piece, but I do not really want to unless I absolutely have to. I will probably be messing with the angle this weekend.
 
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