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Caution: Lower control arm failure could be ball joint failure


#1

In my oft-repeated list of “The Big Seven” things likely to strand a vintage car (fuel delivery, ignition, cooling, charging, belts, clutch hydraulics, and ball joints), it may seem that ball joints are a forced fit. Nearly everyone who has distance-driven a vintage car has had the points close up at an inopportune moment, or had the temperature gauge swing into the red in traffic, or had a bad alternator fail to charge the battery. But fewer people have lost a ball joint while driving.


This is a companion discussion topic for the original entry at https://www.hagerty.com/articles-videos/articles/2018/11/19/lower-control-arm-failure-could-be-ball-joint-failure

#2

Having done the same replacement on the same model car, I’d advise replacing the ‘thrust arms’ or ‘tension arms’ at the same time. These are the ones you can see in the photo looking very dirty and unkempt facing towards the front of the car.

In the E39 these are fluid filled bushings which control the ‘thrust’ of the car- especially when you put on the brakes. Checking the underside of the frontmost bushing (under the plastic cap) you’ll find that many higher mileage cars (probably every 40-60,000 miles) the rubber will fail and leak the damping fluid out. The telltale clunk on sharp braking and wobbling front end will occur - may feel like an out of balance wheel but it’s just looseness in the suspension osciallating.

If you have an E39 and plan to keep it for a while, spend the bucks and replace the thrust arms, control arms, sway bar links and sway bar bushings. Then you’ll find out why all the motoring magazines raved about them back in the day. The youngest E39 just turned 15 this year, and they are all due some love in the front end.


#3

Given there are no safety inspections in the state i live ( ca) Im surprised there are not more issues like the ones noted in this article… I live in an area with bumpy, windly back roads (many of which are gravel surface) and it not unusual too see a car or truck at the roadside with collapsed front suspension due to detached ball joint on the control arm… one local has a 70s GM 1/2 ton flatbed truck that drives along the road like a crab… been the same for years… rear axle is well out of alignment with front … typical of broken spring center bolt…execept those GM trucks are coil sprung at rear… I dont drive too close as it looks like an accident waiting to happen…


#4

As a mechanic, I have seen and driven some pretty terrifying vehicles that should not be allowed on the road. On certain vehicles a ball joint failure would have been best case scenario, worst case would be the subframe separating from the body when you went over the rail crossing.


#5

A word of caution when testing for bad ball joint. Know where the spring or torsion bar attaches. Most torsion bars and many coil springs on vintage cars transfer the load of the car to the spindle through the lower control arm. Other cars, including any with McPherson struts (the McPherson strut is the “upper control arm” on a car so equipped), transfer the load to the spindle through the upper control arm. On a vehicle with the spring or torsion bar bearing on the lower control arm it is necessary to jack the vehicle by the lower control arm to remove the weight of the vehicle from the ball joint before testing. Conversely, on a vehicle with the spring bearing on the upper control arm, or a vehicle with McPherson struts, it is necessary to jack the vehicle by the vehicle frame to remove the load from the ball joint. Use the wrong jack point and even the worst worn ball joint will test “good”. However, even a bad ball joint may pass the test described. Better is to use the screening technique used by safety inspection stations here in Massachusetts. With the wheel a couple inches off the ground use a pry bar under the tire to lift the tire. No movement should be felt in the ball joint. Of note, a ball joint that fails the screening test is likely already well beyond its service limits and needs to be replaced. The only precise way to test a ball joint is with a dial indicator to measure the actual play in the ball. While you’ve got the tire in the air, grab the tire at 3 and 9 o’clock and twist it back and forth to feel for play in the tie rod ends, drag link, etc. As with the ball joint, no free play should be felt. Each side needs to be tested separately. Don’t have ball joints? With the aid of a helper the same test can be used to screen for badly worn king pins/spindle bolts. As you pry on the tire have your helper watch for movement in the king pin. Ideally there will be none.