I was riding in Moab a couple days ago (first time!) and while riding up a slick rock hill on a trail, I heard a loud bang. When I stopped, there was blue smoke everywhere and oil dripping under the swingarm. Rolling around on top of the swingarm was the shock reservoir and there were aluminum threads stuck all over the place. We found some other internals from inside the reservoir on the trail where it blew up. Is this an expected way for A WP shock to fail? I wasn't riding that hard but the reservoir was definitely very hot. Some history: About a week earlier, I had the shock and forks in the local shop to put on the 'R' suspension kit and the ride in Moab was the first time off road after the work was done. They also replaced the rebound adjuster because it was seized. Would they have had to take the reservoir off to put the new spring on or to replace the adjustor? I'm wondering if they could have botched the job somehow.. maybe damaging the threads causing the reservoir to blow off like that?
:huh Never seen anything happen like that. I'd take it to the same suspension shop and ask for some explenation.
VVOVV There is alvvays a first. I´ve never seen that. I vvould think that the suspension guys maybe have a finger in this. But that is, like everything i say, assumptions. Though the rearshock tend to get really vvarm. That should be one of the reason Mr Pyndon vvent vvith longer reservoir. Threaded vvrong vvould be my thought. Take it to the candyshop and ask hovv the h... Mikael
Thanks.. I didn't think this was normal. The shop that did the work was just the local ktm dealer so they aren't really suspension specialists. They mainly deal with dirt bikes. I didn't want to be fed some line about this being from normal wear and tear when I go back and ask why this happened.
Did you notice the threads that were scattered about ? And the wear marks from the cross threading of the shock if not do not pass go do not collect 200 dollars
Do you mean that if I can't find evidence of cross threading, then this was a failure from normal wear and tear?
There is no 'wear and tear' that fails like that. Look very closely at the reservoir and see if it's cracked. If the shop over filled it, so there wasn't enough air space, it could blow up like that. But, that's a major mistake to make.
No cracks that I can see. I don't have much confidence in this mechanic so I wouldn't be surprised if he messed this up somehow. A couple weeks back I got into a 15 minute argument with him about brake fluid. He was trying to tell me to use DOT 5 fluid instead of 5.1 for my 990. In fact, he only carried DOT 5 in his shop... This is a KTM shop... So he's been putting silicone based DOT 5 fluid in all the KTM bikes he services? I need to be prepared to deal with his BS when I talk to him about this so this info really helps. Thanks. :)
+1 The impact of a 500+ lb. bike on a sharp bump and a over-filled hydro-locked shock is the only way I can imagine blowing the reservoir off like that.
My guess is that the piston in reservoir was set up with too small a space for the gas. So when the shock got hot and fully compressed to the bump stop gas pressure skyrocketed due to the high compression ratio of a small gas space and something had to give. Ask the shop guy to what height he set the gas piston. If you get a "huh" kinda look well, you have your answer. FYI, I set the piston about 10 mm in from the wet side, the cylinder is mostly gas-filled. And I check the final installed height with a probe through the vent port before buttoning everything up final.
After a through cleaning what did you find? Let us know. I stand by my first opinion, especially after showing the pohoto around.
I've already taken the shock back to the shop so won't be able to post any more pictures, but I can confirm that there were no cracks anywhere. What was left of the threads on the upper section and reservoir didn't show any evidence of cross threading but every thread was stripped off from the top right down to the last. I could almost slide the reservoir back onto the upper without turning it so it definitely blew straight off. I talked to the mechanic and he said he used some special machine to set the piston height to 10mm and that he torqued the reservoir to spec and used locktite. This was the first 990 shock that he had worked on however but he insisted that he was on the phone with KTM during the rebuild process to confirm he followed all the right steps. He is fixing it free of charge - including a new upper, new reservoir and seals and using the old lower. After looking at the prices for the upper vs the entire shock I'm kind of wishing he'd have just got a whole new shock since I'm going to constantly be worrying that his new rebuild will fail the same way this one did.
I got my shock back from the shop yesterday. After taking it apart, he still doesn't know why it failed like that. Anyway, the repaired shock is under warranty so I'm going to try my best to break it again Here is the video from the Moab trip. The shock failure is in Part 3 http://advrider.com/forums/showpost.php?p=21369627&postcount=1171
+1. It was either overfilled, or they buggered the reservoir cap threads when they took it apart. For the first disassembly, you need to use a heat gun to loosen the thread locker. If you just use brute force, the threads are likely to ball up. They could have also cross threaded on reassembly. They would have had to take this apart to remove shims to lengthen shock travel. I would definitely demand that the shop fix your shock. 90% of the time, mechanical issues are related to the something that was recently worked on. I've rebuilt dozens of shocks and never heard of an issue like this.
Is it possible that it wasnt tightened down properly during the reassembly? That could explain why only the upper threads got pulled up. Just a thought. D
