HELP - MKIII Lockheed Brake Lock-up

Friends:

The rear (original) Lockheed brake on my "new to me" 1975 Commando MKIII is dragging to the point of locking up when it gets warm after a few miles of riding (piston pushing the pad against rotor). I've reviewed quite a few posts on the site reporting similar problems, and it seems folks run straight out and rebuild the caliper or the master cylinder, assuming one of them is the culprit. However, I've also noticed that often times it turns out to be some other thing that's actually causing the problem.

While I am far from a certified mechanic, my usual approach to fixing problems I encounter with any of my motorcycles is (1) ask for help from more knowedgeable owners, (2) start with the easy/cheap fixes first and work your way to more expensive conclusions, and (3) if your going to rip something open, replace everything while you're in there (not just the broken bits) to hopefully avoid ripping it open again.

I've not tinkered with the brakes before, so I'm hoping some of you will weigh in with a list of things to check to troubleshoot my brake problem. What should I check first, second, etc.? How will I know the caliper needs a rebuild? How will I know the master cylinder needs a rebuild?

Your wisdom and guidance are greatly appreciated!

Scott

Welcome Scott,



If the problem isn't the caliper pistons sticking, then the reason will very likely be due to excess hydraulic pressure being unable to vent out of the brake system when the brake is off.

1.) The most likely cause is that the return bleed port, (also known as a bypass port) in the master cylinder (B in diagram below) has become blocked. The lower part of the port drilling into the barrel is only a very small diameter, although the upper counter bore is larger.




Excess fluid pressure is trapped in the brake system, so the brake won't fully release, which leads to brake drag, and that drag can get steadily worse as the heat in the system rises.





2.) If the master cylinder barrel assembly has been screwed one too many turns into the alloy housing (over-adjusted, - see fitting instructions below) then the master cylinder piston will not be able to move back far enough when the brake is off to uncover the bleed port, and the result of that would be exactly the same as (1).








3.) If the brake still has an old rubber hose, it has been known for the inner lining of the hose to deteriorate and detach itself internally, and that can act as a "one way valve" - allowing pressure/fluid to pass in one direction but not the other.

4.) The caliper pistons are partially seized in the caliper?

I suggest that you unbolt the caliper or remove the rear wheel (leaving the hydraulics all connected) and, with the master cylinder reservoir cap and diaphragm removed, attempt to lever the caliper pads/pistons back into the caliper (with a pry bar, or tyre lever/tire iron, etc.)?
The pistons should move back into the caliper without too much force being applied to them, and the fluid level in the reservoir should rise slightly?

If excessive force is required to push the caliper pistons back, or if the pistons won't move at all, try loosening one of the hydraulic fittings and see if the pistons will move then?
If so, then one of the things I mentioned (except 4) above is causing the problem, and the master cylinder assembly will probably need stripping and cleaning, or the barrel assembly position re-adjusting? Or a new brake hose is required?

BRILLIANT POST! Thank you. I can't wait to get started. Is there any chance you could send me a full electronic copy (.pdf etc.) of the brake repair manual from which posted the very informative excerpts?

Scott

Yes, certainly. If you send me your e-mail address through the website PM or e-mail service, then I will send you the pdf.

LAB, would you be so kind as to tell us the name of the excellent manual you referenced for this answer? Where may it be obtained? Thanks.
Gene

Gene1 said:

LAB, would you be so kind as to tell us the name of the excellent manual you referenced for this answer? Where may it be obtained?

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The dragging Lockheed hydraulic brake problem which affects both the disc model Triumphs and Norton MkIII's has, I suppose, been known about since these bikes were reasonably new?
Although reference to this actual problem does not appear to be in any official manual, - as far as I am aware?

However, there are certain publications available, like the UK "NOC Service Notes" and the "INOA Tech Digest" that contain lots of useful technical information, but this website is really one of the best sources of information for Norton Commandos that I know of.

I had exactly the same problem I posted on this site about early August I think. I had already serviced the rear caliper when I bought the bike, the only way I could release the pressure in the caliper was to unscrew the bleed nipple.....I made the mistake of rebuilding the mastercylinder and was then unable to bleed the system out. It was then I discovered that I could not pass air or anything through the rubber flexible hose. I think its a good idea to remove the caliper end of this hose and see if you can pass brake fluid through it freely....I disected my old one to find that it had delaminated inside,they probably have service life of about 5 years I think mine where originals....the bike is a 1977 :shock:

see this post I was wrong it was July not August
Posted: Wed Jul 09, 2008 7:13 pm Post subject: Ever had this happen

My Mk III has exactly what the original post describes - the rear brake tends to drag, and the drag gets worse when the brake heats up until it's pretty locked up. I tore down the caliiper - it wasn't bad, but I'm doing SS pistons and seals since I have it apart. The hose isn't blocked - easy to blow through it. So I'm looking at the master cylinder, for which I have a rebuild kit. But I can't get it apart. That set screw seems larger than 5/64" and smaller than 3/32" (also larger than 2 mm and smaller than 2.5 - figured I'd try and see if there was something close). Can anyone tell me for sure what that set screw really is?

Also, can anyone point me to any written material on rebuilding the master cylinder in addition to what's posted here? So far I haven't found anything.

I notice that when I put the reservoir on the master cylinder body it hits the casting and doesn't center on the bolt. Is this OK? I assume the 2 ports communicate under the O-ring so that positioning doesn't have to be exact.

Thanks - Peter

ptourin said:

So I'm looking at the master cylinder, for which I have a rebuild kit. But I can't get it apart. That set screw seems larger than 5/64" and smaller than 3/32" (also larger than 2 mm and smaller than 2.5 - figured I'd try and see if there was something close). Can anyone tell me for sure what that set screw really is?

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The set screw/grub screw allen key size should be 3/32". Plenty of heat and penetrating oil are often needed before the tiny screw will loosen.

ptourin said:

I notice that when I put the reservoir on the master cylinder body it hits the casting and doesn't center on the bolt. Is this OK?

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No, that's not OK, it definitely sounds as if the master cylinder barrel assembly has been screwed too far into the casting (see the "set the pushrod" info how to set it the correct number of turns, in my post above) if the master cylinder is screwed in by only one turn too many, then the small vent port will never be uncovered by the piston when it moves back, so the residual pressure remains locked in the system and cannot vent to the reservoir, and that is almost certainly the reason why your brake is dragging if the cylinder has been screwed in too far.

I'll look at this again tonight - it looked to me like the reservoir was being pushed perhaps 1 mm off center - and yes, that's what would happen if the master cylinder is threaded in too far. Maybe some PO messed with it, unlikely as it seems. Still hard to believe that 3/32" will fit the setscrew - but it's soaking in WD-40 today and we'll see tonight what happens. A local bike show wants vintage bikes entries so I'm trying to get this sorted out before Saturday, at least enough so I can ride over and back - it's not far.

This is a bike with some history - wish I know the details! It came to me with a 38mm Mikuni on it, and turned out to have triple springs and a Norris drag/fuel cam in it, and pistons with valve notches. Seized almost immediately once I got it to run at all - so rebuilt engine and gearbox last winter. Physical bike looks beautiful, but lotsa trouble getting the engine to run well - now has a 34mm Mikuni on it, never could get the 38 to run well. Did shocks, still have to do steering head/forks - maybe this winter. It's got a starter conversion and starts well. I'm starting to feel good about local riding - anything less than 3-4 hours away.

Peter

ptourin said:

It's got a starter conversion and starts well. I'm starting to feel good about local riding - anything less than 3-4 hours away.

Peter

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It's got a what? Pictures are demanded!

swooshdave said:

ptourin said:

It's got a starter conversion and starts well. I'm starting to feel good about local riding - anything less than 3-4 hours away.

Peter

Click to expand...

It's got a what? Pictures are demanded!

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Calm down, it's a MkIII !

Well, right on! I finally got the setscrew cleaned up so I could get the allen key into it - no problem loosening it - and the master cylinder adjustment was WAAAAYYYYY OFF - basically, screwed in as tight as possible. Tore it down, cleaned out the gunge, fitted the rebuild kit - no problem. So I'm hoping that I can just put it all back on the bike tomorrow night and I'll be a going concern again. So much for the shop guys saying, "I can't believe anyone would take that apart and change the factory setting" - there were a lot of things on this bike that were on the odd side - if only bikes could tell stories about their PO's...

Thanks - Peter

Peter, I have a '77 Mk3 and it had many issues that were previous owner related, but most were (as far as I can assume) factory / reciever related.
eg, cylinder to case machined so the cylinder leaned slightly forward, and a machined with a realy blunt tool.
the head was slightly machined to lean to the right, and done with the same blunt tool.
the clutch was 6mm outboard from lining up with the primary sprocket, the best I could get it was about 2mm, by removing the spacer behind the clutch basket and relieving the inner case.
I can only assume the last of them were put together with what ever parts were available? (reject parts bin?)

The previous owner stories would be nice to know, but I'd love to know the factory story in the last days.

graeme