Rear Brake not very effective

[Simeon 30]

Afternoon all. So after doing my first successful chain and sprockets replacement I took it for a spin and noticed the rear brake was nowhere near as effective as it was pre chain change. I virtually have to bottom out the pedal travel to achieve the same level of braking.

 I don't know whether this was necessary but I removed the rear caliper from it's mounting by undoing the two bolts 12 and 14mm. The fluid connection remained intact. When fitting it back the 14mm bolt (front) was incredibly tight to do up. Definitely not cross threaded. Is there meant to be some endfloat between the bolt head and the caliper?

[Steve T 1,342]

The 14mm is one of the caliper sliders, located onto the alloy caliper mount. You needn't have removed it, just the 12mm that forms part of the other slider, then the caliper will just rotate over the other slider and lift away from the wheel. Did a C&S change yesterday and removed the rear caliper as described.

 

Did the excess movement happen on every brake press? Could be that the pads just needed to be re-seated onto the disc.

 

Just my tuppence worth.

 

Steve T

 

 

PS - mines a manual gearbox version, so no parking brake

Edited April 19, 2023 by Steve T

[Simeon 30]

Thanks for the reply Steve. I've taken it out three times now and it has'nt improved. I'm still confused about the 14mm bolt, maybe it does'nt need to be done up fully trying to bend my spanner as there would be no lateral play to allow the caliper to fully grab the disc and it would not pivot the caliper once the 12mm bolt is removed.

[Andy m 23,585]

Nothing needs to be done up so tight it'll bend spanners. There is nothing that needs setting to leave heads not up against what they are fastening. All bolts should run to the head finger tight then need three finger pressure on normal length hand tools. 

 

I would remove the calliper again and run the bolt in without it fitted to check the thread. 

 

Was the calliper left dangling upside down? Put something in the removed calliper like a bit of nice solid cardboard or better still sheet metal to simulate a disk and push the pedal. If it stops in a normal place you have mechanical issues with the slider. If It's soft after three full pumps you have air in there. Make sure whatever you use to simulate the disc is think enough to let you get in to push the pads back for reassembly.

 

Andy

[Simeon 30]

Yeah, I'll take it off again and report back

[Skidt 1,315]

I’ve recently done the chain & sprockets on mine and cleaned the brake callipers whilst I was at it.
 

I wasn’t particularly careful whilst cleaning the pistons, with regard to keeping the calliper upright. As a consequence, my rear brake pedal also felt soft / spongy / less effective initially, although my pedal travel wasn’t significantly different. 

Fortunately after a few decent rides, it has returned to more normal functionality. It could probably in all honesty, benefit from a bleed, as I think I may still have a little bit of air in the system. I’ll get around to it soon no doubt, as I need to MOT it before the France trip.

Hope you manage to get it sorted. 

[Andy m 23,585]

There is the lazy bleeders method; use a bungee or brick on string to weight the control at the extremity of travel. Wait 24 hours, pump the control,repeat.

 

With the brake applied you hope the air rises naturally to the top. On a non-ABS system chances of it working were 50/50. It's less effective with ABS, but if trying it cycle the ignition a few times at the pumping stage.

 

Andy

 

 

[Simeon 30]

OK chaps i've got to the bottom of it. Turns out I had cross threaded the slider bolt. It seems very easy to do when you have limited access due to the exhaust can being in the way also a steel bolt going into an alloy thread.

Anyway so I took the exhaust can off, removed the caliper and like you said tried the slider straight into the caliper. My heart sank when it went really difficult to turn the spanner with the slider bolt needing to travel down another 5mm at least. Removed it cleaned everything and ran a tap through the caliper side. Lubricated everything with silicone grease and put it all back together doing the slider before the rear bolt. Three pumps of the brake and it was perfect. So what did I learn from this. Because the slider was cross threaded it felt like it was done up fully when it was'nt. When the brake was applied it went asymetric and did'nt push on the disc properly.

1. Don't remove the slider bolt unless you have to

2. Remove the exhaust can if you have to remove the slider bolt

3. Don't remove the slider bolt

4. Last of all don't remove the slider bolt