Topic: How pitted is TOO pitted?

[jstfkndi]

So I have been working on the front brake of my CB350F and finally decided to put a new caliper seal in it. When pulling out the piston, a friend of mine asked me how it looked and said if it was pitted, it would not be good to use. It seems ok, but there is light pitting. So hom much pitting is too much? I am trying to get some pics up soon for any answers. Maybe someone has used some that were worse and it turned out ok?? New piston is about $94...and that is if I can find one!!

[jstfkndi]

Here is the worst of it.

[iron_worker]

#7 From the link below is 44 Euro ($55). You'd have to pay shipping but I think it would be a bit cheaper overall.

http://www.cmsnl.com/honda-cb350f-four-germany_model14635/partslist/F06.html#results


I don't think I'd use it. Looks like if the seal sits on the pitting it will definitely leak. You really want your front brakes to be working properly!   

IW

[Magilla]

How well did it work before you started to "fix" it?

[Duke McDukiedook]

Those look deep and not cosmetic. Phenolic may be in your future.

[BeSeeingYou]

If you don't want to pay for a new one try this:

Clean with acetone and fill them with JB Weld and then shave off any excess with a thin razor blade that will conform to the curve of the piston.  You have to be very neat and precise but it works for me.

[MCRider]

How well did it work before you started to "fix" it?

Right. The pits occur in the part exposed to the environment. No problem if you're using the old pucks.

The problem comes if you wnat to replace the pucks. Then you'll have to push the piston in to allow room for the new unworn pucks. That will put the pits in the area of the seal, and you'll have problems.

Pistons are readily available and shouldn't cost that much. I just bot some, have one for sale.

[jstfkndi]

They didn't work before. I did a master cylinder rebuild and put new pads in. The piston will compress but will not release. I couldn't see much evidence of leaking, but it is hard to tell because there was grease behind there and it could have mixed with that, but no drippage. I haven't tried it with then new seal yet because I don't want to waste anymore brake fluid (not that it is that expensive, it just freaking gets everywhere). I guess it can't hurt to try it again, but frick man! I turn around and this thing needs a part that they no longer sell anywhere!!

[jstfkndi]

Thanks for the link iron worker. I checked it and it will be 77 euro with the shipping, so about what I expected to pay, but at leaast I can get it I might as well just give this bike my wallet!

And I am sorry I have not heard of phenolic. What is it?

And would JB Weld stand up to the corrosive properties of the brake fluid? Funny thing is...this is the solution I was thinking of before I asked! That stuff can cure about anything!

[MCRider]

They didn't work before. I did a master cylinder rebuild and put new pads in. The piston will compress but will not release. I couldn't see much evidence of leaking, but it is hard to tell because there was grease behind there and it could have mixed with that, but no drippage. I haven't tried it with then new seal yet because I don't want to waste anymore brake fluid (not that it is that expensive, it just freaking gets everywhere). I guess it can't hurt to try it again, but frick man! I turn around and this thing needs a part that they no longer sell anywhere!!

I may have mispoke, CB750 pistons are readily available, maybe not CB350F.

Anyway. Pistons not releasing is 99% of the time a problem with the return hole in the master cylinder being plugged with debris, often from the inside of the hose breaking down. many threads on this problem.

[jstfkndi]

I hear you. I am positive I did the master cylinder right and cleaned out everything. The caliper has been apart and it wasn't clogged up, but got a thorough cleaning as well. Guess I should look at my lines...

[Tugboat]

Don't reuse that one. Get a new piston.

[TwoTired]

The piston IS reusable.
Don't worry about leaks, it won't.
Don't worry about braking action.  That will be fine, also.

The only possible issue with that piston *might* be retraction.
The square section seal goes (distorts) parallelogram during brake application.  When pressure is released the seal returns to square and pulls the piston back with it.
When the seal encounters piston pits, it changes how the seal is shaped at the pit area and that has an effect on it's retraction ability.  A few pits have very little impact on the this ability.  But, the detriment increases with the population and depth of the pits.
I wouldn't think that the small amount of pitting shown in the picture would be noticeable, and I've reused pistons with far more pitting successfully.
If it has any problem, it will show up as a dragging brake.  (Realize there are other causes to dragging brakes, too.)

The second issue with the pits is the loss of the plating and susceptibility to further corrosion.  However, if you fill the pits with the proper Dow Corning high vacuum pure silicone grease.  Water can't get at the de-plated steel and corrosion is thwarted.

Certainly a new piston won't hurt.  But, there is still service life in the one pictured, imo.

Cheers,

[MCRider]

I hear you. I am positive I did the master cylinder right and cleaned out everything. The caliper has been apart and it wasn't clogged up, but got a thorough cleaning as well. Guess I should look at my lines...

many of us have been fooled by the MC. Did you clean that hole with a very fine wire? That's about the only way you can be sure. Or air pressure.

First hand experience: I cleaned (soaked in my parts washer) my MC twice, it was oly when i concentrated on THAT tiniest of holes with a wire did i get results.

[jstfkndi]

Ok, thanks! I feel I may have bought the wrong grease then. It is a standard run-of-the-mill from Advanced. Does it have to be the Dow High Vacuum? And perhaps a place I could obtain it or is it a online item only? I am going to go through the line whilst they are empty and see if there are any compromises. What in the lines should I look for? Flex? No flex? I mean, I know they pump up and don't leak

[jstfkndi]

Guess it can't hurt to check it again. I really don't want to take the wholething apart, but in order to clear this hole, does the MC have to come all the way apart? Freaking C-clip was a pain!

And thanks for all the quick replies!

[MCRider]

Guess it can't hurt to check it again. I really don't want to take the wholething apart, but in order to clear this hole, does the MC have to come all the way apart? Freaking C-clip was a pain!

If its like the CB750 (my first hand experience) no it doesn't have to come apart. You would want to get it level (turn the HBar to make it so) soak/suck all the fluid out of the reservoir. (This may not even be necessary) There should be two holes visible in the floor of the reservoir. The tiny one is it. Many use a teeny guitar string. I found a strand of electrical wire from an AC ext cord would fit. Run it in and out. Should get 1/4 to 1/2" penetration to be sure its not blocked.

Now if that works, you've got to realize that crud is still in there, and may eventually make its way back. At least you know what's up.

[jstfkndi]

Wooord!

[Teatimetim]

I allways find it amazing when your working on something, and you think about say pitting, then come to this forum, and the question is already being asked and answered.

[jstfkndi]

Teatimetim, dealing with the same issue I presume?

[TwoTired]

Ok, thanks! I feel I may have bought the wrong grease then. It is a standard run-of-the-mill from Advanced. Does it have to be the Dow High Vacuum? And perhaps a place I could obtain it or is it a online item only?

I feel it does have to be the one and only for this app.  No petroleum based product has the no-creep, no-bleed at any temperature property.  If it finds the pads and rotor, there go your brakes!
I bought mine from a local industrial supply business. 10-15 years ago.  I saw some posts a while back where it was purchased online and in small quantities.
This caliper design is NOT like the ones found on cars.  What is appropriate and acceptable there is NOT appropriate and acceptable for the SOHC4 brakes.

I am going to go through the line whilst they are empty and see if there are any compromises. What in the lines should I look for? Flex? No flex? I mean, I know they pump up and don't leak

Ever open a brand new pack of rubber bands, take one out and stretch them?  Notice that the first stretch has more resistance that following stretches?
That's a property of rubber.  It loses some resilience and adherence to original shape as it is "worked".

The rubber brake lines are reinforced with embedded woven fibers to keep them from blowing up like a balloon when under pressure.  Still the they do flex a bit, and the repeated flexing causes fatigue, whereby they flex even more.  It does this at a certain pressure, and as you hand creates more pressure some is diverted to the expanding the lines rather the applying the pressure to the pad/rotor.

Unless you fins cracking in the rubber lines externally, the only way to determine if you rubber lines have reached end of life is an actual pressure/performance test.
The old ones will work, the new ones work better.
I have seen a failure mode where the inside of the rubber line chunked off and became a one way valve.  You could apply the brake, but it wouldn't release.  I only found this cracking the joint bolts at strategic places to relieve the pressure build up.  It was a lower line in this case, and the cure was a new line.
I can recommend SS brake lines.  These have a more rigid inner liner that is very resistance to expansion under pressure.  This allows all of the pressure built up by hand to be directed to the pad rotor.  The lever is harder, and the hand pressure modulation during braking has a much more precise feel.

Cheers,

[Tugboat]

I have a tube of the Dow Corning vacuum grease.. found it online last year. Cost like $40!! But, small price to pay to make sure grease doesn't melt at high temps and ruin my pads (as stated above). Thanks for the insight TT.

[lucky]

Thanks for the link iron worker. I checked it and it will be 77 euro with the shipping, so about what I expected to pay, but at leaast I can get it I might as well just give this bike my wallet!

And I am sorry I have not heard of phenolic. What is it?

And would JB Weld stand up to the corrosive properties of the brake fluid? Funny thing is...this is the solution I was thinking of before I asked! That stuff can cure about anything!

Brake parts can get over 500ºf easily,and disc brake grease is good to 1000ºf.

[steam-powered man]

haven't gotten to the brake yet on my project, but i am curious and found that bikebandit.com lists the same part number for cb350f and cb550k and others.  then i did a search and found a stainless steel piston for $38 plus $6 shipping on ebay.  the ad says the piston fits these bikes: 

CB350F (72-74)

CB350G (73)

CB360 (74)

CB360G (74)

CB360T (75-76)

CB400F (75-77)

CB450 (72-74)

CB500 K0-K2 (71-73)

CB500T (75-76)

CB550F (75-77)

CB550K (74-78)


not a bad price for new, stainless.  ebay seller has 11,753 happy customers.  i may go this route is needed.

[TwoTired]

Brake parts can get over 500ºf easily,and disc brake grease is good to 1000ºf.

Disc brake grease will still lubricate at 1000 F, as it's specification indicates.   But, it will not stay put at that temperature.  It will weep, liquify, and creep into both the caliper pad and rotor of the SOHC4.   The Dow corning Silicone grease will not.

So, pay attention to the material properties that are required.  The SOHC4 caliper and rotor does NOT need lubricant.  It needs a water barrier that won't be dissolved in water and stays exactly where it is placed under elevated temperatures.  Honda used when new and specifies the silicone grease in the shop manual.  And, there are very good and specific reasons for doing so.

[MCRider]

haven't gotten to the brake yet on my project, but i am curious and found that bikebandit.com lists the same part number for cb350f and cb550k and others.  then i did a search and found a stainless steel piston for $38 plus $6 shipping on ebay.  the ad says the piston fits these bikes: 

CB350F (72-74)

CB350G (73)

CB360 (74)

CB360G (74)

CB360T (75-76)

CB400F (75-77)

CB450 (72-74)

CB500 K0-K2 (71-73)

CB500T (75-76)

CB550F (75-77)

CB550K (74-78)


not a bad price for new, stainless.  ebay seller has 11,753 happy customers.  i may go this route is needed.

I was thinking there are sources other than OEM for these at better prices than OEM. I can't remember the forum members name that was selling the phenolics, at the time he was hit or miss on availlabilty. Seems I paid $35 each for those as well. (CB750) I think he sold on eBay as well.

[TwoTired]

For phenolic, try Kevin400F.

Cheers,

[MCRider]

For phenolic, try Kevin400F.

Cheers,

That was him, thanks TT.

[brewsky]

The piston IS reusable.
Don't worry about leaks, it won't.
Don't worry about braking action.  That will be fine, also.

The only possible issue with that piston *might* be retraction.
The square section seal goes (distorts) parallelogram during brake application.  When pressure is released the seal returns to square and pulls the piston back with it.
When the seal encounters piston pits, it changes how the seal is shaped at the pit area and that has an effect on it's retraction ability.  A few pits have very little impact on the this ability.  But, the detriment increases with the population and depth of the pits.
I wouldn't think that the small amount of pitting shown in the picture would be noticeable, and I've reused pistons with far more pitting successfully.
If it has any problem, it will show up as a dragging brake.  (Realize there are other causes to dragging brakes, too.)

The second issue with the pits is the loss of the plating and susceptibility to further corrosion.  However, if you fill the pits with the proper Dow Corning high vacuum pure silicone grease.  Water can't get at the de-plated steel and corrosion is thwarted.

Certainly a new piston won't hurt.  But, there is still service life in the one pictured, imo.

Cheers,

I'm confused now.......I thought the silicone grease was NOT to be used on the piston or seal, just on the pad sliding surfaces, and assembly lube or brake fluid was the only thing to lube the seal/piston with?

[TwoTired]

The seal divides the piston into two areas one side of the seal has brake fluid and the other side is exposed to air a water from without.  Directly under the seal is ideally nothing, but to help it slide during assembly, we use some assembly lube.

The piston pitting is predominantly on the piston side exposed to water, salts, and atmospheric impurities, notably oxygen.
Once the chrome plating is breached on the piston, the far more reactive underlying steel is exposed.  To arrest further corrosion the silicone grease fills to pits, blocking water and oxygen access to the piston's base steel, arresting deterioration.

Clearly if the pitting is excessive, silicone grease cannot take the place of steel.  But, as the silicone does not combine or dilute with anything, it is not washed away by water or brake fluid.

Ideally, you do not want any silicone in a DOT3 containment vessel.  But, if the piston pits are small and under (or beyond) the seal instead of inside the DOT3 vessel, silicone grease does little harm.   However, if you must have uncompromising ideal conditions, then get yourself a new piston.

Also, be aware that it's not just the piston beyond the seal that is environment exposed, the aluminum caliper walls are as well.  A thin coat of silicone grease there, arrests corrosion of the caliper body.  Remember, the grease stays put unless mechanically pushed of placement site and isn't diluted with anything.  A very very thin coat is an excellent water shed.  And, if it sheds water, it blocks oxygen (therefore corrosion), too.

Cheers,

[brewsky]

Thanks for the clarification TT, now if it would just stop the squealing I would really be sold!