waggy doo

iTrader: (1)

Well,i still having problems.Symptoms now are if i put foot on brake with even pressure and hold it there as the car slows down the brakes grab then release and continue to do this until the car stops.I hold the pedal in exactly the same position but the brakes kind of work and then dont its as if i am taking my foot off then back on repeatedly.

HELP
HELP
HELP

anyone got good tech knowledge of braking system that can throw some light on this.

Thank you

PETENAUD

When u say grab and release, how often???

Had a similar prob that almost felt like the abs coming on, but wasn't. Any way i had a warped disc

Have you checked the discs with a DTi gauge???

waggy doo

iTrader: (1)

Petenaud
The front discs and pads are brand new pagids.I will try and explain.If i get up to say 50mph and and gently brake as if i was slowing for a roundabout the pedal travels along way and is very soft,i keep my foot in the same position on the brake pedal and over a distance of about 150yds the the brakes will bite( not severly) about every 20 to 30 yds.If you can imagine driving along and then just dabbing the brakes this is the feeling im getting.I have had warped discs before and am familier with the symptoms.As said in my original thread i have changed to four pots,new discs and pads,braided lines and have bled the system to many times to mention.Any idea how to test a servo??
Is it likely that air somewere is causing this.
I have a feeling i will be taking it to garage but dont see that will do anything i havnt already,other than throw lots of parts at it.

Again HELP anyone with any ideas whats so ever.

Petenaud thank you for the comments

PETENAUD

Some one put me right if i am wrong but to test a servo do the following :-

Get in car and put foot on brake pedal and press down under normal pressure.

Start car

The pedal should move down a bit.


I think the impreza has a dual stage master cylinder and dont know nuch about it, but did you bleed the brakes with a kit or did you pump the pedal,

Pumping the pedal can cause damge to the seals as they trave into the area that not used inside the cylider and this can be pitted and damge the seals. As i say dont know much about the impreza system but would have thought if its the master cylinder then brakes would just fade / pedal sink.

When the brakes come on and off, does the pedal move at all, if it stays in the smae place then i would think that there is no air trapped.

I have a tech page on impreza brakes some where i will have a look at it.



[Edited by PETENAUD - 12/17/2003 8:34:29 PM]

PETENAUD

have u tried bleeding it with a vacuum bleeder?

waggy doo

iTrader: (1)

Hi Pete
I used the normal method of bleading,attached blead pipe to blead nut put one end in pot full of brake fluid and pumped the brakes,i have done this with dozons of cars in the past with no problems. The brake pedal moves when the brakes are comming on and off. I will try your suggestion with servo test.
Whats strange is that after i changed to 4 pots etc the brakes were exellent for about 5 weeks.
Thank you for your suggestions i will keep trying to get to the bottom of this.I will try vacumn bleading the system also.

magnet

just a thought, but ...

have you got the calipers up-side-down?

the bleed nipple is at the top? yes?

sorry if this has been mentioned before.

waggy doo

iTrader: (1)

Magnet
Thanks for your input,i have checked this when mentioned before.
I welcome all suggestions as this has really got me stumpped.

Cheers

PETENAUD

If it was ok for about 5 weeks, then started doing silly things, it has to be a problem with the new parts. I would put a dti on the discs before doing anything as it wont take long.

I can understand brake fade or the pedal sinking but to pulse then god knows.

Getting desperate i know but i once had a volvo with strange brakes, turned out to be the wheel bearing!!!

My impreza had a prob, the discs were not warped as such but had a low spot, about 1" wide, that sort of pulsed, but at a slower speed, about 20mph

If i think of any other ideas i will post it.

Sorry if any above has been suggestef before, but i bet its something silly.

regards


pete

waggy doo

iTrader: (1)

Pete
Yes i will check discs at weekend with dti,then car up on axle stands all four wheels off and vacumn bleed the entire system.
I am almost tempted to put old 2 pot stuff back on just to see if prob goes away.

Thanks again for your ideas

Godspeed Brakes

iTrader: (259)

From what you are saying in your first question , I would say you have warped discs , if you are holding the pedal in the same spot and it grabs and lets go,it is the disc moving side to side in the calipers , this will also give you a spongy / low pedal , if the discs are moving side to side in the caliper , then it will push the pistons back into the caliper , so when you use the brakes the next time it needs to bring the pistons back out again before they clamp to the discs , hence the long travel ,

Did you clean the hub face up to make sure they were perfectly clean before you fitted the discs , if you didn't , and they are rusty or dirty ,then the disc won't sit properly and will give you the indication of warped discs , but this would have shown up straight away . have you changed a wheel at the time all this started , if you have taken the wheel off there is a chance a bit of crap has dropped behind the discs and is not letting the disc sit flat on the drive flange

Just a few thing to look for

Cheers Ian

waggy doo

iTrader: (1)

Hi Ian
I did clean the hubs with wire brush to make sure disc sat flush.
The strange thing is if they were warped i would expect the brakes to grab and release quicker than they do. if i am doing say 50mph they grab every 20 yards or so.If the discs were the problem i would expoect to get the grab feeling every rotation of the wheel.
The discs are brand new pagid grooved and have only done about 300 miles.Is it possible that i am getting a servo leak or something.
Keep the suggestions commimng please as i will try anything.

Thank you

PETENAUD

doubt if its the servo as they are pretty simple things and when they dont work you know it immediately.

When you have it up on jacks check the bearings as if there is play in them it can give the same feeling as a warped disc.

This advice has been given to me by a mechanic so its worth a try.


IF U FIX IT LET US ALL KNOW.

waggy doo

iTrader: (1)

Well guys here it is. My findings this morning.Very pissed off.
I decided to take front wheels off and check discs with guage to see if they warped.To my horror i found heavy scoring on outside edge of my brand new pagid discs.I went to remove pads and realised the whole hub was moving,at 1st i thought it was just the discs moving on the hub,but very quickly noticed the hub nut was about 1 1/2 turns from comming off.I can only guess someone has replaced wheel bearing at some time and not tightened up enough.I also noticed that the bit of nut that should be punched down to stop it moving had not been touched.I am hoping that i can have the face of the disc skimmed and that no damage has been caused to hub etc. I cant beleive i haved not spotted this before, i was so focussed on callipers and bleeding that i diddnt give the rest a look.I am however pleased to have found the cause of all my problems.

Any one know the torque setting for front hub nut please???

PETENAUD

GLAD U GOT IT SORTED MATE, TOLD U IT WOULD BE SOMETHING SILLY


now stake that nut up properly and enjoy the car


best regards


pete n aud

waggy doo

iTrader: (1)

Petenaud
Cheers mate,i am looking forward to driving it with good brakes.
Also i was starting to notice the front end feeling strange.Bloody obvious now.

Happy christmas and a good new year to you