How To: Driveline Angles 101

I've noticed many people asking about the proper way to set driveline angles, especially the pinion angle, so I thought I would write up a tech article to address the basics. You could write a book on this subject if you addressed all the geometry, physics, etc., so please accept this as just a general guideline.

The principle goal of setting proper driveline angles is to have the u-joint angle at the transmission (or transfer case), and the u-joint angle at the pinion yoke as close to zero as possible under normal operating load conditions. What does that mean in English? You want the transmission, driveshaft, and pinion to be in as straight of a line as possible while you're driving normally.

Now that we understand the goal, let's quickly talk about a key consideration to keep in mind when setting the pinion angle: how the suspension reacts under different loads. When you accelerate, the rear of the vehicle sinks down, right? Right. It's important to know that the rear suspension compression causes the pinion angle to point up. The more suspension compression there is, the more the pinion will point up. Now, when you decelerate, the rear of the vehicle raises up, right? Right. As you may have guessed, the rear suspension extension causes the pinion angle to point down. Again, the more suspension extension there is, the more the pinion will point down. When you are just driving around normally, the rear suspension will compress just a bit, hence why you want the pinion to point slightly down when parked. The compression of the suspension under regular driving conditions is your normal operating load. How much your suspension compresses and extends defines the working driveline angle range. This can be extremely important to keep in mind if the vehicle is airbagged. We will take a look at this further into the article (see Step *5).


1.) The first step to setting the proper driveline angle is to as align the transmission tailhousing with the pinion. When looking down the tail of the transmission at the pinion yoke, you want the tail to be as vertically and horizontally centered with the pinion yoke as possible. Most of the time, adjusting the transmission is not possible, it simply is where it is. The transmission tailhousing being vertically, horizontally, or both, out of centered alignment with the pinion yoke is often just a reality, and is typically not an issue for 15 degrees or less of misalignment, which is almost always the case for street rods. So you are likely ready to move on to Step 2. However, if you are rebuilding your rod, swapping in a new motor and/or transmission, or making modifications to the transmission crossmember, be sure to align the transmission tailhousing with the pinion. Here is a picture of how a properly centered drive shaft should appear, looking from the rear pinion towards the transmission tailhousing (click on thumbnails for larger image).



Notice in the picture the transmission tailhousing / slip yoke sits at ~ -3 degrees:




2.) Now use an angle finder to measure the angle of the driveshaft. Notice in the picture the driveshaft sits at 0 degrees.



3.) Now use an angle finder to measure the angle of the pinion yoke. The best way to measure this to turn the yoke until one of the flat yoke facets faces the ground, and then place the angle finder on that flat surface. Notice in the picture the rear pinion yoke sits at ~ +3 degrees.



4.) Now for a bit of math. We know in this particular example the driveshaft sits at 0 degrees, and the rear pinion angle is ~ +3 degrees. Now, when parked, the rear pinion angle ideally should point slightly down. Why? Remember that bit about normal operating load, how the rear suspension compresses just a bit under normal driving conditions, and that causes the pinion angle to tip up? Well, now is the time to apply that bit of knowledge. A very general guideline is that the normal operating load will cause the pinion angle to tip up by ~ +2 degrees. So how do we figure out how to set the proper pinion angle for this particular application? Like this:

Pinion Angle = Drive Shaft Angle - (Pinion Yoke Angle + Operating Load Angle)
PA = 0 - (4+2)
PA = 0 - 6
PA = -6 degrees

What does that mean in English? It means that you will need a 6 degree shim if you have a leaf spring suspension, or you will need to adjust your upper control arms to achieve a 6 degree pinion correction if you have a triangulated or parallel 4-link. This 6 degree adjustment will cause the pinion angle to point down 2 degrees, which will thus put the pinion and driveshaft in perfect alignment (0 degrees) under normal driving conditions. There, wasn't that simple *lol*?

*5.) Now what about vehicles with air bags? Let’s use my '59 as an example since I am running air shocks on it. Its parked height is as low as it will go, which is to say that the suspension is as compressed as much as possible. My air shocks have a 4" stroke, with 2" of extension being driving height (the extra 2" of stroke to maybe clear a speed bump). That's all fine and great, but what does it mean for the driveline angles? It means that raising the suspension 2" will result in ~ +3 degrees of change in the angle between the transmission tailhousing and driveshaft, and ~ -3 degrees of change in the angle between the driveshaft and pinion yoke. Remember how my transmission tailhousing sits at ~ -3 degrees, and my pinion angle sits at ~ +3 degrees? That means that at ride height, under normal driving conditions, the transmission, driveshaft, and pinion will all be in alignment, and the driveline angles will be 0 degrees. Cool.


Hopefully this was informative as a general guide. Cheers.

 

Dude, if you're gonna write TECH make it accurate. The goal is NOT to keep "everything in line" - in actuality you want the rear end and trans in line - preferably you want the driveshaft at a slighlty different angle. Stated another way - you want the working angle bwteen the trans and driveshatf to be the same as the working angle between the driveshaft and the rear end. Having the driveshaft at a slightly different angle is a GOOD thing - it keeps the rollers in the ujoint lubricated. If everything was inline the ujoints don't "work" and fail prematurely. I didn't read past that part........

 

Could of saved lots of time by just cutting and pasting this:

http://www.vibratesoftware.com/html_help/html/Diagnosis/Propshaft/Propshaft_Angles.htm

Better. Accurate. More comprehensive. Less static.

-Bigchief.

 

well, i think its for real...i mean, shit,,, he is from THERE!!! those folks never lie!

nice wagon though....where you from 59 ford....lets all get to know ya!!!

 

I didn't read anything past "You want the transmission, driveshaft, and pinion to be in as straight of a line as possible while you're driving normally" because TECHNICALLY that's not correct.

If ya' were writing a research paper for me in Automotive Class 101, ya' just flunked.

U-joints are designed to work at a slight angle.

I'll teach ya' how to do the angles on a three (3) piece driveshaft after ya' get the one piece shaft correct.

AND ...... I almost forgot. Your part about adding the shim is also bullshit. When ya' put the shim in ya' don't just change the angle of the rear u-joint. It also changes the front angle at the same time to a different angle. So, your math is also in error. That's OK ya' can learn the correct way when you're repeating the class next semester.

 

This is also how I understand it. I just can't find the site address where I read it. A further detail of how I understand the way to keep it "out of line" is that the trans and pinion must NOT point AT each other. The article said you must get the rear of the trans square to the floor and the pinion also square to the floor but they must be at different heights so that when you draw a line through each paralel to the ground, those lines must be at different heights. That's the GOOD thing HemiRambler mentioned as it keeps the U-joints "working" and not sitting idle.

Further to this I also understand that through the suspension travel you're supposed to try and keep this configuration. Is that correct?

 

ha ha i love this place.
its harsh as fuck.thats why its good.
sure theres a bit of "Not the whole truth" going on there..but goddamn at least hes TRYING to make a contribution.

 

We understand that BUT when writing a Tech artcile with incorrect facts, guys that don't know any better will take it as gospel. Those guys then build an incorrect setup that's full of vibrations and which causes premature u-joint failures. They then have to go through a whole bunch of trouble to troubleshoot and rectify the problem.

I really do love his body channeling tech thread though.

 

Not trying to be harsh - just accurate. If one wanted to be harsh one could even put my comment under the microscope - matter of fact I'll do it myself. previously I wrote about keepign trans/rear inline. Depending on how one interprets that it too could be misleading - the better way to state it would be to say that you want to keep the trans and rear axle parallel.
The way I was taught driveline setup was to remember THREE basic key factors. Balance, Phase, Complimentary Ujoint angles. Beyong that the biggest consideration is maintaining a decent working angle (not too big) that angle is in part based on driveshaft speed.

Granted there's alot more to be said. Misinformation helps no one.

Last month I was convinced that teh adjustable proportioning valves worked one way when in reality I had it all backwards. At least I stood up and admitted it.

To the origional poster - I'll give you an A for effort. But .....

 

so i guess the question is, how many people here have had u-joints go out on them??

 

Probably not many.

Maybe a better question would be: How many have had a drivetrain vibration that was cured by correcting U-joint operating angles?

 

Not to be the weenie.... there 'is' some good stuff in the original post though. This is one point that's missed by a lot of people:

"...hence why you want the pinion to point slightly down when parked. ""

In my Jeep-building circles (I also have a Jeep with a SOA on 35's.) rear driveshafts are typically angled to the max in an attempt to lift the suspension as much as possible. UNDER LOAD, the driveline angles need to match. On a vehicle with leaf springs in the rear, the angle of the rear axle can change quite a bit when it's under load, assuming it doesn't have an anti-wrap bar. And under load, it will rotate upwards. Hence the desire to have it point down a degree or 2 at rest, with respect to the angle of the trans output. On a 4-link type rear (i.e., something held more rigid) this may not be as great of an issue.


Just my $0.02.
Pete

 

Is there any truth to this part of his post?

"The transmission tailhousing being vertically, horizontally, or both, out of centered alignment with the pinion yoke is often just a reality, and is typically not an issue for 15 degrees or less of misalignment, which is almost always the case for street rods."

 

There may in fact be tons of good info in the first post, but when an error is discovered then MAN UP and correct it. Placing the trans, driveshaft and rear all INLINE is the WRONG way to set this up. Plain and simple. Will it work?? Yes it will, but it will also come to have issues - if THAT was adressed then I personally would find it as an acceptable TECH. But mis-information is simply that.
Personally I have posted incorrect info before -(which I hate to do) when I realize it I go back and correct it. No harm no foul!!! What's the big deal?

 

15 degrees is a BUNCH for a Ujoint’s working angle. I think most fellas shoot for the 5 – 7 degrees range as a max value. Could you get 15 degrees to work?? I’m sure those 4x4 guys do, but I’m equally sure they’ll be the first to admit their pushing the limits. A “problem” with too large a working angle is that the driveshaft speed variation is also increased. At 5 degrees the speed error is about 1/3 of a percent. At 15 degrees the speed error about 3-1/2 percent. And while those numbers might not mean anything to you – what you should notice is that the error is going up disproportionally. In a nutshell: as the working angle increases shit goes to hell in a hurry. Also if you stay close to the manufacturer’s recommended working angle’s you will be rewarded with an efficient design – forgiving of small errors and it will last a long time. Ignore good practice and you will be equally rewarded. Of course there are always exceptions to every rule – if you feel lucky then go for it.
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And to comment to a couple of the other posters. Have I had a Ujoint fail early due to lack of working angle ? Yes I have.
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Have I fixed a vibration problem by changing the rear axle angle?? Yes I have – as have countless others.
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Guys what were’ talking about here is known as “Good Practice” - IMHO a well written Tech article would cover good practice and then get into “pushing ones’ luck. Why have people believe 15 degrees is fine for a working angle when it’s really way out there on the edge??? I don’t get it.

 

Ryan warns you when you join this deal that folks don't take much crap on this board. I agree that's good. Heck most everything I know was learned by do'in it wrong the first time.

"Experience is what ya' get from not havin' it when you needed it."

 

Most manufacturers run 2-3 degrees negative angle in the rear yoke because it will rotate up under load into about a zero degree difference. On leaf spring cars that are used for drag racing, you should increase this to 5-7 degrees because of the increased spring deflection will let the pinion rotate more.

Any more is hard on u-joints. I would consider 15 degrees to be the MAX by far, and I prefer less than 5 degrees. You can get funny virbration problems otherwise.

We are chasing a 65mph vibration in a t-bird that has the pinion at 5 degrees negative (angle of the u-joints) vertical and 12 degrees horizontal. The 12 degrees seems to be the issue, as we move the axle closer to center which reducesthe u-joint angle, the vibration lessens. It was really bad when we were at 18 degrees and killed the u-joints, pinion bearing, and slip yoke bushing in the trans. Unfortunately the rear suspension is out of wack on this car and we are ladder barring it to get everything straight and true.

 

I don't disagree with you Hemi --- there was incorrect info in the first post. Ideally everything should not be 'in-line' as was stated. A few degrees is usually desired for the ujoints to get lubed properly.

My only comment was that the point about pointing the pinion a degree or two down with respect to the tranny angle is a good one -- the rear will flex up under load.

If anyone wants a little primer on ujoints, and geometry, how they are not a constant velocity item, etc., go visit Tom Woods driveline. Tom is a drivehsaft builder for the 4x4 crowd and has some good tech.

http://www.4xshaft.com/index.html

Pete

 

Now I'm laughing my ass off....

one of his replies to a question on the same post on OSR...

I don't want to get too far into the intricate details of this topic because every application is different. And with that being said, what is correct becomes relative to the application. I also hate playing the who's right and wrong game. But in this case, I stand by the information in this article as being accurate.

Secondly, not to ruffle any feathers, but I want to address why it is never correct to have the pinion angle set to the same angle as the transmission tailhousing. For very low vehicles, like my '59, the transmission tailhousing angle and the pinion angle may very well indeed be the same. However, the pinion angle should always be set relative to the driveshaft angle, and here's why. The more suspension lift there is on a vehicle, the further the vertical distance between the output yoke of the transmission and the pinion yoke becomes, resulting in greater and greater u-joint angles.

Remember that the goal of a properly set driveline is to have the transmission, driveshaft, and pinion in as much of a straight line as possible. If you have a lifted vehicle, there are only so many things you can do to try to align the transmission tailhousing with the pinion yoke (e.g. taller motor mounts, transmission crossmember drop), and there is a very finite limit to how much you can adjust things. Even after such alterations, more often than not, there is still a significant u-joint angle at the transmission yoke (this is especially exacerbated if you have a short wheel-base vehicle). This can result in driveline vibrations, and often requires a double cardan (CV) joint at the transmission yoke. So it stands to reason that if you have a severe u-joint angle at the transmission yoke, and you set the pinion angle to match the transmission tailhousing, then you are going to have a severe angle at the pinion yoke. That's why you set the pinion angle relative to the driveshaft angle, and NOT the transmission tailhousing angle. Make sense?

Here is a graphic to help explain things (please excuse how lame it is). Cheers.

And the associated image...

 

man, i hate to defend the newbie, but he is sort of correct on this part...if you are building a lifted 4x4! this is exactly how short wheelbase 4x4s are setup.

 

Pete1930, I didn't take your post that way- much to the contrary I fully agree with your point about axle wrap up. It's often overlooked or intentionally ignorred. Some people get away with it - some don't. Matter of fact I just went back and reread your post about your 4x4 experiences. Won't argue with any of it!!!!

Guys - I work in a Engineeing environment - as a result we speak plainly - something's wrong and we state it that way. I've disagreed with others (and been proven wrong) and learned something in the mix. That's why I am here - and I sorta figured that's why most of us are. Gonna write a TECH article - don't get your feathers ruffled if someone takes issue with it - either stand up and take your medicine OR defend your point because you KNOW it's right.
Not everything is always cut and dry , but it sure is interesting!

 

Okay ... another Newbie guy here. I just read the entire thread and my eyes are bleeding from shaking my head.

Can I build my rod with everything intact ( approximate angles) an then give it to an alignment shop to clean up or fine tune?

 

He is wrong in his use of the word "never" in there... I've always been taught to try and keep the angles the same, it cancels out vibration, especially at high speed, which probably isn't a 4x4 problem. This comes from classes, books, old dudes, just about everwhere.

It's always set up the tailshaft and pinion on parellel planes. Match the u-joint angles... Now there may be soem deviations from this but for a regular car this is the norm/rule/m.o.

 

you are right about the use of absolute terms. i was commenting on his whole answer.

i guess the real question is why is this guy trying to post every tidbit of tech he's ever read, whether it relates to our hot rods or not. who is he trying to impress? cause it sure isn't making him look all that smart.

like mom said, better to keep your mouth shut and have people think you're an idiot, than to speak up and remove any doubt.

 

What about this easy to understand explanation

 

i think he might be the guy that built this


seems like a whole lot of superfluous and erronious information when one sentence can sum it up

if you keep the angles close to equal and opposite, itll work fine...that vibration you feel is probably those wobbly ass wheels u got cheap for your RAT anyways

 

Who cares? The guy probably stole this write up from another site just like his turbo writeup.

LINK TO "HIS" 'WRITEUP'


LINK TO THE ORIGINAL PLACE WHERE HE GOT A MAJORITY OF HIS INFO AND JUST CHANGED A FEW WORDS....

I'm not all about bashing newbies, but this guys a fucking joke.

 

Shit I just wasted about 10 minutes readin that. Can we put a disclaimer on top of his 30 tech posts of the last 2 days "May or may not know what he's talking about." Good thing I scrolled down a bit or else I woulda been screwed. I always though you wanted the angles roughly the same, thought this guy was a little bullshitty.

 

I'm running a 4 rod trianglulated an coil over set up on a Maverick rear end ( the rear end is offset). How does this change the whole angle thing?

 

The drawing in ZMAN's post showing a large angle at the transmission and the pinion at zero degrees to the driveshaft is correct only if you have a CV joint at the transmission output - as on a '70s Bronco, for example. Otherwise you generally want the trans output and pinion angles relative to the driveshaft to be complementary (subject to the compensations shown in ORNs drawings).
HEMI mentioned that the greater the angle, the greater the speed variation in the driveshaft. True, but that variation (trans output to driveshaft) is cancelled by the driveshaft to pinion universal. (But I don't mean to suggest that large angles are OK.)