Bleeding brakes.

Post by **MattH** » Wed Jan 22, 14 8:49 am

Ok, new rear wheel cylinders, new pipes and hoses throughout, good master cylinder and calipers.
Front brakes bleed really easy, rears, cant get any fluid there at all.

Is the proportioning valve a problem, should I do something with it before bleeding or just take it all apart ? Never taken one apart so i'm not sure what's inside it.

Are they different inside? I have the cast one, but a spare brass one that i could try instead. Anyone had this frustration before??

Its for 1973 Challenger with front discs. Thank you!

Dave-R · Post by **Dave-R** » Wed Jan 22, 14 8:51 am

Is the switch thingy for the brake warning light centered?

Pete · Post by **Pete** » Wed Jan 22, 14 8:53 am

That would be my guess too.

The only time I experienced this was when the rear hose collapsed but as you have changed that, it is very unlkely.

I am not sure if there is a specific sequence for bleeding to avoid the system "sensing" a leak and the shuttle moving over to retain some braking capability.....

Ivor · Post by **Ivor** » Wed Jan 22, 14 9:08 am

I don't want to teach grandmother and all that, but I always bleed the brake furthest from the master cylinder first.

Have you slackened off the rear brake line from the proportioning valve on front chassis leg and pumped the pedal to see if you have fluid coming through first?

MilesnMiles · Post by **MilesnMiles** » Wed Jan 22, 14 9:18 am

Matt, this may not be relevant, but on my Buick there is sometimes a need to re-set the proportioning valve via a button as if the rear brakes 'fail' it cuts of the supply. May not be relevant on a Mopar though.

Dave-R · Post by **Dave-R** » Wed Jan 22, 14 9:24 am

MilesnMiles wrote:Matt, this may not be relevant, but on my Buick there is sometimes a need to re-set the proportioning valve via a button as if the rear brakes 'fail' it cuts of the supply. May not be relevant on a Mopar though.

Yeah that is what the warning light switch does on a Mopar.

And Yes. Always bleed the rears first starting with the right side on a Yank.

MilesnMiles · Post by **MilesnMiles** » Wed Jan 22, 14 10:51 am

cheers Dave, not come across that. Never had a brake warning light work yet on my Mopars

Pete · Post by **Pete** » Wed Jan 22, 14 11:12 am

I've never had Brakes that work on a Mopar.

They "GO" a lot better than they "STOP".

That is the perverse attraction, I suppose......

Dave-R · Post by **Dave-R** » Wed Jan 22, 14 11:19 am

Having said all this....I am not sure if it will cut off the pressure to the rears or not?

Worth looking at though.

Pete · Post by **Pete** » Wed Jan 22, 14 11:30 am

I would think as the shuttle moves over (and lights the "BRAKE" light) it would block the defective outlet port.

MATT - A good way to check woudl be with a meter of a light bulb to see if the warning light activating switch has triggered

Dave999 · Post by **Dave999** » Wed Jan 22, 14 11:35 am

warning light switch definately

cuts off the circuit it belives has a leak. in total.

the end of the slidy piston ends up directly in the path of the pipes for 1 circuit or the other and is held in that position by the end of the switch which completes the circuit to light the dash brake light.

undo the collar round the spade connector 4-6 mm

listen for click

do it up again.

if the system is full and only if it is full of fluid and you are just chasing the odd air bubble to remove spongy peddle

stand on the brakes a couple of time to get the cut off piston centred

Then

bleed brakes like you were tickling the chin of a tiny baby and it won't pop back and cut off the rear circuit again.....

if pressure in the front circuit overcomes the piston spring pressure the piston will move and cut off the rears again

unless you have a failed wheel cylinder or a burst pipe these thing should be called danger swicthes, not safety swicthes..especially if your dash light doesn't work. check it by pulling the hand brake or shorting out the cable to the switch on the back of the hand brake

or shorting out the wire to the switch at the safty switch block or master cylinder (some MC have this integrated into the cylinder body)

Dave

Pete · Post by **Pete** » Wed Jan 22, 14 11:38 am

You have FARRRRRRR too much time on your hands, Dave

Dave999 · Post by **Dave999** » Wed Jan 22, 14 11:43 am

am supposed to be writing report on my Capacity Items...

but as per usual everything is ok no capcity exceeded in any area

so i don't see why i need to write anything other than

boss won't see it that way

Dave

Post by **MattH** » Wed Jan 22, 14 2:29 pm

Thanks guys, this would make sense, I bled the nearest first and Im bleeding an empty system for the first time.
I had run out of initiative by 10.30 last night after flaring another five pipe ends.
I know what I will be doing tonight!

Post by **MattH** » Wed Jan 22, 14 10:10 pm

Hmm, had a look tonight, there is a pin that rises up which might be the button described above, it has a rubber shroud round it and can be pushed down.
I tried holding this down and then gently bleeding the brakes with a willing pedal pusher helper but still no fluid coming out at the rear bleed screws.

I have stripped out the big plunger with the spring which seems to block the rear pipes, just to see how it all works.
It seems that i might have to completely disconnect the front master cylinder pipe from the safety switch and block it to bleed the rears as any pressure from the front is preventing fluid going out to the rears.

I have tried to do it by completely opening the front bleed screws but all that happens is the fronts bleed away merrily and the rears still get no fluid.

I will look again tomorrow but it seems it is a technique to try to bleed the rear before the fronts get any fluid, but because my fronts already have fluid I cant backtrack and do the rear first.

Its tempting to just ditch this safety switch and have two seperate systems just with a connector block. Has anyone done this before?