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I am preparing to adjust the pinion angle on my mostly street driven 65 Mustang (leaf spring). If I understand the various articles I have read, it seems this will be an exercise in compromise. Can the experts please either confirm or correct the following:

- For optimal high-speed freeway use, the pinion angle should be < 3 deg. (nose down W.R.T. the driveshaft angle)

- For optimal drag race use, the pinion angle should be 5-7 degrees (nose down W.R.T. the driveshaft angle)

- Angles of > 3 degrees should be avoided for street use, because they will likely cause a noticeable vibration at some freeway speed.


If I set the pinion angle to say 3 degrees (nose down W.R.T. the driveshaft angle), what effect will the missing 2-4 degrees (from optimum) have on drag strip performance???

- Is this mostly an efficiency issue, i.e. minimal angle possible yields least losses. If this is so, any idea how what kind of losses (%) occur when you have a 2-4 degree error?

Or

- Is this mostly a traction issue, If this is so, how does pinion angle effect traction?
 

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This is an issue that I have argued about for years with different people. In my opinion, and this comes from many years of racing, pinion angle does not affect traction at all. I have run leaf sprung and coil sprung suspensions on drag race and circle track applications and tried every differnt pinion angle setting that was possible. I have broke plenty of U-joints, and driveshafts experimenting with different angles in the search for the elusive traction that was supposed to be had, but to no avail. I always wondered why a 10,000 pound monster truck could leave the line with the wheels 5 feet in the air with the rear pinion pointing straight up!!! If more downward angle gives you more traction, why does the monster truck leave so hard with the pinion pointing up? I read an article about a year ago by Sleepy Gomez in Circle Track magazine, and his article explained how it was possible to get extra traction with different pinion angles, but the article left me with more questions than answers. The article had more to do with tires than anything else. I will try to find it and post it.
 

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Woah!

I am baffled as to how the angle of the drive shaft link to the rear end it's self can effect the traction of a vehicle! Changing the angle will Nnot add weight to the tires, or change the tread (or lack thereof) pattern upon the ground... Tires and the whole suspension setup is where your traction comes from right...? The angle of the pinion could be Backwards, straight up or straight down and it would not change any of the positioning of the rubber, or add weight.
Changing the pinion angle can increase lubrication or decrease it, it can also make it easier or harder to deliver energy to the rear gears, but I cannot see it increasing traction to any point.

Or.... Am I missing something?

FE
 

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I agree with the Falcon guys. Pinion angle CANNOT affect traction! Where the misconception comes in may be due to confusion about rear suspension adjustments. For example, take a ladder bar setup. The rear of the bar is welded/clamped to the rear axle housing. The front of the bar attatches to the car frame with a series of holes. Mounting the front of the bar in different holes changes the instant center, rear lift or squat, and weight transfer, which in turn affects traction. Raising or lowereing the ladder bar is obviously going to change the pinion angle, BUT, it is not the pinion angle change that affected traction!! With a leaf spring/slapper bar setup, you can leave a gap between bar and spring or preload the bar. Again, you may change the pinion angle, but it's the position of the bar, not pinion angle that affects traction. A U-joint is like a hinge-it's "floppy". The driveshaft has two u-joints so it can't support nor transfer any weight, can it! The front of the driveshaft has a slipyoke; it's free to move back and forth in the trans so you can't "force" any weight onto the rear axle this way, either (ever see what happens when the yoke 'bottoms out' in your tranny? Not pretty!).
 

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I think it's the u-joint angle that's important. In most cases it's the same as pinion angle.

Under hard acceleration the actual angle will change, so a greater nose down angle could leave you closer to zero which will have less HP loss.

I could see possible running very slightly faster if the actual angle under load is close to the angle the u-joint is most efficient. If it's set to say 2 degrees, you might end up 3 degrees pointed up for the majority of the run. 5 degrees down might be close. Probably depends on a dozen variables.

A street car isn't usually under the same loads, so the angle would stay close to whatever it's set at, and will wear out sooner/vibrate.

That's my theory. I also can't see it effecting traction.

Maybe someone with a very repeatable bracket racer could measure a change in ET. It also might be measurable on a chassis dyno, espescially if you could figure out a way to adjust the angle while it's running. Just one of a hundred things that would be fun to measure on a dyno if I had the money.

I've also heard 2-3% loss per U-Joint, and that probably depends greatly on u-joint angle. A 0 degree angle should be close to zero loss, but I understand that's bad for u-joint life.

_________________
Eric
La Habra, CA
--------------------
1964 Falcon Club Wagon - Bone Stock
1965 Econoline
408w SCAT crank, SCAT rods, Probe forged pistons, AFR205's XR286R, Victor Jr, AED 950 602hp at 6400


<font size=-1>[ This Message was edited by: etcetera on 6/1/06 3:20pm ]</font>
 

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The key here is, in your intended use of the vehicle, at the point the driveshaft is taking the most abuse, you want to make sure the ujoint has about 1-2 degrees angle to keep the u-joint rollers moving but not bind a shaft with excessive angle

That being said, look at the squat and spring wrap on a drag car, leaf spring. Thats why guys use more, when its "digging in" the pinion is trying to come up through the floor (equal and opposite reactions from physics)

Road car, high speed, less torque proprtional to shaft speed, less pinion angle.

The only thing that I think may effect traction, is a gyroscopic effect of the driveshaft./pinion combo but I am not even sure about that. Theory is the driveshaft will try to straighten out, but if the pinion angle goes overcenter (past the plane of the driveshaft) you'll get hop because it tries to go back

I dont buy it really, because the tranny end will still have an angle, and a fixed mount should transfer the energy down the shaft too

Bottom line, I think you are in good shape, put some traction bars to manage wrap up if you plan to drag. More pinion angle would just eat u-joints on a street car
 

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I have seen it (pinion angle) affect traction one time. The guy broke the leaf mounts and the rear turned straight up in the U-bolts. Traction went to zero after the driveshaft exited the trans. Other than extreme angles (usually caused by suspension problems) causing trouble, I've never seen any other case of results from messing with the pinion angle.
 

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you are not going to gain or lose traction via change in pinion angle. But, you can however change the angle to increase/decrease the leverage that the drive line places on the pinion. If the angle is changed 10-15 degrees, the shaft is no longer in line with the pinion and you will start to see less of a "hit" on the rear suspension which can be used as a tuning aid to reduce the 60' times slightly. I've never seen more than a couple hundredths difference. When I first baselined my 4 link, I would change the IC locations...but forgot to go back & re-check pinion angle. At one time, I had 18 degrees positive (pointed up) and a 1.37 consistent 60' time. Dropped the pinion angle down to 1 negative and the 60 times instantly went to 1.33-1.34 which is where it has stayed for the last 2 years for the most part. 1.28 was the best...but the DA that day was ~750 feet...great for a drag car.
 

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if your pinion angle under power points up, you WILL break driveline(u-joints) components. and for best performance under take-off or "launch" you want the pinion and drive-line to be perfectly straight. and that will lift the pinion up which will force the tires down, thus giving a minor traction improvement which may make that tenth of a second give you the win!
 

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No, "lifting the pinion up" will NOT "force the tires down". The upward movement of the pinion is merely a result of spring wrap-up (which leads to wheel hop and LOSS of traction when the spring unwinds). If you stiffen the spring and/or add traction bars, the forces that were wrapping up the spring now go to trying to lift the front of the car. This puts more weight on the tires and gives added traction. Pinion angle has no effect on traction.
 

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not going to argue with opinions-- i race dirt track anyway. and never broke u-joints by using correct pinion angle.

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tommy

<font size=-1>[ This Message was edited by: sevenfromsun on 6/5/06 6:31am ]</font>
 
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