Rev3 Rear Brake

[neonsurge]

I know rear brake bleeding has been done to death recently, but I'm not sure that this is a bleeding problem: Since replacing the pads on my Rev3, I've had a very long rear brake. It still works, but needs to be depressed almost the entire available travel before it bites. My first reaction was that I'd managed to somehow get some air into the system, probably while pushing the pistons back into the calipers so I've bled it for (literally) hours and I'm pretty confident that there's no air in there.

Last week I resolved to fix the problem once and for all and set about loosening the piston rod (connecting the pedal to the master cylinder) when I noticed that it was almost all the way out and at the absolute limit of adjustment. Under normal circumstances, I'd expect this to lock the wheel but it was in this state that I was having the opposite problem - obviously something is not right. I also noticed that the rod wouldn't adjust in the opposite direction and it appears that the threads are stripped either on the rod itself or in the pedal.

Not a problem, I can clean up and/or carefully retap/thread the relevant parts, but during my investigations I noticed that there's a component on the Beta parts diagram (no. 150 on the attached image, labelled "pump pin w/spring") that I think I'm missing. It's not obvious where it should sit - does anyone know where this should go? Any other recommendations on how I should go about resolving my problem?

Edited February 21, 2005 by neonsurge

[philswiv]

I've bled and re-bled the rear brake of my '97 Techno. I've posted messages to this effect with the usual "have you stripped it/cleaned it?" well intentioned but obvious answers. I now have the whole system rigged up on my bench.

I tried using a different calliper - still no change. I tried a different caliper and a differnt brake hose - still no change. I tried a new master cylinder seal set (

[malky]

i think you will find that that spring is the pin for holding the rear brake pedal to the rod

[malky]

oh you could try to reverse bleed the system using a pump oil can filled with b fluid attached to the nipple by rubber hose and pump pedal at same time .....malky

[scorpaf]

Pressure bleeders are available from car shops for not a lot of money (

[landrover]

take the caliper back off ,then pump the brake a little at a time ,keep trying the brake on the disc till the pistons come back out enough to brake with out binding they will also come out in time . if you adjust them up to much they will start to lock on themselves with heat from the disc it's trial and error until you get them to your liking. a lot of the time they are pushed back more than they need be when fitting new pads, i hope this helps

[neonsurge]

i think you  will find that that spring is the pin for holding the rear brake pedal to the rod

Hmmm. Makes sense. I wonder why they call it a "spring" though... maybe because of that metal clip (the exact purpose of which I've never worked out)?

landrover, your suggestion seems a good place to start - I did push the pistons all the way into the calipers when I changed the pads, so that might be it - thanks!

If all else fails, I'll try the "reverse bleed" method.

[philswiv]

If all else fails - swear very loudly, throw down whatever spanner is in your hand and march to pub. Chew somebodys ear off about how you suffer for your art. Totter back home with a self satisfied "four pint glow" and go to bed. Repeat this process over several nights untill you get the correct pressure at the brake lever ( I still havn't cured my rear brake problem, much to the benefit of the local pub landlord).

[ronm]

Neon,

If your brake is firm, but just takes too much pedal travel the problem is that the caliper pistons are retracting when the pedal is returning. This is not an uncommon problem on both front and rear brakes. Think about it, when you push the pedal way down and a large volume of fluid moves the pistons out. When you release the pedal, the pressure is released, but one of two things is going to happen.

1- the pistons have enough friction in the seal and caliper to resist the negative pressure caused by the return spring acting on the master cylinder piston. ( don't forget, these things pump both ways). They stay in place and as the mastercylinder retracts, fluid bypasses the seal (which mainly seals in one direction, but can also seal a certain amount in the "wrong" direction). Then when you take a second pump on the pedal, the previously displaced volume is already filled, and only a normal stroke is required. This is how things are supposed to work.

2- The negative pressure caused the pistons to retract and you basically keep pumping the same volume of fluid back and forth each time you depress the brake pedal. I would say from your description that your bike is doing number 2

The fix is to take the caliper off and the pads out and pump the pedal until you get the pistons sticking well out of the caliper. Then push them in enough to put the pads in. Then spread the pads just enough to get the pistons to slide onto the disc.

Tighten it all up and the brake should be back to normal.

I hope this helps.