Driveshaft Balance Question
 

Since I have my differential disassembled and I wiped off my sharpy alignment marks between shaft and yoke it got me thinking. (mark didn't mean much anyway as the driveshaft spent 40 years in the trunk of the car and I'm sure I didn't mark it 40 years ago.)

I've always heard the driveshaft should go back in in the same orientation to the yoke that it came out. How does that work if a pinion is being changed? Yoke is not going to be in the same location in relation to the pinion.

What exactly is the driveshaft balanced in relation to? Can't be the trans or the pinion as the yoke can slide on/in any relation it wants ... and surely they didn't balance the shaft/yoke/pinion/trans output all at the same time at the factory.

Are they just balanced in relation to the front and rear yoke? Which means they would have to have been balanced dynamically with both universals and yokes in place.

Or is just the shaft itself balanced?

You can have the best in world balance job done to your driveshaft, but if the centering of both the U joint in the trans end yoke and how you bolt up/ center the rear joint in the piñon flange is not within .010” then a good part of the balance job will be canceled out.

A magnet base dial indicator should be used to center the rear joint in the piñon flange if nothing else.

If you balance a wheel and stick it on one corner of the car indexed a certain way on the lug nuts, does that mean if you remove the tire you can't rotate it to another corner of the car? Of course not, the driveshaft is balanced as a seperate entity, it has nothing to do with the other rotating parts in the driveline.It's balanced the same way a tire is, off the car, on a seperate machine. In 50 plus years I've never marked a driveshaft to return it the same orientation. If your servicing both U joints, how in the world are you going to return it to the original orientation?

Over 50 years in the automotive repair field and I have quite a bit of instructional time in Vocational tech, as well as GM service instruction. I have never heard anything about returning a driveshaft to the same location in relation to the pinion flange orientation from any instructor, book, or other instructional aids.

I've pulled hundreds of driveshafts, and never had a vibration problem after returning one back to the car it came from, or even swapping shafts from one car to another. If the shaft is out of balance, or has a runout problem, it will be out of balance in any car it's in.

I'd file that with the prefilling an oil filter during an oil change myth to prevent engine damage upon startup.

:2cents:

Excellent, just the answer I was expecting. Although ... I'm pretty sure when I replaced the universals on my late model truck it wanted the rear of the driveshaft put back in the diff yoke in the same orientation.

Typically I setup the rear universal in the hoops with a dial indicator like this:

https://forums.maxperformanceinc.com...7&d=1692166637

Actually I've seen driveshafts with a lot more runout than .010 that ran as smooth as any shaft new, or old. It isn't always as critical as some people would have you believe it is. A twisted driveshaft that is undetectable is much worse than one that has some runout as when it was built.

One that has the planes off on the U joints. If someone shortens one, and doesn't get the yokes welded on on the same axis front, and rear, you'll have vibrations that come, and go, with harmonics at different RPM.

There's a reason that some of the most expensive cars use a rubber isolated balancer ring on the shaft, or a cardan double U joint on their driveshafts. It all makes a difference. GM has used heavy wall cardboard tubes inside of the tubing in some of the 60s cars to dampen vibration. Ford hangs weights along the transmission sometimes. There is more to it than just balance, and runout.

The 2004-06 GTOs have a two piece shaft, with three joints, and carrier bearing. The aftermarket thought that making a performance driveshaft one piece with two U joints would be a better alternative. When the one piece driveshafts get swapped for the two piece shafts on street driven cars they many times vibrate, even though they are built by topnotch manufacturers, and balanced to perfection. Sometimes even when you have everything as you think it should be, you still get vibrations that seem to have no source to correct.

Over the years I've seen setups that I thought would shake your fillings out of your teeth, that ran fine. I've also seen ones that should run smooth that rattled the steering wheel at speed.

After searching around on the internet, I'm certainly not the only one that has heard the recommendation to use marks and align it the same as it came out. Just can't see how it would matter a bit on a shaft that uses u-bolts on the rear.

Just checked the Haynes manual for my 2011 GMC and it includes marking the shaft and yoke for alignment on reinstallation to "preserve the balance". I know Haynes isn't the bet reference in the world, but I've read it other places too ...

Just checked the 68 Pontiac service manual ... yep it says to mark the shaft and pinion yoke to "retain proper alignment" .. page 4C-1.

Still can't figure out why this would be, either the shaft is running true and is balanced or it's not. Perhaps this is recommended because of corrosion or something on used pinion yokes .. I have no idea.

https://youtu.be/gmV4qwLfOMY

This is an excellent example of driveshaft angles

Far as alignment goes. If there are more than 2 ujoints they need to be aligned. Any time we replace u-joints we mark the shaft so it goes back together the same way. Have not marked alignment to the rear axle yoke though.

After checking the net sources I have seen that they suggest marking the driveshaft to return it to it's original position in the companion flange, but then it contradicts itself by saying all driveshafts are balanced independant of the other driveline components. The main reasoning I gleaned was if it didn't vibrate before removal, it won't vibrate after re-installation, and if runout was correct in the OEM position it wll be the same after installation. If the companion flange is made correctly, and there is no corrosion in the seats of the caps, there should be no change to balance, at least in my reasoning.

I can tell you from experience of never marking one, that the 50/50 chance you get it back in the OEM position. Either I was very lucky, or it really has no effect. Most driveline vibration I've seen are weights falling off, or twisted tubing that puts the joints out of the axis of the other end of the shaft.

I'll return to the original explanation, that a balanced tire/wheel assembly can be removed, and replaced on the same hub in a different position without causing vibrations. It can also be rotated to a different corner of the car without causing a new vibration.

Even when I worked at a Pontiac dealer when we had a balancer that would balance the whole assembly, the hub components, and the wheel/tire assembly on the car, we didn't mark the wheel relationship to the hub. If the wheel got removed for brake inspections, it had a 1 in 5 chance it would go back on in the same position.

I'm guessing that mostly no one checks runout after they R&R a driveshaft, so putting it back in the same relative position is precautionary if you're not going to dial indicate each and every R&R of a driveshaft. Not centering the caps on the companiion flange has caused more than a few new vibrations in my experience. Or a dropped needle bearing inside of the caps is more of a worry in my mind, but I didn't write the book on proper R&R of driveshafts.

I'll probably keep doing what I've been doing that my real world experience has shown me is perfectly fine, and not concern myself with what ifs. If you are concerned it's going to make a difference, by all means mark it.

I'm out on his one.....;)

I agree. Probably some left over habit from days gone by that is no longer necessary. I can't see a reason for it unless something else was wonky with the yoke or shaft.

The "mark it" ship sailed about 40 years ago on my vehicle :)

Excellent question as I changed U-joints on my wife's Sequoia last week and marked the position because I've seen that instruction multiple times. Well, I changed the entire rear end on my GTO a couple of years ago so, I wondered...WTF?

Never thought of that ... all the people that have changed the entire rear end.

At some point in time, for some reason, it became a "thing". Makes me wonder why.

The only driveshafts I`ve ever marked were the split shafts.

Ain`t seen too many of them on our Pontiacs.;)

The wheel balance analogy is somewhat flawed, yes you can reinstall the wheel in a different position on the car since its independently balanced... but marking the driveshaft relation to the yokes when replacing u joints would be like if you had to break the tire bead on the wheel for something like replacing a TPMS sensor... you would want to mark the position of the tire to the wheel so it can be reinstalled in the same position it was originally, in order to not mess up the balance. Thats how i see it anyways.

Granted, if everything was perfectly balanced with the yoke and the new u joints then it wouldnt need to be marked, but apparently the engineers who designed these cars felt the need to mention it to avoid any possible out of balance issues.... i know not all aftermarket parts are made to be perfectly consistent and could be out of balance, not a big deal to take 3 seconds to make a mark on the shaft to yoke(s).

If/when there are new parts installed like trans yoke, or both u joint ends, its a good idea to have the unit checked or rebalanced or keep your fingers crossed the balance is not an issue. But again, not a big deal to mark it.

I'm one of the engineers that designed these cars (well - trucks, anyway).

The shaft was balanced independently, so it doesn't make any difference from a balance standpoint.

There was a movement to "system balance" the shaft with the rear axle in later years, like with the '85 and up M/L Astro vans. The large cabin volume made them super sensitive to imbalance and "booms" (low frequency responses) and so it was considered to be worth the effort. Parts were packaged up and sent to Balance Engineering (aka DynoTech) in Troy Michigan, where they were balanced as a unit, marked, disassembled, and shipped to Baltimore as a set. It was abandoned when they went out of style. (Vans and Suburbans were really sensitive to all kinds of disturbances).

One other consideration would be "pinion companion flange runout"; that is - if the pinion flange is not running true then it will whip the driveline around like a jump rope. There is an existing Kent-Moore tool to check for this.
Not really an imbalance issue, but it will generate a first order disturbance just like an imbalance. If a guy was lucky (I never am) and any residual imbalance in the shaft was offset by the runout, then you would want to put that setup back like it was. That's about the only situation I can think of where it would make sense (other than a system balanced driveline, which these were not).

K

It is an excellent video - but it is a distinctly different topic.

Driveline angles generate a second order disturbance (ie, two "kicks" per rev); Shaft imbalance is a first order disturbance (ie, one "kick" per rev).

Different problem, different feel and different solution set, even though it is generated by the same part.

K

Incidentally, that's when the ID stripes were added.

After the shaft was balanced, but before it was removed from the machine, the operator would grab his paint brush and spin the shaft by hand, slopping the various colors onto the tube in order to identify its intended usage (ie, manual vs auto, etc).

http://www.wallaceracing.com/drive-shaft-colorbands.htm

K

My comment was regarding when the "balanced independently" shaft is taken apart to add new aftermarket parts of varying quality/balance, doing that can & many time will change the independent balance of the shaft. Just like changing the location of a tire on a wheel will change its original balance.

The engineers of these cars mention/suggest marking the shaft when changing parts or position of the shaft starting in the 60's and through the 70s & 80s from what Ive seen in manuals, one member said its in the 68 pontiac manual as well as 2011 GMC truck manual. When or why that changed or if its needed for other vehicles I dont know, just saying that the engineers of many vehicles felt the need to mention marking the shaft, and many mechanics/shops do it too.

What I also find a bit strange is that they often only specify marking the rear of the shaft in relation to the pinion yoke and nothing about the front.

Still hard to figure out why when the shafts were not balanced in relation to the pinion yoke to begin with (on the vast majority of vehicles).

I have a feeling it had to do with other concerns like corrosion on the yoke creating a "pocket" for the universal ears or something like that. Bear in mind these recommendations assumed a certain amount of wear or aging on the parts, who knows how the driveshaft balance might affect the pinion after 50K miles.

I'm still confused :)