Ando81 2,949 Posted November 24, 2014 Hi all, as the title suggests my brake pedal is firmer than it used to be. I recently replaced the master cylinder on my xf, in the process I stuffed the thread on the bleeder on a front caliper so had to put a second hand caliper on. The piston moved back fine when I installed the second hand caliper so I didn't think it was siezed but since bleeding them all the best I could it seems that the pedal is firmer than normal. I stabbed the brakes on a dirt road and all wheels locked up evenly. Also, there doesn't seem to be any vacuum leaks anywhere around the booster. Any ideas? Share this post Link to post Share on other sites
gerg 10,871 Posted November 24, 2014 You might have had air in the system all along, so when you went and bled it up it took the sponginess out, which before you took as being normal. Or do you have to push harder to achieve the same stopping power? If that's the case, you may have booster problems. Share this post Link to post Share on other sites
Ando81 2,949 Posted November 24, 2014 It's firm and have to push harder for the same amount of braking as before. Dare I say it, it's like a bad booster but can't hear any vacuum being lost when pushing the pedal. Share this post Link to post Share on other sites
SPArKy_Dave 8,892 Posted November 24, 2014 Partially seized piston could cause a hard pedal. Share this post Link to post Share on other sites
Outback Jack 6,352 Posted November 24, 2014 It's funny you say that Ando, I have a new booster and master cylinder and was experiencing the same. All my calipers are recond and new discs/pads. The pedal is quite firm and if you want to stop in a hurry it doesn't give you a confident brake feel. Works, but a lil skitish. I still have to check for vacuum leaks on the intake manifold from the booster forward. Thats all I can think of, besides a re-bleed on mine. Booster works like it should, pump up the pedal with ignition off, start car and it should drop. Kinda got me stumped. Jack. Share this post Link to post Share on other sites
jca25 1,034 Posted November 24, 2014 Booster works like it should, pump up the pedal with ignition off, start car and it should drop. Jack. Plus 1 on what jack has said try this you wont always hear the vac leak on the booster Share this post Link to post Share on other sites
Ando81 2,949 Posted November 24, 2014 Cheers lads, I will try Jacks trick in the morning. If that fails I will pull the caliper off and see how free it is. The master cylinder was free as a bird before I put it on. 1 Outback Jack reacted to this Share this post Link to post Share on other sites
Thom 6,654 Posted November 24, 2014 Could just be a result of a fluid change who knows how old and how broken down the old fluid was Share this post Link to post Share on other sites
Ando81 2,949 Posted November 24, 2014 I'm not sure Thom, it's like I'm stopping en extra tonne of weight now though, I was paranoid in the rain today that if I pushed the pedal any harder that I was going to lock a when but it wasn't slowing down very well. If I can't work it out I will get my local mechanic to check it out. Am leaning more towards the partially seized caliper theory though. Thanks for all of the ideas though, really appreciate it! Share this post Link to post Share on other sites
Ando81 2,949 Posted November 24, 2014 So Jack's brake booster test proved that the booster is fine, pumped up the pedal till rock hard and started the pedal and it lowered a few inches. Maybe I need to check the quality of the second hand caliper. 1 Outback Jack reacted to this Share this post Link to post Share on other sites
bear351c 10,273 Posted November 26, 2014 Is the m/cyl exactly the same as the old one?? The diameter of the piston, inside, changes the force on the pedal as well. I dare say, that after 30 years, you could have had anything on there. Is it for disc/drum or 4 wheel discs? Smaller piston, more pressure at the wheels, larger piston equals harder pressure on the pedal. (25mm and over) Share this post Link to post Share on other sites
Ando81 2,949 Posted November 26, 2014 It's 4 wheel disk, will check the size of the old cylinder tonight compared to the new one. Also I have gone from a pbr to a protex unit. 1 Outback Jack reacted to this Share this post Link to post Share on other sites
Trev Vaa 1,185 Posted December 5, 2014 urgh protex... they cant even machine a fucking thread properly. sick of their shit. you can buy PBR brand new, use that. on the flip side, did you grease the pins/slides with copper grease? rebuild the caliper etc? probably a lot of crap behind the piston. Share this post Link to post Share on other sites
Ando81 2,949 Posted December 5, 2014 Shit, I was hoping their stuff was good. I only went with protex to support the local bloke, could have got pbr off eBay but the local bloke is battling so I try to use him as much as possible. Didn't pull the caliper down yet but I may have to soon. Share this post Link to post Share on other sites
Outback Jack 6,352 Posted December 5, 2014 I'm going to be having a look at mine next week as well Ando, so if I find anything, I'll post up the results. Bloody frustrating isn't it? LOL Jack. 1 Ando81 reacted to this Share this post Link to post Share on other sites
Ando81 2,949 Posted December 5, 2014 It's frustrating but my own fault for being time poor and not pulling it down to have a good look first. I need to make time and get it sorted. 1 Outback Jack reacted to this Share this post Link to post Share on other sites
