3rd Gen CMC quick DIY

I had a hard time finding good pictures for a 3rd gen of where to cut for a CMC, so I took a few to hopefully help anyone looking to DIY a CMC. I went to post the pics and decided to write up a quick DIY post.

What is a CMC?

• You do a CMC to cut back the cab mount to fit larger tires.
  
• This is pretty much required for 33" tires.
  
• My tires are Pathfinder AT 285/75/16s, at 33".

For some more background, I went up to 33" tires with 2.5" of lift on Fox suspension on stock rims with 1.25" spacers. I rubbed even in parking lots, so a CMC was absolutely required. I shopped around a bit, and the lowest quote I had for a CMC was $250. I thought that was a bit much given I had all the tools in this post on hand, so I spent around 3 hours of work for a large cost savings and outlined it here.

What was used?

• Jack, jackstands, lug wrench, a hammer (you should already have these)

• 4.5" angle grinder https://www.homedepot.com/p/RYOBI-5-5-Amp-Corded-4-1-2-in-Angle-Grinder-AG4031G/205558109 with cut off wheels from Harbor freight and grinding wheels
• Deburring tool
  $16 AFA Tooling - Deburring Tool with 10 Extra High Speed Steel Swivel Blades - Works on Metal, Resin, PVC Pipes, Copper, Plastic and 3D Printed Edges - Plumbing & 3D Printing Burr Removal Reamer Tool
  https://www.amazon.com/dp/B01L2XR4P2
  
• Roll-on bedliner paint
  $39 Rust-Oleum, Black Automotive 248915 Ounce Truck Bed Coating Quarts, 32 Fl Oz (Pack of 1), 2 Pound
  https://www.amazon.com/gp/product/B0070S7U4Y and foam brushes
• PPE - RESPIRATOR, EYE PROTECTION, HEARING PROTECTION. Seriously, don't skip these. If you're EVER using an angle grinder, the dust is extremely bad for you and it is very easy to get injured from a broken cutting disc. They sometimes shatter, turning into a knife flying at your face. Personally, I use
  $31 3M P95 Respirator, Half Face, Disposable, Spray Painting, Pesticides, Construction, 53P71, Large Size
  https://www.amazon.com/dp/B00079FOK0/ and
  $60 Howard Leight by Honeywell Impact Sport Sound Amplification Electronic Shooting Earmuff, Green
  https://www.amazon.com/dp/B001T7QJ9O/ (foam earplugs are fine if you're cheap) and
  $32 UVEX by Honeywell Bionic Face Shield with Clear Polycarbonate Visor (S8500)
  https://www.amazon.com/gp/product/B001VXXUWK/

The process:

First I jacked up the truck. I put the wheels and jackstands under each side... jackstands definitely were there after taking the picture, trust me.



Next, I taped off the cuts. The lower left taped area is the cab mount. Just to the left of the cab mount on only the driver's side is a wiring harness, be VERY careful not to nick that with the angle grinder. I cut the wheel liner first, then stuck that piece of plastic over the harness to make sure it didn't get damaged.

The upper right area to cut is the wheel liner. The pinch weld for the cab is behind there, and that needs hammered down when you do the CMC or you WILL rub offroad. I have a 2.5" lift, if you don't have a lift you may have to cut higher and hammer down higher. Every truck is different (due to alignment), and every wheel is different (due to backspacing and variance in tire specifications).

I'm using the stock SR5 rims, which need spacers to fit 33s, so I'm running 1.25" spacers.

Anyways, here's the taped off cuts from the driver side:



Note that the area I taped leaves the hole cutout intact around the cab mount, protecting it from anything that may get kicked up while you're driving. You can see that a lot better from the bottom view. Remember, I'm cutting inside the tape.:



The first two pics were the right side, the next one is the left side after cutting. Cutting took 3 discs total, one of them exploded when I had too much angle cutting. Without the broken wheel, I could have probably done it with two cutting discs easily.

WEAR EYEWEAR and a RESPIRATOR! You can see in the left off the hole where there's a square support, that is a bit of a hassle to grind through, and was why the wheel broke on me - I twisted too much while cutting. Just go slow, each side was about 30 minutes of grinding.



You can see in the top left of the above the pinch weld. That is hammered down in the next picture. I just used a standard hammer, starting from the bottom and taking my time. It took about 10 minutes per side of hammering to get the weld flat, including a couple of breaks to catch my breath. I'm in shape, but swinging a hammer over and over is hard work.



After using the cutting wheel, I switched to a grinding wheel and ground down to smooth. I then used the deburring tool to remove all the metal flashing that was left from grinding.

You can see the pinch weld is now hammered flat in the above and below pictures.



Here's a view from below. Look how nice and flat the hammer wend is in the top left. It definitely needs painted over and resealed, just to be safe. You can use RTV for that if you want, but I just used a few layers of bedliner instead.

The below picture is back to the driver's side, you can see the cut off piece of trim wedged in to cover the wiring harness mentioned earlier.



I painted everything with 3 coats of roll-on bedliner, put the wheels back on, and had a beer or 3. It's hot here in Georgia, and it's impossible to drink beer with a respirator on.

Some people weld in fill plates. I did not put fill plates in, and don't see the need to - I feel completely safe with me, my wife, and two young kids in the truck like this. Bigger tires plus lift drastically reduces and spreads any shear force on the cab mount lower and lesser. In a small overlap collision, I'm confident with my tires and lift that the tire will deflect below the cab, even without reinforcement. With that said, this is a good thread to discuss CMC safety: https://www.tacomaworld.com/threads/cab-mount-chop-food-for-thought.577566/

Hope this helps anyone looking for info on a DIY CMC. It's an easy afternoon project. If you're rubbing, stop waiting and just do it.

 

Great write up OP

 

Looks good, that's exactly where I make the cut as well whenever I do CMCs. About as far back as you can really go. As far as that square tube, it's a PITA to cut through. That's why I toss on a 6" cutting wheel for that part and it'll zip right through it.

Now that you cut (that's the shitty part anyways) you should see if you can get someone local to weld a plate on. Just looks a lot more finished and full-assed.

 

6" wheel on my 4.5" grinder is too dangerous for me. Maybe I'll get a 6" grinder one day.

I don't really look in my wheel well often, so I don't care much about how it looks. I have a welder and could buy or cut out a plate, it just doesn't matter to me. How often do you look at your wheel wells and go "MAN I'M GLAD I SPENT LIKE 2 HOURS WELDING OR WAITING ON SOMEONE TO WELD THAT PLATE?!" I'm spending those hours drinking Jack and writing this post instead!

 

That is forsure a better way to spend 2 hours IMO

 

I’m only speaking for myself, but a cmc start to finish takes 1.5 hours. Only maybe 15 minutes of that is welding/grinding the welds smooth. I buy the BAMF cmc plates for $17 shipped so no time wasted cutting out the plate.

 

You're a legend then, I commend you on your mechanical competence.

I work with computers all day. 1.5 hours including welded plates and cleanup and stuff is insane, I can't imagine how you'd do it that fast. I think a realistic expectation for a shop doing this, that has experience doing this, including you providing plates, would be between 2 and 3 hours.

For me:
30 mins to get tools together, jack up the truck, and get the wheels off
30 mins per side for cutting
10 mins per side hammering pinch welds
10 mins per side grinding, cleaning up, getting ready for paint
10 mins per side paint
30 mins putting all the crap away, getting the truck back together
= almost 3 hours... with no welding

If I had welded,
10 minutes finding all my welding crap in my basement
20 more minutes per side grinding to get everything smooth and flush (don't have to worry about it being flush with bedliner)
1 hour per side making plates from scrap I have laying around
30+ minutes per side welding
20 more minutes grinding my booger welds
= too many hours

I can weld, but I am definitely a novice. I'd be looking at like 6+ hours assuming I already had plates. Again, not for me.

 

I work with computers all day long too, but have turned to wrenching on Tacoma’s on the side for some extra spending money. I’ve done 20+ cmcs which is how I have my system down.

I’m not here to toot my own horn, but I’m just saying welding on a plate and blending it isn’t going to take forever. My first couple times doing it were still at about 2 hours, maybe 2.5.

This is directed at any future readers, just because I don’t want anyone to see this and get intimidated and shy away from the job when in reality, it’s not too horrible.

 

Nice cut job. But I do agree capping it is the thing to do. Function wise, yours does the same thing. But aesthetically, a plate makes it look OEM. This is a 40k+ truck, make it look that way. Also, less of a chance to get mud/dirt/etc caked into the frame. Just my $.02.
I do agree time is money(or beer in your case) but for the little extra time to have a “finished” project, IMO it’s worth it.

 

That square tube was the worst! I actually ended up buying a 6” grinder just because of that when I had to redo mine.

 

Sub’d... my thought is, IF I do this now, it’s a good excuse to tell the wife I need to get a lift and tires.

That’s how I got the garage work bench, bought the bench vise first!

 

Did you end up welding Op? @synaps3

Might do it myself!

 

good write up

 

Ima do this… ain’t no one gonna stick their head in there and check for fill plates lol

 

Hahaha! I would if I was buying a used Tacoma . Might been a hacked up job

 

No you won’t haha

 

Nah just cleaned it up and painted it. No need to weld unless you want more work - it's been holding up great.