Swapping proportioning valve for "T" fitting... Options

[Wanna9146]

ok. what do you figure a known good used valve costs? report back with the improvements the T provides. anticipation? more like assuming. you're prob correct...while replacing all 4 rotors, 4 calipers, 4 corners woth of pads, master cly, and soft lines, the T is a good idea. anticipate everything is garbage and melt down the visa card. don't forget new front bearings and seals too. contact eric shea. he can provide you with everything you'll need.

LOL. As I mentioned previously, the car sat for 15 yrs. So yes, all the stuff you mentioned above had to be replaced (except the rotors...they are in spec).

However, regardless of my bottomless wallet, I am not about to spend $275 for a proportioning valve when a $5 "T" fitting will suffice. If I install it and the braking doesn't improve, or becomes unstable, then I'll work another 1.5 hrs. to pay for the correct part. If the "T" works, then I'll take the $270 I saved and put it toward something else.

[r_towle]

The proportioning valve is really a simple piston and spring.
I have never met a bad one.

If you still have mushy brakes its because you have not bled the air THROUGH the proportioning valve.
This is not as easy as it sounds.
the spring requires 750 PSI to activate, and most people dont get that when bleeding brakes.
It can be done using the old school two person brake bleeding system, but honestly I have never had success with that, nor a power bleeder, nor a miti vac bleeder.
The reason I suspect that I have never had success is because I am the bleeder, not the pumper.
If I was pumping, I would pump them till they were firm and then try to push the pedal through the floor...that will do it.

The only way I know I have rid myself of the nasty bubble is to bleed them the best I can, then go for a ride and STOMP on the brakes about ten times...this produces the required PSI to move the air past the valve.

Then I go home and bleed them again, and I am all set to go.
Be careful because when you finally get the air bubble past the valve, it will feel like you have almost no brakes at all...pedal to the floor.
I stay close to home...its a ten minute ride.

Rich

[Wanna9146]

The proportioning valve is really a simple piston and spring.
I have never met a bad one.

If you still have mushy brakes its because you have not bled the air THROUGH the proportioning valve.
This is not as easy as it sounds.
the spring requires 750 PSI to activate, and most people dont get that when bleeding brakes.
It can be done using the old school two person brake bleeding system, but honestly I have never had success with that, nor a power bleeder, nor a miti vac bleeder.
The reason I suspect that I have never had success is because I am the bleeder, not the pumper.
If I was pumping, I would pump them till they were firm and then try to push the pedal through the floor...that will do it.

The only way I know I have rid myself of the nasty bubble is to bleed them the best I can, then go for a ride and STOMP on the brakes about ten times...this produces the required PSI to move the air past the valve.

Then I go home and bleed them again, and I am all set to go.
Be careful because when you finally get the air bubble past the valve, it will feel like you have almost no brakes at all...pedal to the floor.
I stay close to home...its a ten minute ride.

Rich

Yep, I've tried all this (contrary to the other posters in this thread who think I'm a dumbass who doesn't do his research).

So, I'm assuming (shhh...don't tell "Rhodyguy" I'm assuming something...he doesn't approve!) the proportioning valve is stuck solid. The calipers & master cylinder were totally gunked-up. I didn't even think about removing the proportioning valve when I had everything apart (as you said...it's just a simple spring/piston...not much to go wrong). As I have to move the car around, I figure I'll throw in the "T" so at least it's driveable until I do my 911 brake conversion (sooner/later).

Can the proportioning valve be "saved" by removing/cleaning? Not sure what's involved in a rebuild...(off to do more homework)

[brant]

its emergency situations when the brakes will surprise you

not when your running to the store for milk at 15mph

but more when you decide to take a longer trip that involves the highway
and suddenly when your going 50mph, something drops off of the trunk in front of you... then when you least need to be unsafe, thats when it will bite you...

have fun
I've done it.
brant

[sww914]

I wouldn't automatically blame the proportioning valve yet. If you've just rebuilt the calipers, replaced the pads, and turned the rotors, you will often have a somewhat spongy pedal for a while. The pads and the rotors are not yet making full contact on their faces because they need to wear into each other a bit, and the caliper pistons will need to smash through the paint and/or insulating material on the back of the pads. The just replaced calipers may also not be sitting perfectly true and square due to little bits of grit or corrosion on the mounting surfaces, but they will work their way into a solid position after some use.
Also, you didn't mention having gone through the fun process of adjusting the air gap on the rear pads for the parking brake, if that's maladjusted it will give you a long pedal. If the pistons in the calipers are clocked at the wrong angle, the high part of the lip on the piston will push more on one side of the pads than the other, as it's designed to, but in the wrong spot, thus wearing the pads unevenly. This should be corrected as it will shorten pad life significantly and it will take longer to get a firm pedal until the pads have worn flat to the rotors which would be at an odd angle in relation to the brake pad backing plate.
As you can see, there are several potential problems that a tee won't address.

[SirAndy]

Anyone taking bets that the car won't stop in a straight line?

sure it will. only, you'll be locking up the rear brakes instead of the front brakes. if that's what you want, go for it ...

if you are married, please make sure you have a life insurance policy with plenty of cash to burn for your soon to be single again wife ...
(IMG:style_emoticons/default/bye1.gif) Andy

[Lavanaut]

People here are trying to help you out with real, time-tested knowledge and you're throwing it back in their face. You're talking about a system on your car that's crucial for safety. Cutting corners to save a few bucks in that department is just foolish man. Seriously...suck it up and buy a new p-valve or outfit your front brakes for the t. If you can't afford it right now, save up for a little bit. (IMG:style_emoticons/default/confused24.gif) Nobody wants to hear another story of a wrecked teener.

[jmill]

After doing quite a bit of research on this topic myself, I'm not sure I would yank out the proportioning valve on a stocker. The folks that yank out the valve install 2 different pads. A high quality race pad up front (porterfields) and junk pads out back. They use the pads different bite characteristics to achieve the bias. These guys race their cars and have loads of testing under their belts. Running the same pad material front to rear without a proportioning valve will lock the rears up first.

BTW - Wilwood sells a cheap adjustable proportioning valve if the $275 is too spendy.

You also might want to look at installing a master cylinder support to stop the flex and improve your pedal feel.

[Wanna9146]

I wouldn't automatically blame the proportioning valve yet. If you've just rebuilt the calipers, replaced the pads, and turned the rotors, you will often have a somewhat spongy pedal for a while. The pads and the rotors are not yet making full contact on their faces because they need to wear into each other a bit, and the caliper pistons will need to smash through the paint and/or insulating material on the back of the pads. The just replaced calipers may also not be sitting perfectly true and square due to little bits of grit or corrosion on the mounting surfaces, but they will work their way into a solid position after some use.
Also, you didn't mention having gone through the fun process of adjusting the air gap on the rear pads for the parking brake, if that's maladjusted it will give you a long pedal. If the pistons in the calipers are clocked at the wrong angle, the high part of the lip on the piston will push more on one side of the pads than the other, as it's designed to, but in the wrong spot, thus wearing the pads unevenly. This should be corrected as it will shorten pad life significantly and it will take longer to get a firm pedal until the pads have worn flat to the rotors which would be at an odd angle in relation to the brake pad backing plate.
As you can see, there are several potential problems that a tee won't address.

The pedal is beyond "spongy". It goes almost to the floor. The car will only stop after some pumping and there is no way it will lock-up the brakes for a sudden stop.

I'll dismantle the proportioning valve and inspect/clean. That's really the only thing left that hasn't been addressed. Perhaps it is preventing a full bleed...?

[Wanna9146]

Anyone taking bets that the car won't stop in a straight line?

if you are married, please make sure you have a life insurance policy with plenty of cash to burn for your soon to be single again wife ...
(IMG:style_emoticons/default/bye1.gif) Andy

Now why would I want to screw up my life and do something like getting married? (IMG:style_emoticons/default/biggrin.gif)

When married guys stop by my shop and see all 14 cars/motorcycles, the first thing they say is "You're not married, are you?".

[sww914]

I wouldn't automatically blame the proportioning valve yet. If you've just rebuilt the calipers, replaced the pads, and turned the rotors, you will often have a somewhat spongy pedal for a while. The pads and the rotors are not yet making full contact on their faces because they need to wear into each other a bit, and the caliper pistons will need to smash through the paint and/or insulating material on the back of the pads. The just replaced calipers may also not be sitting perfectly true and square due to little bits of grit or corrosion on the mounting surfaces, but they will work their way into a solid position after some use.
Also, you didn't mention having gone through the fun process of adjusting the air gap on the rear pads for the parking brake, if that's maladjusted it will give you a long pedal. If the pistons in the calipers are clocked at the wrong angle, the high part of the lip on the piston will push more on one side of the pads than the other, as it's designed to, but in the wrong spot, thus wearing the pads unevenly. This should be corrected as it will shorten pad life significantly and it will take longer to get a firm pedal until the pads have worn flat to the rotors which would be at an odd angle in relation to the brake pad backing plate.
As you can see, there are several potential problems that a tee won't address.

The pedal is beyond "spongy". It goes almost to the floor. The car will only stop after some pumping and there is no way it will lock-up the brakes for a sudden stop.

I'll dismantle the proportioning valve and inspect/clean. That's really the only thing left that hasn't been addressed. Perhaps it is preventing a full bleed...?

That sounds like a long pedal. Did you adjust the air gap on on the rear pads?

[r_towle]

The pedal is beyond "spongy". It goes almost to the floor. The car will only stop after some pumping and there is no way it will lock-up the brakes for a sudden stop.

Dont take this the wrong way.
You have not bled the system.
Know that the proportioning valve is adjusted at the factory. keep track of how far in the set screw it...how many turns.

BUT
Try this first, please.
Crack the line that goes from the master to the proportioning valve.
Bleed it there first.
Then, once you remove the large air bubble in that line (trust me there is one)
you will have a better time with the remaining air in the system.

What happens is that you probably introduced alot of air when you changed all the parts...the bubble in the main feed line to the back of the car is the largest bubble that you need to get out.

Also, you need to set the venting in the rear brakes or you will never have a firm pedal.

Rich

[Eric_Shea]

If I do this swap, I'll post a video of my car hard-braking from 50 mph

Make sure your steering wheel is straight otherwise you'll end up in YouTube blooper hall of fame.

How much is a new (rebuilt) proportioning valve? ($275.25)

Have you ever seen one go bad? They "basically" don't. There can be extreme cases but it would have to be just that, extreme.

I have a brand new "T" sitting on the shelf. I'll throw it in with your rebuilds. It's my last one (and I do mean "last" one). Don't tell your life insurance agent where it came from. (IMG:style_emoticons/default/biggrin.gif)

I'm not a fan (if that's not coming through in the writing).

* Do the two man bleed process and have the person inside the car "REALLY" cram on the pedal.
* Use a plastic mallet or a small wooden drift to tap on the p-valve (and rear calipers) when bleeding.
* Once you get a decent pedal, drive the car and hit some bump-itty-bumps. Do some panic stops in a vacant parking lot. Come back home and rebleed.
* Make sure the venting clearance is set to .004" on the high side of the runout.

It's funny, the other thing I see is people wanting adjustable proportioning valves in their cars and they never look to see that they already have one.

The poor stock valve gets a bad rap because it can be notorious for trapping air. Look at Jeff's factory manual thread or a post I made last month and you'll see the inner workings of the valve. The big spring can trap bubbles. The valve body can trap bubbles. Work around those issues with the bleed and you'll be much safer and have a great brake system.

[Cap'n Krusty]

Spongy brakes after rebuilding the calipers is a plague few professionals, much less amateurs, have avoided. I once sent a guy with a '67 911S off on a thousand mile round trip with a TERRIBLE "pedal". He absolutely HAD to be at work that night.He called me 6 hours later from way out in the sticks in Northern California, raving about how good his brakes were. I'm gonna ask this again: Did you go back and fix the venting?

Now, for the Krustiness. If you ask us, a group with an IMMENSE accumulation of knowledge and experience on 914s (not to mention a lot of other stuff), and you ignore our answers, you're gonna piss us off, and the spigot will close, and you'll not get any more help. I've seen it happen. The WORST thing you can do to me is shop a question around (after I've given my carefully considered and worded answer, based on my 35 years professional 914 experience) until you get the answer that confirms your preconceived notions. I WILL get rude to you in front of everybody.

It's a good thing you're on the right coast; You're unlikely to be driving behind me or someone I care about .......................

The Cap'n

[Wanna9146]

Thanks Eric, but don't worry about the "T". I will spend some more time with the p-valve and see what happens.

If I do this swap, I'll post a video of my car hard-braking from 50 mph

Make sure your steering wheel is straight otherwise you'll end up in YouTube blooper hall of fame.

How much is a new (rebuilt) proportioning valve? ($275.25)

Have you ever seen one go bad? They "basically" don't. There can be extreme cases but it would have to be just that, extreme.

I have a brand new "T" sitting on the shelf. I'll throw it in with your rebuilds. It's my last one (and I do mean "last" one). Don't tell your life insurance agent where it came from. (IMG:style_emoticons/default/biggrin.gif)

I'm not a fan (if that's not coming through in the writing).

* Do the two man bleed process and have the person inside the car "REALLY" cram on the pedal.
* Use a plastic mallet or a small wooden drift to tap on the p-valve (and rear calipers) when bleeding.
* Once you get a decent pedal, drive the car and hit some bump-itty-bumps. Do some panic stops in a vacant parking lot. Come back home and rebleed.
* Make sure the venting clearance is set to .004" on the high side of the runout.

It's funny, the other thing I see is people wanting adjustable proportioning valves in their cars and they never look to see that they already have one.

The poor stock valve gets a bad rap because it can be notorious for trapping air. Look at Jeff's factory manual thread or a post I made last month and you'll see the inner workings of the valve. The big spring can trap bubbles. The valve body can trap bubbles. Work around those issues with the bleed and you'll be much safer and have a great brake system.

[Wanna9146]

If you go back and read, I only responded negatively to the folks who had nothing to add except pablum and insults. If you can't answer my question, or just want to throw in a jab, don't post!

I did respond politely to those who provided the requested information.

Yes, the venting has been adjusted.

Now, for the Krustiness. If you ask us, a group with an IMMENSE accumulation of knowledge and experience on 914s (not to mention a lot of other stuff), and you ignore our answers, you're gonna piss us off, and the spigot will close, and you'll not get any more help. I've seen it happen. The WORST thing you can do to me is shop a question around (after I've given my carefully considered and worded answer, based on my 35 years professional 914 experience) until you get the answer that confirms your preconceived notions. I WILL get rude to you in front of everybody.

[Wanna9146]

Thanks, I'll give this a shot.

BUT
Try this first, please.
Crack the line that goes from the master to the proportioning valve.
Bleed it there first.
Then, once you remove the large air bubble in that line (trust me there is one)
you will have a better time with the remaining air in the system.

What happens is that you probably introduced alot of air when you changed all the parts...the bubble in the main feed line to the back of the car is the largest bubble that you need to get out.

Also, you need to set the venting in the rear brakes or you will never have a firm pedal.

Rich

[904svo]

Read this, It will explain the problems if you install a T fitting with a stock brake
master cylinder

http://www.pelicanparts.com/techarticles/9...MW_calipers.htm

[Eric_Shea]

Man I wish that article would go away but... it won't.

Upgrade it is not. (IMG:style_emoticons/default/dry.gif)

There are "real" ways to upgrade a 914 brake system (which 90% of the time doesn't need "upgrading"). They all cost money. Once you delve into a real rear handbrake solution, they usually cost more money than 80% of us have in our 914's

Just the facts mame, just the facts.

[brant]

have fun spinning off the road backwards into the ditch/tree/parked car/etc.

Cool! I look forward to it. Especially as I always race to the corner store for milk and cruise the beach @ 15mph... I can't even get the rear tires to break loose. Knowing that adding this "T" is going to get my car to spin-out is excellent. Does it really make the top speed/HP better? (IMG:style_emoticons/default/beer.gif)

I've personally gone off the road/track backwards into a 12foot ditch at 85mph
its real fun...

I'm not being a smart ass, I just don't recommend this modification
at least I tried it in a controlled environment.

bleeding a stock valve when a system has been opened up is a real challenge.
I've bled literally 100's of non-teener myself, and once on a 914 restoration I couldn't get my brakes right after a dozen bleed attempts and a few cans of fluid. I took the car to a porsche shop, literally to bleed the brakes. a 250 mile distance by trailer if that helps make my point.

try a professional power bleeder, break the lines open, uses the mallet... everything... you'll be impressed with the brakes when you get the air out.

oh... pads... the key to good brakes is good pads... try the RS4S