[AJS&M] Front Brake Cover Plate Alignment (2024)

#55535

Hi Dick,

Thanks for your comments and advice. The issue may well be a build-up of tolerances like you say but that is what the adjuster nut is there for - to take out the build-up.

My shoes look to be pretty flat with the cover plate and have minimal clearance. From a design perspective having shoes inside the drum would not cause problems for disassembly as you would simply have to slacken the brake cable right off and the shoes would return to their min diameter and clear the drum.

The bike is a 'new to me, 1st time strip and assemble'. I think the bike before I brought it was originally intended by the previous owner(s) to be on the road and then it got converted somewhere to a 'show bike'. My goal is to have a road worthy running bike - even though I won't be doing any long trips on it. Because of its checkered history I really have to take the bike all apart and see what I have, what is missing, etc. I have never worked on an old bike before - except when I polished the petrol tank of my dad's A10.

The only other thing I thought strange on reassembly was the fit of the new (replacement) seals on the spindle. There were a very gentle push fit whereas the similar new seals on the rear wheel spindle were very tight. Perhaps the spindle go modified in some way before the bearings were fitted in the hub.

Packing the hub with some washers would require the outer races to be pressed back through the hub and I don't really have the facilities to do that. May cause more problems than its worth. My only other thought was to recess the adjuster nut slightly so that it would screw further along the spindle into the hub - but I would lose thread depth of course. But its not a heavily loaded nut and not too critical if it failed.

Cheers.

Tim

---In Ajsmatchless@..., wrote :

Hi Tim: Yes, quite strange. I went looking for a 50s SpringTwin Instruction manual without success. I did look at several 50s G9 manuals and saw the lack of a seal cup on the brake drum side. Your assembly order is exactly as specified. It may well be possible that what we are seeing is the normal consequence of “tolerance stack-up” where a bit here and a bit there equal a small hiccup. Plumstead did not build Swiss watches.

Is this a ‘new to you 1st time assembly’ or a strip, service and re-assembly?

It sounds to me as if the lip on the brake backing plate enters the groove on the edge of the drum, creating the desired Labyrinth-Seal. Looking at several photos I have, and saw that the brake shoes ride a bit proud of the backing plate surface, and hence, “most” the friction material will protrude inside the drum, and the brake should function properly.

Quickly moving into theoretical: Any part of the friction NOT running on the drum is lost braking. Taking this for granted, I can see where an designer might give up a small percentage of braking efficiency to avoid designing a brake that would allow a shoe to wear a groove in the drum and create disassembly problems in the future.

Were it my bike: IF I was satisfied the Labyrinth-Seal is sufficient to keep out small bits of rock and sand, I’d assemble the brake, clamp the front brake on hard to center the shoes (temporarily secure handlebar lever with Bungie), tighten the outer nut(s), and be done with it.

If I had access to an extra washer or two (11913) I might disassemble the bearing pack and add one or two to the brake drum side. From memory, these washers are about 0.040” (1mm) thick.

Best wishes for your project… and the New Year. And please let us all now how you proceed.

Ciao,

Dick Casey

On Jan 4, 2018, at 6:38 AM, Tim Deaves deaves.tim@... [Ajsmatchless] <Ajsmatchless@...> wrote:

Hi Dick,

Yes, pretty much. The brake plate has a chrome cover to it. This covers wraps around the brake plate on the cover's circumference. This lip extends into a similar groove in the circumference of the brake drum. This lip and groove forms a sort of seal to keep debris out of the drum - so you can't actually see the shoes. If the chrome cover was not there, then you could. My original illustration with the ruler shows mimics the brake plate being positioned on the drum. The adjuster nut should not be so far proud of the straight edge. The amount the nut protrudes is going to be equal to the gap between the edge of the drum and the brake plate.

By the way. I did answer you previous email last night about the order of the parts and a view of the other side. See below. I don't think it made it to the Forum. Could be the photos were too big. Who knows.

Hi Dick,

Here are a couple of photos;

1. The parts cleaned and ready for reassembly - except the seals are the old seals. So the order of parts on the circlip side are,

Circlip

Flat plain washer

Spacer around the oil seal and oil seal

Flat plain washer

Bearing. I know it was the bearing as I could see some numbers stamped on the side of it.

All washers were checked for flatness, etc. before reassembly. The spacer was the same thickness as the seal..

(This is a one of many photos I have for a website I am building showing the fun and games with this particular bike).

2. The other side of the hub showing the adjuster and lock ring (secured). You can just see the steel oil seal cup around the spindle. All looks good to me.

I did find an exploded view of later front hub that shows that there is an oil seal cup on both sides. (Fig 33 on page 65 of a 1950 Springtwin Instruction Book). But if I put a cup on the circlip side, that will cause the spindle to poke further out - once I press the outer bearings through the hub. I want the spindle to go the other way - back towards the adjuster.

#55536

#55537

On Jan 5, 2018, at 5:54 PM, deaves.tim@... [Ajsmatchless] <Ajsmatchless@...> wrote:

Thanks Dave. The drawing is very useful. If it is 'reasonably to scale' it does show a considerable gap between the outer edge of the drum and the inside face of the brake cover plate which would cause a step to be worn in the shoes. It also shows the labyrinth seal with quite a depth from the cover plate into the groove on the drum. The adjuster nut is tight against the end of its thread on the spindle indicating that there is no adjustment necessary/required. It also shows a washer between the adjuster nut and the inside of the cover plate. I thought this washer went between the outside of the cover plate and the large nut (on the outside) to stop the nut damaging the chrome. Of course this washer just increases the gap between the brake drum and the cover plate making my situation (potentially) worse. I did however get the large nut on the outside the right way round with the flats closest to the cover plate. All the other parts in the drawing make sense and I have all of them in my hub in the correct order of assembly.

This afternoon I ground a small recess (less than 2 mm) into the adjuster nut. This allows it to be threaded further onto the spindle bringing the cover plate closer to the drum. This worked pretty good and I still think it will be fine once I take it apart (again) and move the washer inside the cover plate, as per your drawing, as I now have some small adjustment on the nut.

Of course it is hard to adjust it all correctly as the plate is a large diameter to be located on the smallish adjuster nut. And then my chrome cover is a bit bent, the labyrinth seal looks to have stopped some large rocks at some time, the plate/shoes may not be concentric with the drum, etc., etc. And when you tighten the large nut to lock it all up and you hear something rubbing you have no idea where. Is it the labyrinth seal, the plate on the edge of the drum, the shoes, . . . where?

All-in-all I'm now a happy camper and I can see my way through this.

Thanks everybody for your help.

Tim

#55538

Tim,

‘Apply force’ does not mean hitting it. Don’t be tempted. Poorly prepped you will be. Never ever Hit em, they don’t survive. Sharing my wisdom!

David

From: Ajsmatchless@... [mailto:Ajsmatchless@...]
Sent: Saturday, 6 January 2018 1:55 PM
To: Ajsmatchless@...
Subject: Re: [AJS&M] Front Brake Cover Plate Alignment