KYB vs Monroe Quick Struts: An Honest FAQ From a Technician Who Has Replaced Both

Over the past eight years, I've ordered, installed, and occasionally wrecked more suspension parts than I want to admit. I'm not talking about a textbook list. I'm talking about the $5,800 worth of mistakes I've personally documented since 2017. Some were small: wrong torque specs, reused hardware, one badly over-oiled K&N filter. One was expensive: I replaced a catalytic converter that didn't need replacing.

Here are the questions that show up in the shop and in my inbox. Straight answers, no fluff. If you want the short version: the brand debate matters less than the mount kit, filter care matters more than people think, and a P0420 code does not automatically mean 'buy a catalytic converter.'

• KYB vs Monroe Quick Struts: which should I pick?
• What does the KYB SM5753 Suspension Strut Mount Kit include?
• How do I use K&N air filter cleaner without making things worse?
• Why does an LS DBW throttle body need cleaning?
• How do I know if my catalytic converter is bad?
• Why does a new KYB strut still clunk? (That's the question most people forget.)

KYB vs Monroe Quick Struts: Which Should I Pick?

It's tempting to think one brand is simply better. But the strut brand is only part of the job; the mount kit and the rest of the suspension matter just as much. Monroe Quick Struts are a complete pre-assembled unit: strut, spring, mount, and hardware. With KYB, the equivalent setup can be a KYB strut plus a mount kit like the SM5753, depending on the vehicle and part number.

When I compared a Monroe Quick Struts unit and a KYB strut with the SM5753 mount kit side by side, I finally understood why 'which brand is better' is the wrong question. Monroe's valving tends to be softer, so the car feels a little cushier. KYB's valving is firmer and, on a lot of Asian and European nameplates, closer to the ride the car had when it left the factory. If you want a quick, budget-conscious swap, Monroe is fine. If you want a controlled, OEM-like ride and you're willing to install the mount at the same time, KYB gets my vote. Bottom line: neither is a 'bad' strut. The better pick depends on the vehicle, your driving style, and how many parts you plan to replace while everything is apart.

Oh, and don't mix a new quick strut on one side with a 100,000-mile original on the other. That's how you end up with a car that dives under braking and wanders on the highway.

What Is the KYB SM5753 Suspension Strut Mount Kit, and Do I Really Need It?

The KYB SM5753 Suspension Strut Mount Kit includes the top strut mount, the bearing that lets the strut turn with the steering, and the hardware needed to secure the top of the strut to the chassis. It's the part you don't think about until the old one starts making noise. If you've ever replaced a strut and left the old mount in place, you know that feeling: new part, same clunk.

Most DIYers focus on the strut itself and completely miss the mount kit. It's tempting to think a new strut cures everything. But a collapsed mount can let the strut rod move around, and that movement gets amplified through the spring tower. On a car with 80,000 miles, replacing the strut without the mount is a gamble. On a car with 120,000, it's nearly a no-brainer to do the mount at the same time.

I made this mistake once. The redo took about an hour longer, and the customer wasn't thrilled. (Should mention: the first strut was covered under warranty, but it still cost me two hours of labor and a lot of embarrassment.) If the mount kit is in the order, install it. Your alignment guy will thank you.

How Do I Use K&N Air Filter Cleaner Without Breaking Something?

K&N air filter cleaner is a solvent-based cleaner made for K&N-style cotton/gauze filters. Spray it on both sides, let it sit for about ten minutes, then rinse with low-pressure water from the clean side to the dirty side. Let the filter air dry completely before adding K&N filter oil. The oil is just as important as the cleaner. An over-oiled filter can coat your mass air flow sensor, and that will give you a driveability headache you didn't expect.

Here's what you need to know: do not use K&N cleaner on a paper filter. I know it looks like a cleaner and smells like a cleaner, but soaking a paper air filter with it will wreck the fibers. Pulling paper fibers into the intake is a red flag, not a hack.

A little technical side note: if you cleaned the filter and then your idle starts hunting or you get a lean code, check the MAF sensor first. The cleaner itself wasn't the problem; the over-oiling was. Clean the MAF with a proper MAF sensor cleaner, not throttle body cleaner, and avoid touching the wire. Reference: K&N's published recharge instructions and a whole lot of cheap lessons from my own engine bay.

What Is an LS DBW Throttle Body, and Why Does It Get Dirty?

LS DBW throttle body means an LS engine with drive-by-wire throttle. There is no throttle cable. The computer uses a motor inside the throttle body to open and close the plate. When carbon builds up around the plate, you get sticky idle, delayed throttle response, or a check engine light with codes like P0121 or P1516, depending on the vehicle. But don't quote me on the exact code list; those vary by platform.

The cleaning method matters. On a DBW throttle body, never force the throttle plate by hand. The gear train isn't designed for that kind of load. Instead, remove the intake tube, clean the bore with a shop towel and throttle body cleaner, and let it dry. Then plug it back in and let the computer do an idle relearn. On most LS platforms, it takes a few minutes of idling or a short drive. I want to say the exact relearn procedure is in the service manual, but I'd still check the manual for your specific truck or car.

The part people miss: carbon doesn't always mean 'replace the throttle body.' It usually means clean it. Replacing a $300 throttle body because you didn't try a $12 can of cleaner is the kind of mistake that used to make my weekly warranty list look bad.

How to Know Your Catalytic Converter Is Bad

The signs are not always obvious. A bad catalytic converter can show up as a rotten-egg or sulfur smell, lower fuel economy, a lack of power above a certain RPM, a rattle when you rev the engine, or a P0420/P0430 code from the oxygen sensors. But a code by itself doesn't prove the converter is dead. I replaced one in 2019 based on a P0420, and the car still set the same code a month later. The real problem was a small exhaust leak upstream. That was a $700 lesson, though I might be misremembering the exact figure because I tried to block it out.

Here's what you need to know before ordering a converter:

1. Check for exhaust leaks first. A leak near the O2 sensor can pull in air and make the converter look bad.
2. Watch the downstream O2 sensor. If it's mirroring the front sensor, the converter isn't doing its job. If the front sensor is switching and the downstream is flat, the converter is probably working.
3. Use a backpressure or vacuum test if the car feels restricted. A clogged converter usually shows up as high exhaust pressure or a noticeable vacuum drop.

A rattling converter is a different story. If you can hear ceramic honeycomb chunks rattling inside, that's a physical failure. No amount of sensor cleaning will fix that. At that point, the catalytic converter is bad, and replacement is the answer.

Why Does My New KYB Strut Still Clunk? (The Question Everyone Misses)

If you just installed a new complete strut assembly, whether it's a Monroe Quick Struts unit or a KYB with a new mount, and it still clunks over bumps, don't blame the strut yet. Check the strut mount first. Reusing a bad upper mount is the most common reason a new suspension part sounds old. That's where the KYB SM5753 Suspension Strut Mount Kit comes back into the picture. It replaces the bearing and the rubber mount that absorb top-end shock. Without it, the new strut rod has nothing solid to push against.

Other causes: loose sway bar links, worn control arm bushings, or a coil spring not seated correctly. I've been caught by all three. It took me about four years and maybe 300 suspension jobs to understand that a new strut is only as good as the components around it. The fundamentals haven't changed; the execution has transformed. You can't shortcut hardware that was already 120,000 miles old.

Take it from someone who has ordered a second mount kit for a car that 'should have been fine': replace the mount, torque everything to spec, and don't let the car leave the bay without checking for loose links. That checklist would have saved me about $2,000 in comebacks over the years.