Looking for help with brake performance

[ScottM]

Like the title says, I am looking more confidence and predictability in my rear brake setup. I know practice and skill is everything and the brake does work somewhat good but I do feel a little held back because of my lack of confidence in it. It doesn't help that last year it slipped out causing me to sprain my ankle (I should have known better, got it a little damp and I use tar).

Setup is as follows, mid 2000s ZOO Pitbull? 26" long frame, modern Raceline hydraulic brake with stock green pads (I believe they are the TNN LGM pad material), ground Hashtagg rim, TNN shimless clamps, and beefy Tensile 4 bolt booster. I've tried violin rosin, a trials branded rim rosin, and plain black tar to try and increase the bite.

My experience level is fairly novice, I'm a busy 40 year old and been riding trials bikes off and on for 7 or 8 years. I also have a Hex with rear Saint disc and EBC red pads and while this doesn't have that rim brake instant feedback that brake is always predictable to me. I have played a little on a buddies more modern Echo (Mark V or something) which doesn't even have a brake booster but feels amazing. This frame does have the machined brake yoke section which I suspect has something to do with the issue. He has a ground rim that he doesn't re-grind often at all and the same pads.

What I am noticing on my ZOO is that even though I set the brake bosses up flat with each other etc, the pads are wearing such that they have a greater gap at the leading edge with respect to the rim than they do at the trailing edge of the pad. Am I primarily dealing with frame flex here or is there something else that could be causing this? Does that sound normal for these older frames? I can't find any cracks or anything. One thing I just noticed looking at Tartybikes is that the pad backing doesn't have the ridges machined in that the TNN backings have. Could this make that much difference? Also I used to ride with the ADM black pads on a V brake on a different frame when I was more of a beginner and I always thought it was good enough....

Maybe what I am dealing with is normal on a frame like this or maybe there is more I can do to perfect the setup? Maybe the frame has nothing to do with it? I know plenty of people did high level riding on these frames years back so maybe this is just how it is? Can I get more predictable performance out of this thing? If this is a frame flex issue would a new frame like the Ozonys Skill be any better or likely the same?

A big thanks for any input and I can try to get some pictures if it will help. 

Edited March 12, 2023 by ScottM
corrected information

[La Bourde]

Hello,

 

Hope  you recovered well from your sprained ankle.

It seems strange to me, that the brake slips.

I can't tell you the solution but here the things you can check:

- the brake is bled correctly. Sometimes the brake feels inconsistent (and often spongy) due to air in the system

- the brake fluid is thin enough. I noticed that when the lever does not comeback fast enough, I let slipped the brake (I cannot really explain why)

- maybe the brakepads are too old or they altered faster due to some kind of contamination. I got some Coustellier brakepads with an used bike, that were really hard (only the rear ones!) I now own a durometer, I will measure the shore degree they have. But I am pretty sure, there will be a big difference.

- did you check for a tiny leak?

 

I rode only disc brakes for many years. I had to accommodate to the lever feeling of the HS33, that can be really stiff. So one has to ensure, he/she is always applying a constant force on the lever.

Edited March 12, 2023 by La Bourde

[ScottM]

Hey thanks for that response. I don't think it is spongy but I do plan on bleeding it soon just because I haven't done it since I installed the brake and I do think I get a tiny bit of wandering bite point. I'm wondering now if Magura fluid or some Putoline 2.5wt I have used in my Shimano brakes would be better.

I am editing above to say that the pads wear more on the leading edge than the trailing edge which makes more sense. 

[AdamR28]

You didn't mention a grind... do you have one?

No chance of wandering bite point on a closed system brake. If the pads move as soon as the lever is pulled, with TPA all the way off, you're golden. No need to rebleed.

[La Bourde]

I use Putoline 2,5w in my HS33 too (got also Shimano disc brakes).

It is quite good, better than the original Magura fluid for sure.

But I compared recently on a really cold day with the brakes of a friend, that uses the trialtech fluid.

The Trialtech fluid seems even better.

(I wonder what it is, maybe a silicon based fluid?)

 

[ScottM]

Adam, I do have a grind although I'm sure my technique could use improvement.

Good to know the bite point won't move. With the TPA adjuster wheel threaded in (clockwise) so that that piston is further out, there is indeed some free play of the lever before the pads move. Is this what you mean by the TPA off or do you mean threaded the other way? With it threaded where the lever is further from the bar the pads do move pretty much right away.

Unfortunately I don't see that Trialtech fluid available anywhere now. Maybe I'll try the Putoline if I need to bleed it. 

[Daan]

The Trialtech fluid is just water with some additives. I'd only bother it if you think your pads are not retracting fast enough.

[AdamR28]

23 hours ago, ScottM said:

Adam, I do have a grind although I'm sure my technique could use improvement.

Try an old, used disc and literally just "tickle" the rim. Shallower, sharper grinds tend to work better. Downside is they need refreshing more often.

[Luke Rainbird]

55 minutes ago, AdamR28 said:

just "tickle" the rim

Such a tease.

[ScottM]

On 3/14/2023 at 8:23 AM, AdamR28 said:

Try an old, used disc and literally just "tickle" the rim. Shallower, sharper grinds tend to work better.

I tried refreshing my grind yesterday and I think I made it worse, I killed the bite! I found myself kind of letting the disc bounce lightly off the rim but I'm realizing that's maybe not what you meant by "tickle". I had assumed a fresh disc would give the sharpest grind and the best results but sounds like not? What I have are 40 grit "Masonry" discs, less than 2mm thick, maybe there is a better choice? I have watched several of the youtube videos on this but just haven't really figured out how to get a good result.

[AdamR28]

45 minutes ago, ScottM said:

 I had assumed a fresh disc would give the sharpest grind and the best results but sounds like not?

That's what I thought too - but I found them to dig in to the rim quite deeply, and you lose bite and power.

Although... you said 40 grit. Are you using a solid disc or the 'flap discs'?

[ScottM]

6 hours ago, AdamR28 said:

Are you using a solid disc or the 'flap discs'?

It is a solid disc, made for cutting I think.

Edit to say I probably need more practice, I’ll try again and be sure to take my time.

Edited March 22, 2023 by ScottM

[Muel]

This helpful old bean made a video about the best technique. 

 

[AdamR28]

Was hoping that video wouldn't rear its head... 12-years-ago me isn't a pretty sight 

[ScottM]

3 hours ago, AdamR28 said:

Was hoping that video wouldn't rear its head... 12-years-ago me isn't a pretty sight 

Quite helpful though! I didn’t see that one when I looked. 

[ScottM]

So this will do it 😆 The one was not even really glued at all anymore and the other pulled right out of the backing. I can't believe it took me so long to figure this out but after re-gluing the pads in the backings the difference is night and day. I did also touch up the grind and starting to get more comfortable with that, thanks to all for the advice and videos!

[duster34a]

My experience level is fairly novice, I'm a busy 40 year old and been riding trials bikes off and on for 7 or 8 years. I also have a Hex with rear Saint disc and EBC red pads and while this doesn't have that rim brake instant feedback that brake is always predictable to me. I have played a little on a buddies more modern Echo (Mark V or something) which doesn't even have a brake booster but feels amazing. This frame does have the machined brake yoke section which I suspect has something to do with the issue. He has a ground rim that he doesn't re-grind often at all and the same pads.

[duster34a]

My experience level is fairly novice, I'm a busy 40 year old and been riding trials bikes off and on for 7 or 8 years. I also have a Hex with rear Saint disc and EBC red pads and while this doesn't have that rim brake instant feedback that brake is always predictable to me. I have played a little on a buddies more modern Echo (Mark V or something) which doesn't even have a brake booster but feels amazing. This frame does have the machined brake yoke section which I suspect has something to do with the issue. He has a ground rim that he doesn't re-grind often at all and the same pads.

 

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[oscarrussell]

It sounds like you're experiencing a combination of issues that might be affecting the confidence and predictability of your rear brake setup on your trials bike. The uneven pad wear and the gap at the leading edge versus the trailing edge could indeed be indicative of frame flex, especially considering the age of your mid-2000s ZOO Pitbull frame. Older frames can sometimes flex more under stress compared to newer, more rigid designs, which might contribute to the brake performance feeling less predictable.