Giant Conduct brake system rant

Hi all,

So even though I’ve owned my bike for over a year now, I’m just learning about the issues with Giant’s conduct hybrid braking system. First off, I learned I cannot change my stem length without buying a brand new conduct master cylinder. Since they cylinders are not sold separately, I need to spend $200+ to buy the whole brake system.

Second, my brakes have started to get pretty squishy and I wanted too see if I needed to bleed it. To do that, I will need to purchase a proprietary brake servicing kit for $65+ and it’s pretty complicated to do myself.

Lastly, for some reason which I don’t quite understand, having Conduct brakes means you can only fit 140mm brake rotors. I’m taking part in a gran fondo with lots of climbing and descending, I’m 215lbs so I was hoping to get 160mm brake rotors for more solid braking but I guess that’s not going to happen.

I’m OK with things being proprietary if they make the bike better, I just wish something so critical to the function of the bike wasn’t phased out in a year. 2018 was the last year they used the conduct system as Shimano released the R7000 105 with hydraulic disc brakes, which means having to service or replace the master cylinder will likely get more expensive.

I dont know if it’s changed, but I had a 2017 Contend with the Conduct, and I had no problem using other stems with the bike. I tried several and the bolt pattern always lined up fine.

Again, maybe they changed it, but I believed its either TRP or Tektro that make it for Giant and their normal bleed kits work. I put over 3000 miles on mine and they never had an issue.

I have the bleed manual in my Google drive. I can send you if you want it.


Thanks, I actually just came across an older post on reddit showing Tektro kits work. To be fair, I’ve got 3,200 miles on my Defy and the brakes haven’t given me any issues either. Even now, with the brakes getting spongy, I have no complaints with it. As for the stem, I don’t think they would change it so maybe I’ll do some more research. Maybe it’s because there is some damage to the master cylinder itself?

Yeah, just pick any old stem you have laying around and try switching it. I tried a Bontrager stem and a couple of the old Performance Bike stems and they all lined up and worked fine.

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I could never really comprehend why Giant would invest in developing such a system. I love innovation as much as the next geek but surely their budget would have been better spent offsetting the 105 hyd premium or just even specifying TRP-HYD for a while?

They must be closer to knowing the new Shimano product releases than most?

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Whoa… there’s a lot of nonsense / misinformation you’ve been sold there!

Stem length: Any stem with the right bolt pattern (4x100 IIRC?) I’ve got several stems that don’t match, and others that do. Or just get a giant stem and disgard the faceplate. The master cylinder block replaces the usual face plate. That simple (I’ve done it).

Bleed - TRP bleed kit. Mine came from Epic Bleed Solutions, and was not expensive (I’m uk based so that might not help).

Rotors - nonsense. They’re just TRP calipers. Mine is on a 160 front, 140 rear setup. Depending on your frame you may need spacers/adapters on the caliper mount. My setup coped well with some spirited descending in bike touring mode (massive panniers all over the place). I’ve a vague idea that they say something about using other rotors invalidating the warranty, but yeah, whatever… again they’re just TRP calipers.

You’ve been told a lot of porkies by someone who can’t be bothered to find out I suspect…

Finally, I don’t know why Giant did it, but I’m glad they did… it let me put hydros on my bitsa build using a kinesis cross frame, and an old 6700 groupset I had lying around… Comparing to my mates bikes I’m not sure I could tell the full hydro vs conduct in a blind test, and I didn’t have to shell for a new groupset/commit to anything special. It also means if you’re suitably twisted, you could run hydros with a 3x setup…


P.S. I tried TRP HY-RD… maybe it was just the particular bike, but the were nowhere near as good as full hydro, and not even close to the conduct setup. TBH I wasn’t expecting a lot from it, but I’m pretty impressed.

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Thanks for the detailed reply. The information is coming from another Defy owner as well as online research, the latter of which is always dangerous but the volume of complaints was substantial. I’m putting in an order for the shorter Contact stem as I confirmed the bolt pattern will fit, thanks to everyone here for clearing that up!

As for being in the US, yeah it’s not good for anyone trying to find any Shimano components.

It’s possible the defy frame won’t accommodate a 160 rotor? I have no clue on that front, but for sure the trp caliper is not limiting. Seems a bit odd as I thought 160 fronts were pretty much defacto… Best of luck anyway!

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Confirmed, flat mount brake calipers will only accommodate 140mm disc brakes on the defy.

Also, the latest version of the conduct cylinder has different widths for bottom and top pairs of bolts, so it basically only fits giant contact stems.

I actually like my Conduct brakes, minus the aesthetics

My 2018 Defy fits 160 rotors front and back, successfully. This is not with the conduct system, which was changed out because I hated the “reservoir” thing on the front of my bars.

Yeah, it’s not an issue with fully hydraulic brakes, just with the hybrid system. That said, how did you switch to full hydro brakes?

Purchased the new 105 levers and ran new brake lines.

What a great idea for a bikepacking build!

If they’ve switched it up so you can’t use standard stems, dick move. But you still don’t need to buy a full system at least…

If you can switch to full hydros by just replacing with 105 levers, and run 160 discs (JustInTime), then you’re using the same calipers, and the hybrid isn’t the issue, and you could run 160 discs with they hybrid. The reservoir doesn’t know/care what the caliper is grabbing.

Now, mine is postmount, and postmount spacers are a fairly common thing. I know zilch about flatmount, but from an engineering POV, I can’t see any reason why you couldn’t have spacers that put the flatmount caliper in the right place. The caliper doesn’t know / care what size disc it is grabbing within reason, just so long as it sits on the edge of the disc - and it seems like @JustInTime has those calipers on 160s…
Also realise that what companies claim as ‘officially compatible’ is usually very limited and a lot more conservative than will actually work.

I don’t love the aesthetics of the converter. It’s a bit inconvenient with front bags for bikepacking, and I’ve been pondering a bracket to mount it off/under a conventional stem so it isn’t poking out the front, but it is very versatile, and by far the cheapest way of getting (retrofit) hydros on a bike. Maybe I had a bad set, but I borrowed a croix-de-fer with hy-rd and they were pants - more cable than hydro. Cable worked OK (not amazing) when they were adjusted, but rapidly deteriorated in muddy conditions. So far pretty good with the conduct, is on a par with my 9yo MTB shimano hydros.

I’m a ‘fan’ simply for the ability to decouple the shifting from (decent) braking. Far as I can find there aren’t any other comparable solutions still afloat (hope used to do something, but…)

Finally @mcalista, very much so. The ‘cross’ bike is my swiss army knife… The frame was an impulsive ebay buy intended as a spare parts build, now probably one of my favourites. I’m sure I could have achieved the same by throwing money at a modern groupset, but that wasn’t really the plan, ever:

  • I had my old roadbike stuff in the spares box from when that got upgraded
  • 10s era shimano is cross compatible road 10s road / 9s mtb (pre-shadow) - same cable pull, so if you stick a 9s mtb on a 10s road lever, you get 10s road shifting on a much bigger mech.
  • MTB makes some big cassettes available.
  • Tried cable brakes, didn’t like it, conduct was the solution.

… so I’m running a 36-11 rear, ‘9s’ long cage mtb mech, 6700 levers, front 50/34 with conduct - makes for a pretty versatile setup.
It works well for bikepacking (bit of a fiddle with front bags thanks to the reservior), proper (light) cycle touring with panniers and a rack - no option for front panniers on the frame, but I’m not going round the world/remote, so rear panniers plus front bag and frame bag is plenty. Fast commuter with/without a single pannier, and decent off road with the right tyres (did splurge on some tubeless rims recently), it will take 40’s. Overall very pleased.

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Spots I have 2018 Defy can you send the manual please.

Hey guys, I have a 2017 contend and I’m hoping to upgrade the convertor to a full 105 hydraulic break system - can I keep the existing callipers and just buy some 105 hydraulic levers and new stem, cabling / bleeding kit. Is there anything else I need?

You want Shimano calipers. They use different fluid than the Giant ones, also they come with the levers on hoses that are pre-bled. You want the tools to shorten and bleed them though because they’ll be tool long and you’ll want to route the hoses.

Trim hoses- just use the shift cable / housing cutting tool.
Olive/insert - need these, but not special tools
Bleed kit - need this
Bar tape

If you by from overseas, note there are UK style and normal style brake (F/ R) shifter alignments.

Tip- while you’re running the hoses, this is a good time to 1) change out the bars if you had any thoughts of doing so 2) run some heat-shrink-wrap (12mm) around the brake & shifter cables to clean up the look of the cables.

Amazing thank you! That’s really helped me, I’ll let you know how I get on. I’m in the UK and those Merlin ones seem like the best bet.