80 Series brake pedal sinking problem...

[Surfin Alec]

Can anyone with brake knowledge shed some light on what my brake problem may be?

Ever since I have owned it (2yrs) the pedal goes down to about 2" off the floor every time whilst the motor is running. Turn the motor off or dis-connect the vacuum hose from the booster and the pedal gets rock hard at the start of the stroke and no sinking.

Start the car and the pedal drops and if you try you can get the pedal to just touch the floor (pusing real hard).

I have heard about 80's being a bugger to bleed and trapped air in the M/C so I have tried to bleed on a couple of occasssions. I also tried to vacuum bleed with a sucking pump but still the same.

Is it the master cylinder or got any other clues or (try this's)?

The cruiser is a 97 TD Auto GXL. No ABS.

Thanks,

Alec

[trains]

Alec,
What you describe re pumping the pedal, so you expire all the vacum, then start the engine, and the pedal drops is normal.
If it didnt do this, it would be a vac problem, and trying to stop would require all the pedal effort you could muster.

You have mentioned that the pedal gets rock hard when there is no vac assist happening, so by that I would assume that your brake system is fine with no bypass, or air.

when you push really hard on the pedal, and it almost goes to the floor, are you doing this whilst standing still.......or when your driving, in order to stop.

I would assume that if you buried the brake pedal to the floor in the way you describe, you would have 4 black lines on the road, and a pissed off passenger who was in the back seat, who would now be in the front


Trains

[Gribble]

If your pedal is rock hard with no vaccum then I doubt you have any air in the system.

It could be your MC just creeping with the extra grunt of the vaccum, or it could even be a bloating brake hose too.

Just a few ideas.

[ozy1]

do you notice ant fluid loss over time?

we worked on a an 80 series with ABS, replaced pads and had this drama, turned out to be a leaking seal between the resivour and the master cylinder body, wouldnt loose great amounts of fluid, but we noticed the pedal, we looked for the prob for 2 days, and the level didnt really change that we could notice,

[+dj_hansen+]

do you notice ant fluid loss over time?

we worked on a an 80 series with ABS, replaced pads and had this drama, turned out to be a leaking seal between the resivour and the master cylinder body, wouldnt loose great amounts of fluid, but we noticed the pedal, we looked for the prob for 2 days, and the level didnt really change that we could notice,

Feel around on the inside/firewall for wetness... thats where my clutch master was leaking, not externally very hard to find and diagnose.

[Sic Lux]

Yeah if the pedal is creeping down look at maybe doing master cyl seals firstly look for perished or swelling brake lines also have you put pads in it resently we done a pad slap on a nissan terrano(crapper) with customer supplied pads and went for test drive to bed them in and had a real spongy/sinking pedal after a fair while and master cyl re-build found it to be pads were physicaly compressing under pressure put good quality ones in and all was good.

[midi73]

do you notice ant fluid loss over time?

we worked on a an 80 series with ABS, replaced pads and had this drama, turned out to be a leaking seal between the resivour and the master cylinder body, wouldnt loose great amounts of fluid, but we noticed the pedal, we looked for the prob for 2 days, and the level didnt really change that we could notice,

Feel around on the inside/firewall for wetness... thats where my clutch master was leaking, not externally very hard to find and diagnose.

No point in doing this with brakes. You have a brake booster between the master and the firewall. If it is bad it will leak down the front of the booster, but it sounds like it is not so bad so would need to remove the master and check if fluid is seeping out the back of the master.

[+dj_hansen+]

Good point Midi73, doing homework, talking on the phone, and posting on outers isnt a good combination... (esp when its your GF on the phone and she busts you )

[midi73]

Good point Midi73, doing homework, talking on the phone, and posting on outers isnt a good combination... (esp when its your GF on the phone and she busts you )

Lol, I know what your saying.

[Sic Lux]

do you notice ant fluid loss over time?

we worked on a an 80 series with ABS, replaced pads and had this drama, turned out to be a leaking seal between the resivour and the master cylinder body, wouldnt loose great amounts of fluid, but we noticed the pedal, we looked for the prob for 2 days, and the level didnt really change that we could notice,

Feel around on the inside/firewall for wetness... thats where my clutch master was leaking, not externally very hard to find and diagnose.

No point in doing this with brakes. You have a brake booster between the master and the firewall. If it is bad it will leak down the front of the booster, but it sounds like it is not so bad so would need to remove the master and check if fluid is seeping out the back of the master.

Even sometimes it will pass by with the pressure but not leak out. Not as common but does happen. Also over time the bore of the master cyl can wear into a slight oval there are places around that stainless steel sleve them if this is the case.
Gotta hate the missus interuping outters time

[Surfin Alec]

Thanks, I will have to go and check the flexy brake lines for any swelling. I havent put any pads in recently but the rears where done just prior to me buying it. (But the pedal has been bad since I have owned it).

The pedal creep is whilst stationery, just pushing hard.

No fluid loss anywhere that I can find.

Is it the norm or worthwhile to fix / re-sleave a M/C now a days or do you just lob them. For a new one I have been quoted between $170 to $480!! and all non-genuine. All bucks I would rather be keeping though.

Alec

[midi73]

The problem does sound like what siclux said, that it is creeping past the seals within the master cyl. It could be worth rebuilding, especially if you go stainless like was mentioned above.

[rezpkt]

hey alec i have similar problem in mine.

my brake lines are stainless, but not the calipers.
i have replaced my master cylinder ($120 i think for PBR brand)
there isn't a heap of different and expensive ones as one might tell you, try Bursons.

I still have slight sinking in the pedal, could be anything mate.
I'll swap out my caliper lines for stainless one day.

Have heard proportioning valves have strangely created similar problem.
I have also bracketed and adjusted mine for lift, seemed to make small if any differences, un-mount yours and lift it up and down and see how your pedal is?
Swollen seals?

First place for you is lines, and MC i guess.

good luck

[dow50r]

Gday
the fact it sits hard with no vac probably means a master problem..because vac allows more pressure and more leak... The best way to bleed the master is undo the pipes, fingers over the ports with pressure on them friend to operate pedal, do this till only oil comes out, reinstall lines, break them under master, and bleed again, then next junction etc...use a new bottle of fluid, make sure you bleed the proportion valve too...it has a nipple. If you have abs...best of luck...