Printable Version of Topic

Posted by: watsonrx13 Mar 5 2010, 05:29 PM

Eric's ad selling the 912 rear calipers started a discussion about the brake pressure regulator. I'd like to continue that discussion. Eric mentions that he wouldn't replace the regulator with a 'T' fitting. What I would like to know is how could you test the regulator off of the car? At $300 - $400 a piece from the dealer I would like to test mine before I purchase a new one.

Also, Eric mentioned that the front calipers shouldn't be used on the rear, even with the regulator. Is there any problem installing a set of rebuilt rears on and not installing the parking brake cables?

Any thoughts and suggestions are welcomed. BTW, I'd like to keep this discussion only for the 4-lug wheels.

Also, what are the thoughts about replacing the master cylinder with the larger one how does that effect the brake biasing?

-- Rob

Posted by: SirAndy Mar 5 2010, 05:36 PM

Stock brakes and a "T" is a bad idea that will get you and your car hurt in no time ...


Why do you want to replace your Prop Valve? I have never seen one go bad, what's wrong with yours?
Andy

Posted by: type47 Mar 5 2010, 05:41 PM

... and why would you want to mount rebuilt rear brake calipers and not connect the parking brake cables?

Posted by: Tom_T Mar 5 2010, 05:51 PM

.... hmmmm ..... well - just a guess here - but if you don't connect the cables & park on a hill - then it might just roll away IMHO!

I've also heard that the proportioning valves rarely if ever fail!

So why - as per Andy????

Posted by: watsonrx13 Mar 5 2010, 06:01 PM

I'm not advocating replacing the pressure regulator just trying to bring the discussion to the garage so that it can be research for future references. I have several cars that have the brake systems open (calipers removed) and was wondering if there is a possibility that this could effect the internal workings of the regulator.

I've seen discussions about mounting the front calipers on the rear but never understood the reasoning, which would mean that the hand brake cables wouldn't be connected.

-- Rob

Posted by: watsonrx13 Mar 5 2010, 06:02 PM

Hill, I live in FL there are no hills...

-- Rob

Posted by: Tom_T Mar 5 2010, 06:07 PM

Well there are in the FL panhandle where my sister lives! ... more like hummocks to the rest of the world!

... Okay then - so it could roll off the road, down the drainage swale & into the swamp & give a `Gator indigestion - then you'll have EPA & the Enviro's all over your case!

Cheers!
-- Tom

Posted by: McMark Mar 5 2010, 07:10 PM

The E in E-Brake stands for EMERGENCY. Emergencies are unplanned situations, so you can't plan for them. You should have working emergency brakes in case you find yourself in an emergency. I can never wrap my head around how people can be so cavalier about disabling one of the most fundamental safety features. While you're at it, take out your seat belts since you don't plan to have any accidents.

RANT OVER!

Posted by: SirAndy Mar 5 2010, 07:28 PM

Actually, it's a PARKING brake ...

Andy

Posted by: kg6dxn Mar 5 2010, 07:40 PM

I could see replacing it with an adjustable one.

Problably would not really be needed for a mid engine cars front to rear weight ratio unless it was a full race vehicle.

Posted by: Eric_Shea Mar 5 2010, 07:44 PM

I can't type all that crap again so I'll just paste it here:

That's not a great idea. It takes a LOT of hit or miss and experience with pad compounds to play this game. Dan is the only guy I know that has done this successfully and he races his 914 regularly in wheel to wheel competition. Do me (yourself) a favor, make a quick list of all the brake pads you know of for our 914's. Now list them, in order, from stickier to not so sticky. Ready... go!

The question is; why? When the proper caliper with the proper piston size for best biasing, made off the same casting, with the same pad size is available to bolt on to the same mounting location; why put an irregularly large pistoned caliper back there?



Not on my car. Removing it does not acheive maximum braking ability.

The pressure regulator is SO WAY MISUNDERSTOOD by the 914 crowd. One day, back when we were smashing rocks together for fire sparks, someone said; "If you take the proportioning valve out you'll have better brakes." I bought into it for a while as well, until I did some further reading. There's a page dedicated to it in the factory manual and it's a great read. The funny thing is, the Alfa boys have the exact same valve and if you cruise posts on their board regarding the subject, they would think you were crazy if you wanted to take this out.

That said; the pressure regulator is not a proportioning valve or a bias valve of any sort so it stands to reason it has a purpose beyond balancing our braking bias (which the factory did extremely well with piston sizes... hence the chatting herein). There are two things that you should read to help you put this together in your own mind. They helped make it click for me and I've never gone back to recommending a "T" fitting or an aftermarket bias valve to anyone ever again. Those two things are:

1. Vic Elfords book on Porsche Handling. There's a section about "mid-Engine" and it touches on 914's. We get all pumped up when we tell others our cars are "mid-engine" and superior to God in handling. Vic points out that they are rather good but, the 924-944-968 package is better because, polar moment inertia can cause our little 914's to spin like a top once they get started. Having the weight at the ends (engine in front, tranny in the rear) is much more predictable and controllable. It's a good book to have and a great read when learning all that you can about your Porsche.

2. The page from the manual explaining what this little bugger really is. As stated before, it's not a proportioning valve or a bias control. It (as you rightfully stated) regulates pressure. It ONLY does this when it experiences a panic stop of 535lbs. of line pressure. It shuts the rear circuit down and slowly brings it back in to prevent the rear wheels from locking up. This keeps as much control as possible in the rear of the car in such an instance (no screaching, locked up tires back there).

Bottom line; the pressure regulator sits there and acts just like a "T" fitting, passing all the fluid you can deliver to the rear calipers unless there's an emergency where they may lock up. Then it springs into action.

The only problem is, it sucks to bleed. But it sucks even harder if you're the one bleeding.

I hope that helps someone.
******************************************************

Now to try to help with your questions:

They rarely go bad HOWEVER, In an open system I see Master Cylinders go 30-40% of the time. I can only attribute that to the rubber seals seeing fresh air for the first time in a long time. My "guess" is they crack and it's new MC time. This happens too often to my clients doing a full brake job to ignore it. The reason I mention Master Cylinders is, the seals look identical and may be. I could do some research but, the Alfa guys have a kit I believe.



Go for it. There's way too much internet chatter on this and the affect will be negligable. No, it doesn't affect the bias, just the overall pressure in the system.

The benifit will be a firmer pedal feel and a less expensive Master Cylinder.

The downside is, the pedal is harder to push down. It is only SLIGHT and after about 10 minutes behind the wheel you'll get use to it. This is why I say there's too much chatter going on. When it comes time, everyone should just move to a 19mm and be done with it. That's my $0.08 (adjusted for inflation and devalued for overall worth).

Posted by: watsonrx13 Mar 5 2010, 07:51 PM

Thanks Eric for the update.

-- Rob

Posted by: Tom_T Mar 5 2010, 07:54 PM

Actually it is BOTH !!!!

If the hydraulics fail in the primary system, then the mechanically actuated rear brakes can be used in an EMERGENCY to stop the vehicle, as well as to hold it in place while PARKED on level or sloped ground!

Now play nice Boyz!

Posted by: Eric_Shea Mar 5 2010, 07:54 PM

Also... disconnecting hand brake cables would have nothing to do with the overall effectiveness of the braking system. They are part of a manual system that lives in a hydraulic world.

Handbrakes work best when the cables are hooked up ( ) and the venting clearance is set properly.

Posted by: Eric_Shea Mar 5 2010, 07:58 PM

Read this...

 ATE_Valve.pdf ( 420.71k ) Number of downloads: 352

Posted by: watsonrx13 Mar 5 2010, 08:08 PM

Thanks Eric, very good description.

BTW, is there any way to 'bench bleed' the pressure regulator to get the air out? Or just pump, bleed, repeat until firm?

-- Rob

Posted by: Tom_T Mar 5 2010, 08:09 PM

Great dissertation from the Guru of Porsche Brakes (Eric) !!!!

... cleared up a lot of things for me too Eric!

BTW Rob - for what it's worth based upon Eric's & others' on here advice - I got the ATE 19mm 914-6 MC for my 73 2L too (1/2 the price of 17mm), to swap out from my OE 17mm one, since it's been sitting on blocks in my garage since 5/85 & probably in need of rebuilding anyway. So that - combined with an Eric set of F&R Calipers, Porterfield R4S's, new OEM hoses, etc. should give me a better performing and more reliable braking system on mine when done, which still passes as original if I ever want to do CW insanity! ... oh & NEW E/P-brake cables actually hooked up to boot!

That's my -$0.08 worth - since I'm far less a guru in this than Eric!

Posted by: ConeDodger Mar 5 2010, 09:15 PM

Funny you should say that. I just had a conversation with a paramedic student from Northern Ireland yesterday who failed his drivers test because the examiner told him to set the emergency brake and he didn't know what she was talking about. By the time he figured out she was talking about the parking brake, she was walking away... Ahhh... Cultural cognition. We supposedly speak the same damned language.

Posted by: campbellcj Mar 5 2010, 10:48 PM

Here is the original thread over in the classifieds:

http://www.914world.com/bbs2/index.php?showtopic=101458&st=0&gopid=1283017&#entry1283017

Posted by: pbanders Mar 5 2010, 11:00 PM

Good stuff. FWIW, the "in car" test I was taught for the proportioning valve is that while sitting still with the motor off (even better in a quiet garage), press hard on the brake pedal, and slowly release. If the proportioning valve is working correctly, as you release the pedal, you'll hear the valve go "boing" as the internal pressure drops below the onset threshold.

From the pressures involved, I suspect a "bench setup" to test the valve would be challenging.

Posted by: watsonrx13 Mar 6 2010, 07:23 AM

So why does someone replace the pressure regulator with a manual prop valve? Is it because they have changed the calipers such as replacing the fronts with BMW and putting the fronts on the back?

-- Rob

Posted by: McMark Mar 6 2010, 11:06 AM

If you're a racer looking for every last millisecond, you want all four brakes working as efficiently as possible. So using an adjustable proportioning valve will allow fine control over how much rear brake you're utilizing.

If you're a daily driver, you simple want the safety and the stock valve is fine for that.

What happens, often times, is that people apply race tech logic to daily driver cars and they're not always directly comparable. Some race tech is not a good choice for a street car where you really don't need it.

Posted by: campbellcj Mar 6 2010, 12:33 PM

I can think of at least two reasons:
1) The stock brake bias has been altered by changing parts, and
2) In some situations - such as a race track in the rain - it's possible you might want to shift the bias more towards the front than in other situations - such as a race track in the dry.

As many people including Eric have said, I can think of no reason to mess with this on a street car with stock brakes, or even on most stock-ish autocross and track cars.

Posted by: Eric_Shea Mar 6 2010, 02:52 PM

That's why I always try to stay with a "systems" approach if one is contemplating brake upgrades.

For a narrow bodied 914 42mm/33mm (stock) works extremely well with good calipers, lines, fluid and most importantly; great pads and tires. Moving up? 48mm/38mm works well for both narrow and wide body cars.

Stray from that and you're in a bias danger zone.

The early 914 fronts to the rear is a good example of a bias mis-match. 48mm/42mm (if you're using a larger caliper up front), gets you a fairly brake happy tail. Not what you want in a car that has inherent polar moment inertia. You "really" don't want this is you've decided to take out the pressure regulator valve. Street car or not. My friend Barney, here in Utah, went off the track at Willow "backward" into a berm and flipped his dearly departed factory 914-6 "end-over-end" with a "T" fitting. He was banged up pretty badly in that one.

The best solution I've found for the rears on a track car is a 911 Rear M-Caliper (without the spacers if you're going solid rear rotors). This caliper is straight out of the early 914 front caliper casting. Only the fluid inlet location and the bore size has changed. The use the same size pad and, the 911 caliper has the proper 38mm piston to retain a "system" approach to the upgrade.

You car will be much better balanced from the start.

Posted by: Tom_T Mar 6 2010, 03:22 PM

Eric - others?

I'm basically looking for a bit better braking on my 73 2L for primarily street use & want to keep it for all intents & purposes an "as original" example that I can CW if I want, or maybe AX a little just for the halibut. So are there any issues &/or concerns in brake system set-up - relative to tires sizes - when staying with a more or less stock street brake setup on my early 8/72 build 73 914-2.0?

... i.e.: when using the OE Fuchs 2L Alloys with OE size repro/new OEM 165(/80)HR15 Radials as completely as OE - vs. the "newer" & wider tires more readily available today in the similar speedo error "close" range, such as the 195/65HR15 or 185/70HR15 (or VR's) ????

If it makes any diff. to the answer for the above:

- Brake System-wise - My early 73 2L has late front (2 bleeder) & early rear (1 bleeder) calipers which I'll have Eric do his thang with, add Porterfield R4S pads F&R, using stock OEM rubber hoses all around, upgrading to the 19mm 914-6/911 MC, & I will put on new Zimmerman OE solid rotors & FAG/OEM bearings F&R while I'm at it - mostly so the whole system seats & functions as new. The old rotors were still good - but sat on the 914 in my garage for almost 25 years, & will stockpile them just in case they're NLA 10 years from now, or sell them. BTW - OE pressure regulator stays in!

- Suspension-wise - the 73 2L's all came with the factory sway bars F&R rear (mine incl.), the rear springs & front torsion bars are still OE stock, but I'd changed out Sachs OE for Koni reds at all 4 corners back in the early 80's & they only have about 20k mi' on them before stored in 5/85, & seem strong (will do street/sport Bilsteins if/when they need replaced). I'd run the front only lowered about the 1/2" adjustment you get with the stock suspension set-up (adj. at the Torsion Bars IIRC ??), & will do so now, but will add in all new street bushings F&R and the OEM Lemforder (sp?) Turbo Tie-rod kit (& bump steer kit iff necessary).

BTW - folks, with what you save on putting in a 19mm MC vs. 17mm MC - it basically covers the price diff on OEM & more basic stock type pads - if cost is a concern while you're doing this, or just save more with better braking & firmer pedal with 19mm & stock types pads - both at less. IMHO - it's the way to go even on a street or DD, come time to rebuild the brake system.

Posted by: Eric_Shea Mar 6 2010, 06:20 PM

Tom,

For your car (and about 90% of the others out there), stock brakes, new lines, new fluid and awesome pads should throw you through the windshield at the cones course... and deliver on the lawn at Monterey.

Word of Caution on Master Cylinders: There are Chinese 19mm Master Cylinders out there. I'm not your average import hater etc. but, there have been far too many failures with these units for me to recommend them. Only purchase ATE Master Cylinders for your car. If it's under $200.00, it's probably way jacked up in price and "not real".

I know it goes against the grain for the duct tape and zip tie crowd but, this is a place where you don't want to take a chance.

Posted by: Tom_T Mar 6 2010, 07:07 PM

Thanx Eric!

I agree on the 3rd world cheap crap parts out there! My MC is an ATE from PP (before Pat G & Paul/Nuen Vehrzen pointed me to you/PMB ), but don't recall the price as it was early last year & ordered with the rotors, lines & bits - all of which were the OEM/OES for Porsche.

With your purdy calipers, it would do well at Monterey, but I'd have to work very hard on being as anal as the CW's on here & in PCA!

My approach has been to do a top quality resto/repair/refresh on my 914, & therefore to use the best product available for the function overall, so I won't be messing with it again in 5, 10 or more years for ANYTHING!!

In some cases I've gone with better repro items over OE/OES/OEM - like Mark/Mikey914's bumper toppers & seals using a better rubber & better SS metal bits - since they look exactly like stock but won't rust & dimple like the OE ones.

Posted by: BRAVE_HELIOS Jul 23 2010, 11:13 AM

How does this all apply to the addition of V8 weight and power? The instructions I have from Renegade states that I should replace the regulator with a "T" fitting, which I have done, although I have not tested it. Is there a difference/advantage with the V8? Thanks!

Posted by: campbellcj Jul 23 2010, 12:32 PM

Is Renegade recommending to remove the regulator and replace it with a tee for a totally stock brake setup? If so then I would disregard that suggestion unless they offered a REALLY good explanation for it.

Posted by: Tom_T Jul 23 2010, 12:43 PM

PM or email ERic the brake meister directly on this, or call PMB - if he doesn't answer you here.

The main diff. I can think of is a V-8 weighs a f*ck of a lot more than a T-4 alloy flat 4 or 2.0 alloy flat 6 - plus the weight/CG is much higher on a upright engine vs. a pancake. IIRC Eric said in this thread that the regulator's bias on the 914-4 vs. 914-6 is a bit different (by a couple of % points), & that may be due to the 270 lb. heavier (IIRC) Porsche pancake 6 over the 1.7/1.8/2.0 L T-4's.

Posted by: BRAVE_HELIOS Jul 23 2010, 12:50 PM

In the instructions, it does not specify whether the brake system is stock or modified. What I can see from the pictures (along with the instructions) is that the brakes look 914-4 stock. I don't know why they would recommend doing this for a stock setup when the regulator seems to allow full flow anyway.

Posted by: Phoenix 914-6GT Jul 23 2010, 05:13 PM

Because they simply may not understand what it really is. Eric has done a great deal of research and work on this. He really is THE MAN when it comes to our little cars and brakes.

Posted by: wobbletop Jul 23 2010, 08:23 PM

For a V8 I would start with the regulator in place. The reason for the regulator is so the fronts lock up first and induce under steer instead of over steer (potentially very quick over steer with the additional weight of the V8 in the rear).

With the weight in the middle of the car (as opposed to behind the rear axle) I wouldn't expect the weight of the engine to affect the balance by too much.

And then things like non-stock tires sizes, etc change the balance, so real world testing is the best approach. But I would start the the valve in there.

Just my 2c (Canadian though).

Posted by: Eric_Shea Jul 25 2010, 08:37 PM

If I were Scott or Steve I'd remove that immediately from any instructions. It's a VERY serious lawsuit waiting to happen.

It doesn't matter "what" type of calipers are on a 914; stock to 997. It doesn't matter about the engine or power. It matters where it is and how it affects your car in a spin. This is a devise designed to eliminate spin from polar moment inertia.

It's not something we should ever recommend anyone replace, especially if you're a company with liability issues on the table.

It's basically one of the very first anti-lock brake devices.

Read:

Posted by: BRAVE_HELIOS Jul 26 2010, 08:21 PM

So, I sent Renagade Hybrids an email concerning their instructions and the installation of a "T" in place of the brake regulator. My email reads:


Hello,

In your instructions for a 914/V8 setup (circa 1993), it states that the brake regulator should be replaced with a "T" fitting. Is this still valid? Have the instructions changed since 1993? Are new instructions available? The guys at 914World seem to think that the "T" fitting is a bad idea, even with the addition of a V8. Any information would be greatly appreciated.

Thank you,
Tony

Well, I was somewhat surprised by the response. Not really a clear cut explanation as to why you would install a "T" in a stock brake system with a V8 engine. The response was:


Hi Tony,
There are a lot of ways to go about doing the brakes. Most of the time they are upgraded to 911 calipers and rotors.. For instance I have a car running carrera calipers front and rear, with the T, and it works great both on the street and track. The calipers for the Renegade big brake kit were sized with the T in mind, so they also work very well.

You'll find the stock 914 brakes not well suited for the type of acceleration the V8 is capable of. A few years ago I purchased a 914 V8 that still had stock brakes and I was constantly aware I didn't have enough brake to stop the car if the car was driven with any authority.

If you are concerned, then you can always put in an adjustable proportioning valve between the seats. Then you can dial in the combination of front and rear calipers to your liking. Just be aware that it needs to be set properly and shouldn't be constantly messed with.

Let me know if you have any other questions.


Any thoughts?