BMC or something else?????

[StuC]

Ok so this isnt for a Toyota but same rules apply.
My sistersR31 needed new brakes hoses at the front so i put a set in off a wrecker vehicle. Put a heap of new fluid through, did the 2 man bleed (both at the master cylinder and the caliper as i'd had a bundy tube off also) but couldnt get pressure up. I figured as the car had been sitting around for a while i'd do a full flush and see how it went. Nada - still no pressure.

I repeatedly the bleed at the Master cylinder and the wheels, plenty of fluid, no air coming out, no leaks, pressure started to build up but as soon as the car was started and vacuum assist was there, pedal to the floor. I came to the conclusion that the BMC was stuffed. Today i put another wrecker item in which didnt show any signs of leaking both at the boost, the carpet inside or the back of the BMC (the one i removed had smalls signs of leaking) Repeated the above bleeding procedures and again no pressure.

I even clamped up the boster vac line to isolate the check valve and see if that would maintain pressure (as it should) but even that sunk a little and didnt really hold. It drove fine before i removed any lines and its doing my head in.

If it was leaking at the BMC there would be fluid everywhere and it wouldnt be pushing as much fluid through as it is. If it were leaking at any of the lines i'd be able to see it. If any of the calipers were leaking i'd also be able to see it and again, if it was that bad there would be nowhere near as much fluid coming through on a pedal stroke. If there were still air in the system it should have come out with the amount of fluid having gone through.

Bear in mind this is most definitely not my first brake flush (done 1000's of them) any suggestions? Dont really want to fork out the $270 for a new one to find it does the same thing. I might pull the rear calipers off again on friday and pull them down for shits and giggles, even though they have been rebuilt in the last 2 years and havent even done a set of pads in that time.



Any ideas people?

[lexsmaz]

If you crack the brake lines at the M/cyl with someones foot pushing hard on the pedal or someone stomping on the pedal with the lines cracked does the fluid come out with force as in want to spray / squirt or just dribble out .. if it just dribbles out i would be looking at the m/cyl ..

Personally i try to avoid doing a full pedal travel on a m/cyl if bleeding unless you know the brake system is good as it can cause issues with the cup seals travelling over muck build up in the m/cyl & ending up with a problem like you now have .. Vacuum bleeding at the callipers is the best way ..

You could also try going back to the wreckers & cuting of the old m/cyl lines from the car & crimp them shut etc & fit them to your m/cyl & bleed ( make the cut lines as short as you can to avoid any excessive air being trapped in them when you are doing the test ) the pedal should now be rock hard & no real travel, it will isolate as to wether its the m/cyl thats at fault..

Also have you looked at the rubber brake hoses as you are trying to pump up the pedal, i cant think i have ever seen it, but have heard of old rubber lines ballooning under pressure ..

[fixeruperer]

A MC will bypass inside (fluid will run past the seals) so youll loose your pedal and have no leaks.
if you have no air anywhere, youd have to start thinking MC, maybe just get one rebuilt ? or get an exchange one ?
seized caliper slides can give a shitty pedal too, but if its going to the floor with no air in the system, its probably bypassing inside the MC.

[StuC]

Yeah, I hate manual bleeds too but unfortunately dont have a conpressor or air bleeder anymore. All signs really do point to bnc, i'll get a new one or changeover and go again. Pain in the arse really. Now that you mention the force with which it comes out at the MC only the rear has any gusto behind it. Totally glossed over that. I hate this car - taking all my holiday time away from my cars ordrinking thanks guys!

[StuC]

New bmc in. took ages to get tge air out of the system. Rears where fine, front fookin ages. Im not 100% happy with the pedal either. I think there may be a pin leak at the front lines or something as no matter how much bleeding its still not right. Again, notmuchforce when cracking the lines for the front. I've left it since sunday. I'll go agajn saturday and see if any more air is in the system. If so gonna have to go new lines. Hate this shit

[fixeruperer]

get 2 people, one on the pedal and one at the bleeder.

pump the pedal up, hold it down then undo the bleeder, then once the pedal is down (new master, so you can use full travel) tighten the bleeder and take ya foot off the pedal, and repeat.

pump, hold down, undo bleeder, fluid/air will come out, tighten bleeder then lift off the brake pedal. rpt..

tried clamping a brake line till you get a good pedal ? try clamping the rear diff brake hose. to cancel out the rear brakes. then try clamping the front calipers, one at a time.

[allencr]

...may be a pin leak at the front lines or something... ...gonna have to go new lines.

IT'S never the lines unless they are very obviously leaking/ballooning!!!
A bit of air is easily trapped at every junction's threads. Stabbing at the pedal will shock/break them loose.

[StuC]

Thtas how i blead it - pump up, down, undo and tighten. rinse repeat. done the above with clamping lines - still air coming through. re-bled from LR, RR, LF, RF too. Its had about 3 litres of fluid through and still getting air. I've never ever had one this bad before - it's ridonculous! I'll have another stab and see how it goes.

[fixeruperer]

tried bleading it at the master ? got free travel at the pedal ?

so you still have air in the system, or your not happy with the pedal feel ?

sounds like its being a pain haha.

[StuC]

bled it at the master for about 30 imns. then did a run around to all calipers, then master again, then calipers again. Still getting a heap of air out of the fronts on the last time round. This led me to do the front system at the master again and then the calipers yet again. No freeplay in the pedal at all. There didn't seem to be any air coming out last time round but im not totally happy with the pedal. Pain is a massive understatement! I have never, ever had this much trouble with brakes before.

I'll let everyone know how i go with another blead/burning rag in the fuel tank.......

[fixeruperer]

there should be a lil bit of free travel at the pedal. shine a torch up and look at the clevis pin in the pedal push rod, adjust till you can wiggle the pedal without moving the push rod.