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Car Mechanics and Maintenance

Whatever my current projects are, not meant to be comprehensive.

Quick Washing Your Car

  1. Rinse car with cordless pressure washer.
  2. (optional) Use a bunch of rags (microfiber towels) in a bucket with rinseless fluid. Avoid scratching paint with soiled rag.

Options for pressure washer dispenser bottle:

DIY rinseless wash ingredients:
1 Tbsp Baby Shampoo
1/2 Cup Distilled Vinegar

DIY window cleaner:
1/2 cup distilled white vinegar 10 drops essential oil (optional)

Wash and wax

Travel Without A Spare Tire

AWD Subaru differentials need same size wheels to avoid damage and I'm not sure how long they could be driven on a different size spare. Rather than trying to find a spare for my custom oversized tires, I could try using tire repair in emergency situations.

Tires can be repaired with plugs. Sidewall repair is difficult, but can be accomplished by vulcanizing rubber and mesh fiber into the sidewall. See How I do a vulcanized tire sidewall repair, by Misfit Toys on YouTube.

“Unlike the vulcanization of a patch to a tire, tire plugs rely on the general pressure of the tire hole pushing on the plug to create a compression seal, rather than a chemical seal.”

However, they do make plugs that are vulcanizing, for use with vulcanizing fluid. See Fix Punctures and Sidewall Gashes with Tech's Permacure Repairs, by Tire Review on YouTube. Less expensive vulcanizing plugs are made by Zerint (TS-4430, TS-4460, and TS-2560).

Practical Tire Aspect Ratio

Racing Cars Do Not Use Low Profile Tires

Roads are not perfectly smooth racing tracks, and even indy or stock-car racing use sidewalls that are 6“ tall. Sidewall flex is desirable for grip.

Indy 500 Racing Tire:
Indy 500 Racing Tire

Stock Car Racing Tire:
Stock Car Racing Tire

In the 70s sports cars came with 65 or 70 series tires (like the 240Z, 260Z, and 280Z). People on forums say this is because tire development had yet to evolve to make lower profile tires. I think that's bullshit from people's belief that development is always for the better.

Also see: Tires Are Critical to Effective Suspensions

Low Profile Tires are Like Jewelry

The truth is that low profile tires are just bling appreciated by an immature clientele. Low profile tires cause a lot of damage so they are also appreciated by suspension and tire shops.

Wider Tires Are More Comfortable Than Narrow Tires

Some people incorrectly assume wider tires give a rougher ride. That's because they continue to use the same pressure on a wider tire that they were using on a stock width tire. The pressure should be less on the wider tire to have the same tire deformation expected by the manufacturers.

Tire Pressure Calculator from

A more comfortable ride can be had by increasing the total volume of a tire.

Increasing the width and keeping the tire height constant, decreases the pressure needed to run the tire. For speed bumps the 2 dimensional vertical deformation is the same for both the wider and narrower tires. At least on speed bumps. On irregular surfaces the wider tire with more volume will be more comfortable.

To be more precise, the narrower tire does have a contact patch that is longitudinally longer, so it may “caterpillar track” over a bump. But the increased volume afforded by the wider tire overshadows what may be a marginal dynamic deformation improvement? I think so.

Wheel Balancing and Mounting

This section is unnecessary unless you are in a third world country, where mechanics either don't know how to use their equipment or don't care to use their equipment correctly, or the equipment doesn't function as intended.

An appropriate cone must be used on the inside of the wheel, along with a cup on the outside. If using a plastic hub-centric ring, it should be removed before mounting on the machine. I'm not sure about an aluminum one, but probably so as well.

(under construction)

Charging the Battery

A lead-acid battery, measured without load, should not go under 11.9v. It only takes a dozen or so cycles under this voltage to ruin a battery.

“Batteries can be very long lived if they are charged at a float voltage of 2.20 to 2.30 volts/cell (at 25 degrees C) (13.2V to 13.8V for a 12 V battery).”

For 2000s model cars, it's likely ok to charge the battery while still connected to the car, but newer cars may have more complicated electronics? Connect the positive terminal first, then the negative terminal.

Can You Start a Car with a Battery Charger Connected?

Starting your car when the battery is charged and the battery charger is connected as well isn’t that much of an issue, and you can start the car easily.

Starting a car on a dead battery with a charger connected can cause the fuse on the battery charger to blow out or burn the charger itself.

Will just starting a car and leaving it on charge the car's battery, or does the car have to actually be driven?

ELM327 / ODB2 Scanner

If you have a Bluetooth ELM327, and have connectivity issues, one last thing to try is to download different software. That worked for me. For some reason the software made for my ELM327 doesn't connect.

After reading numerous sites and forums, I think it's fine to clear an error code after logging it for future reference. Sometimes there's a glitch and the error doesn't return. If the problem persists, if the error doesn't return immediately, it will return after driving a sufficient number of miles (50-70). Codes can pop-up from having disconnected the battery.

For emissions related engines light issues, after clearing the code(s) you will have to wait through a “drive cycle” before you know if there is a problem. That can take several weeks, although you can look in your car's owners manual for more specifics.

This Car Scanner app shows which emission tests have yet to pass. I will know there is a problem because the engine light will turn on after the drive cycle. If there isn't a problem, I will know if the drive cycle has finished by checking the emissions tests in the Car Scanner app.

Exhaust Manifold Coatings, Wraps, and Heat Shields

Some super thin ceramic coatings may change surface emissivity but won't much change the surface temperature of the exhaust. I kept seeing really convincing pieces such as this popularhotrodding video. I'm amazed by how deep the marketing rabbit hole goes.

An forum helped guide me away from false marketing.

Engine Sound: Piston Slap or Worn Valve Clearances

My engine has a more faint version of the clanking sound in the YouTube video referenced in this forum thread. Also could be a need for valve clearance adjustment, as can be heard in this video. The sound lasts a few minutes on cold startup, and goes away more quickly if I rev the engine.

Car Sound System


My car came with an amp and upgraded speakers. There is a subwoofer box that is unsecured in the cargo area, that takes up too much space.

I'm thinking of getting a subwoofer that sits inside of the spare tire. Mtld83 on reddit is convincing me to go for a JBL Bass Hub. YouTube video showing Bass Hub innards, showing a downward firing configuration. More reddit comments. thread.

The volume in the spare tire can be slightly larger than under a single seat. Also, it's easier to clean under the seat without a box. No impact to foot space. Tools that go in the spare tire volume can be placed elsewhere under the cargo space floor. However, my spare rim is 4” wide and is dished outwards so the inside height is maybe 2“.

2008 Subaru Impreza Wagon

Suspension Lift Kits

Lifting a car is done by increasing the distance between the strut towers and the wheels. In order to not alter the suspension angles of the A arms or trailing arms, spacers can be placed under the suspension subframe so that everything is moved down along with the wheel. That way the suspension keeps it's original design: the motions are in the range designed by the engineers.

Increasing the acting height between the strut towers and the wheels can be done by a few different methods:

  • Taller strut
  • Spacers placed between the strut and strut tower
  • Stiffer spring with same number of coils on the original strut
  • A spring with more coils on the original strut

If the original suspension is capable of added range, then the last option may be desirable. The increased coil count will give a lesser spring rate, but because the spring is precompressed on the strut, the car will ride higher. The car will ride higher even though the spring affords more motion from the suspension upon going over terrain.

The range of motion of the suspension is limited in both directions. The taller ride height affords less downward motion for the wheel, less than the design engineers intended.

Most lift kits are sold as spacers to be placed above the strut under the strut tower. 2” or taller kits have spacers for the subframe as well. 1“ lift kits I've seen do not use subframe spacers. I hope the slight alteration to the geometry has acceptable performance.

Some DIYers use the taller Subaru Forester struts which add 2”, enough to warrant subframe spacers.

I have strut tower spacers for lift because I didn't think of coil springs with increased number of coils. I am not certain which option would be better.

My strut tower spacers are 1“ aluminum at front and 1.5” rubber compound for the rear. Without subframe spacers, the trailing arms are less horizontal and move the rear wheels slightly forward at resting position. With oversized tires, there is rub at the front of the wheel arch when the car bounces up.

On a Subaru Impreza 2008-2011, the trailing arms are attached to the subframe, mounted on the side rather than underneath the subframe. A longer trailing arm or a slotted attachment point could be used to move the rear wheels back to the center of the wheel arch.

GodSpeed adjustable length rear trailing arms, but only for WRX/STI

So if you are going to install forester struts, your choices are either 2“ trailing arm spacers on impreza trailing arms in the rear, or can you use Forester trailing arms to bring it back to spec?

No; Forester and Impreza trailing arms are the same, it's the bracket and the unibody itself that are different. Just get 2” trailing arms spacers and use your existing trailing arms and brackets. The 2“ spacers will perfectly recenter your rear wheels using Forester forum

With the longer trailing arms, the caster would be shifted back towards original spec (caster defined as the angle of the strut tower).

I think the CV axles will be in their comfort zones based on this nasoic post.

Ok. It's been done.

The trailing arm was welded to be longer and a slot was added to adjust the attachment point of the strut. The rear wheels returned to the middle of the wheel wells.

Custom Welded Extended Trailing Arm

Custom Welded Extended Trailing Arm, bottom view

Slotted Bolt Holes

The wheels needed toe-out with the longer trailing arms, within the range of the existing toe-in adjustment. The bottom ”A arm“ of sorts is the combination of toe adjusting bar and the bottom control arm. The trailing arms have enough play from the bushings that they can rotate to the slightly more longitudinal direction.

The longer trailing arms also resulted in negative camber despite the taller ride height. The lower control arm was swung back from it's forward swept position to be closer to a right angle, but the top A arm remains in its original location.

In order to add camber adjustment, the attachment points for the lower control arm were slotted as well. Now the rear suspension has camber, caster and toe adjustment: an alignment shop's ultimate nightmare.

Slotted Control Arm Attachment

Camber Bolt for Slotted Hole

However, based on the position for -1 degree of camber. I think some camber bolts would have been sufficient. I would have tried that first if it wasn't so impossible to get anything in Peru. Sometimes you get lucky, but you can spend a whole day looking for something with no results. Peru is chaos in so many ways.

YouTube videos on car lift projects

To reduce stress on existing suspension parts with a new configuration, loosen and retighten bolts to relieve stress to the bushings. Bolts should be tightened with the weight of the car on the suspension. Also good to add grease to bolt threads to prevent rust so they don't seize with age.

Front Suspension Rattle

Typically, it is the front, lower control arm bushings which tend to wear out and among those it is the rear most control arm bushings which need replacing. They are usually the first to wear out and can be replaced without replacing the control arm or removing the front suspension.

Part Number: 20204AG011 (or 20204AG01B)

However, my bushings were fine. It ended up being the left strut tower bearing that had gone bad. While everyone says to replace the entire strut cap, a local shop in Peru forced the bearing out and then Frankensteined a new bearing with spot welds to assure retainment.

Replacing Strut Tower Bearing on a 2008 Subaru Impreza

Tires for 2008 Subaru Impreza

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Spare Tire for 2008 Subaru Impreza

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engineering/vehicle-mechanics.txt · Last modified: 2024/05/15 08:15 by marcos