Drilling rear strut towers with a hole saw

[inquirer]

I have a Lancer with Tein adjustable struts and shocks.

Since there is no access to adjust the rear shocks, I'm thinking of drilling the towers in order to be able to adjust them any time without removing them. The idea is to create a similar design with the Evo X. It's safe to drill the rear towers, right? They are not part of the chassis, correct?

 

[Lubener]

If the spring is on the strut, then the towers would be considerd the chassis and support the weight. Myself, I wouldn't drill because the area is weakened and opens the opportunity for corrosion.

 

[inquirer]

If the spring is on the strut, then the towers would be considerd the chassis and support the weight. Myself, I wouldn't drill because the area is weakened and opens the opportunity for corrosion.

The springs are on the strut. I'm not so sure though that the word "tower" is correct for the part that I want to drill.

If you click the 2 links and start playing the 2 videos, they both start at the point where the place where the top mounts of the shocks absorbers is bolted. The 2nd video shows the Evo X and the other the way all the other Lancers of the 10th gen are constructed.

The hole will be drilled in the "pipe" above the place where the mounts are bolted.

As for corrosion, I think that the top mounts have seals and no water enters at that place.

 

[inquirer]

In the first picture I have marked with a red circle the place where the hole should get drilled. Under the circle you can see one of the two mounting points of the shock absorber's top mount. The other is obviously on the other side of the "pipe".

The following picture shows Evo X's rear tower which already has a hole in place. The Evo has a different tower which sits higher.

The question is does the "pipe" above the mounts support any weight? If not drilling it is certainly not a problem.

 

[RooflessVW]

IMO you're fine. A hole there isn't going to significantly weaken anything.

 

[MasterSolenoid]

A 'round' hole with 'no' sharp corners would be best.
A crack could form in a corner and spread.

 

[Hohn]

IMO you're fine. A hole there isn't going to significantly weaken anything.

agree.

 

[RooflessVW]

A 'round' hole with 'no' sharp corners would be best.
A crack could form in a corner and spread.

Hard to drill a hole with corners when using a hole saw.

 

[inquirer]

IMO you're fine. A hole there isn't going to significantly weaken anything.

That's what I think too, but I want to be 100%. Obviously the majority of the weight is supported at the floor level where the nuts are.

But I guess the "pipe" above the shock mounts plays some role in the cars rigidity. Actually after closer inspection what I called a "pipe" is a tube that continues upward and forms the horizontal part of the trunk.

At the point I want to drill, there is an external plate of metal over the tube. Maybe it should be removed first, in order to see the structure underneath it before drilling.

A 'round' hole with 'no' sharp corners would be best.
A crack could form in a corner and spread.

Yes, of course. That's why I mentioned a hole saw.

And after drilling a hole, I will use a primer and paint to cover the bare metal. Ideally, I will also find a cap to put over the hole and seal it.

 

[D60]

Just how large do you need? Hole saw's fine but they walk a little and are kinda dramatic.

You can get step bits up to 1‐1/4" and possibly beyond. A step bit is always my first choice for sheetmetal, but they can get expensive.

I'm not seeing any structural issues based on the pics.

 

[D60]

Up to 1.375" for $30
https://www.harborfreight.com/316-i...-drill-bit-12-steps-and-5-11-steps-64648.html

Good thing to have ANYWAY, for the Man Card 'n all......

 

[inquirer]

@D60

I think 1.5 inches would be adequate, maybe a little less. Fitting the thumb and the index finger in the hole is what needed, in order to turn the small adjuster at the top of the shocks.

Thanks for bringing to my attention the step bits. I have seen them in the past, but they didn't come to mind. I guess they are more stable than hole saws.

There is more than one sheets of metal that should get drilled. The first is a removable cover as you can maybe see from the picture. Mayb that should get removed first to inspect what exactly is under it before drilling.

As for the structural integrity the tube continues upwards and forms the horizontal part of the trunk, so I guess it offers some support, but my estimation is that a hole would make a minimal difference to that position.

 

[97prizm]

I have a Lancer with Tein adjustable struts and shocks.

Since there is no access to adjust the rear shocks, I'm thinking of drilling the towers in order to be able to adjust them any time without removing them. The idea is to create a similar design with the Evo X. It's safe to drill the rear towers, right? They are not part of the chassis, correct?

You shouldn't be drilling anything suspension related as that can cause failure. You should be able to order the Evo X strut tower parts to swap if it's an issue. Why do you need to adjust the rear shocks?

 

[IndyIan]

I would make the hole as small as practical and in the middle of the flat part, away from the corners, just like mitsubishi did with the Evo, as that technically is part of the car's structure.
Also you'll need to plug it, to keep the rain/dust out. Maybe just clean the surrounding metal well and use some gorilla or tuck tape, as these seem to be permanently sticky. That's what I have done for covering holes like that in my car for rustproofing and they never seem to come unstuck.

 

[D60]

@D60

I think 1.5 inches would be adequate, maybe a little less. Fitting the thumb and the index finger in the hole is what needed, in order to turn the small adjuster at the top of the shocks.

Thanks for bringing to my attention the step bits. I have seen them in the past, but they didn't come to mind. I guess they are more stable than hole saws.

There is more than one sheets of metal that should get drilled. The first is a removable cover as you can maybe see from the picture. Mayb that should get removed first to inspect what exactly is under it before drilling.

As for the structural integrity the tube continues upwards and forms the horizontal part of the trunk, so I guess it offers some support, but my estimation is that a hole would make a minimal difference to that position.

Be sure you can get the dia you need before starting with a step bit. Once you're over 1/4" (pilot bit size) it's difficult to use a hole saw.

Starrett does offer an "oops arbor" that houses a hole saw in a hole saw, but it won't work in all circumstances.

Also the Milwaukee hole saws (49-22-4800) with 1/4" hex shank meant for an impact driver are amazing, but you're limited to common electrical KO sizes, again topping at 1.375"

If you truly need 1.5" your original plan of a standard hole saw may be the best and simplest!

 

[inquirer]

You shouldn't be drilling anything suspension related as that can cause failure. You should be able to order the Evo X strut tower parts to swap if it's an issue. Why do you need to adjust the rear shocks?

Well, actually it's above the shock absorber's mounting point.

Why do I need to adjust the rear shocks? Because they are adjustable! First of all to fine tune them. In order to find a setting that's acceptable for different road conditions, I have to test different settings and it's impossible to access the adjuster without removing the rear shock absorbers.

Ideally, I would use different settings for different road surfaces and road types, if I had free access to all 4 adjusters.

By the way, swapping the whole "towers" with the ones of the Evo would be a major modification that would cost thousands and new shocks would be needed as they are not compatible. Of course, that's out of the question.

I would make the hole as small as practical and in the middle of the flat part, away from the corners, just like mitsubishi did with the Evo, as that technically is part of the car's structure.
Also you'll need to plug it, to keep the rain/dust out. Maybe just clean the surrounding metal well and use some gorilla or tuck tape, as these seem to be permanently sticky. That's what I have done for covering holes like that in my car for rustproofing and they never seem to come unstuck.

If I'm not mistaken the shock absorber mount seals that area, but my intention was to use a cap for the hole anyway.
Of course the hole should be centered, no question about that.

Be sure you can get the dia you need before starting with a step bit. Once you're over 1/4" (pilot bit size) it's difficult to use a hole saw.

Starrett does offer an "oops arbor" that houses a hole saw in a hole saw, but it won't work in all circumstances.

Also the Milwaukee hole saws (49-22-4800) with 1/4" hex shank meant for an impact driver are amazing, but you're limited to common electrical KO sizes, again topping at 1.375"

If you truly need 1.5" your original plan of a standard hole saw may be the best and simplest!

1.5'' would make the hole spacious, but I guess 1.375'' could work too.

 

[IndyIan]

Well, actually it's above the shock absorber's mounting point.

Why do I need to adjust the rear shocks? Because they are adjustable! First of all to fine tune them. In order to find a setting that's acceptable for different road conditions, I have to test different settings and it's impossible to access the adjuster without removing the rear shock absorbers.

Ideally, I would use different settings for different road surfaces and road types, if I had free access to all 4 adjusters.

By the way, swapping the whole "towers" with the ones of the Evo would be a major modification that would cost thousands and new shocks would be needed as they are not compatible. Of course, that's out of the question.




If I'm not mistaken the shock absorber mount seals that area, but my intention was to use a cap for the hole anyway.
Of course the hole should be centered, no question about that.




1.5'' would make the hole spacious, but I guess 1.375'' could work too.

Sounds like you know what you are doing and good to go, it will be interesting to hear how the adjustments change the car?

 

[RooflessVW]

Seriously, a 1.5" punch out isn't going to hurt anything.

Should've already drilled them and not given it a second thought.

 

[inquirer]

Sounds like you know what you are doing and good to go, it will be interesting to hear how the adjustments change the car?

The adjustment changes both the bound and the rebound of the dampers simultaneously. In bad quality roads with potholes and bumps you need a softer suspension for comfort. Windy roads, especially during spirited driving, require a stiffer setup.

Of course, by experimenting you can compromise to a setting that is relatively god overall, if you don't want to change the settings every time according to the specific conditions. But even experimenting till finding one desirable setting is not possible for the rear shocks without removing them.

I'm confident that I can tune the damping adequately, i just want to make 100% sure that's absolutely safe to drill a hole there.

Seriously, a 1.5" punch out isn't going to hurt anything.

Should've already drilled them and not given it a second thought.

I wouldn't hurry to say that. In engineering everything is measurable and you need hard data for everything.

There are 3 parameters to consider:

1. What percent of the total width of the tube would the 1.5'' remove?
2. What forces does that tube experience under normal conditions?
3. How critical is that structure under exceptional conditions like crashes?

I think it's safe to guess that in this particular case the hole would not make any measurable difference regarding rigidity, but car engineers would use simulation software in order to get precise data before any redesign they make.

 

[RooflessVW]

but car engineers would use simulation software in order to get precise data before any redesign they make.

Right, but we're not engineers, and this isn't a race car. It's a Lancer with mid-tier coilovers.

If you're really concerned, you can use a hydraulic punch with a dimple die, then the part will most likely be stronger than before.