Pulsating front brake lever..

Message

fatboy · #1 Post by **fatboy** » Fri Sep 05, 2014 6:34 pm

Ok, first port of call will be the bobbins and some brake cleaner.
I dont expect the bobbins to be that slack but how freely should they move?
Should I expect to be able to move them with bit of tight fitting wooden dowel ect ?
Any advice appreciated !

Falco Frank · #2 Post by **Falco Frank** » Fri Sep 05, 2014 6:47 pm

Good question - I used a long Allen bolt with large washers and lock nuts to help spin the bobbin with an Allen key.

I used to get each bobbin to a point where I could spin it easily with a single finger pressure on the end of the key.

One other item to check that I was astounded made such a difference: Front Axle alignment / installation.

Good luck.

Twintin · #3 Post by **Twintin** » Sat Sep 06, 2014 1:28 am

Mine pulses but only just as it's about to stop, last 10m or so? My bobbins freely rotate and nothing is seized, very odd !!!

Falcorob · #4 Post by **Falcorob** » Sat Sep 06, 2014 8:40 am

Could be a very slightly warped disc.

fatboy · #5 Post by **fatboy** » Sat Sep 06, 2014 7:25 pm

I only noticed it yesterday and it was as I was coming to a stop, when I got home I could not turn any bobbins by hand.
Noticed it again today, same conditions as above, didnt get time to look at it today as I had a very disrupted night last night, courtesy of a bunch of fuck wit 4x4 drivers, spent a fair while in police station today, wasting valuable fettle time

spiderwheels · #6 Post by **spiderwheels** » Tue Sep 09, 2014 10:11 pm

You may have the dreaded Disc Thickness Variation.. how old are the discs?

Twintin · #7 Post by **Twintin** » Tue Sep 09, 2014 10:16 pm

Mine are only 12k miles on a 2001 bike

Falconihlist · #8 Post by **Falconihlist** » Wed Sep 10, 2014 4:22 pm

Had a slightly different version of pulsating, when the front wheel locked up. Turned out the pivot pin had disengaged from the plunger!! You could literally have blown on the brake lever and it would have locked up.

fatboy · #9 Post by **fatboy** » Wed Sep 10, 2014 6:41 pm

I can only guess my discs are originals on a 2001, around 29k miles, more noticable at low speed so variable disc thickness may well be the issue, slowing to a standstill you get the grab/roll/grab sensation, does get a bit twitchy if you have to grab a big handfull of front anchor at speed

spiderwheels · #10 Post by **spiderwheels** » Wed Sep 10, 2014 11:04 pm

fatboy wrote:I can only guess my discs are originals on a 2001, around 29k miles, more noticable at low speed so variable disc thickness may well be the issue, slowing to a standstill you get the grab/roll/grab sensation, does get a bit twitchy if you have to grab a big handfull of front anchor at speed

On the road it was grab/roll/grab at very slow speed I noticed first as I tend not to use the brakes hard.

Different story at the track where every corner is an emergency stop.. If you brake hard in a straight line from 60 you should feel the whole front end vibrate like you're running over a cattle grid as the brakes grab and release and the suspension loads and unloads rapidly.

I went round each disc with a cheap micrometer and measured the thickness at 6 equidistant points and found 0.07mm difference between the thickest and thinnest points. I checked the new rotors I bought in the same way and I think there was a 0.01mm variation - needless to say, problem solved.

D-Rider · #11 Post by **D-Rider** » Thu Sep 11, 2014 8:17 am

probably pad material deposition.