scoobyricht

iTrader: (4)

a while ago i fitted newage 2pot rears to my uk turbo wagon, over the last few weeks ive noticed the rear discs have become slightly rusty, ive tried to remove by braking and even left foot braking when no ones about but when i stop the fronts are boiling and the rears are stone cold, and rusty still.

ive got braided lines all round, 4 pots on the front and bled it all.

how much fluid does it take to bleed completely and is there a special order to do it?

could it be another problem?

cheers

Rich

alcazar

iTrader: (2)

Think about having the brake bias mod done: the brake bias valve is removed and it makes the rears work harder.

AS Performance

iTrader: (4)

scoobyricht

iTrader: (4)

im interested in the bias mod... how do you do it? ill get some more fluid and bleed the lot. thanks

alcazar

iTrader: (2)

Mine was done for me, but consisted of removing the brake bias valve and joining the two inlet pipes to the two outlet pipes.

The car now stops flatter and firmer.

scooby800

iTrader: (1)

are these brake bias valves fitted to classics with abs too or is it done in the pump?

ALi-B

iTrader: (1)

I wouldn't advise messing with brake bias on classics with 3 channel ABS, unless you disable the ABS system. Otherwise you can end up with no brakes when a rear wheel locks during sitautions when you are braking hard. The ABS system kicks in and can remove pretty much all the braking effort to both front and rear brakes (don't ask why it removes braking effort on the front when the rears lock, it just does).

Similar situations can occur when using mis-matiching pad compound from front to rear. And one of the reasons why people complained about poor ABS on old scoobs (as noted in the old SIDC driver's FAQ ), prefering to disable the system completely.

Later 4 channel cars are fine (or at least better) as they have EBD.

ALi-B

iTrader: (1)

I usually use a litre. 250ml out each corner. Starting with the front corner closest to the ABS unit (OSF = shortest pipe run). I use a pressure bleeder, which pressurises the reservoir, and use a one-way valve on the bleed bottle. Generally speaking this method/tool usually does the job. But the old two-man "on-off" routine on the bleed nipple usually does the job too.

Other porblems in the system could be sticking pads...were all the guides and slides cleaned to remove the crud when the pads changed? Sticky pistons are also something to look for, so should be exercised when the pads are removed. All this should be done whenever the pads are changed, especially the rear as they spend so much time on the car without being serviced/worked on.

However, one important thing to note is brake pads don't always remove rust from the disc if its bad...heavy rust can act like sandpaper and just wears the pad away instead! Causing uneven pad wear and poor pedal feel once the pad is worn on the area with rust, it doesn't make much contact, so the rust just gets worse, the shiny parts of the disc is the area when its making contact and giving you braking effort.

The problem is made worse if the pad compound relies mostly on cohesive friction...whereby it needs pad deposits on the disc in order to work properly...rust prevents the pad working properly. A pad compound using more abrasive friction will "clean" a disc better, but it has its limits (and are much "dirtier" ).

Really you should clean off the rust. A light disc skim would be the best way of doing this, especially if there is any pitting. Sand the pads smooth and square again and restart the bedding-in process from scratch. Rears need much more bedding in time than the fronts.

Tip: if you wash your car, take it for a drive afterwards to dry off the brakes...DO NOT just park it up and leave it unused for a week. This is probably more important when the discs are still new and pads material has not had chance to leave a layer of material on the disc surfaces.

The Rig

iTrader: (13)

So im guessing it makes it 50/50 braking rather than the 70/30 i assume it currently is ?

any pics of this valve or where it is ?

cheers

ALi-B

iTrader: (1)

Sort of, however the proportioning valves doesn't give a fixed ratio, IIRC the pressure to the rear brakes is directly proportional to fronts up to a certain braking pressure then the rears become more and more limited once a set braking pressure is reached...i.e you brake lightly the rear brakes get the same pressure as the front ( 50:50). However if you brake harder the pressure to the rears becomes limited...brake harder still the fronts get more pressure, but the pressure to the rears doesn't rise as much. ( It really should be called a pressure limiting or pressure reducing valve )

Obviously if you mess with the rear calipers that pressure may not be enough. Hence either swapping or removing the proportioning valve. Its somewhere on the shock tower...just follow the pipes from the ABS unit: 2 go to the master cylinder, 2 go to the front brakes, and 2 go to the proportioning valve.

The Rig

iTrader: (13)

cheers, think i mite remove mine as ive gone from single pot sliding calipers on the rear to the 2 pot upgrade , i dont have ABS tho so does the 95 wrx still have this valve ?

ALi-B

iTrader: (1)

It will still have a valve, but I think the non-ABS cars have a slightly different one, it'll still look the same and be in the same place though. Just the pipes go straight to the master cylinder instead.