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Removing dead travel?


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I am sure it is just an unfair comparison with the Cayman that has an uprated GT3 master cylinder and so a very firm pedal from the start but there seems to be an awful lot of dead travel in the pedal on the 3.2.  

The brakes work fine but there is an inch or so travel in the pedal before they bite.  This is not loose travel like the pedal box is fubar but slack in the hydraulic system.  Reading the workshop manual this doesn't seem to be adjustable and it in fact goes so far as to say as much. Anyone know any different?  I fitted a new master cylinder recently and hoped for a change but it is still the same.  I overhauled the callipers a few years ago and had the sticky seal issue for a while but that sorted itself. I don't think it is air in the system as bleed the brakes really well when the m/c was done and ultimately the brakes work just fine.

I would just like a little more confidence in the pedal as since my brake fail in the alps 5 years back I have always been waiting for it to happen again and that initial travel reminds me every time.

TIA

Richard..

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Posted (edited)

Is it not the 'pull back' from seals? When I fit pads I use a thin wooden strip and press the pedal a few times onto it. Then remove the strip and lever out the pistons just enough to fit the actual pads. I learned this from this forum years ago and have always done it and believe my pedal to be good - certainly as good as the Boxster although I haven't got a GT3 master in that.

Sorry - just realised you considered the sticky seal issue! Just come off the roof and I'm shattered!!

 

Edited by Roy M
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Probably not the full answer in this case.

Different brake fluids have varying amount of lubricating qualities.

Some of the very high performance fluids have reduced lubrication and result in the pistons 'pulling back'.

An accumulation of minute play in pivots will result in change in feel at the pedal.

 

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I would say that there is still a small amount of air in the system.When I did my Calliper refurb and flexible hose replacement I did two bleeds with a pressure bleeder to get the hard pedal. About 6 months later I had the same soft start before the brakes bit, and whilst they worked fine I found it unnerving, probably made more so by the fact that I was jumping from one car to another.

The third bleed I did was a two man job , foot hard on the pedal whilst undoing the nipple and then closing when the pedal is on the floor.did this 4 times on each wheel .because the fluid shoots out it was hard to see if there were any bubbles, but at then end the pedal was a solid one so I figured there must have been a tiny bit in there.

Got to be worth a try.

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  • 3 months later...

I've just spent 2 hours bleeding the system since I refitted the front Calipers and hard lines to the calipers. The system is flushed and there are no visible air bubbles in the bleed hose but I don't have any brakes until I pump 5/6 times.

Is it case of perseverance, I don't see any obvious fluid/air leaks

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1 hour ago, flappa2 said:

I've just spent 2 hours bleeding the system since I refitted the front Calipers and hard lines to the calipers. The system is flushed and there are no visible air bubbles in the bleed hose but I don't have any brakes until I pump 5/6 times.

Is it case of perseverance, I don't see any obvious fluid/air leaks

Are your brakes standard?

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1 hour ago, flappa2 said:
3 hours ago, flappa2 said:

I've just spent 2 hours bleeding the system since I refitted the front Calipers and hard lines to the calipers. The system is flushed and there are no visible air bubbles in the bleed hose but I don't have any brakes until I pump 5/6 times.

Is it case of perseverance, I don't see any obvious fluid/air leaks

New seals?
If the seals are sticking on the pistons they can pull the pistons back giving the pedal feeling you have. You can get special assembly lube to build up the seals and pistons but many just use regular brake fluid.

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7 minutes ago, Leicestershire said:

New seals?
If the seals are sticking on the pistons they can pull the pistons back giving the pedal feeling you have. You can get special assembly lube to build up the seals and pistons but many just use regular brake fluid.

New seals and pistons, is there a simple way to fix this without stripping down the caliper. Pads out -application  of brake fluid in front of the new dust seal then push the pistons back ?

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26 minutes ago, flappa2 said:

New seals and pistons, is there a simple way to fix this without stripping down the caliper. Pads out -application  of brake fluid in front of the new dust seal then push the pistons back ?

You could drive it and put it through several heat cycles. 
** Caution- there is the obvious risk of using a car with brakes that are not 100%. **

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Pads out - thin strip of wood in place of them - pump pedal until firm - move pistons back until new pads just fit in - fit pads. Always works for me

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1 hour ago, Busybee said:

If it’s 5 or 6 pumps till you get a firmer pedal, has to be air in the system Mike. Do you have a pressure bleeder? 

Yes, firmish pedal after pumping but doesn't hold. 

No pressure bleeder, X2 humans - x1 Flexi hose with non return valve

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8 minutes ago, flappa2 said:

Yes, firmish pedal after pumping but doesn't hold. 

No pressure bleeder, X2 humans - x1 Flexi hose with non return valve

Doesn’t that mean that there’s a leak somewhere Mike? You’re getting pressure then it’s releasing slowly. So it’s either at a hose connection/at the calipers themselves or upstream at the master cylinder/servo?

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50 minutes ago, Busybee said:

Doesn’t that mean that there’s a leak somewhere Mike? You’re getting pressure then it’s releasing slowly. So it’s either at a hose connection/at the calipers themselves or upstream at the master cylinder/servo?

I need to take another look, I would expect that a leak would show itself as fluid in the areas where I have worked, only X2 areas on the front Calipers each side and all appears tight and dry. I will take another look armed with all of the suggestions. 

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Not unusual for a high mileage master cylinder to get slightly damaged seals if when bleeding the brakes the pedal travels further than usual and the "tired" seals travel into a part of the MC bore that is not as polished or even has some slight corrosion. A master cylinder rebuild may be in order?

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22 hours ago, sopor said:

Not unusual for a high mileage master cylinder to get slightly damaged seals if when bleeding the brakes the pedal travels further than usual and the "tired" seals travel into a part of the MC bore that is not as polished or even has some slight corrosion. A master cylinder rebuild may be in order?

Sounds like the caliper piston scenario, I plan to try X2 more tweaks before looking at the MC. Clamping the breather and replacing shims for the pads. 

Cheers

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