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MG MGA - Brake drum plugs

I am rebuilding my rear axle and rear brakes. I ordered part #264-525, brake drum plug from Moss. I thought this was, indeed, a PLUG for the brake adjusting hole to keep dirt and water out of the rear brakes. Imagine my surprise to find that the part sent by Moss is just a plastic tube (see image).

Can anybody tell me what the function of this part is? It certainly does not Plug anything.

H Speer

According to the Clarke Spares MGA catalog that part is actually listed as a Dust Seal Ferrule and not a plug. It lists two different sizes 3/4" and 1/2" I guess it depends who drilled the holes at the factory. I still can't see what it is supposed to seal with a hole in the middle unless it is deep enough that it goes all the way to the brake backing plate. I don't have them on my "A". Todd's catalog does show a plug shaped metal plug for the front wire wheel brake drum again in 1/2" AND 3/4". I don't have those either because I have front disks.
Keith Lowman

Instead of a "Dust Seal Ferrule" it should read as a "Ferrule for a Dust Seal".
A ferrule is a ring that holds something in place, so I suppose you fit the ferrule and then insert a dust plug.

Mick
M F Anderson

A close look at the plastic tube gives the possibility that the small diameter fits into the drum and the larger diameter presses against the disc wheel. This would give a dust seal. Note Moss say that it only for disc wheels, not wire wheels.


Mick
M F Anderson

Mick is correct. If you install the wheel correctly, it lines up with a hole in the wheel, where it both seals out dirt and guides your screwdriver to the brake adjuster. You will note that there are two holes in the wheel, at different spacing, for different size brakes. The hub cap or nave plate covers the lot.

FRM
FR Millmore

I remember seeing the original parts on one of my dad's projects. Did they have an equivalent piece for wire wheels, or did the factory just leave the hole open in those cars?
Del Rawlins

The factory 1500 Service Parts list lists an equivalent item for wire wheel cars.


Mick
M F Anderson

Those things were fitted to the Z type Magnettes, and as FRM says, they go between the steel disc wheel and the brake drum. Has your car got steel wheels Henry?
Lindsay Sampford

I would like to give FRM a cigar today. Not only did he get it right, but he taught me something new today. I knew there was only one hole in the brake drum, and two holes in the steel disc wheel. I also knew from prior experience that the hole in the wheel does not always lineup with the hole in the brake drum, so I had sort of given up on the idea of trying to align the wheels in that manner. But until now I didn't realize that the two holes it the wheel are in different radial location. I just grabbed a spare wheel to inspect and measure, and sure enough one hole is 1/2-inch farther from center than the other one, obviously for different cars with different brake setup.

I have always known about the "Plug for brake drum" being a tube, but I have never seen them actually installed on any MGA, including the ones I drove in the late 1960's. My own car has been sporting open holes in the brake drums for decades with no noticeable detrimental effect, so I suppose these parts are not particularly important to survival of the other parts.

Incidentally there should also be rubber plugs for the hole(s) in the disc wheels, 8 per car or 2 per wheel according to the Service Parts List. I have no idea why they would want to plug the second hole, but the plastic tube and rubber plug together serve to keep road dirt and water out of the brake drum (perhaps also keeping brake dust off of the wheel).

The blanking plug is for the front brake drum on wire wheel cars only That one may be keeping brake dust off of the wire wheels as well as keeping road dirt and water out of the brake drums. There may be some reduction of wear on brake linings with all of these plugs in place. The disc brake cars definitely show reduced wear of inboard brake pads when the late production brake shields are installed. It is not clear from the SPL, but I suppose the rear drums should also get the blanking plugs on wire wheel cars.
Barney Gaylord

Thanks for the info guys. Yes, I am using disk wheels. Now that I understand the plugs function they make sense. Actually, this is a clever way to give access to the brake adjusters with the wheel on and still seal the drum from dirt and water.

The shop manual also mentions rubber plugs for the hole in the wheel. Since I have the tube plugs I might as well use them. I am sure the OEM were metal, who knows how long these plastic plugs will last.
H Speer

My '55 Magnette came with its original and intact brake adjuster tubes and they looked identical to those Moss ones and were made of plastic. Never seen metal ones or rubber plugs to put in them. Once you get your hub caps on, nothing is going to find its way in there, Lindsay.
Lindsay Sampford

Interesting topic. For the record, I am still driving the 1959 MGA 1500 my family purchased around 1965. Still running the original wire wheels and drums. One drum still has the original dust plug. It is soft metal and just presses into the hole a slight distance (has metal claws); not the tube one that fits disc wheels. I never replaced the other three but Moss does show a picture that looks like the original type(it may be made of rubber, now). I recently purchased a restored TF and the new dust plugs are bigger and made of rubber and I had to trim them to make them fit better between the spokes.
E.W. Haynes

In an earlier post Barney said "the two holes in the wheel are in a different radial location. One hole is 1/2-inch farther from center than the other one".
Were the rear brake drums on the MGA 1500 originally a different size? There is no mention of it in Clausager nor the Service Parts List. The early Triumph TR2 changed from 9 inch rear drums to 10 inch rear drums at about the time the early MGA 1500 was built.
Alternatively, was the MGA disc wheel used on another car?


Mick
M F Anderson

Mick-
I don't have enough books or time to figure it all out, but the extra holes would line up with 9" brake adjusters. I have seen them on some BMC car, but can't recall what. All MGA/Magnette Z* used 10" drums, but there were lots of Austin/Morris/Wolseley/Riley that may well have used 9" drums. MkIII & IV Mag used 9" brakes but had 14" wheels. Magnette parts book shows two sizes of dust excluder, changing around car #2385, and the rubber plugs for the wheels, 10 req.
Saw lots of the plastic tubes on MGA/Mag, never a metal one - been working on them since mid 60s. I do recall metal or rubber plugs in drums on WW cars. I have a MGA WW axle with chrome metal plugs, which was common.

FRM
FR Millmore

This thread was discussed between 10/07/2009 and 12/07/2009

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