tiger1964 

Hi! Usually I'm on the Classic and Vintage sub-forum. However, a neighbor who helped me with some house wiring asked be to look over a mountain bike he picked up. Immediately I see I need to address the front brake, and I'd have no problem if the brake said MAFAC or Campagnolo Record on it.

However, it says nothing. And it's a disc brake to boot. I found the name Peak on the levers and on the convention rim caliper on the rear. The first thing I found was the brake is dragging on the rotor a lot. The hub-side pad is dragging, but the fork side pad is far away from the rotor. So, is there a way to center the caliper over the rotor? I see a few spots for Allen keys but, before I indiscriminately start changing things, I would not mind guidance on how to adjust the brake. Lever & cable do not seem to bind, I do not think I need to "go deep" into this brake, just adjust it.

Andrew R Stewart 

Most all disk calipers have slotted mounting holes allowing the caliper to be positioned side to side WRT the disk. Your caliper is a close copy of an Avid BB5 with it's concave/convex mounting washers. and one adjustable pad. The spherical washers allow angular alignment so the pads and rotor are in parallel planes. If the pads contact the rotor flat these washers need to remain as they are. If the pads contact the rotor at an angle (like a toe in/out with rim brakes) then the caliper will want to be angularly repositioned.

I usually will slightly loosen one mounting bolt slightly and the other a lot. The slightly loosened bolt acts as a pivot while maintaining the caliper's angular relationship (to the rotor) but allow the caliper to swing in/out. Then snugging down the fully loos bolt and loosening the previously snug one will let the caliper swing it's other end over and, again, maintain the angle WRT the rotor. With the hub side pad being non moving (but adjustable within the caliper) I aim for it to barely clear the rotor. the moving pad gets located by cable tension.

I strongly suggest that you check the rotor mounting bolts for their tightness, the rotor for any wobbles (which like an untrue rim will hinder best performance) and make surte those axle nuts are kept tight. Disk brakes produce a force on the hub that wants to push the axle out of the drop out, Not a good thing when riding. The photos show that the axle retaining washers with their tabs are missing. Without this tab in hole back up all that keep the front wheel in the fork while braking is the nuts.

There are many on line vids and fuller instructions for the searching. The Park Blue Book is a great first resource for this kind of instructions. Andy

tiger1964 

Thanks. After reading your post a couple of times, I may have some comprehension. In the photos, there are two red parts. One is bolted to the fork, the other has the pads, etc. These two are connected by two Allen-key bolts that are perpendicular to the camera's POV in these photos. Can I presume these are the bolts for the "slotted mounting holes" and "concave/convex washers"? If so, I may be seeing the path forward. If I have it wrong, please let me know.

Roughly how much "free play" in the cable is common on these brakes?

WOW, thanks for the heads-up about the forces on the wheel mounting under braking. Hmm, I wonder if the washers w/tabs are available from local bike shops? I'm out of my comfort zone here, the only bike I have with bolt-on wheels is a track bike, brakes need not apply. I'll check into the Park book, I like their tools if it's the same company; but no idea how often I'll be working on a "modern" bike. The only service guide I have is from 1974, and that's mostly for thread sizes, chairing BCD's, etc.

Andrew R Stewart 

Free play- If you mean how far the lever is pulled before the pads begin to contact the rotor...That's determined by the pad clearance WRT the rotor and the lever/caliper relative leverages. The less lever pull wanted means less pad clearance. At some point the pads rub all the time and most will not want that.

If you mean that the cable is slack and the initial lever pull does not make the pad move then zero free play. Generally you want the pad to move right away, when pulling on the lever. The caliper, and likely the lever, has a barrel adjuster to fine tune the cable tension and the lever pull amount before pad contact. Andy

tiger1964 

Again, thanks.

Well, after 8 or 9 attempts, I think I have the caliper centered over the rotor. Fiddly; I don't ever want to hear someone complaining about adjusting MAFAC brakes ever again!

Alas, this means that now the rotor faintly drags against the hub-side pad for part of the rotation, and the fork-side pad for another part. Yes, that's right, the rotor is not 100% straight. How do you true a rotor? Rubber mallet?

Andrew R Stewart 

I prefer using pry tools and not impact ones. The rotor is thin enough so it will easily bend and impacts are rather challenging to control. The industry offers various "disk truing tools" that are just a strip/bar of, usually, steel with a thin slot cut in it. The slot will slide over the rotor and grip it so the bar/lever can manipulate the rotor back and forth. 6 or 8" adjustable wrenches do much the same. You can place the wrench(s) over the rotor's outer edge or onto one of the "spider arms" extending from the hub. When doing this for the first time go slow and learn how much tool movement equates with how much rotor change. Do clean the wrench jaws as rotors and pads dislike contaminates, like oils. Thus never spray lube your chain if you have a rear disk brake. Andy

WizardOfBoz

There are tools available to bend rotors (see below - no experience with that specific one, it's just a "fer instance"). Although I do agree with Andrew: a "fine adjustment tool" (aka mallet) is not the tool for a rotor.

Andrew R Stewart 

Never saw a disk truing fork with the slot lengths indicated on it. Maybe mine are now obsolete Andy

tiger1964 

Doh! Treat it like a chainring. Got it. Can do the two-wrench thing in my sleep.

grizzly59

It looks similar to a Tektro Aquila

https://www.tektro.com/upload/Produc...15859uWPB9.PDF

https://www.google.com/url?sa=t&rct=...Izdxs0ighIMhoL

tiger1964 

I got it kinda close, it does not drag now. Also watched video on the rear brake, apparently they are called "linear pull" and got that working. It shifts OK but I found 3/4" (NOT A TYPO) side play in the bottom bracket, that comes apart next, presuming it does come apart. Trying to get it roadworthy for zero dollars -- wish me luck!

Andrew R Stewart 

Good job.

With that mush play in the BB a replacement BB is likely the best long term solution. While not hard to replace there's, of course, a few details and tools that you'll need. Andy

Jeffraugh

I am a bike mechanic who has successfully adjusted many mechanical brakes. I have the same issue with adjusting these PEAK brakes. There simply is not enough travel on the piston side to get a good grab on rotor. In order to get any stopping power at all I had to leave some drag on both sides of the rotor. Very poor design and I would recommend avoiding this brake system at all costs.

btw, these brakes came on a bike that was internet purchased for $200 US. Frame is labeled Tanwyn. These brakes are likely cheap knockoffs of a real design.

cobba

tiger1964 

Thanks for that. I "finished" the bike and gave it back to the neighbor a year ago; need to follow up and see if he kept it and rides it, or he sold it at a yard sale, or whatever.

Maybe someday I'll have my own set of discs. Just Wednesday I had to listen to an old friend who has long since "gone carbon" who went on a tirade about how behind the times I am because I do not have a carbon frame, electric derailleurs and hydraulic brakes.

I'm still faster than him so...

dabac

Sounds like a cable pull mismatch to me. What kind of levers were they used with?

Gresp15C

For every dispute in cycling, there's a list of arguments for whatever side you take. So you have to join the "steel is real" movement. At least, until you get a carbon bike.

tiger1964 

Fair enough! That said, a high % of my objections to modern tech are aesthetic; not that I am in the market for more bikes, but some of the early straight-tubes-with-lugs carbon fiber frames have appeal for me.