THE INTERNATIONAL JAGUAR 'S'-TYPE REGISTER FORUM

Hi Alan,
It would seem you have narrowed down the issue to the Servo & peripherals. It's likely the Vacuum/Atmospheric pressure control valve that your remote filter connects to with your model servo. If you can get parts rebuild it. I hope it's nothing deeper in the Servo. Check the vacuum system for leaks. I've got a Barratts rebuild/exchange unit on my car ~ 8 inch with integral filter. They do a beautiful job. Not criticism ~ please ~ but you need to use that car a little more often. 10 miles in 8 years is not sufficient.

Rock hard pedal that does not soften on start up is typical Servo & related as I mentioned earlier.

Change your brake fluid ~ DOT 4 or DOT4+ ~ Bleed/flush from longest line to shortest line.

Good luck!

Welcome Giles.

Giles, thanks for your interesting comments. Your locked up brakes and hard pedal sounds exactly like my condition although your servo has a different air valve, I guess you call it. The one on my servo vents via a hose to a filter head next to the radiator. Since my brakes unlocked after I rapped on the valve body, I suspect something is going on inside, maybe a stuck valve. Parts are available to rebuild that assembly. Anyone try that?

I bought the servo new from SNG Barratt maybe 7-8 years ago. Part number is C19612R and it cost $440. I had to send them my old unit as a core. Out of warranty I'm sure even though it has only about ten miles on it.

Much appreciated, I will go take some photos while I have it on the lift and do a quick write up shortly.

[quote Also have a question regarding propshafts which is strangely a 2 piece setup in my car but cannot seem to figure out how to post on a new topic??
[/quote]
Thanks for the Info Giles.
On the page "Forum Index" click the subject you wish to discuss ie "Engines and Drivetrain"
Top left under Engine and drive train there is a tab that says "New Topic"
Click on this tab and you can then enter you topic and write up and once done hit the "Submit" tab at the bottom.
Hope this helps.

Ah yes, I mistakenly thought the info and photos I submitted initially upon registration carried across to the forum - sorry!

My brake problem was completely self induced of course having misplaced the spring initially, then forgetting about it a year or so later.

I am an ex-pat from Birmingham living/working in Southern California for 30+ years now. Ex ProDrive WRC rally/race mechanic back in the 80's and now tinkering with old Jags & Porsches in my spare time here.

Forgot to post image of the reaction valve rebuild kit...

Also have a question regarding propshafts which is strangely a 2 piece setup in my car but cannot seem to figure out how to post on a new topic??

Welcome Giles and thank you for your input not something anyone has come up with before.

Can you put you location in your personal information so we know where you are please.

Hello All, new member here (1965 S Type 3.8 MOD)

Saw this post and thought I would chime in with my recent experience of the same issue. After a full mechanical rebuild of the car over several years, and upon first startup I discovered a few small vacuum leaks on valves and diaphragms. Once I had a functioning vacuum system with both Reservacs and all diaphragms holding vacuum I had complete lockup on the brakes and a pedal that felt like a brick. After some tracing I realized I was missing the small spring that regulates vacuum pressure on the servo reaction vacuum. Turns out I had inadvertently knocked of the white plastic protective cap on the brake servo reaction valve when installing the engine last year and had pushed the plastic cover back on minus spring in all the excitement of getting the engine/gearbox back in situ after 10 years. With a new spring installed from a Moss Motors rebuild kit (182-291) all was well and brake pressure was normal. May well not be the exact problem on your car but hopefully helps narrow down the options.

Since Glyn's last comment on Jul 30, I have not had an opportunity to continue with the diagnosis of my very hard brake pedal or the some times locked-up brakes. Yesterday I decided to move the car out of the garage and see what happened. First I disconnected the electrical feed to the anti-creep switch at the carbs so that that system would not be operative. I started the car and let it idle a bit until the choke kicked off and then backed it out into the driveway where I let it idle for ten minutes or so, then shut it off. No problem with locked brakes at that point.

An hour or so later I decided to put it back in the garage, but before doing so I wanted to try the test to see if the servo was working as it should. That being, with the car off, pump the brake pedal several times and then hold it down and start the car. If the pedal sinks when the car starts, then the servo should be OK. The pedal didn't move. Not good. When I tried to move the car forward in drive, it would not budge, the brakes were locked. I checked the brake lights and they were on. I then went in and got my wooden handle hammer, opened the bonnet, and gave a few hard whacks with the butt end of the hammer on the top flange of the air valve housing on the side of the servo. The brakes released and the car rocked back. I immediately drove it into the garage and turned it off. The brake lights had not come on.

Things seem to be pointing to the servo but I don't want to go there until it is definitely proved to be the culprit. Maybe a faulty check valve at the vacuum tank, a collapsed line, or some other thing. I have studied the servo system and still don't completely understand how it works. Of course, it could also be something amiss in the master cylinder as Rob mentioned, particularly with the very hard brake pedal that has only 1/2" free play if that. Any more thoughts?

I have mentioned this before but will repeat. You have just got lucky or may have a failure in waiting. There is nothing wrong with silicone brake fluid but many elastomers, of which Alan's E Type clutch is an example, are not compatible with it.

The braking & elastomer/rubber/seal industries are hopeless in informing buyers of the compatibility of there products with fluids. This remains a problem to this day. The number of servo failures I've seen in recent years due to the use of silicone fluids is high.

So as an oil company man I find it appropriate to warn people of elastomer compatibility/incompatibility. Some plants don't even do seal swell tests from batch to batch of rubber produced. We sell all the fluid types so it's no skin off our noses. I don't know of an OEM that uses silicone fluid in new vehicles.

Our S Types have single circuit brakes. Don't take unnecessary chances of brake failure.