A stripped thread doesn’t have to mean replacing your fork or lower legs.
Can you install a helicoil to repair stripped threads on a suspension fork brake post mount? Clearly you can; but would you feel comfortable riding a fork with this type of repair?
I recently found myself forced to find out recently when the threads on the lower post mount simply gave up when adjusting a brake caliper. While prepping my bike the evening before a ride, I had loosened the bolts securing the brake caliper in order to improve caliper alignment. Upon securing the bolt, it almost secured, but the usual resistance at the wrench never came. Adding a quarter turn at the allen wrench, it still didn’t secure.
This is the part when panic sets in. Backing off the bolt, I tried again, a bit more gingerly, with the same results. Backing the bolt all the way out, my concerns were realized. There was thread material on the bolts and the brake post threads had clearly stripped.
My first step was to thread a longer bolt in to see if I still secure the caliper reaching deeper to threads that were more secure. Perhaps the fork would still usable for my ride. Unfortunately, the process was repeated; the existing threads simply didn’t have enough mass to hold the bolt in. Shit.
The first part of installing a helicoil requires nuking the previously established threads. It does feel weird to do this part.
Step one: research
It’s been years since I’ve had to address stripped threads, and the first time I’ve experienced with the issue on personal equipment. During a my tenure as a mechanic in top level service departments at premier bike shops, I’ve solved a multitude of problems, but since I’m rusty I took a step back to assess my options.
I could do one of three things to address the issue:
- Replace the fork lowers
- Determine a way to repair the threads
- Buy a new fork altogether
I was understandably upset the thread gave up the way they did, so purchasing a new fork was the first thing that crossed my mind. I’ve been really happy with the performance of the Rockshox Pike and its been our go-to for our trail bikes. The X-Fusion Trace was going to need some tuning anyway, as the fork’s spring rate has been far too linear for my preferences, bottoming out when riding aggressively on burly trails.
However, I already have two Pike forks lying on the floor of the garage. Unfortunately both are for 650b wheels as opposed to 29″, the size required. The reason I chose to go with the X-Fusion in the first place was cost based, and until I did something with the Pike forks, it was going to be hard to justify the purchase of new equipment. It was time weigh the pros and cons.
Cutting in new threads with the tap.
Option one: replace the fork lowers. I wasn’t excited about the prospect of acquiring new fork lowers. After all, I had just recently assembled this bike, and to top it off, added sweet custom decals to make this thing unique. I’m a rather lazy bike mechanic, and even if I was able to secure replacement fork lowers as a warranty or low cost replacement, I’d still have to disassemble the fork. (I had recently adjusted the travel of the Trace from 100mm to 120mm). Plus the replacement lower legs would lack the cool custom decals. This would be a massive pain in the ass, so it was demoted to the last option.
Option two: repair the threads. Thread repair kits are common solutions to stripped threads. When threads are damaged, the first thing to try would be repairing the existing threads with a tap, and trying a longer bolt. As I had already tried this approach, I was moving on to attempting to repair the threads by installing new ones in the form of a Helicoil insert. Helicoils are thread repair kits that replace indigenous material with a stronger steel threaded insert that is threaded in. (the Heli-Coil Kit I purchased is the M6x1 Metric off Amazon)
Unfortunately, none of my local auto or hardwear stores had the thread repair kit, so I turned to Amazon and had everything I needed in a few days.
Installing a Helicoil thread repair kit
The first part of the repair is to properly prepare the hole. This aspect of the repair definitely the most nerve-racking of the process, as it consists of drilling out the old threads. Fortunately, there’s quite a bit of documentation online, making it a straight forward fix for a handy and experienced home mechanic. (scroll down to view some embedded video walk-throughs)
The helicoil insert threaded completely in.
Removing the installer. After unthreading the inserter, I broke off the stop. I added some threadlock as well.
Viewing the new threads of the insert.
There are plenty of how-to articles on installing a Helicoil thread repair kit, and seeing how rusty I am, this article isn’t meant as a how-to but a documentation of the before and after. The real question I wanted the answer to is, “Do I trust the repaired threads?”
Fast forward: 3 months later
I’ve been riding the fork with the repaired brake post threads for a few months without issues. The steel insert is arguably stronger than the stock threads in the fork.
However, I’m not entirely confident in the security of the repair for a few reasons; one, I believe this to be a warranty issue. I didn’t put a lot of force on the threads when they stripped. If it had been user error, I’d be a lot more confident in this repair. The fork was mounted on a 5″ travel Evil Following and I’m a skilled rider that enjoys high speeds, technical terrain, and hard braking. I’m confident in the steel threaded insert, but seeing as how the fork had soft materials that failed, I could see my newly cut threads failing a second time, especially considering the forces from the 7″ rotor I run on my forks.
While I don’t plan on replacing the lower legs any time soon, I’ll have more fun riding if I have full confidence in my equipment, so I pulled the fork. I’ll end up running it on another bike down the road, but likely on a hardtail. I don’t push it when riding rigid frames, and tend to ride hardtails on less steep terrain. I’ll also utilize a 6″ rotor instead of a 7″ rotor which would put less stress on the mount.
Looking to learn more on thread repairs? Here are a few videos I dug up on YouTube to get you started.
