What Not To Do

[FJCamper]

What Not To Do

In our 2007 Carrera Panamericana run, we had the almost unprecedented incident of both rear wheel axle nuts failing us within the first two days of racing.

Both nuts were brand new, from CB Performance, and advertised as strong, hardened, and better than the stock nut.

The symptoms were the threads on the nuts just failed. It literally cost us a win. We were running mid-pack of over eighty cars at the time, leading in our class, and gaining on the overall.

I had some sharp words with CB Performance, who took the position that they had one more better grade of nut we should have bought.

But, it appears the nut failure may have been our own fault. Not absolutely sure, but probably. We went down with quick-release pins in the axle nuts rather than a proper steel cotter pin. These pins have been popular with some off roaders, and seem to solve the problem of faster drum or disk removal.

After long deliberation, it is likely the pin allowed enough movement to let the axle nut slightly loosen, and the threads were gradually damaged by this.

Our team first discovered loose axle nuts on the second day of the week-long race, hastily retightened the nuts, and by the next day both nuts were worse. We finally lost a wheel, damaging the axle. We were out two days of seven for repairs.

Prior to the trouble, we had posted three days of podium finishes (top three to finish in class), and were working our way into the leading cars, for overall position.

Moral to the story. Don't risk the spring pins. Stick with the cotter pins.

FJC

[Gerrelt]

But, it appears the nut failure may have been our own fault. Not absolutely sure, but probably. We went down with quick-release pins in the axle nuts rather than a proper steel cotter pin. These pins have been popular with some off roaders, and seem to solve the problem of faster drum or disk removal.

After long deliberation, it is likely the pin allowed enough movement to let the axle nut slightly loosen, and the threads were gradually damaged by this.

Hi FJCamper,

First off: I regularly read your posts, and allthough I am not a racer, I think your postings are always excellent.

But are you sure on this one? I always thought that it's the torque that holds the axle nuts on, not the cotter pin. The pin is
only a safety net.

Couldn't it have been caused by insufficient hardening of the nut? Or could it be the ring I see sitting between the nut and the drum?

Greetings,

Gerrelt.

[FJCamper]

Hi Gerrelt,

The drum (with special spacer) in the photo was not on the Mexico Ghia. It had rear disks. I used the photo here just to show the spring pin.

Like you, if I thought about it at all, I thought the torque kept the axle nut in place. But, on reflection, the factory used a castle nut for a reason, and I believe that reason was the brake drum or disk gets very hot, then cools, again and again, and that expansion and contraction promotes movement.

The steel cotter pin locks the nut down in a way no shifting or micro-wiggle is possible.

My first thought at the nut failures in Mexico were soft metal alloy. Having had time to really think this over, I realized I've seen a few wallowed-out brake drum splines in my time, but never a nut with stripped threads unless it was on loose and could move.

I can't be 100% positive that my spring pin theory is right, but we've raced the Mexico car with cotter pins since, and never had a problem.

FJC

[perrib]

It's the China syndrome trickling down. I had someone bring me axle nuts that were $2 apiece. They looked cast. The first one broke at 75 ft lbs of torque. He went back and ended up paying $20 for a pair of old German ones. As for the Cotter Pin it should act as a wedge. I'm not sure if it matters as I used a coat hanger in my rails rear axle. I know it looks hokey but it has been there since 2008, the nut is still tight and it makes for conversation. If you have seen my videos I don't baby this rail. I can see the hot drum theory. I alway check mine after the first test run after reinstalling and they usually need a bit more torque. The comparision may be moot as with 33" and 35" tall tires I may not be getting the parts as hot as on a road course with smaller diameter tires and much more braking going on.

[Ol'fogasaurus]

Traditionally the material in that “Diaper Pin” style of locking device is of a comparatively pretty soft material; I have easily bent several by hand (trying on purpose). They always seem to be used in “big hole” (read sloppy holes) situations and will shear or fail at times. I have also had one used on the locking pin of a VW tow bar fail (hopefully a softer material than what you are using) and drop out of the latch pin and cause the latch pin to fall out of the tow bar and put myself and other in jeopardy. I have also had used (not proud of it) Cotter Pins fail and allow the nut to back off when both ends of the Cotter pin were broken off by the castellated nut backing by the combination of off during hard use of brakes and acceleration and/or the nut being not torqued on properly.

I replace the same style of pin on towing pieces (a better material than the tow bar material); e.g., hitch, and tow bar locks, because of their potent for failing or dropping off. The few times I now use them: I run the pin on the pin it is to lock, past the alligator tooth, all the way to the big loop, to ensure that they do not worry themselves off. I think I can understand why this was done but I don’t really recommend it as I don’t think that their design is intended in that direction (after all, you have one side (the big loop) heavier than the other and potentially centrifugal force could cause the pin to fly off if the pin was not under load by the castellated nut; no locking via the eye at one end and the wings of a bent cotter pin on the other end).

Lee

[Piledriver]

If you have to rely on the cotter pin/external locking device, you have already lost.
Over time, if there is any movement, the splines in the drum will beat/strip out.

The cotter in is a final safety device and indicator only, IMHO.

If it keeps loosening, you have crap axles, nuts, hubs, spacers, or some combination.

[Ol'fogasaurus]

If you have to rely on the cotter pin/external locking device, you have already lost.
Over time, if there is any movement, the splines in the drum will beat/strip out.

The cotter in is a final safety device and indicator only, IMHO.

If it keeps loosening, you have crap axles, nuts, hubs, spacers, or some combination.

Probably true. Materials do stretch and this is planned for but then after a while, it can stay stretched as the material weakens/ages; the threaded part being the weakest area usually fails at the start of the thread. You can keep tightening cycles until, over time, the material ends up with the strength just short of being (and looking like) dog doo. Self locking devices only last so many cycles and mechanical locking devices are only good for so long as wear and stretching takes its toll. The trouble is that, in case of something like a stub axles, you just can’t go to the hardware store and for a max of say, $5 get a new part.

Another thing is I suspect that a lot of the spacers made now days are not made of sufficiently strong materials so they wear or compress quite easily.

Lee

[Dale M.]

If you have to rely on the cotter pin/external locking device, you have already lost.
Over time, if there is any movement, the splines in the drum will beat/strip out.

The cotter in is a final safety device and indicator only, IMHO.

If it keeps loosening, you have crap axles, nuts, hubs, spacers, or some combination.

I agree.....

I am using "hair pins" on back of Auto-X car and so are several of my buddies and as of yet (3-4 years now) have not had any bad experiences.... I have always thought of it as "torque" that holds nut/hub/axle in relationship.... The cotter pin is there to keep nut from backing off and hub from falling off..... Its quit disturbing to see one of your wheels & tires pass you...

Dale

[Joe vw]

The splines should tear out before the threads on the nut. Your first diagnosis was correct the nuts are crap. For some reason every aftermarket disk brake conversion with integral splines loosen up after around 100 miles. I think the hub section is soft and crushes then "sets".
I retorque the nuts several times in the first week of use after learning this. Once the set they seem to hold their torque.
Those cheap nuts appear to be cast- I would never use them. Cotter pins are faily soft also so those clip pins should be fine. Even if the nut could back off 2 degrees it should still be tight enough.

[Bruce2]

..., I thought the torque kept the axle nut in place.

This thought is 100% correct. The cotter pin is just a secondary safety device. When installed correctly, it does not prevent the nut from turning since the hole for the pin is sloppy. Whenever I take mine apart, they are always tight with no play in the drive flanges. I know that I can completely remove the cotter pin and safely run without.

In your case where you had things coming loose, it was due to crappy aftermarket parts compressing. A big culprit on IRS cars is the spacer between the two bearings. The genuine VW one is hardened steel to prevent it from crushing. Some aftermarket ones are soft crap that squish due to the tension in the stub axle when torqued. Same goes for the other spacers on the axle, both IRS and swing axle.

A second cause is play in the splines of the axle to drum. If a car is driven while the nut is loose, (like you did), the constant wiggling wears out the splines. At that point, no amount of torque will stop the loosening. Replacement is the only option.

[Marc]

If you have to rely on the cotter pin/external locking device, you have already lost...

Absolutely. I raced circle-track cars for years with NO cotter pins (would've stuck `em in if the tech inspectors demanded it but they never noticed); even under the stress & strain of high-G corners on 10-11" slicks and a locked differential I never had a single one loosen up. I only used OE German flanged (`68-up) nuts. Spacers between nut & drum, or soft third-world drum castings, might've caused a problem; I've never used (or seen) aftermarket nuts but until there're no OEG ones left on the planet I see no reason to try them.

[FJCamper]

Our PanAm Ghia is a 1965 with original swing axles. The rear brakes at the time of the Carrera Panamericana were aftermarket disks, which of course are splined like drums.

Our bearing spacers were original VW.

The drum splines did not wallow out, it was the threads on the nuts failing. The splines were remarkably unharmed, and those disks are on another car now.

We obtained some OEM axle nuts and finished the race on those.

FJC

[Bruce2]

I've never used (or seen) aftermarket nuts but until there're no OEG ones left on the planet I see no reason to try them.

This is my approach too.
We know the genuine article is good. Why risk an unknown aftermarket part when the genuine article is so easy to get?

[FJCamper]

Hi Marc, Bruce2,

Yes, OEM is best. At the time I ordered other than OEM axle nuts from CB Performance, we had only one spare OEM nut in the house and needed at least two more for Mexico, and the ad copy on the CB site portrayed their nuts as just nothing short of great.

In all my years of VW/Porsche work, from shadetree to line mechanic to service manager, factory team racer, etc., I had only seen one OEM nut break, and it was on my own Bug. I was alone in my home garage, and had just torqued it, and was going to find a cotter pin and heard a loud "pop" sound and something hit my work bench like a thrown rock.

Half of the nut had sailed across the room, the other half fell straight to the floor.

Go figure.

FJC

[Bruce2]

.... the ad copy on the CB site portrayed their nuts as just nothing short of great.

From now on, when you need a stock part, go to the classifieds of the Samba.