LF Harris T140 Master Cylinder for Commando MK3

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L.A.B. said:
Is it 13mm or standard 5/8"? As p400's problem was excessive pedal (, pushrod and piston) travel because the "one full turn and however much it takes to align the grub screw slot" procedure for setting the standard 5/8" master cylinder may not be enough for the 13mm cylinder as the piston/seal dimensions are different, therefore, the 13mm assembly could need an additional turn (or two?) although it is still extremely important that the bleed port should not be covered by the piston seal when the brake is released.
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Since my system was intact I just disconnected the hard line from the cylinder and blocked it off to stop the brake fluid from draining out. I then installed the new 1/2” cylinder and adjusted according to the Lockheed manual. I re-installed the master cylinder, added just enough brake fluid to cover the bottom. I then filled a syringe with brake fluid and forced the fluid from the caliper towards the master cylinder. Since the only air was in the master cylinder itself it bled very easily. I then bled the system the regular way.
I also had a lot of free play so I had to move the cylinder in farther. Be cautious with this adjustment.
Pete
 
Deets55 said:
new 1/2” cylinder
Click to expand...

Yes, there is also a 12.7mm, 1/2" cylinder with "a vented socket head cap screw" in place of the stud and feed port so not excacly the same as the Harris 13mm cylinder.
LF Harris T140 Master Cylinder for Commando MK3

"12.7 mm Triumph type master cylinder barrel assemblies are 100% brand new parts, so no exchange is needed:

99-2770/A is sold outright and suits all Lockheed equipped Triumph front applications. (While it will also fit rear Triumph as well as Norton 850 Mk3 rear master cylinders that had the removable plastic reservoir attached, due to the greater braking power we only recommend it for front Triumph to avoid rear wheel lockup.) These are made of anodized aluminum for durability and appearance, and have stronger construction than the original while still looking stock"
 
L.A.B. said:
snipped (While it will also fit rear Triumph as well as Norton 850 Mk3 rear master cylinders that had the removable plastic reservoir attached, due to the greater braking power we only recommend it for front Triumph to avoid rear wheel lockup.) snipped
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Les, do you recommend using the smaller bore master cylinders for the Mk III rear brake? Or do you agree with the recommendation above?

Charlie
 
chaztuna said:
Les, do you recommend using the smaller bore master cylinders for the Mk III rear brake? Or do you agree with the recommendation above?

Charlie
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I haven't used the 13mm as a rear brake master cylinder so I couldn't say.
 
chaztuna said:
Les, do you recommend using the smaller bore master cylinders for the Mk III rear brake? Or do you agree with the recommendation above?
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If you fit rearsets and so lose leverage with the shorter brake lever then it makes sense.
 
chaztuna said:
Les, do you recommend using the smaller bore master cylinders for the Mk III rear brake? Or do you agree with the recommendation above?

Charlie
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I fitted one and have been seriously underwhelmed! No quantum leap forward (or should that be back?) compared to slimming down the front master cylinder.
Will overhaul my caliper when the fancy takes me (parts are all there, but it WORKS so why rock the boat?).
My take is you can never have enough braking, more so if you ride two up or downhill a lot, but always try them out first to see if they'll bite you in an emergency. As with the throttle, the brake lever isn't an on/off switch :-)
 
EstuaryBoy said:
I fitted one and have been seriously underwhelmed! No quantum leap forward (or should that be back?) compared to slimming down the front master cylinder.
Will overhaul my caliper when the fancy takes me (parts are all there, but it WORKS so why rock the boat?).
My take is you can never have enough braking, more so if you ride two up or downhill a lot, but always try them out first to see if they'll bite you in an emergency. As with the throttle, the brake lever isn't an on/off switch :)
Click to expand...
Quite the claim of danger of locking up the rear wheel. I wish , might be fun.
 
EstuaryBoy said:
I fitted one and have been seriously underwhelmed! No quantum leap forward (or should that be back?) compared to slimming down the front master cylinder.
Will overhaul my caliper when the fancy takes me (parts are all there, but it WORKS so why rock the boat?).
My take is you can never have enough braking, more so if you ride two up or downhill a lot, but always try them out first to see if they'll bite you in an emergency. As with the throttle, the brake lever isn't an on/off switch :)
Click to expand...
As per the warning I quoted above, do you find it to easy to lock the rear brake? Does the smaller bore make it easier to modulate brake pressure? Or is there no noticeable difference? Why did you mention overhauling the caliper???
 
chaztuna said:
As per the warning I quoted above, do you find it to easy to lock the rear brake? Does the smaller bore make it easier to modulate brake pressure? Or is there no noticeable difference? Why did you mention overhauling the caliper???
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Its a balance between the diameter of the master cylinder bore and the caliper piston bores, you are aiming for 27:1 for best feel versus braking.
LF Harris T140 Master Cylinder for Commando MK3


Its not the only variable, the leverage of the pedal or handlebar lever also has an effect but that is not included in the table.
 
chaztuna said:
As per the warning I quoted above, do you find it to easy to lock the rear brake? Does the smaller bore make it easier to modulate brake pressure? Or is there no noticeable difference? Why did you mention overhauling the caliper???
Click to expand...
Not at all.... As mentioned, after the night/day difference that the smaller bore made to the front brake I was expecting/hoping for a noticeable difference with the rear.
To be honest I'd be hard pressed (braking pun!) to tell the difference.... Hence my wonder if my caliper could do with overhaul. Braided line, Ferodo platinum pads and new Roadrunner complete the picture...
Not in a hurry to do it yet though, as I made a conscious decision that unless there was danger of damage to either the bike or me, I would leave the spanners alone and just RIDE the damn thing, rather than run and pull everything apart at the slightest provocation :-)
 
"I would leave the spanners alone and just RIDE the damn thing, rather than run and pull everything apart at the slightest provocation"

Sounds like good advice in the general sense...
 
EstuaryBoy said:
Not at all.... As mentioned, after the night/day difference that the smaller bore made to the front brake I was expecting/hoping for a noticeable difference with the rear.
To be honest I'd be hard pressed (braking pun!) to tell the difference.... Hence my wonder if my caliper could do with overhaul. Braided line, Ferodo platinum pads and new Roadrunner complete the picture...
Not in a hurry to do it yet though, as I made a conscious decision that unless there was danger of damage to either the bike or me, I would leave the spanners alone and just RIDE the damn thing, rather than run and pull everything apart at the slightest provocation :)
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I've heard that termed "benign neglect". Have you noticed any difference in pedal travel?
 
Neglect?? Nooooo! Just prioritising why I bought it in the first place (great believer in: 'mechanical sympathy'). Pedal travel? Without a direct before/after comparison it would be hard to give an accurate answer, adding to the equation the fact that the rear lever isn't compromised by handlebar and the hand is a bit more sensitive than the size 10 boot!
 
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I'm rebuilding front and rear on a MkIII.

These brakes were in a crud laden, barn find condition and I have cleaned them with anything I can find to dissolve the old hardened fluid that laid in there for years. I plan to try using the existing cylinder, hope I don't have to pull it apart later and search for SS.
I just got the parts kit from Old Britts for the rear and all is going to plan so far. What I can't find is any mention to use or not use any sealant on the master cylinder threads. I'm ready to screw it back on. Any recommendations?
 
I fitted a 13mm rear cylinder kit from AN, if helpful their instructions read:

'Use Permatex or equivalent anti-seize compound sparingly between the male 25mm stainless steel threads on the master cylinder and the female 25mm aluminium threads of the parent housing. Also use anti-seize compound on the socket head cap screw at the bottom of the billet mount'

I assume the last refers to the grub screw?
 
Rondo said:
I'm rebuilding front and rear on a MkIII.

snipped What I can't find is any mention to use or not use any sealant on the master cylinder threads. I'm ready to screw it back on. Any recommendations?
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No sealant is needed on the threads of the front brake hose/master cylinder joint, as the sealing is done via the flare on the end of the hose and at the bottom of the threaded hole in the master cylinder housing. If there is no flare fitting, sealing will be done via a copper sealing washer, similar to the washer used on the brake light switch. That said, Estuary Boy's suggestion to apply anti seize to the threads is good. It will prevent the steel hose fitting from seizing to the housing. [dissimilar metal corrosion].
More info needed regarding the rear master. I would use anti seize on the threads between the steel barrel [#1F] of the rear master cylinder and the aluminum housing [#1B] it screws into, again to protect against dissimilar metal corrosion [aka galvanic corrosion]. For the steel line [#17] which screws into the back end of the rear master cylinder barrel, again, the bubble flare on the steel tube seals against the bottom of the threaded hole. Sealant on the threads here will accomplish nothing. If the bubble flare fitting fails, fluid would leak between the tube bolt fitting and the steel tube of #17. Application of anti seize to the threads of the tube bolt on the steel line is good practice, but not absolutely necessary. I also like to coat the steel tube section that passes through the center of the tube bolt. Doing so prevents the steel tube bolt from rusting to the steel line [that takes years].
Andover Norton refers to the actual master cylinder as the barrel [#1F], in the link below. The tube bolts are the fittings on item #17

Rear brake parts exploded view

The female fitting on line #19 is called a tube nut.
 
NB: My comments were a direct quote from ANs 13mm REAR cylinder fitting instructions (06.5776/13 assembly and separate 06.7247 barrel), recommending anti-seize on two places only....
 
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chaztuna said:
No sealant is needed on the threads of the front brake hose/master cylinder joint, as the sealing is done via the flare on the end of the hose and at the bottom of the threaded hole in the master cylinder housing. If there is no flare fitting, sealing will be done via a copper sealing washer, similar to the washer used on the brake light switch. That said, Estuary Boy's suggestion to apply anti seize to the threads is good. It will prevent the steel hose fitting from seizing to the housing. [dissimilar metal corrosion].
More info needed regarding the rear master. I would use anti seize on the threads between the steel barrel [#1F] of the rear master cylinder and the aluminum housing [#1B] it screws into, again to protect against dissimilar metal corrosion [aka galvanic corrosion]. For the steel line [#17] which screws into the back end of the rear master cylinder barrel, again, the bubble flare on the steel tube seals against the bottom of the threaded hole. Sealant on the threads here will accomplish nothing. If the bubble flare fitting fails, fluid would leak between the tube bolt fitting and the steel tube of #17. Application of anti seize to the threads of the tube bolt on the steel line is good practice, but not absolutely necessary. I also like to coat the steel tube section that passes through the center of the tube bolt. Doing so prevents the steel tube bolt from rusting to the steel line [that takes years].
Andover Norton refers to the actual master cylinder as the barrel [#1F], in the link below. The tube bolts are the fittings on item #17

Rear brake parts exploded view

The female fitting on line #19 is called a tube nut.
Click to expand...

As understand it, Rondo was referring to the rear master cylinder barrel assembly threads, not the hydraulic joint threads of either front or rear, so anti-seize.

Rondo said:
I just got the parts kit from Old Britts for the rear and all is going to plan so far. What I can't find is any mention to use or not use any sealant on the master cylinder threads. I'm ready to screw it back on.
Click to expand...
 
The latest master cylinders from LF Harris and some US supliers are not the same as those they supplied a couple of years back. The the new version does not fit as the piston is different. Not had time to look at the latest version in detail, but it needs to be screwed further so the set screw can sit on the flat. The problem is that as you screw it in to align the set screw you are operating the piston. It would be possible to assemble the brake on the bike with the master reservoir removed and monitor the piston to ensure it does not travel past a hole as the body is screwed in. You would need to do the same when adjusting the push rod.
I have tried both and didn't like the pedal travel and switched back to standard bore.
 
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