If you’ve ever owned a bike with gears you’ve heard that grinding, clacking, chattering sound by a poorly adjusted shifter system. This article is a complete guide to adjusting both the front and rear derailleurs on a Mongoose mountain bike.
To help with where everything is and define the Mongoose Mountain Bike Gear Parts take a look at the illustration below.
TWO important notes:
- If your bike has been ridden for many years and the chain jumps and shifts by itself the odds are the chain is worn out. Bike chains are designed to wear-out before the gears.
Go to this article: How Long Does a MTB Chain Lasts and When to Replace. – link to another article here on DIY Mountain Bike.
- If the shifters are not working properly, it is possible for the derailleur to jam into the spokes and cause serious damage to the rider and the bike.
Adjusting the Front Derailleur (Shifter) on a Mongoose Mountain Bike
I’m going to start these instructions with the front derailleur. (aka front gears) This is the shifter closest to the pedals. The front derailleur controls or the shifter is usually located on the left side of the handlebars.
Adjusting the gears is best done with a bike stand. If you think you’re going to “get into” mountain biking a repair stand is an essential tool. You can read about the one I use in this article – Best MTB Repair Stand for the Money. – link to article
- 9mm open end wrench
- Phillips Screwdriver
- Needle Nose Pliers
IF you’d like to read further about the full set of tools to work on a Mongoose or any mountain bike read this article -> Mountain Bike Tools: The Ultimate List for On and Off the Trail
Get a FREE Download of the PDF instructions for Adjusting the Front and Rear shifters on a Mongoose Mountain Bike Below.
The steps for adjusting the front derailleur on a Mongoose MTB
- With the pedals turning shift both the front and rear gears into the lowest gear. On the mongoose shift the left-hand shifter into position 1. The right-hand shifter moved to position 1.
- On the front gear set insure the chain is on the SMALLEST diameter gear. This is often called the chain wheel or front ring.
- Disconnect the front derailleur CABLE. This is pretty simple to do using a 9mm open end wrench. Just loosen the cable anchor bolt and let the derailleur mechanism return the home position.
- The home position is where the derailleur spring pushes the mechanism without cable tension.
- Do a quick double check to insure the chain is on the smallest gear in the front and the biggest gear in the back.
- Adjust the derailleur LOW LIMIT SCREW so the derailleur CAGE is centered to the chain.
- Pull all the slack out of the cable and reconnect.
- With the pedals turning shift the front derailleur into the HIGHEST GEAR. (The biggest Chain Wheel)
- Sometimes when you shift into the high gear the chain will actually fall of onto the pedals. If this happens re-mount the chain and immediately turn the HIGH LIMIT SCREW until the CAGE is centered side to side to the chain.
- If the derailleur is touch the chain, turn the high limit screw until the CAGE is centered to the chain.
With the steps above completed and the pedals moving, cycle through the front derailleur gears a couple times. Usually some small adjustments are necessary to the high and low limit screws.
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Adjusting the Rear Derailleur (Shifter) on a Mongoose Mountain Bike
The rear derailleur is a little more complicated than the front derailleur to adjust. It has two primary functions, first as you might guess is to cycle the chain through the gears. The second function is to take up slack in the chain when the bike is bouncing along those bumpy trails. Because the derailleur mechanism hangs down close to the ground it is prone to damage. The most common item that gets bent is the derailleur hanger bracket.
If you’ve bent or smashed your rear derailleur consider getting a new one. The standard derailleurs with the Mongoose do not have a sacrificial “Hanger” First identify if you have a HUB or DIRECT mount derailleur. With this information head over to AMAZON and get a replacement.
You can read more about the derailleur hanger bracket in this article titled – What is a derailleur hanger bracket. 🙂
- If you need a HUB or Drop-Out Derailleur check out this link to Amazon = Shimano Tourney TY300 6/7-Speed Rear Derailleur with Dropout Claw Hanger
- If your bike has a DIRECT MOUNT you need to get this derailleur = SHIMANO Tourney 7/8-Speed Mountain Bicycle Rear Derailleur
Steps for adjusting the rear derailleur on a Mongoose MTB
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- With the pedals moving, start by shifting the rear (righthand) shifter into the highest number gear. This should move the chain into the smallest gear on the rear cassette.
- If the chain isn’t in the smallest gear, physically move it into the smallest gear by hand.
- Adjust the HIGH (H marking) limit screw so the guide pulley (the gear hanging down) is lined up with the center of the gear.
- With the derailleur center, cycle through the gears to check that the shifts are quiet and quick.
- Fine tuning can be done by turning the barrel adjuster (located on the righthand shifter body) Turning clockwise will loosen the cable tension – resulting in the chain moving away from the wheel.
- Next shift the rear shifter into the lowest gear (1) and place the chain into the largest gear.
- Adjust the LOW (L marking) until the gear is centered.
- Cycle through the gears again, making sure the chain moves smoothly through the gears.
NOTE: You can see how having a bike repair stand makes this so much easier. Holding the bike up, turning the pedals and cycling through the gears requires three hands 😊
- Small adjustments to the H and L are usually needed to get the system working well.
PRO TIP: Often times if after doing the above procedure you can’t get the chain to stop “skipping” it usually indicates that the chain is worn out, the rear derailleur dropper is bent or the rear cassette gears are worn out.
What to do if you need to REPLACE a Mongoose Gear Shifter
Aside from the rear derailleur getting bent or damaged another common problem is the shifter gets beat up or the cable breaks.
Steps for replacing the Mongoose Twist Shifter mechanism
Identify shifter twist shifter model. Mongoose used two main shifters.
SRAM MRX 3 x 7
SRAM 3.0 Comp
- Order shifter and wait for delivery
- Use a 9 mm wrench to loosen cable from derailleur assembly.
- Pull of the handle bar grips.
- Remove the shifter from the handlebar using a 4mm hex. Look closely a small set screw is on the body of the unit.
- Re-assembly the new shifter in the reverse order.
- Follow the adjustment procedures outlined above.
Learn a couple tricks for extending the life of your Chain and Derailleurs
It really doesn’t take much time to clean and lubricate the chain and derailleurs. This system takes so much stress. Think about the forces applied to that tiny chain to move hundreds of pounds.
A simple cleaning and lubricating habit can help make your transmission system last. Believe me breaking a chain on the trail and walking miles home isn’t fun.
I wrote another article about HOW LONG DOES A MOUNTAIN BIKE CHAIN LAST – link to article.
MTB Tools I Love and Recommend
I own each of these tools and only recommend things I own and use.
- Bike Hand Bike Repair Stand. Nice mountain bikes don’t have a kick stand so keeping your MTB safe but conveniently stored is essential. I keep my bike on my stand whenever I’m not riding it. This makes it easy to lube the chain, inflate the tires and adjust the derailleur. Highly recommended – Bike Hand Bike Repair Stand (👈 Link to Amazon to see what thousands of others have said)
- A basic MTB toolbox for replacing a chain, adjusting brakes and dialing in the fit. Bike Hand has a 37-piece box that has most of the specialty bike tools to keep your MTB properly maintained. The Bike Hand brand is value packed for the avid rider. Check out the competitive prices with this link to Amazon 👉 Bike Hand 37 pcs Bike Repair Tool Kit
- Get a good air pressure gauge, if you get just a tiny bit serious about MTBing you’re going to start playing with tire pressure. A couple psi can make your tires sticking or not. Get a good gauge, I highly recommend the Topeak Smartgauge D2, it’s accurate, flexible and easy to use. An Amazon best seller, here’s a link 👉 Topeak Smartgauge D2
- Carry a multitool with you on every ride. I’m serious, most of the time you can MacGyver something to get back to the trailhead if you have a multitool. I’ve got the Crank Brothers M19, it’s worn, rubbed and abused – but it still works. Thousands sold on Amazon – check it out with this link 👉 Crank Brothers M19