Author Topic: Cheap TLS rear drums! (Read 18425 times)

MidnightLamp · « **on:** December 01, 2010, 05:31:41 PM »

So, I happen to have a bike that has VERY cheap parts available for it, and was having a big sulk at the lack of spoked wheel rear brake upgrades available for the 750K. The options seemed to be: running a stock drum, or upgrading to a disc (for which I either shell out serious $$$ or spend a long time looking for a '75F hub). Then a thought hit me. What bike do I have that happens to have a new production 7" TLS drum.

Plate is for a Enfield Interceptor, but the new repros are made in india for around $70 with shoes. You'd be looking at around $100 for a brake plate with pair of shoes to your door with duties taxes and stuff. Check out the pictures below. What would need to be done is a inner spacer, and an outer spacer. The mounting method involves a rib on the forks normally, but I image that can be modified for a rear brake stay. I by no means recommend doing this, but I'll be putting this together on my spare rear weel to see if it is actually worthwhile! I'll update with pics.

Stock CB Hub
http://i55.tinypic.com/2ziofao.jpg

Twin pivots

http://i54.tinypic.com/2gsie4x.jpg

Does it Fit

http://i55.tinypic.com/312jk34.jpg

Details!
http://i54.tinypic.com/2zr3of8.jpg
http://i56.tinypic.com/21jsor6.jpg

Cheers!

Ricky_Racer · « **Reply #1 on:** December 01, 2010, 06:19:42 PM »

19mm rear axle? Could be cool on a rigid chopper, too, if it works. No add-on rear stay necessary. RR

MidnightLamp · « **Reply #2 on:** December 01, 2010, 06:41:42 PM »

16mm front axle, because it's a front brake. The rear is a 5" half width brake, so you're probably better off with shoes on ground

The full hub 5"er is the upgraded rear for those guys.

I'll be boring the brake plate out to CB rear axle specs (sliding fit) with a tool room lathe, and machining aluminum spacers (one on the inside, one on the outside). The inner one needs to be only about 3mm thick.

I was thinking of it for a cafe part as just something a little different but better than stock!

Ricky_Racer · « **Reply #3 on:** December 01, 2010, 07:55:23 PM »

A front on a rear... great idea! Keep us apprised on how it works. Rather than welding a hanger on the brake, you might be able to weld a dowel onto the swingarm to locate the brake plate. RR

Sam Green Racing · « **Reply #4 on:** December 02, 2010, 05:35:00 AM »

Sorry to piss on your fireworks but it won't work.
The Interceptors front drum in on the left as you sit on the bike.
The rear Honda drum is on the right.
By doing this you will end up with a twin trailing brake which will be less effective than the stock single leading Honda unit.

Sam.

Ricky_Racer · « **Reply #5 on:** December 02, 2010, 08:42:24 AM »

Damned Brit bikes! Everything is backward on them. Must be because they drive on the "wrong" side of the road! Bwahahahahahah!

RR

Sam Green Racing · « **Reply #6 on:** December 02, 2010, 09:03:50 AM »

Most Jap bikes with drum brakes have the plate on the left up front.
Some brit bikes had the rear drum on the same side as the chain.

Sam.

MidnightLamp · « **Reply #7 on:** December 02, 2010, 11:26:18 AM »

Of course you're right sam

Dammit! Yeah, the rear is a messed up brake on those bikes. Part width drum INSIDE the rear sprocket. Braking from speed is interested. The chopper guys are the best through...remove the front SLS brake and keep the 5" half width rear. Might as well stop with your feet!

I guess this begs the question if it's possible to fit a brake from a bike with a front right mounted 7" drum. There are countless new repros of brakes on ebay, including the old 4TLS brakes for brit bikes coming out of the far east right now for rather cheap. One of the big advantages I see is tire fitment as well, because my idea was to have a rib on a boxed swing arm (like a dresda copy) that is bolt on, that would hold the brake in place. This would remove the brake stay out of the equation when fitting wider rear tires. Also, many of these brakes are nice and easy to polish or to swiss cheese

I'd be very interested in the least and have a tool room mill and lathe to make it work. Now that everyone knows about the 76 hubs for the rear brake swap, they've become really hard to get, and realistically a 70's single slug caliper is not that much to write home about for how much the full swap would cost (for a rebuilt/presentable setup). The cycleX setup looks gorgeous, but it seems like it's a lot more than what i need for the bike.

jaguar · « **Reply #8 on:** December 02, 2010, 12:53:53 PM »

you have links to the repos that you are talking about?

i was looking at using a CB77 rear on a race project.
i think that is the only TLS rear that honda made for the street

Sam Green Racing · « **Reply #9 on:** December 03, 2010, 02:09:26 AM »

Quote from: jaguar on December 02, 2010, 12:53:53 PM

you have links to the repos that you are talking about?

i was looking at using a CB77 rear on a race project.
i think that is the only TLS rear that honda made for the street

Jag, this Enfield brake has the same problem that the CB72 brake has that we were talking about last week, It's made for the wrong side of the bike, reversing it will make it trailing shoe.

Sam.

fastbroshi · « **Reply #10 on:** December 04, 2010, 03:58:07 PM »

Quote from: SamCB750A on December 02, 2010, 05:35:00 AM

By doing this you will end up with a twin trailing brake which will be less effective than the stock single leading Honda unit.

Sam.

Sam, can you explain the difference between a leading and trailing brake? I can't seem to tell what the difference would be if you flipped any of the components.

Old Scrambler · « **Reply #11 on:** December 04, 2010, 04:26:44 PM »

Drum brakes - single leading edge
The next, more complicated type of brake is a drum brake. The concept here is simple. Two semicircular brake shoes sit inside a spinning drum which is attached to the wheel. When you apply the brakes, the shoes are expanded outwards to press against the inside of the drum. This creates friction, which creates heat, which transfers kinetic energy, which slows you down. The example below shows a simple model. The actuator in this case is the blue elliptical object. As that is twisted, it forces against the brake shoes and in turn forces them to expand outwards. The return spring is what pulls the shoes back away from the surface of the brake drum when the brakes are released. See the later section for more information on actuator types.

The "single leading edge" refers to the number of parts of the brake shoe which actually contact the spinning drum. Because the brake shoe pivots at one end, simple geometry means that the entire brake pad cannot contact the brake drum. The leading edge is the term given to the part of the brake pad which does contact the drum, and in the case of a single leading edge system, it's the part of the pad closest to the actuator. This diagram (right) shows what happens as the brakes are applied. The shoes are pressed outwards and the part of the brake pad which first contacts the drum is the leading edge. The action of the drum spinning actually helps to draw the brake pad outwards because of friction, which causes the brakes to "bite". The trailing edge of the brake shoe makes virtually no contact with the drum at all. This simple geometry explains why it's really difficult to stop a vehicle rolling backwards if it's equipped only with single leading edge drum brakes. As the drum spins backwards, the leading edge of the shoe becomes the trailing edge and thus doesn't bite.

Drum brakes - double leading edge

The drawbacks of the single leading edge style of drum brake can be eliminated by adding a second return spring and turning the pivot point into a second actuator. Now when the brakes are applied, the shoes are pressed outwards at two points. So each brake pad now has one leading and one trailing edge. Because there are two brake shoes, there are two brake pads, which means there are two leading edges. Hence the name double leading edge.

Read more: http://www.carbibles.com/brake_bible.html#ixzz17ByCv7sl

Old Scrambler · « **Reply #12 on:** December 04, 2010, 04:54:34 PM »

The Car Bible is not really clear (correct?) because they ignore the twin-pivot double leading shoe design we are discussing. To me, the leading edge is the end of the shoe that first contacts the drum and (assuming it had an arrow indicating the edge was forward) it would engage the drum against its rotation. A trailing edge (think feathers on the end of the arrow) engages the drum WITH its rotation. With the twin-pivot design, the adjustable linkage can make both shoes perform in the leading-edge mode.

For clarity.........a HONDA CB450 TLS drum and brake-plate is larger in diameter than the CB72-CB77 brake. The 450 hub is a 36-spoke design and was used on the '66 & '67 CL77. The same size brake and hub was also used on the front of the 3 models but with 40-spokes.

MidnightLamp · « **Reply #13 on:** December 04, 2010, 05:57:34 PM »

What these guys said! ^^^

For clarity, fastbroshi, The TLS design uses two pivots, and two cams. Each shoe goes to one pivot and one cam, with one cam at each end. The cams are turned in the same direction (one has the brake actuator attached to it, other is hooked up via linkage). When the cams turn, both shoes move out, but the leading edges of both of the shoes are the same. This design moves both shoes out, but since both shoes PIVOT out, the direction is important. The enfield drum mounts on the opposite side, so both shoes pivot WITH the rotation of the wheel. This means when the shoes make contact, the friction will pull them in. If the wheel rotation is reversed, as soon as the shoes catch, the force from the wheel will try to push the shoes away, hence brake force will be reduced.

Below is a picture of the CB77 hub.
http://www.flickr.com/photos/1962_cb77_restore/3297221074/

I guess one thing I was thinking of is machining a plate with the pivot holes built onto it. I've been looking into 2LS and 4LS brakes, but all the discovolante stuff and italian replicas are bloody expensive. An example of a machined plate is below (albeit for a SLS triumph rear). The enfields are available without the plate (just the cams, pivots, etc... as everything is pressfit or fits right in), so I was thinking of taking 3/4" aluminum stock and my mill to turn that into a rear plate.

http://cgi.ebay.com/ebaymotors/6Rib-Aluminum-rear-Brake-Plate-Triumph-cafe-race-bobber-_W0QQcmdZViewItemQQhashZitem4cf37f19e0QQitemZ330502707680QQptZMotorcyclesQ5fPartsQ5fAccessories

Phil · « **Reply #14 on:** December 20, 2010, 06:02:55 AM »

... and don't forget: fit the the 2LS CB72/77 rear brake on a CB750 and ... it's a twin trailing shoe - wrong side again! Also, I know the 2LS are correct for CR750 reps but they are (surely?) hardly necessary - who needs so much power in a rear brake?? (I know, I'm jealous...)

Sam Green Racing · « **Reply #15 on:** December 20, 2010, 06:24:05 AM »

Phil, stopping a 400lb motorcycle from 160mph required a lot of brake power

Sam.

Phil · « **Reply #16 on:** February 15, 2011, 09:15:58 AM »

I bought a classic race bike (chain on left, same as CB750) fitted with a CB72 rear wheel. It was a "twin-trailing shoe"! The last owner reported it worked fine and finished the Manx. I understand the science (sort of!) but why should a trailing shoe be inferior to a leading shoe?

Sam Green Racing · « **Reply #17 on:** February 15, 2011, 09:29:10 AM »

It's the point of contact where the front edge of the shoe meets the drum.
Think of running your hand across a snooker table surface against the knap, it's sorta like that.

Sam.

Phil · « **Reply #18 on:** February 20, 2011, 02:48:26 AM »

Yes, I see your point. I personally never liked twin-leading shoe (front) brakes because I found them to sharp and snatchy with a tendency to lock the wheel. Was this because they were set up incorrectly? The thought of a big snatchy rear brake seems scary to me. We so rarely use the rear brake on a modern bike for anything but steadying it. Is this because our front brakes are so good these days? I guess I'll stick with my oh so heavy standard CB750 SLS rear brake (beautifully modified by Voxonda!). I am seeking a superlight CB350 K4 rear brake though!!

Sam Green Racing · « **Reply #19 on:** February 20, 2011, 05:25:29 AM »

Phil, the easy way to understand how the brake works in relation to leading and trailing shoes.
Hold your stock rear brake plate in front of you just as it would fit in the bike with the anchor point down at the bottom. The spindle that the brake arm fits on to will be around 7 or 8 oclock and the drum will rotate around it in a clockwise direction.
Now spin it round so you are looking at it from inside the drum, the anchor point will still be at the bottom (perhaps now the other side of 6 oclock) and the spindle will now be around 4 or 5 oclock and the drum will now be traveling anticlockwise.
If you now opperate the brake (remembering the way the drum is rotating) the spindle will open the two shoes so they come into contact with the drum. The first point of contact is the two edges of the shoes closest to the spindle. The edge of the top shoe is the leading edge (leading shoe) as it contacts the drum. The lower shoe (trailing shoe) dosen't bite as hard because the drum is not contacting the shoe edge but sliding over it the opposite way.
Hope this helps.
Where do you live in Woodbridge, anywhere near the Grove House Hotel ?

Sam.

Phil · « **Reply #20 on:** February 28, 2011, 09:42:28 AM »

Thanks Sam, I did not know how a TLS brake works. I have just acquired a CB350K4 rear hub. only 20mm less diameter and about half a ton lighter! I am tempted to try it. Grove House Hotel is about a mile away - you know it, obviously?

Sam Green Racing · « **Reply #21 on:** February 28, 2011, 02:12:42 PM »

Phil, PM sent.

Sam.

Phil · « **Reply #22 on:** March 01, 2011, 03:44:34 AM »

Thanks Sam - I respect your experience and your comments are noted - I will heed your advice. Trouble is, the more money I spend on the engine the more I realise that I must shed weight if My CB750 is to be competitive against pesky Tridents!!. I want a competitive race-bike and not just a pretty parade bike. A P&M frame is the same price as the magnesium TLS CR750 rear brake which is why I deliberate. Richard Peckett said I could have one but I have to wait! I now plan to use a mildly tuned engine in my CR750 rep. and parade it and use my best engine in a P&M in the hope it will be fast. Meanwhile, another season begins...

MidnightLamp · « **Reply #23 on:** March 02, 2011, 04:34:50 PM »

Now a question comes up for those with a lot of race experience (NOT me) would be about the feel of a TLS rear brake. I've been doing some digging on this subject for my automotive engineering class, and it seems the rationale behind having SLS drums in general for a rear drum is to provide a more linear brake feel. Leading shoes in general seem to be known as "twichy" in operation, where they transition hard from no brake to full break (have a tendancy to have rather non-linear feel). Correspondingly, with a SLS drum you have less of this, as the trailing shoe looses some force as it doesn't cam in. In some of the research I did, there were race teams (automotive) back in the 50's and 60's who were swapping the smaller TLS drums for large TTS drums to provide a more controllable brake feel.

The point of this would be to say that maybe a TTS drum would provide a more controllable feel for a CB, and at the same time provide more than enough brake force than what's needed. This stems from the desire to upgrade the brake system from a functional perspective rather than a power perspective (because IMO at least for city and amateur track driving, the rear brake on a CB does seem to be adequete, but rather twitchy...but that might just be lack of experiance

) I don't know if this is out to lunch, but I figure it couldn't hurt to consider it.

Cheers!

Old Scrambler · « **Reply #24 on:** March 02, 2011, 06:36:37 PM »

I like this question, but I am not a racer. I just know that when my CB750 rear drum is worn in and warmed up, I get a dependable and even feel from the pedal. I occasionally use the rear brake on long turns like an express-way ramp to hold speed while I am lightly adding power. I think they call that trailing brake action. If nothing else it gives me the feeling of slightly faster acceleration coming out of turn.

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Author Topic: Cheap TLS rear drums! (Read 18425 times)