Shop Press

Shop Press is the news and idea hub for everything related to working on cars and trucks, focusing on repair, technology, and wrenching lifestyle.

From the creative minds at:


Hot Off the Press

Brake booster valve – ASE practice questions (VIDEO)

Description A customer states the brake pedal falls slightly when the brakes are applied while starting the engine. Technician A says that a faulty brake booster check valve may be to blame. Technician B says this can be caused by a leaking brake booster diaphragm....

The final days (and cars) of AMC

In the last days of AMC, two employees brought a video camera into the Kenosha, Wisconsin plant to document the end of an era. Billy and Danny take a thorough tour of the old AMC buildings and production line, which was producing its last L-body Plymouth Horizons and...

What is a core charge?

The article title is a question I asked when I was a young counterman, and most of you oldtimer mechanics and parts people of course know the story: the core charge is a way to be sure the smoked part makes its way back to the parts counter. A core charge is a deposit...

How do you inspect a serpentine belt for wear?

Performing a visual inspection of a car part is usually the first step in assessing its condition. In the case of the serpentine belt, any sign of physical damage to the belt means the belt should be replaced, and may indicate the need to more closely inspect the...

The importance of testing engine coolant (VIDEO)

How to test for blown fuses in a car or truck | Fast and easy methodDescription Dorman Training Center instructor Pete Meier explains why you should be testing engine coolant on vehicles in your bay. With a simple test strip, you can quickly check the coolant's health...

How to use a refractometer

I used to feel real dumb when I didn’t know what a tool was. After fixing things for a bit, I have come to learn that there are a lot of specialized tools and the only dumb thing is not learning about them. So when Dorman Trainer Pete Meier showed up recently with a...

Transfer cases: Married vs. divorced FAQ (VIDEO)

There is a paucity of divorced transfer cases fitted to vehicles traversing the roadways in 2024. In fact, some technicians—especially younger ones—aren’t even aware a setup beyond the married arrangement exists. If you’re unfamiliar with them, our own Technical...

Square drive: make or buy before you need ‘em

by | Mar 7, 2024

As a new tech, all I did was borrow tools from mechanics who were good to me. They usually lent and trained me on etiquette just after. (If you need to borrow it more than once or twice, maybe you ought to buy your own.) It’s not that often that I find myself without a tool these days in part due to having most of what I need and also in part to not being so pressed for money. But recently I found myself under a car needing something I didn’t have, so I thought I’d send out a little PSA for those of you who could end up in the same boat.

I was about to perform a service that doesn’t come up very often: a manual transmission fluid exchange. I’ve written before about my good friend the drain plug, so this was an interesting development: I had some trouble removing one recently, but that was no fault of the plug. Here’s what transpired on the Nissan that found its way onto my lift.

I can’t speak for you, but I personally always crack fill plugs before drain plugs. The fill plug was a little plastic butterfly affair. Easy-peasy; I spun that out and it was no problem.

See all that tire mounting compound? Getting sloppy here also helps when trying to index the valve stem; a slippery tire can just be held while the table spins to the correct spot.

Hmm. Not as straightforward as I thought. Photo: Lemmy.

Moving along, I readied the drain pan and spied what I thought was your standard 3/8” square drive slot broached into the plugs. I waltzed over to my box, grabbed a 6” extension, and when I inserted it, it was not fitting. No go. Maybe it was 1/4”?

Nope. Way sloppy.

I thought I knew what was going on, so I walked over to my lathe, which is imported, and grabbed the chuck key, an 8mm. I’ve only ever seen metric square stuff on Asian three- and four-jaw lathe chucks, but happily I had a tool on-hand to deal with them thanks to that. I popped it in, and bingo! That was it. I proceeded with the service uneventfully.

See all that tire mounting compound? Getting sloppy here also helps when trying to index the valve stem; a slippery tire can just be held while the table spins to the correct spot.

An unlikely solution to my problem was fortunately close by. Photo: Lemmy.

So today’s PSA is to grab (or make) yourself some tools to deal with these little things. Order some square stock, file down some junker hex keys or grab a set of sockets. I bought a set for my drawer; it was oddly cheaper than buying the stock to make my own.

This 8mm was on a Nissan, but Suzuki uses this style of plug on their cars and light trucks, too. Engines, trannies, and diffs all might have similar plugs on BMWs, Fords, Renault products, and Toyotas. (This depends on the vehicle model and market.) Through the grapevine I’ve also heard lots of domestic T-cases make use of this plug, too.

See all that tire mounting compound? Getting sloppy here also helps when trying to index the valve stem; a slippery tire can just be held while the table spins to the correct spot.

Ordinarily, I’m not a tool junkie. But fluid exchange happens a lot. I’m certain I’ll get my money out of these sooner rather than later. Photo: Lemmy.

Evidently, 10mm squares are also in use on some oil drain pans, and Honda uses them in their auto transmissions and diffs. I imagine a 3/8” might stand in for those in a pinch—with a caveat. I personally chose to purchase a tool since these plugs are shallow. The chamfer that makes it easy for us to pop a socket onto a ratchet or extension offers reduced bite in the shallow square broached into the plug. I like making do with what I have as much as the next fellow, but for the low cost of entry and high probability of servicing or checking a fluid level, spending some coins here seems like a no-brainer.

The articles and other content contained on this site may contain links to third party websites. By clicking them, you consent to Dorman’s Website Use Agreement.

Related Articles

Shop Press Comment Policy

Participation in this forum is subject to Dorman’s Website Terms & Conditions. Please read our Comment Policy before commenting.

Notify of
Inline feedback
View all comments

Get Articles In Your Inbox

Subscribe to receive a monthly email summary of our latest Shop Press stories.

Shop Press

I agree to the above privacy statement and T&Cs

Thanks! You're now subscribed.