Hope tech brake bleed advice

[ishaw]

Thanks for the detailed reply. They are the hope tech range, not tech 3s, though have a set of those but the ones in question are 2 pot with the lever adjusters.

I won't have time for a few weeks to further fettle, but have hunters lube and bleed kit, bit not the bore tools. I can probably suffice without and get the pistons out. Have some spares and steaks so if a clean fails I'll bite the bullet and replace.

 

[ishaw]

Finally had some time to tackle this.

Managed to do a strip and rebuild of the callipers, replaced the pistons and seals successfully (see pic of calliper after removing everything).

It would seem that despite doing this, nothing has really changed.

I've obviously bled the brake after the seal and piston replacement, but I'm still in the same boat.

Lever feel after bleed isn't the same as the rear, it feels like there's a bit of nothing initially when pulling the levers then it's biting on the rotor. There's not a lot of pull before the brake is stopping the wheel spinning. I'm also struggling to get it all aligned so the rotor is not rubbing on the pads.

I'm at a loss as I've done lots of hope breaks fine but the front has me stumped this time.

My son is desperate to start riding the bike but as it stands I can't get this front brake right.

What am I doing wrong?

Piston seals are brand new, seated right and lived with hunters. Pistons are new. Bleed process has been done a few times now, block between pistons, no air left in the system I think. Only other option I can think of is to do the seals in the lever but it seems fine as it is.

Any ideas or suggestions?

Going to have another stab tomorrow.

My last thought is the rotor isn't very true but I've tried to tune that with a tool too.

 

[Twozaskars]

Can you switch rotors front to rear?

 

[Twozaskars]

I'd expect some sort of give or softness until the fluid hits the pistons.

The fluid will always be at the pistons. The entire system should only contain fluid, not air. Air is compressible whereas fluid isn't.

To answer your previous point about how hydraulics work, just to clarify here is a rough and ready drawing (there will be better on the net I know) that shows how it works.

Red = lever, hose and calliper
Purple = lever piston
Blue = caliper piston
Yellow = seals
Green = fluid.

As the smaller purple piston (lever) moves you are forcing a tiny amount of fluid (in the direction of the black arrows) into a large, lower pressure space around the blue piston (caliper). It's really easy to do.
Then, imagine if the pistons were the same size then one will move the same amount as the other.
Finally, imagine trying to do it the other way, pushing on the blue to move the purple. You would be trying to force all that fluid through one small hole and it would take a lot of effort.





*Not to scale.
**Drawing remains the property of the artist.

 

[bikeworkshop]

Here's a quick symptom list:

If the disc is bent, It will go tssk tssk tssk as you spin the wheel.
You will also see the wobble if you look at it entering the caliper.
It won't affect the brake feel.

If there is air in the system, there will be a spongy feel at the lever.
If there is no air, the brake will feel firm at the biting point.

If the lever piston is binding, there will be slack at the lever before you feel anything happening.

If a seal is failing, then the brake will set up ok but lever travel will increase over time.

You will probably find fluid leaking after a while.

If the caliper pistons are binding, the brake will stay on, or keep rubbing continuously.

If the caliper is misaligned, the brake will rub constantly.

(you can push the caliper pistons back and then set the brake up over the disc by eye, then watch closely to see where the problem is. If the paid are binding you won't see any retraction at the caliper)

There are other detail problems but I think you're amongst the above
Good luck

Iirc if you are totally baffled,
hope offer a rebuild service

 

[ishaw]

Can you switch rotors front to rear?

No, different sizes but I'm sure I have another rotor somewhere.

 

[Twozaskars]

No, different sizes but I'm sure I have another rotor somewhere.

Which brake is now giving you the trouble?
Could you post some photos of them fitted to the bike from directly above and from the side?

 

[ishaw]

Here's a quick symptom list:

If the disc is bent, It will go tssk tssk tssk as you spin the wheel.
You will also see the wobble if you look at it entering the caliper.
It won't affect the brake feel.

If there is air in the system, there will be a spongy feel at the lever.
If there is no air, the brake will feel firm at the biting point.

If the lever piston is binding, there will be slack at the lever before you feel anything happening.

If a seal is failing, then the brake will set up ok but lever travel will increase over time.

You will probably find fluid leaking after a while.

If the caliper pistons are binding, the brake will stay on, or keep rubbing continuously.

If the caliper is misaligned, the brake will rub constantly.

(you can push the caliper pistons back and then set the brake up over the disc by eye, then watch closely to see where the problem is. If the paid are binding you won't see any retraction at the caliper)

There are other detail problems but I think you're amongst the above
Good luck

Iirc if you are totally baffled,
hope offer a rebuild service

I'm no noob, but thsnks.

New pistons and seals fitted in the calliper. Same for master cylinder. Rear is fine after I've worked my magic, just can't set the front up.

Pistons seem to move freely, no lazy side or sticking. I even swapped the adapters over to roper hope ones which has helped to a degree and given me a bit more adjustment space.

Going to have another go at it today and see what it yields. I've not been beaten yet.

And yes, hope do offer a rebuild service at £75 a brake. I've effectively done that so shouldn't need to send it away.

 

[bikeworkshop]

Early discs took a lot more alignment and spacing than modern ones - i remember endless use of the mount facing tool and drawers of tin washers in 3 sizes. Basically you just don'tneed that stuff any more.

- it's worth visually checking that the pads are looking parallel to the rotors, that can mess with the setup

 

[Cloverleaf]

Early discs took a lot more alignment and spacing than modern ones - i remember endless use of the mount facing tool and drawers of tin washers in 3 sizes. Basically you just don'tneed that stuff any more.

- it's worth visually checking that the pads are looking parallel to the rotors, that can mess with the setup

I still preferred washers; once you knew the correct number for your frame that was it. No fuss each time you removed it, just straight forward re-aligned every single time. Then again it required patience and some finesse, something MTBers aren't well known for.

Personally I reckon you should look at a lever seal kit @ishaw. If there's something not working right, it's logically the only thing left to do. Did you get any black bits coming out when you pulled it apart and bled it?