Hydraulic Disc Brake Servicing

DMax

New Member
I have an Aventon Pace 500 with about 750 miles on it. Front brake is essentially “gone” (brake handle goes all the way to the grip) and rear brake is close behind. Label on the reservoir say “Mineral Oil”. Is it really mineral oil that I can pick up at Kroger or is it a special mineral oil I need to purchase from a bike shop
 

Timpo

Well-Known Member
You need an actual brake fluid for bicycles.

Shimano Hydraulic Mineral Oil (100ml) [Y83998020] | Maintenance -  Performance Bicycle
 

FlatSix911

Well-Known Member
I have an Aventon Pace 500 with about 750 miles on it. Front brake is essentially “gone” (brake handle goes all the way to the grip) and rear brake is close behind. Label on the reservoir say “Mineral Oil”. Is it really mineral oil that I can pick up at Kroger or is it a special mineral oil I need to purchase from a bike shop

Here's a good article and how-to video... ;)


 

fooferdoggie

Well-Known Member
its not too complex and long as you have the kit and follow the instructions. worse case you waste some fluid. make sure everything is really clean.
 

Latitude

Well-Known Member
Does seem odd. I have over 3000 km on my Trek hydraulic disks and they are fine, although I think I compromised the rear set last night, cleaning the chain and cassette. Rear brake seemed weak on my ride today, but recovered over the course of 30 km. Maybe something has compromised the disk pads?
 

MikeDD

Active Member
Wow, at 750 miles? Sure there isn't a crack in a hose? Seen any fluid on the floor, any loose fittings? I have 4,600 miles on a Haibike and haven't touched the brakes except to check on pad wear. I can make it to at least 5,000 without changing the pads.

In my hilly area and some singletrack, its new pads every 500 miles. If I ride to town, 1 mile distant, I can hit 30 mph easy without pedaling. That's to fast for this 70 year old.
 

TOOSLOW

Member
I have an Aventon Pace 500 with about 750 miles on it. Front brake is essentially “gone” (brake handle goes all the way to the grip) and rear brake is close behind. Label on the reservoir say “Mineral Oil”. Is it really mineral oil that I can pick up at Kroger or is it a special mineral oil I need to purchase from a bike shop

Baby oil, aka mineral oil. Dollar store.
 

FezUSA

Member
Thanks. Is this something a “rookie” can handle or should I take it to a shop?

You can handle this providing you've got a bleed kit, mineral oil, the videos on YT, and a little patience. I've never had hydraulic brakes before and my wife's brand new bike arrived with a mushy rear brake that 10 minutes after test riding the new set up, went to nothing (straight to the bar, brakes not engaged). Closer inspection revealed oil dripping from the shifter, directly under the brake lever/ reservoir. They offered me replacement parts & oil and I could either take it to an LBS (they'd cover it) or fix myself. I opted for the latter after watching some YT videos but asked them for a bleed kit as they had only sent oil and the olive fittings. They reimbursed me for a kit from Amazon.

Once everything arrived and I determined which fittings from the kit would fit the bleed "port" on the top reservoir and the "port" on the calipers, I set to and replaced the top brake lever/reservoir and then pushed oil from the caliper end until the syringe was almost empty (and the syringe on the reservoir filled up some), then kept squeezing the brake lever until all bubbles were gone. Honestly I think I spent more time watching the videos and figuring out which fittings to use than actually doing the job!! Do make sure to remove the pads and put a bleed block of some kind in, and do make sure you clean up any oil that "escapes", especially on the calipers before reinstalling the pads.

You've got this, and you're also on the road to bike maintenance!!
 

Handlebars

Well-Known Member
I have an Aventon Pace 500 with about 750 miles on it. Front brake is essentially “gone” (brake handle goes all the way to the grip)
Very possible that the tiny screw in the brake lever where it pivots has unscrewed itself. Usually they put blue thread locker on it but if it came loose you can screw it back in and the lever or handle will go back to how it used to be. Use thread locker or it will keep working itself out. Try that first. Beware of the cheap bleed kits. If the assembly is as bad as the Tektro kits I bought, you can have the oil splash all over the front disk and pads when it pops off.
Also I find that baby oil works better than the Tektro mineral oil at a fraction of the cost.
 
Last edited:

Handlebars

Well-Known Member
no you need to use stuff made for bike brakes any contamination can cause failure.
Obviously the name brands have things other than mineral oil in them, such as whatever colors them. More specific help would be good. People have been using straight mineral oil and even baby oil for long periods and in one video it shows a lab could not detect any problem in the brakes after one year. I trust Johnson's more than Tektro.

 
Last edited:

Handlebars

Well-Known Member
It's also good to note that any guarantee on the brakes would be voided by use of anything but the name brand. I couldn't even find any commercial product at normal price that would arrive quickly, so after mishap after mishap with the kit's tubes and plunger on my first attempt at bleeding brake lines, eventually even running out of fluid :) - I would have liked to be watching the fun, myself - baby oil went in to purge and then fill.
 

Handlebars

Well-Known Member
... my wife's brand new bike arrived with a mushy rear brake that 10 minutes after test riding the new set up, went to nothing (straight to the bar, brakes not engaged). Closer inspection revealed oil dripping from the shifter, directly under the brake lever/ reservoir. They offered me replacement parts & oil and I could either take it to an LBS (they'd cover it) or fix myself.
That happened with my bike but it was a very slow leak so I didn't even know at first. Since then I dropped the bike and the other brake now has the same slow leak at the same place... I googled for what broke and the only thing I could guess is a piston plunger type of rubber membrane/seal has a tear or separation.
Can you perhaps help me with finding out what parts might fix my brakes? What parts did you need in order to repair your wife's bike? Also, do you know the model of brake? Thank you!
 

FezUSA

Member
That happened with my bike but it was a very slow leak so I didn't even know at first. Since then I dropped the bike and the other brake now has the same slow leak at the same place... I googled for what broke and the only thing I could guess is a piston plunger type of rubber membrane/seal has a tear or separation.
Can you perhaps help me with finding out what parts might fix my brakes? What parts did you need in order to repair your wife's bike? Also, do you know the model of brake? Thank you!
As it was a brand new bike they agreed to send replacement parts and oil. I expected to receive a new brake lever/reservoir and hoped for oil with a bleed kit. What they sent was the complete rear brake assembly: brake lever/reservoir + separate hydraulic line (rear length) + disk brake/caliper; plus a small bottle of Tektro oil with a couple of olives/inserts.

I then bought a bleed kit from Amazon being careful to pick one that had a good selection of 'connectors' to provide the most chance I'd receive ones that would fit the bike-branded brakes (turns out they're re-branded Tektro's), as well as all of the other necessary parts. I was very happy that the kit did indeed have connectors I needed, and was even happier that where the small plastic tubes fit onto the syringes there was a kind of bushing to prevent the tube coming off under pressure and squirting oil everywhere! Where it fits onto the nipples that screw into the brakes though is still the weak link and probably means the tubes are a one-off use as they are essentially just stretched over the nipple. The kit included multiple tubes though, so I was ok with that.

I did not use the line or the replacement caliper & pads, will keep those for possible future use, at least the pads for sure. I just disconnected the hydraulic line from the existing brake lever, as well as the motor cut-off cable, removed the grips and then loosened/removed the brake lever. Installed the new one, connected it all back up and rotated the brake lever so that the reservoir was level and the bleed port at uppermost. Removed the bleed port screw and connected a nipple and tube/syringe with a little oil in it (kit didn't have one of those little screw-in type cups that some Shimano kits have). Then I removed the rear caliper, took out the brake pads, installed a brake block, took out the bleed port screw and inserted a nipple/tube/full syringe of oil. Pushed the syringe and watched the upper syringe attached to the lever/reservoir start to fill. Then I squeezed the brake lever a whole bunch of times and watched some bubbles come out at the top. Once done, disconnected, cleaned up, reinstalled. Done.

When calling the bike company about the leaking brake, I had checked the membrane and couldn't see any issues. The oil seemed to be coming out from the bottom side of the unit. It was easier/cheaper for them to just ship a replacement, especially as this was a new bike that had just been delivered. As far as I'm concerned, Biktrix couldn't have handled the situation any better!