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#71161 - 09/09/07 2:14 am Rear brake still weak  
Joined: May 2007
Posts: 97
rickt Offline
BritBike Forum member
rickt  Offline
BritBike Forum member

Joined: May 2007
Posts: 97
Woodbury, MN
I've been unable to determine the cause of a weak rear brake on my '75 Commando.

I installed a stainless line and bled the system again. Stops fine when spinning the rear wheel with the bike on its center stand, but still no respectable stopping power on the highway. I've ordered rebuild kits for the MC and the caliper, but I don't think either is defective. The pads have less than 500 mi. on them. I checked the thickness of the disk - 0.238 in. The shop manual indicates that the rear disk should be 0.260/0.250 in. I had both front and rear disks trued and lightened at Old Britts, but I can't imagine that the disk is too thin now to work properly.

Is this assumption wrong???

rickt


rickt

'74 Trident
'75 Roadster
'82 BMW R65LS
'87 BMW K75C
'78 Suzuki GS750
'10 Yamaha FJR 1300
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#71162 - 09/09/07 3:44 am Re: Rear brake still weak  
Joined: Feb 2004
Posts: 1,956
norbsa48503 Offline
BritBike Forum member
norbsa48503  Offline
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Joined: Feb 2004
Posts: 1,956
Flint,Mich
Disk thickness is not the problem. You are moving a very small amount of fluid and the braking effect felt will only be as good as the weakest parts pushing the fluid. Fluid does not compress rubber parts do. You need to revisit the seal insulation sounds like one is backwards?


norbsa
1960 TR6
1963 Super Rocket
1965 650 Star
1966 441
1968 Thunderbolt
1969 Twinkle 250
1972 Fastback
1974 Roadster
1970 S.S
Way too many BSA's not named
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#71163 - 09/09/07 2:50 pm Re: Rear brake still weak  
Joined: May 2007
Posts: 97
rickt Offline
BritBike Forum member
rickt  Offline
BritBike Forum member

Joined: May 2007
Posts: 97
Woodbury, MN
norbsa,

Thanks for the information. When the kit arrives, I'll disassemble the MC and check things out.

rickt


rickt

'74 Trident
'75 Roadster
'82 BMW R65LS
'87 BMW K75C
'78 Suzuki GS750
'10 Yamaha FJR 1300
#71164 - 09/12/07 2:58 pm Re: Rear brake still weak  
Joined: Mar 2006
Posts: 226
injunmort Offline
BritBike Forum member
injunmort  Offline
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Joined: Mar 2006
Posts: 226
sugarloaf ny
fwiw, i experienced the same on my commando rebuild, could not find any leaks all rubber renewed, brakes bled and would work in shop, barely enough to feel any resistance on road. turned out to be the brake line coupling was not seated in caliper fully and was leaking through the treads. could not see any fluid as barely any came thru but i guess enough under pressure to assure the brake would not work properly. cleaned out treads and re tightened, bled the system and now will lock up rear wheel.


1948 indian chief
1937, 1939, 1962 norton es2
1950 triumph trw
1970 triumph bonneville
1975 norton commando
1972 bmw r75/5
various projects
#71165 - 10/11/07 12:52 pm Re: Rear brake still weak  
Joined: Dec 2002
Posts: 706
beltdriveman Offline
BritBike Forum
beltdriveman  Offline
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Joined: Dec 2002
Posts: 706
Dont suppose anyone has considered they might have pads with a low Coefficient of Friction value fitted.....Halve the Cof F value and you halve the braking effect.....
Ferodo made for Norton several different pads employing different material with different C of F values The pads are marked with the material number on the side of the friction material. I know of one British spares emporium with some of these still in stock.
2424F A high friction material
2430F A medium low friction material.
Later pads were made by Ferodo using 2453 material for which I, with a few 2424F ones in my loft didnt bother to enquire as to its C of F values.... As only the 2424F and 2430F ones came out of Nortons at the close as loose unboxed pads in a steel bin (which I sorted) I assume the 2453 ones were made long after Norton closed. It was the different numbers that had me ask Ferodo why they were different...and thus i found out something I hadnt known before!... As I understand it the Ferodo boxes would of been marked marked FB88M or FB88H but I have NO idea(or care) if H = HIGH friction and M = MEDIUM friction or whether one was for plain cast iron discs or the other for what Norton called chromed discs with its lower C of F value compared to plain cast iron.( My local hard chromers who de chromed a few new rust pitted chrome discs for me said that in their opinion they had merely passed through the same town as the chrome works....they were NOT impressed with the chroming quality.)
So what is the frictional value of the pads you are using? Did you run them in as per the instruction sheet?
Once phoned a British company supplying new Commando pads they were having produced inn the Far East.. I asked what their C of F value was. I was told it replicated the material used by Norton. When I asked whether that was the high or the medium /low C of F material they were refering to the phone was put down.. Have NEVER used that British company ever since. They I doubt even knew what Coefficient of Friction meant.
Woulnt suprise me if lots of people moaning about the Commando front brake had the wrong pads fitted..along with forgetting that it was designed to replicate the braking power of the twin leader(which would lock up the front wheel) but to do so without the problem of fade as suffered with the drum brake after a couple of heavy applications. ...
Just a thought as no one else had raised it.....

#71166 - 10/11/07 1:34 pm Re: Rear brake still weak  
Joined: Aug 2007
Posts: 221
Jim Clausen Offline
BritBike Forum member
Jim Clausen  Offline
BritBike Forum member

Joined: Aug 2007
Posts: 221
Port St. John, FL USA
For any brake issues on a Norton contact http://www.vintagebrake.com/ . Mike Morris (Vintage Brake) is a one man show in Sonoma, California. He knows brakes! You'll never be sorry about any money you spent with him. I had a lazy rear drum brake on my 72 Commando. I tried everthing I knew to fix it with no results. Sent the brake to Vintage Brake and got back an excellent stopper.

I have no experience with a Norton rear disc brake, but if it's anything like the front disc stopper the master cylinder is WAY too big. I found that a 11mm master cyclinder with a Grimeca 2P caliper is an excellent stopper for the front. With this setup I have a ratio of about 27:1. It's all about the ratio of master cylinder piston area to caliper piston area. .

#71167 - 10/12/07 7:53 pm Re: Rear brake still weak  
Joined: Dec 2002
Posts: 706
beltdriveman Offline
BritBike Forum
beltdriveman  Offline
BritBike Forum

Joined: Dec 2002
Posts: 706
Of course also in my loft there was once a big box filled with ex Norton stock 7 inch rear brake Ferodo green racing AM4 lining.nfortunately a friend keps borrowing a few on a regular basis for vintage race bike front brakes.... Oh Uncle Sid of MCE.. please come back with that big steel bin full of them so I can replace them!!! Dont suppose many remember the celler full to overflowing with very cheap Combat crankcases.. new RH6 heads still in boxes... complete Commando wheels... front and rear hubs... twin leader front brake plates complete with cams stiffening kits etc etc.... Happy days. New PROPER (Ransom and Marles 6MRJA30)superblend bearings...1.50 each.. there were two boxes amoung the hundreds of boxes full of 8MRJA30 ones and no one knew the difference between the 6 and 8 ones so i bought the two boxes..8 per box.... Friends have borrowed most of them as well! Yet another loss leader.

A few average values given in the Ferodo data sheets The AM series were oft used for our British bike drum brakes.
AM1..0.35 at low temps reducing after 200C.
AM2..0.40 at temps 0-300C, reduces at higher temps
AM3..0.38 ish up to 250C, reduces at higher temps
AM4.. the good olde green 'racing lining....0.44 up to say 250C reducing to 0.4 by about 380C. Bloody lethal when damp and bumping the bike first thing in the morning.Put the front brake on when still side saddle and one could easily end up in a heap especially on a wet road in Derby Square at 5 am about to ride up to The Bungalow to walk out round the the Les Graham memorial hut at Bungalow Bridge for a bit of MGP early morning practice and sheep chasing(to get them out of the road!!)... Been there seen it got the T shirt but not the scars anymore.!!Well not those scars anyway.
Assuming modern friction material manufacturers use the same test and safety factor criteria for their listed C of Fs I suspect there will be non asbestos materials now available giving higher C of F values BUT from what I hear from people working in the friction industry these non asbestos materials are a lot more agressive resulting in greater wear rates to drums and discs. Once mentioned this to my car servicing guy and he said something like ' Yes not that many years ago it was a once or twice, at most, a month event to have to change discs but we now do it several times a week. Guys in the crane and lift industry moan a tad and thats being polite...... Some even dare to suggest that in a few years modern 'safer' friction materials will be found to be more dangerous to health than asbestos!! A friends Father died of asbestosis... of course as he was boiler lagging warships in Chatham dockyards during WW2 and after with asbestos..... I bet he was told asbestos was perfectly safe .... 'it gets caught in you nose and lung hairs and you cough it out'.... Gosh I seem to remember something similar being said at Crompton Parkinson regarding mica dust as one undercut the mica seperators beteewn the commutator bars of DC motors/generators as I served my apprenticeship.... is that why I have a fresh pretty 9 inch scar ( slightly inverted 'v') on my belly now I wonder???
A BIG increase in braking with drum brakes could be obtained simply by fitting new oversize linings and correctly machining them to suit the freshly skimmed drum. Ever looked at the positions of drum brake brake levers on peoples bikes in Classic Bike. I was taught that they should be coming up to right angles when fully applied NOT well past right angles as many are even before operating the lever!! Or was I taught wrong?
No spell etc checks.

#71168 - 11/08/07 10:03 am Re: Rear brake still weak  
Joined: Oct 2007
Posts: 722
norton bob Offline
BritBike Forum member
norton bob  Offline
BritBike Forum member

Joined: Oct 2007
Posts: 722
bromley uk
Hi --I had my sls drum fittd with o/s linings and turned on lathe, vast improvement,interesting that the specialist said the sls was a far better brake than the tls .We have both,and they are about equal.

#71169 - 11/08/07 1:19 pm Re: Rear brake still weak  
Joined: Dec 2006
Posts: 76
mitchp Offline
BritBike Forum member
mitchp  Offline
BritBike Forum member

Joined: Dec 2006
Posts: 76
UK
Quote:
Originally posted by beltdriveman:
....Ever looked at the positions of drum brake brake levers on peoples bikes in Classic Bike. I was taught that they should be coming up to right angles when fully applied NOT well past right angles as many are even before operating the lever!!
Absolutely spot-on. Correct set-up of the cable to lever geometry makes an astonishing difference to the performance of the tls brake on my 1970 BMW R75/5, and application of the same principles plus attention to the cable gave a big improvement on the rear brake of my 850 MkIIA.

Quote:
Originally posted by beltdriveman:
....Bloody lethal when damp...first thing in the morning.....
As is (and always has been) the front brake of my R75 (original BMW shoes & linings). On a damp morning it locks solid at the slightest touch until it has been applied three or four times, making the first 50 yds a series of tyre-screeching hops. From then on, it's the best tls brake I've ever used. I know this isn't a question about a Norton, but can anyone (BDM?) explain why this happens?

Thanks

Mitch


Minds are like parachutes - they only work when they are open.
#71170 - 11/08/07 8:23 pm Re: Rear brake still weak  
Joined: Dec 2002
Posts: 706
beltdriveman Offline
BritBike Forum
beltdriveman  Offline
BritBike Forum

Joined: Dec 2002
Posts: 706
I have NO idea why drum brakes should work so well on first application on damp cold mornings!!
Guess would be the C of F acting between the friction material and liner is greater due to the lower temp on first application.
Asked a clutch designer and a friction material Co. gent and neither knew. Dont suppose either has ended up on top of a bike as one bumped it down hill side saddle on a wet Manx morning, put on the brake and ended up in a heap....Only did it the once. Quick learner in those days.

#71171 - 11/08/07 10:59 pm Re: Rear brake still weak  
Joined: Apr 2006
Posts: 1,393
johnm Offline
BritBike Forum member
johnm  Offline
BritBike Forum member

Joined: Apr 2006
Posts: 1,393
New Zealand
Yes to the BMW front brake locking first thing in the day!!!

A mate loaned me his R60 (I think) one morning to go to the shop 200 m down the load. Damn near fell off 3 times. Most memorable brake in 39 years!!


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