I'm getting my fair share of 'knocks' at the moment, now wifey said Yeti is rattling all the time over bumps. Test drove it at 15mph on quiet road violently swinging the steering right and left. Sure enough, a metallic front end knock on both right and left swing of the front suspension. Anybody who has gone fault finding for front knocks will have a list to work through e.g:

Broken front coil spring, bad shock absorbers, loose bolts on shock mounts, loose shock fixing nut, front strut swivel bearings, bottom suspension ball joint, engine mounts, exhaust or hangers and anti roll bar (ARB). Search the web and you find many inconclusive investigation reports for Skoda and vags.

 

I had both front struts off a VW last year, it is tedious, but the best way to get to the bottom of that illusive knock. This time I checked the coil springs for breaks first then started with a pinch bar and the front suspension normally loaded, huffed and puffed, pulled at everything - an MOT PASS, but the knocks were still there(?)

 

Then I decided to hack into the anti roll bar. The best way with those is to remove the tie rod connecting the ARB to the strut at one end, hang a length of 2" steel scaffold tube on the end of the ARB then test the centre mountings and far end tie rod left connected. Those centre bushes are hard to access but I found no play. Repeat for the second tie rod.

 

I started to undo the nut on the ball joint connecting the tie rod to the ARB. I've learned that is the best one to start with! Strange the nut on the left side was tight, but the nut on the right side turned (?). It wasn't, loose but the ball joint spigot was turning. I fitted a spline key into the end of the joint and attempted to tighten the nut. If I had carried on, the spline would have been wrecked and a new tie rod would be required. As the left side tie rod was disconnected I poked my short length of scaffold tube on the ARB end and waggled it up and down. Immediate metal to metal contact from the thread of the right side lower ball joint hitting the hole in the ARB! I had to find out what was going on because so many have just replaced the tied rod (with ball joints) but my ball joints had no play.

 

On the basis that new nuts are cheaper than tie rods, I cut a slot in the ball joint nut with a 1mm disc grinder whilst avoiding the threads on the joint end. A couple of chisel smashes later the nut could be turned with a spline key in the joint acting as the counter turn. So what is going on? These ball joints have plain M12X1.5 parallel threads and there is no taper fit on the ball joint. The hole in the end of the ARB is 12.5mm diameter which is 0.5mm oversize. They rely on the ball Hex collar nut torque giving sufficient friction to stop the thread moving around the hole in the ARB. Unfortunately, they screwed up because the 'collar' on the ball joint is narrower with a smaller contact area than the collar nut. They got the collar nut about right. but not the other half of the sandwich!

 

I'll leave it to your imagination to decide what you can do with a short 8mm wide strip of 8 thou brass shim and a M12 penny washer. I replaced both left and right lower tie rod ball joint nuts part N015 081 6 for £2.50. Test drove Yeti and there were zero knocks from the front suspension.

 

This fault is very hard to find and many have just replaced the tie rod and ball joint assembly. I bet the dealers do this too. I think the sequence of events is the lower ball joint nut slackens off first, then rusts on the thread. Anybody using the spline key and wrench will find the nut torque in limits when the nut has actually seized and locked. The test is to try and tighten the lower ball joint nuts. If they turn along with the thread, there is no friction to stop the thread banging around +- 0.25mm in the hole.

2" Scaffold pipe and a keen mind, what a combination!

my kind of man

I take it, it's all about cheapness of manufacturing and assembly.

Yep, If they had used more expensive taper ended ball joints for the ARB tie rod, reinforced the end of the ARB and the strut mounting to take the taper, there would not be a problem. I suspect the ARB is not given the same priority as the lower suspension ball joint. If the ARB system knocks or fails you don't lose the front end of the car.

Edited 17 February, 201610 yr by voxmagna

...So what is going on? These ball joints have plain M12X1.5 parallel threads and there is no taper fit on the ball joint. The hole in the end of the ARB is 12.5mm diameter which is 0.5mm oversize. They rely on the ball Hex collar nut torque giving sufficient friction to stop the thread moving around the hole in the ARB. Unfortunately, they screwed up because the 'collar' on the ball joint is narrower with a smaller contact area than the collar nut. They got the collar nut about right. but not the other half of the sandwich!...

Excellent deduction. Would be nice to think that a Skoda (and probably VW, Audi, SEAT etc) manager will "print this off" and send it to service departments and their engineering team...

Would it be beneficial to use some kind of gap filling, retaining compound like Loctite 660?

I don't believe in using goo, even shim isn't the best fix. You start with a fundamental design problem because they rely on friction from torque to stop a 12mm bolt slopping around inside a 12.5mm hole. The ARB is continually springing about putting high impact loads on the torque clamp 'sandwich'. There are two ways to solve the problem. Best is they should have used taper end ball joints with female tapers in the ARB and the strut mount. There are plenty of cheap taper ended ball joint possibilities. Another way is to manufacture the ball joint thread with a short plain 12mm diameter shoulder and reduced M10 thread, then bush the ARB and struts to be a thou oversize. I spotted another issue which aggravates the problem: They appear to have powder coated the ARB. After torquing down the ball joint, both the back of the joint and the nut are torqued against the coating. You can see this when you remove a lower joint, because the contact pressure surface is compressed compared to the surface around.

 

As I said, if you can turn the lower link to ARB ball joint nut and the thread moves, you can expect knocking. Skoda owners or those with VAGS using the same system will get charged up for replacement tie rods to stop knocking. When a tie rod is replaced the ball joint back nut is re-torqued and the ARB knock problem 'appears' fixed (for a while) and you think your money well spent.

Will there be posted any photos of these details and the tools used for fixing this?

Will there be posted any photos of these details and the tools used for fixing this?

I take a responsible line when working with suspension and brake parts. The skills and competency of individuals can vary. The internet is a good place for sharing information and ideas. However, individuals do not have access to the same resources and in-house testing as manufacturers. If you want no risks or come back, you just buy the approved OE replacement tie rod ball joint assemblies, keep them torqued to spec and keep checking the torques. That is what you would expect to pay the dealer for until Skoda designed and tested a new part or released an official modification. Because many other vags use a similar design for the ARB system, modification or improvement pigs are unlikely to fly in my lifetime! More likely the manufacturer would just write a check line in the routine service procedure.

 

The problem comes after the ball joint thread has been knocking in the ARB hole. Either the nut siezes due to rust or the ball joint thread gets damaged, the nut locks up and the torque you appear to have, is not holding the 'sandwich' together. Then what you have could be a nut meeting torque spec., but an assembly which is loose. I am pleased as Larry MY12 Yeti now has really tight front suspension with zero knocks as it probably left the factory. I shall be inspecting my VW for early signs of a similar problem.

 

If you are getting knocks from the front suspension you cannot 'tie down' (pun), do the check I suggested on the bottom link rod ball joint nut first.

 

I'll leave it to your imagination to decide what you can do with a short 8mm wide strip of 8 thou brass shim and a M12 stainless penny washer.

 

Hi, this was a great read, so detailed, my yeti is doing exactly that, light knocking front o/s, I was just wondering, and assuming you used axle stands, where did you place the jack? It's just that I would love to take a look at this job myself, but I am not going under the car on a jack only, and there seems to be differing ideas on the jack/axle stand placement, as there only seems to be limited lifting points. So since you have ( i'm assuming) jacked up the yeti and used axle stands how did you do it? And also can you post some pic?

On another note, this is the first forum i have ever joined, so i do apologize if my protocol is incorrect.

A common place is at the base of the A pillar (just in front of the front door hinge)............you should see a ‘doubled up’ weld seam there.

Hi, thanks for response, but if i jack it up there, then were do i put the axle stand? I was rather hoping that i could jack it up on, lets say the front suspension somewhere, and put the axle stand under the A post. I have done this before on other cars, but i am not sure the yeti is up for that type of procedure, and i really don't want to damage it. So, if any one out there has jacked up their yeti anywhere other than the A post, and it worked out okay, i would love to know

Yeah, the undertrays all cars seem to have these days are a right pita.

Keeps the engine clean, i like that part 

1 minute ago, Likeglass said:

Keeps the engine clean, i like that part 

It’s there for the aero drag reduction/lower emissions.

And that

It's a while now since I did this and no knocks have returned. I have a number of tricks I use for front end jacking. From memory with the underbody tray removed, I think I used a long length of 4" X 4" timber across 2 places and just rearwards to give plenty of room around the anti roll bar. Then I put the trolley jack in the center with small pressure, removed both wheels and up she went to reveal all.

“For undertray removal, first jack up the front of the car”..............errr right

Thanks V