Brake pressure regulator Options

[watsonrx13]

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

[McMark]

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.

[campbellcj]

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

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.

[Eric_Shea]

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.

(IMG:style_emoticons/default/agree.gif) 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.

[Tom_T]

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? (IMG:style_emoticons/default/confused24.gif)

... 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) ???? (IMG:style_emoticons/default/confused24.gif)

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.
(IMG:style_emoticons/default/smile.gif)

[Eric_Shea]

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.

[Tom_T]

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.

Thanx Eric! (IMG:style_emoticons/default/smile.gif)

I agree on the 3rd world cheap crap parts out there! (IMG:style_emoticons/default/mad.gif) My MC is an ATE from PP (before Pat G & Paul/Nuen Vehrzen pointed me to you/PMB (IMG:style_emoticons/default/sad.gif) ), 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! (IMG:style_emoticons/default/biggrin.gif)

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!! (IMG:style_emoticons/default/dry.gif)

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.

[BRAVE_HELIOS]

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.

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? (IMG:style_emoticons/default/idea.gif) Thanks!

[campbellcj]

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? (IMG:style_emoticons/default/idea.gif) Thanks!

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. (IMG:style_emoticons/default/huh.gif)

[Tom_T]

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.

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? (IMG:style_emoticons/default/idea.gif) Thanks!

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.

[BRAVE_HELIOS]

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? (IMG:style_emoticons/default/idea.gif) Thanks!

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. (IMG:style_emoticons/default/huh.gif)

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. (IMG:style_emoticons/default/huh.gif)

[PeeGreen 914]

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.

[wobbletop]

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).

[Eric_Shea]

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.

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:

[BRAVE_HELIOS]

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?