# Mk3s without Brake Proportioning Valve????



## evol_mk3 (Dec 27, 2001)

I've pulled my rear beam out of my 97 GTI VR6 and there is no brake proportioning valve on the beam... 

Did some come without them??? Need help... 



Thanks! 
Juston


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## greyhare (Dec 24, 2003)

Do you have ABS?


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## evol_mk3 (Dec 27, 2001)

yep


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## harmankardon35 (Sep 16, 2009)

then there ya go...abs cars had no prop valve:thumbup:


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## GTijoejoe (Oct 6, 2001)

harmankardon35 said:


> then there ya go...abs cars had no prop valve:thumbup:


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## GTI Jay (Feb 11, 2010)

if that's the case then why does my 1995 gti vr6 have abs and the brake prop valve? I know it has abs because there are abs rings and sensors on all 4 wheels and the abs controller off the master cylinder. And is there a way I can delete the brake proportioning valve on my car? It's been leaking for quiet a while. I need to do my rear brake lines soon as well but id rather not spend the 100$ on a new valve if I can SAFELY delete it.


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## harmankardon35 (Sep 16, 2009)

if you just bypassed it your rear brakes would get grabby and probably cause an accident sooner or later (hard braking in the rain for example) In my mk3 i bypassed the prop valve as it was leaking, and cost about 300 bucks in canada to replace, not to mention the allen headed bolts simply will never come out so you would be forced to drill them out or cut the bracket off the rear beam...i said forget that noise and picked up some flex hoses for the rear beam, but used them to bypass the valve. then i ordered some mk2 fixed prop valves that go on the master cylinder and couldn't be happier. sure i lose the load sensing feature of the mk3 valve, but most mk3's are driving around with non-functioning valves anyway. I got through the winter and i can say the brakes work well with this set-up.


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## OddJobb (Nov 6, 2004)

GTI Jay said:


> if that's the case then why does my 1995 gti vr6 have abs and the brake prop valve? I know it has abs because there are abs rings and sensors on all 4 wheels and the abs controller off the master cylinder. And is there a way I can delete the brake proportioning valve on my car? It's been leaking for quiet a while. I need to do my rear brake lines soon as well but id rather not spend the 100$ on a new valve if I can SAFELY delete it.


That's really odd because the ABS system prevents lock up of the brakes and therefore does not need the rear proportioning valve. The Bentley manual even states that cars with ABS do not have the rear proportioining valve. Are you the original owner? If not, somone may have swapped out the rear beam at one time. I would think that the proportioning vale WITH ABS would cause problems during hard braking. I would think you could/should remove it.


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## JohnStamos (Feb 3, 2010)

OddJobb said:


> That's really odd because the ABS system prevents lock up of the brakes and therefore does not need the rear proportioning valve. The Bentley manual even states that cars with ABS do not have the rear proportioining valve. Are you the original owner? If not, somone may have swapped out the rear beam at one time. I would think that the proportioning vale WITH ABS would cause problems during hard braking. I would think you could/should remove it.



That's not the point of the proportioning valve...


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## GTijoejoe (Oct 6, 2001)

JohnStamos said:


> That's not the point of the proportioning valve...


Actually, in a round about way it is. 
You're vehicle's brake system is designed for GVWR loading, which of course is the heaviest weight the vehicle is rated for, therefore the brake system pressures are such to give the rear brakes enough line pressure to produce enough brake torque per loading.

Since you rarely drive at GVWR, when you are by yourself, it would severely over pressurize the rear brakes causing lock as the vehicle weight is significantly less... so by the prop valve limiting rear line pressure, it limits wheel lock, similar logic of an ABS system besides its not active.

On a side note, be aware that the Bently is not always 100% correct


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## JohnStamos (Feb 3, 2010)

GTijoejoe said:


> Actually, in a round about way it is.
> You're vehicle's brake system is designed for GVWR loading, which of course is the heaviest weight the vehicle is rated for, therefore the brake system pressures are such to give the rear brakes enough line pressure to produce enough brake torque per loading.
> 
> Since you rarely drive at GVWR, when you are by yourself, it would severely over pressurize the rear brakes causing lock as the vehicle weight is significantly less... so by the prop valve limiting rear line pressure, it limits wheel lock, similar logic of an ABS system besides its not active.
> ...



Actually, it functions in MORE then just that way. 

First it has a pressure split, then a pressure RAMP, then LASTLY, it is biased via the load by the ride height. 


There is a built in pressure split, that decides the front to rear pressure bias, then there is a pressure ramp, that sets how the pressure will ramp up from that setting, as more pressure is applied, THEN it is fine tuned via the load. It does NOT control the rears from locking, in ANY way close to ABS.

ABS is a huge deterrent to braking performance, it GREATLY lengthens braking distances, to provide more steering control, for inept drivers.

The proportioning valve, is a TOOL to set up the brake system to work at the highest level possible according to the situation. It greatly SHORTENS stopping distances, both to professional, and the to even the worst of drivers.


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## GTijoejoe (Oct 6, 2001)

JohnStamos said:


> Actually, it functions in MORE then just that way.
> 
> First it has a pressure split, then a pressure RAMP, then LASTLY, it is biased via the load by the ride height.
> 
> ...


Great name btw.. at least you have some type of technical knowledge.
Although, for most of your statements I will have to disagree with you, as someone who works in the brake industry I would question where you got these points of view.

A prop valve has no control on FR bias (maybe I misunderstood your statement), but correctly, does have an initial setting with a ramp rate to better suit real vs ideal brake curves.
Since ABS limits wheel lock by reducing brake pressure and so does a prop valve, I would say essentially they do the exact same thing to limit wheel lock just in different ways. 

Stating an ABS system 'greatly' lenghtens stopping distances is a very bold statement, in 99% of the time is completely false. Its true that the system is only as good as its tuning quite like an engine for example but it is still VERY rare to beat a proper ABS system.
I'd ask have you ever had an opportunity to try? ... and I mean with actual testing equpitment which us professionals use?
In my experience, it is possible to beat ABS in dry conditions, although it is still extremely difficult... sometimes I can win, sometimes I lose, but most likely out of ten stops, you won't win all 10. In wet conditions its almost impossible to beat, snow.... basically impossible... and yet this is still all in a straight line, not even going to discuss turning.

ABS can do things you nor your prop valve can do, it can releave pressure on 4 wheels independently of each other. Without ABS, as you try to regain traction by releaving pressure by your foot, you are simultaneously decreasing brake torque at least in another wheel which has traction... the net effect does not balance out. In both theory and real world senarios ABS comes out on top majority of the time, fact not fiction, I've seen it dozens of times :thumbup:


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## JohnStamos (Feb 3, 2010)

GTijoejoe said:


> Great name btw.. at least you have some type of technical knowledge.
> Although, for most of your statements I will have to disagree with you, as someone who works in the brake industry I would question where you got these points of view.
> 
> A prop valve has no control on FR bias (maybe I misunderstood your statement), but correctly, does have an initial setting with a ramp rate to better suit real vs ideal brake curves.
> ...



Are you saying that threshold braking is less efficient then ABS assisted braking? Really?

And you contradicted yourself one paragraph in, FYI.

Yes, the ABS system in our 14 YO cars GREATLY lengthens stopping distances over proper threshold braking. A TON.

And saying that because they both "reduce pressure" makes them one in the same is ridiculous.


Now if you are talking about taking a system with a proper ABS system, and just rendering it inactive, then measuring, yes the ABS assisted stop is going to be shorter, as the brake system is NOT setup properly to ran without it. With a proper setup, you will absolutely be able to beat it. It's not a hard concept.


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## GTijoejoe (Oct 6, 2001)

honestly, I see no contradiction, perhaps miscommunication/understanding. 
You may continue to believe what you wish, its appearant there is no changing your mind even with the advice or experience of ppl who do this for a living. It seems you understand enough about brake systems to make you dangerous but not enough to understand how you could be wrong.

and FYI, OEM systems are CERTAINLY designed to run without the active ABS system, that is just a silly statement to make and clearly shows your lack of full understanding... I could explain it to you, but you would either ignore me or just not believe it.


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