What is the most accurate method for setting pinion angle on a 4 link rear?

[CTSV]

ive done searches on this forum and via the net and there tends to be so much conflicting methods and theories on this

i recently had my upper control arms changed to a new ridetech version with spherical rod ends with adjustments. i am getting a very mild vibration now above 60 when i am in the throttle. they were just installed out of the box which im sure was a dumb move.

i wanted to take time and adjust this myself at home but really want to know what is the best approach to doing so.

my car has a gear vendors overdrive unit and i was thinking if i need to put my angle gauge on the output flange of my GV and then on the pinion yoke on the diff then compare the degrees etc. Some sources say to put the angle finder on the driveshaft, on the crank pulley, under the floor etc so it really is confusing the heck out of me. Am i ultimately looking for 0 degrees when the car is on the ground with the suspension loaded?

visually i can see my pinion yoke is a bit pointing upwards so reading suggest i must shorten the upper CA and bring the pinion down slightly but i need to know to what degree. I want to get this perfect if possible

[andrewb70]

Here is the short answer: Under load, you want the front and rear operating angles to be equal, but opposite, and be as small as possible, without being zero. Here is a picture that should make it all clear:

https://static1.pt-content.com/images/noimg.gif

What kind of car do you have?

Andrew

[CTSV]

Here is the short answer: Under load, you want the front and rear operating angles to be equal, but opposite, and be as small as possible, without being zero. Here is a picture that should make it all clear:

https://static1.pt-content.com/images/noimg.gif

What kind of car do you have?

Andrew

my car is a 70 mustang fastback with the ridetech 4 link air bar and coilovers. so now ive read that the angles should not be greater than 2 degrees,what is a good baseline here for angle numbers in setting this up properly? also how do you know what the angles will be under load? i have a 4 post lift at my neighbors which is where we plan to do this one night this week.

[diesel25lrs]

Not sure exactly what you mean by this?
"so now ive read that the angles should not be greater than 2 degrees"


My tail shaft is -3* so i set my pinion to +3*....many cars are over 2*...you should not be more than 1/2* off between the two or it will induce vibration
Under load- means weight of car needs to be on suspension as if it were on the ground- not jacked up & free hanging.
Hope this helps.




Here is the short answer: Under load, you want the front and rear operating angles to be equal, but opposite, and be as small as possible, without being zero. Here is a picture that should make it all clear:

https://static1.pt-content.com/images/noimg.gif

What kind of car do you have?

Andrew

my car is a 70 mustang fastback with the ridetech 4 link air bar and coilovers. so now ive read that the angles should not be greater than 2 degrees,what is a good baseline here for angle numbers in setting this up properly? also how do you know what the angles will be under load? i have a 4 post lift at my neighbors which is where we plan to do this one night this week.

[19,69camaro]

Under load- means weight of car needs to be on suspension as if it were on the ground- not jacked up & free hanging.
Hope this helps.

Im no expert but, under load can also mean under throttle.
Since the rear pinion has the tendancy to try and climb the ring gear, the the input shaft of the differential want to rise when under throttle. You see this with drag racers who set the rear pinion angle a few degrees down to compensate for leaf springs twisting or compliant bushings.

[andrewb70]

By "under load" I meant under throttle. Of course, the car needs to also have the suspension loaded and be at ride height.

Again, the critical angles are the operating angles. You have the measure the angle of the driveshaft and use that as a reference point to determine the front and rear working angles. With a 4 link style suspension and poly or heim joints, there should be minimal pinion climb under throttle. Some experimentation might be needed in the rear to achieve smooth operation under light loads, such as steady highway driving.

Andrew

[diesel25lrs]

Andrew- Not to sharpshoot- but how do you measure pinion angle under driving load?- for my education...

[andrewb70]

Andrew- Not to sharpshoot- but how do you measure pinion angle under driving load?- for my education...

You really can't. One thing that you can do is take one of the many available portable video cameras, like a Go-Pro, mount it under the car and capture video of some hard pulls. This will give you an approximation of how much the pinion moves when under power. The general rule has been that leaf spring cars can have as much as 4-5 degrees movement, while 4 link cars tend to be 2-1 degrees.

Andrew

[exwestracer]

I'm sure there are different opinions, but here's the method I use. Since you have a 4 link, the pinion will pretty much do the same thing every time under a hard launch (unlike a leaf car). You need a way to measure chassis separation (anti squat) to find out where the pinion is under full load. Make a simple travel indicator (2 small grommets on a piece of welding rod works pretty well). If the car squats under launch, you can use the the rubber donuts on the shock shaft as indicators. Launch the car as a hard as possible WITHOUT excessive wheelspin. Measure how far the chassis lifted (or squatted); then remove the coilovers and use a floor jack to set the axle at that "loaded" height. Then adjust pinion angle to match the trans.

[19,69camaro]

Ray thats a great idea. Just curious if you adjust the pinion angles to be equal during hard launches, wouldn't this be different than it would for part throttle?

[exwestracer]

Ray thats a great idea. Just curious if you adjust the pinion angles to be equal during hard launches, wouldn't this be different than it would for part throttle?

Yes, and I believe that gets to Andrew's point. You have to set up for one particular situation, and it would be to have the driveline parallel under the hardest abuse...
:6gears:
even though that probably won't be where it spends most of it's time.

[DRJDVM's '69]

Did you do a search on this topic? Tons of posts.....and quite a few different opinions of some of the details..

My take.....the big thing you are shooting for is havent the working angle (the angle of the driveshaft vs the u-joint) at each end be as small as possible (but not zero) and have them be equal but opposite......

However...in some of these cars its imposible to get equal but opposite and have decent working angles.... the working angle shouldnt exceed about 3 degrees.....so you often have to compromise soemwhere..

In my car, the driveshaft goes up towards the rear of the car....so I'm forced to have my trans down 1.5 degrees and my pinion down 1.5 degrees....this get my working angles decent... this is based on a recommendation form a very knowledgeable suspension shop

If I did the "eqaul but opposite" plan, my working angles would be way to big....

All of these measurments are at ride height, with the suspension loaded in a static car....once you get the angles set, you can usually fine tune it some if the car has issues on acceleration, decelleration etc

[CTSV]

well we adjusted the upper control arms to be identical in length to the ones i replaced and my vibration is worse.

why am i only getting the vibration at exactly 60MPH and above and not at a lower speed?

[andrewb70]

well we adjusted the upper control arms to be identical in length to the ones i replaced and my vibration is worse.

why am i only getting the vibration at exactly 60MPH and above and not at a lower speed?

Because the higher the speed of the drivesaft the mose sensitive it is to working angles. Did you measure anything?

[CTSV]

Because the higher the speed of the driveshaft the more sensitive it is to working angles. Did you measure anything?

well the problem that makes this difficult is my neighbors 4 post backyward buddy lift is not even close to being level on the ground then the ride height from left to right on his lift showed a 1/2 difference so we really could not get a good gauge of the car loaded level and with the suspension at a static height, no matter where we put the digital angle gauge it was giving all different readings. now this is becoming a real pain!!

[exwestracer]

well the problem that makes this difficult is my neighbors 4 post backyward buddy lift is not even close to being level on the ground then the ride height from left to right on his lift showed a 1/2 difference so we really could not get a good gauge of the car loaded level and with the suspension at a static height, no matter where we put the digital angle gauge it was giving all different readings. now this is becoming a real pain!!

Park the car on any surface that you're sure is reasonably level. Make sure the fronts are pointed straight ahead. Run the angle finder along the rocker panel to get a baseline chassis rake. Side to side will be a little tougher, but it's not all that critical for pinion angle. Now when you go back on the lift, you will have a number to add or subtract from the indicated angles to get the pinion and trans relative to the ground.

Also, your angle gauge must be straight up and down (no side angle) when taking readings off the differential and trans. The most accurate way is to pull the driveshaft out and measure the end of the actual trans shaft and pinion flange. If you don't want to pull the driveshaft all the way out, unbolt the rear flange and pull the yoke back a couple of inches. Then take the ruler off of a combination square and put the short side of the frame (where the ruler slides in) against the bottom of the slip yoke. Put your angle finder against the long side of the square frame. To measure the pinion, go off the machined surfaces where the u-joint bolts go through.

[andrewb70]

The angle of the car is totally irrelevant. Remember, the critical angles are the working/operaring angles (I already defined the definition). The working angles don't change with the attitude of the car. They remain constant whether the car is level or standing on the bumper pointing at the moon.

Andrew

[exwestracer]

The angle of the car is totally irrelevant. Remember, the critical angles are the working/operaring angles (I already defined the definition). The working angles don't change with the attitude of the car. They remain constant whether the car is level or standing on the bumper pointing at the moon.

Andrew

True. However, we do have a tendency to relate the angles to the ground ("level") when building or setting up a suspension.

[andrewb70]

True. However, we do have a tendency to relate the angles to the ground ("level") when building or setting up a suspension.

Ray,

Yes, we do have a tendency to do that, and I think that is precisely why so many people get confused when discussing this issue. I am quite sure that you agree with me in that the operating angles are truly what matters and not the angle with reference to the ground.

One approach that I have found people seem to understand is when I tell them that the driveshaft is the main reference point. In other words, whatever the angle of the driveshaft, the output shaft of the transmission and the pinion gear are measured relative to it. Also people tend to forget that the angle of the driveshaft is the same whether it is measure in the rear or in the front. If it is not, then the tube might is bent. This is why it pays to measure and use the driveshaft as a reference point, because it can possibly uncover other problems that can cause a vibration.

Andrew

[MonzaRacer]

On race cars I tune "bite" with pinion angle, leaf springs on drag cars I tend to reach for no more than 4.5* down pinion angle, then tune for track they run at. Also they can swap shims if car lights up and shock compression or tire pressure cant alleviate.
4 links I usually try to run 1.5 to 2.5 or less as needed for actual launch (all cars launch, some need more pinion angle to allow for "wrap")
What I was taught many years ago was to fight to adjust so that at "launch" the "wrap" creates ZERO pinion angle and then as car unloads your runnin g angle comes back.
You also MUST tune angle up or down to dial out vibration, big reason for pinion angle also is do the rollers dont sit in one spot, they need to roll back and forth.
Stock stuff the engineers try to make rollers move for more ujoint longevity. Less angle, less roller movement.
Also if you get too much/hard of pinion UP angle (pinion up/DS down) it will buck and can destroy a rear end also pinion up, drains oil away from pinion bearings.
One of my learning books was How to Make Your Car Handle by Fred Puhn .

[exwestracer]

Andrew, I think a lot of the "racer's" reason for using ground level has to do with mounting the engine and trans at 0deg (level) in purpose built racing cars. Then we just eliminate that whole end of the equation and set pinion angle off of level.

Not disagreeing with you about the potential complications BTW...

[67cougnut]

tagged for reference. thanks everyone who has contributed