When I originally did the brakes on my J15 I swear they were rock hard with the pedal at the top.
For various reasons Ive have to take front and rear circuits apart. Now I cant get rid of some pedal travel.
I always assumed it was air and a bleeding problem as the rear circuit is rock hard but the front has some travel. Wouldnt really call it spongy either, more springy as the pedal will allow about another 30-40mm of travel if you press hard.
I think ive read every article on the web about bleeding brakes and have tried most. Bench bled master, traditional bleeding (pumping pedal), even reverse bleeding, shaking caliper while bleeding, whacking it with rubber mallet etc etc but it resfuses to change. I tested the master with a bleed nipple on the outlet and that was rock solid so its not that. I also loosened the caliper mounting bolts so it was fre floating in case of alingment issues.
Only other things I can think of are leaks (nothing visible) and maybe that they need bedding in but why are the rears OK and why wasnt it like that before? Disks are very lightly rusty now though.
Masters are Wilwood and calipers are Wilwood 4 pots.
Any help would be very gratefully received as I'm tearing my hair out over this one!!

Have you bled all 4 nipples on the Willwoods those at the top and those at the bottom on each caliper?

quote:

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Originally posted by big-vee-twin
Have you bled all 4 nipples on the Willwoods those at the top and those at the bottom on each caliper?

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I used the easibleed for mine, uses tyre pressure to push the fluid through bleeding is easy and calipers can remain on car.

Quite possibly calliper flex, the powerlites are not the stiffest:

https://www.youtube.com/watch?v=kgiLzdwBbag

quote:

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Originally posted by rodgling
Quite possibly calliper flex, the powerlites are not the stiffest:

https://www.youtube.com/watch?v=kgiLzdwBbag

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Depends entirely on the brake system setup and the effort in that test video, but I've seen calipers designed for greater demands displace under pressure by more than that. Aluminium calipers towards the limit of design can soften if they are overheated (>250°C).

However, certain calipers will definitely contribute to pedal displacement. Just looking at that though it wouldn't concern me too much. The greater factor tends to be lengths of flexible line (as opposed to hard pipe), disc and pad material, and most importantly, bleed quality. Considering the cost of new calipers compared with the rest, the namesake of this site I would be trying the other options first.

Hope that helps!

The issue only became excessive after you took the system apart: therefore it is a problem introduced when you put the system back together.

As you have bled the system properly and checked for leaks it points to a caliper issue. It is true these calipers flex but this would not explain the sudden appearance of the problem. Likewise softening (annealing) of the caliper material could create excessive travel but it would not cause a springey feel. Brake hoses OEM or aftermarket contribute very little to pedal travel unless the reinforcement mesh is totally blown.

So working logically:
(1) Check the callipers are aligned correctly with the disc -- ie the brake pad is being presented "squarely" on to the disc by the caliper less than a 0.5mm miisalignment will caise a spongey pedal. The symptopm are exactly as you describe the pedal has a distinctive springy feel that starts only once a certain pedal pressure is exceeded. Apart from the obvious checks using feeler gauges you can usually detect this problem by feeling the calliper while an assistant thumps the pedal hard on and off, or if you have acess to one a dial test indicator "clock gauge".

If the aligment appears Ok then:
(2) Check the callipers for seized caliper piston or pistons s as this will give the exactly same symptoms.



[Edited on 28/2/16 by britishtrident]

I cant be 100% sure the pedal was hard from the top when I did it first time.

To check the alignment issue I loosened the calipers so they could float around on the disk which I hoped would rule that out.

I saw some of the pistons move when I was using the reverse bleeder as it blows fluid into the caliper to push to air back up and out of the reservoir. Cant be sure they are all free but i'd be surprised if one was seized on a new caliper.

I had this on mine a little while back, turned out to be some trapped air that I couldn't get out through bleeding normally. I ended up using bleed nipples to block up the system and bleed it section by section.
So with bleed nipples in all ports of the master cylinder it should be rock solid. I then reconnected, bled and tested the system in the following order:
1) Front Left
2) Front Right
3) Master to Rear T
4) Rear Left
5) Rear Right

Worked OK for me!

Do you have a hydraulic brake light switch? Worth a check incase air is trapped there.

Are you running 4 pot Willwoods at the back as well or the sierra caliper with the built in handbrake mechanism?

If you've got the Sierra caliper at the rear don't forget the rotate it to bleed it to get the bleed nipple right to the top.

Last time I had this issue I drove the car for a few days and the brakes bled much easier... I guess the shaking moved the air around