[solved] rear-end clunk on articulation

[photoleif]

posting for posterity.

i had a clunk coming from the right-rear side on compression and extension, particularly on wavy and rutted roads. it was quiet / drove fine on smooth pavement. the sound was definitely a clunk, not a squeak or chatter. i went through some of the usual suspects -- re-torqued upper and lower control arms, replaced sway bar bushings, checked for cracked mounts... nothing.

when i hopped on the back bumper, i got way too much bounce so i ordered new shocks, thinking one was perhaps bottoming out in addition to being shot. turned out that the right rear shock pin had completely sheared off above the mount, and so of course it was clunking. put new bilsteins in there and problem solved, plus the 4R feels less 'loose' in general.

 

[repo]

Sheared off or rusted off? Those mounts are impossible to keep clean, the drain hole clogs up with pebbles. I have to reach up there a few times a year and scoop out handfuls of dirt and sand and rocks. When I put my last shocks in I lathered those bastards with antiseize and put long vacuum caps over the end to cover threads and the stupid Bilstein hex socket.

 

[photoleif]

Sheared off or rusted off? Those mounts are impossible to keep clean, the drain hole clogs up with pebbles. I have to reach up there a few times a year and scoop out handfuls of dirt and sand and rocks. When I put my last shocks in I lathered those bastards with antiseize and put long vacuum caps over the end to cover threads and the stupid Bilstein hex socket.

edit: i had a much closer look in better light, and the pin's diameter is about half of what it ought to be, due to rusting out. it appears that once it was weakened in this way, it broke and then got banged around and blunted. so mainly the culprit was rust, but it also seems to have sheared (not surprisingly).

previous comment (partially invalid): your question is quite valid, and unfortunately the damage to the metal is such that the cause is difficult for me to determine. the edges are a bit rounded off and though there's some rust on the surface where it broke, it doesn't entirely look rusted off. you're 100% correct that the mounts fill with crap -- dust, pebbles, dirt, everything. it's a design they clearly didn't think through.

pin.jpg - Google Drive

i'm attempting to share this image off google drive, since photobucket puts their overlay on images. if it doesn't load, let me know.

i like your approach of slathering the thing with antiseize and capping. do the caps stay on as desired?

 

[photoleif]

Sheared off or rusted off? Those mounts are impossible to keep clean, the drain hole clogs up with pebbles. I have to reach up there a few times a year and scoop out handfuls of dirt and sand and rocks. When I put my last shocks in I lathered those bastards with antiseize and put long vacuum caps over the end to cover threads and the stupid Bilstein hex socket.

i did exactly that, a few days ago based on your idea. thanks for sharing that. i feel better about their longevity, or at least my ability to take them out when it's time.

 

[repo]

i did exactly that, a few days ago based on your idea. thanks for sharing that. i feel better about their longevity, or at least my ability to take them out when it's time.

Hopefully you put antisieze or fluid film or something all the way down between the bushing because thats where the rust snaps them. I've seen some people drilling out the drain holes in the top mount "dish" bigger to try and avoid it clogging up but dont know if it works. I havent tried taking off the vacuum caps but they are long enough to cover the whole threads tightly, with antiseize on the threads. Last time I had to grind level spots in the rod to grab with vice grips to unbolt them, because that hex hole filled up with grit and rusted and was impossible to clean out. I think those caps should work. And I suppose making sure the bushings are good and tight so the rod doesnt grind on the mount would help.

 

[photoleif]

Hopefully you put antisieze or fluid film or something all the way down between the bushing because thats where the rust snaps them. I've seen some people drilling out the drain holes in the top mount "dish" bigger to try and avoid it clogging up but dont know if it works. I havent tried taking off the vacuum caps but they are long enough to cover the whole threads tightly, with antiseize on the threads. Last time I had to grind level spots in the rod to grab with vice grips to unbolt them, because that hex hole filled up with grit and rusted and was impossible to clean out. I think those caps should work. And I suppose making sure the bushings are good and tight so the rod doesnt grind on the mount would help.

hi. sounds like i have a little more to do. i applied antisieze over the exposed threads after they were mounted, then filled the vacuum caps with more antisieze and stuffed them on, and left all the squish-out on the short bit of threads that weren't fully covered by the caps. it's not as thorough as your suggested approach, but i really don't want to take everything apart to add more grease. we lightly greased the washer and cleaned out the 'dish' (mounting bracket) before installing the shocks and tightening down so the bushings as you mention are firmly compressed. i suppose ideally the cup would be cleaned down to paint or whatever is there, then squish grease all around above and below the cup, and then install. i suspect that wiping a big blob of grease on the nut even now would be better than zilch. even though it's going to collect dust, sand, grit and so on, thinking about wads of grease elsewhere like where it gets thrown up onto body panels from driveshaft joints, that area is 'dirty' with dust all over and in the grease, but it's essentially rust-free on my vehicles due to the grease coating.

any weep hole there quickly fills with gluck. i believe there's one small hole per side on my 4R, around 1/8" diameter, and they were jammed with grit, and in the cup / perch area there were a bunch of pea gravel size rocks on sand and such. it's an essentially inexcusable design that should have been more patterned off how the front shocks mount to a convex lid that sheds debris, not a cup that seems designed to capture it.