Replacing 50mm brake blocks with 70mm?

thelarkbox

Esteemed Pedelecer
Aug 23, 2023
857
259
oxon
I did what the title says.. and the brakes continue to rub a bit worse when pushing the bike backwards. its been well over a week now and 'usually' on changing brake blocks i get a wee rub for a day or two perhaps. but this is a continual rub and the brakes are not as tight as i would like either??

are my brake arms too low speck/loose for the extra length of blocks should i replace and if so what with? disks and replacement forks are a nogo due to the fork 'sweep' so its a brake arm replacement i Think i need or do I ??

Yes i am ignorant of most things from the last 30+yrs of bike development it was all 10 speed and drillium when i was on the bike'ball'..

fwiw the method of setting the blocks I used was to apply brakes with the blocks loose and tighten them under compression before tuning the cable length/tautness..
 

saneagle

Esteemed Pedelecer
Oct 10, 2010
5,172
2,502
Telford
I did what the title says.. and the brakes continue to rub a bit worse when pushing the bike backwards. its been well over a week now and 'usually' on changing brake blocks i get a wee rub for a day or two perhaps. but this is a continual rub and the brakes are not as tight as i would like either??

are my brake arms too low speck/loose for the extra length of blocks should i replace and if so what with? disks and replacement forks are a nogo due to the fork 'sweep' so its a brake arm replacement i Think i need or do I ??

Yes i am ignorant of most things from the last 30+yrs of bike development it was all 10 speed and drillium when i was on the bike'ball'..

fwiw the method of setting the blocks I used was to apply brakes with the blocks loose and tighten them under compression before tuning the cable length/tautness..
They're either not set properly or your wheel isn't running true. Do they rub continuously or just at one point in the rotation.

One thing you do need to get right is the tension in the arms. It must be equal. There are adjusting screws in the side of the arm at the bottom where the spring is. If you screw in, the tension increases and makes the other side move more, and the opposite if you screw out. Generally, they work better with more tension, so always screw in to adjust if you can. Watch the two arms. They should move the same as each other when you operate the brake lever. I'm guessing that this is the adjustment that needs correcting on yours.

Also, very important is the spacing that often needs to be changed when you fit new pads. When you operate the lever, the arms should be vertical or just past when they touch the rim. You get a couple of spacers with the blocks on the screw shaft that need to be moved around to get the right result. I always add washers to get it exact if necessary. It's not unusual to have different spacing on each side, though that probably means that the rim isn't central and can be better solved by spoke adjustment, though that's more work.

To summarise, look at the arms when you ally the brake. The action on each side should be more or less symmetrical. They both should move together and end up at the same angle, then return to their original positions together. I'm going to bet that one side of yours is moving more than the other.
 
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thelarkbox

Esteemed Pedelecer
Aug 23, 2023
857
259
oxon
Thanks, The wheel is pretty true, no wobble when rotating, I think the blocks are orientated on the rim ok, and am pretty sure the wheel sits equidistant between the blocks,

I used the brakes under tension to set the position of the blocks on the rim.

Though will check and report back.. with pictures to confirm

I will check out a few utubes on the subject of setting brake blocks too
 

thelarkbox

Esteemed Pedelecer
Aug 23, 2023
857
259
oxon
On checking the brakes again there was some extra gap one side which i adjusted using the small grub screws i had overlooked before, and the block on the close side needed some slight adjustment too as it was toe out? (the back end was too close in.. )

And i am now ridding with no front brake rub Phew!! and even better no squeal on pushing backwards ;)
Thanks.