Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties Improved braking on 43 U

Improved braking on 43 U

Post Thu Dec 27, 2007 3:41 am

Posts: 93
Location: Norway
Hi. I'm new on this forum. I live in Norway and own a 43 U believed to come from South Africa. This is my only bike and because I use it in everyday traffic, i want to improve braking. My current idea is as follows:

Rear brake:
Modify a brake drum from 58-62 or 63-72 to fit the original backing plate assembly. Then I will have cast iron drum instead of drawn steel.

Front brake:
Make a twin leading shoe brake with mainly HD-parts:
Alt. 1
Modify the backing plate with aditional pivot stud and brake cam. I will have to modify the brake shoes to fit of course. This seems to be the easiest to do.

Alt. 2
Modify front brake drum of 49-72 to fit the springer fork if this is bigger than the 36-48 brum. I will then have to make the backing plate myself.

Alt. 3
Modify the rear brake assembly from 58-62 or 63-72 to fit the springer. The backing plate will have to be modified from hydraulic to mecanical operation.

Do anybody know the internal drum diameter and band width of the following HD's:
* front brake big twin 49-72
* rear brake big twin 58-62
* rear brake big twin 63-72

I'm also thankful for any comments on the ideas.


Post Thu Dec 27, 2007 8:37 am

Posts: 1654
there's a thread called 'better front brake' which is live just now, about fitting BSA or Honda front brakes. The 45 Depot twin can brake is also discussed
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Thu Dec 27, 2007 10:10 am

The rear brake doesn't do much, and IMHO isn't worth much expense in conversion.
The front, however, is terrible and is too small to work well on such a heavy machine no matter what you do.
The advantages of alt 1 & 2 (although more complex than your brief description) are that both will bolt to a star hub wheel, but even the 1949 is too small. The 3 elements that comprise an effective drum brake are:
1. radius if drum ID
2. lining area (width × circumference)
3. cam operation (single or dual leading)
If you must use a H-D brake, the only serious candidate is the 1964-72 Sportster/Superglide 8" full-width drum converted to 2LS as you described.
The star hub has been modified to accept another drum on the off side, but I have no details. For the 1936-48 brake the backing plate will be working in the wrong direction so some engineering will be needed. For the 1949-72 brake there are left and right side backing plates to make this easier. A 2nd drum is, of course, a huge increase in power but also in weight.
If a drum is required but brand is not, a complete British wheel saves a lot of work - just buy a 1968-73 Triumph or BSA 8" 2LS brake.

More info:

Post Thu Dec 27, 2007 3:05 pm

Posts: 1654
I would comment that the rear brake could be converted to hydraulic type using panhead parts. Whether the resulting improvement is worth the cost, is a matter of how much you value originality.

I agree with panic that whatever you do with the front brake, it is completely inadequate for such a big, heavy machine. The BSA / Triumph wheel conversion is a good option.
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Fri Dec 28, 2007 4:38 am

Posts: 93
Location: Norway
Japanes/british brake is an improvment but does not look like HD on a Bigtwin in my opinion. Thats why im considering other possibilites.

The rear brake is the brake that is stopping the bike today. The stopping power is almost adequate, but the feel of the brake is not. Converting to cast iron drum is therfore worth very much for me. As a bonus I get a drum that is round all the time.

As for the front brake I realise that my ideas may not give modern braking power. But this is not the goal either. If so I would have bought a modern bike. I want to improve braking without having to sacrifice the apperance. I hope for a conversion that looks like it couldt have been made by the factory.

Thats why I'm still very interessted in the drum diameters/lining widths I listed above.


Post Fri Dec 28, 2007 5:14 am

Posts: 2688
Location: Los Angeles, CA
Th early '58 type cast drum can be used with your mechanical brake backing plate. No modifications. Fact is that the early '58's actually ran the drawn steel drums.

Post Fri Dec 28, 2007 2:21 pm

There is probably a better coefficient of friction from the iron drum vs. the pressed, but I don't know how much.
The widest star hub rear drum is the 1963-66. The 1967-72 is roller bearing, which is IMHO an improvement but you'll need the hub as well.
If you adapt the 1958-62 drum to your plate you'll have only minor improvement, but to use your plate in the 1963 drum you'll also need to adapt the wider 1-13/16" shoes (1958 is 1-5/16") and modify your axle parts for the extra width. In the alternative, it may be easier to convert the 1963 plate to cam and lever - but the shoes are quite different.

Post Fri Dec 28, 2007 10:46 pm

Posts: 93
Location: Norway
Thanks for valuable information. As I understand all the big twin rear brakes 37-72 is the same ID. 58-62 drum is interchangeable with 37-57.

The 63-66 drum is wider and extended towards center of the bike, right? If so, adapting this drum gives the same location of the rear sprocket?

Post Sat Dec 29, 2007 6:37 am

Posts: 1654
well quite, it's a matter of what your objective actually is. Personally I think the BSA A10 style 8" SLS brake ( rather than the later 2LS type ) is a good addition, it is very like a K type or early Sporty in appearance, and better than anything you will ever achieve with the HD unit, but that's up to you.

from experience of Vincent twin-drum set-ups I would say that they look good and can work well, but take a lot of initial setting-up and ongoing TLC to get the best out of them.. which tends to make me feel that twin-drum wheels using HD parts probably aren't that great, apart from the weight which would be undesirable in itself

later cast drum plus 45 Depot twin-cam brake plate is probably your best option under the circumstances. I would suggest that nothing compromises original appearance like a quick trip into the back of the car in front, but that's up to you.

At least on FHP you can have a sensible discussion of the subject, rather than all the "I've had a suicide clutch and no brakes for 30 years, I can shift faster than a Fireblade and ride with Ducatis, and you are a pussy who should be riding a Honda if you don't" attitudes you get on some boards
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Sat Dec 29, 2007 12:21 pm

"58-62 drum is interchangeable with 37-57."
The drums interchange as far as they bolt attach the same way, but according to Palmer, the 58-62 shoes are wider. Whether this is "hidden" in the drum I don't know.

"adapting this drum gives the same location of the rear sprocket"
You may need to make or mod parts on both sides of the drum, but the chain aligns the same with both the 58-62 and 63-72, same swing-arm, so it has to match.

The greatest possible area on the front would be the 1963-* drum (your choice of which hub) because of the width, but then you have the problem of all that hydraulic stuff (ugly + heavy + hoses) or attempting to convert the wide shoes to accept cams. I don't know if there's enough room between the fork legs for this?
It may be possible to just weld the ends of a pair of 36-57 shoes (cam and anchor shapes) to replace the ends of the 63-* shoes (rather than try to fabricate the shapes), and extend the location of the cam and anchor deeper into the backing plate.
There are even bigger inexpensive drums, but they look foreign - Moto Guzzi El Dorado is a 220mm (8.66") by 40mm (1.575") 2LS that goes for under $100.

Post Sat Dec 29, 2007 12:39 pm

Posts: 607
Location: Menomonie, Wisconsin, USA
I have run the 67 to 72 hubs and rear drums on 2 of my knuckles since sometime in the 80's. The rear drum I had to machine the outer lip off of it to clear the backing plate if I remember right. I also shimmed out the brake material on the shoes because I did not like all the pedal travel I was getting. Use stock backing plates. On the front I welded in a sleeve for the bearings like the 67 to 71 front drums have.

Made all the spacers and axles on both ends.

Right now I am in the process of making my own front backing plate so that I can mount Hydra-Glide shoes and use a 67 to 71 type drum. I have good braking as is but this should help loads. This will add an inch to the brake diameter and still look real stock. The bike is 90 cubic inches.

If any of you guys have a junk front backing plate with a usable center - I am still looking and intereasted. Hate to spoil a good one.


Post Sun Dec 30, 2007 3:04 pm

Posts: 93
Location: Norway
Thanks for the nice welcome on this forum. I aprectiate the advise and opions you have wrote on this.

I have done som research today. I went to a buddy who have a -71 FL an tried to messure. It seems like all drums for front 49-71 and rear 58-72 have internal diameter of 8". The rear drum 63-72 is not extendet towards center of the bike as I thaught, at least not by much.

What I think I will do is to use a 58-62 drum for the rear with stock backing plate. For the front I will try to use 63-66 drum and fabrikate a backing plate and shoes. I will try to maintain as much drum width as possible. It is tight as it is. So there is not very much to gain, but hopefully some.


Post Sat Mar 29, 2008 3:20 pm

Posts: 74
Location: Wichita, KS
I like the idea of modifing the current front brake to a double leading edge, been considering that myself. This has given me a few ideas. Here's a totaly wacky one, given that you want to keep a nostaligic or period look, run dual drums on your springer. I gota go check that idea out, it sounds to cool, imagine dual double leading edge drums on a naked 18" wheel shod with super sport rubber on a board track styled bike.

Anyway, just a thought

Post Sat Mar 29, 2008 3:29 pm

Posts: 1654 ... inger1.jpg

go on, I give up.. I'm trying to post a pic here of a knuckelehead with a BSA front wheel
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Sun Mar 30, 2008 10:12 am

Posts: 2688
Location: Los Angeles, CA
I am in the process of fitting a hydraulic rear brake to a rigid frame. I have set up both the 1958-1962 and the 1963 and later units. The 1958-62 can be installed with no frame modification. Simply by making an anchor link from the lower sidecar mounting hole in the frame to the anchor on the brake backing plate will get it in. Then you have to shorten the spacer that fits between the frame and the backing plate by 3/16". If using the juice brake axle it must be shortened 3/8". And if using the juice brake spacer on the axle it must be shortenrd 3/16".
The 1963 and later requires the brake anchor area on the frame to be removed. Not a good idea for an original frame.
Last edited by Chris Haynes on Sun Mar 30, 2008 1:42 pm, edited 1 time in total.

Post Sun Mar 30, 2008 10:17 am

Posts: 1676
Location: Interlaken, NY USA

45Brit, What are all the extra do-hickies below the oil tank on the right? Looks to be a filter and a ??? One neat bike. Good brakes, disk/sprocket rear/ DLS front, Like the bike.

Post Sun Mar 30, 2008 12:26 pm

Posts: 1654
It's not my bike and I don't really know, but I would guess that the extra fitting under the oil tank is a drain fitting / sludge trap of the Honda type. Could also be an in-line automatic valve to prevent sumping?

I'm no fan of sprocket rotor type brakes, I think that brake pads and chain lube should be kept as far apart as possible.

but it IS a nicely balanced bike, isn't it?

Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Mon Mar 31, 2008 5:21 am

Posts: 1676
Location: Interlaken, NY USA

45Brit, I just picked up on it being the later DLS brake setup. I've heard rumors over the years that they resolved the poor braking performance with alterations to actuating arms, etc. You're on that side of the pond, what's your take on whether it works or not?

Post Mon Mar 31, 2008 9:23 am

Posts: 1654
It was always known over here as the 'comical hub' which sums it up really.

The main problem with it was always lack of braking surface area, and none of the changes made any significant difference to that. The early versions suffered from poor lever geometry but this was improved in later years, however my guess would be that with a bike the size and weight of a Big Twin, braking through a 3.00 x 21" rim on a springer, you would probably not notice the difference between SLS and 2LS brake plates.

the best 2LS is the full-width hub. On the other hand, if you don't mind the appearance of the full-width hub, the Honda 2LS one is better all round, once you get the mountings right that is.
Shoot, a man could have a good weekend in Dallas with all that stuff...

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