Outer Limits 4x4 Board

Well, I think it’s a master cylinder.

You have to pump up the brakes till they go hard and then if you leave your foot on it sinks to the floor. They used to work ok though.

So on Sunday, I bought an S/H master cylinder from pick and payless and it seems a bit better. Sometimes it doesn’t drop in the floor. Still have to pump up the brakes for hem to work. I braved it and took it for a test drive and the brakes are all over the place. One minute they are in the floor and still don’t work, next they pull up but wont lock up, Then they might go hard and don’t do a thing. And occasionally you can get the rears to lock up.

The whole time they have been Spongy.


So what are your thoughts on this? A relative who is a mechanic told me he has seen this sort of thing before on old inter fire trucks and could be a master Cyl or just a heap of air that won’t bleed out. I have spent ages bleeding and rebleeding but still no joy

So what is you thoughts, before I go and spend more money on this ? What symptoms would it have if the brake proportioning valve wasn’t working properly?

mine did that, it was the sliders on the front disc calipers sticking, just needed cleaning up, a light sand and some rubber grease, and all is good.
But this does depend on type of calipers.

Also had this happen on a previous car, and that was a woern wheel bearing, so 1st pump straightened it out, so loose bearing wasn't obvious.

hope its something cheap n easy to fix.

christover

ps. modded brake systems often dont have the bleeders on the top, they may be front or back, so calipers need spinning round to get a proper bleed....assumoing any mods been done.

my rear discs have to be bled this way.



of course new 2nd master could also be stuffed, but my money is on mud and crud and rust in brakes.

christover

I have (a few times) had a pedal that you could get hard but would (slowly) sink to the floor if you hold your foot on. This was caused by a failed seal at the back of the MC - which let the fluid slowly flow back into the reservoir.

you can eliminate parts of the brake system by blocking off each wheel one at a time and checking the brake pedal for example get a few pairs of vice grips or a hose clamp tool and crimp each rubber brake line one at a time untill the pedal comes good if you cut off all 4 brakes you know your master cylinder is crook just a easy way to check brake problems, if you dont understand what i mean PM me.

Insane, Yeah i was going to try that tomorrow ?

I wish i had modded brakes.

And, Christover, did your pedal sink in the floor with the crud or was it just unreliable? More food for thought

At least with all the rain on the mud, It makes me feel like ive just been out wheeling.

Thanx and keep em comming

pongo wrote: Christover, did your pedal sink in the floor with the crud or was it just unreliable? More food for thought

good point, no it didn't, once I had a pedal it stayed, in both situations.
A leaking seal in master, or wheel, or disc cylinders is more likely.
Isane's idea, the blocking off of lines, to discover the location of prob is the best idea.

christover

Yep replaced master cyl and its almost all good. More air than a Stripper at a buks party. Was only $125 from scotts auto one blacktown

cheers

dunno if this will help but after fitting a extended rear brake line to my 40 i couldnt get any rear brakes spent 2 days and some bux trying to get them to work found out the pushrod from the brake pedal to the booster/mc is ajustable in length to allow more fluid to flow

dunno if this will help on your vehicle but it made mine stop better than it ever has in its life

Bit off topic, but when I had a Series 2 RX7 my brakes went all spongy and pedal would compress to the floor.

The rubber seals in the MC were shot. The seals were 6 rubber O-rings. Mazda wanted $100, Maz Spares at Bankstown way had aftermarket for $30. BARGIN. Fixed it no probs.

Steve

it may be a booster vacuum leak. First application there may be enough stored vacuum, second quick application and there's bugger all power assist and difficult to pull up. Constant pressure will also make the pedal sink

Check the booster like this. Engine off, couple of pumps. Hold the pedal and start the engine. the pedal should sink slightly.

also what the others said - internal leaks (my 80 did this) or leaking into the booster.

try a pressure bleeder if you can get hold of one

NAh not the booster. I checked like you said. I just spent another hour bleeding adn its all good.

I also adjusted the brake pedal right out so i have more stroke before i hit the floor. Didnt really need to do it but i decided to whilst i was there anyway.

Thanks again for all your help everyone. I might actually get to drive it tomorrow