End cutting in mill

Ok, if it's brass then forget the aluminium washers.

Maybe a Spotface cutter would do the job.

The problem with trying to re-machinne the face is that it must be spot on perpendicular to the banjo thread. For that reason I would not machine it. If really stuck you might scrape the face using the banjo bolt & banjo for blueing.

Have you checked the banjo for paralell across the faces? Have you checked the bolt for bentness?

Martin

The Mustang, with aluminium washers, has steel banjos presumably alleviating the risk of corrosion.

The bolts aren't bent - they're substantial, at 9/16" diameter and short. I have checked the banjo for parallel between faces, and noted about 0.002" difference, so that needs addressing. It's relatively easy to identify where attention is needed as gripping it gently with a vernier caliper gives a 'pivot point' at the high spot. Reversed to other side of banjo as a check. The fit surface on the steel banjo bolt is good, as is the new wheel cylinder (the 8th and innermost contact face). The cylinder face has the fine concentric rings as manufactured.

I think the consensus is correct, in that trying to machine this is not likely to end well - too many opportunities for operator error. The operator in question is much more at home with a Mig torch in his hand... I have blued the faces and the surface of the brass is not as good as it should be, so have persisted with the abrasive paper 'washer' around the bolt head machined land and twisted, facing the brass union land. I have slightly biased the pressure applied when using this to correct for the very slight parallel difference.

Another new pair of annealed copper washers, and it's reassembled and ready for a trial re-bleed, my wife's favourite job. Not.

If you have a reasonable level of skill, you could try filing it! Not any old file, you need a fine single cut of good quality, new and sharp, perhaps Vallorbe. It needs the file to be on a flat surface, and the banjo held flat in contact, and only a few careful strokes. With a suitable file, this will produce a fine matt and untorn surface. Clearly for it to be recoverable, the damage must be slight.

Assemble without washers, check with finest feeler for adequate contact all round, and rectify if needed. It is also possible to finish with a diamond lap to get a near polished surface.

I do a lot of metalwork so would hope my skill levels are good enough. I also have a set of fine Vallorbe files, which is what I have used to address the parallel issues.

A diesel fuel and injection speciallist should have good copper washers, I would not use alli. The seals in a brake system are a polymer so as long as the dowty washer was correct would work.As for boiling silicone fluid which is not hygroscopic like polyglycol fluids would point to old fluid containing moisture still in the system as the silicone fluid boils at 260c, or a VERY overheated system and other problems. I have only come across this problem once in 50 years of working on vehicles, a Range Rover with a slightly dragging front caliper. Total failure, only 30 mins later brakes had a solid pedal again. Boiling fluid due to moisture absorbtion is believed to have caused several accident years ago that seemed to have no obvious cause. Then there's brake fade ! Noel.

If you know a brake fitting is defective, you should REPLACE IT.

..sheesh..

Not entirely straightforward with parts nearly 70 years old...

I think that is what the OP is doing, but he is trying to improve on the accuracy ang fit that the parts were originally made to, sort of blue printing ! The sealing washers ar being REPLACED ! Noel.

On further thought, facing the banjo on a diamond "stone" would probably quickly clean up to a sealable surface. It is quite surprising how much better these are than abrasive paper, and they work fine with most metals including brass. An example is Arc Eurotrade 070-030-00300, or from other suppliers, and they are cheaper than files these days. Water can be used as a lubricant, so very convenient to keep the process free of debris.

As you probably already know, to keep the faces parallel simply match the number of strokes one way with the same in the opposite direction, or a similar averaging technique such as a figure of eight pattern.

Apologies for shouting.. ..it bothered me that an elderly brass fitting subject to hydraulic pressure is 'repeatedly leaking'..

- please do satisfy yourself that it's not compromised in other ways that may be harder to detect..

It's a pretty solid hunk of brass - they did things properly in the fifties!

The problem is purely the finish of the mating surfaces, otherwise all six are sound (twin leading fronts, single rears). Which is just as well, as the modern reproduction replacements are vastly inferior (thinner, wrong shape, made cheaply in China), extremely expensive, and currently on back-order with no date given!

I would find a very fine file which was wider than the banjo diameter and carefully smooth off the faces. Check that the faces are kept parallel. I would also anneal the sealing washers before installing, as I don't entirely trust them to be in the soft state even when new.

Because silicon fluid is not hygroscopic any water in the system remains as water, and ends up as small pockets of low boiling point fluid. It only takes a small pocket of steam to knacker the system to the point of no brakes. The reason for microscopic fluid is the more general degradation of boiling point in the whole system.

And yet Harley Davidsons used silicon DOT 5 brake fluid from 1973 until just a few years ago when ABS required a switch to DOT4 conventional fluid. Never ever heard of the silicon fluid giving problems, and there are some serious braking forces and heat generated on their heavier touring models with half a ton of gear added on to them.

Harley specifies no change intervals for the silicon brake fluid, just inspect and top up. Indeed, I have had Harleys go for 10 years and more with the same silicon fluid without problems. But in our wet tropical environment here I have to change the conventional DOT4 fluid in my car and other bikes every two years or less, otherwise it tests over the allowable moisture content and if left will corrode the brake system internals. The hygroscopic fluid seems to suck atmospheric moisture in through the pores in the rubber hoses or around the copper washers, seals etc. Silicon does not.

So all my other bikes without ABS I have converted from DOT 4 to DOT5 silicon and saved a lot of maintenance. Been doing it for years with total success.

US military vehicles all use silicon fluid for this reason too, and I  believe NATO vehicles. Except for the ABS fitted ones. Silicon is too viscous to work in an ABS system.

Edited By Hopper on 08/06/2023 01:29:36

Hopper has touched on an interesting point about silicon fluid - it's viscosity ! I have heard comment on this in racing circles and the delay in brake operation being the reason some won't use it !

US military vehicles even as far back as the 60s used silicon fluid. I still use it on the LARC XVs. Noel.

My braking is not up to MotoGP standards so I have not noticed any difference in that aspect with the silicone!

Love the old LARCs. Did a trip along the Queensland coast years ago. Fun stuff.

I hate the stuff, I haven't used it for 20 years now. Don't forget, if converting to it, or back from it, you should change every rubber component in the braking system, quite a job.

I have washed the old DOT4 components and rubbers in methylated spririts and reused them with DOT5 Silicone when I had to in a pinch. But usually if I have the system stripped down for cleaning, I will fit all new rubberware. Usually the system needs all new rubbers anyway if the system has sat unused for some years with DOT 3 or 4 fluid in it. As old motorbikes tend to do. Quite often new pistons and honed bores are in order too, in both master cyl and calipers.

It is essential to get rid of all the old DOT4 out of the system befori adding DOT5 Silicone as combining the two can make a nice sludge that gums things up. Hence full strip down and flush with methylated spirits, wash with DOT5, reassemble, fill with DOT5.

I have been told that seals designed for DOT5 will not stand up to DOT4, but I have never made the conversion in that direction so don't know for sure.

Edited By Hopper on 09/06/2023 11:33:12