Brake Proportioning Valve

[UpstateDieselGuy]

What would be the side effect of bypassing the Brake Proportioning Valve?  Increased rear brake wear?  Bad braking?  I ask because I bypassed mine and it is working for now, although I need to bleed it a little more (ran out of time) and see how it feels.  Just looking for some input.  The bar looks good under there, but everything associated with the Valve is shot and the lines broke off coming out of it.  I ran lines directly to the wheel cylinders building in a coil to account for axle travel.  Thanks in advance, Chris

[LeeG]

Rear proportioning valve is supposed to reduce rear brake pressure as the rear of the car lifts.  With it bypassed, you might find that the back brakes lock up too soon -which can make braking as you enter a corner adventuresome.  

The coiled brake line wont last.  If you have several coils it might last for a while, but I wouldnt want to guess how long.

Both these items will get you failed on a safety inspection.  You probably also open up a liability window if you sell the car or get in an accident.  Fix it right.

[52 horses]

I by passed mine but under the hood my '82 Jetta had inline proportioning valves already on the car.. It seems to work alright although I havn't really put it through the test of locking up the breaks.. I'm kind of scared to something else might break.. :lol:

[Master ACiD]

on another car on own, not a vw, the preportioning valve was actually just a pressure limiting valve that worked independantly of the front brakes. ie: it did not give something to the effect of 60/40 or 70/30. it just limited the total ammount of pressure the rear brakes could get under any circumstances.
i bypassed it to get full braking out of the rear. i found out that i could still lock up the front wheels before the rears locked up, even with the valve bypassed. what this tells me is that atleast in the usa, the rear brakes are highly limited in pressure to help stupid drivers.
they basically design rear brakes to not be able to lock up in any conditions. not rain or mud or snow.

now i can lock up the rears if i want, but the fronts still lockup well before the rears do.

i am planning on doing this mod to my vw to see how it works.

[UpstateDieselGuy]

Thanks for the input guys.  I replaced the Right Rear Wheel Cyclinder last night and bled the brakes.  Everything is great so for.  I will keep everyone posted.  Chris

[MacGyver]

I ran lines directly to the wheel cylinders building in a coil to account for axle travel.

Surely you don't mean this is your only flexible piece from the underbody to the axle, if so...VERY BAD IDEA. :shock:
Metal line will fatigue from the constant movements of the axle.
You need a rubber flex line to cross any pivot or movement zone.

[wyldman]

Yes,you must have a flex line. Not only is it unsafe,but it's also illegal.

[Master ACiD]

unsafe? how many people here are running with 25 year old rubber lines? in a pinch id much rather trust a well coiled metal line to a nasty old rubber one.

untimately, i believe a coiled metal line would be OK for emergency use or testing, but ideally a new rubber line should be used.

[LeeG]

Ever blown a brake line when you stomped the brakes 'cause you needed em?  Its a nasty feeling.  

25 year old brake hoses can be visibly inspected for cracks and bubbles. 25 year old brake line can be inspected for rust.   How do you inspect a coil of metal line for stress fatigue?  its going to let go before it rusts out.

In a pinch I'd be walkin.  I'm all for the bailing wire and ducttape approach to auto maintenance, but not on brakes and suspension.  If money is tight, get good used hoses.  If you get caught with that coil of metal around here, they'd condem the car and you would not be able to license it until it was signed off by a licensed inspection station and THEY would look at the whole car not just the brake hose.

[Master ACiD]

you cant visibly tell by any sort of inspection of a brake hose which is internally swelling. i have had that happen a couple times and the results are a locked up brake which wont release. real scary stuff when youre trying to stop in bad conditions. hell its scary enough in good conditions.

[MacGyver]

I'm all for the bailing wire and ducttape approach to auto maintenance, but not on brakes and suspension.

Indubitably.

Steering too.

[UpstateDieselGuy]

If coils are bad why are there sharp bends going into the Proportioning valve?  Not being acusatory, just inquisitive.  When I get a cnace I am intending to put some rubber lines in.  I am just hoping the thing holds together long enough to get the TDI I want.  The body is wasting away day by day.

[MacGyver]

Sharp bends in & of themselves are not a problem, but if you look closely you will not find OEM steel lines, bent or coiled or otherwise, going over a pivot point ie any place that there is movement.
Take for eg a classic rear drive domestic car. Rubber line to each front wheel, and one to the rear axle, which then splits into a steel line running to each wheel...along a SOLID axle. Sharp bends up to the wheel cylinders from there, which experience no movement.

So as I asked earlier, are you talking steel line from body to axle assembly, or another location?

[UpstateDieselGuy]

I bolted into the rubber lines that go to the axle.

[MacGyver]

You retained the rubber lines over the flex point then, good.
That negates the above arguements that were based on conjecture.
The rubber lines should be secured at both ends, making any coils in the steel lines on the axle unnecessary.