Having read all the inputs with interest, I think we need a little clarification of principles.
Firstly, brake efficiency and brake effectiveness. Brake efficiency can be defined in two ways:
1] the rate of retardation of the vehicle expressed as a percentage of "g". Where "g" is the acceleration of a falling body due to gravity. "g" being accepted as 32 feet per second per second . Or 9.81 meters /sec/sec. Thus, if your Box saloon will slow you down at a rate of -16 feet/sec/sec. Your brake efficiency is 50%.
2] The total braking force applied by the four road wheels, expressed as a percentge of the total weight or mass of the vehicle. Thus if your Box Saloon weighs 1000 Lbs, and your four wheel can apply 500 Lbs braking force, your braking effiency will be 50 %.
Effectiveness is the ratio between brake pedal pressure and brake efficiency.
Leading Shoes/ Trailing Shoes. As has been stated, a leading shoe expands in the same direction as the brake drum rotates. On contact with the brake drum, the drum tends to pull the brake shoe into contact with the drum. "Self Servo Action". A trailing shoe expands in the opposite direction as the brake drum rotates. On contact with the brake drum, the drum tries to push the brake shoe "off".
Both systems are capable of producing the same brake efficiencies! Rate of retardation or braking force at the road wheels. The leading shoe arrangement is more effective as it requires less brake effort at the pedal.
Twin trailing shoe arrangements where commonly used to provide the earliest forms of automatic brake adjustment, in combination with vacuum servos on large saloon cars in the mid fifties. Only being outdated by disc brakes.
So the only advantage of leading shoes over trailing shoes, is lower effort at the brake pedal! They are more effective not more effecient! So if you have been using front twin trailing shoe systems for years, and can cope with the pedal pressure, why change?
We now need to the consider the advantages of hydraulic braking compared to mechanical systems. The major advantage is the equal application of braking force at the four wheels. [We can ignore front/rear proportionality for now] Mechanical systems can never match hydraulic systems in ths respect. Even when very carefully set up, cable or rods will never match a hydralic system for even brake force application at the wheels.
lastly we need to consider the design defects inherent in the Austin 7 braking system.
Firstly, the centres of expander cam and the brake shoe pivot of the standard Austin are fixed. As the leading shoe is more effective than the trailing shoe, it will wear at a faster rate. So we reach the position where the trailing shoe is pushed hard against the brake drum, but the leading shoe, being worn has limited contact. This reduces effectiveness. This problem was overcome, by Girling and Bendix mechanical systems,by allowing the expander unit to move or "float" on the back plate. Hydralic systems do not sufer from this problem.
Secondly, the Austin front brakes are applied by pulling the brake levers backwards at the bottom of the back plates. As the brakes are applied the front axle twists and reduces the tension in the brake cables, So you have to press harder on the pedal! The Bowdenex conversion, pulls the front brake levers forward, so the twisting axle increases the the cable tension! The system is more effective, it reduces pedal pressure.
Hydraulic systems eliminate this problem.
However, all braking force is applied through the 5/16 diameter bolt locating the radius arms to the ball joint and chassis. while this is adequate for for the cable brakes, the radius arms were "beefed up" for the semi Girling brakes. I wonder are they upto a twin leading shoe hydraulic arrangement.

Location: south wales, slightly drier

Thanks Alan for the photographs, that is useful, particularly for the flexible hoses, seeing these at the front to avoid all the steering gear at the rear! Thanks for your trouble.

Regards

Gary

Location: Saltdean, Brighton

Thanks everybody for your input and it has confirmed my thoughts that a twin trailing shoe set-up is not the way forward (even though this gives the best space for connections).

I think the space between the wheel cylinder & the steering arm is less than you have on your car (Ruairidh's photos), but looking at your pictures again, Ruairidh, the fixing bolts to the wheel cylinders are orientated in the same way as my first picture, which is for the twin trailing shoe set-up, so perhaps your system is thus and not twin leading?

I would be interested to know if that was the case and I would appreciate any trouble to confirm this as a matter of fact - bearing in mind your brakes have been in service for 50 years something must be working right!

In terms of the flexible hose & bleed nipple, these are not fitted, just screwed in to illustrate where they might go, so no constraints here!

In view of RR's comments, in view of the almost zero space, I am now wondering if the connection above the steering arm is best blanked off (as a minimum a bleed nipple could be fixed in position and cut off flush) and the uppermost connection fitted with an adapter (the same as the rears) to enable a flexible hose to be fitted and the bridge pipe to the front. The only drawback I can see with the pipework in this orientation is that the flow of brake fluid for bleeding purposes could trap air (but that would be the case on the rears anyway), and this might be the way to go with careful bleeding.

BTW, the rears are one leading & one trailing.

I was thinking about silicone brake fluid and agree that this is worthwhile to fit.

Thanks again, and any further comments gratefully received.

Gary

Location: Saltdean, Brighton - sunny today!

Reckers,

I'm very glad that I posted the picture, it is twin trailing (sorry to give you a bum steer on that one Gary) and I will do my best to try and rectify it, I agree with the comments about the pipes but its the only way it would fit but I will look carefully at how it can be improved. They do work, very well in fact, but I do have to constantly adjust the snail cams to keep it working.

Interestingly I was thinking along the same lines as Gary as to how to overcome this, that of using one of the rear-type extension bleed nipples, need to look carefully at this but intend to do it soon so will post back.

Many thanks,

R

p.s. Reckers, my father has sent me a picture to upload for you, will attend to this just now.

Sorry there's a typo on one of my earlier posts - A7 rears are trailing/leading and not trailing trailing as typed (OOps!)

Ruairidh, I just found this whilst having a surf - whilst you may find that your brakes are OK, swapping them to twin leading shoe should show a marked improvement in efficiency:

Some brakes have two wheel cylinders, with one piston in each cylinder. When the brakes are applied, hydraulic pressure forces each piston to move outwards, pushing on one end of the brake shoe. The direction of rotation of the drum produces a wedging action on both brake shoes, so they are both called leading shoes.

This system was once popular on front wheels because it is very efficient in the forward direction. This is due to the self-energizing or self-wedging action of the shoes as the drum rotates. Its main disadvantage is that it is only about 30% as efficient in reverse, so it is usually combined with a single leading shoe arrangement on the rear to provide a balanced system.

Reckers,

I cannot stand people who make mistakes, thank goodness I've never made one.

The following is from my father and was taken in 1974, I am in my carry cot in the rear of the blue Chummy.




Thanks again for your advice, very much appreciated!

Can you not rotate the backplates 90 degrees? Then the inlet could be at the bottom and the bleed at the top. I guess there is a reason why not because else someone would have done it by now!

Steve
edit
I see that the bottom one may foul on the axle? I'm just thinking out loud! I've never seen it in real life!

Nice idea Steve, and would most probably work but my backplates can only be rotated 180 degrees, unlike the girling ones which are circular.

Cheers

R

On the same subject....sort of...

Motorbikes used cable operated twin leading shoes. It seems quite simple when you look at a motorcycle front brake. Has anyone ever done this on a Seven instead of hydraulics? I seem to remember a discussion like this some time ago when I was setting up my Girlings, regarding floating shoes etc but my memory is not that good.

Steve

Steve, I think the system you may be thinking of is the Bowdenex conversion.Apparently works with great effect and has been used many times by austin seven owners for many years,
cheers Ian.

Location: wet murky Worksop

Have struggled to get Photobucket to obey me and show you this but below is the best I can manage. Anyway, here's my solution. How I dislike hydraulics! And Photobucket!
PS the bleed nipple has a cover on it.
http://i179.photobucket.com/albums/w283/stuartu/2011_0108diabolical0001.jpg

Regards, Stuart

Stuart,

that's perfect, exactly what was going through my head when I was trying to work out how to overcome it this afternoon, very useful.

How did you block the bottom part of the slave cylinder that the rubber pipe goes into?

Cheers

R

Well at least you could see the picture, R.
Answer: with an Allen headed grubscrew pressing on an appropriately sized ball bearing.
Regards, S.

There was another discussion a year or so ago around converting cable to run as Twin Leading Shoe. This could use a motorcycle type way of doing it with the outer cable on one leg and the inner cable on the other leg. The harder part is converting to twin leading show. Involves creating a new cam at the top, with a new pice bolted onto the back plate.

There was a very smart setup by Bernard. I am not sure if he still reads this - or if he got his car finished?

Jack French had some designs in the 50's as well.

Peter

Just seen the picture posted by Stuart, that is also along the lines I have been thinking about this afternoon and unless the steering arm is re-designed I cannot see how twin leading shoes can possibly fit. The back-plates can only be rotated 180-degrees and I guess that the wheel cylinder position has been determined to give the required space for the adjustment mechanism.

Alan's set-up is along similar lines, but on his car he has not got any bleed nipples! So, it looks like this has been a problem for a considerable time, interesting that there has been very little comment that I have seen.

Ruairidh - many thanks for the confirmation about your installation, although, I cannot see that the adjustment of the snail cam would make any difference if it were trailing or leading. Thinking about it logically, the rate of wear of the brake linings should be the same no matter which way the drum is rotating, the difference between trailing and leading is the effort required and the efficiency of that effort, but no matter what system there is, the contact of the brake lining is what stops the rotation and it will not care how or where that comes from! So unless your snails are worn so that they slacken off???

Reckless Rat - on the conversion I am undertaking - you can see on my photos at the top of this post, the two wheel cyclinders that have been fitted to the back-plate in the manner you describe.

From my reading around the subject it seems like it was the late 1930's that the leading shoe arrangement was first introduced - an edition of Practical Motorist dating from 1939 explains the set-up to readers and they say it has a 30% improvement over previous arrangements (probably leading/trailing).

Well, having seen the set-up on Stuart's car, I think that arrangement with the lower connection blanked off is the best way to go.

It would be interesting to know how many cars have been set-up with twin trailing shoes.

Thanks everybody for their input - it does show how useful this Forum is at sharing ideas to mutual benefit - modern technology can sometimes be useful!

Gary

Location: Saltdean, Brighton

As Peter mentioned I manufactured a TLS conversion for my special but it uses few original parts. The reason for having four shoes was to make use of a motorcycle component that's available in the correct diameter.

The car is nearly finished but I've yet to try the brakes!

Regards Bernard

My comments regarding the set up were meant to be for Ruairidh whose arrangement is probably trailing/trailing. However, Ruairidh - take one of the hubs off to make sure! If you take off the nearside wheel & hub, the front cylinder should be acting on the bottom brake shoe and the rear one on the upper shoe (so they open in the direction of rotation)

Gary, I can see your intention is to go the right way.

However, having seen your set up and the suggestions regarding a blanking plug for the rear cylinders I would opt for an arrangement similar to Stuart's. It's important that the brakes can be properly purged, so you need a bleed nipple on each hub (on the other cylinder to where the flexible is mounted), but also you need to ensure that there is no obstruction/stress to the modification when placing the wheels on full lock - be careful regarding the location and securing of your flexible hoses so there is no over stretching/excessive bending of the flexibles, and of course that they can cater for full bump & rebound of the suspension.

It looks like a nice job. I hope you manage to sort it all out. Good Luck.

Location: Downhill from that place on Ian Dunford's photo

Gary,

FYI, I found the Morris 1000 springs not sufficiently strong to be effective and changed to A7 Semi Girling ones which worked much better and are easily available. The snail cams could well be worn, I'll check them also.

Reckers,

I will check the internals, but I am certain it is wrong from what you have said. My father and I think that is has been like this since he purchased in in 1964! We believe the conversion was done in the late 1950's...

Stuart's design looks good and that will be my first move once I have located the correct banjo union.

Thanks again.

In my humble opinion one of the most valuable technical discussions in a while.
Thank you Gary for your initial question and clear pictures.
This has revealed a very serious problem with what appears to be a readliy available conversion. Although I would not use this (being a sad vintage car traditionalist) I can see the attraction.
Thank you for the expert evaluation of leading versus trailing shoes and confirmation of the need for leading (or at least leading and trailing) shoes on front brakes.

This brilliant evaluation and solution would have been very difficult without the forum, shown by the continuing use of incorrect assemblies over many years. I would hope that the producers of this conversion are advised of the difficulties and and methods needed for the correct assembly.

Tony.

Location: Melbourne, Australia.

Whilst I of course accept that all the above details of the dangers of the trailing shoe situation are undoubtably correct ,I have to point out that the actual result in driving around for 46 years,in this parlous condition(only means of transport until 1970,and well over a quarter of a million miles in total)I have never actually run into anyone myself,but I did on two occasions manage to lose-weigh rapidly enough collect two rear-enders I have however had a few exhilarating moments on trying to turn around on 1in3 hills(having lost forward motion for some inexplicable reason), to find that going rapdlly back down towards sea-level,in reverse the brakes do not actvate without vigorous pumping. I should have looked into this decades ago.

Location: Frampton Cotterell

Ruairidh,The components required should be as per standard morris minor rear brake set up(eg banjo, bolt and bleed nipple) all are readily available from any minor specialist.

Cheers Ian

Location: At work in sheffield

This is an old problem, I remember seeing quite a few hydraulic braked Sevens at Beaulieu in the 60s and their answer to the problem was to fit the track rod in front of the axle. I don't care to think what it did to the steering, but the Ackerman principle was probably lost.
One of our Sevens was twin trailing shoe when we got it in the sixties and it worked well however I wasn't happy with the basic principle and changed it to twin leading shoe. I removed the nipple end from the bleed screw flush to the hexagon to get clearance with the track rod arm. To bleed the system I removed the track rod and arms and push a small diameter hose into the nipple and use an Easi Bleed one man bleed system so there is no risk of drawing arm back in. After all that there wasn't a great improvement in braking with twin leading shoe. That particular car has since been converted back to cable brakes because with the linings that are now available from our suppliers they are as good as hydraulic. The hydraulic conversion remedied the problem of useless brake linings that were available in the 60s
Another problem I found was on fitting a spare rebuilt track rod assembly to the car was it wouldn't fit because one of the arms fouled the bleed screw-the track rod arm was bent.
If you need stronger brake shoe return springs Ruairdh it suggests that you have a master cylinder for disc braked Morris Minor which has a pressure sustaining valve in it.

Location: Stockport

Dave, I knew I should have stayed in bed this morning!

When recomissioning this car 5/6 years ago, as a suprise for my parents (they went to Norway on their Honeymoon in this car), my gut reaction was to return the braking system to it's original uncoupled system (which I do know, understand and trust). However, I decided to replace what was there, at great cost, ah well...one step closer to getting it right...maybe?

Ian B, many thanks, I had thought this also and will investigate.

Ian D, do you want it back, not sure I can get Willow and twins in the back?

It's snowing up here again!

Ian
Thanks, I am familiar with the Bowden type cable brakes, it was the twin leading shoe bit that interested me! .

pgs, fantastic pictures, that has trigered my memory a bit now and I seem to remember more of the previous thread now!

Re the track rod facing forward to give clearance , I have seen several racers which do this so maybe the obvious effect on the Ackermann geometry is not that noticable with narrow tyres? This would solve the problem.

The stub axles in the pics look like Girling ones? If so could a backplate arrangement allowing the fitment of cylinders top and bottom be arranged or is there not enough room to do this? I take the point that the current set ups only allow movement of 180 degrees.

Steve

Steve,

"Re the track rod facing forward to give clearance , I have seen several racers which do this so maybe the obvious effect on the Ackermann geometry is not that noticable with narrow tyres? This would solve the problem."

I would have thought that putting the track rod arms in from the front would have compounded the problem causing 'toe in' on cornering. Or is there enough room to reverse them side for side with a lengthened track rod?
Or perhaps, as with the twin trailing brake shoes on the front, the non Ackerman effect doesn't really matter.

Tony.

Location: Melbourne, Australia.

Some 40 years ago I was offered a kit of hydraulic conversion parts from the chap up the road who had just scrapped his special! I had to do all sorts of inventing to fit them into my Box Saloon and ran into the problem of the interference with the track rod as shown in Gary's picture on 6 January. As suggested earlier the solution was to use a pipe nipple to trap a small ball bearing on the cone face of the fittings. This has served me well since then. The track rod is tapped out whenever there is a need to bleed the brakes.
Ron

Location: Thornbury S Glos

Gary,Anothere solution to the problem of the arms fouling the bleed nipple would be to heat the arms up and put a dog leg in them sufficient enough to clear the niple as per a dropped front axle setup.I`ve done this on the RTC and it works with no clearance issues at all.

Ian.

Location: Worksop

Using a twin trailing arrangement for front drums is not without precedent, but the whole system needs to be designed from the outset to take its characteristics into account. A vacuum servo is likely to be needed to reduce pedal pressure, unless the car is a lightweight.
I would worry about incorrectly assembling a system to be twin trailing rather than twin leading. OK, you may be able to muster a much higher pedal pressure (i.e. hydraulic pressure) to get the fronts to work, but spare a thought for the back brakes. Unless their slave cylinders are reduced in diameter/area compared to the fronts, the braking force will be higher on the back wheels than the front. This is exactly what you don't want, as with weight transfer during braking the load on the back wheels is considerably reduced. There is then a risk of rear wheel lockup, especially under low friction road conditions.

Tony
Yes I agree with you re the ackermann issue, but several racers seem to get away with it? I have also seen the arms reveresed as you suggest and the backplates cut away to clear steering arms!

I've been to Simms today and tried to look at some brakes for ideas, but its difficult when they are covered in mud and bouncing off the ground when they drive past .

Steve

Trackrods are frequently sited ahead of the axle, particularly on a lowered car, 'cos there isn't much room behind. Simplicity's like that now, though wasn't always.
The alternative, as mentioned above, is to bend the steering arms and that neatly solves the brake issue as well.
Mind you, I think that with 2LS hydraulic brakes there's far too much front-end braking and I remember cutting half the linings of each shoe off Martin Eyre's Ulster when I raced it in 1973. Last I heard it was still like that.

Location: Richmond, Texas

I think my car has trailing shoes,cant get to it at present,but it is possible to lock up the front wheels if breaking hard.
moving the track control arms forward increases the turning circle,tried it.

Gary

In response to your original post, (and now that I've got the hang of the html thing) pictures as follows (twin leading shoe set-up all using early morris minor parts)





hope this helps

Location: Bunkerton Castle

Very smooth Snoots, but I wouldn't expect anything different!

Regards to the good lady and number one!

Cheers

R

p.s. where would I get those natty double banjo joints, they make for an excellent set up?

Ruairidh.Have you noticed the brake cylinder rears.They`re not the usual two hole type.The likes of which I have not come across.If you look at the back plates they have been altered, presumably to take the different cylinders.

Location: Worksop.

Ian,

Lord Snooty (another Ian in reality), has a very interesting special which was built in the 1950's by an RAF pilot. The car is very well built and even has "flying Controls" on the dashboard!

The back plates look to be Girling ones that have been modified. I do like the double ended banjo unions which would be very useful.

Cheers

R

The double banjos are probably out of the RAF stores!!

I recognised the colour scheme on the axle immediately. Ian, can we have some pictures of the rest of the car?

Regards

Rob

Location: The 3D shed,Tewkesbury

I agree Rob. Lets see some more of this car please!

Location: worksop

My take on twin leading front hydraulics on my racer, made easy with dropped steering arms and lowered radius arms.

Location: Windy Surrey

The Morris Minor early wheel cylinders for the Series MM cars are listed as being available as patten parts only from Morris Minor specialists - but as I have new Lockheed wheel cylinders fitted as part of my back-plate kit I would not wish to change this!

But the set-up on LS's car looks very neat.

I have ordered some parts from three different suppliers - grub screw, banjo & banjo bolt, I have just been told that the UNF banjo that I had ordered is not longer available - the ones available for the Morris Minor are UNC, which is not a problem as a UNC connection could be made, but the layout in Stuart's set-up would need to be varied as the brake hose end is UNF!

Once I get the parts I will see how the fit together and then post the results here to share.

Gary

Location: Saltdean, Brighton

I've been round to see my RP owning friend (who hasn't moved into the computer age) who experienced the same problem Ruairidh. Brakes binding because the brake shoe springs weren't strong enough. Apparently there are a variety of master cylinders for the Morris Minor-13/16" and 7/8" dia and some have a pressure sustaining valve set to maintain 8 psi in the system with the brakes off. Also there are different brake shoe springs. His solution was to remove the pressure sustaining valve. Your solution of fitting stronger springs sounds better.

Location: Stockport

Thanks Dave.

R

Chaps, here she is ....... (the smaller one of the two)



My modified Swallow two seater - not to everyone's taste, but great fun. Originally built in 1930, then modified in the early 50's after the tail was damaged.

Location: Bunkerton Castle

Thats certainly different your lordship.But I like it!

Location: Worksop Notts

The Bowdenex system does not increase cable tension.
As the axle twists forward, so does the outer cable anchorage move with it, assuming it's mounted on the backplate.
And if it isn't mounted on the backplate, I can't imagine where it'd be!

Location: Richmond, Texas

Bowdenex cable tension does increase with brake application. One inner end is attachhed to the brake shoe lever, the other end is chassis mounted at the cross shaft. The outer cover is only a guide.

Location: south wales, slightly drier

I'm sorry to disagree John but, all Bowden cables operate on the same principle, i.e. that the "pull" of the inner is against the restraint of the outer. The outer most definately is NOT only a guide.

Location: Shropshire

Thank you Ian, saves me explaining it!

The ultimate proof is to disconnect one or other of the outer attachments and ask the doubter to hold it in place while you apply the brake pedal. Why would it move with such vigour if it were only a guide?

I'd also quarrel with the argument about the 5/16" bolt. It only holds good if the rest of the ball joint and bushes are clapped out. The bolt serves only to secure the radius arms and their bushes to the ball. The bolt should never be in shear.

Location: Richmond, Texas

Roger,

Correct on both points. The Bowden Cable outer sheath is a compression member. At the pedal end the inner cable is pulled against the outer sheath fixed at this end to the chassis, at the brake end the inner cable also pulls against the same outer sheath fixed to the chassis via the hub back plate to operate the brake lever.
The 5/16" bolt through the ball joint holds the arms with two brass cups to the chassis ball by tension, not shear. If it so loose it is in shear then the whole assembly will fail.

Tony.

Location: Melbourne, Australia.

If, as is often suggested, you do a forum search on, say, Bowden Cable you will see this has been discussed before, with some Austin 7 expert having the wrong story on how a Bowden cable works also, which has probably lead others astray. Have a look at a bicycle brake system to confirm the way it works.

Tony.

Location: Melbourne, Australia.

Just a note to bring matters up-to-date on the extra parts needed to make the wheel cylinder connections work for a twin-leading shoe set-up.

It has not been as easy as I would have thought to get the parts, I guess the demand for the components is low and these are no longer stocked/made.

Anyway, I have almost achieved success - one part I am not totally happy about!

So, the parts I have obtained are as follows:-

1. UNF grub screws for use with an Allen key, these were obtained from

www.modelfixings.co.uk

- these come in a packet of 5 for £1.50, but there is a minimum order of £3.00, so I had to buy 10! I will keep 2 as spares, but that leaves three pairs - if anyone wants a pair, private e-mail with your address and I will post to you.

2. UNF brass banjo adapter female - this is 30-degree angle fitting, which actually will work better than a straight connection, but anyway was the only one that is available now, the other shown on the website is not! - this came from Think Automotive -

www.thinkauto.com

Part Number BF41-3, cost each £8.91 each plus VAT and postage.

3. UNF Brakelight switch banjo bolt - this is for a Mini, and obtained from

www.minispares.com

Part Number 7H7995, cost £5.38 each plus VAT and postage. It is this bit that I am not too happy about - the thread (for the brake light switch when used on a Mini) does not seem quite right for a UNF, I have tried fitting different brake light switches and I am wondering if this is metric! If so, then I will need to introduce metric threads into the equation!

Here are photos of the parts I have bought and I have quickly put on the back-plate just to show how they go, once the thread issue has been sorted out I will properly plumb the brakes together.

Very many thanks for all the comments and observations made by members, much appreciated!

Gary

Location: Saltdean, Brighton - where it was sunny today!