Shimano GRX Hydraulic brake issue….

[Yellow Saddle]

Apologies. I missed this.

Avid bike, car fettler here who’s dabbled with hydraulic systems periodically. And a mechanical Engineer by trade - so I comprehend what you’re saying.

None of which explains 2 x bikes in my fleet / 3 total in the household with Hydraulic systems - two of which took minimal adjusting to achieve zero rub ever. The other coming ‘perfect’ from new and has never been fettled since. And remains 100% noise / rub free.

From my experience it’s the one currently rubbing that’s the odd one out. Not vice versa.

I get what you say, but let's face it. There is only one reason for rub - insufficient gap between piston and disc. Whether that is via warp, out-of-square mounts, too little movement in the piston or flex. All these factors differ amongst your various bikes and there is no mystery third force at play. Car discs do rub - just jack up a wheel and spin it. You'll hear it., but not f rom inside the car.

It would be interesting if you could get your bike on top of a workbench in the normal position with wheels at eye leven and under good light. Get someone to pump the brakes whilst you look at the gap from all angles with a torch. If you can adjust it so there is a visible gap, but it still rubs, we're onto system flex.

 

[13 rider]

Would it be possible to contact the seller and get them via your LBS to agree to part of fully fund any work which sounds like should be covered by warranty ,which is obviously complicated due to buying on line

 

[sevenfourate]

Would it be possible to contact the seller and get them via your LBS to agree to part of fully fund any work which sounds like should be covered by warranty ,which is obviously complicated due to buying on line

I’d of course thought of this too. And took photos of the work being carried out last night - in readiness for being required. Let’s hope this first line of attack is the correct solution. Then I may well contact them…..

 

[sevenfourate]

Brand new Caliper purchased. Swapped over in its entirety - and showing exactly the same sticking tendency as the original.

LBS text me this info. I asked them ‘What next ?’ - also asking if they have access to a ‘Shimano Technical helpline’. Which he says they do.

I’ve asked them to use this service next - as opposed to spending more time / effort chasing unknowns.

They (Same one employee has worked on this on his own) sounds slightly lost if i’m honest. Whilst also saying they’ve never experienced a failure of factory supplied new parts of this grade / level.

I suggested they try another (Known working) Caliper on mine. Or mine on another bike. To see if it’s Caliper or other (Master cylinder, partial hydraulic line blockage 🤷‍♂️) issue…..

Any thoughts on the Technical solutions / problem solving here ?

 

[Yellow Saddle]

Like I said, get the bike on a workbench, secure it and start looking at the gaps/lack of gaps in good light and with a torch. We can speculate till the cows come home but one examination is all that will give the right answer. Out-of-square caliper mounts cannot be adjusted, but can be milled to square. All good bike shops should have such a tools.

 

[sevenfourate]

Hmmmmm.

Some Googling on ‘GRX 400 brake rub’ brings up pages of previous issues…..🤦‍♂️

Does of course mean Shimano must be very aware of this problem…..

 

[Dogtrousers]

I tried "GRX 400 piston retraction" and found something similar. It would appear that it's a thing.

https://www.reddit.com/r/bikewrench/comments/135dunc/stuck_brake_pistons_on_new_shimano_grx400_brake/

Not that I know anything at all about disc brakes I must hasten to add. I'm just curious.

 

[sevenfourate]

I tried "GRX 400 piston retraction" and found something similar. It would appear that it's a thing.


View: https://www.reddit.com/r/bikewrench/comments/135dunc/stuck_brake_pistons_on_new_shimano_grx400_brake/


Not that I know anything at all about disc brakes I must hasten to add. I'm just curious.

More good info. Cheers.

This you found is great info:

I did alude to the same above and said ‘partially blocked system’. Maybe: just maybe…….

 

[raleighnut]

More good info. Cheers.

This you found is great info:

View attachment 763075


I did alude to the same above and said ‘partially blocked system’. Maybe: just maybe…….

That'd do it, it would act like a 'clack valve'

 

[sevenfourate]

That'd do it, it would act like a 'clack valve'

Right. Bike was left at the shop. I’ll be ringing at 9.00am on the dot Monday and telling them what I’d like done next. Ie: Remove front hose from lever and very carefully check for obstructions.

Thanks for your research once again. I will of course let you know !!

 

[fritz katzenjammer]

I genuinely hate certain levels of GRX calipers… too little clearance in the design. I still have one new caliper on my bench that nobody in the shop could make work.

When some shiny new fresh out of the box bike with this issue on GRX calipers is giving me grief I’ve had luck by removing the wheel and pads and pumping the pistons forwards a bit, lubricating them with silicone lubricant or brake fluid and then resetting them and cycling them a few times to get the seals lubricated. I’ve soap used as well but find that fix kind of questionable.

I’m told the newer models have increased the internal clearance on the bottom end models so I hope this issue has gone away.

 

[sevenfourate]

I genuinely hate certain levels of GRX calipers… too little clearance in the design. I still have one new caliper on my bench that nobody in the shop could make work.

When some shiny new fresh out of the box bike with this issue on GRX calipers is giving me grief I’ve had luck by removing the wheel and pads and pumping the pistons forwards a bit, lubricating them with silicone lubricant or brake fluid and then resetting them and cycling them a few times to get the seals lubricated. I’ve soap used as well but find that fix kind of questionable.

I’m told the newer models have increased the internal clearance on the bottom end models so I hope this issue has gone away.

You’re right. I’ve spoken to a seller literally this Morning - who tells me:

“ The 820 is indeed Ultegra level quality. They will shave a bit of weight, and have ceramic pistons which offer better heat dissipation. Also there is a claimed 10% more pad clearance with Ultegra, Dura-ace, and RX-820”.

 

[Yellow Saddle]

You’re right. I’ve spoken to a seller literally this Morning - who tells me:

“ The 820 is indeed Ultegra level quality. They will shave a bit of weight, and have ceramic pistons which offer better heat dissipation. Also there is a claimed 10% more pad clearance with Ultegra, Dura-ace, and RX-820”.

Ceramic pistons have nothing to do with heat dissipation and everything to do with the opposite. The thermal conductivity of ceramic is pretty low. Ceramic is used to prevent heat from reaching the oil behind the piston. Had they wanted to dissipate the heat, they would simply use aluminium. The worst kind of science often comes from the trade.

 

[sevenfourate]

I tried "GRX 400 piston retraction" and found something similar. It would appear that it's a thing.

https://www.reddit.com/r/bikewrench/comments/135dunc/stuck_brake_pistons_on_new_shimano_grx400_brake/

Not that I know anything at all about disc brakes I must hasten to add. I'm just curious.

Pat yourself on the back…🙏👋👍✅

I’ve not spoken to my mechanic yet. But he said the line / Master cylinder was full of ‘shoot’. I suspect many others suffer from the same traits I did to some degree because of these issues. The internet is full of people complaining about GRX 400 rubbing problems……

 

[wonderloaf]

Wow, who'd have thought eh? I've also been suffering the GRX brake rub issue, I resorted to sanding a small amount of the brake pads to create extra clearance to the caliper, still not perfect but at least bearable, guess what I'll be doing in the very near future?