The only reason I replaced mine with oem is that warranty paid for it, otherwise I would never do anything but a top quality unit. The labor is the vast majority of the money and the headache so it's not worth ever having to do it again. You can sell the oem for a big discount on ebay and mitigate the loss on it.

On most cars, the balancer is something that is never touched or even thought about until the car goes to the crusher, so the oem unit on the Vette is definitely defective in design and should not be used again. Also, there is no evidence that they have changed or improved the oem design over the years...stay away from it.

 

I posed the previous questions in an attempt to better understand the root cause of failures on this particular part and avoid those circumstances if possible. Until I bought my Vette in '07 and joined this forum, I had never known of HB failures. Of course, when I started messing with cars in the mid 50's there was no mass communication medium like that in the last 15 years. Manufacturers had the same problems trying to identify issues and logically worked on the most common ones first. Until a problem reaches a threshold where the warranty costs approach the estimate to cure the problem and safety is not a concern, the bean counters won't approve a fix. Possibly that dollar amount has not yet been reached.

In reading the service manual about HB replacement, there appears to be no concern about orientation for automatic trans cars. I can only assume the reason is due to the need to correctly relate to the flywheel balance on manual trans engines. In viewing the OP's photos and assuming he has a M6 trans (Hurst shifter in profile), it looks like there may either be 2 balance weights near the 135 degree position or 1 at 270 degrees or maybe all 3 places of his OEM HB. According to the SM, the same weight needs to be installed in the replacement HB and then mark the new HB crankshaft locator in the same relationship to the added weight as the old HB. That relationship is what was confusing for the OP and also what I had forgotten about. The weight sizes are described in the SM, but not the method of installation or retention.

Now the engineer in me sees 2 sizes of holes on the new HB, but only one size on the old one. The old HB holes are spaced at 30* intervals except for a few grouped at 7.5* to fit in a 45* section. Strangely, the new HB has larger holes spaced at the same 30* intervals, but smaller ones that appear to be 10* from the large ones and separated by 5*, which cover a 90* segment and may indicate that it's a "fix" to better control the balancing. Unfortunately for the person doing a replacement, the multiple size weights and slightly different locations now create more problems and questions.

irok's mention of several A6 cars needing HB replacements follows the general pattern of roughly 2/3rds of production are automatics. However, WW7 notes that his car has already had 2 replacements. After reading the SM part about HB cleaning and inspection, which indicated concerns with loose weights and improper installation, my thoughts instantly went to failures caused by loss of weights. If the factory weights fell out, it wouldn't make any difference between autos and manuals. It also would account for the mechanic who changed the HB to not know how much or where weights were needed, which caused a multiple replacement problem. Of course, I'd also guess that some mechanics simply swapped HB without dealing with weights, either out of ignorance or a desire to profit by doing the job more quickly.

Hopefully the OP reads this and can report the location of weights and/or where weights may have been at one time.

 

If we theorize that weights might come loose and fall out, then I interpret:

"note the location of any existing balance weights, if applicable."

as meaning there might or might NOT be any weights in a HB with a manual. Since there was no "definite article", if there are no weights in the old one, then one has to wonder whether there were any weights in the first place, or they fell out....

 

Pretty much my point for cause and for repeats and with autos included.

I also noted the beige dot on the OP's old HB and blue on the new one. My guess would be that it relates to the initial balance and maybe the blue X meant no factory weights needed or included. We'd need a trained tech to answer that question.

Maybe irok has some input regarding the weights, since he's seen repeat failures at really low miles.

 

I have no way to verify if weights have ever fallen out of any I have worked on except observing that I couldn't feel any noticeable vibration in any hb that had failed.some may have no weights added but the final balance also depends on weight removed i.e. different amount of holes drilled in hb.wide range in number and depth of holes drilled in hb.I believe the only cause of the failures is the bonding agent used on the elastomer rubber to attach inner and outer hub to each other and environment at time of manufacture

 

I thought the stock GM balancers were neutral balanced , and the holes and weights in them were what they used to achieve the neutral balance... The aftermarket balancers should be neutral balanced from the manufacture and shouldn't require any additional weights... Do you just bolt the aftermarket units on and call it a day?? ..WW
.
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One more step in the "thought process". Now what happens when we go aftermarket HB and no longer consider transferring any weights as there is no real way to do that without some sophisticated equipment to test engine rotational balance in a fully assembled running example.

Now we need to rely on history. Is there a history of any engine performance anomalies including failures on manual trans cars BC the original HB was replaced with an aftermarket?

 

Mine went out around 27,000 miles...

 

both become neutral balanced once producer adds or subtracts weight but not in their as cast condition.

 

If you look at the pics in the OPs first post - In manufacturing of the HB, because it's an assembly of a cast part, rubber center ring, and turned, outer ring, they achieve neutral balance essentially, by drilling (and removing weight) numerous holes. First, there is a series of evenly spaced holes, then when they locate the place where more weight needs to be removed to achieve neutral balance, a number of holes are drilled on both sides of that imbalance. That is why you see the "cluster" of holes.

This neutral HB with lots of holes goes on both A6 and M6 models. The M6 models have a unique balancing issue at the rear of the engine with the much more massive flywheel and clutch assembly. Assembly, being the operative word, induces an imbalance back into the rotating assembly, that GM attempts to neutralize in the front of the engine by adding weight back into the HB where the cluster of holes are. They, of course, first position the HB on the KEYLESS crank with the cluster of holes opposite of where counter weight needs to be and then add weights back into the HB to neutralize the entire rotating assy. And, I'm sure it is within some acceptable tolerance and not perfect balance. And, I'm pretty sure that's why there is no crank key in the LS engines.

So, there are special instructions with an M6 option when replacing the HB. Essentially, putting a reference mark through the HB and crank before removing the old HB so it can be repositioned in the same orientation. Then they want the new "neutrally" balanced HB with it's cluster of holes in the same location and instruct the weights be removed/replaced in the new assy so the now imbalanced HB matches as closely as possible the old assy and in the same orientation on the crank as the old.

Now, that's theory, here's reality. HBs fail, and clutches (flywheel, pressure places, discs) are replaced through wear. Whatever minute fine balance achieved in manufacturing/assembly using this process will eventually be lost as the car ages and parts replaced over time.

So, I am concluding, this is all entertaining hypothetical discussion, but from a practical sense, I think this is nothing to agonize over.

I put a Powerbond on my M6 to replace a wobbling GM HB and had no way of transferring weights over. I wouldn't have chosen the GM replacement because of the counterweights over the more reliable aftermarket Powerbond with the tradeoff that I might have induced some minor harmonic vibration back into the rotating assy.

 

Blindspot,
Thanks for the excellent explanation.. I had my whole clutch assembly replaced earlier this year.. I guess when the time comes to replace the balancer again with an aftermarket unit, I will just bolt it on and hope all the small imbalances cancel each other out.......WW

 

I think you are seeing a different manufacturing process than what I envision. In a high production mode, it's far more economical to drill the same pattern of holes in every outer ring and then add weights to balance it after assembly. The photos show the OP's new unit has a larger array and at different spacing, which allows more precise balancing. My assumption, partially based on the SM instructions for M6 applications, is that no factory replacements are pre-balanced, which requires the mechanic to do the job on an as required basis to match the unit being removed. I still lack the understanding of how the factory determines what weights are necessary to match/counter the flywheel balance weighting, when the expectation is they are initially individually zero balanced. Of course, that introduces a question of how the replacements can be either zero balanced without weights or unbalanced enough to require specific weights.

The aftermarket units appear to either be internally self-balancing or real tough to break, so matching another condition doesn't matter.

It seems we have more questions than answers.

 

I'm not seeing more questions here. BC these units must satisfy replacements for both A6 and M6 variations, the only "common" field replacement is a balanced unit; otherwise, you would need an infinitely variably inventory of "pre-balanced" assemblies that would need separate P/Ns to satisfy all potential replacement possibilities of M6s, plus balanced units to satisfy A6 replacements.

From a manufacturing standpoint:
All units in manufacturing start out unbalanced. But, all units MUST be neutral balanced...or balanced. The nature of a casting sub-assembly as part of a final assembly called a rough/unfinished HB is that it will invariably be unbalanced. With an unbalanced final assembly that must be balanced, you can either add weights to the assembly or remove weight. The most efficient manufacturing process for removing material is a drill/drilling. If it were just matter of removing enough material to balance the assembly (drill holes at the right place to remove material to balance), there would only be a few holes located at the point along the hub where the imbalance is greatest. However, in order to satisfy a "field R/R requirement" of attempting to restore the original factory balance achieved in the manufacturing process, the tech will need to "field" restore weight to the balanced replacement by copy catting the weights in the old HB, and with almost infinitely variable options from one repair to another. Therefore, in order to remove enough material to to achieve balance, and provide a number of options to add weight back in, the manufacturing process would include drilling many more holes around the imbalanced arc to allow numerous options and numbers of weights to be removed and replaced in the new unit.

I believe that is why, looking at the OPs new and old HBs, the new hub has far more holes drilled in a tighter pattern obviously to present greater field options to mimic the original balance that were not necessary in the original, much more tightly controlled manufacturing process.

Hopefully, We both know, from a basic mechanical engineering standpoint, if we needed to balance the HB shown in the OPs first post by removing material, even if we were doing it with lab/shop methodologies outside of a controlled manufacturing process, it would never end up with that hole pattern that we see in that pic. That has to be the first "why" question we ask. Why so many more holes in the replacement? That many holes are not only unnecessary to achieve balance, but also not cost effective in the manufacturing process. But, absolutely necessary to satisfy field replacements

 

I've always heard that the LS engine is an internally balanced unit. This usually means that both the clutch/flexplate assembly on one end and the balancer on the other end are neutrally balanced and do not compensate for any internal imbalance. The harmonic balancer is there to absorb harmonics (individual power pulses from the pistons) and not static balance of the rotating assembly.

 

I agree with your first sentence. The second sentence contradicts the first BC both the clutch/flywheel assy and the HB are external to the the internally balanced assembly. What do we do with those?

I can see how to balance the the HB. It is a fixed rotating assy. Just a single mass spinning, externally, off the front of the internally balanced assembly. But, how do you balance the rear which is a complex assembly of much greater mass, consisting of two fixed externally rotating parts and one independently rotating disc which might or might not impact the balance of the complete assembly based on whether the clutch is depressed?

If we accept this theory, then why the GM process to mark the exact location of old HBs and transfer weights (variable, unit to unit) to new HBs on M6 only?

Needed to add: the last sentence - it's true that the harmonic balancer absorbs harmonic resonance in a rotating assembly, which is a dynamic process, but statically, the components need to be balanced mechanically. Two separate issues.

A wheel tire is a crude example. We can have a wheel assembly out of balance. The rubber inflated tire absorbs much of the harmonic resonance that occurs in the entire moving mass of the car going down the road, but if the wheel is out of balance, this induces a new set of vibrations not necessarily defined as harmonic resonance or generated by the moving mass, but now inducing new and different vibrations by the out of balanced assembly. HBs act is a similar way, but they still have to be balanced or counter balanced within an entire rotating assembly.

 

Wow. Lots of good conversation's been going on here.

The tan dot is just a dot, but the green one is a weight. As noted, the SM mentions putting new weights in the same locations as the old. It doesn't say how/if you can get them out. It describes how to determine the weight size by measuring it, but again, unless you can get the old one out, you can't measure it. Most importantly, no parts catalog/diagram appears to have these weights. So I have no idea how to get new ones!

On the other hand, the TSB makes a good observation:
"31. Place the old and new balancers on the bench and orient them the same way (i.e. face up with a weight balance hole at 12 o'clock). Scribe/mark the new balancer in the same location as the old balancer. Do not transfer weight pins on manual transmission equipped vehicles. Most vehicles will be balanced without the use of any additional weight pins. Because some balancers may have spun on the crankshaft, transferring weight pins to the same position would produce a random imbalance. For vehicles that exhibit imbalance (very rare), contact Technical Assistance."

If the pulley is neutral balance, I'm not sure what value reproducing the same orientation gives if you don't reinstall the same weights.

Also, I have an M6.

 

I know most people that install aftermarket balancers, just put them on and tighten them as per the instructions.. I don't ever recall seeing anyone on this site say they had problems with vibration after installing their balancers that way..Flexplates and flywheels usually have weights on them to get them to neutral balance also.,... WW

 

Like a lot of GM instructions, contradictions, confusion, change of direction in TSBs, etc. Just do it! And still suggest go aftermarket and be done with it.

 

Oh, I could have said that the status update it that my PowerBond pulley arrived. Installed it last night and things went smoothly. This weekend when I get another set of hands, I'll start re-assembly.

Thanks!

 

I had to chuckle when you said "I'm not seeing more questions here." in response to my "It seems we have more questions than answers." and then proceeded to post 4 more questions.

It seems we both see confusion, but from a different perspective.

From a manufacturing standpoint and a further review, drilling balancing holes after the ring to hub assy does make sense. I envision all the rings are drilled with the 12 hole pattern and spaced in 30* intervals prior to assembly. Then after assembly, it's spun to determine the quantity and location of balancing holes needed. A shot of paint (beige on the old one and blue on the new) is put on at the balancing operation as a locating point for the fixture to start the drilling operation. That creates a zero/neutral balance condition. Then for the M6 cars, an extra weight can be added in one of the 12 original holes if necessary. I say one of the 12, because on the old one, that's where the weight is located and on the new one it appears the secondary holes are slightly smaller than the others, probably to avoid a tech from trying to stuff a weight in those.

The remaining question is similar to yours. "..why the GM process to mark the exact location of old HBs and transfer weights (variable, unit to unit) to new HBs on M6 only?"

Since the added weights come in 3 different sizes and would be installed in a location of +/- 15*, the deeper question would be "How does GM originally determine how much weight to add to which hole and how to orient that on the crankshaft at the initial assembly?" Maybe the paint dots play two roles.

I'm currently at a loss for the reason why a M6 balancer wants to be out of balance.

So here's another question for irok. Did you ever notice weights in the bad balancers you removed from A6 cars?