Driveshaft and Half Shaft Weights

[Rick R.]

I bought a new driveshaft and half shafts through Zip Corvette. They seem to be of high quality, but there are no external balancing weights on them. I don't know who their vendor is and the sales kid is no mechanic. I've never seen a shaft on any type of car that didn't have a weight on it, but I don't work on/pay attention to the new stuff ( meaning anything newer than 40 years old, lol.) I've had several custom drive shafts built for me over the years for drag cars or street rods. My question is: Is the technology now such that shafts can be built true enough that no external weights are required, or did I get shafted? A google search on this subject was shall we say, "inconclusive." Obviously, I can haul them 60 miles to the nearest drive shaft shop and have them checked, but I would like to learn a little more first. Judging points are a separate issue. Thanks.

Rick

[David B.]

Re: Driveshaft and Half Shaft Weights

I think your concern is a valid one. Chevrolet lists at least 5 different weights that are welded on "as required" . For a driveshaft, prints state: "Paint no. 248-0679 yellow or equiv. opt 248-59863 light green or equiv. marking to be at rear of tube next to nearest exposed trunion and as close as possible to light side at rear of assembly when balanced" Further instructions noted: "max. run out of assy. at points A,B,&C to be .010 TIR Assembly must be within 3/16 in. oz. dynamic balance at front end and .10 in. oz. at rear end when tested at 3500 RPM." Further notes are listed but you get the idea. Without looking at half-shaft specs. I would venture a guess they would have similar specs. Maybe new technology no longer requires this method to balance but I would be leery.

[Gene M.]

Re: Driveshaft and Half Shaft Weights

It is easy enough to find out.........have the driveshaft house check them out for balance, true, and straight.......why guess.

[Gary B.]

Re: Driveshaft and Half Shaft Weights

... Without looking at half-shaft specs. I would venture a guess they would have similar specs. Maybe new technology no longer requires this method to balance but I would be leery.

David,

I have never seen a half-shaft that had balance weights, which makes me think there was a runout and balance tolerance included as part of the basic manufacturing process and not done via added weights.

Gary

[Michael W.]

Re: Driveshaft and Half Shaft Weights

Half shafts don't have balance weights, one main reason being that they only turn at wheel speed and not transmission output speed.

[Rick R.]

Re: Driveshaft and Half Shaft Weights

It is easy enough to find out.........have the driveshaft house check them out for balance, true, and straight.......why guess.

Because maybe I'll spend more money having a drive shaft shop screw up something that aint broke to begin with. Like I said - trying to learn more about the manufacturing.

[Joe R.]

[Gary B.]

Re: Driveshaft and Half Shaft Weights

JR,

Even if no weights were used, I have to think there was some rotational balance spec that the supplier to GM was required to meet.

Gary

[Richard G.]

Re: Driveshaft and Half Shaft Weights

Because of the driveshaft speed and length it should be balanced. The half-shafts don't really require them (per GM's on specs) because they are short and run typically at 1/3 the speed of the driveshaft. The unbalance is not a liner force but is exponential so this is a big difference in forces.
Back to the drive shaft, their is a run-out specification and a balance specification. Hitting both these specifications is almost impossible without weights. Some shops send a spec sheet with the shaft.
The residual run-out is often dealt with by heating and spot cooling the shaft to get it withing specifications. This is after the shaft is built and typically when it is installed in the balancer as it saves a step. The shaft balance also accounts for any residual unbalance left from the small amount of run-out that has to still be there. Could they hit this specification on a random basis, sure. Is it likely, no. I would have the balance and run-out checked at the nearest drive-line shop. Let us know what they find. A shaft balance it typically not that expensive. Document it and possibly you can negotiate an reimbursement from the manufacture. This is the exact same stuff I dealt with when I worked as a Vibration Analyst for 21 years.
Rick

[Rick R.]

Re: Driveshaft and Half Shaft Weights

Because of the driveshaft speed and length it should be balanced. The half-shafts don't really require them (per GM's on specs) because they are short and run typically at 1/3 the speed of the driveshaft. The unbalance is not a liner force but is exponential so this is a big difference in forces.
Back to the drive shaft, their is a run-out specification and a balance specification. Hitting both these specifications is almost impossible without weights. Some shops send a spec sheet with the shaft.
The residual run-out is often dealt with by heating and spot cooling the shaft to get it withing specifications. This is after the shaft is built and typically when it is installed in the balancer as it saves a step. The shaft balance also accounts for any residual unbalance left from the small amount of run-out that has to still be there. Could they hit this specification on a random basis, sure. Is it likely, no. I would have the balance and run-out checked at the nearest drive-line shop. Let us know what they find. A shaft balance it typically not that expensive. Document it and possibly you can negotiate an reimbursement from the manufacture. This is the exact same stuff I dealt with when I worked as a Vibration Analyst for 21 years.
Rick

Richard, thank you for taking time to share your obvious expertise in this area. Very informative. It will be some time before I get to it, but I will have it checked and report the findings.

Rick.

[Gene M.]

Re: Driveshaft and Half Shaft Weights

Because maybe I'll spend more money having a drive shaft shop screw up something that aint broke to begin with. Like I said - trying to learn more about the manufacturing.

You stated “I've had several custom drive shafts built for me over the years for drag cars or street rods. My question is: Is the technology now such that shafts can be built true enough that no external weights are required, or did I get shafted? A google search on this subject was shall we say, "inconclusive."

Well, did they screw up those drive shafts? Your response in post #10 was acceptance of advise already given much more wordy but same, and you previously rejected it. What better place for enlightenment than where the task is performed? Go figure.

[Joe L.]

Re: Driveshaft and Half Shaft Weights

Richard, thank you for taking time to share your obvious expertise in this area. Very informative. It will be some time before I get to it, but I will have it checked and report the findings.

Rick.

Rick------


The driveshafts were originally balanced as an assembly with u-joints installed. That's why when u-joints are replaced the existing weights are "meaningless". I recommend having the u-joints installed by a competent driveline shop and have that shop subsequently balance the assembly.

[Ron G.]

Re: Driveshaft and Half Shaft Weights

Driveshafts have always been balanced from the factory, but I have never seen balance weights to balance the half shafts.

[Guest]

Re: Driveshaft and Half Shaft Weights

Half shafts were all balance with weights at the factory, always been

[Ron G.]