B50 hydraulic drum brake

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BasilF
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B50 hydraulic drum brake

Post by BasilF »

1608825214707.jpg
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With lots of help from Beesa71 I've been converting a conical hub backplate to hydraulic. It's now ready to road test but the weather isn't really suitable (I'm not doing hard stops on wet or icy roads at my age). If it proves to be any good I'll do a how to write-up.
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Re: B50 hydraulic drum brake

Post by SteveS »

Hi Basil

Hope it works out :thumb . Looking forward to a write-up
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Re: B50 hydraulic drum brake

Post by BasilF »

Finally got a day with the roads not frozen and almost dry so I could test the hydraulic brake.
At moderate deceleration the lever force seemed about the same as the mechanical brake but as you brake harder it is much more proportional than the mechanical brake. There is also much less lever travel. I'd need to ride much more before I could definitely say that its the best thing since sliced bread but so far it seems pretty good. I'm now working on a prettier version that used chromed banjos instead
Newversion1.jpg
of large brass British Leyland parts.

If there is any interest I'll post the full details of the conversion.
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Re: B50 hydraulic drum brake

Post by minetymenace »

BasilF wrote:If there is any interest I'll post the full details of the conversion.
Oh yes please!
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Re: B50 hydraulic drum brake

Post by SteveS »

+1

Nice work
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Re: B50 hydraulic drum brake

Post by BasilF »

Post 1.
We all know that Mead and Tomkinson did their own hydraulic front brake conversion for racing but I recently read “Thunderbolts and Lightning by Peter Crawford” where he states that it was the intention to introduce a hydraulic front brake for the 1971 season based on BMC Minor and Mini components but that the idea was rejected before production. However mechanical brake that we ended up with uses brake shoes and snail cam adjusters from the Mini and the mechanical mechanism that was used had similar dimensions to the mini wheel cylinders. (All the red lines are the same distance apart).
01minorbackplate.jpg
0bsabrake.jpg

The Mini wheel cylinder was a cast iron one and the mounting and plumbing wouldn’t have looked very good on a motorcycle,
03.jpg
so Mead and Tomkinson used MG TD cylinders which are alloy and use banjos to connect the hydraulics. The key dimensions are the same as mini cylinders even though the mini brake is 8inches and the MG one 9inches.
04.jpg
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Re: B50 hydraulic drum brake

Post by minetymenace »

How much machining did you have to do to the inside of the brake plate?
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Re: B50 hydraulic drum brake

Post by BasilF »

Post 2 of 3
The conversion is straight forward (the second time round). Get a BSA OIF backplate and dismantle. Keep the shoes, snail cam adjusters and return springs. Put the rest on Ebay at exorbitant prices.
Cut off the part where the mechanical cams were down to a level about 1mm above the brake shoe rests (red oval).
0004.jpg
Turn over and cut off the raised collars where the brake arms went into the back plate and file level with he face of the back plate. Make pieces of aluminium to fill the hole left by the mechanical cams and weld them into place. You will also need to build up one area with weld as one mounting stud on the MGTD cylinders extends beyond the end of the BSA mounting pad.
00009.jpg
You can now file the welds to smooth the front face and mill or file the back face so it is level with the shoe rests (red ovals again).

Then drill the cylinder mounting holes to the dimensions in the drawing.
BSAbrakedims.jpg
The mounting studs are 3/8” and the central hole is about 20mm. Depending how you orientate the drawing you will either have a mounting bolt interfering with the air scoop or the brake torque bolt or a bit of both. Also check before drilling that you aren’t about to make a twin trailing shoe brake. You will need to counterbore the stud holes on the front face as the cylinder studs aren't long enough otherwise.
00015.jpg
0007.jpg
You can now mount the cylinders, brake shoes, adjusters and springs. The springs are on the backplate side of the shoes on BSAs as this holds the shoes against the back plate without the “anti rattle” pins and springs used on the car version.
0006.jpg
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Re: B50 hydraulic drum brake

Post by beat »

+ 1
nice work :!: :!:

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Re: B50 hydraulic drum brake

Post by minetymenace »

Shouldn't the cylinders be tangential to a circle whose centre is the centre of the wheel spindle, or doesn't it matter?
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Re: B50 hydraulic drum brake

Post by BasilF »

The red rectangle on the hole layout drawing represents the front and back faces of the cylinder.. These are symmetrical about and tangential to the circle centred on the axle. The cylinder mounting studs are not.
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Re: B50 hydraulic drum brake

Post by minetymenace »

My bad, that's clear now, thankyou....
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Re: B50 hydraulic drum brake

Post by SteveS »

Hi Basil

I was going to raise the same query as Gerry. Now you have explained it I can see the offset from the picture of the brake cylinder you provided
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Re: B50 hydraulic drum brake

Post by minetymenace »

What diameter master cylinder are you using please?
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Re: B50 hydraulic drum brake

Post by JB »

minetymenace wrote: Wed Jan 13, 2021 10:19 am What diameter master cylinder are you using please?
It's the T140 style that accepts the 71 style Lucas block switches our bikes were fitted with. It might be worth trying out a smaller cylinder from a 125 bike (my daughters Rieju 125 has a very small piston) as the drum brake slave cylinders combined area will be a fair bit smaller than the Lockheed calliper the Tri***h originally had.

Very interesting topic and nice job you have done of this Basil :thumb :thumb :thumb
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Re: B50 hydraulic drum brake

Post by BasilF »

Post 3 final.

You can now start on the hydraulic lines. Mead and Tomkinson used chunky BMC brass fittings as used on the mini at the time. For my second conversion I helicoiled the banjo thread on the cylinder from 3/8 BSF to 3/8 UNF which allows the use of much prettier and more modern looking motorcycle parts. The Master cylinder is a good old TRIUMPH T140 BONNEVILLE T160 73-78 FRONT BRAKE MASTER CYLINDER 60-4102 which will take the original switches if you get longer bolts. I believe these are 5/8" piston dia but they may also be available in 1/2" as the later cylinders fit the earlier holders.
https://www.thebonnevilleshop.com/produ ... s-99-9918/
Not sure what I've got but I'll measure it some time.
0s-l1600.jpg
For my road bike I routed the hydraulic line on the same route as the brake cable had been but for an M & T replica I would run it down the front of the fork leg as they did. It just means a bit of rearranging the fittings.
Hydraulic line issues:-
I got the lines and fittings from venhill.co.uk and www.carbuilder.com/uk/ and the BMC mini and MG fittings from various Ebay suppliers. Venhill also do a 3/8banjo bolt incorporating a brake switch.

There are several issues to consider.
The flexible hoses don’t like being twisted even 1/4 turn. If you are using the self assembly type with olive fittings this means that at least one end should have a swivel fitting. If you use the venhill powerhose plus system this is already taken care of but the hose itself has to be ordered to a predetermined length and they are more expensive than the self assembly ones so you need to get the length right when ordering.
The MG wheel cylinders have 3/8” BSF threads and the 3/8 BSF banjo bolts and fittings of the period have a 7/16 dia shoulder.
s-l500.jpg
s-l500.jpg (7.75 KiB) Viewed 741 times
banjos.jpg
The 3/8 UNF banjo bolts are 3/8 all the way and can be used with a modern 10mm banjo fitting. The carbuilder banjos are fatter than the Venhill ones making the very nice venhill banjo bolts a bit marginal in length (go in 4 turns) while carbuilders bolts are 3mm longer but they don’t do one with a bleed nipple.
310375dc_3_l.jpg.jpg
210375dc_3_l.jpg.jpg
0033691_banjo-hose-end-38-unf_510.jpg
Re-reading this section on fittings, it may be confusing to anyone who hasn't tried it. All I can say is that the fittings took more far more time, effort and wasted components than the conversion of the back plate but I think it is going to be worthwhile and was certainly interesting to do.
1610376152109.jpg
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Re: B50 hydraulic drum brake

Post by minetymenace »

Excellent, can't wait to hear more when you have ridden it for a while. Where will you put the servo? :ban

I like the idea of re-threading the slaves to accept a greater variety of fittings, did the slaves come apart easily for swarf cleaning?

JB, I'm not sure a smaller master cylinder is necessarily the way to go, disc brakes only require a tiny amount of fluid displacement to push the pads against the disc, a lot more movement is required to move the shoes out, maybe a bigger master will be required, I guess it will come down to how much movement and feel you get at the lever, either way it will be interesting to see how it goes....
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Re: B50 hydraulic drum brake

Post by Mark Cook »

Nice to see some creativity, well done. Stan would have liked this.
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Re: B50 hydraulic drum brake

Post by kommando »

Not sure if the 27:1 recommended ratio for a disc caliper works for a drum brake but here is a table of ratios, don't think it covers the mini slave diameter though but at least it covers the master cylinders.

Image
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Re: B50 hydraulic drum brake

Post by eebtr7 »

I hate to be the one to 'piss in the porridge' here. I see the rubber seals deteriorating in a few years, the brake fluid soaking up moisture, thus requiring frequent brake overhauls, just like I used to do on a 1957 Plymouth back in the 1960's. Meanwhile, the front brake cable on my September 1971 B50SS continues to be perfectly fine in it's function with only a light squeeze of grease into the fitting every so often.

I do like and appreciate your creative handiwork here. I just hope it all works out in the end.
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Re: B50 hydraulic drum brake

Post by SteveS »

Hey eebtr7, just remember if the BSA designers had got there way back in the early 70's your B50SS would have come fitted with a hydraulic front brake as standard from new :smile:
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Re: B50 hydraulic drum brake

Post by minetymenace »

eebtr7 modern brake fluid is not very hydroscopic (times have moved on since the 60's!), and seals on master cylinders last years if not decades. Apart from being an experiment, I guess the reason M&T went for this method was to remove the sponginess you get from a cable. I hate cables with a vengeance, if the bike is ridden often they are far more maintenance intensive than a hydraulic system in the UK's climate. If future reports are favorable I think I might have a go at doing this mod too.

The very clear instructions and well presented topic is what this forum is all about i.e very few topics here cover concourse machines. (This is my opinion as a member, not as the moderator).
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Re: B50 hydraulic drum brake

Post by kommando »

Mini drum brakes are 7" so you could use one as a rear brake plate, rears are SLS and 1.25" shoe width, fronts are TLS with 1 .5" show width.
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Re: B50 hydraulic drum brake

Post by eebtr7 »

Okay, I'm back with a fresh bowl of porridge.

Minetymenace, Yes, we do have opposite types of weather here in South Central Texas compared to your Salisbury Plain. The seals I refer to are the slave cylinders in the brake drum where heat and exposure to water are boiling the fluid and condensating moisture inside the cylinder. My TR7 brake cylinders are coming due for a seals overhaul after some five years, as well as the deteriorating brake hoses. If I still had my 1927 Chevrolet from back in 1970, it's rod operated brakes would still be fine.

Now, do I want to go back to 1927 rod operated rakes? That is a Big Negatory. However, the 50 year old brake cable on my 310lb B50 has yet to require any servicing, while hydraulic brake rubber hoses, seals, and fluids sit there and rot away over time and use. Time, which continues to tick away despite our efforts to slow it down. Has my brake cable ever let me down? Not hardly in my riding styles over the past half century. In fact, I feel more safe & secure clamping down on the BSA front brake than I do on any vehicle I have driven, two or four wheeled. But, that may be attributable to Texas roads and weather versus your liquid sunshine and road surfaces.

In any event, to each his own.

And, Steve, I often wonder why the 1973 & up disc brake setup has not been more widely retrofitted on the 1971/1972 drum brake models across the model range by our fellow bikers? Isn't it pretty much a bolt-on setup?
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Re: B50 hydraulic drum brake

Post by SteveS »

Hi eebtr7

I understand your username a bit better now re: TR7, as kid my late Father had a TR2, much fun was had :razz:

What has been known for a while and has now been further detailed in print (*) i.e. the brake plate on your B50SS was originally designed to accommodate a hydraulic brake set-up i.e. hydraulic drum brake.

I understand that the later disc brake set up available for the Triumph brand from 73 is a pretty straightforward bolt on alternative for the B50. I believe there are a few members running this set up.

Gerry
I guess the reason M&T went for this method was to remove the sponginess you get from a cable.
Nigel Rollason indicated that if the correct cable was used then the sponginess was not an issue. He used a Bowdenex double lined cable to overcome the problem.

* Thunderbolts & Lightning, Peter Crawford
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Re: B50 hydraulic drum brake

Post by minetymenace »

SteveS wrote:I understand that the later disc brake set up available for the Triumph brand from 73 is a pretty straightforward bolt on alternative for the B50. I believe there are a few members running this set up.
Certainly are!
front end small.jpg
But requires wider yokes and different fork tubes.

I wonder if anyone knows what slave cylinders BSA (as opposed to M&T) had in mind for the comical brake plate? Most of the metalwork on BasilF's conversion is to do with mounting the slaves, I have been trawling images of period slaves that might also be suitable (which I guess BasilF and M&T also did). It only needs to be located with a circlip, but have found nothing yet....Any clues in your drawing collection SteveS?
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Re: B50 hydraulic drum brake

Post by Mark Cook »

A couple of simple cnc programs would sort the brake plate Gerry, as long as BasilF didn't mind.
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Re: B50 hydraulic drum brake

Post by BasilF »

Kommando; Slave cylinders are 7/8" dia so the ratios are 3.9 for the 5/8 master and 6.16 for the 1/2. My current master is 5/8 but I've ordered a 1/2 to try although the 5/8 seems OK. I expect that the 27 recommended for a disc is because they have no self-servo effect like a twin leading shoe drum.

Minty: Slave cylinders virtually self-dismantle when you cut the cable tie (see earlier photo) as they have a spring inside to keep the piston extended. Cleaning out was easy.
BSA could have cast the slave cylinders integral with the backplate. Machining would have been no more than they had to do with the mechanical system.

Mark Cook: No objecting to others using the inf. I was given lots of help by Beesa71 and am happy to pass it on.
However 1. It needs lots more road testing which it unlikely to happen until te weather warms up (in UK) and the roads dry.
2. Please don't assume my dimensions are correct.
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Re: B50 hydraulic drum brake

Post by Armstrong Phil »

Great Job, certainly got me thinking for my A65 (I'm happy with the stopping power on my B50).
One though, could you remove studs from slaves and use Allen bolts, wouldn't break into scoop/anchor point? Maybe not need to mill out the recesses as could get longer bolts?
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Re: B50 hydraulic drum brake

Post by BasilF »

The studs are cast into the slave cylinder with a T top holding them in. Not enough thickness on the alloy slave cylinders to rely on just threads.
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Re: B50 hydraulic drum brake

Post by SteveS »

Hi All

I guess a welder that knows what they are doing could weld the aluminium brake cylinder directly to the back of the brake plate. Assuming there was no distortion in the cylinder caused by the welding process it would make the front face look a little neater as there would be no need for the studs. However we need to wait for Basil's road test report before we overthink things :razz:
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Re: B50 hydraulic drum brake

Post by Mark Cook »

I'm sure you have mentioned it, but what are you doing about "slack adjusters"?
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Re: B50 hydraulic drum brake

Post by BasilF »

kommando wrote: Wed Jan 13, 2021 10:14 pm Mini drum brakes are 7" so you could use one as a rear brake plate, rears are SLS and 1.25" shoe width, fronts are TLS with 1 .5" show width.
Looking at my notes, the BSA brake uses the shoes, springs and snail cams of the late model Morris Minor, not the Mini.
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Re: B50 hydraulic drum brake

Post by Mark Cook »

Ah ha, I see the little devils now :)
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Re: B50 hydraulic drum brake

Post by kommando »

BasilF wrote: Thu Jan 14, 2021 5:43 pm
kommando wrote: Wed Jan 13, 2021 10:14 pm Mini drum brakes are 7" so you could use one as a rear brake plate, rears are SLS and 1.25" shoe width, fronts are TLS with 1 .5" show width.
Looking at my notes, the BSA brake uses the shoes, springs and snail cams of the late model Morris Minor, not the Mini.
I am talking rear brake not front brake, so you get a rear hydraulic brake to complement the front.
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Re: B50 hydraulic drum brake

Post by Velofello »

After I demolished the front end of my '71 Trident 30 years ago, when a car pulled a left turn in front of me, I installed the later disk brake, which I subsequently upgraded to a dual disk with those alloy Grimeca calipers. On my B50 bitsa, I am currently upgrading the front brake to a Grimeca 230 MM 4 leading shoe brake. The stock 8" comical hub worked fine, but I was given the Grimeca (already laced up to a nice Borrani alloy rim) for $300 on the condition that it went on my B50. Should be done soon.

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Re: B50 hydraulic drum brake

Post by minetymenace »

Vellofell, why not start a topic in Project Bikes and document your progress? I can move and link your post here to that, I'd love to comment on Grimeca hubs, but fear it would be off topic here.
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Re: B50 hydraulic drum brake

Post by Canberra »

One really good bonus when you fit a later fork with disc is that you have rubber mounting for the handlebar. I have one from a '79 model and there was very little weight difference as the conical hub is so heavy. It cuts out a lot of vibrations from a big single. Brake is set and forget with no issues that can arise from trying to set up the original conical hub. From memory had to add some weld to the stops when used with the larger steel tank. Otherwise very straight forward change and the later switches are better that the original Lucas. I used the later speedometer mount and the headlight is the larger model with good rubber mounts. Best change I ever made. The B50 two up and loaded stops well as it is a lot lighter than the twins and triples they fitted those brakes to.

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Re: B50 hydraulic drum brake

Post by BasilF »

Final chapter:-
Fitted a smaller diameter master cylinder.
IMG_20210116_100717_1.jpg
This gives a lighter lever pressure but more lever movement.
I've had problems bleeding the system. It seems to work best if I do it on the bench with the banjos uppermost and the master tilted with the outlet high.
IMG_20210116_121116.jpg
However it does limit your pipe routing to routes you can get the master cylinder through.
I've taken it for another test ride.
test ride.jpg
My observations are as follows. Both versions allow much harder braking than with the cable which seemed to give less and less extra as you increased the lever pressure. In contrast the hydraulic systems show a disadvantage of a twin leading shoe drum over a disk in that if you double the lever pressure then the braking more than doubles. However I think I can get used to that. Haven't decided which master cylinder I prefer but I'm definitely going to leave the hydraulic brake on and look forward to some warm, dry roads in the spring.
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Re: B50 hydraulic drum brake

Post by minetymenace »

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.....unless you are brake testing your B50!

I would hope that once you have the air out of the slaves and the bottom pipe, the top part of the system will be self bleeding. I guess the exponential progression is due to the multiplying nature of twin leaders. Hope you report back when you have got used to the system, should be second nature by the summer...
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