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Front brake

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My Mk3 Commando has a sleeved down master cylinder, braided Goodrich pipes, AP racing caliper and an RGM 11 inch floating disc but the brakes are only adequate even by comparison to a friends bike with none of the above. The pads have plenty of meat on them. I can only assume that its the pads. Can anyone recommend good pads for this caliper that may give better braking?

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Evening Tim

The choice of your fitted components is not optimal. A sleeved master cylinder will improve the brake using the standard caliper which has a piston size of 1.75" The hydraulic ratio is 11.67 to 1

The standard master cylinder to standard caliper ratio is 7.86 to 1 so you can see how much the sleeved master cylinder improves matters.

Does the goodridge hose run all the way from the master cylinder to the caliper? No hard pipe between the yokes and round the fork leg? The standard set up with the two lengths of bundy tube has little to no flex and is as good as a full goodridge set up. I.E. No gain!  

The AP racing caliper has a piston size of 1.625" so negating some of the advantages of the sleeved down master cylinder. Its hydraulic ratio is 10.072 to 1  that's taking the sleeved master cylinder is 13mm dia. Its all to do with the ratio of mastercylinder to caliper piston size. The pad area of the AP caliper is greater. Try SBS or AP racing pads in the AP caliper. Failing that, go back to the standard caliper with AP racing pads from AN (standard organic formula) and sell the AP caliper and disc.

 

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Tim

here,s a useful chart from the Vintage Brake website. Good info and advice similar to your problem. 

http://vintagebrake.com/mastercylinder.htm

Standard Commando 1.75" piston is 44.45mm so use the 44mm (2) figures for both pistons. Based on Peter,s figures, looks like your 1.625"~ 41mm (2) calliper with a 13mm master cylinder gives a 19.89:1 ratio. Worse than a standard calliper and 13mm. Probably needs 11mm bore for optimum 27:1+.

My twin standard calliper setup still uses the original 5/8" master cylinder to give a ratio of 30.72:1 Higher than he states but perfect in use with excellent feel and plenty of lever travel. Ferodo Platinum FDP88 pads by far the best with my 276mm stainless floating discs. 

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I went for a 12.7mm bore based on the Vintage Brake recommendations on Neil's link. I made my own alloy sleeve and modified a 12.7mm shaft with seals to get the seal and relief area's in the same position as the original. That gives me a ratio of 25.5 with Brembo P30/34 4 piston caliper.

I have attached a drawing of the original shaft and of the ratio chart as it may disappear soon.

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Hi Tim,

I have just fitted the same setup to a Mk3 project but find the lever comes back to the bars if squeezed hard enough, is your lever travel similar? I have almost the same setup on my Mk2 except it has a AP 5/8 master cylinder and that works very well. I`m thinking the sleeved down master cylinder doesn`t suit the AP caliper and might try switching back to a standard unsleeved unit on the Mk3. As previously posted, a sleeved master cylinder seems to work well on a standard caliper and a standard master cylinder works well with a twin disc setup.

Best regards, Al.

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Thanks everyone. Of course once you have sleeved down a master cylinder you can't unsleeve it! A modification ensures that the lever doesn't pull right back. I have a solid brake pipe to the lower yoke then a Goodrich hose  to the caliper. The back brake has an AP caliper on a standard disc and is excellent, so I still have pretty good braking. Before making a major change I will look at levers and pads. 

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My sleeves are reversible, held in by loctite and a grub screw and the alloy insert can be pulled out and replaced with a new sleeve with or without a change in ID. 

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I have a similar issue with my Mk111.It came to me with a big front disc,Gremica caliper,braided hose and standard master cylinder fitted with a rather long brake lever. You needed hands the size of shovels and an iron grip to get the brake to do anything.I have since fitted a 13mm master cylinder,the lever travel is ok now but the brake is still poor.Any suggestions as to what to do next please?

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Bleed the system until you can guarantee all the air is removed.  Make sure the pistons are not hanging up in the caliper, this gives all the symptoms of air in the system. Especially when aftermarket pistons are fitted with the wrong surface finish. This can also happen to modern bikes that have not been used regularly. Change of pads next, i don't know what the availability of different type of pads is for the grimeca caliper but try and get better ones.

report back if still a bother

 

 

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With the Mk3 using 13mm MC you should be able to get the lever to stop about 1'' from the grip. Look at the standard caliper which was designed for pre-MK3 and all becomes clear. It also helps to use freshly purchased brake fluid as well. 

The ideal system would be a standard caliper with 12''disc using 13mm master cylinder, some say this would cook standard pads but I doubt it.

The standard bore master cylinders are still available, most are used by racers using twin discs. 

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My preference is for the RGM sleeve kit (i,ve done quite a few of these) as you can adjust the piston pusher to suit your handle bar lever and 'dial it in' to maximise fluid travel whilst still allowing the fluid to return to the reservoir. Wish we could fit a 12" disc with the standard caliper. May be AN could market a modified fork leg to move the std caliper upwards to allow the bigger disc, please? I dislike the adaptor plates that are used to mount different calipers.

I would buy one tomorrow if they did....

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Peter, tell Joe, though he may try and sell you his conversion kit. Had the standard caliper existed, also designed by Lockheed, when the proddy racer was conceived, they would have used the standard caliper on the larger 11.5'' disc and not the 2195 or 2696 calipers. 

Some say, with absolutely no evidence, that running a standard caliper at 12'' would cook the pads. 

I have looked at several conversions, complex, expensive and ugly. There was a very good cheap solution using the standard disc, but the calipers are no longer made. Sadly the people who could have promoted it didn't, a missed chance as it would be the norm today. There are at least one club member using this caliper and I have seen it on another Commando. 

 

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To answer Tim's question -

The APLMP123 is a good pad for the road. Anyone riding on the road with 2195 or 2696 fitted should use a road pad. 

Race pads tend to start to function at high speed, ie the speed most road bikes will start to break the speed limit. 

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Thanks for the advice.I have bled the brakes and have a good firm lever.The pistons move freely.Also I centered the caliper on the disc by spacing it away from the fork leg very slightly.I have no idea what make the pads are,they appear unworn but I will try a new set.

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... to centre the caliper? Surely the pistons will automatically hold the pads at the correct equal distance?

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To be honest I’m not sure if the caliper actually needed centering ,it just looked wrong to me sat off to one side.New brake pads on order,hopefully some improvement to come when they arrive.

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Front brake Master cylinder options

As posted December 2021.

Just a note for any potential electric start conversions - see end Note.

My 1978 late production run Commando Mk3 is one of the last 300 made.

R/H switch gear was updated for this year and used Andover Norton part number:

12 - switch r.h., ES (60.7328) (06.5929)

in stock part-no: 60.7462

 

This is the exact same switch gear that was used for the Triumph T140e (1979-1983). Andover Norton part number:

18B (E-Start Models) switch r.h., ES (60.7328) (06.5929)

in stock-part-no: 60.7462

 

The 13mm bore size updated replacement unit for the Norton is expensive, but it will improve brake performance and it will also maintain the original look of the standard 5/8” bore size unit. Andover Norton part number:

7B (13mm gloss black)

FRONT MASTER CYLINDER ASSEMBLY C/W LEVER 850mk3 (13mm bore) PAINTED GLOSS BLACK

in stock part-no: 06.5742/13/1   £319.14

 

Interestingly Andover Norton offer both a complete unit, as above but also a full body unit for non Mk3 Commandos at a reduced price:

8 (13mm Conversion Kit)

FRONT MASTER CYLINDER BODY C/W MIRROR MOUNT (13MM BORE) C/W INTERNALS 

in stock- part-no: 06.1939/13  £239.70

 

So instead of reviewing replacement master cylinders for the Norton, I looked at what was available for the Triumph.

 

The standard Triumph T140e Master cylinder is a 13mm bore size, this is an Andover Norton part and fits directly onto my Commando switch gear.

Andover Norton part number:

1 master cylinder assembly

in stock- part-no: 60.7163    £249.12

I purchased this unit from Classicbikeshop LTD for £165

 

So the new units bolts straight on. 

It is a standard Andover Norton part and was half the price.

Note

Any conversions of pre Mk3 Commandos to electric start may well end up with the latest switch gear (as standard on my Commando).

So consider your master cylinder options at the same time.

The action is solid and instant compared to other set ups and the bleeding of the system was easy. The lever on the master cylinder is an exact match to my original clutch lever.

 


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