Questions You Should Know about Brake Cup Seals

mills94 Guest  
Posts: n/a Brake seals-do they need soaking beforehand? Hi all,

Just a quick question as I'm giving the calipers an overhaul tomorrow with a friend and I've been told I should soak the new caliper seals in brake fluid to make them seal properly from the off. Just want to know is this correct or will they go in ok straight away.

secondly. after 11 years on the original hoses and what I presume on the original pads. will the braided HEL lines and new HH EBC pads make a significant difference as my front brakes have always been spongey since I had it a year ago. Member Mega Poster  
Join Date: Jul Location: here as devil's advocate Posts: 11,569 Re: Brake seals-do they need soaking beforehand? no DONT USE BRAKE FLUID rub them with red rubber grease. brake fluid crystallises behind the seals and causes the recesses in the calliper to furr up which is the main cause of the brakes seizing in the first place.

pads are personal choice and depends on your riding style. hoses are a good idea. Member  
Join Date: Jan Location: Lyne, Surrey Posts: 570 Re: Brake seals-do they need soaking beforehand? Just put the same lines and pads on at the weekend, didn't notice much of an improvement in braking, but got a lot more feel from the lever as well as a shorter travel distance. __________________
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Blue K9 Pointy #2 - Nearly at 120,000 miles! mills94 Guest  
Posts: n/a Re: Brake seals-do they need soaking beforehand? Thanks for all the input everybody, they are now fitted and I have to admit I'm pretty pleased that I've managed to do them myself! I took the word of Bibio and used the red rubber grease that came in the kit. I'm going for a spin shortly to bed the pads in and make sure they are ok but initially the lever feel does feel better and has less travel so we'll see how it goes. still have the rear one to do but am going to wait for some help with that one. wideguy Guest  
Posts: n/a Re: Brake seals-do they need soaking beforehand? I love the EBC HH pads. Once you get them bedded, they will stop you very quickly, but they are also very linear. If you don't use them hard for a while, they may start to feel wooden. Don't worry, just use them hard and they will come right back! mills94 Guest  
Posts: n/a Re: Brake seals-do they need soaking beforehand? thats good, i fitted them a few days ago and took them for a short 15mile ride, i know its going to take a bit longer to bed in but they feel sharp enough, I cable tied the lever overnight and am hoping the lever will keep its sharpness as it went to about half pull which is what it was on old lines. fingers crossed it will be better next time i take it out! Member Mega Poster  
Join Date: Jul Location: here as devil's advocate Posts: 11,569 Re: Brake seals-do they need soaking beforehand? cable tying the leaver does nowt but gas up the bubbles. if you suspect air in the system then bleed it out.

let me explain a bit more. the braking system is hydraulic and works by forcing pressure via the plunger in the master cylinder this make the pressure one way with no way for the fluid to escape. so by tying the leaver back to expel bubbles where are the bubbles going to go?

answer, nowhere they will still stay in the system.

wait till the pads have bedded in completely (about 200 miles) then and only then see how the brakes are. if sponginess is still felt at the leaver (can pull leaver to bar or almost with moderate squeezing) then do another bleed otherwise leave it alone.

you are never going to get on/off switch type brakes with the SV callipers/MC.

OK....now it is time to learn about brakes. My front brake is now doing the deal where it works fine but with steady pressure on the lever, it will pull all the way into the grip. No fluid leaking out of the system. Endless hours bleeding and re-bleeding until I think I have all the air out. I have read the other posts about this and one answer was that it MIGHT be the primary cup in the master cylinder. My question is, what eles should I check before tearing into my master cylinder? If the answere is nothing else to check then in I go. Can't wait! Commando 75,

If I read u right, the lever keeps pulling in toward the grip? That is a damaged cup seal, leaking internally. So it will not show up as a loss of fluid. If you release and re-apply you will get another pul, that will slowly subside.
When you pull the MC apaetlook for a small nick in the cup, maybe in the shape of the small breather hole back into the reservoir. This indicates the piston cups are not correctly orientate to the breather hole porting. I know because I made my own smaller diameter piston, and it worked fine until I had your problem. Also from my experience in making my own pistons, if the relationship with the piston to MC is not correct, I.E. when you pull the lever it does not fully stroke the cyclinder bore, or short strokes, it wil make bleeding a pain and you will end up with a spongy lever. I added a button to my piston, between the piston & lever and it bleed up like magic.

Good luck

Richard Once again thanks so very much for all the info. I took the MC apart today just to get it over with. As usual...nothing scary in there. Richard thanks for the ID of the cup seal as the problem. It looked OK to me but I will tear it apart tomorow and really check it over. Also Richard what do you mean 'added a button'? A spacer of some kind?

I can see where the brake hoses could cause the brake to feel odd but I am pretty sure the symptom of the lever pulling all the way in is a master cylimder issue. It feels exactly like under the constant pressure fluid is escaping to the other side of a seal. Commando, I am runnign a 1/2" bore already, are u running std 5/8"?
I made up a new piston to some dimendions that were posted by a local Norotn Commando Owners club. And I made the piston from alloy with a bronze end button, for the lever to strike on. With the NO dimensions in reference to lenght and where the seals are placed, I tried bleeding up, but could not get a full firm bleed. So I popped the piston out and made a 3mm longer bronze button, these are pressed into the end of the alloy piston assy, interfernece fit. And lo and behold after pushing the piston back in the damn thing had excellent feel withot even re-bleeding.
So if you have an aftermarket piston set up, it could have the same issues my piston had. But if the seal has a mark in it like a little round hole, that indicates it is too far out of the cylinder when pressure is building, and that causes the seal edge to get extruded out through the reservoir hole,

Hope this helps,

Richard