Just for fun, I am trying to re-build a set of original (2-piece caliper) Hope Mini brakes. I've mostly got them back together, but now they leak from the join between the two caliper halves. The indentations where the o-ring sits had a little corrosion, so I have already tried polishing that smooth with a small piece of 400 grit wet and dry sandpaper. I also cleaned up the main flat areas where the calipers bolt up, but no joy.
Was this a known problem? At this point, am I flogging a dead horse?
As a side note, it looks like there was some kind of plating across the whole inner face of each caliper half - does anyone know if this is the case? If so, I suppose making surfaces flat again by sanding through that plating and into the alu body is not a good long-term solution either.
Thanks in advance!
Don't remember there being any plating.
Certainly wasn't a known problem (mine are still going strong), the plating is a hard anodizing, and probably the reason they haven't corroded to a pile of dust like the avids & hayes of a similar era, so probably not a good idea to remove it. A slightly thicker O-ring may help (dot compatible, obviously), but failing that, any of the more modern standard 2 or 4 pot Hope calipers should work fine.
Have you used new seals is my first question
If you are 100% sure they are leaking and it's not fluid from assembly.
If you can't get them to seal. As a last ditch attempt. Use 1000-1200 wet and dry. 400 is quite coarse. On glass with plenty of water. Up and down and side to side sand it. Rather than a circular motion. The reason for the glass is its completely flat.
By the sounds of it you have scratched the surface slightly and it's caused a leak. Or it could be under size o rings. Hydraulic fluid is like water. If there's a hole or flaw no matter how small it will find it.
I think they are anodised. I have a pair I have given up on, I think there is a small leak in one piston. Never had probs with the internal O ring. Surely the flatness of the mating surfaces isn't a big deal so long as the O ring is getting nicely squished between two surfaces that are in reasonable nick?
Thanks for all the advice.
Yes, new seals.
The area where the seal sits was rough with corrosion when I took it apart, so I didn't have much choice but to try and do something about it. (I'm talking about the seal that goes between the two halves).
The flat area on each half of the caliper shouldn't matter, but they also had corroded spots, so I gave them a once-over so they would sit flat and allow the seal to squish properly.
If all of this is taking off a layer of anodising, then I think I may as well give up. I could try a slightly bigger o-ring, but it sounds like I won't be able to get it smooth enough to seal.
As pointed out 400 is too coarse. I'd use 1000 & then 1200 with soapy water, Scotchbrite could be used if you have nothing else. Wet & Dry can also be used on the caliper mating faces to flat them off. Tape the wet & dry onto a sheet of glass or surface table & move the mating faces around until they're even again.
I've had lot of success using Loctite 574 between the halves of leaking Shimano calipers. Might be worth a squirt.
Minis are problem problem problem. I found the bleed nipples or banjo bolts get over tightened and when heated up expand and crack the casing. Look around them for cracks.
The original pistons consisted of two parts, the inner is prone to vibration which is why most squeal like stuck pigs, the plastic replacements that they use to this day are far better.
The corrosion youve sanded down might be causing the leak as the 2 faces should meet exactly and and gap is a gap the fluid can get out of. Might be a mad idea to use an epoxy compound to fill it, but maybe a lot of work for little real success.
As above. Get a caliper seal kit and replace all the seals and if not the plastic pistons, replace them too, or anyway as theyre only a fiver each.
Minis are problem problem problem
Mine on the other and have never let me down since I got them in maybe 2001 or 2002. Have had the seals changed once.
Lucky you, but it doesnt change the fact that when you split the caliper, the pistons consist of the outer and inner. You can revolve the inner with your finger and minutely move it side to side. This will vibrate, and vibration causes squealing.
Basically, you said you're doing it for fun, which is good because it's the only sane reason to be working with such old brakes... But, it doesn't sound like it's fun any more?
They're ancient and they weren't worth the hassle of fixing 10 years ago. Flog 'em to a retro maniac.
Still got a set on the front of my SS - original Minis (not monos).
Mine work fine - but if they're that much of an ache to fix, yes, ditch and replace (and sell on).
If anyone ele wants to join in the "fun"... I have a set of well used mono-minis at home that might be useful for spares. They work, but the lever action is notchy, and one pad had a habit of sticking... I can get photos in a day or so if anyones interested?
If anyone ele wants to join in the “fun”…
Well, I might actually still be interested. I re-built the levers for the set in question, and they are now working quite nicely. Would be nice to have some calipers to attach them to.