Pinion angle

[Cobraman]

I know that somewhere there is a thread that talks about pinion angle and what it's supposed to be set at. I just can't seem to find it. I'm trying to put all this information in my to get done list with instructions so that I can study the process and when I'm ready I will have the knowledge to get it done and move on to the rest of my punch list of some small but important things. Can someone point me in the right direction. Thanks

[gbranham]

If you're running IRS, don't worry about it. Put a couple of Forte shims under the tranny, and send it. People fixate on this unnecessarily. If you're not running IRS, then it's more important, and the assembly manual speaks to this.

Greg

[Jeff Kleiner]

If my recollection is correct you have a 3 link. Assuming so here is a copy and paste from a post I made a decade or so ago which might help:

When we speak of pinion angle we are referring to the pinion shaft relative to the transmission's output shaft. When determining pinion angle you can leave the driveshaft on the workbench, and in fact if you follow my method described below it will be easier if you do just that :)

Don't get caught up or confused on any thoughts of horizontal. Think of it this way; when looking at the car from the side if you were to project one line from the transmission output forward and another line from the pinion shaft forward with your pinion angle at zero they would be parallel. If you put any angle to the pinion the two lines are not parallel and would get farther apart as they go forward. If the pinion were to be angled UP (relative to the trans) it's line would be above the output line; if it were angled DOWN the pinion line would be below. Below is what we're after. Clear as mud? Maybe this drawing that I did back then will help you to visualize it.

https://thefactoryfiveforum.com/attachment.php?attachmentid=216947&d=1514586767

My method for ease of measurement:
Set ride height then put the car on jackstands so that the axle is loaded. We don't care if the frame is dead nuts level; we're only going to look at the difference between output shaft & pinion. We know that the crankshaft and trans output shaft are parallel therefore the face of the damper/ crank pulley is perpendicular to the output. We also know that the pinion flange face is perpendicular to the pinion. See where I'm heading? For me it is easier to get a good measurement with the magnetic angle finder by reading vertically on the crank pulley/ damper and pinion flange rather than trying to work with the horizontal shafts themselves. Once you can see the two angles you can then calculate the difference. Generally with these cars we want the pinion down ~1-2 degrees (once again, meaning the input, or front of the pinion shaft is pointing down in relation to the transmission output shaft). Reason being is so that when the axle tries to rotate it's input upward under acceleration the pinion angle becomes less. This rotation is especially more pronounced on a 4 link car using the soft rubber bushings in OEM Mustang arms vs. a 4 link car with poly bushings or a 3 link with polys in the lowers and the solid upper link. Pinion angle adjustment with a 3 link is easy; simply alter the length of the upper link.

Hope that all makes sense and good luck!

Jeff

[Cobraman]

Thanks Jeff I totally understand it now I'm going to copy this in my notes I'll be working on this in the next couple weeks if I have any other questions I'll pm you.
Thanks again.

[Guardm16]

Jeff K, this is the best explanation I have read; easy for us crayon eaters to understand.

[ProfessorB]

.
I would also like to add one observation that hasn't been covered (it's only a minor point). If you look at Jeff's drawing, the pinion axis is going "down" the farther away from the axle it travels. This axis could also go "up" as it extends farther away from the axle it goes. It could also go "up" at 2 degrees. this means there can be "positive" or "negative" degrees or pinion angle, just as there is "positive" or "negative" degrees of camber, for example. I have NO idea which is positive or negative regarding pinion angle....but if I were seeking input I would make sure I was on the same page as the advice I was getting. Just sayin'

[Jeff Kleiner]

.
I would also like to add one observation that hasn't been covered (it's only a minor point). If you look at Jeff's drawing, the pinion axis is going "down" the farther away from the axle it travels. This axis could also go "up" as it extends farther away from the axle it goes. It could also go "up" at 2 degrees. this means there can be "positive" or "negative" degrees or pinion angle, just as there is "positive" or "negative" degrees of camber, for example. I have NO idea which is positive or negative regarding pinion angle....but if I were seeking input I would make sure I was on the same page as the advice I was getting. Just sayin'

Huh? That's why I said "front of the pinion shaft is pointing down in relation to the transmission output shaft". 2 degrees is 2 degrees, no matter whether it's measured 1 inch from the axle or 10 feet.

Jeff

[gbranham]

.
I would also like to add one observation that hasn't been covered (it's only a minor point). If you look at Jeff's drawing, the pinion axis is going "down" the farther away from the axle it travels. This axis could also go "up" as it extends farther away from the axle it goes. It could also go "up" at 2 degrees. this means there can be "positive" or "negative" degrees or pinion angle, just as there is "positive" or "negative" degrees of camber, for example. I have NO idea which is positive or negative regarding pinion angle....but if I were seeking input I would make sure I was on the same page as the advice I was getting. Just sayin'

Yep, and to add some more confusion, this excerpt from the assembly manual is at odds with what Jeff says. I'd follow Jeff's recommendations...

216980

[tnt_motorsports]

Yep, and to add some more confusion, this excerpt from the assembly manual is at odds with what Jeff says. I'd follow Jeff's recommendations...

216980

Crazy Greg, 2 deg up makes no sense to me at all. I'm with Jeff K, 2 deg down is the way to go.

FWIW, from my days of working on race cars you go down so that as the axle wraps under load it comes in plane better. Not sure if that makes sense how I explained it or not. You also don't want 0 deg on your u-joints.

[ProfessorB]

Huh? That's why I said "front of the pinion shaft is pointing down in relation to the transmission output shaft". 2 degrees is 2 degrees, no matter whether it's measured 1 inch from the axle or 10 feet.

Jeff:p

Jeff...my observation was mostly a question about semantics. Of course, your advice was perfectly clear. You did say down and your schematic even illustrates that. My question was really wondering if the terms (negative and positive) were ever used regarding pinion angle. Example: If a manufacture or someone else said "set the pinon angle at 2 degrees" without a schematic or using the word down. (Camber is one of those examples...there is positive camber and negative camber). Just wondering if the terms "positive" and "negative" are ever used when talking about pinion angle.....

[rich grsc]

Crazy Greg, 2 deg up makes no sense to me at all. I'm with Jeff K, 2 deg down is the way to go.

FWIW, from my days of working on race cars you go down so that as the axle wraps under load it comes in plane better. Not sure if that makes sense how I explained it or not. You also don't want 0 deg on your u-joints.

So, what's the answer if the transmission is angled down 4*? There is NO absolute "these are the correct numbers", every situation can be different. With a solid axle, you want to get as close as is reasonable to the centerline of the engine, transmission and the centerline of the differential, pinion being parallel. That 2* is not an absolute, 0*, 1*, 2* even 3* is all close enough, this isn't a moon shot