Topic: Front brake locking up... pad thickness???

[The Mayor]

First off, Happy Thanksgiving out there.

So, I replaced the pad on my '73 CB350 with some Daido pads I purchased off ebay. The first issue I had was the grove at the top of the pad was just a hair too small, so I had to file it out a bit before I could fit the pads in the caliper. Then, I noticed that with the additional thinkness, the brakes are basically grabbing all the time. The swingarm is adjusted out as far as it can go - and the pad on the piston-side is in to the point that it's nearly flush with the housing. When I tighten down the two bolts on the caliper, it's dragging way too much. I don't have any prior experience with theses bikes (or brakes) so I'm a little confused.

Has anyone else had issues with this brand pad being to thick? Or any brand? Is there something I'm missing?

[mystic_1]

Did you push the piston back into the caliper when you had it apart?

When the old pads wear, the piston moves out further to compensate.  When you fit new pads you have to push them all the way in.

Also, when you had it apart, best practice would have been to pull the piston out and clean/inspect the piston seal.  The seal itself provides the retraction of the piston when you let off the brake, so if it's grimy that doesn't happen and the brake drags.

There are other potential causes but these are quite common.

mystic_1

[Spanner 1]

If the new pads are thicker ( should be ) than the old, the piston will need to be pushed in to the caliper to allow for the extra pad thickness. Seems like you have pushed it in tho', so next would be to open the caliper bleed valve and allow some fluid out that was ' compressed' when you pushed the piston back into the caliper..... still stuck..?, then problem is the fluid return hole in the master cylinder...Search for ' sticking brakes' on the Forum for lots of reading..Happy TG to you too...

[Terry in Australia]

Yep, all of the above, the three main causes that I've experienced with CB750 (but they're all basically the same) brakes are as follows:

1. Brake piston sticking due to craap, corrosion and old brake fluid (you did flush and replace the brake fluid, yeah?)
2. Pad stuck in caliper recess due to road scum (no, not 1% biker types) buildup, and
3. blocked return valve (teensie weensie pin hole in MC reservoir, clean it out with a oxy welder tip cleaner)

Also (and maybe not relevant to SOHC Honda's, but maybe helpful just the same) I've had a real drama with the front brakes on my BMW K1100LT recently, "locking on" and not releasing once I let the lever off? I took it to a BMW dealer and they couldn't fix it, but suggested that my MC might need a "kit" soon, so I had to ride the return trip from Sydney (600 miles) with only the back brake? FAAARK!

After numerous web searches, discussions with other BMW owners, fiddling with the ABS electronics (which wasn't working as it turns out, since I disconnected the battery 3 years ago and neglected to reset the ABS........) I finally found a post on a BMW K series owners forum where one owner discovered that his brake lines had collapsed and were working like a one way valve, allowing fluid through to the calipers (under pressure from the MC) but not allowing the fluid to be returned under the much lesser pressure of the piston seals pulling the pistons back.

I've bought new stainless braided lines from Britain (at a fraction of the price of buying them here in Oz) and had enough left over to buy a "Mityvac" speed bleeder, which I'm really looking forward to using after years of brake bleeding frustration! Cheers, Terry.

[Bill/BentON Racing]

+1.Oh yea you gonna love your mityvac,been using them since'85!,Bill

[The Mayor]

Good stuff, thanks guys. I've had it all apart recently, as it was sticking in general with the old pads. After cleaning it out, replacing and bleeding the fluids, ect - it seemed to stop sticking. My main issue now had become squeal when applying the brake. The pads were old though, so I decided to go with new ones.

The piston I pushed in as far as it seemed to want to go, but even then there was very little clearance with the new pads. Pad is out maybe an 1/8" from the piston housing. I'll try bleeding again, and push the pad/piston back in as far as it'll go. Just seems to have very little room. It's possible the ring needs to be replaced, and maybe the piston. Had some pitting when I pulled it to clean.

Thanks again, I'll hopefully get to play with it this weekend.

[Terry in Australia]

One of the guys here makes Phenolic brake pistons, I've got one in my K1's second caliper and it seems to work well. If your piston is pitted, it's a good idea to replace the piston and seal. Cheers, Terry.

[Tom in Newcastle......Ontario]

 Changed pads on my 74 360 ,a couple weeks ago,and had a sinmilar issue..What I did was to take the pads out ,and sanded them down a bit,I used a sheet 80 grit paper flat on my bench and just did a few figure 8's,seemed to work for me..

First off, Happy Thanksgiving out there.

So, I replaced the pad on my '73 CB350 with some Daido pads I purchased off ebay. The first issue I had was the grove at the top of the pad was just a hair too small, so I had to file it out a bit before I could fit the pads in the caliper. Then, I noticed that with the additional thinkness, the brakes are basically grabbing all the time. The swingarm is adjusted out as far as it can go - and the pad on the piston-side is in to the point that it's nearly flush with the housing. When I tighten down the two bolts on the caliper, it's dragging way too much. I don't have any prior experience with theses bikes (or brakes) so I'm a little confused.

Has anyone else had issues with this brand pad being to thick? Or any brand? Is there something I'm missing?

[crazypj]

Main problem I've seen is fender mounted incorrectly and twisting caliper.
 brake mounting goes directly to fork leg, fender goes 'outside' it closest to wheel

PJ