Braking force distribution

[damusto]

OK then I wont argue about the name, but it seems that we can buy brake proportioning valves for ae86...
... http://www.ebay.com/itm/toyota-ae86-85-8...0833014656 ...
They therefore question, how the specs looks like ?

[ZaX]

damusto Wrote:Ok maybe I'll try to ask this question differently...

... is there any pressure reducer or regulator for the rear wheels, in stock AE86 braking system ?

To my information - yes.
Part no 47190-12040 VALVE ASSY, PROPORTIONING & BY-PASS
http://www.toyodiy.com/parts/p_E_1984_TO..._4708.html

You can see it here bellow Master brake cylinder. Metal part with two lines in and three lines out.
Two upper are going to the front brakes, one is going back to the diff.
On the diff is the splinter for the rear calipers.

This metal part is different for AE86 and AE85, because AE85 has drum brakes in the back.
If you do the upgrade from AE85 to AE86 you must replace this part, otherwise your rear brakes will be to strong and also overheat.

[damusto]

OK thanks ZaX that explains, and shows a lot.

But the question of AE86 proportioning valves specifications still remains open.



B/B' = ?

[Eircamae86]

stock ae86 has perfect balance, swap axle = change bias valve. if not happy buy an aftermarket adjustable bias valve or better again, go pedal box with fully adjustable

[NoHachi]

Sadly, a pedal box is not perfectly adjustable. Look at the above curve, it has a knee in it. As you brake harder, more weight is transferred to the front of the car. This means you need proportionally less pressure going to the rear and more to the front. For every amount of decelleration G's the ratio is different.
That's why you use one of those bias valve knick nacks. It flows 50%-50% in normal conditions (taking into account piston area) and above a certain pressure (which correlates with decelleration Gs) a valve pops open and less pressure is fed to the rears as the rears get lighter. The knee in the curve approximates the gradual decrease you need.
If the knee is too high you get one spot in the curve where the rears lock up, but braking might be fine at higher pressures. Very tricky to set up just perfect and not many bother.

Like this:

[damusto]

Ok so we've discussed the principles and objectives of proportioning valves working. The question are we able to paste any numbers on this graph ?

[NoHachi]

Nope

[damusto]

it's a pity! so I got stuck at a standstill again :-/

[Ivan141]

If you can specify an easy way to measure this, I could try to size mine up (as it is in a box at the moment anyway).

[damusto]

OK thanks Ivan, I find it difficult to say are these methods easy or not.
Therefore I will leave the estimation for You.

Method 1:
Scan the graph with description of accurate service book.
I have one from 1983 - and it doesnt contain such information, not even a mention of proportioning valves ! Oldeskewltoy has one from 1986, He was here, said nothing, so I think that his edition doesnt contain this also. So I find it difficult, but in few next days I should get Haynes SM, maybe it will change something...

if not another method:
Connect manometer in to right place in your braking system, and write down the corresponding readings. This is kinda fun, You need to take into account bleeding the system and the whole fuss with liquids.

Method 3:
Periodic testing of the vehicle.
In Poland we have such stations


No. 4 is for brakes test

This way You get braking torque on axles


So it is possible that You have this in papers but didnt pay any attention, because the car was allowed to traffic.
Of course We have to take into account differences in the size of discs and pads area, but that is not a problem.

Method 4:
This can be costly, professional dyno and detailed analysis.
Stack of printed works with curves and graphs...

But I dont want anyone caught up in the expenses, of course.
Is any of these methods seem like easy enough ?