Thread: Driveline Angle

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My initial search was too broad and came back with no help so I posted a basic question about ideal angle. Then I found a thread that had all the answers http://www.clubhotrod.com/forums/sho...riveline+angle - sorry for the bother.

OK, I still have a question. Is a six degree uptilt, matching the transmission down tilt any concern for coilovers on a four link? I can raise the transmission mount with a spacer to reduce angles, but I'm looking at cutting the hump and doing some fiberglass work - not a big concern.

If---- the car isn't complete---mount the engine /trans so the crank/trans output point direc tly to the pinion---keeping the drive line angle as close to zero as you can--then on high horse power cars turn the pinion down 1-2 degrees so it will run straight under power.

Also be very careful about having normal amount of weight in the car(drivr/pax)

Now, i have a different theory on this all together because of my backgorund. I race dirt late models, the tranny is set at zero degrees, the pinion is 7-8 degrees down at ride height, and they are NOT aligned at all height wise, probably a 2-3 inch drop. Now under power with the bird cages on a full floating rear end, they by theory align the pinion and trans to the correct angle and all that, but, anyone ever seen how much these rear ends move? If the rear end was already lower by 2-3 inches and it drops even MORE its never lined up. All this perfect angle stuff sounds like BS. Those rear ends move 4-5 inches side to side, and a foot or more up and down, and 4-5 inches FORWARD, theres no way the pinion and trans angles are EVER the same or in line, and we NEVER have any problems. Get it close, set them the same angles (Pinion up and Trans down) at ride height, get it centered, and don't worry about it. I am assuming with Coil overs that you are running a 4-link? Darn near impossible for pinion angle to change. If you plant the tires hard, the whole car should raise, thus ruining your alignment both height ways and side to side (assuming 4-link and panhard bar) anyways, but it would rotate the pinion up if anything, so if you are at 6 degrees down on the trans, go with 4 degrees up on the Pinion. Planting 800+ HP we aren't having problems, use quality parts (especially good U-Joints) and you won't have any problems. Obviously different vehicles, and yours will have no where near the movement and changes, but if that can survive and function, your set up will too. Look at a IRS set up, those are short drive shafts essentially, they see way more change than your drive shaft will and they function with out problems.

Floating bird cages, panard bars, circle track are a whole different animal-----

Originally Posted by jerry clayton

Floating bird cages, panard bars, circle track are a whole different animal-----

True, different animal, but still a drive shaft with 2 u-joints. My point is that if it holds up under those circumstances, we have LOTS less movement/variables to worry about on these cars, should be a piece of cake comparatively. It's nothing near the rocket science that people try to make of it. There are a few "don'ts" stay away from those, stick to the basic theory of (as close as you can get it to) opposite but equal angles at pinion and trans and it'll all be fine.

I agree that the dirt track input is really not applicable, but I can't refute that it probably defines an extreme - maybe not one that has any bearing, but an extreme. My chassis is complete with the driveline and suspension details fixed - triangulated 4 link with coil-overs. I have the option of adding a spacer to the transmission mount to flatten it out a bit from the six degree drop that it has now. I have already done some minor clearance surgery on the glass tunnel, and doing a three or four degree lift (to get to the 2-3 degree range) would mean some more involved major surgery - not a big deal with glass, but is it necessary?? That would, of course, increase the driveline operating angle, which is not necessarily good. I have yet to find any written direction that defines some ideal driveline angle, only very clear and specific guidelines that the transmission and differential angles need to be equal and opposite, and further that the operating angle (angle of the driveshaft due to the differences in elevation of the transmission yoke and the differential yoke) is ideally three degrees or less, but not zero, and that if it is more than three degrees it must be less than the limits of your U-joints. Look at some of the Jeep and lifted 4x4's to define extreme. If I am wrong here I welcome guidance with specific references to back up what is wrong.

I think that I will unhook the transmission mount nuts and jack up the tranny to see how much I can decrease the angle without more tunnel surgery. For the tranny I'm OK with a pretty small clearance since it's triangulated and does not lift much with any engine roll. Then I'll go ahead and pull the body, and make necessary mods to the tranny mount while it is accessible. If some additional clearance work is warranted, so be it.

I don't worry a lot about driveshaft angle on a street car anymore...as long as there is some and it's not excessive the driveshaft seems to work just fine. For racing, yeah I get all carried away and try to optimize everything.

With a triangulated 4 bar in a 5 speed car, I usually just shoot for 2 or 3 degrees pinion down and drive it. As long as the tailshaft and pinion yoke aren't perfectly in line at ride height, and it's a good driveshaft with quality U-Joints and well balance things work out just fine...

Originally Posted by Dave Severson

I don't worry a lot about driveshaft angle on a street car anymore...as long as there is some and it's not excessive the driveshaft seems to work just fine. For racing, yeah I get all carried away and try to optimize everything.

With a triangulated 4 bar in a 5 speed car, I usually just shoot for 2 or 3 degrees pinion down and drive it. As long as the tailshaft and pinion yoke aren't perfectly in line at ride height, and it's a good driveshaft with quality U-Joints and well balance things work out just fine...

Dave,
I assume you mean 2 or 3 degrees less tilt than the transmission, meaning if one has six degrees down on the transmission, 3 to 4 degrees up on the pinion is your ballpark? Why would you want a differential and not match the angles?

Just don't really see any reason to get all fussy about matching the angles... Too many launches with a 0 degree tranny and 3 degree down pinion, and that's with slicks and big horsepower. Seems if it's a good driveshaft and joints it will work just fine within about 5 degrees or less.

I know all the "science" and "theory" behind it, and even understand what all the engineer's are talking about. Just haven't seen a lot of problems in application. Our
Comet drag car, for example. The engine sits level at launch, which leaves the trans angle a couple degrees down...The pinion angle is set a 3 degrees down. The car was built 10 years ago, gets about 100 passes a summer, new U-joints every winter, and has never had a failure or a vibration in the driveshaft...Everyone will tell you those angles are all wrong, but it works just fine!!! Look at some of the oddball angles on 4 wheel drive stuff, and they survive...

Maybe all the angles is more important on light duty parts, but I sure haven't seen any problematic failures with angles being not exactly right when quality parts are used... Heck, our old Late Model had 9" of travel on the rear suspension, think how "incorrect" those angles got, and again never a failure???

Maybe I'm just lucky?

Originally Posted by Dave Severson

Just don't really see any reason to get all fussy about matching the angles... Too many launches with a 0 degree tranny and 3 degree down pinion, and that's with slicks and big horsepower. Seems if it's a good driveshaft and joints it will work just fine within about 5 degrees or less.

I know all the "science" and "theory" behind it, and even understand what all the engineer's are talking about. Just haven't seen a lot of problems in application. Our
Comet drag car, for example. The engine sits level at launch, which leaves the trans angle a couple degrees down...The pinion angle is set a 3 degrees down. The car was built 10 years ago, gets about 100 passes a summer, new U-joints every winter, and has never had a failure or a vibration in the driveshaft...Everyone will tell you those angles are all wrong, but it works just fine!!! Look at some of the oddball angles on 4 wheel drive stuff, and they survive...

Maybe all the angles is more important on light duty parts, but I sure haven't seen any problematic failures with angles being not exactly right when quality parts are used... Heck, our old Late Model had 9" of travel on the rear suspension, think how "incorrect" those angles got, and again never a failure???

Maybe I'm just lucky?

Completely agree! this is what i tried to say earlier, figured i would get blasted for it, but i know what i am talking about, i'm one of those engineers that knows and understands the theory behind it too. No reason to fuss over it, i've never had a failure in the dirt late model either and there's no way that thing is ever any where near "correct". Use good parts, and you have no worries, quality U-joints/drive shaft are cheap insurance when you look at the cost of the damage it could cause if it comes apart.

Dave and TooFast,
I would make a guess that in either of the applications cited you would never even realize that there is a driveline harmonic Launching for a 1/4 mile pass and banging gears, or tearing around the dirt oval with angles going everywhere are about as far away from a steady state cruise down the interstate as one can get, and I believe that is where the harmonic vibrations come into play. Sure, I want the thing to hook up on an occasional launch, but I'm much more concerned with a smooth ride on the street and highway, plus long term reliability - changing u-joints in the AutoZone parking lot on a car sitting 4 or 5 inches off the ground, chasing a driveline shake is not a good trip highlight! Your racing applications point out that the setup is not going to break u-joints, and I agree 100%. This is a street/cruise question to me, and one where the high speed NASCAR experience on asphalt may provide some insights, but drags and dirt tracking are probably not really relevant. Just my opinion, and I may be wrong. Thanks for the input, anyway. Everything goes into the decision hopper.

My only point was, that if the angles are a bit off and will stand up to that sort of abuse, the angles being a few degrees off in a street car it should live forever. As for the driveline harmonics, never have had them come in to play. The countering angles on the two ends of the shaft will match in a perfect situation, however I've built many street cars that are a degree or two from perfect and never had a problem with harmonics or anything else. Oh yeah, and going through the traps at 150+ mph will bring in any harmonic or other imbalances that are present in the car...

This conversation is discussing angles in the vertical plane. What about the offset we create in the horizontal plane when we center the pumpkin, which offsets the pinion a bunch? Also, doesn't the triangulated 4-link cause the pinion to drop down at the u-joint end during the majority of the travel in both compression and rebound? I don't think we can set these angles where we can expect no vibration. Just hope for something that we can tolerate. And driveline vibration can drive a guy nuts trying to correct! So many variables to deal with from engine balance, torque converter, etc. right on back. If Roger can modify tunnel for later adjustments, that would help in case he does have a vibration to deal with.

I would like to make a few points to maybe make this dicussion come to a reasonable point.

And please keep in mind the following----

100 passes down a dragstrip = 25 miles with u joints replaced annually
at 150 mph the driveshaft may be turning more rpm than on the street but even with the gear/big tires the number of revolutions per mile will be close to same on street
remember that a 10,000rpm engine only turns 1000 revolutions in a 6 second pass
the zero tranny/3 down differential will run straight under power

Dirt track---those bird cage rears have to have the rear housing mounter with arms/arms with springs/arms with coil overs/etc/etc/etc---and the length of those arms usually will be the same as the length of the drive shaft or in other words the front will be mounted at the trans output distance
The dirt track doesn't spend any time in a certain alignment with anything---it more or less is just contained in an area of aprox one foot circle for the rear joint

It is true that when you center the pumpkin under the rear that the driveshaft will be offset unless you move the engine or angle to rear to the right

I worked as an engineer for 17 years
I was involved with drag racing pro stockers, fuel funny cars and top fuelers
I was involved with dirt stockers that had all of this dirt track stuff
I was involved with stock block Indy cars ( 1980s)

If your drive line isn't within acceptable limits you will---kill U-joints,engine harmonic dampners, and occasionally maybe even break crankshafts

A good test for driveability vibrations---look in your rear view mirror--if the view is shaking, you have a problem

And I don't think that I said anywhere that I know what I'm talking about