Front Disc Brake Problems

[citydaz]

Hi,
Ive finally finished rebuilding my 150dl and have been taking it for a few short trips around the quiet back roads of Cheshire to run it in.
The problem is the very poor front disc brake. After paying top dollar for an Italian remade hub and many problems with the vendor - it being sent back 3 times for rectifications I have set it up and the main problem is that the actuator arm doesnt seem to want to spring back on release of the brake lever. This means that the brake "sticks on" a little after application and then there is loads of slack when I next pull the brake lever. Overall the stopping power is pitiful. I thought about adding a spring to the cable to force the actuator arm back to the start position. I removed the actuator arm this afternoon and noticed that the further in the actuator arm is the less spring back there is. Since the circlip positions the arm I thought that if I added a copper shim next to the disc pad this might position the actuator tight up against the circlip and then allow the arm to fully return to the "off" position.
Any advice?

[Warkton Tornado No.1]

The problem has been posted several times on this Forum, so worth the search.

The fundamental issue is ,as you have intimated, the remade actuators of any manufacture simply cannot emulate the OEM components (unless there has been a recent change I am unaware of)

A good secondhand OEM actuator will transform what you have, but who will part with them

[dickie]

The weak brake is almost certainly due to the dimples in the actuator being of a concave shape rather than the conical shape of the original. This means that the actuator moves faster, the further it's pulled, but at the same time has less force per unit of force applied at the lever. Like WT1 says, the only sensible solution is to source an original one. You get get new plates machined and hardened but I doubt very much if that would be economically viable.

The sticking actuator is probably due to it interfering with the back plate. The slots that the 'ears' slide in are a problem area, the bore diameter and parallel is another.

In my experience, remade discs are just a bit crap. Someone could make a few quid if they made decent actuators.

[Storkfoot]

viewtopic.php?f=10&t=12767&hilit=Actuator

I have three cable operated internal disc brakes. Two actuators I have rebuilt, the other is an aftermarket one. All three work well but, you are right, the actuator arm should return to its starting point. It doesn’t snap back but it does return.

Whilst a poor functioning actuator won’t make for a good brake, if your brake is so poor, I would think you may have other issues too. What pads, disc, thickness of cable do you have? Have you removed the circlip? Are the pins greased? Is the cable reverse pulled?

[citydaz]

Thanks for the replies - lots of information to take in.
I will try and answer the questions you have asked:
The slots that the 'ears' slide in are a problem area, the bore diameter and parallel is another. The actuator is a snug fit into the back plate - should i gently dress the "ears" so that it has more play?
The pads are newfren, the disc is italian, I havent removed the circlip, I dont know about the pins being greased, I would have hoped the shop did that when they assembled it, the cable is a BGM one, what cable is the best to get?
Its a Tino Sacchi re-made disc if that helps.

[Storkfoot]

I have never seen the full Hydra front disc hub before but I have heard of someone who was less than impressed with one. I do have a Tino Sacchi disc in one of my set ups. In my opinion, these discs are the best around. That is assuming that your set up does have this disc fitted. I say that as the one I have has no space for a circlip. It runs free on the pins and is vented.

The cable should be 2.5mm thick, not 2.0mm.

Have you adjusted the pads from the window side?

Is there any chance that you can take the hub off and post some pictures of what is inside? If you want to send me the pictures, I can post them on here.

If the actuator fits into the backplate quite snugly, that would be fine and dressing it would probably make the situation worse. That said, I do think the actuator may well be the main issue. Again, can you please take a picture of the front and back of the actuator?

PS Have a read of this thread:
viewtopic.php?f=10&t=12209#p108661

[dickie]

It's hard to know what 'snugly' means as it's a very subjective word.

But the actuator ears should slide up and down the slots with almost no force at all.

It's hard to imagine that it's not returning because of the actuator itself, but that is likely to be a reason for poor braking.

It's better to separate the issues in your mind or you can confuse symptom with cause etc. If that sounds patronising, I apologise but I've got 3 apprentices at the minute, so it's probably second nature!

[citydaz]

Hi, thanks for your replies and help!.
the cable is 2.0mm thick - its from a BGM cable set. I enquired about a 2.5mm diameter inner cable but was told it wouldn't fit down the outer cable.
I have previously adjusted the pad from the window side, even though the vendor had said he had shimmed it up so that it didnt need any further adjustment (!?)
I will take some photos tomorrow when I have some time to remove the actuator.
Im thinking that if i buy a compression spring and fit it onto the cable this will help the arm move back plus regrease the actuator and circlip this will help.
Cheers
Citydaz

[Fast n Furious]

These disc brakes are somewhat challenged by their design.
The amount of force that the actuator can apply to the moving disc pad is proportional to the reverse force applied in the opposite direction onto the retention circlip, which will readily deflect if pressed beyond a certain point.
Saying that........ I recently did a hydraulic conversion to one of these brakes and even though I could get it so hot and smoking under testing that it would burn the paint on the castings the braking effeciency was really no better than before, which was dissapointing.
I remain optomistic that it can be improved, but have shelved it for now.
Need one of those Eurica moments.

[Storkfoot]

https://www.lambretta.co.uk/product_inf ... ts_id=7420

https://www.scooter-center.com/en/brake ... -bgm6408fb

They are the correct cables. I have used the CamLam one. It has no nylon sleeve so needs the cable greasing.

The proper cable will assist but is unlikely to be the main reason for your problems. In my opinion, you really need to split the hub apart and see what is in there before you do anything.

[dickie]

These disc brakes are somewhat challenged by their design.
The amount of force that the actuator can apply to the moving disc pad is proportional to the reverse force applied in the opposite direction onto the retention circlip, which will readily deflect if pressed beyond a certain point.
Saying that........ I recently did a hydraulic conversion to one of these brakes and even though I could get it so hot and smoking under testing that it would burn the paint on the castings the braking effeciency was really no better than before, which was dissapointing.
I remain optomistic that it can be improved, but have shelved it for now.
Need one of those Eurica moments.

That's kind of hard to get your head around because the job of a brake is to turn kinetic energy into heat energy and it sounds like it's doing exactly that, and pretty well too.

Maybe it generated a lot of heat but over a longer time period than you'd want? Maybe it generated no more heat than a drum brake but poor ventilation and/or high ambient conditions stopped it from cooling sufficiently?

I suspect I'm wandering slightly off topic here.

[Warkton Tornado No.1]

These disc brakes are somewhat challenged by their design.
The amount of force that the actuator can apply to the moving disc pad is proportional to the reverse force applied in the opposite direction onto the retention circlip, which will readily deflect if pressed beyond a certain point.
Saying that........ I recently did a hydraulic conversion to one of these brakes and even though I could get it so hot and smoking under testing that it would burn the paint on the castings the braking effeciency was really no better than before, which was dissapointing.
I remain optomistic that it can be improved, but have shelved it for now.
Need one of those Eurica moments.

That's kind of hard to get your head around because the job of a brake is to turn kinetic energy into heat energy and it sounds like it's doing exactly that, and pretty well too.

Maybe it generated a lot of heat but over a longer time period than you'd want? Maybe it generated no more heat than a drum brake but poor ventilation and/or high ambient conditions stopped it from cooling sufficiently?

I suspect I'm wandering slightly off topic here.

Whilst we are off topic……

I suspect that the issue is with the pads. All disc pads are constructed with a friction material but some are far superior in retarding the vehicle they are fitted to.

The best pads for our inboard discs are fairly obvious in being sintered, but I doubt all are equal.

F’n’F will undoubtedly know what he is doing but it’s worth repeating……IMO - apart from ensuring a good OEM actuator is in place along with the stoutest reverse pull inner cable obtainable for such systems - is to be very methodical in the assembly of the hub. Personally, I don’t drill out the holes or remove the anti-rattle circlip - not even on a racing brake. I do assemble with Copaslip. For ultimate stopping with an internal disc, hydraulic is the way to go but very few conversions can match the old MSC set up. A cross drilled disc to the correct geometry formula makes for better cooling along with an air scoop. The master cylinder needs to be the optimum cylinder diameter & the radial levers such as Brembo are superb. Lastly, often overlooked because certain fluids are kinder to the paintwork, proper race fluid such as Lockheed is a revelation.

[dickie]

WT1, you've reminded me of another 'thing' that I found with remade discs.

The anti rattle clip doesn't need removing, but in the 2 that I've worked on, I had to bend the clip to a smaller diameter or it gripped the pins too hard. I just squashed it in a vice until I was happy. Made a big difference. Before I did this, I could barely slide the disc on the pins; easy after, but still retained its anti-rattle feature.

[citydaz]

Guys - very interesting debate and I feel I know a lot more now than I did last week about disc brakes!

Tonight I removed the actuator to inspect it. The surface where the circlip butts up to was scored and scratched as was the circlip.
I cleaned these up with fine grade sandpaper. I also managed to prize out the pad, the circumference of which i dressed up so that it moved more freely in the housing. I greased up the actuator ears and it slid in with ease. The circlip fitted better into the groove.
I pulled the brake lever and ............. drum roll.....................a much better response from the actuator with it springing back, and minimum subsequent loose play in the lever and the wheel stopping.
So it seems there are many variables in improving the disc brake operation as well as lots of opinions and theories / myths!
Thanks for your help.

[Fast n Furious]

WT1, you've reminded me of another 'thing' that I found with remade discs.

The anti rattle clip doesn't need removing, but in the 2 that I've worked on, I had to bend the clip to a smaller diameter or it gripped the pins too hard. I just squashed it in a vice until I was happy. Made a big difference. Before I did this, I could barely slide the disc on the pins; easy after, but still retained its anti-rattle feature.

Another way to trim the antirattle clip is by relieving the clips grip slightly using a dremmel through the 3 holes. If you over do it,then you can just tap the clip around into a new position and start again.
I plan do do some cost effective experimentation with the pads. The current plan is to use some old stock pads from various cars that I have by cutting then up with a 42mm hole saw and then machine them up to finished size in the lathe.
Not sure when I can get around to this but I'll report back when I do.

[Warkton Tornado No.1]

WT1, you've reminded me of another 'thing' that I found with remade discs.

The anti rattle clip doesn't need removing, but in the 2 that I've worked on, I had to bend the clip to a smaller diameter or it gripped the pins too hard. I just squashed it in a vice until I was happy. Made a big difference. Before I did this, I could barely slide the disc on the pins; easy after, but still retained its anti-rattle feature.

Another way to trim the antirattle clip is by relieving the clips grip slightly using a dremmel through the 3 holes. If you over do it,then you can just tap the clip around into a new position and start again.
I plan do do some cost effective experimentation with the pads. The current plan is to use some old stock pads from various cars that I have by cutting then up with a 42mm hole saw and then machine them up to finished size in the lathe.
Not sure when I can get around to this but I'll report back when I do.

That is a good plan which, similarly, I had been intending to try

The concept is nothing new as sintered pads from motorbikes were used as material before Lambretta specific pads became available. However, getting my head around friction characteristics of not only pads, but the disc itself, I wonder whether a better choice would be to consider racing vehicles of a more similar mass to our own as being the better donor of pads & - possibly - the disc itself.

Until ceramic & carbon brakes came along (the latter which have to get hot enough to work) cast iron discs cross drilled & radially ventilated was probably the best option.

That’s my own current plan, though it’s been ‘happening’ for about 20 years

I have the disc, a couple of Lambretta specific hub mounts - CNC made in a stainless, but should I have been braver & opted for a good alloy? - & several hydraulic backplates with the prospect of offering up a variety of pad footprints.

Unfortunately, what I don’t have is the free time in which to do so many things I have in mind.

Going even more off topic, I tentatively offered up a solution for the crankcases that has mispositioned brake shoe pivot points. I have the lathe, material & the concept - along with many, many others - in my head. So, my apologies to those fellow members that were/are waiting on me. My intention is still to bring these ideas to fruition, but first I have to make my home habitable again……
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