My 427 SOHC Build..... Finally the time has come!

[jayb]

Probably a 2 degree down angle on the pinion is about right.  This allows the differential to rotate up a couple degrees under torque application so that it is well aligned with the driveshaft.  Your angles may be correct as-is, but its hard to tell from your message because you haven't specified up or down.  For example, is the rear of the transmission pointed down 1 degree from level, or up 1 degree from level?  Is the nose of the differential pointed down 6 degrees from level, or up 6 degrees?

[cobracammer]

Hello Jay.  Thank you.  I will try and explain more and try using + and -:

The tail shaft of the transmission is pointing down towards the ground (-1 degree)

The drive shaft is is lower near the rear end (so also pointing down at an angle of -3 degrees)

The rear end yolk is facing towards the front of the car and is facing up at +6 degrees.

so in looking at this as a whole....  I think the rear end is 5 degrees steeper of an angle than the transmission tail shaft (out of parallel).



Many mustang forums says (-2 degrees) to account for acceleration (rotation of the rear end) as well.


It feels like (when I draw it out), that I would have to decrease the rear end angle (make the yolk point more toward the floor so that when the rear end rotates under acceleration, it is equal to the angle of the transmission tail shaft.

If this is the case, the yolk would need to be (-1 degree) so that when I accelerate, it rotates clockwise (pushing the rear end yolk up -or clockwise if looking at it from the drivers side) about 2 degrees making it 1 degree or parallel to the trans tail stock?

Thanks again for your help!

[jayb]

Jason, I think you are right about that.  If the driveshaft is down at the back, and the down angle is 3 degrees, then you should have the pinion end of the differential about level, or maybe pointing up 1 degree.  Having it point up 1 degree would make it parallel to the transmission output shaft, if I understand you correctly.  If you set it up like that, when the car accelerates, the pinion angle will want to go up from level to maybe 2 or 3 degrees, bringing it close to parallel with the driveshaft.

As the car is set up now, again if I understand correctly the angle between the driveshaft and the pinion will actually be increasing under acceleration, which is not what you want.

Time for some rear suspension adjustments 

[cobracammer]

Hi Jay!  Thanks.  I was going to shoot for (-1 degrees) for the rear end pinion (pointing down towards the front of the car).  This way, under acceleration, it will rotate upwards about 2 degrees  making it +1 degree (so parallel with the transmission tail stock).  If I am trying to just get the transmission output shaft and the rear end pinion in parallel under acceleration, why do we take a measurement on the 1 piece driveshaft?  is that angle irrelevant when the rear end and transmission are in parallel?

I just ordered a BMR adjustable Upper control arm.  The Currie 9" i got for this car was a direct replacement for the stock 8.8, so I was able to retain all of the OEM suspension hardware (lower control arms, upper control arm, panhard bar....)

What I wasn't thinking about at that time was that Currie made it as a direct replacement with the stock engine, trans and 2 piece driveshaft!!

With all of these changes, I seem to be off quite a bit (under acceleration, I was  prob at +8 or +9 while the trans output shaft (tailstock) was still at -1...... So possibly the cause of those weird harmonics?

Either way, ill swap it out, adjust it for the correct pinion angle, and let you know what comes of it.      Thanks again!

[machoneman]

With all of these changes, I seem to be off quite a bit (under acceleration, I was  prob at +8 or +9 while the trans output shaft (tailstock) was still at -1...... So possibly the cause of those weird harmonics?

Yes, it is possible yet you'll know pretty quickly after the changes.

Btw, there are a number of sites that talk about and show pictorially what are ideal, if not acceptable, driveshaft angles. In many a low powered car it may not make a lot of difference. But, in yours and especially when you beat on it with all the JB power (!) it's not hard to start breaking stuff even when the angles are perfect (ask me and other racers, current or former, about this!).

Wolfe's is one of many but...note their chart at the very bottom of the page on solid versus poly versus stock mounts. What they are saying is under load, some other variables do affect the car's pinion angle.

https://www.wolferacecraft.com/pinionangle.aspx

[Bolted to Floor]

Jason, there is a TREMEC tool box app for a smart phone that covers driver line angles. You use your phone to measure the angles and it gives you a pass or fail. I doubt the explanation for a fail will be as good as the advice already posted .

[cobracammer]

Thanks Guys....  visited the site and also downloaded the app!

[BigBlueIron]

If I am trying to just get the transmission output shaft and the rear end pinion in parallel under acceleration, why do we take a measurement on the 1 piece driveshaft?  is that angle irrelevant when the rear end and transmission are in parallel?

 Also offset needs to be added for u joint angle. Are the trans and rear pinion perfectly centered in the car? Usually not. But worry about that after pinion angle is corrected. How long is the shaft anyway?

Example for why measuring the shaft matters, say both pinions are at an equal but parallel 2* trans down 2 axle up 2. And theoretical 1* on the shaft. This would provide an operating angle of 1* on the trans u joint and 1* at the axle u joint. Well within the recommend 3*
 Now raise the engine/trans straight up 3 feet with all else being the same, this will greatly increase the shaft angle, say to 8*. Now our operating angle is 6* at the trans and 6* at the axle. This is where multiple shafts and or cv joints come into play.

I would shoot for 0 or +1 Keeping angles parallel is the most important part and key for smooth operation. This is ultimately a cruiser right? If you go to a negative angle on the pinion the only time angles will be parallel is under heavy acceleration as the axle tries to rotate. 

Ether way I bet you see a great improvement. That rear axle is way off lol! Look forward to hearing the results.

[cobracammer]

OK adjustable Control arm came yesterday.  I just spend about 3 hours in the garage trying to adjust this thing to get the optimal pinion angle....  I don't know why this is kicking my butt!!!

Here is where I am now.  Transmission tail stock is pointing down at 2 * ......  drive shaft is pointing down (front to back) at 5*

The rear end pinion yolk is up towards the transmission at 2* 

My iPhone only does whole numbers in degrees, but I was going to go back in later with the Tremex app and get measurements as it measures to the nearest thousandth.

I think setting the pinion angle ideally for a Mustang at -2 degrees per Ford assumes you still have the stock 2 piece driveshaft so with a 1 piece driveshaft, I am not sure if that's different.

Spicer has this:

Rule 1: Universal joint operating angles at each end of a driveshaft should always be at least one-half degree

Rule 2: Universal joint operating angles on each end of a driveshaft should always be equal within one degree of each other (one half degree for motor homes and shafts in front of transfer cases or auxiliary devices)

Rule 3: For vibration-free performance, universal joint operating angles should not be larger than three degrees. If they are, make sure they do not exceed the maximum recommended angles.

I am at exactly 3 degrees operating angles with the whole number measurements above. 

leave as is??

[jayb]

What you want is for the transmission output shaft angle to align with the pinion angle under load.  So, assuming the rear axle housing rotates the pinion up 2-3 degrees under load, then at rest the pinion angle should be down relative to the trans output shaft angle.  Sounds like yours is perfectly aligned at rest.  I would bring the pinion angle down to level (0 degrees), so that when it rotates up 2 degrees under load they will be aligned.

I'm assuming you are doing this with the weight on the tires and the car about level?  That's very important.  Also I'm assuming that your suspension allows the differential housing to rotate a little, which would be normal for a stock type suspension.

[cobracammer]

Hi Jay.

Yes, I have the car up on Jackstands (with the rear jack stands under the axle at about the spring perches.  Front suspension is not compressed, but the car is level.

I just went out and measured with the Tremec app which (I was mistaken in an earlier post), does 1 decimal point rather than whole numbers.

I went off the crankshaft pulley this time for the transmission angle....  getting 2.8 degrees.  When I was measuring before with just the iphone level app, it would say 2 degrees if it was 2.1 all the way to 2.9 (no decimal). So solidly off the crankshaft pulley -2.8 Degrees down.

Driveshaft measured by the transmission output, in the middle and at the rear pinion.... -5 degrees down.

Rear pinion... this time I used a socket to fit on top of the u-joint cap.  Then took my measurement off of the socket as a perfectly flat surface.  I got 1.9 degrees.

It looks like I would need to be at about 0.8 at the pinion so under power, I am at about 2.8 (equal to the trans output).

When I use spicer's pinion angle calculator website, and put in my values with the 0.8 (where my pinion angle should be at rest), I get an operating angle of over 4 (they say not to go over 3).
 
Should I be plugging in my angles with the assumption its under power? so use 2.8 for the rear (since that's where it will be under power?)

Thanks again!

[Nightmist66]

It sounds like you have the jack stands under the axle housing. If that is the case, the rear may be on a bit of a bind with all the weight  resting on it and may change slightly after you remove the jack stands. The best way is to support under the tires on all corners, as it would be on the ground. An alignment rack is your friend for this job...

[jayb]

+1 on what Jared said, get it resting on the tires, at least at the back, before you confirm the angles.

[cobracammer]

Thanks guys.  Before I read this, I was out tinkering.  I managed to get the rear end (pinion yolk) pointing slightly up at 0.8 degrees.  This would mean that under load, it would rise an additional 2.0 degrees and be at a total of 2.8.  With the transmission tailstock (also measured the crank pulley for verification), also at 2.8 degrees, the two should be in parallel under load.

Im still "miffed" that this is such a hard concept to grasp!  I think where a lot of confusion comes from is that all the "how to" and instructions out there has you setting your pinion angles in parallel at rest!  No one mentions anything about changes under load!

Also, anything for a S197 Mustang only shows taking measurements off of the rear pinion and the back part of the 2 piece driveshaft to get your -2 degree.

As I do not have access to a 4 post lift at this time, I will certainly try and locate someone (or try something) to get the rear wheels resting on a solid surface and remeasure.  Hopefully it will still measure the same and I can take it out for a spin.

Also I wanted to mention that there are a few ways in which they say to measure angle on the rear pinion.  First is to find a flat surface on the pinion near where it attaches to the U joint (preferably machined).  The other is to turn the driveshaft until one of the rear pinion U joint caps is pointing straight down.... then use a socket that will fit on top of the u joint cap and take a measurement off of it.

I did both just to see, and I got no where near the same values!  I definitely went  with the value off of the socket on a U joint cap.

[machoneman]

As I do not have access to a 4 post lift at this time, I will certainly try and locate someone (or try something) to get the rear wheels resting on a solid surface and remeasure.  Hopefully it will still measure the same and I can take it out for a spin.

I'm almost hesitant to recommend this as perhaps you've thought of these ideas but....buy or steal some rough wood, the bigger the better, nail same together and place same under all 4 wheels. Better, get 4 steel milk crates and use them instead. Get two of those steel drive-up ramps but with removable ramps. I'm usually hesitant to drive a car up them but they can be used after jacking the car up with your floor jack and just use the horizontal part under the tires.

Heck, even these work well and cheap too: https://www.homedepot.com/p/8-in-x-8-in-x-16-in-Concrete-Block-100825/202323962

I've had to do the same or even build wood ramps to get under really low cars that even a std. floor jack was hard to get under the car. That and getting the car level but up in the air to more easily set toe, caster and check Ackermann angles.