Javelin Hydro Mechnical brakes

[Robin Fairservice]

I have a left hand drive, 1950 Javelin with Hydro Mechanical brakes. I was not happy with the brakes, so I had a spare master cylinder rebuilt with a JOC seal kit. I still could not get them to operate properly. I found that I could get a seal kit in BC, so replaced the seals in my original master cylinder with no better results. I have talked to various people, including Vic Morrison in NZ, but no one has any ideas. Neil Moore from NZ rebuilt a master cylinder for me, so I put that one in, but still the same.

We can bleed the brakes of air, but cannot keep a firm pedal. The pedal can be pumped up, but as soon as I take my foot off, the next appliation goes to the floor. I must be leaking from the high pressure side to the low pressure side, as there are no visible leaks.

I read that there must be 3/32" clearance at the front slotted fork, and I have that. If I set it larger would that help? I have gone tighter, but without effect.

Can some one get me out of my misery, as I cannot drive it and our summer is passing quickly?

[Keith Andrews]

Did you back off the hand brake adjustment, then adjust the brake shoes back up, on each wheel, before bleeding?
This is critical..
THEN readjust the hand brake

I would also suggest that one of the slaves has gone
if one replaces the MC and not the slaves , it is very common for the slaves to fail one at a time, shortly afterwards.
Best practice is to replace slaves if a MC is replaced

[Robin Fairservice]

Somehow my query is in the wrong part of the Forum. It should be under Javelin. How do I move this, or is this a task for the Administrator?

[Keith Andrews]

Admin can...
Or just change the "pre war" to Korean war or 'Nam for now

[Tony Fearn]

Hello Robin,

Can't help you myself as my interest is in the pre-war cars, but today on your behalf I went to visit an friend of mine, Bob Mercer, who lives close by and has had a number of Javelins, and is quite well-versed in the maintenance of them.

He doesn't have a computer so I printed-out your request and he read it.

He said straight away that he personally thought the seals must be at fault.

A number of years ago, he said, he'd had the same problem when he'd re-conditioned his brake master cylinder with a set of seals which he'd purchased from the Club's Spares section.

He told me that there were three seals in the master cylinder and that the smallest one, even though it looked to be ok, wasn't exactly the same as it should have been, and fluid must have been able to leak past it.

From somewhere (this could be 20 years ago) he acquired another set of seals made by the cylinder manufacturer which when fitted were spot on.

Bob also said that Bill Lock's car is hydro-mechanical and, because of Bill's undoubted experience in Jowetts, it might be useful to get in contact with him.

Hope this helps a little,

Tony.

[Forumadmin]

[Forumadmin]

I do not have experience of the hydro-mech, only the full hydraulic; but did experience the same shortly after fitting new seals. It was the wrong size seal in the box! Obviously check the seal is the correct way around so that the fluid forces the lip to close when pressurised. It should also be a tight fit on the piston which should have no blemishes.

Another thing to check is to have about 3 mm play in the actuating rod and that the cylinder returns fully after each application.

You should be able to tell the difference in feel between air and faulty seal through the pedal. The seal will gradually leak once pumped up wheras air will stay hard once pumped.

Make sure all air has been driven out of MC. You might need a litre of fluid through it to purge.

You could always plug the outlet of the MC which would remove wheel cylinders from the test.

[David Morris]

Hi Robin,

Our Javelin is the full hydraulic type, but I have had hydro-mechanical ones in the past and the principles are the same.

Two things that might be helpful. The first is to make sure you have purged the master cylinder completely of all air. Obviously, there is no nipple, but you could try 'cracking' the outlet union by opening the high pressure union just a bit and making sure you get only fluid coming out when you put pressure on the cylinder with the pedal. However, this is much easier, indeed the whole bleeding operation is much easier, if you have a 'Gunsons' type pressure bleeder, which works off the air pressure in the spare tyre. It makes the 'one man' operation simple and saves on domestic friction! Words like "I told you to hold it down. I AM holding it down" used to float around our garage before I bought the kit!

The second point is to clamp off the two hydraulic pipes going to the wheel cylinders with either proper pipe clamps or, as a makeshift, two pairs of molegrips fitted with some spare sockets from your tool box over the clamp faces, to prevent damage to the pipes. This then isolates the master cylinder and you can make sure that you have a really firm pedal, before going ahead and releasing the clamps and bleeding the wheel cylinders. Another really strange effect was traced to bits of loose rubber in the pipes, creating effectively one-way valves. Only cured by new rubber pipes and purging through.

I hope this helps. I once had replaced everything in the system on a Javelin, and it took ages to get all the air out. Residual air in the master cylinder proved to be the main problem, and aided by buying the Gunsons kit, which blew the last of the air out of the 'nooks and crannies'.

All the best,

David

[Forumadmin]

I was warned never to clamp brake pipes as it could break the pipe up inside where you cannot see it.

[Robin Fairservice]

I have been away for a few days, and am catching up with the various comments and suggestions. I have adjusted the rear brakes which I thought seemed to improve things. I took the car out this afternoon, but the brakes were nearly non existent without much pumping. This seems to some down to; either there is air trapped in the master cylinder, so I will try the suggestion of cracking the high presssure connection, or I have seal probelms. Bill Lock says that I am the second person to ask him about seals within a few days, and he is sending out a recuperating seal to compare with mine.

I have also been told that series one Land Rovers are bad for bleeding, and one owner told me that he used to jack each end up to try and purge air out. Also I was told the older Rolls Royce cars had eight bleeder screws, and each have to have a hose attached and into some fluid all, at the same time. They are left to bleed for some hours to flush air out.

I have used DOT 4 (Castrol LMA) because I was told that that was the correct brake fluid. I was told today, that I should be using DOT 3. Which is right?

[David Morris]

Hi Robin,

I have found a site which has stacks of advice on brake fluids and bleeding procedures. It is :-

http://jimsgarage.wordpress.com/2007/01 ... and-dot-5/

In there, and I cannot vouch for its accuracy, it mentions :-

Brake fluid is categorized as one of three ratings. Most brake fluid that comes in a new car will be rated DOT 3. A few will Use DOT 4, and very few will ever use DOT 5 which is a silicone based product.

If you want to look at brake fluids from a chemical standpoint DOT 3 fluids are based on glycol and glycol esters. DOT 4 fluids are much like DOT 3 fluids, but also contain borate esters. There is another rating called DOT 5.1 that consists of borate esters.

The site goes on to mention that, apart from the chemical differences, DOT3 has a lower boiling point than DOT4. Due to the chemical makeups, it does not recommend mixing the two grades and adds that seals that might be OK with DOT3 could start to be adversely affected by DOT4.

I have no idea what Jowett's specified for our cars, but due to the age, I would reckon the earlier specification ( ie, DOT3 ) would be appropriate.

However, I have just been out to the garage to check what I am using and it is DOT4! So, by my experience, I reckon you are OK in using DOT4, as I have not encountered any problems ( so far ) !

I did toy with the proposal to switch to silicone brake fluid, but was put off by the bad press concerning swollen seals etc. when you don't completely flush the system or start again with a completely dry system and use silicone from the outset.

I am sticking with the 'old' fluids!

Best of luck with the bleeding..

Regards,

David

[Keith Andrews]

Silcone is for high end track racing..hence why boiling points are mentioned in specs
General rule of thumb, what works on the track, is bragging rights on the street.....but doesnt do the job designed for.

[Peter Holden]

I have experienced a similar problem on another members car - in that the brake pedal having pressure one minute and none the next and having to pump to get a pedal - like you we went through everything - no leaks - had difficultly in bleeding the system

It was only when the car was up on the lift - four poster lift that is - that we spotted the problem - the problem was that the master cylinder piston was not going fully back - it was only going back about two thirds - we lashed up an addition return spring and a stronger one and hay presto works every time now - we improved the lash up but we now have a pedal and we were able to bleed the brakes without any problem

[Robin Fairservice]

Thanks Peter, I have wondered if this might be the problem. Are you referring to the spring inside the master cylinder, or the spring on the brake pedal arm? Exactly how did you add a spring? Any pictures?

[Forumadmin]

I think I said that in my post on the 7th! This is often caused by the MC not being free on its fixing to the chassis. But an extra spring is another answer.