another disc brake lockup problem

I've been chasing a problem with the front disc brake on my 74 Norton that's driving me nuts. The brake lever simply gets stuck and won't pull in. It's like the piston in the master cylinder is jammed. If I squeeze hard on the lever it breaks free and the brake works normally. I haven't had it lock up while riding yet, this only seems to happen after the bike sits for a while - anywhere from 10 minutes to an hour - and only after use (it's fine the next day). But the prospect of it happening while riding is rather scary.

This issue started last year. The brake is stock Lockheed with the 13 mm sleeved master cylinder. I have sent the master cylinder to Al (the "Brakeman") Miles, the guy who sleeved it 7 years ago, for a rebuild and the problem persisted. Al told me he's never seen this particular problem and he found nothing wrong with the m/c.

This year I rebuilt the caliper with stainless pistons and the problem seemed to have been fixed. But after about 200 miles, it's back.

The brake line is a stainless braided rubber line, and people are telling me that with age (7-8 years now) the rubber breaks down and pieces could be getting jammed in caliper holes. Sounds plausible, but what sources are there for alternates?

maylar said:

The brake line is a stainless braided rubber line, and people are telling me that with age (7-8 years now) the rubber breaks down and pieces could be getting jammed in caliper holes. Sounds plausible, but what sources are there for alternates?

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Stainless braided brake lines are usually PTFE/Teflon. I thought stainless braided 'rubber' hose was generally used for fuel and oil lines rather than for brakes but perhaps not?

Dunno. I bought this one from Old Britts. Their web site doesn't say.

maylar said:

Dunno. I bought this one from Old Britts. Their web site doesn't say.

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I'd say what they supply now is Teflon/PTFE.
https://www.oldbritts.com/brake_line.html
https://www.oldbritts.com/54_800000.html

Could it be related to the lever and the pivot, maybe the hole is worn and somehow the pivot is jamming.

If both the cylinders have been done up they "should not" be the cause of the problem. Maybe change the hose'.

Years ago, an old LIP Vauhall came into our workshop with a brake pulling problem. We diagnosed the right rear brake was staying on. Eventually we found the brake hose to be the fault. We obtained and fitted another hose and the problem was solved. The interior of the hose was breaking down causing a one way valve effect which kept the pressure on the wheel cylinder.

Dereck

Ps. if you undo the hose at the caliper, what happens. If the brake is still jammed, then loosen
the hose at the master cylinder. You "may" then know if the hose is faulty.

"Quotation marks" above mean what they infer. Its over to the mechanic diagnosing the problem to come to the correct conclusion.

I have had an automobile change lanes on me when I applied the brakes. It was caused by a front rubber brake line that had developed a one way flap of rubber that separated in the line very near to the outbound hose clamp. It is confusing to people in that they think the SS braided lines are the best you can get. Not so. The braiding can just as easily be over rubber line as Teflon line. Remember the braiding is used for line abrasion on the outside and does not do much else. Most businesses offering the lines do not even specify the line material. There is a British company we used recently to get a complete set of teflon braided hydraulic lines for an AC Bristol. If I recall, they had some very good information on their site. I will see if I can find their web address.


http://goodridge.brakes-hoses-fittings. ... -types.php

It was caused by a front rubber brake line that had developed a one way flap of rubber that separated in the line

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Me too! quite scary. If you have indeed got a rubber lined hose change it.
Have you checked that there isn't a mechanical problem where the lever contacts the m/c piston face. I have had a similar problem on a CB750 and had to re-shape the lever contact profile.

Dave

He is going to work that out when he loosens the hose at the m/cyl.
Dereck

cash said:

It was caused by a front rubber brake line that had developed a one way flap of rubber that separated in the line

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Me too! quite scary. If you have indeed got a rubber lined hose change it.
Have you checked that there isn't a mechanical problem where the lever contacts the m/c piston face. I have had a similar problem on a CB750 and had to re-shape the lever contact profile.

Dave

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That'll be one of my diagnostic checks for sure. I had a minor accident a few years ago and the original lever was bent. The replacement that I got didn't fit properly, it had a completely different contact profile. I sent the lever to Al Miles when I had the M/C rebuilt and he ground it to the correct profile. But I'll definitely take a look at that again.

L.A.B. said:

maylar said:

Dunno. I bought this one from Old Britts. Their web site doesn't say.

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I'd say what they supply now is Teflon/PTFE.
https://www.oldbritts.com/brake_line.html
https://www.oldbritts.com/54_800000.html

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And Fred Eaton confirmed that. So I need to look elsewhere.

Given your changes you probably have new fluid in there but....I had a related problem a while ago. Caliper locked up solidly. After much investigation, I found some of the rubber somewhere in the system -- seals?; I have braided S/S lines -- had deteriorated enough that a little chunk had plugged a passageway somewhere in the system. First clue is if you see little black "soot specks" in the reservoir or anywhere else in brake fluid. Frequent fluid changes -- once a year absolute minimum -- is my solution.

Good luck.

Just a side note related to lines. I had braided SS covered lines on my water heater thinking they must be great. Wrong. As they aged, I started seeing black residue coming out of my faucets. Got to be a big time mess of tiny particles. Yes, the rubber lines were the culprit. Use only the SS or I prefer the copper flexible lines on your water heater. Or, hard plum it if you like with copper.

kerinorton said:

If both the cylinders have been done up they "should not" be the cause of the problem. Maybe change the hose'.

Years ago, an old LIP Vauhall came into our workshop with a brake pulling problem. We diagnosed the right rear brake was staying on. Eventually we found the brake hose to be the fault. We obtained and fitted another hose and the problem was solved. The interior of the hose was breaking down causing a one way valve effect which kept the pressure on the wheel cylinder.

Dereck

Ps. if you undo the hose at the caliper, what happens. If the brake is still jammed, then loosen
the hose at the master cylinder. You "may" then know if the hose is faulty.

"Quotation marks" above mean what they infer. Its over to the mechanic diagnosing the problem to come to the correct conclusion.

Click to expand...

This one way valve symptom is common on old VW bugs of which I've owned many. Two of them suffered this exact issue. When my 73 850 started to exhibit this problem I changed brake lines and flushed the system. Problem solved.

I like the Al Miles kit because it is the only one which is not permanent (does not use Loctite, I believe) but it seems a few people have experienced long term problems on here?

The only stainless hose kits I can recommend is Goodridge brand. I know they use Eaton Aeroquip AE246 hose in their assemblies. Many others do not because of the cost.

These hoses are supposed to made of automotive quality materials, and hence have the appropriate automotive markings on them. If they don't have those markings then they are not legal and will or should be rejected by the various testing authorities. DOT, UL or whatever is legal.

Dereck

kerinorton said:

These hoses are supposed to made of automotive quality materials, and hence have the appropriate automotive markings on them. If they don't have those markings then they are not legal and will or should be rejected by the various testing authorities. DOT, UL or whatever is legal.

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The laws regarding replacement brake lines in countries outside Australia and NZ are not as strict.

For instance, in the UK, anyone can assemble and fit brake lines and this includes making them with reusable end fittings. No pressure testing, marking or documentation required.

As long as a brake line meets the necessary yearly MoT inspection standard (below) and is not used on the road in a defective condition then that's basically all there is to it.

http://www.motuk.co.uk/mcmanual_320.htm

Reason for rejection
.
.
.
e. leaking hydraulic fluid

2. A brake pipe which is
a- Excessively chafed, corroded or damaged
b. rigid pipes inadequately supported
c. pipes or hoses likely to be fouled or trapped by moving parts
3.
a hose which is excessively
a. chafed twisted or kinked
b. deteriorated, fouling or can be stretched by steering or suspension movement

4. a hose which bulges or any part of the system leaking fluid.

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Just wanted to update the forum FYI that I've resolved this problem. Turns out that the brake lever was catching on the throttle casting where the cable enters.

Rotated the throttle a bit on the bars, brake doesn't jam any more. Operator problems...

eskasteve said:

kerinorton said:

If both the cylinders have been done up they "should not" be the cause of the problem. Maybe change the hose'.

Years ago, an old LIP Vauhall came into our workshop with a brake pulling problem. We diagnosed the right rear brake was staying on. Eventually we found the brake hose to be the fault. We obtained and fitted another hose and the problem was solved. The interior of the hose was breaking down causing a one way valve effect which kept the pressure on the wheel cylinder.

Dereck

Ps. if you undo the hose at the caliper, what happens. If the brake is still jammed, then loosen
the hose at the master cylinder. You "may" then know if the hose is faulty.

"Quotation marks" above mean what they infer. Its over to the mechanic diagnosing the problem to come to the correct conclusion.

Click to expand...

This one way valve symptom is common on old VW bugs of which I've owned many. Two of them suffered this exact issue. When my 73 850 started to exhibit this problem I changed brake lines and flushed the system. Problem solved.

Click to expand...

+1 Saw it on a '73 Mercury Capri (German made, sold under the Ford/Lincoln/Mercury moniker here at the time).