Should I rebalance my driveshaft

[Michael L.]

Guys,

I'm about finished with my driveshaft resto and need to ask if I need to rebalance my driveshaft. If I do then my driveshaft guy has recommended removing all the old balance weight and starting from scratch. Should I do this? Also, which end had the tranny yoke on it from the factory? Near the weights or away? Thanks.

Mike

[Joe L.]

Re: Should I rebalance my driveshaft

Guys,

I'm about finished with my driveshaft resto and need to ask if I need to rebalance my driveshaft. If I do then my driveshaft guy has recommended removing all the old balance weight and starting from scratch. Should I do this? Also, which end had the tranny yoke on it from the factory? Near the weights or away? Thanks.

Mike

Mike------

If you've replaced the u-joints it's a very good idea to re-balance (or, at least check the balance of) the driveshaft (with the new u-joints installed). My advice would be to have a competent driveshaft shop CHECK the balance of the driveshaft with new u-joints AS-IS. If it's OK, all is well. If it's not, then follow the advice of the shop to re-balance it.

I might add that driveshaft re-balancing at u-joint replacement is not a common practice. However, it's a VERY wise thing to do if smooth, vibration-free operation is important to you. It is to me so I always do this.

[Bill W.]

Re: Should I rebalance my driveshaft

Mike,
If your driveshaft is the one installed in your Corvette at St. Louis it should not need to be rebalanced. There are four ways to install your driveshaft but only one is correct. Read your assembly manual then start looking for the identifying paint marks put there by the factory, a wet sponge wiped over the shaft will help you find them. There should also be traces of paint on your diff. yoke. Install your driveshaft so these two paint dabs are together.
The main reason NOT to rebalance your shaft is because when your rear end was built the diff. yoke was spun (not balanced!) to locate the light spot. A dab of paint was applied to this point. The manufacturer of the driveshaft balanced your driveshaft and marked with a dab of paint the heavy spot at the rear of the shaft. The factory then assembled the shaft to the diff. yoke with the two paint dabs in line. If you have a shop balance your driveshaft only, you will have vibration! FYI, I have NEVER found a shop who can balance rear yoke and shaft together. If you have such a place disregard all of the above. Bill

[Joe L.]

Re: Should I rebalance my driveshaft

Mike,
If your driveshaft is the one installed in your Corvette at St. Louis it should not need to be rebalanced. There are four ways to install your driveshaft but only one is correct. Read your assembly manual then start looking for the identifying paint marks put there by the factory, a wet sponge wiped over the shaft will help you find them. There should also be traces of paint on your diff. yoke. Install your driveshaft so these two paint dabs are together.
The main reason NOT to rebalance your shaft is because when your rear end was built the diff. yoke was spun (not balanced!) to locate the light spot. A dab of paint was applied to this point. The manufacturer of the driveshaft balanced your driveshaft and marked with a dab of paint the heavy spot at the rear of the shaft. The factory then assembled the shaft to the diff. yoke with the two paint dabs in line. If you have a shop balance your driveshaft only, you will have vibration! FYI, I have NEVER found a shop who can balance rear yoke and shaft together. If you have such a place disregard all of the above. Bill

Bill------

The driveshaft was supplied to St. Louis as an assembly which included the u-joints and it was balanced as an assembly. Once the u-joints are replaced, the paint marks on the driveshaft are no longer relevant.

[Michael L.]

Re: Should I rebalance my driveshaft

Guys,
the shafts have already been restored so not possible to locate paint marks. Also, the original yoke is missing so I got a replacement. With that in mind would you still recommend no balance or shaft/yoke combo balance only? Also, if I have them assemble and check first should I put the yoke on the side of the shaft closest to the weights or away from them? Thanks

Mike

[Joe L.]

Re: Should I rebalance my driveshaft

Guys,
the shafts have already been restored so not possible to locate paint marks. Also, the original yoke is missing so I got a replacement. With that in mind would you still recommend no balance or shaft/yoke combo balance only? Also, if I have them assemble and check first should I put the yoke on the side of the shaft closest to the weights or away from them? Thanks

Mike

Mike------

I think you're referring to the transmission yoke while Bill was referring to the differential yoke. The original driveshaft was balanced as an assembly including the driveshaft, u-joints, and transmission yoke (I neglected to mention that in my previous response). That's how I recommend that you have it balanced now. However, as I mentioned, have the balance checked AS-IS. If it's OK, leave everything as it is. If not, have the shop balance it as they recommend.

[David H.]

Re: Should I rebalance my driveshaft

... Also, which end had the tranny yoke on it from the factory? Near the weights or away? ...

Does this matter? What was typical location of the weights - near transmission or near differential? Thanks

Dave

[Bill W.]

Re: Should I rebalance my driveshaft

Mike------

I think you're referring to the transmission yoke while Bill was referring to the differential yoke. The original driveshaft was balanced as an assembly including the driveshaft, u-joints, and transmission yoke (I neglected to mention that in my previous response). That's how I recommend that you have it balanced now. However, as I mentioned, have the balance checked AS-IS. If it's OK, leave everything as it is. If not, have the shop balance it as they recommend.

Joe, You are correct that the DRIVESHAFT ASSEMBLY was balanced by the manufacture as a unit. But what was not balanced was the diff. yoke. It was only marked as heavy or light (I forget which) on one side. That side was then matched to the paint dab on the rear of the shaft.
As to weather all this makes a difference or not only the OP will know when he installs the shaft. Since the original shaft is missing I would go with your suggestion and balance and hope for the best. He will be able to tell how good the balance job was the first time he gets the car up to 70 MPH on a smooth road. If his rear view mirror has vibration it most probably comes from the driveshaft imbalance. Bill

[Joe L.]

Re: Should I rebalance my driveshaft

Joe, You are correct that the DRIVESHAFT ASSEMBLY was balanced by the manufacture as a unit. But what was not balanced was the diff. yoke. It was only marked as heavy or light (I forget which) on one side. That side was then matched to the paint dab on the rear of the shaft.
As to weather all this makes a difference or not only the OP will know when he installs the shaft. Since the original shaft is missing I would go with your suggestion and balance and hope for the best. He will be able to tell how good the balance job was the first time he gets the car up to 70 MPH on a smooth road. If his rear view mirror has vibration it most probably comes from the driveshaft imbalance. Bill

Bill------


If the driveshaft was marked prior to the installation of the u-joints, then I don't understand what relevance the mark would have after the u-joints were installed. If the driveshaft was marked after the u-joints were installed (which is likely), then I do not understand what relevance the mark would have if the u-joints were replaced.

As far as vibration goes, there are many causes for this. The far more common and major cause is clutch/flywheel imbalance. Wheel/tire imbalance is another major cause. So, if the OP experiences vibration problems, driveshaft imbalance is only one of the possible causes.

[Larry M.]

Re: Should I rebalance my driveshaft

Does this matter? What was typical location of the weights - near transmission or near differential? Thanks

Dave

TYPICALLY, the weight(s) would be on the rear axle end of the driveshaft. However, I have seen driveshafts that have factory weights on both ends....my own 1967 car is like this.

Don't know if it really matters which end has the weights attached.

Larry

[Bill W.]

Re: Should I rebalance my driveshaft

Bill------


If the driveshaft was marked prior to the installation of the u-joints, then I don't understand what relevance the mark would have after the u-joints were installed. If the driveshaft was marked after the u-joints were installed (which is likely), then I do not understand what relevance the mark would have if the u-joints were replaced.

As far as vibration goes, there are many causes for this. The far more common and major cause is clutch/flywheel imbalance. Wheel/tire imbalance is another major cause. So, if the OP experiences vibration problems, driveshaft imbalance is only one of the possible causes.

Joe,
I believe the driveshaft was balanced after the u-joints were installed. I believe the dab of paint at the rears only purpose was to be aligned with the paint on the diff, which came from a different source.
As for imbalance, yes, there are many sources, but a high frequency vibration in the mirror will be driveshaft. If the OP had no vibration before the driveshaft work was done and things shake now, I would be looking at the driveshaft.

[Edward J.]

Re: Should I rebalance my driveshaft

Mike, I myself think a little different than most, if you were sealing with a driveline vibration before the car was taken apart than yes re-balance the shaft. I have replaced thousands of u-joints over the years and have not re-balanced. even when I was dealing with driveline vibrations trusting, the specialty shops to do a correct job performing this task is at best a gamble. at least in the area I live. as Larry posted weight are generally at the rear. so rotating the shaft 180 maybe required.

[Michael L.]

Re: Should I rebalance my driveshaft

OK guys just heard from the driveshaft shop that one of the half shaft welded ends is damaged. He says that he has a replacement from spicer on the shelf and can cut off the old one and weld on the new one. Of course no harm in doing this now, since unless I do the shaft is junk. But should I just try and source a good used one or does anyone have any experience with this being done?

Mike

[Joe L.]

Re: Should I rebalance my driveshaft

OK guys just heard from the driveshaft shop that one of the half shaft welded ends is damaged. He says that he has a replacement from spicer on the shelf and can cut off the old one and weld on the new one. Of course no harm in doing this now, since unless I do the shaft is junk. But should I just try and source a good used one or does anyone have any experience with this being done?

Mike

Mike------


If the driveshaft shop is competent they should be able to replace the end yoke and you should have a reliable driveshaft thereafter. These guys often actually make up a driveshaft for certain applications for which an assembly is not available for one reason or another. If they can make one up, they can certainly repair yours.

[Larry M.]

Re: Should I rebalance my driveshaft

Let them do it if the $$$ are right. Half shafts do not require any balancing due to the low rotational speed. Of course if they could somehow check the balance after the repair, that is even better.

Used half shafts are relatively cheap and should be readily available.

It comes down to $$$ and your preference.

Larry