• Welcome to the website of the Vincent H.R.D. Owners Club.

    Should you have any questions relating to the Vincent H.R.D. Owners Club, or Vincent H.R.D. motorcycles in general, please contact Graham Smith, Hon. Editor and Webmaster by calling 07977 001 025 or please CLICK HERE.

    You are unrecognised, and therefore, only have VERY restricted access to the many features of this website.

    If you have previously registered to use this forum, you should log in now. CLICK HERE.

    If you have never registered to use this website before, please CLICK HERE.

H: Hubs, Wheels and Tyres Brake drum skimming

overdale

Website User
VOC Member
Having got the wheels rebuilt for my 1951 Black Shadow, I'm now preparing to fit the drums. However closer inspection of the drums shows some areas of corrosion an the braking faces (previously hidden by masking tape) as I think the bike stood outside for some time before I bought it in 1971.
Set up in my lathe jig, the run out on the undamaged faces of the drums are all less than 0.1mm but the rough areas of corrosion need to be removed. They are the standard ribbed cast iron drums and I'm all set up to skim them, but would like to know what is the maximum diameter I can safely take them out to.
 

overdale

Website User
VOC Member
Hi Martyn, thanks for your quick reply. The problem is that the corrosion of the surface is quite deep and concentrated, indicating water standing in the drums for some time when is was left outside motionless. Just to be safe, I wonder if anyone knows if there is a maximum safe diameter for skimming the drums.
 

Martyn Goodwin

Well Known and Active Website User
VOC Member
Hi Martyn, thanks for your quick reply. The problem is that the corrosion of the surface is quite deep and concentrated, indicating water standing in the drums for some time when is was left outside motionless. Just to be safe, I wonder if anyone knows if there is a maximum safe diameter for skimming the drums.
Problem is if you skim the drums then you will need to regrind the linings to match the new diameter - and if you are not careful you can end up with pretty thin linings.

New drums and shoes are available from the likes of V3 (see mph advert) of rom Timetraveller on this forum - but Oh $$$$$$
 

BigEd

Well Known and Active Website User
VOC Member
VOC Forum Moderator
Hi Martyn, thanks for your quick reply. The problem is that the corrosion of the surface is quite deep and concentrated, indicating water standing in the drums for some time when is was left outside motionless. Just to be safe, I wonder if anyone knows if there is a maximum safe diameter for skimming the drums.
Without seeing a photograph of the extent of the corrosion you mentioned it is a little difficult to comment. (Send a photograph if you can. A picture is worth a thousand words.:)) My personal view is that if the corrosion is pitting then a rub with some emery would clean up any upstanding areas of the surface and the pitting would have little effect on braking. If the corrosion is deep then there may be a safety aspect so new drums should be considered. Skimming disadvantages have already been mentioned if you have to remove much material.
 

vibrac

Well Known and Active Website User
VOC Member
Its just a question of the proportion of the hub surface that is affected after all the hub surface is about a third bigger than the shoe area any small loss of braking area will be insignificant and would soon get filled with compacted dust what constitutes 'a small area' is for you to decide consider the area taken up by rivet heads before we used bonding or lost by tapering of leading edges.Structural integrity as Ed says is a different matter.
 

Marcus Bowden

VOC Hon. Overseas Representative
VOC Member
Having never adjusted brakes that soon as they contact the drum they touch continuously for a full revolution. Indication is that all braking surfaces are not true even with the very nicely made Vincent Speet TLS arrangement. Have all ways thought of being able to turn wheels on their own bearings and machine the drums true. It is well worth consideration.
bananaman.
 

Martyn Goodwin

Well Known and Active Website User
VOC Member
Having never adjusted brakes that soon as they contact the drum they touch continuously for a full revolution. Indication is that all braking surfaces are not true even with the very nicely made Vincent Speet TLS arrangement. Have all ways thought of being able to turn wheels on their own bearings and machine the drums true. It is well worth consideration.
bananaman.
Yes Marcus,I have seen a devise sold in the USA that does exactly that BUT then there remains the problem of radiusing the shoes to match
 

overdale

Website User
VOC Member
Thanks for all your replies with some very good points - it's good to get different opinions.
I had already taken onboard that skimming the drum would possibly require thicker linings to compensate and have already organised thicker linings so that the shoes can be machined to suit the drum diameter if necessary. Fortunately, the procedure is well described in previous members posts! Obviously I want to avoid the cost of new drums if possible and will assess whether some skimming within safe tolerances can improve the braking surface without compromising the strength/safety of the drum. Will check things out tomorrow.
 

overdale

Website User
VOC Member
Managed to remove almost all the corrosion by skimming whilst managing to keep diameters within 178.5mm. Standard linings are 4mm thick, and am getting 6mm thick linings fitted to allow for good machining. Thanks for your help.
 

Monkeypants

Well Known and Active Website User
VOC Member
Re Marcus's comment about coming up with a way to skim drums on their own bearings ( and axle)
This is very easy to do.
I had a very strong pulsation in a BSA 2 leader brake. The bike was almost unrideable.
I tried using stick on Emery paper to arc the linings to the drum. That improved things very slightly.
I tested a piece of stick on Emery on the other way, stuck to the lining. When removed it came of cleanly, no adhesive stayed on the linings.
So it seemed safe enough to apply stick on adhesive to all of the lining surface.
With the brake plate back in the drum, the axle was installed and brake plate nuts snugged up.
I used a C clamp ( G cramp UK) to hold the brake arm in a brake lightly on position.
With the wheel laid flat on the work table, spaced up on a couple of blocks ( axle protrudes) and clamped to the table, the brake plate was rotated by hand. I could instantly feel the high and low spots as the drag would hit then release ( pulsation) .
After a few rotations it was time to crank the clamp a bit to move the shoes out a smidge.
After about ten minutes of this I could feel the drag becoming more even. After a couple of Emery changes and 30 minutes of work the drag was constant for the full rotation.
Job done.
Well almost.
Turn the paper around and re-arc the linings. Be careful with this as the lining material cuts off very quickly and you only want to take the minimum.
The finished product is perfect and it didn't take long, no tire removal or jig building required.
Not long after this I had the Vincent fronts relined and had the dreaded pulsation with that brake.
The Emery method worked perfectly on that brake as well.
I use 80 grit stick on.

Glen
 
Last edited:

Martyn Goodwin

Well Known and Active Website User
VOC Member
Re Marcus's comment about coming up with a way to skim drums on their own bearings ( and axle)
This is very easy to do.
I had a very strong pulsation in a BSA 2 leader brake. The bike was almost unrideable.
I tried using stick on Emery paper to arc the linings to the drum. That improved things very slightly.
I tested a piece of stick on Emery on the other way, stuck to the lining. When removed it came of cleanly, no adhesive stayed on the linings.
So it seemed safe enough to apply stick on adhesive to all of the lining surface.
With the brake plate back in the drum, the axle was installed and brake plate nuts snugged up.
I used a C clamp ( G cramp UK) to hold the brake arm in a brake lightly on position.
With the wheel laid flat on the work table, spaced up on a couple of blocks ( axle protrudes) and clamped to the table, the brake plate was rotated by hand. I could instantly feel the high and low spots as the drag would hit then release ( pulsation) .
After a few rotations it was time to crank the clamp a bit to move the shoes out a smidge.
After about ten minutes of this I could feel the drag becoming more even. After a couple of Emery changes and 30 minutes of work the drag was constant for the full rotation.
Job done.
Well almost.
Turn the paper around and re-arc the linings. Be careful with this as the lining material cuts off very quickly and you only want to take the minimum.
The finished product is perfect and it didn't take long, no tire removal or jig building required.
Not long after this I had the Vincent fronts relined and had the dreaded pulsation with that brake.
The Emery method worked perfectly on that brake as well.
I use 80 grit stick on.

Glen
Hmmmm. But Vincent brakes are a tad different. The hole in the backing plate on which the shoes are mounted is intentional larger than the diameter of the axle. So when on the bench the backing plate is NOT centralised, but free to 'wobble' about.

When installing the wheels onto the bike one is supposed to firmly apply the brake and keep it applied so as to centralise the linings to the drums as you tighten the axle up. So because of this I suspect the do it on the bench method may not work fully for a Vin.

BUT I think it MAY work if you did it with the wheel ON the bike.
Sequence would be

1. Remove wheel,
2. remove backing plate(s)
3. Apply Emery as described by Glen
4. Refit wheel
5. with axle loose, apply brake
6. Tighten axle
7. holding gentle pressure on brake lever, rotate wheel.

repeat as required

(idea for OVR - thanks Glen)
 
Last edited:

Monkeypants

Well Known and Active Website User
VOC Member
Thanks Martyn, you've reminded me that with the Vincent this procedure was done on the bike. I can't picture the stock Vincent brake but the racing brake plates on mine are just squeezed between the forks, there are no outer nuts.
I also left out the step of centralizing. This was done on the bench with the BSA just as the brake plate nut is snugged up.
In some ways it's easier on the bike as you have the wheel to grip, so a 1/16 horsepower lathe instead of a 1/64th horsepower lathe ( bench)
The paper changes are easier on the bench.
I believe that it only required one change with the Vincent as the pulsation was not as severe as with the BSA.
It was very annoying though and it is a silky smooth brake again now, very strong too. Both bikes will lock the wheel at speed if braked very hard.

Glen
 

Martyn Goodwin

Well Known and Active Website User
VOC Member
I have those same alloy race brake plates on my front wheel, standard ones on the back.

I am about to give your method, which sounds great, a try

Thanks again for the tip.

Martyn
 

Martyn Goodwin

Well Known and Active Website User
VOC Member
Glen, what brand or what device was the emery paper intened to be used on? My local hardware store did not have any self adhesive so I will need to look on-line
 

Monkeypants

Well Known and Active Website User
VOC Member
These are stick on discs that the autobody shops use. Someone gave me the roll about twenty years ago. It was about double the diameter then.
I cut lining width strips out of the middle.
I lied about the grit, it is 120, not 80.
 

Attachments

  • IMG_20210513_070012.jpg
    IMG_20210513_070012.jpg
    229.5 KB · Views: 9
  • IMG_20210513_070009.jpg
    IMG_20210513_070009.jpg
    248.3 KB · Views: 9

timetraveller

Well Known and Active Website User
VOC Member
Re. Martyn's post #13 above. It is only the racing style plates which have the oversized holes in the centre. The steel originals have holes which are just large enough to fit over the threads which take the thin nuts. If you buy some of the recently produced from billet brake plates it is a good idea to open up the centre hole. I mentioned this to the manufacturer but I don't think that he listened.
 

oexing

Well Known and Active Website User
VOC Member
Come on, this oversized brakeplate through hole is British BS, I´d bush this if I ever found this on any bike definitely. You will not find this bodge on any Fontana, Ceriani, EU bikes with any self-respect. When you machine the linings in the lathe they will be allright , no wiggling about oversized holes.
Don´t go for car painters abrasives, get your metal grinding material and put double side adhesive tape between layers, at least for grinding the drum . For linings the orange type is OK.

Vic
 

Can't Find What You Need?

Buyer Beware: Fake or Real?

The Mighty Garage Videos

List of Forum Categories

Top