GRX question and caliper/ hose compatibility

[eippo1]

So the gist of this is that I have a post mount bike, but want to get the new GRX Di2 shifters. Can I run my existing BR-RS785 calipers with the new levers since I can't use the 810 calipers?

I know that the hoses are different diameters, but will it still interface at the shifter? Alternatively, is a tapered hose available that could go from the caliper to the shifter?

[Kirk007]

I've got this project on my list too; parts are here but I haven't had time to get to it. The external and internal dimensions of the caliper fitting for the hydraulic hose are the same withe grx direct mount calipers and the RS785 calipers; can't imagine Shimano would have made them differently.

[Jaybee]

Originally Posted by Kirk007

I've got this project on my list too; parts are here but I haven't had time to get to it. The external and internal dimensions of the caliper fitting for the hydraulic hose are the same withe grx direct mount calipers and the RS785 calipers; can't imagine Shimano would have made them differently.

M-series calipers (XT, XTR, SLX) should work too, right?

[eippo1]

Originally Posted by Kirk007

I've got this project on my list too; parts are here but I haven't had time to get to it. The external and internal dimensions of the caliper fitting for the hydraulic hose are the same withe grx direct mount calipers and the RS785 calipers; can't imagine Shimano would have made them differently.

So in theory we should be able to use our existing hydraulic hose for the grx shifters?

[eippo1]

So I had the brilliant idea to check the Shimano dealer forums (duh) since I have access and of course this came up there and was answered. I pasted the response below on how to do it, but the short answer is yes.

"the hydraulic hose should match the lever (so BH90 hose if using a newer lever such as ST-R9100, ST-R8000, etc), and you will need a hose that has the straight type connector to use with the BR-RS785. (SM-BH90-SS is the hose kit)

If you instead find yourself with the BR-R785 calipers (no 'S'), you will need hydraulic hose with the banjo fitting on the end instead."

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[bikinchris]

Road bike brake hose is more flexible than MTB hose. The MTB hose is reinforced inside to make it stiffer in use. They do use different barbs inside the hose, but the same olive. Road bikes use the silver barb and MTB hose uses a brass colored barb.

[Kirk007]

It works. Grx shifters with 785 calipers.

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