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Ex Police Interpol - brake on which side?

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Ex Police Interpol - brake on which side?

Posted by paul_smith at November 07. 2018

Hi all,

 

I have a new project and a simple question - I think...

 

Which side does the disk sit?

It a '74 ex Police Interpol - when I picked it up a month a go the brake calliper mounts are on the left leg with the capiller sitting in front of the leg.

When I look at various photos of Mk 2A's I see them on either side - is there a right or wrong side - does it matter at all?

Thanks - Paul.

Re: Ex Police Interpol - brake on which side?

Posted by andrew_mackenzie at November 07. 2018

Paul,

All disc braked Commandos prior to the Mk3 Electric Start model had the brake caliper mounted behind the right hand fork slider.  That configuration was no different on the Interpols. Consequently, if you have a pre-Mk3 bike and the brake caliper is on the left front, a previous owner has altered it.

There have been various explanations as to why Norton revised the caliper location for the Mk3, which I am sure others on this site can elaborate on.

Regards,

Andy

Re: Ex Police Interpol - brake on which side?

Posted by richard_payne at November 07. 2018

It may even have been the original owners who did it ! This photograph was on eBay recently. It shows three Interpols from Lanarkshire Constabulary. GYS 651N clearly has a rear drum so presumably a 2A? It has the front disc on the left though, as does GYS 650N. The latter may have survived as DVLA have a record up to 1991 but poor old GYS 650N hasn't been taxed since 1978...They are both listed as first registered 1/1/1975 which was after the first Mk3s had been built.

 

I have seen front hubs with a circlip bearing retainer as per Mk3 but lacking the radial groove that they usually have, which makes me wonder if late Mk2s had them too - but of course it would have meant swapping brake lines etc. Perhaps these were late deliveries of contracted machines and they were fitted with Mk3 parts from the production line ?

 

Whatever the reason, the Police workshops haven't swapped the 'M' plated bike over.

Attachments

Re: Ex Police Interpol - brake on which side?

Posted by colin_cheney at November 08. 2018

Dear Paul,

From my understanding, the brake disc and calliper were frequently swapped from the front of the left fork to the rear of the right fork on a Mk.III Commando so that the calliper, when behind the fork leg, was less prone to increasing fork dive when braking [leading to claims of better handling].  Some modern bicycle manufaturers have adopted this change of design function for V-type brakes where the machine has a suspension fork.

I did try both arrangements [brake on the right, brake on the left] and found that whilst 'behind the fork leg' did reduce fork dive, it really didn't affect the steering because my machine has always pulled to the left with hands off, just like my twin-disc BMW machines. 

I can't really comment on Mk.II machines or originality, but have you tried contacting the club for ex-service machines?

Regards,

Colin.

Re: Ex Police Interpol - brake on which side?

Posted by paul_smith at November 08. 2018

Guys,

 

Thanks for all the information and a great photo.

I'll get the spanners out!

Paul.

Re: Ex Police Interpol - brake on which side?

Posted by julian_wells at November 09. 2018

I'm at a loss to understand the reasoning here: fork dive is a result of weight transfer under braking; this can be counteracted with appropriate design of leading-link forks, but not with telescopics.

Previously colin_cheney wrote:

Dear Paul,

From my understanding, the brake disc and calliper were frequently swapped from the front of the left fork to the rear of the right fork on a Mk.III Commando so that the calliper, when behind the fork leg, was less prone to increasing fork dive when braking

Re: Ex Police Interpol - brake on which side?

Posted by john_holmes at November 09. 2018

According to the NOC notes the caliper right to left change was to cure a tendency for the bike to wander off to one side of you took your hands off the handlebars. I had that but cured it by a new rear tyre, proper wheel alignment and something else that escapes me.

I reduced brake dive by fitting Show a 20mms shim cartridges to the front forks, they give high damping at slow fork deflection e.g. Braking and low damping with high speed fork deflection e.g. Pothole.

Re: Ex Police Interpol - brake on which side?

Posted by peter_merrick1 at November 15. 2018

Hi Paul.

I have an Ex police 750 Combat Interpol, engine no. 208XXX with a delivery date to Hampshire constabulary of 23rd November 1973.

I've been in touch with a chap who has a lot, but not all, the records of the Hampshire constabulary vehicles. The pictures he sent me of the various bikes in their fleet all have the front brake caliper on the Near Side fork leg in front of the staunchon. Was this a specification requested from police departments?

I have put the bike back into civilian clothing but keeping the front brake on the near side, as I found it. I find the low level exhaust system extremely useful when fitting panniers. The handling is as you would expect from a well set up Norton, Fine!

Hope this helps.

Peter

Re: Ex Police Interpol - brake on which side?

Posted by richard_payne at November 15. 2018

Somewhere in the depths of my memory, I recall reading something about the calipers at the rear picking up more dirt, resulting in increased pad wear with the risk of them being ejected.  At one point they fitted the caliper with a small scraper.

Police bikes of course were heavily loaded and being used all day every day in all weather conditions. Could it be that if there had been incidents of pad ejection, there was a general circular recommending swapping the legs round ?

Re: Ex Police Interpol - brake on which side?

Posted by julian_wells at November 16. 2018

This doesn't sound likely; to escape between the calliper and disc the pads would have to have worn through the friction material and a slice of the metal backing (but of course once the friction material is gone there would be a rather obvious lack of braking power).

 

Previously richard_payne wrote:

Somewhere in the depths of my memory, I recall reading something about the calipers at the rear picking up more dirt, resulting in increased pad wear with the risk of them being ejected.  At one point they fitted the caliper with a small scraper.

Police bikes of course were heavily loaded and being used all day every day in all weather conditions. Could it be that if there had been incidents of pad ejection, there was a general circular recommending swapping the legs round ?

Re: Ex Police Interpol - brake on which side?

Posted by sam_milner at November 17. 2018

It might not sound likely to you, but it actually happened to me.

Many years ago, with a newish purchase I hadn't checked the pads.

I felts the pad/pads eject and the caliper pistons actuate against the disc.

Luckily I got away with it.

sam

Re: Ex Police Interpol - brake on which side?

Posted by julian_wells at November 21. 2018

Hmmm … It's hard to argue with experience. Was the disc much worn, by any chance?

 

Previously sam_milner wrote:

It might not sound likely to you, but it actually happened to me.

Many years ago, with a newish purchase I hadn't checked the pads.

I felts the pad/pads eject and the caliper pistons actuate against the disc.

Luckily I got away with it.

sam

Re: Ex Police Interpol - brake on which side?

Posted by sam_milner at November 22. 2018

No the disc and caliper pistons were ok, I just put new pads in and it went back to being normal.

At the time it happened I was only at low speed , maybe 20mph, I just got lucky really.

sam

Re: Ex Police Interpol - brake on which side?

Posted by ian_cordes at November 22. 2018

The odd one out is the Proddie Racer, which had it's Lockheed caliper on the right-hand fork leg in front of the slider. Just thought i would mention it for the record!Laughing

Re: Ex Police Interpol - brake on which side?

Posted by peter_stowe at December 03. 2018

Iv just read on a moto gp site that calipers a at the rear of the fork leg to put them more in line with the steering axis, thus lowering the rotational moment if inertia about that axis.

Re: Ex Police Interpol - brake on which side?

Posted by john_holmes at December 04. 2018

Previously richard_payne wrote:

Somewhere in the depths of my memory, I recall reading something about the calipers at the rear picking up more dirt, resulting in increased pad wear with the risk of them being ejected.  At one point they fitted the caliper with a small scraper.

Police bikes of course were heavily loaded and being used all day every day in all weather conditions. Could it be that if there had been incidents of pad ejection, there was a general circular recommending swapping the legs round ?

My MK2a has the scraper and it was a factory fitment introduced prior to the MK3 so must be for another reason.

Re: Ex Police Interpol - brake on which side?

Posted by julian_wells at Friday 20:50

That has always been my take on the subject; back in the day I had a Fastback with a genuine Norvil PR brake, and it seemed happier after I swapped it from right to left.

 

Previously peter_stowe wrote:

Iv just read on a moto gp site that calipers a at the rear of the fork leg to put them more in line with the steering axis, thus lowering the rotational moment if inertia about that axis.

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