Trouble with brake pedal travel (excessive)

[Joe 90]

New member here, sort of cheating as mine is a kit car (Gentry) built using Vitesse 2 litre running gear. Just finished rebuilding most things as it’s been stuck in a barn for years. I have rebuild all the brakes with new seals, master, slave, callipers but the brake pedal still goes almost to the floor after bleeding, bleeding and bleeding again, I renewed the flexi hoses as well. Rear brakes are adjusted correctly and pedal comes up a bit on second quick application. They are bedded in and I can lock up the wheels but the pedal is on the floor. Any help on this matter gratefully received.

[glang]

Rebuilding master cylinders isn't always successful so you could check the operation of the recoup seal as I've described in another current thread on here.

[Joe 90]

I believe it’s down to one caliper (forgot to mention that) if I clamp the offside front flexible brake hose the pedal hardly moves, very solid. This calliper I have rebuilt several times and found nothing wrong.

[glang]

I was going to say that sometimes a brake pad can take a long time to fully bed. I've got one caliper that must be slightly angled relative to the disc so that the pads takes ages to finally make contact across their full faces. While they're doing this the pedal isn't fully solid however I do also notice a slight pull to one side until the bedding is completed and the pedal fully hardens up. I've checked it all and can only think the caliper casting/machining is slightly off....

[Joe 90]

Thanks, the brake pads are not new and the face is ( I think) bedded correctly but will check later thanks fir the heads up 👍

[glang]

If not can only think it's air still trapped in the caliper somewhere. Perhaps unbolt it, give it a shake around, replace and bleed again....

[thescrapman]

Put thinner dummy pads in, pump pistons out to contact them, clamp off brake hose and open bleed nipple.

push pistons back in and air should come out.

[Rosbif]

I have a similar problem, brakes work fine just a lot of travel. There have been threads on sites and an article in a club magazine about new calipers having the seals on the pistons set so normal position is too far from the disque, hence the travel.

The tip of putting something thinner in place of the pads and applying the brakes several times is recommended, the theory is that the seals then 'reset' on the pistons. There was no mention of the need to open the bleed nipple.

I have to admit I haven't tried it yet, been much to busy driving the car. I aim to look at it in the next few days.

[RobPearce]

I think you're conflating two separate issues, although they do both produce similar symptoms.

If the piston doesn't slide through the seal properly, the seal will distort on application of the brakes, and pull the piston back off when released. This leads to excessive piston travel, which feels like a soft pedal. A temporary fix is to push the piston further out to force it to slide through the seal.

Sometimes the caliper refuses to bleed properly; air can get trapped in places where it won't escape with normal bleeding technique, giving a soft pedal. A fix for that is to allow extra fluid in - by letting the piston move further out - so that the air has room to bubble to the top, then push it back out.

So, you see, there are two completely different problems, but they have very similar symptoms, and share some of the steps for fixing.

[glang]

Don't forget that it's only one caliper that's doing this and presumably both have been overhauled with the same type of replacement seals so less likely to be the cause of the problem?

[Joe 90]

Yes all brake seals renewed, only one caliper giving problems, have taken pads out replaced with 8mm blanks and pistons pumped out and pushed back several times. Have bled it to death. Going to leave it and use it fir a while to see if it will bed down as the wheels can be locked up, just a lot of pedal travel. Thanks one and all for your input.

[thescrapman]

Is the long travel after driving a bit? Wonder if it is a warped disc?

If you were to apply brakes whilst stationary, would it be long again if reapplied straight away?

Does travel change if you pump pedal quickly?

 

[nang]

My money is on the master cylinder. Had similar problems with my 2500.

Tony.

[ferny]

I can't see why the seal location would have anything to do with it. It's an open system which allows self adjustment. That concept just seems... very wrong.

 

When does the second pump help? As said, it could be a warped disc if it helps during movement, although I've yet to see a genuinely warped disc. Ever. It could be wheel bearings allowing the disc to move around and knock the pads back. Been there, had it happen. That's also highly evident after cornering. 

 

Other than that, it's air in the system. It's the second pump which is key and that isolating a specific point removes the problem. Can't be a leak, can't be the master cylinder - if that one caliper makes a difference. And even if you bleed the terminus points in the wrong order all air should be out after multiple attempts. 

 

I find a technique of personal preference is to pump until it feels hard, then get someone to tweak the nipple and allow fluid to shoot out under pressure and at speed. Rinse and repeat.