99 front brake

At first glance, the operating arms are at less than 90 degrees. If so, you will never get correct leverage on the brake cams and hence poor braking.

My 99 has a standard SLS 8" brake and can squeal the tyre with a bit of a heave on the lever. Yours should be at least that good.

Also your lever pull is now divided into two brakes so total braking force is the same as for single brake. The only advantage with having two is to reduce brake fade since each side develops half the heat.

Hiyah Trevor - I used to use a home-made double-sided 8 inch sls front brake on a '62 650SS on the road and in Production Machine Class racing. I have to say in spite of what David points out, that it was a far better stopper than the standard Dommie 8 inch brake it replaced. Not only did it not fade but it could pull up on a sixpence ! One observation for you though - I found it performed better with the levers pointing forward and I don't believe it was only because of cable routing. I also agree with Gordon that the angle the cable makes with the lever when force is applied should always be less than 90 deg. I used the Amal double-pull lever set up as per Colin Seeley's double-sided brakes. I don't know if you've tried yours with the levers the other way round ? I've just rebuilt the bike so here's a snap. Good Luck, Howard

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Trevor - The levers, brake plate, shoes etc on mine are standard 8 inch, single-sided, Gold Star. The main difference with your set-up is that you have retained the torque stop into your fork sliders ( two right-hand ?) whilst I have had to use two separate torque arms from the cable adjuster pivot to the mudguard support holes in the sliders. I can send you the dimensions of the lever or send you a spare for you to measure as you wish. Another good pointer is make sure that you use cables with a substantial inner thickness (race spec). Some aftermarket ones are far too thin and will stretch. Good Luck, Howard

Previously howard_robinson wrote:

Trevor - The levers, brake plate, shoes etc on mine are standard 8 inch, single-sided, Gold Star. The main difference with your set-up is that you have retained the torque stop into your fork sliders ( two right-hand ?) whilst I have had to use two separate torque arms from the cable adjuster pivot to the mudguard support holes in the sliders. I can send you the dimensions of the lever or send you a spare for you to measure as you wish. Another good pointer is make sure that you use cables with a substantial inner thickness (race spec). Some aftermarket ones are far too thin and will stretch. Good Luck, Howard

Howard,

As I understand it you're saying that you have located your torque arms on the mudguard locating studs.

These studs are 1/4" dia' with a core dia' of about 3/16" and are more than likely mild steel, if they were to shear under braking you would be en route to an accident.

Is it likely that you've taken the precaution of enlarging the stud for a larger dia'high tensile one.

Regards, Ian.

Hello Ian - As you know the studs are 1/4 inch with 26 tpi Cycle threads at each end. I copied the torque arms arrangement and mountings from a double sided Seeley front brake that I bought from Gus Kuhn as an upgrade to the braking system for racing on my Commando. The studs are replaced with 1/4 inch 26 tpi cap-headed allen screws and I did the same on my 650SS . The Seeley forks on the drum-braked Seeleys also used the same mounting arrangement. There is absolutely no chance that the brake power could shear off those four 1/4 inch screws. I haven't measured the thread depth of a 26 tpi Cycle thread form but I expect that it's greater than 3/16 inch. Irrespective, I am living proof that they're strong enough - after all !!

Trev - I'll send dimensions of the lever at week-end. Bye, Howard

Previously howard_robinson wrote:

Hello Ian - As you know the studs are 1/4 inch with 26 tpi Cycle threads at each end. I copied the torque arms arrangement and mountings from a double sided Seeley front brake that I bought from Gus Kuhn as an upgrade to the braking system for racing on my Commando. The studs are replaced with 1/4 inch 26 tpi cap-headed allen screws and I did the same on my 650SS . The Seeley forks on the drum-braked Seeleys also used the same mounting arrangement. There is absolutely no chance that the brake power could shear off those four 1/4 inch screws. I haven't measured the thread depth of a 26 tpi Cycle thread form but I expect that it's greater than 3/16 inch. Irrespective, I am living proof that they're strong enough - after all !!

Trev - I'll send dimensions of the lever at week-end. Bye, Howard

Hello Howard,

Yes I do know that themudguard attachment studs in the fork sliders are 1/4", but the thread in the fork slider is 1/4" whitworth by 20TPI, the thread on the other end of the stud is1/4" bsf which just happens to be 26TPI but it isn't cycle because imperial threads have a 55 degree included angle between the flanks and cycle threads have a 60 degree angle the same as American and Unified. I have always understood that in soft or brittle metals such as brass oraluminium the rule is to always use a course thread.

Regards, Ian

You have missed the point. The studs,and the casting where they screw into the fork slider casting, and not strong enough for braking loads

Paul

Previously ian_hay wrote:

Previously howard_robinson wrote:

Hello Ian - As you know the studs are 1/4 inch with 26 tpi Cycle threads at each end. I copied the torque arms arrangement and mountings from a double sided Seeley front brake that I bought from Gus Kuhn as an upgrade to the braking system for racing on my Commando. The studs are replaced with 1/4 inch 26 tpi cap-headed allen screws and I did the same on my 650SS . The Seeley forks on the drum-braked Seeleys also used the same mounting arrangement. There is absolutely no chance that the brake power could shear off those four 1/4 inch screws. I haven't measured the thread depth of a 26 tpi Cycle thread form but I expect that it's greater than 3/16 inch. Irrespective, I am living proof that they're strong enough - after all !!

Trev - I'll send dimensions of the lever at week-end. Bye, Howard

Hello Howard,

Yes I do know that themudguard attachment studs in the fork sliders are 1/4", but the thread in the fork slider is 1/4" whitworth by 20TPI, the thread on the other end of the stud is1/4" bsf which just happens to be 26TPI but it isn't cycle because imperial threads have a 55 degree included angle between the flanks and cycle threads have a 60 degree angle the same as American and Unified. I have always understood that in soft or brittle metals such as brass oraluminium the rule is to always use a course thread.

Regards, Ian

I understand where you ar all coming from etc, but would just add that the AMC lower leg has the brake torque arm attached to it's guard mountings by both retaining nuts, they have used this arrangement for yrs, I understand there have been some calamities but these seem to be around the brake plate end when the mounting hole ovalates and weakens the surrounding structure causing it to break. kind regards

Previously ian_hay wrote:

Previously howard_robinson wrote:

Hello Ian - As you know the studs are 1/4 inch with 26 tpi Cycle threads at each end. I copied the torque arms arrangement and mountings from a double sided Seeley front brake that I bought from Gus Kuhn as an upgrade to the braking system for racing on my Commando. The studs are replaced with 1/4 inch 26 tpi cap-headed allen screws and I did the same on my 650SS . The Seeley forks on the drum-braked Seeleys also used the same mounting arrangement. There is absolutely no chance that the brake power could shear off those four 1/4 inch screws. I haven't measured the thread depth of a 26 tpi Cycle thread form but I expect that it's greater than 3/16 inch. Irrespective, I am living proof that they're strong enough - after all !!

Trev - I'll send dimensions of the lever at week-end. Bye, Howard

Hello Howard,

Yes I do know that themudguard attachment studs in the fork sliders are 1/4", but the thread in the fork slider is 1/4" whitworth by 20TPI, the thread on the other end of the stud is1/4" bsf which just happens to be 26TPI but it isn't cycle because imperial threads have a 55 degree included angle between the flanks and cycle threads have a 60 degree angle the same as American and Unified. I have always understood that in soft or brittle metals such as brass oraluminium the rule is to always use a course thread.

Regards, Ian

Ian - I am sorry to correct you but the thread in the fork slider is 26 tpi Cycle thread as I already said. As I have also already said this arrangement and sizes have been used for years in racing circles when riders adopted other front brakes to fit in the RH forks. Fontana's, Oldanis, Robinsons, Seeleys, Suzukis and Yamaha brakes all mounted the torque arms to these points. I cannot agree with you that the rule is always to use a course thread - as the Norton engineers did not !! Cheers, Howard

Previously howard_robinson wrote:

Previously ian_hay wrote:

Previously howard_robinson wrote:

Hello Ian - As you know the studs are 1/4 inch with 26 tpi Cycle threads at each end. I copied the torque arms arrangement and mountings from a double sided Seeley front brake that I bought from Gus Kuhn as an upgrade to the braking system for racing on my Commando. The studs are replaced with 1/4 inch 26 tpi cap-headed allen screws and I did the same on my 650SS . The Seeley forks on the drum-braked Seeleys also used the same mounting arrangement. There is absolutely no chance that the brake power could shear off those four 1/4 inch screws. I haven't measured the thread depth of a 26 tpi Cycle thread form but I expect that it's greater than 3/16 inch. Irrespective, I am living proof that they're strong enough - after all !!

Trev - I'll send dimensions of the lever at week-end. Bye, Howard

Hello Howard,

Yes I do know that themudguard attachment studs in the fork sliders are 1/4", but the thread in the fork slider is 1/4" whitworth by 20TPI, the thread on the other end of the stud is1/4" bsf which just happens to be 26TPI but it isn't cycle because imperial threads have a 55 degree included angle between the flanks and cycle threads have a 60 degree angle the same as American and Unified. I have always understood that in soft or brittle metals such as brass oraluminium the rule is to always use a course thread.

Regards, Ian

Ian - I am sorry to correct you but the thread in the fork slider is 26 tpi Cycle thread as I already said. As I have also already said this arrangement and sizes have been used for years in racing circles when riders adopted other front brakes to fit in the RH forks. Fontana's, Oldanis, Robinsons, Seeleys, Suzukis and Yamaha brakes all mounted the torque arms to these points. I cannot agree with you that the rule is always to use a course thread - as the Norton engineers did not !! Cheers, Howard

Hello Howard,

Don't be sorry because you can't correct me if I'm not wrong.

All Norton fork sliders that I have ever handled have, without fail,alwayshad a 1/4" Whitworth thread at the point we are referring to, and I've been involved with Norton motorcycles since 1954.

The stud has always been 1/4" dia', one end being Whitworth the other BSF, the BSF end I will agree is 26 TPI but this doesn't make it a cycle thread, because as I've already pointed out BSF threads have a 55 degree angle between the flanks and cycle threads, like American and Unified have a60 degree angle.

With regard to your reference to "racing circles", are you saying that for instance, a fork slider from a Manx Norton would have a fine 26 TPI thread while a road going Dommie would be as I've suggested.?

If you have any other non racing Nortons take the stud out from the slider and see what you've got, all of mine are Whit/BSF as are the Nortons of my friend and this includes his Commando.

I can't answer for Norton engineers or what they did, but after nearly a lifetime spentin precision engineering I know fine threads in "soft" materials were always frowned upon.

I tend to think that between the pair of us we're beginning to deviate from the original point of the post and might well get our knuckles rapped.

All the best to you, Ian.

Previously ian_hay wrote:

Previously howard_robinson wrote:

Previously ian_hay wrote:

Previously howard_robinson wrote:

Hello Ian - As you know the studs are 1/4 inch with 26 tpi Cycle threads at each end. I copied the torque arms arrangement and mountings from a double sided Seeley front brake that I bought from Gus Kuhn as an upgrade to the braking system for racing on my Commando. The studs are replaced with 1/4 inch 26 tpi cap-headed allen screws and I did the same on my 650SS . The Seeley forks on the drum-braked Seeleys also used the same mounting arrangement. There is absolutely no chance that the brake power could shear off those four 1/4 inch screws. I haven't measured the thread depth of a 26 tpi Cycle thread form but I expect that it's greater than 3/16 inch. Irrespective, I am living proof that they're strong enough - after all !!

Trev - I'll send dimensions of the lever at week-end. Bye, Howard

Hello Howard,

Yes I do know that themudguard attachment studs in the fork sliders are 1/4", but the thread in the fork slider is 1/4" whitworth by 20TPI, the thread on the other end of the stud is1/4" bsf which just happens to be 26TPI but it isn't cycle because imperial threads have a 55 degree included angle between the flanks and cycle threads have a 60 degree angle the same as American and Unified. I have always understood that in soft or brittle metals such as brass oraluminium the rule is to always use a course thread.

Regards, Ian

Ian - I am sorry to correct you but the thread in the fork slider is 26 tpi Cycle thread as I already said. As I have also already said this arrangement and sizes have been used for years in racing circles when riders adopted other front brakes to fit in the RH forks. Fontana's, Oldanis, Robinsons, Seeleys, Suzukis and Yamaha brakes all mounted the torque arms to these points. I cannot agree with you that the rule is always to use a course thread - as the Norton engineers did not !! Cheers, Howard

Hello Howard,

Don't be sorry because you can't correct me if I'm not wrong.

All Norton fork sliders that I have ever handled have, without fail,alwayshad a 1/4" Whitworth thread at the point we are referring to, and I've been involved with Norton motorcycles since 1954.

The stud has always been 1/4" dia', one end being Whitworth the other BSF, the BSF end I will agree is 26 TPI but this doesn't make it a cycle thread, because as I've already pointed out BSF threads have a 55 degree angle between the flanks and cycle threads, like American and Unified have a60 degree angle.

With regard to your reference to "racing circles", are you saying that for instance, a fork slider from a Manx Norton would have a fine 26 TPI thread while a road going Dommie would be as I've suggested.?

If you have any other non racing Nortons take the stud out from the slider and see what you've got, all of mine are Whit/BSF as are the Nortons of my friend and this includes his Commando.

I can't answer for Norton engineers or what they did, but after nearly a lifetime spentin precision engineering I know fine threads in "soft" materials were always frowned upon.

I tend to think that between the pair of us we're beginning to deviate from the original point of the post and might well get our knuckles rapped.

All the best to you, Ian.

Ian - Your quite correct in your assertion that we have deviated from the original thread however I do think that the thread form is an issue because other readers can be fed incorrect information. I too have had many sets of Roadholder forks over the years in long and short varieties. If you would care to visit the Andover Norton international website and Type in part T1085 "mudguard bridge /slider studs" you will see an image of said part and a description of the 26 tpi stud. T1085 is listed in all the parts lists for short RH forks up to 1967. Andover Norton pride themselves on using the actual Norton drawings and specifications so I think they can be trusted on this. I do have a late Mercury and did own a 69 commando and the slider bridge studs on both of these models was to the UNC/UNF thread form. ( !/4 UNC into the slider and 1/4 UNF nuts - part number 06.0356). Perhaps this has confused you ?

There will be a negligible difference on the shear force needed to break these four studs anyway irrespective of the thread form. So I think Paul, you and I should let Trev get on with his work improving his braking issues. Good night and goodbye, Howard