Jupiter Full Hydraulic Braking System

[Mike Allfrey]

Down here in Melbourne (Australia) we have been in lengthy COVID-19 lock-downs and my Jupiter has not had much use over the close to two years of the pandemic.I have been starting the engine and, once warmed through, have driven the car 'around the block', several times. The car has been parked in a dry garage, but we have had a fair (for us) amount of rain over this winter.

Today, the engine was started and warmed through, however, on engaging first gear the car refused to move - nor in reverse. It seems the brakes have locked on, even though the handbrake was not applied. The brake linings are of the non-asbestos type and the wheel cylinders have stainless steel sleeves. Therefore, I am at a bit of a loss about what may have caused such a situation.

Have any other Jowett owners experienced such a situation?

About four years ago, one of the rear non-asbestos friction material linings broke and formed a very effective wedge. Thereafter, I have backed-off the adjusters and put up with a longer brake pedal travel, to ensure brake shoe to drum clearance in an attempt to avoid the lock up problem. While parked in the garage, the handbrake has always been in the completely off position, and the car left in gear on the level floor.

Suggestions most welcome!

Regards,

Mike A.

[ajackson]

Mike,
In a similar situation I had to jack up the car at each wheel, remove the wheel and then really hit the drum with a hammer. Most likely the drum edges are frozen to the back plate. The shock can break the rust. Of course, maybe not all of the wheels are locked, and you will tell once each is jacked up.

My garage was also thought bone dry (well UK standards, not Australian standards!) but I go the lock-up in 3 months,

Good luck, you will crack this one!

Andy

[Keith Clements]

Possibly a wheel cylinder has locked on if you applied foot brake. Another thing to try is push or try to drive in reverse.
Find out which wheel is locked and adjust off.
Possibly also a fault in the master cylinder not releasing. Try manually pushing MC piston fully back. Sometimes the spring is not strong enough.

[Mike Allfrey]

Thanks Andy and Keith,

My plan is to, when my back allows, to jack up the car with all four wheels off the floor. That will establish which wheels are locked on, should all four be locked, attention will be given to the master cylinder - otherwise, the locked wheels will have their adjusters backed-off completely and the hammer will be employed.

The foot brake was not touched yesterday.

Usually, when parking in the garage, brake application is very light (pedal not pushed with any force), hence my bewilderment at present.

All the best,

Mike A.

[trymes]

Another thing that can cause brakes to stick is a bad flex hose. They can collapse internally, and will allow pressure to flow one direction to apply the brakes, but will not allow fluid to flow back and release them.

It’s not likely that’s your problem, but cracking a bleeder will release the pressure if it is.

[Keith Clements]

I have seen some brake return springs snap or rust through. This could cause lock up. If the foot and handbrake have definately not been applied, then that is the only thing apart from rust that could cause this. But I would doubt this would lock up in both directions.
I have had lock ups frequently with clutch plates and once with gearbox and an overdrive or diff could also fail to cause a lock up. Have Insulate Britain protesters been around and Loctited your tyres to the garage floor?
For those not aware of recent UK politics, these protesters have blocked roads by gluing themselves to the tarmac.

[Mike Allfrey]

G'dday Folk,

I have been involved with other matters, but have been steadily working on the braking system. What it boils down to is that the right hand rear was the brake that had locked solid. What amazed me is that, when attempting to drive the Jupiter forward, or backward, there was no indication of the car trying to veer to one side due to differential action.

Then came the task of removing the brake drum, a really tough job on a hot day. Finally, after a lot of labouring, the drum came off with a fair amount of brake lining material still adhered to the drum. No rust, but get this, the wheel cylinder had leaked fluid onto the brake linings. New seals in 2017 in stainless steel sleeves. My understanding of the problem is this - the lining material is made up from silicates (glass fibres), Kevlar, rubber granules, along with a resin (formaldehyde) and flakes of brass. The company who relined the brake shoes, told me that with brake fluid (DOT-4) gets into the lining material, and sudden hot/cool/humid (very) weather conditions occur, the lining will swell and adhere to a brake drum or disc. In my case, the lining portion that had glued itself to the drum, had to be chiseled out. It was a good adhesive! The old Ferodo asbestos never did that.

New linings were bonded and riveted on the shoes, in 2017 I had one lining break away and form an effective wedge, which dislodge when reverse was selected. Hence the rivets. The new wheel cylinder seals (manufactured by An Jee in Taiwan) feel firmer in the cylinder bore, so have now overhauled both sides.

Now, to a question: My Jupiter is old enough (E0 SA 42R) to have been equipped with hydro-mechanical brakes. It has full-hydraulic brakes, and the master cylinder is of full-hydraulic type. I am wondering if the car was updated before I got hold of it. No problem with that, but what is mystifying is that the master cylinder pull rod assembly has a tab for the brake pedal return spring, which om the car hooks onto the brake pedal. Reading the Javelin Maintenance Manual, for removing the master cylinder, the spring should be unhooked from the brake light switch. The question is, where should the brake pedal return spring be hooked to the chassis? The master cylinder's plunger return spring should return only the plunger pull rod and the plunger assembly itself.

I suppose the photo is there. The lug for the spring can be seen on the pull rod.

Comment please,

Mike Allfrey.

[Mike Allfrey]

Me Again!

The photo did appear, and the spring lug is between the jam nut and the slip clevis at right.

Also, neglected to mention that my Jupiter has a hydraulically operated brake light switch, do other Jupiter cars have such a switch and if so, where does the brake pedal return spring anchor to?

The slip clevis slides easily on its pedal attachment pin and the plunger assembly return spring does its job.

I found the plunger support sleeve to be 0.007-in. oval, and the recuperating seal felt really sloppy on the plunger. A new plastic (Nylon) sleeve was fitted, but it was an interference fit (0.0025-in.) in the housing bores - it locked the plunger so solid, no spring would have moved the plunger back into its home position! New reduced outside diameter support sleeve on it way here, probably with lengthy rests at the numerous Australia Post depots, could be here in July from Queensland.

Has anyone dealt with MEV Spares, somewhere in Kent? I tried to order a full-hydraulic Jowett master cylinder seal kit from them, no success and no replies to E-mails either.

All the best,

Mike A.

[Forumadmin]

See viewtopic.php?p=23966#p23966 my arrangement and write up as to why.

[Forumadmin]

New Technical Note in Library.
download/file.php?id=26109
THIS SHOULD NOT BE USED AS MIKE HAS SAID IT IS WRONG.

[Mike Allfrey]

Yes, I am still at it! I have come to a conclusion that my Jupiter was converted to full hydraulic braking system sometime between 1953 and 1962. The master cylinder looks the same as that for Jupiter/Javelin, but it is not (at least internally). The rear body has, I think, a deeper bore for the plunger to reach its home position. This means that when the master cylinder is bolted together, the locknut on the plunger rod is held hard against the front face of the front body. I have seen photos of assembled master cylinders with what looks to be a one-eighth of an inch gap between the locknut and the body.

Over the years I have had trouble when bleeding the brakes due to not enough brake fluid being pumped through the system. My understanding, with regard to my master cylinder only, is that the plunger moves through an extended 'neutral' situation before the recuperating seal blanks off the bleed holes in the plunger. That means quite an amount of pedal movement during the brake application activity.

All of this means that I am not sure what has been fitted to my Jupiter, may have been found in a scrap yard (Riley?). I have ordered a second hand master cylinder assembly and intend to make a set of measurement comparisons. Could be interesting.

Does anyone know what the correct gap between the locknut on the plunger rod (tightened home against the taper) and the front face of the front body should be? To date, I have not managed to find anything about this specification in either Jowett or Girling published material. I suppose that if all components are correct, the 'correct' gap just happens.

The depth of the plunger bore in the rear body is 0.953-in. from the joint face, in my rear body. Does anyone have a rear body that they can measure and advise?

As an exercise I have placed two half-inch plain washers on the top of the plunger prior to fitting the rear body, the three setscrews and tightening them. The washers are 0.063-in. thick and, after the two bodies are bolted together there is a 0.125-in. gap to the lock nut.

Using a breath test at the inlet port, on pulling the plunger rod, the flow of air at the pressure port soon comes to a stop as the plunger moves forward. It is my intention to find out how much the plunger rod travels when the spacer washers have been removed. Will use compressed air from the spray gun reducing valve set at minimum, along with a tuft of wool taped to the outlet banjo fitting so that the fluttering of the wool can be observed while the plunger is in movement.

Could be interesting.

Regards,

Mike A.

[Mike Allfrey]

Please remove the Technical Notes Part 42 - Overhauling The Brake Master Cylinder from the list. It is a fair way out of date already and will be replaced in due course.

I should not have assumed that my Jupiter's master cylinder was an original Jowett item. The perils of being involved with older motor cars!

Sorry about the confusion,

Mike A.

[Srenner]

Mike,

One I have on the shelf measures 1.038" from the mating face to the machined face at the bottom. The bottom is concave from the casting process.
If we need a better sampling, I have several more I could pop apart.

[Mike Allfrey]

Thanks Scott,

That is strange, the bore is deeper than that in my rear housing to the tune of 0.085-in. which would increase pedal travel before compression of the fluid commences.

I have used compressed air to verify the position where the recuperating seal closes off the two drilled holes in the plunger.I used the pressure control on my compressor backed off until the gauge needle was just off its stop peg, A rubber hose was pushed onto the inlet port on the rear body and a piece of wool (three-ply) taped onto the outlet port fitting, hanging over the open port. Just a breath of air was blown into the inlet, with the plunger in the home position. With one spacer washer on the piston and 0.125-in. gap between the plunger locknut and the front face of the front body, the plunger rod was pulled 0.09375-in. to block off the air flow - the start of brake fluid compression, in theory. With the washer removed, the plunger travel increased to close to a 0.25-in. before the air flow was stopped - indicating longer pedal travel prior to compressing fluid.

As far as I can establish, all parts are in correct positions in the master cylinder assembly, which means that there being no gap at the locknut is rather baffling. A photo of the set up should appear here:

A = Gap, B = Air Inlet, C = Thread of Wool, D = 0.125-in. Gap.

I have a complete second-hand master cylinder on its way to me. As soon as it arrives, comparisons will be made.

Regards,

Mike A.

[Mike Allfrey]

Sorry, D should be Locknut! My mistake again.