Disc brakes slipping/pulsating

[LOCO4360]

Hi fellow hubbers, 

 

Ok so I recently changed my front rotor to 180mm from 160mm standard rotor using a Shimamo post mount adaptor 160/180 and 180mm rotor by Definitive Bikes (new parts from LBS). Bearing in mind that the 160mm setup worked 110% fine, no air in the system, pads are still good, etc. using BR-M615 Deore brakeset on Titan 27.5 hardtail with Mavic front wheel 15mm bolt thru. 

 

Centered the caliper and all seemed good until bedding in the brakes. As you pull the brake lever the brakes will either be solid and work correctly or, depending on where the the pads bite as the rotor rotates, the there will be what I can only called a feeling of the rotor slipping, biting, slipping, biting until it locks up or one stops. (at a higher speed this feels like pulsing or vibration) 

 

This is what I've checked so far...

 

Pad spacing/advancement

Realigned caliper 

Checked rotor bolts

Cleaned pads and rotor (rotor cleaned with brake cleaner and pads sanded/cleaned using +- 1000grit paper)

Swapped rear / front pads (problem persists in front - rear stays smooth and solid)

Re-checked pad spacing in relation to rotor 

 

160mm rotor had around half mm of side movement as wheel turned but never slipped, 180mm rotor seems to have same side movement as the wheel turns but just does not bite at certain points in the rotation. 

 

Definitive Bikes brand is a lower cost alternative to the higher end products and I have subsequent bought a SM-RT56 Deore rotor which I don't want to install before getting some thoughts/advice.  

 

 

 

 

[Chavo]

Not sure if this would be a possible cause, but some rotors are specific for resin pads and should not be used with sintered pads. This is normally stated on the rotor and as I say, I'm unsure if this would be the cause of your problem. Just a thought

[Cat2forLife]

Sounds like a warped rotor.

[Skinnyone]

What the Chav said...

 

Also some rotor designs pulse more than others, it is literally where the cut outs are in the rotor that cause the pulsing. I used to get it a lot on the older Avid Juicy brakes - changed the rotors to Shimano and hey presto - pulsing stopped.

[Letum911]

All of the aforementioned are possibilities. It can also be the bedding in process. 

 

My plan of action would be:

1) Check pad/disc compatibility;

2) Check rotor being straight (enough);

3) Pick a long downhill and run the pads/disc in a bit (I found that wetting the system with water speeds it up but I'm not sure how healthy this is)

[jandemoerin]

Switch off the ABS...

[LOCO4360]

Not sure if this would be a possible cause, but some rotors are specific for resin pads and should not be used with sintered pads. This is normally stated on the rotor and as I say, I'm unsure if this would be the cause of your problem. Just a thought

Thanks a million, the packaging doesn't say whether it's for resin or sintered - LBS said can be used for both (I am doubtful on their advice as he told me there is air in my hydraulic line) 

[LOCO4360]

What the Chav said...

 

Also some rotor designs pulse more than others, it is literally where the cut outs are in the rotor that cause the pulsing. I used to get it a lot on the older Avid Juicy brakes - changed the rotors to Shimano and hey presto - pulsing stopped.

Thanks Skinny - I now realize that now all rotors and pads are created equal (guess that's why quality brands cost more). I had some Avid Elixirs that did this before with 160mm Shimano rotor but once I changed to Deore brakes it was perfect... this supports my rotor theory

[LOCO4360]

All of the aforementioned are possibilities. It can also be the bedding in process. 

 

My plan of action would be:

1) Check pad/disc compatibility;

2) Check rotor being straight (enough);

3) Pick a long downhill and run the pads/disc in a bit (I found that wetting the system with water speeds it up but I'm not sure how healthy this is)

I'm thinking it's option one here and possibly option 2 also. Have tried the bedding process to no avail. I'll pop the Shimano rotor on tonight and see.. thanks a ton

[bikebloke]

this - All of the aforementioned are possibilities. It can also be the bedding in process. 
 
My plan of action would be:
1) Check pad/disc compatibility;
2) Check rotor being straight (enough);
3) Pick a long downhill and run the pads/disc in a bit (I found that wetting the system with water speeds it up but I'm not sure how healthy this is)
 

[V12man]

Sand and clean the pads AND disc - wasn't clear if you had done both.

[LOCO4360]

Sand and clean the pads AND disc - wasn't clear if you had done both.

I have sanded down both and cleaned the rotor with disc cleaner. No change at all

[Duane_Bosch]

I had a set of hope brakes & rotors that used to do that. I just rode them like that for years.

Edited March 15, 2018 by Duane_Bosch

[V12man]

I have sanded down both and cleaned the rotor with disc cleaner. No change at all

I would probably try a more aggressive sandpaper on the disk than 1000 - 300 or 400 at most - I suspect you still have residue on the disc somehow.

 

Maybe try a different rotor to see if that solves the problem

[FirstV8]

You went bigger on the rotors from 160 to 180  will the caliper and pad size not be compromised by being too small to accommodate a 180mm rotor ,

[LOCO4360]

I would probably try a more aggressive sandpaper on the disk than 1000 - 300 or 400 at most - I suspect you still have residue on the disc somehow.

 

Maybe try a different rotor to see if that solves the problem

Thanks V12man - I have a new Shimano Deore rotor and I can immediately see the difference in quality I will try and sand the cheaper one down with 300-400 paper and test the new rotor