Pinion angle with a twist

[Pedigry]

Hey guys,

I have a question. I have reviewed every video and forum that I could on this subject and its still not quite clear to me. I have a 70 mustang with a 4 link and coilovers. The car is pretty low. It has a C6 in it with a gear vendors overdrive setup. It's snugged up into the trans tunnel as far as it can go. I am chasing a drivetrain vibration and need some help with the pinion angle.

When I got the car, the measurements were:

engine/trans down 3.5* * (engine slopes down toward rear end)
driveshaft down 1.5* (DS slopes down toward rear end, same as the motor)
Pinion 0* (level with the ground)

After reading a ton on the subject, I felt like I should try an get the pinion to match the engine (apposing angles), so I raised the pinion to 2.8* up (leaving a little for rotation). Now the DS is at .7* down. The issue I am having is that the working angle between the DS and the pinion is now a positive pinion angle. In other words, it doesn't form a "V" like it should, but an upside down "V".

So currently the car is:
Engine/trans down 3.5*
driveshaft down .7*
Pinion 2.8* up (pinion CV is 2.8* point up)

I have read that is a bad thing, as the rear end rotates up under acceleration, that working angle gets worse and is potentially binding. Everything I have read says you never want a positive pinion angle. Most of what I have read states you should just set the pinion 2* downward angle (pinion 2* down toward the ground) and call it a day.

With the current setup I have, I can't raise the tranny anymore than it is without hacking the tunnel, which I won't do. So the only other way to change pinion angle is raise the car up a bit, which I don't really want to do, or simply keep adjusting the pinion angle to try and relieve the vibration (which currently is when the car is slightly off power or on deceleration).

With a 3.5* downslope on the motor and the car being as low as it is, there is no possible way to have the motor and the pinion to be equal and apposing angles. I'm trying to avoid a positive pinion angle. Not sure where to set this thing.

Thanks.

[dontlifttoshift]

Working angles are the only thing that matters. Everything else is noise and should be disregarded.

Old rules of thumb about "equal but opposite" and "2 degrees down" are dumb. Disregard those statements and those like them.

Pinion angle under acceleration/deceleration with a link suspension is minimal and not worth worrying about. (unless you have some really worn out parts) Pinion angle movement through suspension travel can be significant in some link suspensions, especially when there is a large discrepancy between the length of the upper and lower links.

If I understand what you are saying, right now your front working angle is 2.8* and your rear working angle is 2.1*

Your initial measurements have your front working angle at 2* and your rear working angle at 1.5* That was pretty close. From here if you rolled the pinion down just a bit more you could get them to match and get a working angle at both ends of ~ 1.7ish

[Pedigry]

Thanks Donny,

Interesting that you say that. Because after all of this, that's what I was thinking as well. Ultimately, when I was staring at the trans, DS and pinion angles, my thought was that if the working angles are equal than I have reduced the difference between the two as much as possible. No matter what the angles are, if I modify the pinion angle to match the working angle of the trans/DS, then I have reduced both working angles to the lowest common denominator. Makes sense. Versus trying to match angles and having the working angles way out.

I'll make the change and see what happens. Thanks.

BTW, pinion rotation is very small because it's a 4-link. But it's a triangulated 4-link so when the car squats under acceleration, it does rotate. When I slam on the gas, I feel the rear of the car squat. How much it rotates, I have no idea, I might put a go pro under the car and take some vids to see how much the pinion climbs.

All good things, just trying to get the chassis set up. I have learned alot through this process.

[dontlifttoshift]

What ever arrangement gets you the smallest working angles that are the same front and rear is the correct arrangement.

Just get the coilovers out of the way and run the suspension through travel. You can actually measure pinion angle change at various increments as opposed to trying to guess at it.

[Pedigry]

Thanks again.

I have to pull them anyway to adjust the pinion angle because the upper control arms only have a heim on one end.