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Disc Brake Pad wear

Technical help for Series one, two and three Lambrettas. Models include the Li, Li Special, TV, SX, GP, Serveta and API/SIL models

Disc Brake Pad wear

Postby Storkfoot » Mon Oct 25, 2021 7:41 pm

These are the pads from the inboard hydraulic front brake on my TS1. As you can see there is significant lop sided wear on both pads.

Image

The calliper is one that is held in by a circlip. The seals were replaced a couple of years ago so not many miles ago. As you have to on most pads, the outer edges had been filed down to ensure that they dropped into the hub freely. The brake works well.

I am just wondering, is this lop sided wear usual? If not, what is it a symptom of?
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Re: Disc Brake Pad wear

Postby Warkton Tornado No.1 » Tue Oct 26, 2021 12:33 pm

Blimey!

Somethings tipping & whilst you might expect the static pad to do so (with the adjustment screw being the pivot) I am surprised that both sides have been affected. For such wear to occur, the clearance between the pads & their housings must be 'there' but I suspect something else is amiss.

My reasoning is that both pads tend to spin a little in their housings under just a little load until full force is applied. That used to concern some racers, looking for every advantage, & the moving pads were shaped to fit the housing with @ least one ear to counter rotation. Meanwhile, the static side would not have an adjuster fitted, just large shims of various thickness that fitted snugly.

I'd look @ the moving piston of your slave unit because that may be the issue, though don't discount there being an excess clearance issue with that, too. I have no experience of the clip-in slaves as I've only ever used screw in type, but tipping seems a distinct possibility :?
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Re: Disc Brake Pad wear

Postby Storkfoot » Tue Oct 26, 2021 1:54 pm

Warkton Tornado No.1 wrote:Blimey!

Somethings tipping & whilst you might expect the static pad to do so (with the adjustment screw being the pivot) I am surprised that both sides have been affected. For such wear to occur, the clearance between the pads & their housings must be 'there' but I suspect something else is amiss.

My reasoning is that both pads tend to spin a little in their housings under just a little load until full force is applied. That used to concern some racers, looking for every advantage, & the moving pads were shaped to fit the housing with @ least one ear to counter rotation. Meanwhile, the static side would not have an adjuster fitted, just large shims of various thickness that fitted snugly.

I'd look @ the moving piston of your slave unit because that may be the issue, though don't discount there being an excess clearance issue with that, too. I have no experience of the clip-in slaves as I've only ever used screw in type, but tipping seems a distinct possibility :?


Thanks. I have changed the pads now. I shall keep an eye on them over the months ahead.

I know both pads are worn but it is possible that I swapped them over last year and did not notice the lop sided wear.

I am also thinking that, over the past year, I have not adjusted the static pad. I have just let them wear out and rattle around. The “bite” point has been towards the end of the lever travel. In my head, I put this down to needing to replace the DOT4 but, in reality, it was probably worn out pads. Maybe.
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Re: Disc Brake Pad wear

Postby vegansydney » Wed Oct 27, 2021 10:19 pm

Wow! Never seen anything like that.

I can't help with the issue but I've had great results with OEM disc pads. They're hard to find, but IMHO it's worth keeping your eyes out for NOS ones.
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Re: Disc Brake Pad wear

Postby Fast n Furious » Wed Oct 27, 2021 10:50 pm

One of the design failures with the standard disc brake set up is the actuator retaining circlip.
When the brake is applied, it can only apply a limited degree of brake pressure to the pads irespective of how hard you pull on the lever because at a certain point it becomes easier to distort the retaining circlip, which is trying to apply an opposing force. This is why these brakes always feel a bit springy on your fingers.
Because this clip is only partially enclosed, it doesn't distort concentically. It cockles over a bit and applies an offset force to the moving pad, resulting in uneven pad wear.
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Re: Disc Brake Pad wear

Postby vegansydney » Wed Oct 27, 2021 11:26 pm

One of the design failures with the standard disc brake set up is the actuator retaining circlip.... Because this clip is only partially enclosed, it doesn't distort concentically. It cockles over a bit and applies an offset force to the moving pad, resulting in uneven pad wear.


...but why would this happen on an inboard that has been converted to hydraulic, as per the original post? Happy to be corrected, but all hydraulic conversions I've seen use a threaded actuator, removing the need for a circlip.
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Re: Disc Brake Pad wear

Postby coaster » Wed Oct 27, 2021 11:51 pm

vegansydney wrote:
One of the design failures with the standard disc brake set up is the actuator retaining circlip.... Because this clip is only partially enclosed, it doesn't distort concentically. It cockles over a bit and applies an offset force to the moving pad, resulting in uneven pad wear.


...but why would this happen on an inboard that has been converted to hydraulic, as per the original post? Happy to be corrected, but all hydraulic conversions I've seen use a threaded actuator, removing the need for a circlip.


The OP says that its the type of hydraulic slave cylinder that is retained by the large circlip ;)
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Re: Disc Brake Pad wear

Postby Storkfoot » Thu Oct 28, 2021 12:21 am

I have never contemplated getting the backplate threaded just in case I want to revert to a reverse pull. I have run this brake for around 10 years and it has been the best Lambretta brake I have ever had in terms of touch, feel and stopping power.

I have found that the outboard hydraulic brakes I have run have been too fierce, probably because of the capacity of the master cylinder and piston.

I am thinking that I got complacent about its effectiveness and neglected to adjust it when I should have.
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Re: Disc Brake Pad wear

Postby Warkton Tornado No.1 » Thu Oct 28, 2021 12:40 am

vegansydney wrote:Wow! Never seen anything like that.

I can't help with the issue but I've had great results with OEM disc pads. They're hard to find, but IMHO it's worth keeping your eyes out for NOS ones.


When I rebuilt a cable operated disc some time ago, I put some OEM pads in, but I had to go back to the usual sintered.

Sintered pads with a hydraulic set-up (with correct, smaller master piston) combine to make an excellent brake IMO, but racing brake fluid is essential to avoid boiling the fluid.
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Re: Disc Brake Pad wear

Postby hullygully » Thu Oct 28, 2021 8:19 am

I wish I'd have known about the racing brake fluid on my old internal hydraulic disk as it got toooo scarey @ times, espesh on a coast to coast run :?
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Re: Disc Brake Pad wear

Postby Warkton Tornado No.1 » Thu Oct 28, 2021 11:45 am

hullygully wrote:I wish I'd have known about the racing brake fluid on my old internal hydraulic disk as it got toooo scarey @ times, espesh on a coast to coast run :?


I suppose the good thing about that is it proves that the internal disc set-up can be modified to work very hard. As far as I'm concerned, the ethos of a Lambretta with panels was to enclose as much of the necessary workings as possible, so an external disc does not sit right with my idea of aesthetics. Of course, a master cylinder on the 'bars is IMHO essential, but they can be made to look 'made for it'......Before anybody claims that a single external disc is superior, I'd like to see the proof.
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Re: Disc Brake Pad wear

Postby Storkfoot » Fri Oct 29, 2021 6:21 pm

Image

That is the caliper. You can see it flex against the circlip when the brake is applied.

I did try sintered pads years back but they squealed badly so I reverted to standard pads. I never knew there was a race standard DOT4, to be honest.
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Re: Disc Brake Pad wear

Postby Fast n Furious » Fri Oct 29, 2021 8:04 pm

There is...........its called DOT5 :lol: :lol: :lol:
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Re: Disc Brake Pad wear

Postby Storkfoot » Fri Oct 29, 2021 9:25 pm

I’ll give you that one :D

http://goqcrew.com/what-is-the-differen ... ake-fluid/

That does say this though:

“There are DOT4 fluids with boiling points that exceed DOT5 so there’s really no need to consider using DOT5 for on-road use”
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Re: Disc Brake Pad wear

Postby Fast n Furious » Fri Oct 29, 2021 9:56 pm

DOT 5 was pricey when it came on the Market but not anymore.
You get the additional benefit from this silicone based fluid in that it's non hydroscopic, So, no water molecules to boil, gives longer service life and is non corrosive.

Just make sure when converting over to DOT5 that every part of the hydraulic system is absolutely squeeky clean first! Methylated spirit work well. ;)
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Re: Disc Brake Pad wear

Postby Storkfoot » Sat Oct 30, 2021 8:44 am

I have just replaced the brake fluid with DOT4. I’ll follow your advise and go to DOT5 next year when I change it again. Cheers :)
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Re: Disc Brake Pad wear

Postby Warkton Tornado No.1 » Sat Oct 30, 2021 11:13 am

When it comes to the retention of the mechanism, a standard internal circlip is doing it's job, but for a better, full circle solution, a 'Spirolox' multiple turn retaining ring is an option.

However, the fundamental flaw with the slave cylinder here is the excess clearance of it's diameter to the brake housing, allowing it to skew. That's where I'd be looking to improve things. If the slave can be made to bottom out in the housing, then it should no longer be able to tip to one side. If you can source some well fitting, hard shims that can go between the slave cylinder & the circlip/retaining ring, it should solve the issue.

It's all about the elimination of 'play' in areas that cause issues. I have an MSC hydraulic backplate that had not been assembled with the slave cylinder fully bottomed out. The consequences were that the 'C' portion had a crack @ it's base. I reasoned that there is no real shear strength in the 'C' portion & as the thread had been well engineered in the remaining full circle portion, I scrupulously cleaned it all up prior to reassembly with Loctite. That brake has been on a race machine for many years so has been trusted literally with my life..... ;)
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Re: Disc Brake Pad wear

Postby Fast n Furious » Sun Oct 31, 2021 12:15 am

+1 ;)
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Re: Disc Brake Pad wear

Postby Storkfoot » Tue Nov 02, 2021 3:26 pm

There’s about 0.4mm difference in the diameter of the caliper and hub. Having looked at it again, I think the best thing I can do is to check the static pad and adjust as necessary. Something I haven’t been doing often enough.
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Re: Disc Brake Pad wear

Postby dickie » Tue Nov 02, 2021 4:56 pm

I believe the problem isn't really boiling the oil, but getting it so hot that any moisture suspended in it boils. Water expands to something like 2000 times its liquid volume when it vaporises and is obviously massively compressible.

Although i just quick googled it and DOT4 boils at minimum 155c which isn't a massive difference!
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