broken knuckles A-1 & A-2

[Vantage #51]

We have experienced 3 cases of broken front knuckles this season,one ended a cars useful
existance, one nearly so.They break in two
at the top arm that goes from the bottom of the strut housing to the bearing cage.Granted these are parts that have a useful life and should be replaced periododically but three
failures in one season after 7/8 years with none is odd.I have a theory , but would like some input from the crowd.
Derek

[Knestis]

I co-drove in an A2 rally car for years and though we determined the fatigue life of rear stub axles ("Flat left rear? There goes a wheel!") - TWICE - we never broke an upright. We did install later, bigger brakes that (I think) included a different upright in addition to larger hubs and such but that was after a number of years on the original parts.

Welded diff? It might be that loose surfaces don't provide the traction to exert enough force to break them, though dry pavement might. Are you bottoming the strut--though it would have to get the dooky beat out of it before the bearing carrier would fail.

OOPS--sorry! It's not a bearing carrier, is it, Bill? Though that depends on what your definition of "is" is. Maybe I just don't have any good ideas...

Kirk

[itbgti]

Dino,

Curiousity....How old were the knuckles prior to each one breaking (I know you already know this most likely was not the case, but I just would like to know) Also, how often should they be changed??? It could be good to know. And finally, this is the most important question, were in the world can you find these things cheap. I have found them for $225 EACH, and that is the best I can do. At $450 a set, keeping spares is not an option a lot of times, a keep junkyard ones as backup. If you know of a cheaper resource, please let me know.

Note: When building my car last winter, I had 6 knuckles that I had and they ALL looked great. Went to Dick's shop to see if they were straight, FIVE were bent. To any one out there, these things bend A LOT easier than you may think, so check them out every once and a while.

Regards,
Alan

[Bill Miller]

LOL@Kirk!

In all the years that I've been involved w/ VW's, I've never heard of one of these failing (that's not to say they don't fail). The main thing I've heard that fails in a VW front end are the hubs, due to the axle nut not being tight enough. I had a hub failure on my ITB race car last year, and was fortunate that it didn't cause any damage.

Where exactly did these failures occur? Was it at the lower bolt hole for the strut mount, or was it some where below that? I suppose one way to check these things is to have them magnafluxed and look for cracks. And a way to extend their life would be to have them shot peened to relieve any stress in that area.

I'd like to know more about what you guys feel contributed to the problem. Also, did all the failures occur on the same side? What else have you done w/ the suspension of the car? I'm converting my car from ITB to LP GProd for next year, and I know the forces on the front suspension will go up (from using slicks as well as going to a locked diff.). Any info you can provide will be appreciated.

[This message has been edited by Bill Miller (edited September 25, 2001).]

[racer_tim]

[quote]Originally posted by Bill Miller:
[B]LOL@Kirk!

In all the years that I've been involved w/ VW's, I've never heard of one of these failing (that's not to say they don't fail). The main thing I've heard that fails in a VW front end are the hubs, due to the axle nut not being tight enough.

I've heard both sides of the house on the front torque on the axel nut. If you put too much into it, you crush the bearing.

I just had a similar failure @ Sears Point on August 24-26. It looks like the hub itself broke, and then the axel nut sheared. I have since taken a set and had new German hubs and new bearings installed. That has been my first failure while road-tracing. Auto-xing is much harder on the front end parts.


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Tim Linerud
San Francisco Region
#95 ITB GTI

[Bill Miller]

Tim,

My understanding w/ this is is to essentially put as much torque as you can on the axle nut. Some people use a breaker bar and a big pipe, I use a 175PSI compressor and a 3/4" impact gun, and then tweak them w/ a big breaker bar. I know I'll play hell if I have to change one at the track, but it held up so far. The other thing I've heard is that you should just change the hubs/bearings every 4-6 races as a matter of course.

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MARRS #25 ITB Rabbit GTI

[Dead Skunk]

Since I went to the later hubs with the thicker shank, I haven't broken a hub. I tighten the center nut with the help of a 6 foot pipe,too.Never even seen a broken upright, even after rolling the car and bending both front wheels in the process.

Warren

[Ralf]

Speaking of knuckles. The '89 and newer A2 knuckles are supposed to be beefier then the older ones. My question is, are the late style A2 knuckles the same as on the A3 cars?
Thanks
Ralf

[Bildon]

This thread is veering a bit off course....

The original poster (Vantage) was concerned about the bearing carrier or "knuckle" as he called it.
These things almost never break. But they do bend a bit ...usually easily aligned again within specs. You must have another problem. Are you sure you are not bottoming the strut ...ever?

Later posts are discussing the hubs themselves. 85-87 Golfs have hubs which are only a bit beefier than a Rabbit. 87/5 - 92 Golfs have even thicker hubs which are bullet proof.

As far as the '89 hub carriers being beefier...don't think this is true. And are they the same as A3 cars? Definately not the VR6 cars but perhaps some of the early 4 cylinder cars shared A2 parts. I think the brake calipers mount differently though. Would have to go pull the tarp of the next project to be sure.

- bildon

[Bill Miller]

Bildon,

It's not a bearing carrier, just ask Denver! http://Forums.ImprovedTouring.com/it/wink.gif

I'm still curious as to exactly where the failures occured on these cars. Bildon may be on to something w/ the strut bottoming. A bottomed strut may cause a significant load on the strut/knuckle interface. But that's still a beefy piece of steel.

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MARRS #25 ITB Rabbit GTI

[itbgti]

Bildon,

I have on my VW GTI the larger and "beefier" spindles/knuckles from the later golfs, however, I know they can and have the tendency to bend. My question to you is how often should they be changed (if at all), can they be "re-tweeked" back to spec, and where can you get them cheap, I always like to have spares, adn since I am building another, I will need them.

Thanks in advance for the help,
Alan

[Bildon]

I don't think there is a "duty cycle" for bearing carriers. Any cast peice that bends significantly should be scrapped. If you can still align the car easily then I'd run them.

Junk yards are a racer's best friend.
Shot peen them if you want to be sure they are stress relieved. It's about $20 or $30 per part to do it. You can magnaflux them too if you are nervous.

- Bildon

[Scirocco#28]

Originally posted by Bill Miller:
Bildon,


I'm still curious as to exactly where the failures occured on these cars. Bildon may be on to something w/ the strut bottoming. A bottomed strut may cause a significant load on the strut/knuckle interface. But that's still a beefy piece of steel.



Bill,

Think two bolts that attach your steering knuckle to your strut housing (where you adjust your camber)and then look maybe an inch or two south. I've seen all three of these failures first hand and two had very nasty consequences. I was following the second when it happened and the car just shot off the track with no warning and ended up in a concrete barrier approx 75 ft off the pavement. I don't think it was the shocks bottoming out. These guys run pretty beefy front spring rates. Dino, do you think it has anything to do with our new curbing?

Steve

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88 ITB Scirocco
www.geocities.com/highspeedconnectionracing (http://www.geocities.com/highspeedconnectionracing)

[Colin Harmer]

To try and clear things up a little bit. As one of the Vantage Cars maybe I can shed a little light here.

The Hubs (knuckles) are breaking about 1.5" below the bottom strut bolt. It's a shear break in the cast metal that runs right across the tang that attaches to the strut.

These are the larger (what we call 100mm) hubs that came on the A2 models. We have broken 1 of these larger hubs and 2 of the smaller A1 hubs.

We are running between 500# to 650# front springs depending on the driver. Bottoming out may be the problem, but at the moment we don't know.

As far as keeping the front hubs together, we have had great luck in getting ours to last a full season. Heres how:

We built a plate with a 3 grease nipples (in a cicle that matches the radius of the bearing) on it that we can clamp on the top of the bearing. We remove the seals from both ends of the bearing, clamp on the plate and pump in AMSOIL synthetic grease until all the stock stuff is pumped out the other end, put the seals back on and press them into the hubs. The AMSOIL grease seems to take the heat from the brakes a whole lot better then anything we have found and the bearings last. As far as the tourque goes, I run a 1/2" impact gun on it at full blast until the compressor kicks in and then do it again...It makes sense to use the new nuts that come with the CV joints each time to ensure that they don't back off.

Bearings aside, can anyone relate any info on the broken hubs(knuckles)?

Keep us posted!

Thanks!

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Colin Harmer
ITB #2 Red Gti
Halifax, NS

[This message has been edited by Colin Harmer (edited September 26, 2001).]

[Knestis]

I am brainstorming here and, depending on your strut/spring dimensions, this might be impossible but...

High spring rates might not matter if the spring wire diameter, free height and number of turns allow them to coil bind when they really clout the curbs. Put small tie wraps around the coil wire on both sides--if they get "snipped" off during a session, then the spring is collapsing to the point that the spring rate is going to "holy crap".

Also, since I seem to remember some sage suggesting that smart strut manufacturers use dimensions that bottom the external bits before the tender internals, you might be able to do the tie wrap trick on the shaft as well. If it gets squashed, then you are over-travelling the strut. If the strut (sans spring) can be compressed to the point that it stops with shaft still not inside the strut body (heck, or even if not), good bump rubbers are strongly advised. Some folks even think of these as "helper springs" that can provide an increased rate when things get rough. You should be able to hunt up a variety of lengths and rates, probably from your strut mfgr.

It would also be interesting to look closely at the break and see what it might have to say. If it is a uniform, rough surface, then it is likely a catastrophic failure. If it has two different surfaces (one rough like sandpaper and the other smoother, perhaps with "beach marks" that look like contour lines on a map, then it is spending some time as a crack before it gives up. This might suggest the failure mode and/or if you can catch the problem with routine magnafluxing. Point of interest--those two busted stub axles that that I mentioned earlier failed in exactly the same way, with cracks propagating to the center of the diameter and then big spontaneous failure, within less than an hour of rally stage time of each other!

If that is worth anything, remembering that I am working on a PhD in Education--NOT Engineering!

Best wishes,

Kirk

[Vantage #51]

To answer some questions ,none of these knuckles were any where new, could have been on the car as many as 5+ seasons.We are now changing them regularly.My theory in that
at some time the car has been too low or not enough travel in front suspension and severe bottoming has occurred.we put shocks on one,
the A-2, and it had been bottoming enough to
split the end out of a HD bilstien.Our track is Very rough and i suspect that the fractures occurred over time by looking at the remains . Thinking of getting some one who knows metalurgy to have look.Really suprised
as the last one we replaced, unbroken, but bent at 20 or 30 degrees on the top arm after trying to move the concrete wall at NHIS.
As for pricing we purchased some at BSI,new,
for around 100 US$ if memory is correct.
Derek
#51 Golf GL
IT-B

[Bill Miller]

Collin,

That bearing packer sounds like something out of Paul and Karl Hacker's shop. There was a great picture of one in Greg Raven's book.

And, the hubs and knuckles are two different parts. The knuckle is the big piece of steel that the strut attaches to, the tie rod end attaches to, the ball joint attaches too, and the hub/bearing mounts in. The hub is the part w/ the female spline and the flat plate that the wheel attches to, that is mounted in the bearing, in the knuckle.

Bildon,



I suppose one way to check these things is to have them magnafluxed and look for cracks. And a way to extend their life would be to have them shot peened to relieve any stress in that area.


Look familiar? http://Forums.ImprovedTouring.com/it/wink.gif Great minds think alike!

I find it hard to believe that one of the knuckles would just fail if there were not already damage/weakening done to it. I can see a crack developing from a severe jolt that went unnoticed until it propogated enough to allow the part to fail. Or possibly a part that had been damaged (bent) and restraightened.

I can see a bottomed spring/shock leading to an 'oh my God' (nice Kirk http://Forums.ImprovedTouring.com/it/wink.gif ) spring rate which means that all that force has to go some where. Flexing at the weakest point between the two ends seems to be likely.

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MARRS #25 ITB Rabbit GTI

[Knestis]

Since Vantage has 'fessed up that they bottomed the suspension enough to have stabbed the shaft through the end of a strut housing, I do believe that it is time for the awarding of the prize for the first person to suggest that answer. Ahem.

And I expect something better than a copy the home game this time! At least they validate parking on the Hollywood Squares...

Is it that late?

K

[Bill Miller]

Gee Kirk, it's a good thing you're double-jointed!!! http://Forums.ImprovedTouring.com/it/wink.gif http://Forums.ImprovedTouring.com/it/wink.gif http://Forums.ImprovedTouring.com/it/wink.gif

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MARRS #25 ITB Rabbit GTI

[Eric Parham]

The only other story I've heard of broken uprights was a Rabbit/Bilstein Cup racer who had "adjusted" his camber with the help of a torch. I myself have accidently bent many front uprights while on (read: off) track, and never broken one. They appear to be quite ductile! I've also never tried to salvage a bent one, and wouldn't recommend it. In light of your parts failures, I plan never to let a torch anywhere near a VW front upright (balljoint, tie-rod, strut bolt, etc.).