Shimano Rear Derailleur - 9-Speed - Shadow Design - Direct Attach - Black [MPN: ERDU4000GS]

Not sure if a part fits your ride? No problem—we’ve made it easy! You’ll find a fitment tool right on every product page (and on our homepage) to help you check compatibility with your vehicle. If you’re still unsure, just reach out—we’re always happy to help you find the right fit.

In many cases, yes we do! We’re all about giving you the best deal, so if you find a lower price elsewhere, let us know. You can check out all the details in our Price Match Policy.

At Motomentum, we stand behind the products we sell because we only carry brands we trust. Most of our items are covered by the manufacturer’s warranty, but don’t worry—we’re always here to help. If you ever run into an issue, reach out to us first. We’ll gladly assist with warranty questions and help you navigate the process to make sure you’re taken care of.

We accept Apple Pay, Discover, Google Pay, MasterCard, PayPal, Shop Pay, Venmo, & Visa. We also offer a "Buy Now, Pay Later" option with Shop Installments through Shop Pay.

Motomentum accepts returns within 45 days of delivery, as long as items are unused, unaltered, and in resellable condition with all original packaging, tags, accessories, and paperwork included (some exclusions apply). See our full Return Policy or start a return from your orders page.

If you’re in the continental U.S., odds are good you’re getting free shipping. And how fast is it? Most orders arrive in 2–3 days. Sometimes faster, especially if a warehouse near you is locked and loaded.

We ship most items free of charge, unless it’s the kind of thing that won’t fit in your trunk (unless you drive a box truck). Oversized stuff may cost a little extra—but we’ll always keep it real with you upfront.

Need it even quicker? At checkout, you’ll usually have 2 express options ready to go—because sometimes, you just can’t wait.

Bottom line: we want you to get your gear fast, at the best price, with no surprises. Check out our Shipping Policy to see all the details.

Absolutely! Just give us a quick shout before you order so we can double-check things for you. Since we ship from multiple locations across the country, your item might not be at our HQ—but don’t worry, that usually means it’ll reach you even faster!

It’s easy — and free! Just create a Motomentum account, and you’ll automatically be enrolled in the MotoMoney Loyalty Program. From there, you’ll start earning points on eligible purchases right away. No extra steps or sign-ups required. If you already have an account, view your Loyalty account and make sure your status is turned on (green).

It’s easy — and free! Head on over to our Membership page to sign up. We’ll email you all the details, plus your exclusive Motomentum Members-only coupon code.

You can find all our current discount codes and deals in one handy spot right here. Check it out anytime to snag the latest savings!