Reply To: [Solved] Looking for a Step-by-Step Guide to Replace Brake Pads (GV125S EFI)
Sorry for delayed reply, but since one was not made, I will use your topic to make my reply as a tutorial if it helps others too (add your replies with pictures if you get stuck!).
Step-by-Step Guide: Hyosung GV125S EFI Front Brake Pad Replacement (and CBS Care)
Since there isn’t a dedicated guide on the forum yet, here is a complete walkthrough for the GV125S. It is a very manageable DIY job, but because it uses a Combined Braking System (CBS), there are a few unique quirks you need to watch out for.
Tools and Supplies Needed:
- New brake pads (which you have ordered of course)
- Socket set & strong allen keys that wont round off (for caliper bolts)
- Flathead screwdriver / small spanner (it helps pry things off incase they have been jammed by miles and miles of road dirt)
- Brake cleaner spray and an old toothbrush
- Silicone or copper grease
- A small block of wood or a G-clamp
1. Removing the Caliper and Pads
- Locate the two main bolts securing the front caliper to the fork leg. Loosen and remove them.
- Slide the caliper off the disc. Do not let it hang by the rubber hoses—use a bungee cord or zip-tie to tie it to the frame, mudguard, or steering bar, or let it sit on top of a tiny table.
- On the bottom front of the caliper, you will see a small “mini” blanking nut. Unscrew this to reveal the threaded sliding pin hiding underneath it.
- Unscrew and completely remove this internal sliding pin. The old brake pads will now slide right out.
2. Managing the 3-Piston Caliper & CBS (Crucial Step!)
The GV125S features a 3-piston front caliper because of the linked CBS setup (where the rear brake pedal also activates the front pistons).
- ⚠️ Golden Rule: Do not touch the rear brake pedal while your front caliper is off. Because the fluid lines are linked, pumping the rear pedal will instantly shoot the front pistons right out of their bores, spilling fluid everywhere.
- Cleaning the Pistons: Before forcing the three pistons back into the caliper to make room for thick new pads, they must be clean. Spray them down with brake cleaner and scrub off all road grime with an old toothbrush. If you push them back in while dirty, you will drag corrosive road grit straight past the delicate rubber seals, causing the caliper to seize up later.
- Pushing them back: Use a flat piece of wood or an old brake pad across the pistons to push them back evenly and slowly. Keep an eye on your front master cylinder reservoir to ensure fluid doesn’t overflow (We don’t know if a garage previously put too much fluid when they serviced the bike brakes before you came along. Don’t forget the GV125-S EFi has been out since 2018, so we have older models that were likely re-serviced with new brake fluid previously. It is wise to make sure it gets a fresh fluid flush every 4 years, but this is more of an advanced job for another time—if your bike is a 2023 model and it is 2026 today, then you likely have 1 year before Hyosung mandates the lines get replaced and fresh fluid. But I digress!).
3. Reassembly & The “Hyosung Brakes Rust” Check
- Take your sliding pin and give it a thorough clean. Apply a very thin smear of silicone or copper grease to the smooth shaft of the pin. Do not get grease on the brake-pad friction material!
- Drop the new pads into place, slide the greased pin back through, and tighten it down. Replace the mini blanking nut.
- Mount the caliper back onto the fork leg and torque down the two main bolts. Make sure it is tight so the caliper doesn’t fly off when applying brakes during a ride. If in doubt, get a small torque wrench and use a setting of around 15-20 ft-lbs (or roughly 20-27 Nm) to tighten the bolts until it clicks.
- Pump the front brake lever a few times until it feels firm. This resets the pistons against the new pads.
Casual afterthought: While you are doing this, inspect the condition of your original fasteners. Hyosung pins and caliper bolts are notorious for rotting, rusting, and seizing up in UK weather. We actually keep full stainless steel hardware kits down at our shop specifically for these GV125S models to stop them from ever seizing up again—just browse the shop if you ever need a set down the line!
🔍 While You’re There: Don’t Forget the Rear System!
Since you are working on linked brakes, it is highly recommended to do a quick health check on the rear setup at the same time:
- Check the Rear Master Cylinder: Because of how the GV125S is designed, the rear master cylinder sits quite low down and is highly exposed to road grit, salt, and water. Give it a visual check for any weeping fluid or accumulated crud.
- Do You Need to Change Rear Pads Too? Front and rear pads wear at completely different rates (usually fronts wear out faster, but CBS can balance that out depending on your riding style). You don’t need to change them at the same time, but you must check them.
- The Easy Rear Visual Check: Luckily, the rear caliper sits openly in the middle of the top of the rear brake disc. You don’t even need to take it off to inspect it. Get a torch, look into the back of the caliper, and check the thickness of the remaining friction material against your brand-new front pads. If they are getting down to less than 2mm, swap them out next.
Hope this helps! Keep us posted below if you have other braking questions!
Safe braking!