Brake seals-question

[Forumadmin]

Whilst investigating the cause of the failing brakes at Goodwwod Revival I decided to clean out the system and refurbish all the wheel cylinders. I do not think that these were the cause but it is a long time since the cylinders were looked at. Indeed inspection showed that the bores needed a good polish having accumulated rubber and oxide on the surface which caused some sticking of the pistons. This was not enough to prevent operation but a clean with some Tcut on a rag rapped around the brake cylinder honing tool brought them up nicely. There was also an accumulation of 'gunge' around the spreaders at the end of the springs whiche were cleaned in meths, as was the whole unit. The seals were inspected and any showing some scuffing on the lips were replaced. The components were blown dry and assembled with silicone fluid.

The reason for this post is to ask some questions.

1. I noticed that the service kit instructions said thet the front spreaders (deep spring housing) were different to the rear ones (part number H5323) . Although I did have different ones I had no part number H5323, but only some with no part number or H3112 which were black plastic or H5605 that were grey aluminium or mazak. I could see no dimensional differences. Can anyone comment?

2. I have a number of service kits of various ages. The seals fitted in the rear were Part number 362261 which I had in some kits but also had part number H5123 which look identical. I also had some kits without part numbers which I guess are the after market and not Girling, Lucas or whoever now owns the title. Is there any difference between front and back seals?

3. The balls in the bleed valves were rusty so I replaced them. I noticed that the front balls are .154 inch, 3.93mm and the rear .186 inch , 4.73mm. Is this correct.

4. I tried cleaning out the threads of the pipe and bleed screw and found the 3/8inch National Fine 24 tpi to do the job. But could not find a tap for the handbrake mechanism screw holes. I think they are 28tpi with .180 inch 4.58mm diameter thread. I tried BSF , Whit , Metric, BA, UNF and UNC and a few pipe taps that were lying around but that does not mean it is not one of these. Anyone any ideas?

[RandalColman]

An old thread, this, and I am surprised there were no replies.

Starting with the spreaders, I have not swapped any about but if the springs are the same diameter front and rear then it looks to me that the spreaders would be interchangeable. They don't seem to do much. The cups are definitely the same front and rear, just your basic universal 7/8" cup. While we're on the subject, I used a front wheel cylinder from a Mk 1 Zephyr and I heard someone say recently that the same brakes were used on some Austin or Hillman or something. If anyone knows, that would be useful information.

As regards the bleed nipple balls, I have just stripped a front wheel cylinder which had a 1/8" ball in it. I was lucky to get it out. I have heard of these balls getting wedged irretrievably when the screw is overtightened, so I would definitely replace it with a 3/16" ball. (I was actually using it in place of the other cylinder, the one with the hose feed, so I didn;'t need the bleed screw.) Presumably Girling increased the size because of the problems from overtightening. The 1951 parts book lists the front one as 3/16", and I would assume it's the same at the back. But you could use either 5/32" (4mm) or 3/16" (4.8mm).

The brake hoses and fittings on the full hydraulic Javelin are UNF, but it's a bit deceptive, since some of them use BSF hex sizes. I went and ordered new hoses to be made up some years ago, thinking they were BSF; UNF hoses would have been readily available off the shelf. The older hydromechanical Jowetts used BSF throughout. This was a trap for Tony Gray, who recently replaced the single-leading-shoe brakes on his PB with double-leading-shoe brakes from a PC. He had to get hoses UNF one end and BSF the other, or perhaps he made an adapter of some kind.

[Drummond Black]

Got rid of these troublesome ball over 20 years ago. Made Stainless Steel bleed screws with a point which seals the bleed hole. Never a problem since, no corrosion or sheared bleed nipples. The thread is 3/8" UNF. The small screws that hold the handbrake plate on are all 2BA on all my cylinders and this also includes the ones still on the shelf. Hope that helps.

Drummond

[Keith Clements]

Thanks all. I do not know why the 2BA did not feel correct. I will try again!
Drums, Did you turn down a 3/8 UNF bolt to do the job or did you make out of some rod with a die?
Did you drill a hole part way down and then another hole on the radius to let the fluid out?

[Drummond Black]

All mine are turned from 12 mm Hex Stainless Steel bar ( EN 316 or 316L ). Turn threaded end first using a Machine die then part off and turn in chuck to drill a 3mm hole to correct depth and m/c profile for bleed tube. Make sure you make the hex section longer than standard then you will not round the hex edges. Drill a 1.5 mm hole in the tapered front section into the 3 mm hole to release the fluid. Takes about 10 mins per bleed nipple to complete.

Drummond