Slight loss of brake assist until pumped once

[philkoolemagic]

Hi I'm a fairly new user to this site, although I've been reading and enjoying all the posts. I have a 1973 TR6 that has just developed a problem with the brakes. When the car is running or moving, I get a slight loss of brake servo assist, (even just backing down the driveway) I have to push the brake pedal down further the first time I go for it. If I pump the pedal once it returns to normal, and feels normal.

Here's what I know for sure... The brakes are all new installed by the PO. There are absolutely no leaks at any of the wheels wheels, nor by the master cylinder, or brake junctions. Fluid level is normal and not losing. Valve on the servo is working normally, and the hose to the intake is working with no leaks. There are no leaks around the pedals. I took the rubber boot off and found the filter in there had disintegrated, I will replace this but could this really be the cause of the problem? A piece of round foam? All hoses on the car are correctly connected.

Now if this is a slight bit of air in the system, I'm wondering how this could have got in there all of a sudden? The brakes were working perfectly. Any help is appreciated.

Best regards, Phil.

Phil Jackson's 1973 TR6 gearvision@mac.com /ubbthreads/images/graemlins/england.gif

 

[Guest]

Loss of assist is going to make the pedal harder to press. It sounds like you have increased travel.

I had this exact thing. I swore there were no leaks. There was - at the rear flexible hose where it mounts to the hard line. You couldn't see it unless you were pressing the brake pedal and looking at the right spot...

Check your discs are true and your hubs are tight enough too. If they aren't then the wobble will push your pads back and you'll have to press further than normal the first time to get them back.

 

[Don Elliott]

TR racers have developed a stronger front axle design to prevent a problem like this on the track. When there are a series of light curves where they don't use the brakes, the curving action moves back the front caliper cylinders and brake pads. It's the force of the curves and the flexing of the short front axle spindles that causes this. Then when they get to the next severe turn and brake hard, the pads are back off the rotor. So they used to have to tap the brake pedal before they got to the corner to put the pads back close to the rotor. Now with the new stronger front axles, the pads stay where they should be and they don't have to tap the pedal before they get to the next hard corner. Braking before the next corner was slowing them down. Now they get faster lap times.

Don Elliott

 

[swift6]

Under normal street driving this could also be a sign of loose front bearings. Check em, they probably need tightening. The spindles actually flex a bit during the scenario that Don lays out and it's that flexing that pushes the pads back against the cylinders and then back into the calipers. Loose bearings make it worse.

Oh, and welcome to BCF!

/ubbthreads/images/graemlins/cheers.gif /ubbthreads/images/graemlins/driving.gif

 

[bobh]

Phil,
You said the brakes are all new. What about the master cylinder? If the master cylinder is beginning to fail you will feel a soft pedal. Pumping the pedal regains some of the pressure. The master cylinder won't necessarily leak when it begins to fail. The internal seals may not be up to holding the pressure.