Spongy Brakes Help !

[whutn18885]

I have a 92 Raleigh Dyna-Tech. I have been upgrading / Changing parts over the last month or two. I have scrapped the old cantilever brakes (they were naff even with koolstop pads) and put on some Deore V brakes with matching Deore V Brake levers.

The front brake is running awesome but the rear brake is spongy. I have tried new cables / new housing / different pads (Avid RW2 / Shimano and Koolstop Salmon) but nothing seems to work.

The brake engages fine and the pad position is spot on but the lever still feels spongy - The brake arms take longer to return to position after releasing the lever (twice as long as front brake). I am a bit stumped ?

For the record the brakes are brand new and the bosses were cleaned and greases prior to install and the issue remains regardless of which hole the rear brakes go into.

Would running full housing to the rear brake provide a more positive 'feel' as at the moment there are 3 cable stops along the route of the brake and despite having the plastic ferrals in place where needed there does seem to be some unwanted movement.

Advise please.

Thanks

 

[frank.youngman]

Re:

Have you tried increasing the spring pressure on both arms by screwing in the adjusting screws?

 

[whutn18885]

Yep tried that as much as I could go

 

[whutn18885]

The only thing I can think of is that with all the brakes in the cable for the various cable stops maybe there is some movement. Is there any real disadvantage to running a full cable to the rear brake other than having to zip tie to the frame and the marginal weight increase ?

 

[whutn18885]

*Breaks (typo)

 

[hamster]

Re:

Sounds like you have some friction somewhere in the cabling. Check for kinks, but did you check that all the cable ends are smooth whne you cut them? I usually tip the ends with a grinding wheel to remove any bent outer spiral. Also, check that the liner is not crushed.

Running the cable with breaks on the frame usually gives a firmer feeling as a frame will not compress at all, unlike a cable outer.

 

[whutn18885]

Ah ok thanks I will have a closer look, I don't have a grinder but I have a file so I can probably file down the ends to see if that improves things.

Cheers

 

[REKIBorter]

Re:

The brake arms need to be parallel when the pads touch the rims. Swap the spacers round until they are. If the brake arms are either in a \/ shape or /\ shape when the pads touch the rims you are not getting maximum braking efficiency.

Do brake levers have an adjustable pivot position?

 

[xerxes]

Re:

The rear brake is always slightly more spongy than the front. The cable is longer, so there's a bit more give over it's length than the front. Also, have a look at the rear stays when you squeeze the brake, if the stays are quite slender you may see that they flex outwards slightly, whereas the front fork is generally a lot beefier. If the rear stays flex quite considerably, you could try a brake booster.

 

[unit3]

Re:

Could the spongy feel be down to the rear stays flexing? Have noticed this on a few occasions.

Also check the curved cable guide into the v's, a slight kink in it would pinch the cable.