[bally]

So iv put new brake lines in the 95 wt sierra. Mc appears to have drained very low whilst i was doing this. However iv bled the brakes at all corners and the mid chasis bleed point too and the pedal is still very soft. Iv bled the mc a heap as well (pumped it up then cracked the lines leading out) and this gave a slightly better feel again. Then i thought to clamp off the rear line altogether and hey bingo the pedal goes exactly as youd expect, solid and firm. So iv isolated the issue to the rear brakes ( i think... as there are some peculiar things happening .....) with the car running and pumping the brake, the reservoir fluid is completely free of air..... if the brake is pumped with the engine off, lots and lots of tiny air bubbles come up into the reservoir. I now also have a high pitch squeak coming from the center valve/bleed point on the chasis when the brakes are pushed in hard and fast. This has me really scratching my head trying to nut it out. Obviously have checked for leaks at all new hose connections and none are present.

what next???

Cheers
josh

[AckerDackerly]

It sounds like you have done a thorough job of bleeding the brakes.

That said, I am curious about one thing - did you bleed starting at the farthest-away brake cylinder?

Doing so allows you to flush out all the air in the main lines to the farthest brake cylinder. Subsequent bleedings of each of the next-nearest brake cylinders bleed from where that particular line joins the main line to the brake you are bleeding. This method insures that pockets of isolated air bubbles do not remain in the system when you are done. Any air in the lines - no matter where it is located - will cause spongy brakes.

Since I tend to not have a helper when I bleed the brakes on my Samurai, I have installed "speed bleeders" - bleeder bolts with a one-way valve in-built - so that I do not have to have someone hand-close the bleeder bolt every time I press down on the brake pedal. This keeps air from getting sucked back into the system. VERY handy items that don't cost much!

Finally - is it possible that you might have air in the rear brake cylinders?

The following is just an idea - I have never tried it but it seems logical:

Remove the drum and shoes, crack the bleed nut and then squeeze the slave brake cylinder pistons together. This forces all the fluid (and trapped air!) out of the slave brake cylinder itself. Holding the pistons in the compressed position, tighten down the bleeder nut to reseal the system. Naturally, if you have speed bleeders installed, you do not have to worry about having two people do this. You can also do this on the front brake calipers, too.

Don't forget to keep the brake fluid resevoir replenished. I keep forgetting about that

I hope that this helps!

[fordem]

bally wrote:

if the brake is pumped with the engine off, lots and lots of tiny air bubbles come up into the reservoir

Where exactly is the air "coming up" from - if I assume it's from the master cylinder ports, that would suggest there is still air trapped in the system or a leak allowing air to be drawn in when the master cylinder piston is retracting. Because this does not happen with the engine running, you could have a booster related issue that causes a vacuum to be applied to the master cylinder - I would suggest removing the master cylinder and checking to see if it's leaking past the boot.

Quote:

. I now also have a high pitch squeak coming from the center valve/bleed point on the chasis when the brakes are pushed in hard and fast

The "center valve/bleed point" is a proportioning valve - it contains a plunger or shuttle that moves back & forth, that is where the squeak is coming from.

[bally]

the air is coming up from the master cylinder ports into the reservoir. iv checked all connections in the brake hoses that were undone and none of them show signs of leaking fluid. none of the connections points at bleed nipples or hose-brake connections are leaking either. what has me stumped is that if it were sucking air back into the system id expect to see it being pumped back to a bleed point and then pushed out when bled.... also the fact that clamping the rear line off and the pedal becomes perfect leads me to think its only the connection points after the vice grips clamping the rear rubber line that could be the issue: rear most rubber-hardline connection and the bleed nipple on the passenger side (rear left). Unless by losing fluid the drums have somehow reacted badly?

[1DYX]

Adjust the rear shoes.?

[whincup]

1DYX wrote:

Adjust the rear shoes.?

and handbrake.

[bally]

how does changing the rear brake line affect the handbrake and shoes? shouldn't it stay as it was previously?

[madmacca]

clamp your lines at the rubber hose that goes to the calipers at the front and just above the diff at the rear (I use vise grips , btw they dont have to be super tight) see what pedal you get , then go around removing one clamp to isolate your issue

if your rear shoes are not adjusted right (same shoes are for the handbrake) you will get a spongy pedal as the slave cylinders have to extend and retract further .

[bally]

iv done that and found that the rear is the issue. rear brakes felt like they worked fine before changing the rubber lines to newer units. havent touched anything else other then the hoses.... may as well open them up and see what i can find i guess. handbrake worked extremely well prior to the hose change too so im expecting the brakes to be adjusted fairly well.

[fordem]

madmacca wrote:

if your rear shoes are not adjusted right (same shoes are for the handbrake) you will get a spongy pedal as the slave cylinders have to extend and retract further .

What exactly do you define as a "spongy" pedal? The easiest way to describe a spongy pedal is to have the person you're describing it to get a dish (or a car) washing sponge, drop it on the floor and step on it - soft, springy and a distinctly different feeling to long travel with a firm pedal at the end of travel.

Out of adjustment rear brakes will cause increased (longer than normal) pedal travel because the wheel cylinders have to extend & retract further - the pedal WILL be firm once the shoes/linings come into contact with the drums.

A "spongy" pedal will usually be caused by air within the system - the compression of the air is what causes the softness - if there is no air, the softness isn't there.

[bally]

[quote="fordem"]


Out of adjustment rear brakes will cause increased (longer than normal) pedal travel because the wheel cylinders have to extend & retract further - the pedal WILL be firm once the shoes/linings come into contact with the drums.

quote]

that's actually really helpful! reading this seems to suit the symptoms and makes me think the term spongey wasn't the right term. curious as to how dropping the rear hose off and subsequently the fluid from them has changed their adjustment???

[bally]

Drums off, shoes are low so will be replaced. Also found that afer i pumped the brakes twice a jet of brake fluid came from the rear right cylinder.. beats me why it never leaked out of the drum itself but i guess thatl explain why the brakes became good with the rear line clamped and shit when it wasnt.

Where is the best place in aus to buy new shoes and cylinders??

[fordem]

Applying the brakes with drums off will usually force the pistons out of the wheel cylinders - normally the drum will limit the movement of the shoes which limits the movement of the pistons - there MAY have been nothing wrong with those wheel cylinders.

[bally]

most likely not but they're cheap and didnt look real flash to start with so ill do it while im replacing the shoes...

[bally]

have used a brake sucker to bleed the brakes, was a LOT of air in the rear cylinders. have come across another issue though, with the shoes adjusted out as far as the drum will allow, I still don't get clamping pressure in the rear. hand brake works awesomely, but I cannot stall the car with the rears in the air and the brakes on as hard as can be possibly pushed down.... cant adjust the shoes out any further or the drums wont go on, have tried the reverse adjustment by having the rear on axles stands and driving through the brakes in reverse but this has made no difference too.... getting really low on ideas now

[fordem]

First - vacuum bleeders have a way of sucking air in through the bleed nipple threads, giving the impression there is air in the system when there isn't.

Second - as I mentioned previously that "center valve/bleed point" is a proportioning valve - it's function is to limit the pressure to the rear wheels - make sure there is no air trapped there, and that it is working properly.

[bally]

Already bled it from there a lot bud. Just going to live with it. Brakes are good enough fpr a weekend trail rig as they are now