AudiWorld Forums - For those wanting to know why control arms fail and a cure that works

Ever since I encountered my first lower control arm failure at 18k miles on my A4 1.8QTM I've been obsessed with finding out why and how to cure it.

First thing I've noticed is that the control arm balljoint is one of two ball joints that are oriented with the ball at the top. The other ball joint that is oriented that way is the tie-rod. Both have a history of failure tho the control arm being a higher-stressed item and closer to a known heat source (brakes) is the clear winner in the war of attrition.

The culprit causing failure is two-fold. First thing thats wrong is that Audi saw fit to design a suspension that would only allow the ball joint to be oriented at the top instead of the bottom. What happens is that the balljoint in constant movement and next to a high heat and internal friction encourages its lubricant to liquify and collect in the rubber boot or leak out through the flimsy retaining ring that keeps the boot secured to the tapered shank threaded bolt.

The number 2 culprit in the control arms is the grease. A black, lightweight moly-appearing (molybdinum disulfide) grease that has the heat-shear and liguifying properties of butter. This stuff becomes totally liquid at just over 100F. I've tested it in the oven in a cookie sheet stacked sideways and it liquifies and runs down the vertical surface before 110F and puddles at the shallow side lip of the pan. This is a ridiculously low-temp/light body grease for such an extreme pressure/high temp area!! If anyones got an old control arm with any grease remaining in the rubber boot, pull some out and dab it on something and put it in the oven and test it yourself. I was gape-jawed it liquified so easily, quickly.

An interesting aside is that I've pointed my laser IR temp gauge at the control arm balljoint after just driving around in rush hour traffic and I get readings of 160F off the balljoint. After 5-7 laps around the local roadcourse the same balljoint is 240 and spit wiped on the balljhoint with a finger sizzles and evaporates off immediately.

Now the cure: Many here know I have installed "zerk" fittings in my control arms and using a high temp synthetic red moly grease rated at 500F and that my groaning/creeking control arms have never returned. I've also done this mod on 7 other local cars that were making noise and they too have had no problem since. It seems to cure them forever as one local car has over 50k on it since I did his without reoccurence and he hasn't re-greased em yet.

My next set of control arms is on the bench and I'm going to do this set REALLY right. They are brand new Audi control arms and I'm removing the boot and cleaning out all the factory grease and refilling them with the good stuff. I'am also adding the zerk fittings with removeable dust caps in the top in the event they ever get noisy again and need re-lubed. Additionally I'm going to use stainless steel safety wire to affix the boots to the balljoint housing/tapered shaft so there's no chance of the grease leaking out.

I'll post pics of this procedure in a before/afterstep-by-step fashion and also try to do some pics of the stock grease liquifying at low heat over the weekend.

If anyone's interested I can probably build sets of these control arms in the $400-450/pr price range using brand new OEM control arms. Or it's an easy DIY project with a 14x28 tap/zerk fittings/safety wire pliars, SS wire and a grease gun.