OK, now i thought i was fairly good with brake issues, but this one has
me stumped.

Always had lots of pedal travel - could always stop but it felt a
little spongey - bled the system twice with no luck. Pedal always feels
resistance and doesnt sink under constant pressure but will go right to
the floor (good sign of air in system, but after two
pressure-bleedings?)
Swapped rotors for some nice new ones, new pads (needed doing, wasnt to
cure this problem) and the problem became more pronounced. Last night i
had to do an emergency stop from 45 and the last car length or so the
pedal just hit the floor and fortunately the car stopped eventually, in
a cloud of smoke (not tyre smoke - didnt slide, the ABS didnt kick in
either). Checked the hoses, fluid levels, new pads and rotors, checked
the hard-lines. Checked the calipers immediately after stopping and
they were just warm to touch, discs were hot naturally.

Any ideas? Should i just re-bleed again and see?

J

"Coyoteboy" <coyoteboyuk (AT) hotmail (DOT) com> wrote


Are the rear brakes drum or disc?

Did you clean the protective coating off of the rotors with brake cleaner
when you replaced them?

What is your history with the vehicle? Have you owned it since new?
Acquired used? Have you check the master cylinder pushrod adjustment?
--
Ray O
correct the return address punctuation to reply

Hachiroku wrote:
Thats because im not sure on it. The pedal doesnt sink with constant
pressure, and even on excessive travel it always forces back with the
same force i pressed down with hence i assume MC seals are ok. Servo
assembly holds vacuum flawlessly, hose is in perfect condition, as is
the one way valve in it.

J

Ray O wrote:
Hehe, so many questions...let me try to answer completely:

Its a '91 Celica Alltrac, vented discs up front, solid rears. Had the
car for 18 months, brakes were initially very good (but anything would
feel that way coming from a Peugeot 205), gradually got worse and i
noticed the pedal travel becoming spongey and increasing. This was when
i first bled it, before the new rotors were fitted. This didnt cure it
but i needed new rotors 6 months later (here we are today) so they have
just been done.

Rotors were cleaned and all mating surfaces were cleaned of junk with
fine sandpaper. This weekend it was bled again, from calipers back to
MC (no change) and back the other way - pushed nearly a litre of fluid
each way. Bled the ABS actuator block by cracking each connecting pipe
- got a couple of squits of air out of it which improved the initial
pedal travel noticably.

Now with the servo vacuum detatched or the engine off the brakes travel
1 inch then firm up nicely and i cant force it past half way with all
my leg strength (you can see the pedal arm flex instead), still feels a
little flexy but not spongey. But with the vacuum *on* I can still hit
the pedal on the floor with a decent bit of force (read as *the force
needed to do an emergency stop*).

I've felt round all the flexi hoses - you can feel them 'stiffen' on
brake application but they certainly dont appear to balloon at all. All
the hard lines were replaced 12 months ago due to excessive corrosion
on one back corner of one line. At the time it didnt make a difference
to the pedal feel so i assume it was bled out fine then (or at least
that hasnt been a contributing factor).

It seems entirely linked to the servo assist unit - with it off it
behaves as normal, with it on it feels like the pedal arm is made of
spring steel. I dont think its the pushrod adjustment - the brakes come
on pretty early - a good bite occuring at about 1 inch, noticable
retardation earlier than that. If only it would stay somewhere near
that one inch mark on firmer application id be happy with them, but it
doesnt and it doesnt seem to exhert any more force on the pads.

J

"Coyoteboy" <coyoteboyuk (AT) hotmail (DOT) com> wrote

I think you're on the correct track - check out the vacuum booster (servo
assist unit).
--
Ray O
correct the return address punctuation to reply

I dont know any clear way of checking it to be honest. The vacuum uni
holds vacuum perfectly well, the one-way valve in the hose works fine -
i cant think of any other test i can run on it

A slight alteration to the pedal feel i noticed this morning - if i
press the pedal, while driving, once rapidly i can feel a springy feel
then a sort of 'moving damper' effect - the pedal feels as though its
hit something a little more viscous, then it continues to the floor. If
you press the pedal slowly it takes more travel to hit the 'more
viscous' feeling bit.

I'm almost tempted to go against all my normal feelings and drop it in
at toyota to be checked out, but they'll probably take the pi$$ with
the bill.

J

Hachiroku wrote:
Well its a hard one to figure out - it only happens when the booster is
active, yet it could still be something in the MC thats failing with
the additional pressure.


No junkyards round here have anything like the alltrac, and those at
the other end of the country want £100 for a used MC.

J

Hachiroku wrote:
Im not sure to be honest. I do know that the alltracs from 87-98 have
about 7 different part numbers with slightly different specifications
for each, depending on whether they are JDM, UK, ABS or not within each
country etc and have heard of problems with fitting even the JDM
version to the same model UK so im guessing they are alltrac specific.
Just my luck eh!

J

Hachiroku wrote:
Funny eh, always the way. Try Peugeots, at least an older one. After
dropping mine into a ditch i replaced the whole rear suspension, front
lower body panels, front lower arms and joints, two alloys and two
driveshafts for £250 - parts from various models of peugeot and
citroen lol.

J