zjrog

Bike is a Performance Access XCL 9r, Sora 3500 9 speed brifters on Woodchipper bars. Pulling Shimano SLX RD, SRAM X5 FD. Brakes are Avid BB5 mechanical disc brakes 180mm front, 160 rear.

Last year the rear brake just didn't seem to grab tight anymore. Before that, I could lock it up on pavement and slide it. I put new pads in, cleaned the rotor of dirt and grease. I can get it to lock up, but it drags. If I loosen it up so it doesn't drag, it barely slows me down. Conversely, the front nearly throws me over the bars, I can lock it in dirt...

My frustration is at the point of feeling unsafe on gravel descents. I'm considering swapping in a 180mm rotor and proper adapter, and getting an Avid BB7 road specific caliper. Any ideas before dropping the bucks for new parts?

smashndash

By “drag” do you mean the pads rub the rotor? If so, you could have a cable issue. Take the cable off and see if the brake arm still snaps back after engagement.

If you mean the “dead” pad, then I’m not sure what to say, really. Is the rubbing intermittent or continuous? If intermittent, try truing your rotor to get the dead pad closer?

Are you using compressionless brake cables? That would be a wise investment for mechanical discs. Also, if you do feel the need to go with a new brake (you shouldn’t, all of a sudden), a lot of people have praised the TRP Spyre as a good modern brake.

Fundamentally, though, if a brake is good enough for your front, it’s good enough for your rear.

zjrog

Yes, dragging the rotor. I have tried a number of different adjustments, pad seatings. The arm snaps back readily with the cable off. And the rotor seems quite true.

As I didn't assemble this bike in this configuration, I'm not sure if the brake cables are compression less housings are not. I hadn't even considered that.

I agree, good enough for the front should be good enough for the rear.

I will swap brake cables and see if this helps.

Thank you.

cobba

How true is the rotor?

Wilfred Laurier

Are these road-compatible BB5s? If they are the MTB 'long pull' version they will be very difficult to get to work acceptably with 'short pull' brake levers. A mm lost in housing compression or to pad wear will throw everything off.

We discovered the same thing in the mid '90s when V brakes first came on the scene - if the stars align correctly you can get a scary powerful brake, but the odds were just as good that they would simultaneously rub and not provide braking power before the levers are squeezed to the bars.

curbtender

smashndash

I don’t mean that the reason for the issue is that you don’t have compressionless housing. I just mentioned that because, if you are getting a new cable housing, it will help quite a bit.

I suspect the real issue is just grit and gunk in the rear cable. The rear cable usually has an exposed part running across the frame, and thus has greater opportunity for contamination. It is also longer, so there’s more room for grit to exist.

dsbrantjr

If it has worked in the past it should be able to be made to work again. I am betting that new cables (both inner and housing) will be a big improvement. Did you bed-in the new pads per the manufacturer's recommendations?

zjrog

True enough they don't wobble and stop the wheel...

They may be old enough, they were only MTB, but I don't know. This bike was a gift 5 years ago...

I've done that. Most of it at least.

As the bike is a drop bar bike, it was built with cyclocross inline levers on the tops as well. From that point to the rear brake it is all in brake housing. No exposed inner cable till the bottom.

As I don't know what housing was used, and I don't know the history of the bike before me, I see some prudence in changing to a better compressionless set up. I have that on 2 of my roadbikes, and feel like both stop very well.

As it has worked fine in the past, it should now. As for bedding the pads, I don't think they did bed well as I couldn't stop as strong as I wanted. Which I originally thought was worn pads. I may order new pads again just to rule them out.

I have toyed with a front to rear swap to see if it is a caliper issue. But I will what new cables and pads offer first.

zjrog

Figure, Might as well show the bike...

cobba

You're using a mountain brake with a road lever.

Mountain BB5: https://www.sram.com/en/sram/models/db-blbg-5m-a1

Road BB5: https://www.sram.com/en/sram/models/db-blbg-5r-a1

Rick

If cobba is correct I would go with the BB7 road verson for replacement and put the Yokozuna Reaction Brake Cable System on it. All other compressionless housing is weak and will compress. Yokozuna is the only trually compressionless housing sold.

cobba

I'd get a pair and replace the front caliper too, even if the front brake seems to be working ok at the moment.

https://www.ebay.com/itm/2QTY-SRAM-B...W/333221201946

With the current setup, the levers are only pulling half as much cable as what's needed, as the pads wear down on the mountain calipers, you won't have as much pad adjustment as you would with a road caliper.

Kapusta

If it is the case that you have the MTB version of the BB5 on there, that would go a long way to explain why the brakes were super powerful when they work, but are extremely hard to set up not to drag.

The road levers pull less cable, so the caliper can’t move as far as it needs to.

replacing with road version should take care of that.

Also, as others have suggested, compression-less brake housing makes a big difference, especially on the rear.

Kapusta

How can you tell from his picture they are the MTB and not Road version?

cobba

Road BB5's have always been silver.

If black is the original color and it hasn't been repainted, it's a MTB BB5.

zjrog

Not knowing anything of disc brakes, how long has the BB 5 been offered in road and MTB? I know this bike was built with what my friend had on hand at the time...

Kapusta

KHow do you know that?

If you look under “specs” for the BB5 road it lists back as a color option (Gloss Black, Platinum, Silver). And here is one for sale:

https://www.rei.com/product/847061/a...sc-brake-160mm

In any event I assume there is a model number somewhere in the caliper.

cobba

Never seen a black BB5 Road before.

Just had a look at some old archived SRAM pages from a couple of years ago on the web archive, they only list Platinum as the color for Road BB5's, maybe those extra colors on the current page are something new.

hokiefyd 

Nice bike, and nice scenery!

Your rear caliper looks to be adjusted at near its full cable travel. That's generally going to result in a pretty heavy brake, and doesn't really have any advantages (that I'm aware of). If you replace the cable and housing, I would adjust it so your caliper is mounted so the outboard pad (the one closest to the outside of the bike) is JUST BARELY clearing the brake rotor (no rub), and then thread the backer for the inboard pad (the one closest to the hub of the bike) in so that it, too, is JUST BARELY clearing the brake rotor (no rub). The activation arm should be all the way relaxed in this position, and the cable completely slack. At that point, you have the least amount of preload on the internal spring in the caliper, and your brake lever pull will be the lightest.

That is, of course, assuming that you have compatible pull ratios on the caliper and lever.

cobba

Road versions have been around for over 10 years, the MTB versions were always black, the Road versions used to be always silver/platinum.

If you can, ask your friend if the brakes were the original ones that came on the bike when it had flat handlebars.

Kapusta

Is there are model number anywhere on it?

I’m with cobba in suspecting that you have a MTB version, but extra verification would help.

BB7s are a bit easier to get set up right... but even those take some practice. I’ve used BB7s for almost 18 years, and it took a while to get the art and science down for good setup.

GamblerGORD53

Yes throw that POS crap in the GARBAGE, I had them for too long also. Road<>MTB ?? WTF is the diff ??
Get a TRP Spyre caliper with both side moving pads. Keep using the softer resin pads that grip better and don't squeal. They don't seem to care what the gap is either, I like more so they can't rub.
I've had them on my tour bike Rohloff 203 disc, they can lock instantly. Only will need adjustment after 1 or 2 thousand miles. I have long pull SA levers on comfort bars. The LBS pro said I had the wrong ones, so obviously it doesn't fricking matter.
Now I don't have to worry about getting off, just pull the lever and I get thrown off. LOL
I have a DIY welded on plate with a homemade Alu bracket for extra adjustment slots.

The BB7 is way clunkier than the Spyre also, I made the mistake of trying it first.
And these are the same levers I use with SA drum brakes.

hokiefyd 

The expected cable pull is the difference. Road versions are designed to be used with short-pull levers (such as most drop bar levers) and MTB versions are designed to be used with long-pull levers (such as most MTB brake levers, often used with linear pull brakes).

TRP has both road and MTB versions of their brakes, too. Spyre is the road, or short-pull, version and Spyke is the MTB, or long-pull, version.

AndreyT

Huh? But TRP Spyre vs. TRP Spyke is exactly the same division between Road and MTB.

Actually, get five or six TRP Spyre calipers (at least!) and try them all, one after another until you find one that works. QA and manufacturing tolerances on TRP Spyre are so crappy that buying just one caliper for each wheel will almost surely turn into an extremely frustrating experience, waste of time and waste of money.

BB5 and BB7 are much better made and offer exactly the same braking performance as TRP Spyre. No difference whatsoever.