How to inspect flex plate for cracks using a borescope – 2001 Toyota 4Runner

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transmissionWe started having a clicking sound coming from beneath our 4Runner, somewhere between the engine and the automatic transmission. After doing a lot of searching online to figure out what it might be, I concluded that it might be a cracked flexplate. Replacing a flex plate is a big job, since it requires removing the transmission. Before paying a lot of money to get it checked before even knowing if that was the problem, I decided it would be best to first inspect the flex plate myself to verify that it was broken/cracked.

Here are some some links to some very interesting pictures from other people who have had their flex plates fail:

Here is a link to an MP3, showing how someone else’s broken flex plate sounds. My ticking sound was exactly like this.

The 4Runner’s flex plate can be inspected by removing a very accessible access cover. However, the access cover does not give access to the entire flex plate, and you actually won’t be able to see enough of the flex plate to see where the cracks normally would occur. The solution: after removing the access cover, there is enough space to insert a borescope to see if there are cracks in the flex plate.

Materials Needed

  • 12mm socket
  • socket entensions (6-inch should be fine)
  • socket wrench
  • USB borescope, 7mm diameter or smaller, with built-in LEDs
  • laptop or netbook (for viewing the borescope output and taking pictures)

borescope and laptopI used the Weanas Borescope from, which worked OK for this flex plate inspection. The built-in LEDs were bright enough to illuminate just a short distance in front of the borescope’s camera. One of the great features is that it has a button on the handle that allows you to take a snapshot without having to touch the laptop.

Become familiar with applicable vehicle parts

The flex plate connects the engine and the transmission. If you think about what that means, then you can probably correctly guess where you will need to look underneath the vehicle to find the access cover for the flex plate. Think about it this way: the engine is underneath the vehicle’s hood and the transmission is generally directly beneath the front seats of the vehicle. That means that the flex plate should be directly beneath where the dashboard and the engine bay meet.

If you get underneath the 4Runner, from an angle below the driver’s side door, you’ll see where the transmission connects with the rest of the engine. The picture below was taken from below the driver’s door, looking forward toward the engine area. Various components have been labeled. Most importantly, notice the annotation that points out where to look for the flex plate.

Components near the flex plate. The flex plate connects the engine to the transmission. The front drive shaft partially blocks access to the flex plate’s access cover on the driver’s side, so it is better to get access from the passenger’s side. Click image to enlarge.

The following two pictures show where the bolts are located that hold the access cover to the flex plate’s housing. You don’t have to worry about making an oily mess or anything when removing the access cover – there isn’t any oil or other fluids involved with the flex plate. Note that the bolts are on the side not visible from the transmission’s side of the flex plate.

bolt locations from transmission side
Viewing from the transmission side, here are the bolt locations for the access panel. The bolts are on the backside (engine side) of the tabs where the arrows are pointing. The red inset shows bolts #3 and #4 better, from the passenger side. Click image to enlarge. bolt locations from engine side Looking at the backside (engine side) of the lip mentioned above, here are the bolt locations and the access panel. This is from the passenger side. Bolt #1 is accessible from the driver side. Click image to enlarge.

Notice the last image above, where the access panel is visible. This is the viewing angle you’ll want to use later on when you’re using the borescope to inspect the flex plate.

Inspecting the Flex Plate for Cracks

  1. engine-cover-smallengine-cover-smallRemove lower engine covers. Using a 12mm socket, remove the 9 bolts that keep the engine covers underneath the engine. Be careful when removing the bolts – support the covers so that they do not fall or bend any of the bolts. You will need to use a socket extension (around 6 inches) to reach some of these bolts. Note that while it is not necessary to remove the engine covers to get to the flex plate’s access cover, you won’t have a good angle of attack for getting the borescope in the right place without removing the engine covers first.
  2. access-coveraccess-boltsRemove the access panel. Three of the access panel bolts are accessible from the passenger side. One bolt is accessible from the driver side. If you have a 2WD vehicle, then it is easier to access the bolts on the driver side.
  3. access-cover-scopeborescope-entryIdentify where to insert borescope. It is a pretty tight fit for the borescope between the oil pan and the flex plate. The only place I could get the 7mm borescope to enter was at the edge of the oil pan, where it curves away from the flex plate.
  4. Look for cracks in the flex plate or loose bolts. Once inserted, move the borescope around to look for cracks in the flex plate and for loose bolts. I couldn’t get the borescope to go all the way around the flexplate just from the one entry point. I could reach about half from the passenger side and the other half from the driver side. The snapshots below are from the borescope as I was probing around. Notice how you can see the cracks in the flex plate – they look like light-colored, very straight lines where the light from the scope hits them. Not to be confused with the scraggly, yellowish marks that were made when the borescope scrapes across the rust-colored flex plate. All of the bolts were tight, so at least that wasn’t part of the problem.






After getting all those borescope pictures, I wanted to try to stitch them together to get a better sense of what the overall crack looked like. Here is what it looks like, from one side of the flex plate. The crack looks almost identical to the cracks that other people had (see the links at the beginning of this post) – where it extends between each hole in the flex plate.

The flex plate, with a crack shown extending from the hole at the left to the hole at the right. The crack has been marked with a purple line in the image below. This image is a composite of several other smaller images from the borescope that have been stitched together. Click image to enlarge. annotated_composite_small The image is the same as the previous one above, but has annotations indicating which parts of the flex plate are cracked and showing from what angle the flex plate is being viewed. Click image to enlarge.

My flex plate didn’t have the entire hexagon-shaped crack like the other people had, it only had a couple of the hole-to-hole cracks. This is because my flex plate hasn’t completely failed yet. It will eventually fail the rest of the way, so it will have to be repaired. At least now I know my original diagnosis was correct, and I know I’ll be spending the money on the actual problem, instead of paying someone to try to figure out the problem. And playing around with the borescope was pretty cool, too!

Update: 8/12/2014

I took the 4Runner in to the Toyota dealership to get the flex plate replaced (hooray for no more clicking sound!). I took a picture of the flex plate, and it pretty much matches exactly what I showed above. Here it is:

Flex plate removed - with cracks
The flex plate after removed by the mechanic. The cracks are exactly as I had scoped out with the borescope.

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7 thoughts on “How to inspect flex plate for cracks using a borescope – 2001 Toyota 4Runner”

    1. It is very expensive – it was about $1500. I had it done at the Toyota dealership which made the repair somewhat more expensive, but with a flexplate it is the best option to make sure everything gets aligned correctly when they reassemble everything. If the alignment of the transmission-to-flexplate-to-engine isn’t perfect (within small fractions of an inch), then the flexplate will crack again prematurely because there is too much stress on it. This is how mine cracked in the first place – I had my transmission replaced about 20,000 miles prior to this, and they didn’t align it all correctly, putting too much stress on the flexplate. You could get it done cheaper at an independent repair shop, but if that’s what you choose to do then make sure it is a shop that specialized in transmissions and that does a lot of 4Runners (for example, a transmission shop that is known for doing a lot of off-roading modifications/repairs). Then they might be familiar with this alignment issue.

  1. Thanks for the information. It seems like a smart idea to take a look at the flex plate in your car yourself before taking it to a mechanic. Now I can see repairing a flex plate is a very big job. It would be difficult to take a look at it without removing the transmission first. It seems like it takes a lot of steps just to get to the plate. I’ll be sure to follow these instructions carefully so that I can safely remove the transmission before getting to the flex plate.

  2. Thanks for the information! I suspect that the flex plate in my car has a few cracks, but I’m not sure how to check. It’s a good thing that there’s a way to check for cracks using a borescope. The information about how to insert the borescope properly between the oil pan and the flex plate will really help me out. There isn’t a lot of room between the oil pan and the flex plate in my car, so it’s definitely going to be a tight fit. I hope that I can get it to fit in the edge of the oil pan like you did.

  3. Hi,
    Is there a chance you could let us know if the dealership swapped out any other parts like the torque converter or bolts for example?

    Thank you,

    1. They did NOT replace the torque converter or the bolts. If all you have is a cracked flex plate, then there’s really no reason to change out those other parts. I get what you’re saying though – since they have already dropped the transmission and have everything taken apart, why not replace anything that might go out eventually. Well, I don’t think either the torque converter or bolts are items that will need to be replaced during the life of the vehicle (although same goes for the flex plate…). If you really think you’ll have the vehicle for a super long amount of time, then maybe you could ask them to replace those, but it really seems like an unneeded extra cost.

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