Hydraulic rim brake clamp torque specs and other brake clamp questions.

[trialscrab]

Hi!

I have a Jitsie Varial Race bike/frame (2021 model, I think) and I'm wondering about brake clamp torque specs. I've noticed that when the brake clamps are overly tightened, (I think) it causes the slave cylinder pistons (right terminology?) to lock up and/or return slowly (is that normal?). So I just ordered a bike torque wrench and some new M5 25mm bolts (the Jitsie are not good and I've stripped one already and will need to dremel a slot to get it out) and intend on trying to figure out what torque would be sufficient on the clamps to keep the slave cylinders from slipping whilst not being so much that it inhibits proper piston movement.

I just had the brakes bled by a professional (also a trials rider) yesterday. The lever action is now excellent, but after riding a bit, I noticed the rear pads were returning into the slave slowly after the lever was depressed and released. This makes it so the wheel stays locked for a faction of a second longer than you'd expect when you e.g. try to gap, which is not good (i.e. a good way to face plant).

The clamps are the ones that come with the bike. I think they're just the standard Jitsie aluminum ones. They do seem to deform some when tightened down.

Any and all suggestions and knowledge regarding best practices for setting up and maintaining hydraulic rim brakes are welcome as I'm completely new these type of brakes.

[aener]

Is it a new brake, or from an older bike? You really shouldn't have them if it's new, but it sounds like you've got sticky pistons. Clamping tightly doesn't restrict piston movement. Fair idea to have, but people would routinely do bolts up tight enough to strip threads out of frames without it effecting the piston.

There's a bunch of methods people have mentioned for combating this and I'm really not good with brakes so don't take my word for it, but:

Remove the slaves from the frame.
Take the pads off.
Have a good wipe around the pistons to get rid of the accumulated crap and grime.
Hold your thumb or put some sort of clamp (not tight - just to stop it moving) over ONE of the pistons and pull the lever. This means the piston that can move moves much further.
Apply some lube to the sides of the piston when it's all the way out, spread it about with a finger and pump it a bunch of times.
Let the piston return and wipe off any excess lube so it doesn't get on your pads etc.
Repeat the above for the other slave.
Reassemble and reattatch.

 

It probably won't make it like-new, but it should improve things a bit.

...Unless it's the piston in the lever that's causing the slow return, in which case I'm definitely letting someone else take the reins on detailing a fix!

[trialscrab]

I bought the bike second-hand, but it's relatively new. I did have a sticky piston in the lever. That was solved - it glides like butter now. It's just the rear slave. I was under the impression that torquing down the brake clamps shouldn't affect piston movement in the slave, but I swear it has happened before (the rear wheel axle moved on a static hop and I had to re-adjust the rear and re-align the wheel and brakes and remember having to untorque the clamps to get it to move freely). Maybe the slave piston is indeed sticking. It seems to only be one side as far as I can tell.

I'll go through the process you outlined and I'll report back. What lube do you recommend using?

Thanks!

[Chakers1998]

If it is still happening after lubing the slave cylinder pistons, take the lever apart and use some silicon grease to lube the piston bore and piston O-rings. Slightly stretching the spring can also make a difference, as TartyBikes have said that this needs to be done with the Clean levers sometimes. 

[trialscrab]

So, definitely not the clamp. I took the right rear brake off, took the pad off, and watched the piston go in and out. It's going slow unclamped, but only the right rear. The left rear (where the brake the hose goes to first) moves quicky and with almost no delay to the lever squeeze -- it's practically instantaneous -- and on-point throughout it's stroke. The right on the other hand has a delay on the release. I can squeeze the lever in and then drop it, and I hear the "thud" of the lever well before the piston goes back to its resting state. I cleaned it and lubed it with a silicone spray, pumped the handle several times, then wiped all down and it still goes slow. I'd say it's maybe marginally better than before. It almost seem like some kind of pressure difference or blockage on the return of the piston. Thoughts?

[AdamR28]

9 hours ago, trialscrab said:

It almost seem like some kind of pressure difference or blockage on the return of the piston. Thoughts?

Possible I guess, but very rare to be the cause. Only way to tell is to strip the hoses off and inspect.

[Szymon]

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Edited September 12, 2022 by Szymon

[Szymon]

I had a similar problem with the backings. I had backings from the echo brakes. Which have different dimensions and are able to block.

[Mark W]

On 9/9/2022 at 4:34 PM, trialscrab said:

I was under the impression that torquing down the brake clamps shouldn't affect piston movement in the slave, but I swear it has happened before

It's rare but it can. It tends to happen more when the cylinders are older or a bit more worn around the section that they get clamped on. You have to be really tightening the bolts up for it to happen. 

When you got the bike, were the brakes bled with water, oil or ______? 

[trialscrab]

On 9/12/2022 at 2:31 AM, Mark W said:

It's rare but it can. It tends to happen more when the cylinders are older or a bit more worn around the section that they get clamped on. You have to be really tightening the bolts up for it to happen. 

When you got the bike, were the brakes bled with water, oil or ______? 

I don't know what was in it. I'd guess it was just the stock royal blood unless Jitsie bleeds them with something different at the factory before shipping them out. These are the Jitsie Race levers/master cylinders with HS33 slaves. The bike was purchased second-hand but was maybe only used a year with a handful of rides.

In any case, they seem to be working now. I honestly don't know what exactly changed. Maybe the lube finally worked its way in. Maybe an air bubble in the crossover floated off elsewhere. Maybe the new bolts and a more precise readjustment of the calipers did something. I rode the bike today, had no issues. Watched the pads go in and out multiple times and they are now both on point.

I'll keep an eye on them and report back if anything changes. Thanks everyone for your help and guidance!