i will put it in four main points to help me understand the concept and requirements involved and also avoid confusing you guys during the process... the main three points are:
1- my understanding to what P valves do
2- my understanding to how P valves do what they are supposed to do
3- my findings regarding OEM p valves on our daewoos
4- the required modifications to OEM P valves given the rear disk conversion and what parts of the P valves are involved
First part:
This is what i understand as far as P valves go... in the simplest definition, they are used to decrease the brake pressure going to the rear wheels from the one going to the front... this is done simply because the rear tires are more vulnerable to lockup under braking due to weight shift and locking the rear can cause a car to spin out of control thus we must have the appropriate rear brake pressure that will allow the front to lock before the rear.
from the research i have done on the internet i found many topics but this one is the most informative:
http://www.stoptech.com/tech_info/wp_pr ... lves.shtml
now this article shows that their are two characteristics for a P valve... and that is the knee point and the slope, knee point is the point where proportioning starts, the slope is the ratio of proportioning between front and rear... so simply it is "when" and "how much".
By all means feel free to correct me if i go something wrong.
Second part:
this is my understanding to how P valves actually works... after dismantling the OEM P valve of a lanos i found out it consists of a ported valve, spring and a spring loaded plastic part... i suppose the big spring is the one responsible for the location of the knee point on the graph since a spring is sensitive to pressure and as far as i understand it will compress at some point changing the brake fluid passage and thus start restricting the pressure so spring power is related to the knee point.
the size of the port in the valve itself is deciding the slope of the curve after the knee point... since port sizes and all affects pressure in a circuit so i suppose the bigger the port the less slope angle you will get (if the valve was totally blocked you would get zero pressure to rear after knee point)
Third part:
i have found out that Dewoos have two different P valves... i was at the mechanic's shop during the rear brakes conversion and found out the following:
1.5 Lanos P valves are marked 3/40 while 1.6 Lanos and Nubira P valves are marked 3/30... no idea what does them numbers refer two, i have dismantled both valves and found out that both internal valves have the same port ( i didn't have a measurement tool to do so and i relied on my eyes... if their was a difference then it will be very very minimalistic) so as far as i understand both valves got the same slope after the knee point.
the major difference i saw was the spring... they both got the same thickness but the 3/30 valve got a longer spring than the 3/40 one so as far as i understand i suppose it is applying more pressure on the valve thus creating a different knee point and the 3/30 valve that has the longer spring have a higher knee point than the 3/40 valve
Fourth part:
the rear brake upgrade for my car involved dual piston rear calipers with needs more work from the brake master to move the bigger pistons... i suppose this translates to "higher knee point" thus i should be using the 3/30 valve springs or even stronger springs to elevate the knee point to compensate for the bigger volume of fluid required at the rear
as for the slope... i have no idea what i should have...
should i have more sloping as the rear disk setup is supposed to be stronger and more vulnerable to lockup?
Should i have less sloping as i still suffer from the big volume requirement after the knee point as well?
Should i keep it as it is as the knee point adjustment is enough to handle the big volume requirement yet the rear setup is not that powerful to lock the rear anyways?
i know this is rather confusing and will require some testing for various setups but at least i want to know which rout i should go with first to avoid testing a thousand possible combinations so I'd like some theoretical analysis and advice from you guys to have a plan for testing
and again this is my current understanding to fluid pressure and P valves so i might be wrong in one or more areas here so please correct me whenever i am wrong
MMamdouh
