Need some fairly urgent advice, I am due to be at Brands Hatch tracking the ‘5 on the 9th! Essentially, my brakes are useless. I bought the car knowing they were soft and the pedal had a bit of travel, but I had assumed a good ol’ bleed would sort the issue out. Unfortunately, I have bled the system twice, Nick at Skuzzle has bled it once, and no joy. The pedal firms up beautifully when bleeding, but the moment you fire the engine up, the pedal goes soft and super long.
A few suggested the master cylinder, I had a known working one in a donor car which I swapped in and rebled the entire system, no joy. I then thought that as the issue only happened when the engine fired, it could be the hose that housed the check valve going from the inlet manifold to the brake servo, so I replaced that… No joy. I am not losing any fluid anywhere, so there isn’t a leak in the system.
The car is running large 1.8 brakes from a 2.5 sport, the pads appear to have a good amount of treat left and to have not worn unevenly, although I haven’t had the calipers off properly yet to inspect. Although I seriously doubt they are the cause of the problem.
The handbrake works a treat.
At the moment my thoughts are:
Replace the brake servo 2) C-Clamp all of the calipers and see if the pedal firms up 3) “gravity bleed” the system for a few hours during the day, with regular checks on the fluid level. 4) Bite the bullet and swap the entire brake setup from my donor car
Any suggestions would be very welcome. I read through a very long thread where a chap across the pond had a very similar issue, which turned out to be air trapped in the hard lines near the master cylinder, god knows how.
See, most other people have said that. But here is my problem with that theory; the servo assists the brake pedal to make it easier for our legs to push the pedal and apply force, if it were broken, the pedal would go massively firm but braking effort would be minimal, right? It’d be unlikely that it was getting too much vacuum and “over assisting” wouldn’t it?
A little update, I got a load of air out last night after fiddling with the front calipers and winding the piston in and out a few times, to make sure it traveled nicely. The passenger side didn’t travel very well at all, so I gave it a clean up and a few winds in and out to restore proper mobility of the piston. I did a bit of a naughty and just bled the front after doing this, with the intention of doing the same to the rear tonight and then re-bleeding the fronts again after.
However, I think I may have introduced a problem… In changing the master, I found a small trace of brake fluid around the proportioning valve, cleaned this off and re-checked tightness of the hard line pipes, I was able to get another quarter turn on each pipe! Will check the valve again later on to see if there are any traces of fluid around it. If so, it would seem so far all I have done is introduce a new problem by changing the master cylinder!!
A spongy pedal is normally air compressing in the system, but, it’s good with engine off ? The servo multiplies the foot pressure on the system then indicating air present.Does the pedal remain firm after bleeding after a while,without starting the engine, if it softens it’s got to be air in the system. Good luck.
Hi, about 25 years ago I had a similar problem. It turned out to be a seal on the master cylinder had a tiny split which allowed it to suck air into the system when you released your foot from the brake pedal quickly. You could bleed the system and have a firm pedal , but as soon as the engine was started and the servo was helping it would suck a little air in and the pedal was spongey again. It never leaked a drop of fluid and had me baffled for a whole weekend. I can’t imagine this is your problem because you’ve already changed the master cylinder. But there could be a seal in the system somewhere doing the same thing. It’s been a long time since I’ve worked on hydraulics of any kind. I had a career change 25 years ago. But it sounds like it’s sucking air in somewhere.
Made some progress last night - one shot rear caliper identified and replaced, another sticky one rectified. Replacing the proportioning valve tonight as a matter of course (and I’ve replaced everything else now!) and then giving the system a bleed. If that doesn’t do it, I’ll be hauling the entire brake setup out of my donor car onto this one, had enough of chasing my tail already!
Sticky calipers will give you a long travel, you can also normally check by the shape of the pads, looking wedge shapped.
The caliper does not move. When you press the pedal it actually twists the caliperor the pad, but it springs back afterwards so clerances are not taken up. The pedal gets longer and longer as you need to “bend” everything further each time. WIth the engine off you probably don’t have enough push to do this.
If you own an Iveco van you will know this situation well!
Last night I went through and rebled everything, still no luck - pedal spongey as hell!
I noticed I hadn’t quite seated a couple of the hard lines that well and they were weaping ever so slightly, so I am going to “bench” (or actually engine mounted…) bleed the master cylinder, by disconnecting the two hard lines. Am also swapping all of the calipers and stainless lines from my other car, just to be safe. If it’s not any of the above, then it’d have to be the brake servo or proportioning valve, but i’d be very surprised if it was!
After a bitterly cold session fitting my dump valve and going back over the brakes, I totally missed that i have MK 2.5 sport brakes! Yay for having big brakes, boo for having NO SPARES! Got to rely on my mates theory of the master cylinder having air trapped in it… Have got a half day today so off to do battle in a bit. Will update everyone later.
Managed to get the issue fixed. Turned out that the caliper bleed nipples (well, three of them!) were leaking slightly. Only found this after pulling fluid through with a suction gun. Once we found and replaced them, we still had a very long pedal, but with effort at the bottom. We adjusted the pedal up and got everything working. It was far too high the first time though, and the brakes bound on after a test drive -.- . We have got this all adjusted now though
Brands was great for the first few sessions, then the charger sprung a leak. Gutted, because I have put in so much effort in the last three weeks. Will pop a thread up about getting it rebuilt in the appropriate section.
