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Kobayashi

1.6 rear Drum to Disc Brakes - Question on Pressure

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Kobayashi

Hi, I am aware that there is an excellent pinned thread on brake upgrades here, but the discussion seems quite dead there.

So:
I will be upgrading my rear brakes from a 205 1.6 GTI drum setup to rear 306 calipers with 247mm discs (should be quite the same as 205 1.9 GTI).
As most of you will know, the stock 1.6 braking system features just one brake line to the rears, and a 1.6-specific pressure compensator.
My plan is to keep that single brake line, BUT ditch the 1.6 compensator and use a Wilwood adjustable proportioning valve instead.

Front brakes will be upgraded to 266mm discs (using 206 calipers on 205 1.9 hubs, et cetera). This combination upgrade has already been done many times, but I am only aware of 1.9 cars which, as said, have a different brake line and compensator setup.

-> Question is, will the rear calipers receive enough pressure in this setup?

Thanks for any good advice. Maybe someone here has already done something similar?

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petert

Yes, it will work fine. I ran the same setup on my previous race car for many years. If anything, they receive too much and you’ll find you have the new valve just cracked open, effectively giving 99% front and 1% rear. If you want more control, add a second course/fine valve in series. 

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Thijs_Rallye

The original compensator is regulated on the assembly angle & vehicle angle. I'd try that first. If you change the angle you'll change the pressure as well if my memory serves me right.

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Kobayashi

I see, thanks. The willwood lever type valve should be the same as the wilwood knob type valve I already have, apart from the lever vs. knob mechanism. Data and technical description are the same.

@Thijs, I did not know that, thanks. Might have a look at it, too.

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Thijs_Rallye

I used to have a section view of such a compensator but it has been years since I've seen it last. Here is a (short) description of how it works: http://www.peugeot205.ru/peugeot205-205.html

 

There is a ball (comparable to a bearing ball) that has to "roll up a hill" and then shuts a valve which limits the pressure to the rear. So if you change the assembly angle of this valve you'll change the gradient of the "hill" and therefore the pressure limit. Grussli!

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petert
16 hours ago, Kobayashi said:

I see, thanks. The willwood lever type valve should be the same as the wilwood knob type valve I already have, apart from the lever vs. knob mechanism. Data and technical description are the same.

You may have missed my point. The knob type is infinitely variable. The lever type has six positions. If you only have the knob type, you'll be right at the limit. ie half a turn is enough to lock up the rear brakes. Thus it's beneficial to add a lever type in series with the knob type, then you'll get more control. ie you need BOTH.

 

As said though, it's worth experimenting with the standard compensator first.

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Kobayashi

Ok now I got you (both of you) - thanks!

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Kobayashi

I am thinking about changing the master cylinder, too. Maybe it's just me being paranoid, but sometimes it feels "odd", and while I'm at it...

Any recommendations for my above mentioned setup?
(266mm fronts, 247mm rears, steel braided brake hoses, proportioning valves just like discussed above)

Thanks in advance.

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Kobayashi
On 11/14/2020 at 4:34 PM, Kobayashi said:

I am thinking about changing the master cylinder, too. Maybe it's just me being paranoid, but sometimes it feels "odd", and while I'm at it...

Any recommendations for my above mentioned setup?
(266mm fronts, 247mm rears, steel braided brake hoses, proportioning valves just like discussed above)

Thanks in advance.

I'd prefer to avoid starting another thread for this little "bonus" question if someone would like to share their experiences here:

(A) stick to a 20,6 master cyclinder (like the one fitted from factory)
(B) or upgrade it to xyz  (for my above mentioned setup)?

Thank you very much.

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Thijs_Rallye

Keep the master cylinder stock, if you don't like the slight extra pedal travel you can always switch master cylinders later.

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wicked
On 10/17/2020 at 12:38 AM, petert said:

Which one do you prefer?

 

On the wilwood it says:

Quote

Pressure adjustments range from 100-1000 PSI and provide for a maximum decrease of 57% in line pressure, the most of any available valve. This proportioning valve has six preset points actuated by moving a lever allowing racers to quickly adjust brake bias during a race.

Any clue on the max pressure you'll see from the master cylinder? 

 

On the AP I cannot find pressure spec's, but it has 7 presets.

 

The wilwood is only half the price of the AP; does the finer resolution make up for the price diff?

 

 

Edited by wicked

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welshpug

from memory the 1.9 valve has a knee point of 20 bar (292 psi)  so I think you'll never see any more than that.

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wicked

I have the 1.6gti rear drum compensator and want to remove that for a lever type valve, so I could see anything from 100psi to max brake pressure. 

 

If I would have the Wilwood, it would mean I would have these setttings in psi (100-1000 in 6 steps): 

 

100
280
460
640
820

1000

 

So position 2 would be equal to 1.9 compensators and 1 would be less and all the others settings would be kind of useless for a trackday car.

 

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Kobayashi

Just for the record, and to conclude on this, after doing the conversion:

The Question was
 

Quote

Will the rear calipers receive enough pressure in this setup? (266mm fronts, 247mm rears, 20.6mm master cylinder and an adjustable proportioning valve on a car that originally had drum brakes and just one brake line to the rear, as with i.e. a 1.6. GTI; however be aware that some of them used smaller master cylinders)

 


After testing on both road and track, my answer is:
Yes. It all works very well and safe. Technically, there is enough brake pressure to lock up the rears first, but the proportioning valve (I fitted a Wilwood knob type one to the rear brake line) can be used to reduce rear brake pressure to make the fronts lock up first.
With my setup, this is the case with the reduction valve being about 2/3 open.

Full story here:

 

 

Edited by Kobayashi

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