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A A A A Author Topic: TC brakes locking on  (Read 122 times)

dangerous

TC brakes locking on
« Started on: 18-Jul-21, 15:50 »
ok, so... the bike has had little use over the last 10yrs, iv got it running good now but the front brakes are pissing me off... they lock on but one caliper wont release, here's what I have done so far
CX500TC
new caliper kits
new master kit
eased and greased all pivots and mechanics related to the caliper
new fluid...
BUT still with front wheel of the ground it spins pull the brakes on and it stops spinning, do this several times and the wheel binds up more and more... to the point where I have to crack the bleed nipple to release the pressure... WHATS with this its got me buggered???

CX PHREAK

Re: TC brakes locking on
« Reply #1 on: 18-Jul-21, 16:04 »
Likely a blocked MC return hole. I've just left you a more detailed reply on the US site.

Seagrass

Re: TC brakes locking on
« Reply #2 on: 18-Jul-21, 16:42 »
Second vote for a blocked master cylinder return hole.

This is a common problem and cleaning out the hole is always one of my master cylinder rebuild tasks.

Seagrass

dangerous

Re: TC brakes locking on
« Reply #3 on: 18-Jul-21, 17:21 »
Second vote for a blocked master cylinder return hole.

This is a common problem and cleaning out the hole is always one of my master cylinder rebuild tasks.

Seagrass

where do I find this hole... I replaced the guts of the master today and gave it a good clean.... but I may have over looked something???

Seagrass

Re: TC brakes locking on
« Reply #4 on: 18-Jul-21, 18:51 »
Under the master cylinder reservoir are two (or maybe three) holes. One of these holes is used to feed fluid into the master cylinder and the second smaller hole allows for the fluid to return to the master cylinder reservoir as required (to “equalise” the pressure in the brake lines).

You may need to remove the reservoir to clean out the smaller hole. If you do need to remove the reservoir you will need to install a new “O” ring seal. I just purchased one from Honda here in Australia for $14.55 ouch! The “O” ring needs to be EPDM (not nitrile) rubber as nitrile rubber swells when exposed to brake fluid.

Seagrass

iansmith

Re: TC brakes locking on
« Reply #5 on: 18-Jul-21, 19:27 »
OP states that one of the calipers doesn't release (so the other one does?).

Not an expert but doesn't sound like the return hole in the MC to me. Would that affect both calipers equally?

My thoughts:
1. check the brake disc on the side that doesn't release - is it warped?
2. check the wheel bearings (not as likely as 1. but this caused same symptoms on my shadow)
3. strip and clean the offending caliper again - perhaps you missed something? piston sticking? etc.


CX PHREAK

Re: TC brakes locking on
« Reply #6 on: 18-Jul-21, 20:48 »
There is the possibility of old rubber hoses internally shedding rubber. This can function as a one way valve as the master cylinder can exert more pressure than the return.

muzza

Re: TC brakes locking on
« Reply #7 on: 19-Jul-21, 04:16 »
I would swap out your brake lines to new ones .

dangerous

Re: TC brakes locking on
« Reply #8 on: 19-Jul-21, 15:44 »
ok guys.... heres the master, hard to tell due to the blue fluid but its a clear plastic cap with one hole... im thinking under the cap it looks like the return... can this cap be removed?


dangerous

Re: TC brakes locking on
« Reply #9 on: 19-Jul-21, 15:52 »
now that i look at it... if some one else with the same master can look into theirs... the hole on the right is the feed into the lines... what looks like another hole to the left is actually a lump of something... wonder if thats the return... just that I cant get to it under the plastic cap we are looking through in the photo

Seagrass

Re: TC brakes locking on
« Reply #10 on: 19-Jul-21, 18:03 »
You can remove the cup with a large screwdriver, I have just done this on my CX500 Euro which has the same master cylinder.

As mentioned in my previous post you will need a new O ring before assembly or you will have a brake fluid leak.

Seagrass

CX PHREAK

Re: TC brakes locking on
« Reply #11 on: 19-Jul-21, 20:31 »
To check an individual brake line if only one side is holding pressure undo the lines union banjo bolt at the splitter. If it releases at the nipple but not at the top of the line the line is the issue.

To verify if the issue is the master cylinder after doing the preceding you can do the same again at the masters banjo. If the brake releases now you have isolated the issue to the master cylinder.

nodrog

Re: TC brakes locking on
« Reply #12 on: 20-Jul-21, 00:11 »
My two bobs worth,

I find it strange that Only one caliper is locking on, if this is the case, the problem is more likely to be a blockage before the splitter (Caliper side of the splitter). The small hole in the master cylinder, when the Master cylinder is released, is positioned  so that the Cup Seal retracts just beyond the hole, thus allowing the Brake fluid free passage to the reservoir. I have seen Motorcars have problems releasing brakes due to a oversize cup seal. You see, the front of the seal lip rests very close to the hole (To keep free travel to a minimum) thus minimizing handle travel.  I learnt very early with my CX that there are a couple of variants of the Master Cylinder, Is it possible to have fitted the wrong size Cup seal thus it will block the hole. In most cars the seal is set back just .015" from the hole when at rest. This does not leave much room for error.
On another note, thought i should point out that the Piston seals in the Caliper have a square cross section because they are used to create what is called retraction. This is achieved due to the fact that the bottom of the Piston groove is not flat, therefore creates a rolling effect on the seal. When pressure is released the Square Seal retracts the piston ever so slightly to eliminate drag.

Sorry about the rant, But I was employed by PBR Automotive for many years. We didn't make brakes for Motorbikes but we did for many many cars.

Thought i should add, I have seen Cup seals of the correct size block this hole mearly because the rubber lip was a little bit to thick. If the lips is a bit thick the seal must squash down just a bit further and thus it can block the whole.

dangerous

Re: TC brakes locking on
« Reply #13 on: 23-Jul-21, 18:00 »
I find it strange that Only one caliper is locking on, if this is the case,

sorry mate my bad... both were locking on, so back to the master...
left work early today and hooked into it... compare the two photos...
found the pin hole return under a shell of crud, which I thought was part of the casting... we have brakes people, thanks for the help.


Seagrass

Re: TC brakes locking on
« Reply #14 on: 23-Jul-21, 19:13 »
Thanks for the update and feed back, we are always happy to help.

Good to know you have it all working now.

Seagrass

dangerous

Re: TC brakes locking on
« Reply #15 on: 24-Jul-21, 07:30 »
oil and filter and a half decent ride today the weathers mint for a change....

nodrog

Re: TC brakes locking on
« Reply #16 on: 25-Jul-21, 21:39 »
Great news, as Seaqrass has already said, thanks for the update.

 


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