Brake bias valve

[JamesO]

I have kicking around in my stash of parts everything I need to convert to Brembo 4 pot callipers. However I'm not sure if my 2.7 has a bias valve, I am under the impression that the S has one and know that the turbo and s2 have the valve.

Does anybody have a photo showing where the valve is fitted so I can have a quick gander?

I know the ATE callipers were good enough for 928's and 911's but with my 3 litre nearly ready to go in more brakes can only be a good thing.

 

[944 man]

I dont believe that NA eight valve cars had a proportioning valve (from memory). Are you going to use an OEM part with differing lines to suit, or are you planning on using a competition type adjustable bias valve?

 

[Neil Haughey]

Funny this should pop up. I was looking in the PET last night as I though the 968 and 944 ABS was different, wrong. Part numbers the same for the ECU,pump,bias valve etc. etc. apart ISTR from the relay. Now the interesting thing is the PET lists 2 different bias valves, one for the turbo & S (assume includes S2 as pretty sure its the same no.) and a 928 part no. one for the "other" cars. I assume this means late 2.7 cars with ABS fitted. Over in the US of A a popular mod is to change the valve to a 928 one which gives a bit more pressure to the rear brakes.

 

[Hilux]

Over in the US of A a popular mod is to change the valve to a 928 one which gives a bit more pressure to the rear brakes.

Why? The 928 is a heavier car so I can see why it has better line pressure. Particularly with regard to weight reduction I cant see how this is a benefit for rear brakes locking up is a disaster as the rear will want to overtake the front.

 

[Neil Haughey]

Because the standard valve allegedly is too biassed towards the front end. I have to say this is very much the impression I had on track as well as I found trail braking was difficult as the car wants to oversteer even with gentle trail braking. This may have been partly down to my setup though, as ISTR when suspension and everything is bone stock one can brake really hard in a corner without the back end slowly coming round but this was at road speeds, so ? It makes sense that Porsche would design the valve such that the rear brakes or more or less never likely to lock up, hence a lot of the time the rear brakes will not be doing enough of the work.

 

[JamesO]

Cheers for that, will have to check the PET (didn't think of it). So the 928 part is considered an upgrade? If I find its there I may just fit the hubs, callipers etc and see how it goes. After my trip to the ring I have decided track days are the way forwards and a return to the Ring in Easter is a must. Now to just time up the cams, blank off the variocam solenoid hole, sort the leaky brand new sump gasket and swap the engine. Oh and tune it, not much to do at all...

 

[Hilux]

Because the standard valve allegedly is too biassed towards the front end

Not quite how I would approach it but I bow to experience []

This may have been partly down to my setup

I (personally) found that with a good suspension set up and decent ARB`s well balanced flat turn in was improved and oversteer tended to be too fast into corners but lifting off produced immediate turn in with the tail balanced on the throttle. The ABS allowed trail braking [] The alternative was to spin in the middle of the corner exit (which I also managed [8|])

 

[Neil Haughey]

Paul I don't know if anyone in this country has changed the valve to the 928 one, I certainly haven't. I guess it comes down to how much you or we trust the experience of racers state side. Did you have weltmeister arbs by any chance? ISTR Fen said they where a huge improvement on the 968 M030's.

 

[944 man]

Why change the OEM valve for another pre-set part? If youre changing then an adjustable bias vale is the only way to go: surely? If need be it can be fitted out of the drivers reach and lockwired, in order to meet any relevant regs... eta: itll need new lines of course, but as youll be bringing them inside the cabin anyway, this isnt a big deal.

 

[Hilux]

Why change the OEM valve for another pre-set part? If youre changing then an adjustable bias vale is the only way to go: surely? If need be it can be fitted out of the drivers reach and lockwired, in order to meet any relevant regs... eta: itll need new lines of course, but as youll be bringing them inside the cabin anyway, this isnt a big deal.

Exactly my thoughts............In fact I`ve done this to my Golf as discs were fitted to replace the drums and the original load sensing valve removed however due to the lack of weight the rears were overbraking and I had a few brown trouser moments.........................now I can dial in and out the rears as I like.

The other option is a pedal box with bias bars. I`m going to do this to the Golf next year so I can do away with the servo for anyone that has driven cars with no servo will appreciate the total feedback you get through the pedal ie: you can sense and feel the brakes through the bottom of your foot.

 

[Hilux]

Did you have weltmeister arbs by any chance? ISTR Fen said they where a huge improvement on the 968 M030's.

Ohhh yessss..............[8D] I`ve been banging on about them ever since. With the KWV3 I used to get totally even tyre wear and temperature running at 29 cold (33 hot), superb, highly recommended, fantastic flat cornering in fact they are the same quantum leap over Mo30 as KWV3 pssssssst.....as they are adjustable you can use them to help dial out oversteer or bring in more understeer so dont let on to anyone [] FRONT

REAR

 

[Neil Haughey]

Cheers Paul, its something I am keeping in my back pocket so to speak. The arbs have to be at best 968 M030 in order to be compliant with PCGB championship rules, however Future Classics don't have such a restriction so I could at a later date fit weltmeister arbs. In fact the looser rules in FC actually makes the car prep a bit cheaper because I don't have to spend nearly 500 quid on new torson bar spring plates etc. just yet.

 

[sawood12]

ORIGINAL: Neil Haughey Funny this should pop up. I was looking in the PET last night as I though the 968 and 944 ABS was different, wrong. Part numbers the same for the ECU,pump,bias valve etc. etc. apart ISTR from the relay. Now the interesting thing is the PET lists 2 different bias valves, one for the turbo & S (assume includes S2 as pretty sure its the same no.) and a 928 part no. one for the "other" cars. I assume this means late 2.7 cars with ABS fitted. Over in the US of A a popular mod is to change the valve to a 928 one which gives a bit more pressure to the rear brakes.

Only the early 928's had a 5/33 bias valve. After a certain year they shared the same valve as all 944's. The 5/33 basically means that the same pressure is applied to the front and rear up to 33 bar and after 33 bar the rear gets 50% less pressure than the fronts. I can't remember what the proportioning bias of the stock 944 valve is but it proportions more to the front after a lower pressure. It isn't an 'upgrade' as such, it just different and tends to suit cars in wet conditions and not considered to be ideal for street cars from what I can gather from reading alot of posts on the subject. Some people who upgrade to Big Blacks/Reds sometimes think it is necessary as they think it compensates for what they consider to be an increase in forward bias the larger calipers provide. In reality this isn't the case because as big blacks/reds are larger in physical size they share the same piston size as the later turbo's medium blacks so the braking force remains the same for a given fluid pressure and the turbos with small blacks shared the same brake bias valve as the turbos with medium blacks. Personally I decided to stick with stock.