Nine Inch Pinion Angle

[ShannonW]

I recently purchased a Nine Inch housing from Currie. I had them weld on a set of spring perches to what they said was the factory setting for pinion angle.

After I installed the rear end I notice a small vibration in the driveline. I began to investigate and noticed that the rear pinion is pointing down approx. 4 degree's.

Can anyone tell me if that is the proper angle or if it matches a Nine inch in your own car.

Thanks for any input.

 

[Ronstang]

The pinion should point UP approximately 3 degrees for a factory setup. Sounds like someone was suffering from a hangover when they welded your perches on.

 

[mustang70]

I always thought that the pinion should point down a little so that when you start moving and torque is applied to the rear end it'll rotate up and be straight with the tranny.

 

[Ronstang]

If it pointed down it would be out of phase with the engine/tranny.....call and ask for exact degree....static drivetrain angle on Mustangs is 3 degrees but the rear COULD be set at 2 to compensate for movement under load....I just don't know exactly and I am leaving in an hour for 2 days so I don't have time to measure the one in the garage.

 

[ShannonW]

I just checked my invoice from Currie and it indicated that the perches were set at 2.5 degree's. I went out to the car and also measured the bottom of the spring plate and found it to be pointing down at approximately 7 degree's, hence the 4 degree's at the pinion.

Are your leaf springs pointing down at the perch position?

 

[Route666]

Sounds like your driveshaft may be too long and is pushing hard on the diff and rotating it and the springs. Very unlikely, but maybe? The spring perches are supposed to be level, well all the ones I've seen are. Perhaps the shackles on the front or back or both front and back of the springs are wrong, and pointing the springs at funny angles.

Hope that helps!

 

[SandSprite]

I think the pinion angle is supposed to match on both sides (tranny to driveshaft, and rear end to driveshaft). I think you want to shoot for 1-3 degrees. You can get shims/angle plates to change the rear pinion angle. Lowered cars tends to need them.

 

[302 coupe]

do you compare the pinion angle with to the downward angle of the driveshaft, or do you compare it to a true horizontal surface? It would make more sense if it were measured with respect to the driveshaft.

 

[BobV]

You want the transmission output to angle down about 3*, and the rear yoke to angle UP about 2* (+/- 1/2*). The U-joint operating angles are more a function of driveshaft length - not really adjustable easily. The important thing is getting the input and output angles parallel.

Good Article
Another Article

 

[Gummi Bear]

9" sense

First - pinion should never point down. If you're having that much axlewrap that you have to compensate for it by turning it down, you need a traction aid, else you'll bend your springs into a 'W' (been there, done that) 9" will oil just fine pointed up around 5*, so don't let that be an issue with setting the perches. It sounds like the numbskull that welded in your perches put them on 2.5* the wrong direction. They owe you a proper installation, talk to them about taking it to another shop, and having new perches (no torch and move) welded in the correct place. Your pinion should compliment the angle of the driveshaft. Get it fixed now, or you'll break the yoke and tear up a bunch of u-joints unnecessarily. If you're gonna pay that much for a new axle, make sure that it's right 100%.

PS - new spring perches for a 9" should run about $12 ea.

PPS - if you're turning enough torque to warrant a 9", you may want to look into a traction aid. Ladder bar with a subframe connector, 3 link, 4 link, etc. The little springs on a 'Stang will be wrapped up in no time, once you apply that torque to the ground.

 

[Mustang67Coupe]

Will the pinion angle remain the same in a 3 link, 4 link, and ladder bar setup?

 

[Gummi Bear]

Will the pinion angle remain the same in a 3 link, 4 link, and ladder bar setup?

Yes. It will never move.

The corny traction bars that were so 'rad' in the 80's on every mullet sporting camaro don't work. Not now, not ever.

First: Axle wrap is the combination of two motions, not just one as is popularly perceived. The top of the axle will try to rotate forward, as the pinion gear tries to 'climb' the ring gear. Also at the same time, the bottom of the axle will try to rotate backwards. Addressing only one of the motions will leave you will reduced axle wrap, but you will still have it to deal with (broken joints, cracked pinions, seperated shafts, etc)

A 'true' 3 or 4 link, will move in the same arc as the rear axle as it articulates, but will not allow the pinion angle to change. This is traction. A true ladder bar does the same thing. It is welded to the axle, has two attachment points to keep the axle from wrapping both planes.

To understand how a 3 or 4 link works, go to Pirate 4x4 and do a search of the general 4x4 forum, there are threads explaining how it works, and some animated models of it's function. I understand that the needs of a street machine and a rock crawler are very different, but the concepts are still the same, just adapted for your particular application. I could go on for hours on how it works (idea: try 'how stuff works' website, I'll bet something is there too) but won't, I get too excited and start stuttering.