Broken rear upper trailing arm

Sparky

Original poster
Member
Dec 4, 2011
12,927
Per Roadie's recommendation after I mentioned this in another thread I'm posting this thread.

Friday early afternoon I was accelerating and merging onto a highway. Traffic was fairly heavy and the ramp was short, so I wasn't being light with the accelerator. I was focused more on traffic than potholes and, well, one was a doozy. I hit it hard and the end result just about threw me into the semi truck next to me and I had to catch the vehicle. Now I've hit harder bumps before but never really had one throw the vehicle like that. I caught it and realized that going straight the wheel was now cocked to the right, something just felt off in the back end, and when I would hit the gas more than just light-moderate it felt like it wasn't pushing the vehicle straight forward :worried: It didn't pull to the side when I turned the wheel to go straight, but it was off a decent amount.

I got off the highway and pulled into a parking lot to check stuff out. Checked the front first of course and I didn't see anything obviously wrong. Started poking around the rear and found my rear upper passenger trailing arm is snapped off!

View attachment 20803

The rust is just surface rust, the metal is still plenty thick. When I replaced my rear axle with an 8.6" last year I used the 4 best arms of the bunch, and none had more than some surface rust on them.

I should have some time tomorrow evening hopefully so I'm going to pull the wheel and check everything else for any damage (such as the lower arm) and also check over the front end for any damage aside from a whacked out alignment. Good thing I have my summer fun car so I can still go to work until I get this thing fixed.

If anyone has an upper trailing arm lying around let me know as I need one. There is a local junk yard that has both a trailing arm and a TCCM (my 02's died recently), their price on the trailing arm is decent enough (50-ish bucks), the TCCM is a little more than one off ebay but if I go there the convenience factor may be worth the extra.
 

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redleg6

Member
Apr 10, 2012
686
ouch, I hope its a simple fix once you get the part...

makes me want to go check mine more thoroughly tomorrow morning
 

jimmyjam

Member
Nov 18, 2011
1,634
not hard to swap

but jeez thats scary i'd check everything holding your axle to the frame
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
Forgot to look this weekend with Mothers day stuff, but will look tonight for an arm.
 

redleg6

Member
Apr 10, 2012
686
my little noise wasn't a broken part...just a really loose one

(driver side rear stabilizer bar endlink)
 

Sparky

Original poster
Member
Dec 4, 2011
12,927
That's not too uncommon. They like loosening up. I figured you didn't have something similar, because trust me, with the arm broken it is quite apparent that something isn't right!

Side note - I drove that stretch of highway again today in my other car, looking for the pothole. Nothing, there is no pothole there :confused: So now I'm wondering what the heck happened on Friday.
 

LikeEnvoy

Member
Apr 17, 2012
128
Winnipeg, MB
Just adding to this thread for interest. My Rear Upper Control Arm broke in two today. Rusted metal, very thin. It broke about 3 inches back from the front bushing. Ordered new pair from Rock Auto. Left it off for now so I can drive SLOWLY to the supermarket.
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,159
Brighton, CO
Before you bought the control arms, you should have checked the structure around the control arm mounts, and to see if you can even break the bolts at the frame and axle loose.

Usually when you have a broken control arm, there is other rust cancer you have to take into consideration to see if the repair is even viable.
 
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LikeEnvoy

Member
Apr 17, 2012
128
Winnipeg, MB
Thanks TollKeeper, good advice. I actually removed the broken ends after ordering ( it was coming up to a weekend and I wanted to fix it asap so I can use the car.
After I scraped out the limestone dust and gravel from the pocket and then scraped the metal surface to get the surface rust layer off, luckily the pocket and surrounding area seems thick enough still. Tapping the area sounds like good metal too. The bolts came out easily and the threads look good.

I applied rust converter fluid, ready for the new part. Will probably paint it with rust paint then cover in grease before fitting the new part. The rear bracket is in perfect condition and still has the paint finish intact.
Strange how one end can be good and the other end awful. That pocket design doesn't help, eh? It should have been more open to allow drainage and let the gravel/dust out.
RearUpper TrailinglArm.jpg

I'm curious if others have found the arms broke at the same spot; may have been a weak area.
(p.s. This Envoy has just over 263,000km on it.)
 

budwich

Member
Jun 16, 2013
2,068
kanata
yep... just did both mine a couple of weeks back on a 2008. One snapped during a start from stop. Large bang and the front end popped in the area. After that, shudder happened in 1-2nd gear transitions. Thought my tranny was in trouble. Anyway, replacement of the arms cleared things up... but rust in areas might be a significant issue as time moves forward. My fingers are crossed that the areas will hold up for a few more years.
 
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Sparky

Original poster
Member
Dec 4, 2011
12,927
Heh old thread.

Looking back at this, I'm convinced it was not a pot hole (since it wasn't there) and that maybe the arm just fatigued and snapped for whatever reason. It failed where I've since seen others fail also. I never figured out why my front alignment when totally whack at the time. The other side arm failed a while later and it had a different kind of symptom on that side (expected given how torque application would twist the axle different ways left vs right side). Either way, replacing the arm in both instances fixed it, and that old Trailblazer is long gone now
 
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