Front Brake Cylinder Small Bolt Head Size

[pettefar]

Hi, I am trying to remove the front brake cylinders but don't have a socket to fit the small bolt that holds the cylinders in place (as well as a larger 1/2" bolt).

Does anyone know the correct Whitworth or AF size please? It's 8.5mm across the flats.

[Orkney]

Did mine recently, cant remember but might have been lucky and had an 8.5mm socket, did take a bit of messing about with at the time.

[alex_holden]

Not sure but I suspect that's 3/16" BSF which needs an 1/8" Whitworth spanner/socket.

[HarryMango]

Alex is correct 1/8W socket - 11/32AF is a very close fit though.

Rog

[pettefar]

Thanks chaps!

Will get onto my toolshop right away (eBay).

Nick
Swindon

[youngun]

1/8W it is

[bmcecosse]

You won't get that in Hellfrauds! I'm sure I found a little metric socket that was a very good fit.

[HarryMango]

You won't get that in Hellfrauds! I'm sure I found a little metric socket that was a very good fit.

As mentioned 11/32AF is a good fit which are available through Mangos Sockets (along with many others - spanners too) PM your wants

Rog

[svenedin]

Sorry to revive a very old thread but I'm doing this job right now and having terrible trouble with the same small set screw that holds the brake cylinder on.

1/8 Whitworth is suggested as the right size but it is too big and slips. 5/16AF is too small. I do hope 11/32 AF is correct because I have had to order a spanner. If all else fails I am going to have to file down the set screw head until 5/16AF will fit. As usual, what appeared to be a fairly straightforward job turned out to be anything but.

[IslipMinor]

1/8" BSW / 3/16" BSF head size is 0.338" AF, so is slightly smaller than 11/32" (0.3438") by 0.006". An 11/32" AF open ended spanner is more likely to slip than the 'correct' 3/16" BSF.

A 6-point socket of either 3/16" BSF or 11/32" AF would be my first choice, and after that 2BA is smaller at 0.324" AF, so a sturdy 12 point socket could knock on to a worn 3/16" BSF head?

For metric, 8mm is smaller than 2BA and 9mm is larger than 11/32", so would not be the most likely solution.

[svenedin]

Thank you for your explanation. So 1/8 BSW is actually smaller than 11/32 AF. This is not good news because I am using a 1/8 BSW socket and it slips. It "feels" like the perfect size but slips as soon as there is any torque. I have tried it on both small set screws because I suspect I have mashed the head of one of them somewhat. 5/16 AF is a very close fit but the spanner is just too small. These set screws are very corroded so perhaps this explains the trouble.

Actually I did try some metric sockets as well. It's somewhere between 8 and 9 mm but I don't have an 8.5 mm socket and I don't know whether they even exist.

[IslipMinor]

Do you have a 2BA socket to try?

[svenedin]

No I haven't got any BA sockets or spanners. I'll have to buy one.

[katy]

If you have to buy a socket make sure you get a 6 point one.

[bmcecosse]

The screw thread is 1/4" UNF - I have seen various different size heads on these screws. May be as well to just drill the heads off if THAT stuck - especially if changing the cylinder anyway! Spot of copper slip when you refit them....

[svenedin]

It may come to that. I hope not. I do not know how to dissemble further at this stage and I am away from home a long way from the car at the moment. I would have to get the backplate off the car because I can't drill out the set screws in situ. It is another example of dissimilar metal corrosion. A steel set screw in an alloy cylinder with hygroscopic leaking brake fluid.

[alexmcguffie]

Once I managed to get mine out I replaced them with high tensile allen screws. With or without copperslip the heads never deform or round off. I should have some knocking around if needed.....

[bmcecosse]

As long as you fill the head with a blob of grease...

[svenedin]

Allen screws do sound a good idea. So how do I get the backplate off? Brake lines are all disconnected and shoes are out.

[bmcecosse]

Remove the hub - just pulls off (after removing the split pin/nut and washer) - if a bit tight refit the wheel and wiggle gently.. Then undo the 4 bolts securing the backplate and PULL!