Front brake drag after new master cylinder and lines

[Guest]

So I finally decided to put some stainless brake lines on my bike, it was long overdue and so was the fluid change. Along with that, I wanted to replace the master cylinder because the original wasn't working well with my updated handlebars (replaced the L buckhorn bars with straight ones, Daytona I believe? It was a while ago.)

Anyway, the brakes always worked fine aside from being a bit spongy. Now, after having the new line, new master cylinder and some fresh fluid installed, I noticed that the pads are dragging pretty badly. Tough to turn the wheel or push the bike around. I have not looked at the Pistons yet or anything but... Wondering if anyone has any advice on where to start? Should I dismount everything and pull the caliper apart? I've never cleaned it up since owning the bike but like I said, it always worked fine before swapping the master cylinder and lines... Why would that mess it up?

[gsrick]

So I finally decided to put some stainless brake lines on my bike, it was long overdue and so was the fluid change. Along with that, I wanted to replace the master cylinder because the original wasn't working well with my updated handlebars (replaced the L buckhorn bars with straight ones, Daytona I believe? It was a while ago.)

Anyway, the brakes always worked fine aside from being a bit spongy. Now, after having the new line, new master cylinder and some fresh fluid installed, I noticed that the pads are dragging pretty badly. Tough to turn the wheel or push the bike around. I have not looked at the Pistons yet or anything but... Wondering if anyone has any advice on where to start? Should I dismount everything and pull the caliper apart? I've never cleaned it up since owning the bike but like I said, it always worked fine before swapping the master cylinder and lines... Why would that mess it up?

Maybe it is just a coincidence that it is happening now. You could try removing the caliper bolts and rocking the caliper back and forth to push the pistons in and try them again. See if that makes a difference. It also could be the master just not allowing the fluid to fully return. There could be machining debris clogging up the return hole. Is it an OEM or aftermarket. Is it the same piston size?

[exzachtly1]

Thanks for the suggestions, I'll give that a shot. The MC I bought is this one https://www.amazon.com/Cylinder-Rese.../dp/B01B1BNQTS technically it says it's for ATVs but read some reviews of people using it on their 1980s CB650s. It does not specify piston size on the product page though? It really did seem like a 1:1 replacement compared to the original part. Only difference was how the brake wire connects.

[gsrick]

Yeah, I looked at it and I'm not sure how it compares to stock, but I can almost guarantee it's made in China and you might want to check those tiny holes in the bottom of the master. Especially the the one furthest away from the lever. It could be blocked by a shaving from the machining process or not even all the way through.

[exzachtly1]

Will give it a look tomorrow I think. I figured it was worth a shot for the price, my old MC was kinda shot and never fit right with the new handlebars. No doubt made in China and I'm usually cautious about this stuff but, it did have good reviews and actually seems pretty high quality to me. Worst case is I need to hunt a new one up or reuse the old one for now.

Regardless, it's been a good learning experience to do this project. I feel better about working on brakes now... Assuming I do get it all sorted out ��

[gsrick]

Will give it a look tomorrow I think. I figured it was worth a shot for the price, my old MC was kinda shot and never fit right with the new handlebars. No doubt made in China and I'm usually cautious about this stuff but, it did have good reviews and actually seems pretty high quality to me. Worst case is I need to hunt a new one up or reuse the old one for now.

Regardless, it's been a good learning experience to do this project. I feel better about working on brakes now... Assuming I do get it all sorted out 🤣

Google, "clearing master cylinder return hole" and you'll find a lot of useful information. That return hole is very very small and wouldn't take much to block it up. Like I said, depending on quality control and or if they test them before shipping them out, it's a good possibility it may not be all the way through, then again you may need to take the calipers apart and give the seals and piston a good cleaning. Dirt and or deteriorated dust and fluid seals both could hang up your brakes. They are designed to grab the piston and pull it back when released. If they are still the stock 40 year old seals, the elasticity may be gone and it is just that time to show up. Especially since you have a new system that can push out the piston better with no swelling hoses to displace fluid that should go to the piston, it may be exceeding it's ability to pull it back sufficiently to back the pads off the disc. Remember it's only a paper thin distance between the pad and rotor. Good luck.

[exzachtly1]

Well after doing a bunch of research and coming up with a plan to clean the MC return, i went outside to check things out. Surprise - got both wheels off the ground to check and it's actually the rear that's dragging

Must be a coincidence because I have not touched anything on the rear brakes... and they were working fine last season as far as I could tell. I do plan on redoing the lines on the rear anyway so I guess I'll be inspecting the caliper piston as well...

This bike must be trying to tell me something because every time I fix one thing, something else pops up.

[Big T]

It's telling you that it's pushing 40 years old and that brake line that should have been replaced in 1986 is overdue.

[exzachtly1]

It's telling you that it's pushing 40 years old and that brake line that should have been replaced in 1986 is overdue.

Hah, yes indeed man. I was working on this bike hot and heavy for a while a few years back, but since then I've had newer bikes so now it's become my occasional project bike. I am really enjoying taking on jobs like this when I have the time and learning how to do these critical maintenance items... the knowledge will transfer to my new bikes. I have the supplies to do the rear brake so I will be taking that on as soon as it's not 25 degrees out

[Gorminrider]

pads tend to stick overwintering...the rear maybe picks up a little more dirt-salt or whatall.

Swing the caliper up, crack the nipple and force them back a wee bit with a wedge. While you are t it, you might want to service the caliper pins with some cleanup and "silicon based brake grease.

[exzachtly1]

Yeah took the rear caliper apart today because was super seized up on one side. Brake lever was not pushing the piston out at all. Once I got it all apart, there was a ton of gunk and grunge in there under the seal... I'm really glad I finally did this. Currently de-rusting all the bolts before I put it back together but I'm hoping I cleaned em up enough to get things moving again. The pistons actually didn't look bad, and the seals were in good shape. I was able to push the pistons back in with my fingers so I guess that's a good sign . I used these steps http://gsarchive.bwringer.com/storag...r_overhaul.pdf. Only thing I wasn't sure about is that I was hesitant to use sandpaper inside the bore, because I didn't want to mess up the rubber ring that's in there. There was a bit of corrosion but hopefully I got it good enough, mostly just went at everything with a green scotch-brite pad and some picks around the lip where the seal sits.

So new stainless lines front and back, new master cylinder, back caliper has been cleaned up... kinda thinking I want to do the same to the front caliper now.

[mrbill5491]

Yeah took the rear caliper apart today because was super seized up on one side. Brake lever was not pushing the piston out at all. Once I got it all apart, there was a ton of gunk and grunge in there under the seal... I'm really glad I finally did this. Currently de-rusting all the bolts before I put it back together but I'm hoping I cleaned em up enough to get things moving again. The pistons actually didn't look bad, and the seals were in good shape. I was able to push the pistons back in with my fingers so I guess that's a good sign . I used these steps http://gsarchive.bwringer.com/storag...r_overhaul.pdf. Only thing I wasn't sure about is that I was hesitant to use sandpaper inside the bore, because I didn't want to mess up the rubber ring that's in there. There was a bit of corrosion but hopefully I got it good enough, mostly just went at everything with a green scotch-brite pad and some picks around the lip where the seal sits.

So new stainless lines front and back, new master cylinder, back caliper has been cleaned up... kinda thinking I want to do the same to the front caliper now.

Use a very fine grit sandpaper, 1000, or 2000 grit. Higher the number the finer the grit.

[limeex2]

You must install new caliper seals and use only oem parts. After market brake parts are junk. There will be corrosion behind the seals that must be removed. Scothbrite works like sandpaper but more easily conforms to a round bore. I use a dremmel tool to remove the corrosion in the seal groove, in which case I use a brass bit or be very gentle with a stainless steel bit.