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Ball joints and separation 1

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dicer

dicer

Automotive
Feb 15, 2007
700
Was working on an LS400 1990 vintage, studying the front suspension I was surprised at the design of the lower control arm and the way the ball joint is loaded. I think there are other brands that do the same as well. Personally I think its asking for trouble, all the weight and road shock allocated to that shock spring assy is on the small surface area side of that ball joint. Why didn't they load it to push the ball into the socket instead of pulling out of the open end?
Not going to be very comfortable driving these cars now.
 
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Every upper-and-lower-A-arm suspension with the spring acting on the lower control arm (and that's most of them) is like that. It's been done that way for decades.

Having the spring act on the upper arm would require putting the spring very high in the vehicle.

MacPherson doesn't have this situation, but the geometry isn't as good.
 
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Removing a ball joint from a spindle requires tremendous force with a press after the nut is removed. Try removing the nuts from your lower ball joints and driving around for awhile and see if the ball joint pulls loose even without the nuts.
 
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like this?

It can sure be a problem if the ball joint wears severely without detection.
Google up Honda ball joint separation. It happened to my daughter's Accord not long after getting the annual Massachusetts inspection sticker, which is supposed to include checking suspension for exactly such conditions. One front wheel went << blah >> driving on a neighbor hood street approaching a stop sign. The cool NAPA impact tool for removing and replacing Honda joints now resides in my tool box.

I believe it >> could << have been designed to fail safe, not unplug.

The brake rotor mounting of that vintage is also noteworthy for being contraridly inside out.
 
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The odd thing is that the 'spherical joint in tension' design passes any reasonable durability test, so long as the boot doesn't split. Once the boot splits the life of any spherical joint is just a matter of time, whichever way it is loaded. Sure, you have to use a (~3mm) bigger diameter part for SJiT, but the packaging advantage is enormous.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376
 
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Oh Yes, the Honda ball joint boot(s) were split. They cracked on the OD, and the loading and molded boot contour was such that rather than being obviously open, they were more like pursed lips like the selfie duck face pose popular amongst young women.

Once upon a time I bought a well worn AMC Hornet for short money and as expected with a host of mechanical maladies. The springs were mounted on top of the upper control arms. The schoolmarm previous owner drove it so long that one balljoint popped thru the top of the ball joint housing like a compound busted hip. I'm not advocating drive-it-to-destruction maintenance (as is seemingly encouraged here in the US by States without inspections) , but it Still drove pretty good. And, it had not subjected anyone to what civilian folks would call a "busted axle" on the highway in high speed commuter traffic or even a more tranquil city streets.
 
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Brian, evidently someone, well lots of someone's have awakened. I never said to locate the spring differently.
Just the position of the lower ball joint. Even Lexus woke up as it looks like the newer 430's etc. have them flipped.
And there are many other makes that do the same. Even if the joint is worn to the point of separation in the flipped position at least the sprung weight on that side will hold the arm on the ball, and a much more safe design in my opinion.

This shows a proper positioned ball joint. Personally I do not approve the removal method.
 
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Yes, I think the ball joint in compression design is likely to become the defacto standard for the weight bearing outer ball joint. The degradation in steering that results due to increased compliance is just one of those esoteric things that will suffer, but I don't think it is a deal breaker.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376
 
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Learn something every day; I've never run across an upper-and-lower-arm design with the knuckle extending below the ball joint like that.

High-performance example done the traditional way: Chrysler Viper.
Old skool example, and GM did it this way for decades - although it appears that GM flipped it around to "your way" around 1999
 
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dicer said:
Not going to be very comfortable driving these cars now.
Click to expand...

Just tell yourself these ball joints are less loaded than their «higher» counterparts, thus less likely to break. [bigsmile]
 
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Ford, GM, and Chrysler all did it that way for years and years.
If you have an old car or one with a lot of miles, its suspension should be closely inspected at least once.
Those ball joints lasted for lots of miles, especially if properly lubed.
And the steering gets pretty sloppy when they get worn.
We are sooo spoiled with modern cars...
(I love it!)

Jay Maechtlen
 
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One other design aspect - since most tires have much lower profiles than 20 years ago, there's more room for the ball joints - can get reasonable distance between upper and lower pivot points even with the lower in compression.
fwiw
jay

Jay Maechtlen
 
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JackAction, Not in the case of the early 90's LS400's just go look at one. The lower ball joint has all the spring load pulling it out of the ball socket. The upper control arm is an idler the spring bypasses it. So the upper joint is way less loaded than the bottom one.
 
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dicer,

I was referring to the fact that, given the same space is available inside the wheel, if you load it to push the ball into the socket instead of pulling out of the open end, the first case will be more loaded laterally than the 2nd case because the ball & socket are slightly further away from the tire contact patch (lever effect).
 
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GregLocock, you’re right about the Chinese sourcing. There are a few manf/distributors that offer quality, but price has driven the race-to-the-bottom. While quality makes sense for safety and in view of the ball joint AND installation cost, the average customer generally won’t see the difference within his attention span.

With reference to the initial issue, ball joints usually have a plastic insert in the “bottom” of the ball socket for lower friction (and maybe noise). So they’re designed to take the load at the round end of the ball rather than the stud end.
 
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RE: "Ball joints usually.... "

Maybe over 51% of vehicles use ball joints operating with the stud in compression, but Hondas were pretty popular back in the 90s.
Here is a picture of the somewhat infamous Honda design of the 90s .

Spring force is applied to the lower control arm via a clevis on the lower end of the spring shock assembly.
Tire and steering knuckle is forced upward at contact patch. The knuckle and ball joint stud are above the control arm, so the stud is in tension.

It is of the same vintage as the universally admired inside out brake rotor design.
Wanna change the brake rotor? Just Disassemble the whole front suspension and press the hub out of the knuckle.
Do they really do it that way in Formula 1?

I genuinely admire Honda's elevated and usually clever engineering on consumer products, but there have been a few times when it seems like the choices were made by the guys behind the monitor without any callouses on their hands, except the one on the finger with their college ring.

 
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" ball joints usually have a plastic insert in the “bottom” of the ball socket for lower friction (and maybe noise). So they’re designed to take the load at the round end of the ball rather than the stud end."

I sort of disagree. The plastic liner goes around most of the ball, it obviously has a hole for the stud.

20140423160251_44732.jpg



If the manufacturer of the part said it was OK for a tensile application (and they still do, I think as I said above typically you need a 3mm bigger diameter for a given set of load cases) then there didn't seem much to prevent people from designing suspensions that way, since they did pass durability testing. The ball joint will only fail (typically) if the boot fails, and if the boot fails the ball joint is not long for this world whether in tension or compression. If a bootfails in durability sign off that is a big red flag. The big differences recently are the post failure behavior and customer expectations, coupled with longer service intervals, so split boots are no longer seen, and perhaps some bitter lessons to do with suppliers making post J1 changes. The record for that by the way that i know of is 80 differences between the J1 drawing and the production part one year later (not on a ball joint admittedly, but from a big multinational supplier with HQ in the USA).

Having said all that I have completely failed to find design tables for a spherical joint showing the difference in load rating in compression and tension.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376
 
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