Loose subframe bolts
Loose subframe bolt repair on mk5 VW
There are somewhat well-known issues with the bolts used by VW to hold the subframe. The subframe, LCA rear brackets, and the subframe bracket, all have holes which are larger than the bolt diameter. After a hundred thousand miles or so, (sometimes more, sometimes less) they can loosen a bit, and if so, may result in a thump when you take off in a turn, or may result in alignment not being steady (goes out of alignment frequently). mine got so bad they would clunk in minor bumps which made the ride seem like the tires were rocks..
This is a somewhat fuzzy photo of the bolt which holds the subframe bracket onto the frame. This bolt is accessible through the hole in the Lower control arm (LCA). As you can see here, a coating of oil from a previous leak is seen to be scraped away, both under the bolt, and where the bracket mounts to the body. you also can see the oil was removed where I used a socket to test the tightness of the bolt.
http://www.ecstuning.com/News/MKV_Subframe_Spacer/ES2102460/ has spacer (like super lock washers) and replacement bolts and a nice video.
The bolts used are M12x1.5x110 and are different strength than the oem black ones with varying diameter on the shaft.
besides these, which are at the rear of the subframe, I replaced the following as well.
N105-286-02 M12x1.5x75 two needed to mount the front of the subframe to the subframe bracket.
N910-398-02 M12x1.5x90 four needed to mount the subframe bracket to the body, and the LCA rear bracket/bushing to the body.
all these get torqued to 70 NM plus 90 degrees.
you also can get a more expensive subframe bolt and bushing kit from tyrol sport. the site also has a nice video for reference.
http://www.tyrolsport.com/volkswagen audi gti jetta a3 TT TTS TTRS subframe clunk repair rigid collar bolt kit
for reference, Here is figure from http://www.vwpartscenter.net/parts/...iteid=215911&vehicleid=206828&diagram=F507060
The subframe is #16, the subframe bracket is #18. the subframe to bracket bolt in the fuzzy photo above can be accessed through the hole in the LCA #2.
Before figuring out this was the problem, I went through several sets of tires, (they have a 30 day ride quality deal, but still costs mounting) and became aquainted with a couple local alignment places. the ride is now much better with suspension parts that stay where they are supposed to be.