steering knuckle/spindle replacement

During a race last year the right spindle on my 2nd Gen. RX-7 broke half in two. It was a clean break and the spindle showed no outward sign of wear. Now I am somewhat concerned about the left side. My car is an old warrior w/ about 60 events (events - not races/sessions) on it. I have no idea how many miles the chassis has on it but it was a SpeedSource car and I think they started w/ decent cars, not junkers. I have removed the spindle and it looks fine. I have 2 options: 1. put this one back on; or 2. replace it w/ the one off my parts car, which has 158,000+ street miles on it. Looking at the 2 side by side I would have to say that the one on the race car looks better. The one from the parts car has some slight marring of the finish but it is still smooth to the touch. What should I do? Oh, yea, a new one is over $400 so forget about option 3.

Bill--I don't know, I would have thought the left would be more prone to breakage.

In any event, why not clean up what you have (and the spares) and get them maganfluxed?

If good, don't worry about the age.

Cheers.

Bill, maganfluxed is one good method to gain some confidence & $400 is cheap as compared to the potential results of a serious you know what.

Cheap in that respect, but is it compared to the cost of new uprights?

I learned the hard way that, given modern manufacturing processes and tolerences, when a right rear stub axle on a Golf rally car fails, the other one will fail identically - not kidding - within a dozen stage miles. It wasn't fun either time, even if we got some good drinkin' stories out of it.

K

"Bill--I don't know, I would have thought the left would be more prone to breakage."

Indeed; this was at Memphis, a predominately right turn track, and it broke coming out of a sweeping right.

"In any event, why not clean up what you have (and the spares) and get them maganfluxed?"

What exactly is magnaflux? I did a search but did not find a good explanation - is it a test or a treatment?

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What exactly is magnaflux? I did a search but did not find a good explanation - is it a test or a treatment?
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It is a test to detect for cracks. It works on the principle that a crack creates a magnetic field when voltage is applied to the part. That magnetic field attracts small iron particles which can then be revealed under the proper lighting. It works well but prices can vary. You're local automotive machine shop should be able to help you out.

Matt, is it reliable? I wasn't thinking that any of these spindles had even microscopic cracks but "metal fatigue." Can't a part fail due to metal fatigue w/o any external indication that it is about to go?

Bill, It's a well proven technique, automotive machine shops use this regularly to inspect cranks, blocks etc which is why most of them (at least the goods ones) have the equipment on site. But, I don't believe it would pickup fatigue issues unless some fairly substantial microcracking has already started.

Without seeing the failure it's hard to say if the cause was fatique, damage, corrosion etc. Although if you wanted to send it to me I can have our metals failure investigator take a look at and see what he thinks. We regularly do failure analysis work on heavy industry pieces (steel mills, mine equipment, cranes for shipbuilding and so on) and the guy in charge of that here really now his stuff. I'd ask for pictures but it's difficult to get the level of detail needed for a real analysis. Let me know if I can help.

I guess I should have saved it as a souvenir but I threw the broken one away. It was a fairly clean break and there was no evidence of wear, scouring, etc. I suspect that the magnaflux will not show anything on either of the 2 spindles I have. So, which one would you use?

when I raced an F Production Sprite, I magnafluxed my spindles post season, found faults at the root of the spindle/inner brg seat, got replacement (used) spindles, magnafluxed them (OK) and ran them for the next year. Did this every subsequent year and always found cracks where there hadn't been any before use.
So what caused the big one? Rear axle hsg failed!

It seems really unlikely to me that an OE spindle would just spontaneiously bust.

What you are looking for - post-mortem - are called beach marks. Up close, a crack, once it fails, looks like concentric rings (like a tree or clamshell) that will be pretty smooth once it fails. The part that gives up, once there's insufficient cross-section to support the load will be crystaline looking - like sandpaper. Typically, once a crack propegates something approaching half way, its bustin' time.

Magaflux, used by someone who knows what they are doing, will likely catch a crack like typically causes ferrous cast parts to give up.

K

EPILOGUE

I took you guys' advice and had both spindles Magnafluxed this morning. The one of the other side of the race car indeed had a crack in the very same place where the other one broke. :o The one off the parts car shows some scouring but seems to be free of cracks, so I will use it. The guy did it while I waited and only charged me $10. Which might be the best $10 I ever spent.

<kyle> I think we learned something here today... </kyle>

It&#39;s useful to note that, as models as seemingly "new" as 3rd-gen RX7s get older, we have to start paying attention. One really important contributor to stress cracking is corrosion. A little pit in the wrong place becomes a stress raiser, focusing loads on the weakened point, ultimately propegating a crack.

Keep cast parts clean, painted, or lubricated to help keep this in check.

K

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<kyle> I think we learned something here today... </kyle>



Keep cast parts ......, or lubricated to help keep this in check.

K
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Which makes it all the more amazing that any British car ever had a fatigue failure, because everything aft of the engine never lacked a good coating of oil.....


;)

I can name a few people who are no longer with us because of broken spindles. PLEASE PLEASE everyone, check yours at least occasionally. Magnaflux is preferred, dye checking is a reasonable second choice.

When I first started racing I was told by my peers I WILL get my spindles and king pins magnafluxed every winter and after any hard impact (including agricultural racing and curb crunching). I had the spindles checked as soon as I purchased my latest ride, and both were cracked. Then one on the driver&#39;s side was so bad that I found I could see the crack with just a magnifying glass! Of course the car was sold as ready to race. Yeah, right! In other words, don&#39;t trust anything, check it yourself. For those in the DC/Baltimore areas, Coleman Machine Shop is an excellent place. They have been checking suspension and engine parts for more years than I can count. Prices are reasonable too, and if you are in a hurry they do their best to accomodate. For those familiar with Coleman&#39;s, Bill moved to a shop behind his house, he&#39;s now in Linthicum. The phone number is the same.

Dye checking is not quite as sensitive, and takes some experience. Keep those old cracked parts, they are great to experiment with! Kits can be purchased at a number of locations. Mostly just the dye is needed as brake clean can be used to clean the parts first, and a very light powder, like Desinex or Micadin (sp?), can be used for the developer. I typically magnaflux suspension parts in the winter, dye check at the track or between races if I have a reason. I haven&#39;t successfully used dye on crankshafts, rods, or blocks.

When I was shopping for some spacers for my Audi TT some guys on a TT forum cautioned against the increased stress on bearings and spindles caused by moving wheel/tire weight outward. I have about 1" spacers on my race car and I saw some recently that a buddy had custom made that were a good 2". Of course, we are generally using lighter wheels and tires than stock but it seems logical that the extra lever effect along w/ stiffer shocks and springs could lead to premature failure.

"Keep cast parts clean, painted, or lubricated to help keep this in check."

I suspect that painting them would intefere w/ the ability to magaflux them so I&#39;m just going to clean and oil mine.

:018: If I could enter this discussion, I might point out that the parts you are using as examples of failure that need magnifluxing, are MOST PROBABLY "forged" parts, not cast.

I spent 15 years as a "Hot Forging Inspector" at the Chevrolet Tonawanda Forge checking for flaws in the forgings that we made. They usually were caused by worn dies that created some type of overlapping of steel during the multiple hammering stages of forging, and some were not visible after the proceedure was done. All these parts ultimately went thru an industrial magniflux process to check for internal flaws before release to the machining process.

Parts made that I was responsible for inspecting were connecting rods, spindles, crankshafts, gear blanks, axle shafts, and steering components...tie rod ends, connecting links, and pitman arms.

Forgings are usually visually identifiable by the characteristics of the trimming of the flash (material squeezed out of the die/mold). Usually molds leave a very narrow flash line and dies, because of the constant wear, leave very wide flash lines. They are recognizable by the thickness of the visible trim line.

Just a little trivia. :024:

Good racing.

Bill