KYB Rear Shock Absorbers and Auto Maintenance: 8 Common Questions, Answered by a Fleet Buyer

When I took over purchasing for our company vehicles in 2020, I figured the job was simple: find the cheapest part and move on. After the third warranty claim in one fiscal year, I learned that the cheapest quote is rarely the cheapest outcome. I manage maintenance buying for a 40-person logistics company—roughly $120,000 a year across six vendors—and I report to both operations and finance. This FAQ covers the questions I actually get asked, from KYB rear shock absorbers to what really goes in a radiator.

• Is KYB a good brand for rear shock absorbers?
• What is the KYB Gas-A-Just KG5785 shock absorber?
• How do I know when to replace rear shock absorbers?
• Should I replace shock absorbers in pairs?
• How much does a car alternator replacement cost?
• When should suspension control arm bushings be replaced?
• What goes in a radiator?
• Can I mix OEM and aftermarket parts on the same vehicle?

Is KYB a good brand for rear shock absorbers?

From the outside, all shock absorbers look basically the same. The reality is that internal valving and gas pressure make the difference. Based on five years of buying parts for our delivery fleet, KYB is the brand I approve without a second thought. We've gone through maybe 200 rear shock absorbers across 12 trucks. Maybe 180—I'd have to check the spreadsheet to be exact.

Our fleet runs a mix of Ford Transit vans and RAM 2500 trucks. KYB shocks have been solid on both. That's more than I can say for the no-name budget brands the previous buyer used. What I've noticed with KYB specifically: fewer early failures. Their Gas-A-Just line also comes pre-pressurized, which saves our mechanic installation time. In my budget, labor counts as much as the parts themselves.

Per FTC advertising guidelines (ftc.gov), product claims have to be truthful and backed by evidence. KYB's warranty record in our fleet backs up their marketing, in my experience. But don't take my word—or their ads—as gospel. Check the warranty terms and get your own mechanic's opinion before you spend.

What is the KYB Gas-A-Just KG5785 shock absorber?

The KG5785 is a gas-charged rear shock from KYB's Gas-A-Just line. It fits specific vehicle applications, so verify your exact year and trim before ordering. That part number does not mean universal fit.

The difference from KYB's standard Excel-G line is the twin-tube gas design. In plain English: the gas pressure keeps the hydraulic fluid from foaming during hard use, so the damping stays consistent on rough roads. The rear end doesn't bounce as much after a bump.

The trade-off is price. Gas-A-Just costs noticeably more. Here's how I decide for our fleet: if the vehicle carries heavy loads or sees rough roads, the gas-charged shock handles heat better and earns the premium. For a commuter car on smooth highways, the standard line is probably fine. At least, that's been my experience with our trucks.

How do I know when to replace rear shock absorbers?

The signs, in the order I see them across our trucks:

• Excessive bouncing after speed bumps
• Rear-end squat under hard acceleration
• Uneven tire wear, especially cupping
• Visible fluid leaking from the shock shaft

A quick check you can do yourself: push down on the rear bumper and let go. If the vehicle bounces more than twice before settling, the shocks are likely done.

The general rule of thumb is every 50,000 miles. That's a starting point, not a promise. Our trucks average maybe 40,000 miles between replacements, give or take, because of the loads they carry. A highway commuter car can stretch further. Don't put it off. Worn shocks don't just ride poorly—they add stress to the suspension control arm bushings, and that's a bigger, more expensive job.

Should I replace shock absorbers in pairs?

Yes. Replace both at the same time. I learned this the expensive way.

In my first year, I approved a single rear shock replacement to save about $90. Two weeks later, the truck was pulling to one side. The alignment shop charged $140 to diagnose what was already obvious, and we ended up paying for the second shock anyway. Total "savings" from that decision: negative $350.

Shocks wear at similar rates, so when one goes, the other is close behind. Doing both together saves labor and avoids the handling imbalance. The lowest upfront cost wasn't the lowest total cost. That pattern shows up everywhere in this job.

How much does a car alternator replacement cost?

For our fleet, I budget $300 to $700 depending on the vehicle. The alternator itself runs $150 to $400 for a quality remanufactured unit, and labor adds $100 to $300 depending on how hard it is to reach.

When an alternator starts going, the first signs are usually dimming headlights at idle or a battery warning light that flickers. Catching it early is cheaper than dealing with a dead battery on a job site.

The trap I've fallen into more than once: the shop quotes the alternator only. The new belt, the mounting bolts, the diagnostic fee—those get added separately. I've watched a $380 quote turn into a $610 invoice. So now I ask one question before approving any repair: "What's NOT included in this price?" The vendor who lists everything up front—even when the total looks higher—usually costs less in the end.

When should suspension control arm bushings be replaced?

Control arm bushings are one of those parts people forget about until the problem is hard to ignore. The symptoms we see:

• Clunking or rattling from the front suspension over bumps
• Vague steering, like the vehicle wanders on its own
• Uneven tire wear

In our fleet, bushings last 60,000 to 100,000 miles. Road conditions matter more than time. Our city routes are stop-and-go with potholes, so we're usually at the lower end of that range.

Worth knowing: if a shop is already replacing your shocks or struts, ask them to inspect the bushings while they're in there. The labor overlaps, and that overlap is where real savings happen.

What goes in a radiator?

Coolant. Specifically, a 50/50 mix of antifreeze and distilled water. Not plain water, not straight antifreeze.

The 50/50 mix gives proper boiling and freezing protection and helps prevent corrosion inside the cooling system. I've seen a radiator fail early because someone topped it off with tap water. The minerals in tap water can scale up the internal passages over time.

Two more things: never open the radiator cap when the engine is hot. Pressurized coolant causes serious burns. And use the coolant type your owner's manual specifies. The wrong color can do more damage than running low.

Can I mix OEM and aftermarket parts on the same vehicle?

This is the question I wish I had asked earlier in this job. When a shop recommends KYB rear shocks but a different brand for the control arm bushings, is that a problem?

Usually not. Reputable aftermarket brands engineer their parts to meet or exceed OEM specs, and shops mix brands within a suspension system all the time. The catch: not every aftermarket brand is reputable. Budget brands keep prices low by cutting corners in the rubber compound or materials. You can't tell the difference by looking at the box.

What I do now: verify the brand, read the warranty terms, and confirm the part crosses over to the OEM part number. The real question isn't "what's the lowest price?" It's "what am I actually getting, and what happens if it fails?" That transparency lesson—the one about asking what's not included instead of just asking for the price—has cost me the most to learn.