Potentially dangerous construction mistake, rear lower wishbone 3200

Robbe

Junior Member
Messages
86
#1
Hi all,
Last week I was both unlucky and very, very lucky. After a drive, I was almost home, already in my neighbourhood, just 100 meters to go, last speed hump (which I take very slowly), suddenly a big bang.
The car immediately shook and moved a bit to the side. I was driving 10-15 km an hour, and that was my luck.
What happened: The balljoint on the lower wishbone at the right rear had snapped off. Incredible!
The wheel was turning to the right as if it was the front wheel in a tight bend. My luck was that it happened at 15 km an hour, and not with 120 on the highway (ok, 140 then ). That would have been a very serious accident.

The construction of the rear lower wishbone is very peculiar, with a reversed balljoint where it is connected to the hub itself.
Normally a balljoint ends in a threaded part where a nut can be screwed on. But with this wishbone it is the other way around: the balljoint ends in a threaded tube where a bolt goes into.
And that is where the problem can arise.
Below 2 official Maserati publications of the situation:
3200-3.jpg
3200-4.jpg

In the parts diagram you might be able to see that the bolt that goes into the balljoint (nr 11) has 2 different sides: one side has a short part with threads, and the other a longer part.
But: in the workshop manual, the drawing shows only one part of the bolt, and that part has the long threads.
Notice how that part is shown as the side that connects with the stud holder arm.
Now, what did I find in my broken balljoint situation? You guessed it, the bolt was used the wrong way around.
Bought another wishbone from Steve Strange, and that one came with that same bolt. Also the wrong way around.
here are some pics of the difference:
3200-1.jpg 3200-2.jpg

When the short side is screwed into the balljoint, the construction is weak and can lead to very dangerous breaking of the balljoint. As it did in my case.
The long side has to go into the balljoint, even so deep that it screws into the part of the balljoint on which the new ball joint rubber sits (don't know how that is called), so all the way in.
I had no clues and saw no signs that my wishbone had ever been opened (car has done 120k km), and the manual drawing also shows a long threaded part on the wrong side, so it can be assumed my car is not the only one with reversed bolts.
Needless to say that I will be checking the other side as well before I drive in the car again.
Please keep this in mind for your car, have it checked!!!
When more cars have this, it is in my opinion reason enough for a recall.
 
Last edited:
Messages
849
#2
Definitely worth checking if it has had any suspension work, if the shank of the stud is well inside the hub carrier it would be clear that it is the wrong way / or something not right.
I had the rear end apart on mine so must check! My work!
But I remember not being able to remove one stud as it was so tight, so left it alone for fear of damage and more parts needed...
Thanks for sharing
 

Robbe

Junior Member
Messages
86
#5
Yes, now that it is all bolted together again, the protruding part is about 6-7 mm, I assume it originally was more like 1 -1.3 cm or so, but I was not paying attention to that at the time of unbolting.
The other side of the car is around 8-9 mm, so not sure what I will find there.
In the new and correct situation the short side threads start just where the bolt leaves the hub. If you remove the nut and washer, and see the beginning of the threads, you should be safe.

And to be clear about the first 2 pics of maserati themselves, the parts diagram shows it the right way, but the Manual shows it the wrong way...
 
Messages
71
#6
I don't think that reversing the bolt is the issue. The issue is whether or not the link dimension 'B' is set correctly. Get this wrong and the wishbone will be under static stress...

.. but I don't suppose that anyone who fits the bolt the wrong way round won't understand that.

Duncan
 

Robbe

Junior Member
Messages
86
#7
Distance "B" sets the toe-in, and if you follow the factory setting of 25.5 cm on that, you have massive Toe-in (in my car at least). But it is a good starting point from which you can set the toe-in to alignment specs.
It does not cause stress on the wishbone as it is balljointed...
And reversing the bolt IS the issue, my wishbone snapped where the bolt ended too early in the balljoint tube, as it couldn't be screwed in far enough because the short treaded part is too short . If it had been installed correctly, i.e. reversed from what the manual shows, the bolt would have gone as deep as the collar , and to fail, the bolt would have needed to snap as well. And that is not going to happen.

Thing is, if you remove the bolt, and do not take off the wishbone completely, you can't see if the short sided part of the bolt is too short or not, as you do not see the length of balljoint tube.
So there were no alarm bells for Luigi and Mario that it was installed the wrong way.
 
Last edited:
Messages
849
#9
Any photo of the broken parts?

Did the whole ball joint pop out of the wishbone socket or the ball joint threaded section fail?
 

Robbe

Junior Member
Messages
86
#10
The tube broke off at the point where it did not have the bold in it to strengthen it, so about 4-5 mm or so from the collar. So only the treaded section failed, as that is only a hollow tube when the bolt is not in it when it is installed wrongly
The picture in my first posting with the short side of the bolt, shown against the replacement wishbone, shows where the bolt ends in the tube when it is installed wrongly. There it snapped.

The replacement wishbone also came with a bolt. See picture below.
The nut that holds the stud holder arm (the arm marked with a triangle in the first pic, and also shown in the pic from the wsm ) was rusted solid onto the bolt, so it is clear the donor car had the bolt installed wrongly as well!! Note how much thread is not used, and this way goes into the bushing of the stud holder arm. Why have a threaded part into a non-threaded tube/bushing, obviously not correct!
Now I do not know who did that, the factory or a dealer on a later occasion, but 2 out of 2 sofar is not good at all...
3200-5.jpg
 
Messages
1,923
#11
Thanks for posting this, definitely worth checking, Its been a while since I was in this area ( well a couple of years probably) so not sure I have noticed this or not, I was conscious the bolt had a right way round but now I see this I am not so sure I have got this right. The extension of the threads on the end of the bolt would be a bit of a give away. I will be checking this soon!!!
 

hladun

Junior Member
Messages
75
#12
The nuts on the upper and lower ball joint nuts are to be sealed with Loctite and torqued to 78 Nm (57 ft lbs) according to the 3200 GT manual and this is quite low. My guess is that someone over-torqued the nut and that cracked the collar. So my advice is when you check don't be tempted to just torque it a little bit more.

Also, the manual says B should be 250 mm so 255 would give too much toe in. Regardless, toe in should be set by doing an alignment.

The real culprit could be the the parts are just not strong enough for the pounding the suspension gets on real roads. That lower ball joint is where all the force from the wheel goes to the suspension.
 
Last edited:

Robbe

Junior Member
Messages
86
#13
you are right, it is 250 mm, not 255. (I have the manual but made a typo).
It could be that it was overtightend at some point, no idea. No way to check.
But my point is that the bolt was used backwards, on both my left and right wishbones, and on the one I bought to replace my broken one

The partsdiagram shows it the right way, the Workshop manual shows it the wrong way.
It is as simple as that.
Guess what specialists and dealers and maybe even the workforce that built it look(ed) into for guidance...

Before anyone considers this an incident, I was very lucky to escape a terrible accident, and I am trying to wake you guys up to prevent someone suffering this at a normal speed.
I can't believe my wishbone will be the only one that will ever suffer from an old mistake in putting it together.
Our cars are almost 20 years old, and some mistakes just take some time to surface.
 
Messages
71
#14
I've copied this diagram from the Eurospares website:

RearSuspension.gif

It shows the rear wishbones and hub, with the all-important bolt (item 15).

If I am correct, the ball joint on the lower wishbone sheared at about the point where the threaded section of
the bolt ended inside the tube which forms part of the pin of the ball joint.

I can think of 2 plausible causes for failure.

1) The front lower tube of the hub carrier (1) exerts a shear (sideways) force on the ball joint pin at the point where the ball joint pin meets the hub carrier. If the bolt isn't driven into the ball joint further than that point, then the hollow pin must resist that shear force on its own. The bolt, if driven in past that point will add strength to the pin at that point.

2) The bolt exerts a tensile (pull) force on the ball joint pin. If the nut on the end of the bolt is done up too tightly, then an extra tensile load on the bolt under dynamic load may cause the ball joint pin to shear. In this situation, it wouldn't matter which way round the bolt was fitted.

I honestly can't be sure which was the cause of failure, but I suppose the way to avoid both causes is to assemble parts according to the manufacturers drawings and to use the correct torque settings on nuts and bolts.

Duncan
 
Messages
594
#15
0
Before anyone considers this an incident, I was very lucky to escape a terrible accident, and I am trying to wake you guys up to prevent someone suffering this at a normal speed.
I can't believe my wishbone will be the only one that will ever suffer from an old mistake in putting it together.
Our cars are almost 20 years old, and some mistakes just take some time to surface.
Your highlighting this possible issue is very much appreciated, believe me, anyone who has read this will (or should be) checking :thanks2:
To add, when I replaced the tie rods the mm were 257 & 258, but that was from the back of the locking nut.
 

Robbe

Junior Member
Messages
86
#16
Duncan,
the diagram you show (the old diagram I assume, Eurospares these days shows the one in my first posting), pictures a bolt with 2 equally long threaded sides. The new diagram on Eurospares shows more (correct) detail.
Maybe Maserati is aware of the problem and now shows it the right way?
As for causes, I strongly believe nr 1, as the broken off hollow part sheared right off at the exact end of the bolt. Metal fatigue maybe. But if there had not been a hollow section (i.e. the bolt had filled that up when installed with the long side into the balljoint), it would not have sheared.
As I have seen the 2 bolts on my car, and the "spare" that I got with the replacement wishbone, it is 3 out of 3 that are installed wrong, leaving a hollow section in the balljoint tubed end... it is just 4 or 5 mm, but can cause a huge problem...
Maybe the combination of all factors, combined with speed bumps and potholes and 20 years of use..(18 in my case)

Lozzer, measuring has to be done from the front of the large locking nut (as you probably know), and then it has to be set at 250. But I think your values sound good (subtract the thickness of the nut, which is 8- 10 mm or so to get 248 -250 or so). Alignment is more important than a starting point which I think 250 mm should be considered as.
I think my values were a bit lower, but I have had not had my car aligned yet. It now surely needs that!
 

hladun

Junior Member
Messages
75
#17
If you want to see how much deeper the bolt (stud actually) can go into the ball look at the bolt picture in Robbe's post above. (Mine sticks out about the same.) If you reverse the bolt and it goes into the ball joint further you have the length that is now above the nut available. A word of warning here, if you reverse the bolt you must make sure there is enough depth and thread available in the collar. If you bottom the bolt in the ball and then over-torque it that is the quick and easy way to crack the collar.

It's unfortunate how this thread wanders between the stud bolt and the rear link. Been dazed and confused for so long it's not true
 

Zep

Moderator
Messages
1,850
#19
Without wishing to poor petrol on the fire, but I can see Duncan's point. I also find it unlikely that you would have 3 wishbones that would all have been incorrectly assembled - if this statistic was born out across all of the cars in the field and was the cause of the failure then we would have seen many, many more failures.

I also don't think it is a good design to have a stud completely bottom out in the ball joint socket. As a rule when putting a bolt (or stud) into a blind hole you do not want it to bottom out in the hole, as Duncan and Hladun have pointed out, this is another point of failure as it will increase the tensile load on the ball joint nose at a very localised point. So for me, the longer thread should not be in the ball joint. Lets be clear, no matter how far the stud is screwed into the ball joint there is always going to be a part of it where the stud ends and the ball joint body begins where the it is going to have to do the job on its own - or in this case with the hub carrier supporting it.

As Duncan has pointed out, the nose of the ball joint is intended to be fully seated into the hub carrier. In this way, the nose of the ball joint is not subjected to any shear forces along the length of the nose - all of the stress is concentrated at the face of ball joint before the shank. From my experience putting this assembly back together, if you wen't paying attention, you could snug up the nut, see that the toe link is against the hub carrier but not check the ball joint insertion and think all is well.

So to summarise:

1 . If the stud is inserted short threaded end into the ball joint and over-tightened it will increase the tensile load on the ball joint nose and potentially case a failure. If think the forces required to cause the ball joint - which is a hefty bit of kit - to exceed its tensile strength would mean a significant amount of over-tightening.

2. If the stud is inserted long threaded end into the ball joint, bottoms out and is over-tightened it will increase the tensile load on the ball joint nose and potentially cause a failure. This is far more likely than scenario 1.

3. If the rear hub is assembled incorrectly and the ball joint nose is not fully seated in the hub carrier, this will cause a shear force on the ball joint nose in a place that it is not designed for and will cause a failure (for me at least, this is far and away the most likely scenario in this case).

For me what has been seen here does not make the case for assembling the rear hub outside of the manufacturers drawing. It does suggest that we should make absolutely sure that the ball joint is fully seated into the hub carrier and all bolts are correctly tightened.
 

Robbe

Junior Member
Messages
86
#20
1) it is safe to assume all cars have been assembled with the short side into the balljoint up to the point where there is no threaded section left on the stud. The non-threaded part acts as a stop.
That way the stud leaves about 8 -10 mm of threaded section in the balljoint tube unused, creating a hollow tube exactly ate the part where the balljoint tube does not sit in the hub carrier.
All forces are then on the hollow part of the tube instead of a stud in that hollow tube as it would be if the stud was reversed with the long side in the balljoint. So not logical in my opinion.

2) because then the longer threaded section is on the nut side with the toe-in adjuster, the threaded section sits in the bushing of the toe-in adjuster.
So a bushing over a threaded part of a stud! Not logical.
If you however reverse it, then the bushing exactly has the plain part of the stud and you can just see where the short sided thread begins (and then you put the big washer over it so the nut does not reach that beginning)

3) the parts diagram shows that the longer side has to go into the balljoint ( agree, WSM shows other way around).

4) In my case the balljoint tube broke at the point where it was hollow. So it happens. Metal fatigue takes some time to develop, so the fact that it is not a common problem now does not mean it is not going to be in the future.

My facts above are facts, not possible alternative circumstances which might be true in themselves, but can't be verified to what extent they were also contributing to the real life failure that I suffered.
And in the mean time these alternative circumstances weaken the warning, meaning: "it happened obviously because someone had overtightened it. Maserati did not screw up." Well, I beg to differ.
I did not start this thread to discuss everything that also might have contributed, I started it out of obligation to fellow enthusiasts, to warn for a potental dangerous situation.
I consider my duty of warning fellow owners done.
 
Last edited: