Really sluggish Shimano hydraulic discs (road)

[Rob.]

I've had nothing but grief from the brakes on my new bike build.

I got a full set of BR-RS505s (105 road hydraulics) from eBay. I cut hoses, ran internal lines and bled the rear with CHM hydraulic fluid - everything works spot on.

However, on the front, the fun started when I managed to crack a piston (or it was already cracked when I got them). I tried cheap AliExpress replacement pistons, but couldnt get it to bleed. Next step: give in and purchase a new replacement caliper. I followed the same bleed process as the rear, but the front is slow to grab the disc, and comically slow to retract after. I don't see how it can be the caliper as it's brand new, but what could be causing this within the lever?

Also, to top it off, I have deafening squeal at even the slowest speeds. I've tightened the bolts, cleaned the discs and gave the the pads a bit of a rub down with 240 grit (they were definitely a bit glazed). I don't have "good" pads to compare, but how rough should I sand them?

[frisbee]

You can sand them pretty rough,120 grit, but if they've got more than a few drops of oil on them then they are dead. You may also want to scuff the disk up as well, the pad has been polishing it.

Didn't the new calliper come with pads?

Bleeding the front isn't too bad but I would still follow the Shimano instructions to the letter.

[Bathroom_Security]

I have had a nightmare with mine. Cracked two 105 pistons and I then I upgraded the caliper at the rear to ultegra, seems to have worked as it has been on since October 2020. I have also had 2 cracked piston on my shimano XT mtb brakes

Road bikes really are pathetic given how much abuse my trail bike gets and still functions

[upsidedownmark]

Throw the pads away. Buy new ones. I'm normally mr fix-anything, but when it comes to discs not working, new pads every time. clarkes are cheap as chips, and decent. nukeproof been good for me in the past. Don't waste money on fins.

Probably stating the obvious, but a) take the pads out and put them in another room (I exaggerate, but only slightly) when bleeding, and b) depending ont the levers, the bleed procedure includes altering the tilt of your bars to get the air out. It's a fiddle, but once done once / properly should be fine. Slow retraction sounds odd tho.

[Rob.]

I have some new pads, but thought I'd have another attempt at bleeding before fitting them.

A few minutes ago, depressing the level would release fluid from the bottom bleed screw. It still wasn't working properly, so in an attempt to drain all the fluid and start from scratch, I've currently got the top and bottom bleed screws open. Fluid is not dripping from the bottom port on its own. If I pull the lever, it feels rock solid. I have the bleed cup full with oil and the bottom screw open, but no fluid is being drawn through.

What is going on?!

[frisbee]

Stupid question. Are you sure you are pulling the right lever?

[oddball1313]

My Ultegra calipers have never felt brilliant since the day i bought the bike, conversely the Campagnolo disc brakes on my BMC are amazing.
My mate has had a 105 caliper leak and due to the global parts shortage is replacing his calipers with HOPE units due to only a 4 week wait, be interesting to see what the braking improvement will be.

[NorthDave]

You shouldn't need to if they are new but do the pistons need a bit of silicone grease applied? My MTB pistons need lube'ing fairly often and this manifests itself as the pads not retracting.

[lufbramatt]

oddball1313 said:

My Ultegra calipers have never felt brilliant since the day i bought the bike, conversely the Campagnolo disc brakes on my BMC are amazing.
My mate has had a 105 caliper leak and due to the global parts shortage is replacing his calipers with HOPE units due to only a 4 week wait, be interesting to see what the braking improvement will be.

I do wonder if Shimano had a dodgy batch of these calipers. I just had a leaky GRX-810 caliper replaced under warranty (basically the same as the Ultegra caliper). The original one was always a bit meh in term of power and was very on/off. I assumed that how they were. Over time it got less and less powerful and was contaminating pads. I put the new one on at the weekend, bled it properly and bedded the new pads in and its WAY better then the original one ever was- bike will easily lift he rear wheel using the front brake and the modulation is brilliant.

I was assuming I'd have to wait ages for the replacement one to be sent out but Ribble appeared to have one in stock straight away to send out to me. I was thinking of replacing the brakes with Hope RX4+ but I'm so impressed with this new caliper that I don't think I'll bother.

[oddball1313]

lufbramatt said:

I do wonder if Shimano had a dodgy batch of these calipers. .

I’ve thought the same, another guy in the village has a Giant with the same groupset and brakes as my winter Canyon and the difference in the braking power and feel between the two is night and day

[anonymous-user]

Rob. said:

I've had nothing but grief from the brakes on my new bike build.

I got a full set of BR-RS505s (105 road hydraulics) from eBay. I cut hoses, ran internal lines and bled the rear with CHM hydraulic fluid - everything works spot on.

However, on the front, the fun started when I managed to crack a piston (or it was already cracked when I got them). I tried cheap AliExpress replacement pistons, but couldnt get it to bleed. Next step: give in and purchase a new replacement caliper. I followed the same bleed process as the rear, but the front is slow to grab the disc, and comically slow to retract after. I don't see how it can be the caliper as it's brand new, but what could be causing this within the lever?

Also, to top it off, I have deafening squeal at even the slowest speeds. I've tightened the bolts, cleaned the discs and gave the the pads a bit of a rub down with 240 grit (they were definitely a bit glazed). I don't have "good" pads to compare, but how rough should I sand them?

I’m not sure what CHM hydraulic fluid is, but I hope that it’s mineral oil. Shimano brakes only work with mineral oil.

[anonymous-user]

I needed a new calliper for my mountain bike.
By the time I got the caliper, new pads , fluid and a bleed kit, it was actually cheaper ( albeit a sale item) to buy a filled sealed and bled complete brake system ( from the lever to the calliper.
Minutes to install, works straight away. May not be available for every bike , but a no brainer if it is.

[Mazinbrum]

Try lubricating the pistons with red rubber grease, wipe any eccess off when pushed back in. I bleed from the bottom bleed screw using a syringe pushing the fluid up into the reservoir, no need to bleed after as pushes the air out.

[emicen]

oddball1313 said:

lufbramatt said:

I do wonder if Shimano had a dodgy batch of these calipers. .

I’ve thought the same, another guy in the village has a Giant with the same groupset and brakes as my winter Canyon and the difference in the braking power and feel between the two is night and day

Interesting. My Boardman running GRX calipers has been a pain in the backside from day one.

Very short travel in the lever to bring the brakes on and a nightmare trying to get the pistons to sit back properly and not have constant noticeable pad drag.

Finally thought I had the pad rub sorted, then it hit me with contaminated pads. Replaced the pads and couple of weeks later, its not hit me with contaminated pads again and the front lever is suddenly back to the bars.

[lufbramatt]

emicen said:

oddball1313 said:

lufbramatt said:

I do wonder if Shimano had a dodgy batch of these calipers. .

I’ve thought the same, another guy in the village has a Giant with the same groupset and brakes as my winter Canyon and the difference in the braking power and feel between the two is night and day

Interesting. My Boardman running GRX calipers has been a pain in the backside from day one.

Very short travel in the lever to bring the brakes on and a nightmare trying to get the pistons to sit back properly and not have constant noticeable pad drag.

Finally thought I had the pad rub sorted, then it hit me with contaminated pads. Replaced the pads and couple of weeks later, its not hit me with contaminated pads again and the front lever is suddenly back to the bars.

Put the bleed block in and leave it overnight with a zip tie or strap around the brake lever pulling the brake on. If there's brake fluid visible on the bleed block in the morning, get the caliper replaced.

[emicen]

Just went out to have a look as see if there were any signs of weeping, didn’t see any and the pads were dry when removed.

However, there’s very obvious signs of corrosion beneath the surface coating on both callipers which isn’t a good sign: