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Remachining Constant Velocity Joints

Rzeppa CV joint
CV joints can be rebuilt by regrinding and remachining on special equipment.

There has been a great deal of controversy among component parts rebuilders over the pros and cons of grinding constant velocity joints, but it is mostly a rhetorical debate these days because everybody who is in the front-wheel drive axle shaft rebuilding business knows it is difficult to be price competitive with FWD halfshafts unless the CV joints are reground (rather than new). Whether or not grinding works, therefore, is not the real issue anymore. The issue is the best way to grind CV joints

Though the overall demand for FWD shafts continues to expand, prices have remained low due to competition between rebuilders and retailers for market share. Almost everyone who is rebuilding CV joints and shafts say they are selling everything they can build.

To minimize the cost of rebuilding a FWD shaft, the CV joints are typically remachined or ground rather than replaced if they are worn.

According to several rebuilders, roughly half the CV joints they rebuild are salvaged and reconditioned by grinding. Another 20 to 30 percent can be rebuilt using sightly oversize (.001 to .003 inch) balls and cages. An equal number often do not need much of anything except cleaning and reassembly with fresh grease. And only about ten percent are unrebuildable because they are broken, cracked or damaged beyond repair.


No one disputes the fact that grinding can salvage many CV joint components that would otherwise have to be discarded and replaced.
But opinions differ on the effects of grinding on joint durability. The emerging consensus of opinion is that grinding does no harm as long as it does not go too deep. The depth of the case hardening on CV joints varies depending on the application and process used (induction hardening or carburizing), but typically ranges from .048 inch to .100 inch or more. Limiting the amount of material removed to .010 inch to accommodate a .020 inch oversized ball, therefore, should have virtually no significant effect on joint durability. Consequently, a .010 inch cut has become an "unofficial" standard for many who grind joints.


The key to reconditioning a CV joint by grinding, say those who do it, is to duplicate the original arc in the housing and race, a process which requires precision machining and cannot be duplicated by hand.

"If you try to buff out a dimple by hand with a die grinder, you are going to create a low spot or pocket in the track which does not solve the problem or do anything to restore clearances. You have to precision grind the entire length of the track from end to end following the OEM arc," says Mark Bourgeois, vice president of Car Component Technologies, Bedford, NH.

"Right now, we have 23 grinding machines, more than anybody else in this business, and we are running them 24 hours a day, five and a half days a week. We are building 80,000 to 100,000 shafts a month, and will probably do about a million axles in all this year."

Does grinding work? "You bet it does, says Bourgeois. "It allowed us to go from 12 employees and 2,000 axles in October 1992 to nearly 500 employees in April, 1997. That is faster than anybody else has ever grown in this business."

Bourgeois said Car Component Technologies has ten Constant Velocity Systems and thirteen Oliver grinding machines in their 160,000 square foot facility. He says each type of machine has its own advantages. The CNC controlled Constant Velocity System machines are very fast, can do three cages at once and grind all six windows in a cage in less than a minute. The Oliver machines are very strong and are good workhorses.

"There is no way for someone to get into this business today unless they can build an axle for $40 and make money on it. To build an axle and sell it for that price, you need volume so you can buy your parts at a competitive price. It would be hard for any newcomer to buy their parts as cheaply as we buy them because of our economies of scale. We buy grease in tractor trailer loads.

"And to convince a customer to buy their axles, they would have to sell at an even lower price and offer better coverage and inventory than what we can provide. I have 150,000 axles on the shelf. I ship same or next day, and have a fill rate in the high nineties. So somebody would have to beat everything we have just to get a customers business, and then do it for two or three years before they would even start to make any money. That is why you cannot just jump into this business and start rebuilding 50,000 axles immediately.

"The competitive pricing from large rebuilders like ourselves today means warehouse distributors can now compete with the small local rebuilder. Why should an installer buy from a small shop around the corner if they can buy a brand name shaft from a warehouse and get a limited lifetime warranty?" said Bourgeois.


Because some people do nothing more than a "wash and paint job" on the shafts they rebuild, or use a die grinder to buff out dimples and other defects in ball tracks and races, many are concerned of the impact this is having on the perceived quality of remanufactured axle shafts. A few bad apples can tarnish the image of an entire product line.

There has also been a lot of discussion both within and outside the rebuilding industry for adopting standards on rebuilding and grinding CV joints. The Society of Automotive Engineers (SAE) has already developed a recommended practice (J1620) for rebuilding front-wheel drive axles which essentially said no to grinding.

"That document has been temporarily shelved," said Richard Lovely, general manager of Powerline Inc. in Roebuck, SC. "One of the goals of the current APRA study is to determine some type of limit on how far a CV joint can be safely ground. Some people say you can cut twenty, forty or even sixty thousandths out of a joint and do no harm. This study should give us a finite number as to how far you can reasonably go.

"This study is also looking at the geometry of the joint. There are a number of different ways to grind. If you do not grind properly, you have shined up the part but have not really made it any better.

"Once we get back the APRA study results, we may try to set up a committee to resurrect the original SAE document and redevelop it into a workable standard for rebuilding CV joints."

Lovely said another issue created by grinding a joint is what happens a few years down the road when some of these reground cores start coming back? Can they be rebuilt a second or third time? There is a real concern that grinding may diminish the percentage of cores that can be rebuilt a second time.

"With a product like a starter, six to nine rebuilds may be possible before the core is unusable. But we cannot do that with CV joints. Once may be it," said Lovely.

Others say there may be an opportunity to develop "second generation" tooling that would take another .005 inch cut and use a .030 inch oversized ball. This would be a more economical alternative to replacing joints that have already been reground once before.


Mark Veldhuis of Freds Driveshaft, Clearwater, FL, who heads up APRAs CV and Racks committee and writes our "Turn of the Wheel" column, is another who agrees that grinding is not the issue, but how to do it.

"When done right, grinding works very well. We learned a lot about grinding by building our own machines, which we have recently replaced with ones from Constant Velocity Systems. We now have a dedicated machine for grinding cages and a second for doing CV housings. We will be adding a third dedicated machine for grinding inner races in the next 45 days.

"We are doing about 10,000 shafts a month now, and plan to be up to about 15,000 a month by the end of the year. Our old machines could salvage about 80 percent of the cores, but these new machines can salvage 93 to 94 percent, and with greater consistency, too.

"If we as an industry end up developing standards, they need to be our own aftermarket standards, not OEM standards."

Veldhuis said the need for quality and value is becoming more important then ever. "I had a customer who decided to buy some cheaper shafts from somebody else. When I visited the customer, I asked to see these other shafts. I could not believe how loose they were! When I took one of the joints apart and showed the customer how it had been redone with a die grinder, then compared it to ours, they realized the cheap shafts were no bargain after all."

According to Veldhuis, regrinding a CV joint is actually more difficult than building a new joint. When new joints are manufactured, the same forgings are run on the same tooling in long production runs. But when used joints are rebuilt, there is a lot of variance from one joint to the next even for the same model year application. Veldhuis says the tracks the balls ride in may not be exactly 60 degrees apart. He found that Saginaw joints could be off as much as .004 to .005 inch from flute to flute.

What is more, the tracks have to be ground in such a way as to restore not only the original geometry of each ball track end to end but also the proper cross section of each groove. The entire surface of the ball does not actually make full contact with the groove in the inner race but makes contact at two points because the groove is somewhat wider than it is deep. This is called a "Gothic arch" because of the shape. The Gothic arch reduces friction, so if the inner race is reground spherical rather arched premature joint failure will occur.

Housings, on the other hand, can be ground so the ball makes full contact with the groove. Window openings in cages must be perfectly parallel to one another and sized to the ball. If a cage window is not parallel or ground perfectly flat, it will click or wear prematurely.

The key to all of this is removing all the wear from the joint without changing its basic geometry.


One way to succeed in the CV joint rebuilding business is to create a unique niche, which is exactly what CV USA has done. Skip Rullis, general manager of CV USA in Saratoga Springs, FL said his company specializes in grinding CV joints for other rebuilders.

"We do not do any shafts ourselves. All we do is grind parts for other rebuilders."

Rullis said the average cost for many rebuilders to regrind their own joints is $8 to $11 when the cost of equipment, training, tooling, maintenance, etc. are all factored in. "Our pricing is based on volume so it varies from customer to customer. But we can usually save a rebuilder money over what it would cost them to grind their own parts in-house. We can also support joint rebuilders who have their own grinding equipment by doing their extra work. Turn around time is normally about seven or eight working days."


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