[bandit]

im still having caliper issues.

someone,2 weeks ago posted......i can push pistons in with my hands.

might have been Randall??..dont know.



does anyone else do this?



i lube and push in with a g-cramp,and im still having leaks.

how on earth can a hand/push fit be airtight?

 

[Blue Fox]

I cannot tell you a lie, it was I that said that. I have probably done a half dozen or so calipers, some single, some double piston, and have yet to require a clamp to push the pistons in during reassembly.



I just lube the seal and the pistons with brake fluid, try to get a perfect alignment, and they just go right in with thumb pressure. I contend that using a clamp and forcing a misaligned piston by the seal with a clamp can distort the seal. If you examine a piston end carefully, you will find a chamfer that aids in the starting into the seal.



Side note: I can bench press 164 lbs with my thumbs now that I have worked on so many calipers.

 

[Eurovee]

There is a difference;



It should be perfectly possible to push the pistons by hand pressure alone into the caliper body when assembling them (and is an indicator that all is good) , and if force/a g-clamp is needed then there is still something wrong...

However, unless you are Popeye (or Blue Fox!) you can`t push them in when hooked up to the rest of the braking system because you`re trying to force a relatively large amount of fluid through a tiny return hole in the master cyclinder - exactly the opposite of the basic principle of how a hydraulic braking system works!



Bandito, are your calipers connected to the brake lines and bled, or are the calipers still removed?

 

[Blue Fox]

I agree, Eurovee, I have never tried to push them in unless the calipers were off the bike and in my hands.

 

[bandit]

There is a difference;



It should be perfectly possible to push the pistons by hand pressure alone into the caliper body when assembling them (and is an indicator that all is good) , and if force/a g-clamp is needed then there is still something wrong...

However, unless you are Popeye (or Blue Fox!) you can`t push them in when hooked up to the rest of the braking system because you`re trying to force a relatively large amount of fluid through a tiny return hole in the master cyclinder - exactly the opposite of the basic principle of how a hydraulic braking system works!



Bandito, are your calipers connected to the brake lines and bled, or are the calipers still removed?

nah,im not into pushing things backwards,there is enough of that here.always on the bench,eurovee,what i have is a mishmosh,seals varying by imm,ill talk to Blue tomorrow,he is guilty,as charged,CPS told me so.

lol

this right hand caliper is giving me so much grief.

iv gone back to the origional,sheared off bleed valve,im gonna drill it out in the morning,and retap.

i just cant see a pushed in fit will be air tight.

seems the tolerance just does not equate

 

[Blue Fox]

I'll agree, Bandit that the tolerance is small. But it is the flat cross section of the seal and the interface with the fluid around it that provides the seal. If the pistons had to be forced in with a clamp, I doubt they would ever retract enough to operate properly.



I'm not saying that you don't have to jockey and turn the pistons a bit to get them started, but then it just takes moderate pressure to seat them.



I assume that you have the right seal for the caliper? You said you had a miss-mosh of parts? If the seal isn't correct, you will never get the piston in.

 

[Dash]

I concur -- if brake parts are correct and piston seals are new, you should be able to push piston into caliper with your thumbs quite easily. Getting it started can be tricky but once its in, it should go easily. You can even pull the piston back out if you didn't bottom it out.

 

[bandit]

thanks for the help gentlemen,it is a mishmash of parts,ill spend a little more time on it today,and see how i get on.

that is,after iv rebuilt the carbs.......again

 

[bandit]

a long shot...does anyone have a piston to hand,with a seal,that they know is correct.

if so,what is the piston size in relationship to the seal.

example.

piston................30mm diameter

seal external......... diameter

seal internal......... diameter



thanks guys.

edit,banjo bolt thread is 1.5mm pitch...correct

 

[bandit]

just a bump,incase anyone are playing with brakes this weekend.

 

[Eurovee]

piston................30mm diameter



seal external......... diameter



seal internal......... diameter

piston = 30.2mm

seal ex = (a bit difficult to get an accurate reading because of the flexible nature of seal) about 36.5mm

seal in = ( " " " " " " " " """ " " " " ") about 30.5mm



I seem to recall you bought `universal brake piston seals`.



Why didn`t you just buy this kit?:



http://www.wemoto.com/parts/picture/WK-MA-7170947/

 

[bandit]

piston = 30.2mm

seal ex = (a bit difficult to get an accurate reading because of the flexible nature of seal) about 36.5mm

seal in = ( " " " " " " " " """ " " " " ") about 30.5mm



I seem to recall you bought `universal brake piston seals`.



Why didn`t you just buy this kit?:



http://www.wemoto.com/parts/picture/WK-MA-7170947/

thanks Eurovee,thats exactly the information i needed,your possible inaccurate measurments

are probably better than my accurate measuring,no worries,its putting in over size seals and having to[after Blues comments]force the piston in.



the link you provided,well,the left caliper is great[so,the cost was not in proportion],and working well,the right is not from my model,so,i could not buy seals matched up to model,i did,and they didnt fit,the left pistons are bigger than the right.



anyway,with those sizes,i have a clue as to where im going,as seals are varying by 1 mm.its difficult to get right,ill keep at it.

i bought the seals i have from wemoto,i have a selection now,its just getting it right.



thanks again

 

[Eurovee]

the left pistons are bigger than the right.

Are you saying that there are twinpots out there that have pistons of different size (not in the same caliper, i mean compared from one caliper to another)?

Do these calipers with the larger pistons look the same externally to the other type?

I`ve got a filing cupboard half full of `em and as far as i know the pistons are all 30mm.

 

[stern-69]

It sounds like he has dual front calipers, but one is NOT a CX one and was probabaly retrofit onto the bike (I have a set of shadow dual calipers, look a lot like the CX ones, but the pistons ARE bigger. Was going to put the whole Shadow front end on to get dual brakes and solve the fork leak, but the forks are 37mm not 35mm )



If this is the case, you will have to figure out "where" that caliper came from and get the proper rebuild kit for it.

 

[bandit]

Eurovee and mr Stern.



yep,thats what im saying.hence this post.i can normally work thing out,this is a bit tricky.



the 81 has 2 times twin pot calipers.the left hand cleaned and rebuilt,tested and fitted.

the left was shot,sought and found a different caliper,looked nearly identical,bolted straight on.so good start.

order new seals from wemoto 23 march.[great company]arrived,everything super clean,g-cramp ready,all lubed up.seals fitted,centred,ready,,let go,boom,they dropped in to the bottom of the caliper.

.oh why did i get involved.one step forward,3 steps back.

sugar

phoned wemoto,informed me,i must order by piston size,not by model on this occasion.

did that,arrived,but geez,they were tight.hence this thread,i need a reference point.



i know there are strong guys out there,but im no whimp,i understand force,i dont,now im back in to wrenching need a torque wrench.[hope i dont live to regret that comment]

thanks guys for trying to help.

 

[bandit]

looking through old threads,Stubby posted this a while back,so it looks as though go up in 2mm multiples

 

[bandit]

just an update.

i got a right hand caliper that fits the bike,iv got pistons to fit the caliper and seals to fit the pistons.they are both in half way,i can push them in by hand,or pull the out.



so,thanks to you guys that helped me out.

apologies to R.

Eurovee,sizes smack on.



the only problem is it has no bleed valve,that's sheard off,too hard to drill out accurately,im not going to push my luck on this any further.

quite ironic really,i posted this a couple of months ago[in case anyone had an issue],now i just ordered it.....spooky.

thanks one and all.