Bicycle Mechanics - Hydraulic disc brake setup question
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08-21-08, 09:26 PM
I recently acquired a Hayes 22mm caliper to fit the rear of my trek zx7000. The problem is the lever and hose that came with it are wrecked and I need to replace them. As far as I understand, once the hose and lever match each other I could use any brand of caliper as long as I have the correct hose-to-caliper connection. My plan is to use an XT lever I have spare with an XT hose and then connect the Hayes caliper with the hose fitting that came with it on the old hose. Would this work? Also I am aware that Shimano systems use mineral oil where as Hayes use dot 4 brake fluid and I have heard something about incompatibility between hayes brakes and mineral oil, anyone know if this is true?
08-21-08, 10:55 PM
Nope, technically it won't work. The difference in mineral oil and DOT fluid systems is the rubber seals in the caliper and lever. DOT fluid has seal swelling agents in it where mineral oil requires the seals to be the right size to start with so they are a hair tighter fitting and could well be a different rubber. Using DOT fluid in the XT lever may well cause the seals to swell and that'll make the lever stiff and possibly slow or stop it from returning.
Now you may think "GREAT! I'll just use mineral oil then!" Nope, if you do the seals in the caliper will eventually shrink back in the absence of the DOT seal swellling agents and at that point you could easily find mineral oil seeping out of the piston seals and onto the pads and disc.
So you need to use the parts with the oil or fluid they were designed for unless you're willing to risk a leak or a jam. Now with the small sizes we use in our systems it is possible that you CAN get away with a good clean and rebuild and then run either fluid option and not have any trouble. But there is a gamble involved and if it doesn't work then you'll be shopping for a new lever anyway.
You're best off getting a Hayes lever since you know it'll match the requirements for the caliper and that it is DOT fluid compatible. And it doesn't need to be THAT lever. A Mag or HFX will work interchangably since they are both intended to be used with the regular Hayes two piston caliper.
The hose is no problem. Any good LBS that services a lot of off road bikes these days will have bulk hose and the odd olive hose ferrules that Hayes uses in stock.
Also unless the lever is busted you know that there's rebuild kits available?
If you're not worried about hurting the XT lever you can try flushing it first to clean out the mineral oil and then fill it with some DOT fluid. Let it sit and try it daily for around a week to 10 days. By that time it'll be as tight as it's going to be if it is going to tighten up at all. If it's still good and snappy then you win the Brave Brake Lotto and can safely go ahead and fit the parts together. If the lever gets stiff and sticky then you lost and you'll want to strip it and get new seals to prep it for going back to mineral oil. As for trying the caliper on mineral oil I wouldn't bother. A sticky lever is one thing. Oil on your pads and disc is a whole other step in a bad direction. The problem is that it likely won't leak until you're stopping hard. A few of those and then you won't be stopping....
08-22-08, 06:49 AM
Cool thanks for the info!
Yea I'd rather not be taking chances with brakes! I was aware of the rebuild kits for the levers but this one is for the bin, the clamp where it attaches to the bar has been snapped off! So almost any Hayes hydraulic lever can be used? That's the road I'll be taking so!
08-22-08, 07:50 PM
Yep, any of them that were used on dual piston calipers. Even the lever off the Sole looks to be the exact same thing as the HFX9's so I suspect you'd be fine with those as well. But just in case they changed the bore of the pump part try to stick with either the HFX9 or Mag levers just to be certain.
08-25-08, 10:18 AM
Thanks again..! Another quick question, a friend of mine has offered me a hope m4 lever that he had lying around. As far as I can see it should with the hayes caliper, it uses dot brake fluid so the oil is no prob. I am aware however this lever is for a DH caliper so the bore of the pump may be a lot bigger then that originally designed for my caliper. Am I correct in my assumptions? Has anyone here used a hope lever with a hayes caliper before?
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