brentveloar

My rear Shimano Ultegra (8000 series) Di2 Hydraulic Brake has had issues for months now. It's on a 2020 Tarmac Disc. The brake will lose pressure and be mushy about a week or so after full bleed. This has been an issue since I purchased the bike. The local shop has re-bled the brake several times.
After bleeding it feels nice and firm, but after a few rides it starts to take two or three "pump up" squeezes to get it to feel firm again. Then eventually it gets worse from there til another full bleed.

The shop swapped the rear Ultegra caliper for a brand new one for free. A week later I'm having the exact same issue!!
So it's NOT the rear caliper. What could it be?? The brake lever/shifter?? A bad hose?? There isnt any leaking fluid that I can see anywhere. I am at a loss and frustrated. Any advice would be appreciated.

WhyFi

Do you occasionally invert the bike, whether for transport to/from rides or for storage? Bubbles might be working out from the reservoir and getting in to the lines.

brentveloar

Not very often if at all. Obviously somehow the system isn't airtight and letting air in somewhere, but there's absolutely zero indication of mineral oil leaks anywhere. I'm thinking either faulty shifter/brake lever or the brake line itself is compromised. I've done the "easy" bleed and a "full" bleed myself, I've had the local shop and another shop service it and the result always ends up the same. The bike isn't even 3-4 months old. Never crashed to mess up the brake or anything either.

August West

I'd keep after the shop that you purchased it from. You shouldn't have to reach out to BF for help on this. This a warranty item and it is their responsibility to make it right. If they can't figure it out they need to reach out to Specialized or Shimano to find somebody that can sort it out. There aren't that many pieces in the system from the lever to the caliper. It shouldn't that hard to figure out.

brentveloar

I agree. The local Specialized dealer has been good. He swapped the rear caliper for free with a brand new one just to see if that was the issue. I'm thinking run a brand new hydro line and if that doesn't work it's got to be the brake lever itself letting air in.

WhyFi

So you're not hanging it by a wheel in the garage, or turning it upside down to remove/replace wheels or clean it or anything like that? It stays rubber side down *all* of the time?

There are going to be air pockets in the reservoir in the brake lever bodies - this is normal and isn't a problem if the bike stays upright. If it doesn't stay upright, though some of that air can get to the other side of the cylinder, which will give you that mushy feeling. This seems to be the easiest explanation for your problem.

If there were a leak, as you suspect, you'd have to ask yourself where the fluid is going. I can't imagine that it would be that hard to find and I also would think that it would be pretty obvious with braking deteriorating in a very short order, not over the course of a week or two.

I suppose that a ****ty seal at the master cylinder would give you poor performance, too, but that kind of an issue shouldn't be alleviated by a bleed.

SkepticalOne

Had similar issues on original setup of the same groupset. Deeper investigation with most diligent bike mechanic identified a very convoluted Shimano 21-step multi-orientation process for bleeding of this particular R8K hydro brake set. Could be that the tech is using general principles in trying to bleed the system instead of following the extensive Shimano procedure. I've had no issues since this was carried out on my brakes. Note that I have two separate bikes with this same group and both now work flawlessly despite me transporting them inverted from time to time.

Edit: Reason given for the more finicky process was the unique and compact shape of the 8000 brake hoods.

Sy Reene

A 21-step process to bleed the brakes? Really?

If the issue was due to inverting the bike, wouldn't the front brake have the same issue?

SkepticalOne

https://si.shimano.com/pdfs/dm/DM-RADBR01-02-ENG.pdf

pg 31-38

WhyFi

Have you bled brake lines? Do you know how bubbles work? Rear lines are long, and travel horizontally, with a low point at the bb. The front brake line is significantly shorter and mostly vertical; bubbles have fewer sticking points and will more readily work their way back up to the reservoir.

Kimmo 

Chalk up another point for the 'hydraulics are a PITA' crew

brentveloar

Thanks for the replies. I'll try doing the full Shimano recommended bleed method tomorrow.

Anna_Sazzi

Appearance is pages 31-39 and 23 steps. Correct?

RiceAWay

Part of the problem can be chalked up to Shimano using mineral oil rather than brake fluid which has a tiny percentage of the viscosity of mineral oil. I imagine that Shimano does this to avoid fluid leaks. But it also makes it difficult to bleed the brakes properly since air bubbles tend to want to stay in one place in the heavy mineral oil.

brentveloar

I properly bled them myself last night. From the caliper and the shifter. After repeating the "open the bleed screw on the caliper and hold the brake lever down" process a few times. It feels super solid and good now. Fingers crossed.

noodle soup

Mechanical brakes have never failed..Yes it's easier to fix mechanical discs brakes, but everything can break.

The problem is with the way his shop is handling the issue. 1 call(by the LBS) to the manufacturer should have ended with a new caliper, hose, and lever, being sent out to the shop. He has a 1 year warranty on the parts, and this is clearly a defect.

popeye

This is just the beginning.

WhyFi

The beginning of kvetching at every opportunity?

popeye

Faster than a triguy on keto.

mw22224444

OMG, this sounds awful. I'm open to a disc setup for a gravel bike but dreading this type of problem vs the simple rim brake. Maybe the next gen disc will simplify things more.

SkepticalOne

Anyone surprised by this hasn't read a Shimano manual for setting up derailleurs. There isn't anything out of the ordinary with the complexity of the instructions per se...the more compact R8K and R9K simply have different reservoirs that require a particular orientation to in order to ensure the purging of any entrapped air.

brentveloar

21 steps SOUNDS like a lot. In reality it isn't. I did it myself at home and after 60+ miles today the brake still feels super solid and firm. More than likely my local shop didn't really take the time and wasn't super particular when they bled them. I was and it made all the difference.

noodle soup

+1

Quitting drinking isn't a 12 step process either.

The guy that said a Shimano brake bleed is a 21 step process, worded it that way to get a reaction.

#clickbait

SkepticalOne

LOL, no, just trying to help. I worded it just as the gentleman who setup my brakes worded it. If anything, I would intend for those words to be interpreted as signalling care and compliance to manufacturer specifications for any of these systems as opposed to just winging it.

mw22224444

"Anyone surprised by this hasn't read a Shimano manual for setting up derailleurs"

Just trying to help right? Thanks.