SA front drum brake conversion

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SimonCelsa
Posts: 633
Joined: 6 Apr 2011, 10:19pm

Re: SA front drum brake conversion

Postby SimonCelsa » 25 Jan 2020, 5:18pm

I think the correct lever would be the Tektro rl520

Currently only a tenner at PlanetX:

https://www.planetx.co.uk/i/q/BLTEKRL52 ... ake-levers

David
Posts: 130
Joined: 11 Jan 2007, 5:13pm

Re: SA front drum brake conversion

Postby David » 25 Jan 2020, 6:00pm

cycle tramp wrote:I have to say that this hasn't been my experience. I've been using them for 3 and a bit years, the drum brakes have got stronger, and there's been very little wear - indeed I've only had to tension the brake wires once ir twice to take up the stretch... even better during that time I've suffered no wear to my wheel rims.


That's what I was expecting too. I bought the hubs, rims and spokes and built the wheels myself after the bike's orignals had worn the rims through. I wasn't willing to braze a couple of lugs on to the frame/forks for disc mounts so the drums ticked all the boxes - out of the weather, not likely to get contaminated with grit to wear, long lasting, ready supply of brackets for the frame, no rim wear, lower maintenance. Add the dynamo and the 5 speed wide range rear hub and you end up with a brilliant commuter machine.

Two winters was a big disappointment.

Phileas
Posts: 226
Joined: 18 Feb 2009, 6:12pm
Location: Bristol

Re: SA front drum brake conversion

Postby Phileas » 25 Jan 2020, 7:21pm

SimonCelsa wrote:I think the correct lever would be the Tektro rl520

Currently only a tenner at PlanetX:

https://www.planetx.co.uk/i/q/BLTEKRL52 ... ake-levers


I believe those are linear pull levers. I was under the impression that a standard pull lever as used with side pull brakes might be a good choice.

I had assumed my levers were RL520s (for discs) but I’m pretty sure now they must be RL340 so I need to cancel the order I made this morning. :oops:
Last edited by Phileas on 26 Jan 2020, 6:06am, edited 1 time in total.

cycle tramp
Posts: 609
Joined: 5 Aug 2009, 7:22pm

Re: SA front drum brake conversion

Postby cycle tramp » 25 Jan 2020, 10:06pm

David wrote:
cycle tramp wrote:I have to say that this hasn't been my experience. I've been using them for 3 and a bit years, the drum brakes have got stronger, and there's been very little wear - indeed I've only had to tension the brake wires once ir twice to take up the stretch... even better during that time I've suffered no wear to my wheel rims.


That's what I was expecting too. I bought the hubs, rims and spokes and built the wheels myself after the bike's orignals had worn the rims through. I wasn't willing to braze a couple of lugs on to the frame/forks for disc mounts so the drums ticked all the boxes - out of the weather, not likely to get contaminated with grit to wear, long lasting, ready supply of brackets for the frame, no rim wear, lower maintenance. Add the dynamo and the 5 speed wide range rear hub and you end up with a brilliant commuter machine.

Two winters was a big disappointment.


I'm am sorry to hear about the issues you had with the drum brakes... it's possible that we have very different winter conditions. Down in Somerset, the gritting lorries have only been out once thus year...
.....if you're riding worse conditions then I can understand the brake sticking when in use.... I don't think it's a too common occurrence but two cycling blogs have also noted the issue - one of the writers eventually solving the issue by putting an additional spring between the arm of the drum and the adjuster... sadly they didn't give any more information..
I've mentioned it before on this forum... the drum brake could be better with a bit of development.... for a start a 90 mm drum brake size/screw on freewheel hub would be nice... longer arms would be good, as would a floating cam, and a range of brake shoes, offering more grip at some expense of longevity as well as a stronger spring to avoid the issues which plagued your brakes.
I can understand your move away from drums to discs and I'm glad to hear you're having a better experience.

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mjr
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Re: SA front drum brake conversion

Postby mjr » 26 Jan 2020, 12:57am

Gritters are out frequently in Norfolk. Hub brakes are working fine. The front did stick on last winter but that was solved by replacing the cable. The brake may be nearly immune to salt but the cable is even more exposed to it.
MJR, mostly pedalling 3-speed roadsters. KL+West Norfolk BUG incl social easy rides http://www.klwnbug.co.uk
All the above is CC-By-SA and no other implied copyright license to Cycle magazine.

Brucey
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Re: SA front drum brake conversion

Postby Brucey » 27 Jan 2020, 12:40pm

David wrote:
Brucey wrote:FWIW if you don't have a little lube on the cam then the brakes can fail to release fully. Other than that the experience related above I'd describe as 'atypical'. A high wear rate suggests that the brake were dragging all the time or that the brake shoes were contaminated somehow; they will certainly wear quickly if the shoes are contaminated with oil.

Remember that these brakes were designed to meet a requirement that the shoes should last five years of daily use by a postman. There are not many uses which are more strenuous than that, but there are various things which might cause the brakes to perform less well than anticipated.

cheers


No, it was all clean & definitely not dragging. I was surprised at how quickly the brakes went off and needed replacing. I was also surprised at how little wear there was on the shoes when I replaced them. I also got almost no dust out. It was only the front brake I had problems with, the back brake - apart from being a bit weak was fine from a serviceable perspective.

I replaced the front shoes about 18 months because of them jamming on. The new shoes didn't make a big improvement and TBH I couldn't see a big difference in the thickness of the linings. The new shoes lasted about 6 months before they started snatching on and I decided to call it a day with them.

I think you are probably right about this being atypical - I went the drum brake route because I was pretty sure the PO Pashleys wouldn't use them if they were useless. I was expecting 5 years trouble free life from them but the front brake just wouldn't play. Maybe the Posties don't use them in winter on salted roads :D

I eventually scrapped the bike and built a new one but fitted disc brakes - these work fine but I did contaminate the pads and junked them after about 200 miles, the replacement ones have been good for over 1500 miles so far.


There are other things which can catch you out

1) draggy cables; they are supplied dry by SA and (IME) need lube to work properly.
2) cam lube (as mentioned above) but also enough lube to keep the pivot bushing smooth too.
3) shoe profile.

If the shoes were not worn then this means that your earlier statement about the shoes wearing quickly was not entirely correct. The shoe wear can be gauged by the extent of the arm movement on the outside of the brake. Essentially when the linings in the front brake are worn out, the brake arm is in danger of clouting the axle. If the brake works abnormally before then, there is invariably another problem, not lining wear per se.

Most jamming is due to cables or cam being unmaintained. A little can go a long way here; if the brakes are set up correctly to start with then they can go 15-20K miles without attention, even in fairly crummy conditions.

I have experienced a 90mm brake jamming on and in that case it usually happened when I left the bike leant to one side overnight in the rain; the brake shoes swell up if they get damp and this encourages jamming (until they dry out). However I've never had the brake linings get damp whilst riding, not without the brake actually getting submerged.

The shoe profile issue is also affected subtly by the pattern of use of the brake; however simply filing a more generous lead-in on the shoes is usually enough to keep them working well.

I have rarely seen a SA hub brake that couldn't be fixed by a new cable and/or a five minute fettle of the brake plate assy. If that is done right I wouldn't expect to have to do anything else for a year or two, even in the most horrid conditions.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

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SimonCelsa
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Re: SA front drum brake conversion

Postby SimonCelsa » 27 Jan 2020, 4:49pm

I have recently acquired a SA 70mm front drum and it would seem advisable to lightly lubricate the cam and brake shoe pivots. To accomplish this properly it would be beneficial to dismantle the brake plate assembly. In order to do this the 'starlock' washers would need to be removed. It looks like these would have to be replaced with new after removal (i.e removal would probably damage them). Anyone have any idea if they sell these items separately?

They are part of the assembly below:

SA drum brake.jpg
SA drum brake.jpg (9.04 KiB) Viewed 268 times


I can't find the actual part numbers for these washers (there are 2 of them with differing dimensions). Not the end of the World but it would be good to get a bit of vaseline/grease in there to prolong life. Perhaps a circlip would be a better option?

robc02
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Re: SA front drum brake conversion

Postby robc02 » 27 Jan 2020, 7:56pm

In order to do this the 'starlock' washers would need to be removed. It looks like these would have to be replaced with new after removal (i.e removal would probably damage them). Anyone have any idea if they sell these items separately?


You might be lucky and be able to re-use them, but they are readily available from, for instance, Ebay.

Brucey
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Re: SA front drum brake conversion

Postby Brucey » 28 Jan 2020, 2:32pm

the best lube to use would be either silicone grease or copper ease, since both are designed to stay put even when they get hot.

Many other lubes will separate over time (leaking oil onto the linings) and/or melting when they get hot.

the part number for the current 70mm brake plate's starlock washer is

HMW497

Your local dealer can order them eg from 'the cycle division'

BTW there is a wave washer in the cam assembly. This means that if you want to lubricate the cam pivot bushing (through the brake plate) you can; simply pry the brake arm away from the brake plate until the pivot is exposed behind the plastic spacer, and add one tiny drop of oil to the pivot bushing.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

cycle tramp
Posts: 609
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Re: SA front drum brake conversion

Postby cycle tramp » 30 Jan 2020, 6:11pm

mjr wrote:Gritters are out frequently in Norfolk. Hub brakes are working fine. The front did stick on last winter but that was solved by replacing the cable. The brake may be nearly immune to salt but the cable is even more exposed to it.


Well, that's good to hear. I think I'm going to run my brakes until they start sticking and then apply some copper ease, and then run them again until they stick..... if they stick any more than twice in a year, then I'll talk to a spring supplier. I'll keep this post up dated...

niggle
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Location: Cornwall, near England

Re: SA front drum brake conversion

Postby niggle » 30 Jan 2020, 10:54pm

Phileas wrote:Now I’m confused.

I assumed my brake levers were the wrong type because they came from a Genesis Day One Disc which had TRP Spyre callipers.

However, I found a spec sheet for this bike on Evans cycles https://www.evanscycles.com/genesis-day-one-disc-2015-singlespeed-bike-EV223056 which suggests it had Tektro RL340s which I thought were wrong for disc callipers!

TRP Spyres are road pull disc callipers, the correct levers for both them and an SA drum brake are RL340s. The model number of the Tektro levers is marked on the inside of the lever if you want to check. I am using RL340s with a Spyre front brake and SRAM P5 rear drum brake on my ebike, the front brake is awesome and the rear is 'adequate' but has not needed adjustment yet, unlike the front.

Brucey
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Re: SA front drum brake conversion

Postby Brucey » 31 Jan 2020, 3:40pm

NB current road brake levers are liable to have the slightly longer pull/lower MA that is correct for NSSLR brakes. These do not have the correct MA for use with most drum brakes, so the braking will be somewhat underwhelming, more than normal.

For best results with drum brakes I recommend brake levers with an MA of about 4:1.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Phileas
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Location: Bristol

Re: SA front drum brake conversion

Postby Phileas » 31 Jan 2020, 4:25pm

Brucey wrote:For best results with drum brakes I recommend brake levers with an MA of about 4:1.


Can you recommend any particular ones (for drop bars)?

niggle
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Location: Cornwall, near England

Re: SA front drum brake conversion

Postby niggle » 31 Jan 2020, 8:04pm

One thing that affects the MA is the state of wear of brake shoe linings, because it alters the angle of operation of the operating arm. The optimum MA on a drum brake is usually when the arm is at 90° to the cable as the brake is being firmly applied. On motorcycle drum brakes the operating arm normally has a splined connection with the cam, so that this angle can be re-adjusted to 90° as the linings wear, and similarly bicycle mechanical disc brakes normally have pad adjusters which allow you to maintain this angle, which would be altered by only adjusting the cable. I see no way of adjusting this on SA or Sachs/SRAM drum brakes so I presume their performance will vary through the lifespan of the brake shoe linings.

LuckyLuke
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Re: SA front drum brake conversion

Postby LuckyLuke » 31 Jan 2020, 10:54pm

Phileas wrote:
Brucey wrote:For best results with drum brakes I recommend brake levers with an MA of about 4:1.


Can you recommend any particular ones (for drop bars)?


Hi, I use Cane Creek SCR-5 brakes levers with my SA 70mm drum front brake. Details below
https://www.harriscyclery.net/product/c ... s-1410.htm

According to the description they're high MA levers.

I tried Shimano Tiagra road levers, which I like with caliper brakes, but I didn't find them as nice. They felt a bit spongier and the brakes not as strong. Same quality of inner & outer cable and cable prep.

This might be a red herring, but the SCR-5s allow a ferrule to fit the outer cable, where it joins the body of the brake lever. The Tiagra levers don't. Could this be a factor?

Best wishes

Luke.