Topic: 1977 honda cb400f front brake issue/question

[andrsn]

I just replaced my front brake piston and seal. I bought an aftermarket piston from a guy here in Portland Oregon and a Honda seal. The piston feels like a good fit (within .01mm of the original), but I cannot get my brake adjusted (they will not return after engaging). The brake power feels better than it did before (I think I did a good job bleeding the brake). The piston seems to not be returning. On the back of the brake pad there is a hard plastic washer, what does that do? The surface of the new piston where the piston contacts the pad isn't a solid surface like the OEM one was, it is shaped like a cup and only the lip of the cup shape touches the brake pad/plastic ring. The plastic ring seems to be getting bent up, could that be causing the piston to not return?

[bryanj]

small hole in master cylinder

[andrsn]

small hole in master cylinder

I'll check that, but just for the knowledge, why is that plastic washer there and what does it do?

[camelman]

I wrecked my 400F last year about 100 yards from my driveway because of this exact issue.  Try removing the nylon washer.  It isn't made for all models of brake pads.  Keep it around though in case you switch back to the original style.

Be careful with the original style too.  The nylon washer can slip out of place and cause the pad to ride high.  All of these issues only occur with new pads since there is very little clearance in the brake assembly with new pads.


Camelman

[flybox1]

sounds like you have a phenolic piston.
what camelman said.....take the nylon washer out. 
its not needed unless you go back to the solid piston.
i believe its main purpose was to reduce vibration between pad and piston.

clear your return hole in your master cylinder.

[andrsn]

sounds like you have a phenolic piston.
what camelman said.....take the nylon washer out. 
its not needed unless you go back to the solid piston.
i believe its main purpose was to reduce vibration between pad and piston.

clear your return hole in your master cylinder.

It isn't a phenolic piston, it is stainless steel, does that affect whether or not I take the nylon washer out?

[flybox1]

not phenolic, ok. take a picture for us.

if only the outer rim of the piston is the only thing that contacts the back of the pad, then the washer has nowhere to sit.
(with the OEM setup,  the washer is supported by the raised center of the back of the pad pressing againt the center of the piston. it wont slip from this position)

[andrsn]

not phenolic, ok. take a picture for us.

if only the outer rim of the piston is the only thing that contacts the back of the pad, then the washer has nowhere to sit.
(with the OEM setup,  the washer is supported by the raised center of the back of the pad pressing againt the center of the piston. it wont slip from this position)

That is what is happening, the washer isn't sitting on the piston. The washer is just slightly too small and getting crushed by the piston. I was going to go somewhere and find a larger sized washer and dremil it to fit, but if I just don't need the washer, then I'll try without it. I'll take a photo when I get home from work today.

[flybox1]

I was going to go somewhere and find a larger sized washer and dremil it to fit, but if I just don't need the washer, then I'll try without it.

might not be a bad idea to cut down on brake squeal.
this still wont adress your piston return issue. take a small copper wire and dig into that return hole.
are your lines new? braided?
any rebuilds to your MC?

[andrsn]

I was going to go somewhere and find a larger sized washer and dremil it to fit, but if I just don't need the washer, then I'll try without it.

might not be a bad idea to cut down on brake squeal.
this still wont adress your piston return issue. take a small copper wire and dig into that return hole.
are your lines new? braided?
any rebuilds to your MC?

I haven't replace/rebuilt anything aside from the piston and seal. If cleaning the return hole doesn't fix it, I'll tear things apart further and probably replace the lines since they look to be getting a little old.

[andrsn]

I removed the nylon washer and it seems to be working as well or better than ever. No more brake squeak and less drag (but it still rubs a bit). Here is a picture of the new installed piston and the old one in my hand (cup versus solid surface).



I tried to make a larger sized nylon washer but the brake dragged really bad with that one too. Here is a photo of the two nylon washers I bought at the hardware store and then modified to fit. The photo also has the back of the brake pad with the original (orange) washer installed.



Is there any danger in not using the nylon washer? If not, I think the problem is solved, anyone have any similar experience?

[camelman]

No problem at all.  If you get much brake squeal, then just try some of that "squeak stop" goop that you can buy at the auto store.

Camelman

[strynboen]

those open pistons are for parelel moving calipers..dont think it vork vell on this honda who are moving in a radius ..and have a push point in mittel of piston...pareles sistem push on hole pistom area..the first hondaes have a spacer to senter the point of presure betveen piston and break plate but they left that on 400 and 550..sorry for that bad laungisk..hope to learn it some day..

[strynboen]

after some breaks in it vil prob,,work vell..when pads are get eating some materiel off,,be care first trips..it vill not work 100% from start

[flybox1]

andrsn,
should be ok, if:
~ the OD of the newly formed washers is the same as the OD of the new piston (so the contact area and pressure is evenly distributed), AND you hole the center of it to fit over the raised pad center circle.

if you've added new pads or done rotor work, go easy on your breaking until the pads begin to bed...

[andrsn]

andrsn,
should be ok, if:
~ the OD of the newly formed washers is the same as the OD of the new piston (so the contact area and pressure is evenly distributed), AND you hole the center of it to fit over the raised pad center circle.

if you've added new pads or done rotor work, go easy on your breaking until the pads begin to bed...

I made the new washers fit over the center circle on the pad, and the piston was evenly contacting the washer all the way around, but It still was dragging really bad. When I took the washer out it worked great. I think I'm gonna leave it off for a while and see how it goes, if there is some dire reason I should try and get a washer to work in there, I'll try again but if not, I'm gonna go without it and check it in a few hundred miles.