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Belt Tensioner Mounting Bolt Broke Off after Serpentine Belt Replaced? - 2007 Toyota Carolla

I drive a 2007 Toyota Corolla with 111,000 miles on it. I went in to have my alternator replaced on January 6, 2014. They told me that my serpentine belt looked worn and that I should probably have it replaced since I was already there. Six weeks later my car started making a loud squealing noise so I took it back into their shop and they told me it was probably the tensioner and it needed to be re-tightened. I have a self tightening tensioner so I found that odd. Before the alternator went out I only had to do routine maintenance on my car, oil changes, etc. I got to the shop at 8 a.m., and then finally after waiting for 3 hours they told me that it’s not the belt, but the bolt from the tensioner broke off inside of the motor block and they have to remove the engine mounts; lift up the engine to access the bolts; extract the broken bolt and replace the bolt with new hardware. He said it looked like someone worked on my car and did a bad job and tried to put it back together. I found this to be odd as well since they were the only people to ever do any work on my car. He told me that he would speak to the owner but could only take my word for it and agreed to split the cost of the $400.00 repair.

• How can a belt tensioner mounting bolt just break on it’s on?
• The mechanic told me that the belt tensioner mounting bolt wasn’t even touched when they made the repair. Is this true?
• Can you install a new serpentine belt without touching the belt tensioner?
• Is this going to cause any long term damage to my engine?
• Should I be responsible for any cost of the repair?

Thanks for your help!

I went to replace the belt tensioner on my 2003 caravan about 5 years ago because of insufficient belt tension and had to take it to my mechanic because the bold had broken off in the block. He was able to extract it with heat. It had not been worked on before.

To replace the serpentine belt you have to move the tensioner but you don’t touch the mounting bolt.

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This is the belt tensioner assembly

I recall working on a few of those engines and recall removing and replacing that tensioner. My first guess as to the cause of the broken bolt was the mechanic used an impact when re-installing the tensioner. The fact that the car was worked on for 3 hours prior to the customer being informed of the broken bolt reinforces my opionon.

My guess is that the tensioner bearing and/or the hydraulic unit on it was failing. That can create vibration (which may not be noticeable to you) which in turn can stress the bolt and cause it to snap off.

They don’t have to lift the engine to remove the broken bolt.

Ask them if anyone in the shop knows how to weld.


It is usually wise to replace the tensioner when replacing the belt at that mileage.

The whole area is accessible by removing the wheel and the inner fender liner.

Something smells wrong here. What broke, a mounting bolt or the tensioner release bolt? The release bolt (not shown in Rod’s link) does occasionally break off if the tensioner is pulled back by someone not experienced with this system. It takes a lot of torque on the bolt to compress the hydraulic damper, and it needs to be done slowly. The damper needs to be given time to compress. It isn’t uncommon for someone to try too compress the damper too quickly and break the bolt. I personally don’t like the design, but it is what it is.

If it’s a mounting bolt, it makes me wonder of someone tried to use the mounting bolt to release the tensioner. However, the tensioner is still replaceable through the wheel well. And, the bolt should be able to be extracted through the wheel well as well.

My gut feels funny on this one. Can you post a photo?

I don’t believe the bolt broke on it’s own. A ham fisted mechanic using an impact wrench or large socket wrench/breaker bar caused it.

Thanks for the feedback. No, I don’t have a picture. It’s still at the shop. Even though I got there at 8 a.m., they couldn’t get the bolt in time. He said it was the rear belt tensioner mounting bolt. I made him write everything down, because I don’t know a lot about cars. I just want to know if I could prove it or not? Is it worth filing a claim with the BBB? Or can they just deny it saying they technically didn’t have to touch it? If I take it anywhere else, they will charge me full price for labor and parts. We’re new to the area, so we haven’t found a local mechanic yet. I just feel like I’m being bamboozled!

Although we all have opinions none of us can be certain of the damages or the cause in your specific case, @Mindy81. The likelihood that the tensioner assembly mounting bolt was broken when it was installed and tightened seems somewhat significant to me. And these days the most profitable and highly talented employee in a large shop is the man who can turn incompetence into cash.

While I wholeheartedly agree that improper installation of the bolt was at the root of the problem, it is possible that the bolt did not break upon installation but rather was left with a condition that subsequently manifested itself as failure. Overtorqueing a bolt can stretch a thread such that it’ll fail in use. In short, the guy that put the bolt in may have not broken the bolt at that point and may not have realized he introduced a subsequent failure.

Well, thanks guys! Oh well, c’est la vie! Guess I’ll just chalk it up to a learning lesson and will know better next time. NPR really does have the smartest audience in radio.

I was able to pull it out with a right angle drill + a screw extractor by raising the motor up. This $10 bolt is really problematic. I’d have lost $1000 for repair if I didn’t decide to do it myself.

Here’s the quick guide for those who need.

I don’t think there’s much you could have done to prevent this situation @Mindy81 . Bolts are made of metal, and metal fails for a variety of reason. Other than if the breakage was caused by a blockhead mechanic who fesses up, there’s just no way to tell why that bolt broke off. It may have had nothing to do with the mechanic work done, and the bolt could have been defective when the car was newly built and just waited until now to tell you it has decided to break. Hey, maybe that’s where they got the name of that NPR program “Wait Wait Don’t Tell Me” … lol …

And it’s not that big of a problem for a professional mechanic to remove the broken bolt and install a new one. It sounds like the access made it a time consuming job, so the bill was bigger than you’d like to have seen, but that’s all just part of owning a car. Someone here recently was billed 7 hours shop time to replace a water pump. 7 hours for a water pump replacement? A knowledgeable forum mechanic chimed in and said yes, that’s how long it takes to replace the water pump on that car. I doubt it took 7 hours to replace that bolt, so you are right to just take it all in stride, it’s just a bolt, and don’t worry, be happy.

I broke the nut while trying to remove the belt. Is there any possible way to install the new belt without havingto replace the whole tensioner pulley assembly?

Happened all the time with those tensioner

This tread is 4 year old in case you didn’t notice