Squishy Shimano r785 hydro brakes

[kwikki]

Hi. Anybody here have any success getting firmer levers action on shimano road hydraulic disc brakes? The issue is too much lever travel before brakes bite. I don't think it is a bleeding/air issue. Here's the thing, I just bled them with yellow block in. Did the pump and open valve thing to firm up lever (in. No air in system) but when I put the wheel c back in there was still too much travel. So I took wheel out and squeezed brakes with no block or spacer......wheel back in and brakes are great.

I don't really understand this as clearly the pistons have moved out and stayed out, but I don't get how the lever pressure is still firm as the pistons moving out must have vacated some space which would be filled with fluid...but I haven't added extra fluid to compensate.

There is a red spacer for pad spacing, but I found this still resulted in too much travel.

Anybody out there got a failsafe technique?

 

[JackRabbitSlims]

Hi. Anybody here have any success getting firmer levers action on shimano road hydraulic disc brakes? The issue is too much lever travel before brakes bite. I don't think it is a bleeding/air issue. Here's the thing, I just bled them with yellow block in. Did the pump and open valve thing to firm up lever (in. No air in system) but when I put the wheel c back in there was still too much travel. So I took wheel out and squeezed brakes with no block or spacer......wheel back in and brakes are great.

I don't really understand this as clearly the pistons have moved out and stayed out, but I don't get how the lever pressure is still firm as the pistons moving out must have vacated some space which would be filled with fluid...but I haven't added extra fluid to compensate.

There is a red spacer for pad spacing, but I found this still resulted in too much travel.

Anybody out there got a failsafe technique?

No......haven't seen or used in the flesh.

However - have you made adjustments with the Freestroke and Reach Adjustment?

Which "Bleed Technique" did you use?

If you haven't already taken a look - perhaps a thorough read through this could assist - http://si.shimano.com/#categories/133

 

[kwikki]

Hi Jack. Freestroke and reach are set to zero. Frankly I can't believe anybody would want to add Freestroke to these brakes! Bleed technique was oil funnel on top of lever reservoir and waste bag on caliper. Didn't bother with the syringe from the bottom as it doesn't seem to help much.

I have tried pushing in a bit more oil after bleeding but it is against Shimano Law

 

[King Boonen]

The pistons should adjust their position like you describe at the end of your post, but they should do this whether there is a disc in there or not.

Piston adjustment doesn't cause air to enter the system, it's closed, so don't worry about that. Honestly, it just sounds like their 105 calipers aren't great at adjusting, like my Deore calipers on my MTB, and you need to give them a squeeze with no wheel in to get them to pop out a bit.

Once you have done it without the wheel in and the brakes feel right do they stay like that?

 

[kwikki]

Hi. These are the 785 calipers, so the Ultegra ones that are in fact just rebadged mtb ones.

Yes, the pistons have stayed out, but what I don't get is what is causing them to stay out when I initially pressurised the system with the wide yellow block in. Do you see what I mean?

 

[King Boonen]

Hydraulic systems use a bladder at the master cylinder if they are open to account for fluid changes but I think that's mainly for expansion. The systems are designed to adjust the piston position so when pads wear the braking remains consistent, so they are doing what they are supposed to. That's about the best I can do as I really don't understand it that well, if you email Hope Technology they can be pretty helpful.

 

[kwikki]

Thanks. That makes sense. I guess I'm trying to understand how it works so that I can make sense of why the pads only retracted a certain distance when I squeezed the brakes with no wheel in.

 

[King Boonen]

No worries. I can explain why but not how. The systems are designed to retract a certain amount from the stop point. That way, as the pads wear and the braking point changes, the pistons retract less and less so the bite-point and modulation don't change and lever feel remains the same throughout operation. Squeezing the brakes without the wheel in meant the pistons could move freely and possibly went past the point needed for a slight internal position adjustment to happen. With the wheel in this might not have been happening, so while the pistons needed to adjust a bit they didn't, causing the loose lever feel. Chances are if you had ridden for a while and the pads had worn a bit the levers would have firmed up. Also, if the brakes haven't been used for a while pumping the levers and a few hard stops can really firm them back up, at least on MTB brakes it does so I'm assuming the same will be true on road disc brakes.

 

[kwikki]

Well that's odd. I've just rebled the rear, and got it perfect. There are really fine tolerances on the post-bleed spacing and I'm only just starting to get the hang of it. Seems to be a bit of a dark art.

 

[King Boonen]

Having worked with fluidic systems for the best part of the last 10 years I can absolutely confirm it's a dark art!

 

[kwikki]

Well ***.

Thought I'd try a really careful bleed and spacing of the front to try and firm it up. It ended up squishier!!!

In the end, I rebled with wheel and pads in and pushed a bit more brake oil in. Not recommended but it works for a while.

This is confounding me.

I can do everything else on a bike. I've built up loads. Built wheels. Built fixes with complicated chain lines. Rebuilt Campag shifter levers. Serbiced all sorts of rear hubs. All of it. But these brakes. Grrrrr.

 

[JackRabbitSlims]

How many time are you going to bleed these brakes ??

In the OP you said So I took wheel out and squeezed brakes with no block or spacer......wheel back in and brakes are great..

If it aint broke....what are you trying to fix??

 

[kwikki]

Because I'm trying to get to grips with how the thing works. It's a learning process.

It's all about being able to replicate something and understand why.