Hello everyone, I've just bought a 1968 Daimler Sovereign 420 and on first start up the brakes and brake lights are stuck on.

Any and all help will be gratefully received.

Thanks in advance...

 

Check the reaction valve on the end of the master cyl. Most likely stuck.

 

Thanks I will check it out.

 

Just checked it, it has gone completely brittle, cracks everywhere and the "spout" has completely broken off...!!

New one just ordered.

Thanks for the invaluable help..

 

The way the brake lights work is the same as the S Type. There is a pressure switch positioned on the front inner right wing screwed in to a four way junction of the brake lines and has two electrical connectors and wires coming off it.. When you put your foot on the pedal it pressurizes the brake fluid in the brake pipes and this pressure switch is forced on completing a electrical circuit and the brake lights work.
If your brakes are locked and the brake lights are on that will mean you have brake fluid pressure in the brake lines that is not releasing. To release the brakes is easy. Just crack off the brake nipples on each brake caliper to release the pressure and the wheels will rotate. The brake lights will also go off.
What is causing it is a different matter. I would say that your whole braking system needs an overhaul starting with as mentioned the master cylinder. The master cylinder is where the pressure is created but normally once the pedal is released the master cylinder piston retracts and the pressure is released. It is possible that your master cylinder piston is stuck in the down position keeping pressure in the brake pipes. Depending on how old your brake fluid is but old brake fluid retains moisture and eventually it crystallizes stopping the pistons in the master cylinder and the pistons in the calipers from retracting. Brake fluid should be changed every couple of years especially on a car that sits around a lot to stop it getting too waterlogged. Water in the fluid not only affects your braking capabilities because water can be compressed more than brake fluid but the water element will also cause your caliper pistons to rust and stick in the calipers.

 

Just to let you know that I changed the reaction valve and put a new piece of hose and the brakes are now working, thanks very much for your help...

 

Craig good for you and your ride. Most folks do not realize the 420 used the same master as an E type. Your symptoms are--or were---classic reaction valve sticking or damage!

 

Cass also makes a fine point. Brake fluid is hygroscopic (absorbs water) Should be changed ever 2 years. Drops boiling point of fluid so it can boil in the calipers & you will lose brakes.