Brakes

[JRH1500]

Hi,

I've been bleeding my brakes on a 1977 Spitfire 1500 overdirve, I've got pressure on the brake pedal but if I sit in the car push with a bit of force the pedal goes to the floor. I have been bleeding to make sure theres no air in the system and have replaced the seals in the master cylinder. I've also replaced the brake pipes, front hoses and the rear wheel cylinders.

As I've never bleed brakes on a classic car before unsure how there meant to be, but believe its not right. The only thing left to do is to get a new master cylinder but wanted some advice before I brought one.

Thanks

Jason

[//j17]

There are two options.
Either you have a leak somewhere, in which case the level of fluid in the reservoir will drop when you do this or, more likely the master cylinder is just past it.

You didn't mention it loosing fluid and I'm guessing you could have worked out that if it was happening so I'd suggest one of two things. Either you have the main seal in the wrong way around or the master cylinder is just past it.

Usually (check the manual) the main seal isn't just a ring but a section of a cone and should be installed with the narrow end against the piston and the wider skirt facing down the boar. When you press the pedal and compress the fluid the fluid should force the skirt to expand, completely filling the boar. If it's the wrong way around the fluid pressure will be forcing the skirt to fold and letting fluid past. It might be a little different for your car - a '77 may have dual circuit brakes. I've not seen inside one of those master cylinders but that's the deal on the earlier single circuit cars.

If you have wear in the master cylinder the new seals aren't completely filling the boar. They cover 99% so you get a firm pedal with all the air out the system but that 1% leak lets the fluid pass around the seal, letting the piston and from there the pedal move through the fluid rather than pushing against it.

Start by stripping the master cylinder down again and double-checking all the seals are the right way around against the workshop manual. If they are it could just be the fact that, after 33 years the master cylinder is past it and it's time for a new one.

[JRH1500]

I've replace the master cylinder, the new master cylinder has a bigger reservoir and is position at a slight angle not sure why but is. Bleed the brakes and got better resistance but not great, drove the car and try the brakes theres no pressure when braking forwards and stops very slowly.

I have no leaks, its got all new hoses and new 4.76mm x 0.71mm 3/16 brake pipes with some pipes with some of the original fittings, plus a new master cylinder. Its got the original manifolds, new rear wheel pistons and placed new seals and pistons in the calipers.

I've noticed a twist in a pipe so will re-cut and flare but a part from that do not know what to do. If anyone has any ideas please let me know!!

[TriumphVitesse]

Are you still on the old flexible brake pipes? If so try replacing all 4 corners with Goodridge stainless braided brake pipes, available from most Triumph suppliers like Rimmers, Canleys etc.

I had exactly the same problem on my old Herald, could not bleed it up, even after I had bought a new master cylinder. Turned out to be the brake pipes!