Drum brake skim

Onder · Apr 12, 2023

Recently I see I posted on skimming brake drums. Recently as in February 2015! I know that drum brakes are killers and should be illegal etc but a properly setup drum actually can be fine for road work.
Pat Seager posted this service, might be of use to some of us:

Seager Engineering

www.seager-engineering.com

" does your front or back brake pulse when you apply the brakes"
We do Brake drum skimming to correct out round drums on a purpose made lathe. It can swing up to 28" dia....so you can leave the tyres on.... it locates on a mandrel using bearing adaptors and cones... 2 speed... does a very accurate job

£80 plus vat per wheel

Stephen Hill · Apr 12, 2023

As Seager's promotional words describe, turning a drum will get rid of pulsing.
That doesn't mean you will necessarily end up with a good brake. There are lots of other contributing factors.
And if you get everything else right, it still won't stop like a disk brake.

acotrel · Apr 12, 2023

Drum brakes heat up as you use them. If you fit soft linings they work well until they heat up, then you get fade. If you fit hard linings, they need to heast up until they work well. When you are doing 100 MPH down a long straight raod towards are hairpin bend - how do you know what yor brake will do when you need to use it ? THen there is another problem. If you brake has too much self-servo, it might not release fully after you use it. If the front of your bike stays down as you accelerate out of a corner, it will usually take you off the road into the bush.
A few years ago in Melbourne, there was an old guy who went on a club run on an old bike wearing a pudding basin helmet, the brake launched him and he did not survive.
What appears to be quite harmless, often is not.
In Australia, there is a classic race class in which all the bikes have drum brakes - THEY SHOULD BE BANNED. Nothing looks better, but they are extremely dangerous when used on fast bikes..
Our classic racing is run by sidecar guys. They are all dip stcks who would not know. With drum brakes, what you see, IS NOT what you get.
When I think back about what happened to me, I am simply appalled that it could ever be allowed to jhappen. The first time I crashed, I should have been banned for life.
I have had three crashes at speeds above 90 MPH - every one of them was caused by a drum brake.

gpzkat · Apr 12, 2023

Do the shoes get ground/matched to the drum? I remember having that done to a VW once and it helped a lot.

Stephen Hill · Apr 12, 2023

The theory is new shoes should be matched to the diameter of the drum. Matching the diameters is called "arcing" the brake shoes. Most people don't bother and put up with crappy brakes until they wear in.
If you turn a drum, you increase its diameter and the shoes should be arced to match.
Kind of fiddly, a service probably not easy to find locally these days.
There are diy methods using sandpaper stuck to the inside of the drum. I've done it. Works well.

gpzkat · Apr 12, 2023

Oh yeah now I remember arcing was the term, thanks. I was drawing a blank on the term. Many years since anything I've driven or ridden had drums on the front. My N15CS is disc, My '54 Willys has a Scout disc front. Last bike I had with drums was a '66 Bonneville and it stopped well for a drum as it was very well set up by Don Hutchinson for my late brother.

Stevo · Apr 12, 2023

acotrel said:
I have had three crashes at speeds above 90 MPH - every one of them was caused by a drum brake.

Nothing to do with the nut holding the handlebars?

Onder · Apr 13, 2023

You need to have a true drum for starters. Once that is good you can move on to the shoe contact. I posted merely because it is hard to find someone to true a drum with the tyre on. Yes, I know about using a mill.

Seeley920 · Apr 13, 2023

Stevo said:
Nothing to do with the nut holding the handlebars?

A bad workman always blames his tools

YING · Apr 13, 2023

Stephen Hill said:
The theory is new shoes should be matched to the diameter of the drum. Matching the diameters is called "arcing" the brake shoes. Most people don't bother and put up with crappy brakes until they wear in.
If you turn a drum, you increase its diameter and the shoes should be arced to match.
Kind of fiddly, a service probably not easy to find locally these days.
There are diy methods using sandpaper stuck to the inside of the drum. I've done it. Works well.

Stephen,
When doing the drum with sandpaper,what grit paper did you use? I could never find anyone around my area that does this service.
Thanks,Mike

Bernhard · Apr 13, 2023

acotrel said:
Drum brakes heat up as you use them. If you fit soft linings they work well until they heat up, then you get fade. If you fit hard linings, they need to heast up until they work well. When you are doing 100 MPH down a long straight raod towards are hairpin bend - how do you know what yor brake will do when you need to use it ? THen there is another problem. If you brake has too much self-servo, it might not release fully after you use it. If the front of your bike stays down as you accelerate out of a corner, it will usually take you off the road into the bush.
A few years ago in Melbourne, there was an old guy who went on a club run on an old bike wearing a pudding basin helmet, the brake launched him and he did not survive.
What appears to be quite harmless, often is not.
In Australia, there is a classic race class in which all the bikes have drum brakes - THEY SHOULD BE BANNED. Nothing looks better, but they are extremely dangerous when used on fast bikes..
Our classic racing is run by sidecar guys. They are all dip stcks who would not know. With drum brakes, what you see, IS NOT what you get.
When I think back about what happened to me, I am simply appalled that it could ever be allowed to jhappen. The first time I crashed, I should have been banned for life.
I have had three crashes at speeds above 90 MPH - every one of them was caused by a drum brake.

Admit it acotrel, you cannot set up a drum brake to save your life if your past comments on this website is anything to go by

Schwany · Apr 13, 2023

The drum hub or liner can be slightly out of round. Arcing the shoes won't fix it. Turning the drum will. I have this issue on a 230mm 4LS. One side tends to pulse during light use. To help with the pulsing I use sort of a progressive pull on the dual cable with the good side starting before the not so good side.

I've spent a couple of hours spinning the wheel with sandpaper adhered to the shoe trying to do a fake drum turn with shoe pressure against the liner. I'll probably do it again this summer, but if this service was available near me, I'd be standing at the front door of the place doing it before they opened in the morning.

Biggest issue with a pulsing big 4LS front drum brake is trying to ride in the wet. It is an invitation for a low side slide with cold tires. Been there done that. No more riding even with the threat of rain for me. I don't self mend fast enough.

MichaelD · Apr 13, 2023

I was wondering about having my drum skimmed, being desperate to get the brake working better than it did.

Before I went to the trouble and expense of getting the job done, I took out the brake and refitted the wheel into the fork, then spun it and held a screwdriver against the braking surface to see how much of a problem I had. It wasn't perfect, but seemed to be within about half a mm of perfect, so I'll leave it as-is, unless anyone feels that 0.5mm out of true will cause a problem?

Stephen Hill · Apr 13, 2023

0.5 mm is quite a bit of runout, but then you are eyeballing it so it may not be that meaningful.
Ideally you would be within a couple of thousands of an inch. A more practical approach is whether the forks pulse fore and aft. If you can't feel the brake and forks pulsing, the runout is probably ok. Try it at different speeds with different amounts of brake pressure. The pulsing will be more pronounced under some conditions than others.

Ying, you asked about what grit of sandpaper to use to "arc" the shoes. It was some time ago, but if I had to guess I probably used around 80 grit. Coarser will just mean the job goes faster. You aren't really concerned about initial surface finish, because in use the drum and shoe surfaces will bed in on their own.

YING · Apr 14, 2023

Stephen Hill said:
0.5 mm is quite a bit of runout, but then you are eyeballing it so it may not be that meaningful.
Ideally you would be within a couple of thousands of an inch. A more practical approach is whether the forks pulse fore and aft. If you can't feel the brake and forks pulsing, the runout is probably ok. Try it at different speeds with different amounts of brake pressure. The pulsing will be more pronounced under some conditions than others.

Ying, you asked about what grit of sandpaper to use to "arc" the shoes. It was some time ago, but if I had to guess I probably used around 80 grit. Coarser will just mean the job goes faster. You aren't really concerned about initial surface finish, because in use the drum and shoe surfaces will bed in on their own.

Thanks.Going to try this method out.
Mike

Drum brake skim

Onder

Seager Engineering

Stephen Hill

acotrel

gpzkat

Stephen Hill

gpzkat

Stevo

Onder

Seeley920

YING

Pittsboro,NC

Bernhard

Schwany

MichaelD

Stephen Hill

YING

Pittsboro,NC

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