Stainless brake line upgrade

[green71]

My '71 still has rubber brake lines, which I believe are contributing to a soft or spongy pedal. I'd like to upgrade to stainless. If I do the upgrade, will this create excessive stress on other brake parts (esp. cylinders), requiring them to be upgraded as well?

Thanks,

Mark

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1971 1.7l 914
Willow Green

[Jim T]

It is unlikely that your brake lines are the cause of your soft or spongy pedal.

[green71]

I've just had a front brake job w/new pads, turned rotors and a full system bleed. The rear brakes still have 50% left on the pads. In spite of this, the braking system isn't exactly what I'd call "responsive." Aren't stock 914 brake systems notoriously soft?

Maybe a 19mm master cylinder would be a better place to start?

Mark

[Jim T]

A 19 mm will not cure softness or sponginess, either.

[Conrad W Peden]

Did the 'full system bleed' include the proportioning valve?

Couldnt get rid of my sponge till I bled the Prop. valve.

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CWP/VIR
72 914 L20E in rusto.
73 914 L20E 2.0L in resto.
http://members.rennlist.com/a914lover

[green71]

Conrad,

Thanks -- good question. I'll look into that.

Mark

[gruntie]

The cause of the sponginess is the proportioning valve. Garretson Enterprises used to do an adjustable replacement which cured the problem; was available from High Performance House a couple of years ago. I have been warned off stainless flexibles: constant flexing can break the stainless braid, which then cuts into the rubber pipe inside.

[green71]

Interesting you should mention that. Since posting this question earlier this morning, I've consulted my mechanic who has also warned me away from them. He asked if I intended to race the car & I said no; his recommendation was to get new OEM. He also cited potential for leaks.

Whar is this dang proportioning valve, enuhway?

[campbellcj]

Mark,
The proportioning valve is on the firewall (engine side), towards the driver.

[Dave at Pelican Parts]

Look up from under the car; the prop valve is not visible from the top.

The newer DOT-approved SS lines are probably OK. However, the rubber ones generally last about 20 years (or more!). The typical failure mode for them is that they swell and will not let the brake pad let go of the rotor. The typical failure mode for SS lines (particularly the early non-DOT ones) is total failure. It is very uncommon, to be sure. However, I personally want to have the relatively-mild failure mode and not the catastrophic one.

--DD

[johnboy914]

Contrary to what everyone seems to think here, I had very squishy feeling brakes, enough so that I was uneasy if I had to stop quickly. I replaced them with SS lines and, after bleeding the brakes, I had a very solid pedal. I stomped on the brakes going about 70 (with plenty of runout room in case of failure) and my car screeched to a halt. I was very impressed. I have auto-x'd them once and they were awesome.

my two cents

[HMeeder]

I have replaced my lines with the SS lines and have had no problems.

However, after replacing them, I felt no improvement in pedal feel (yes I bled them!)

I then replaced the proportioning valve with a simple T and holy cow! I got some brakes!

There has been discussion on the forum about whether to delete the valve or not. I am very happy with the T and do not feel that the braking system has been compromised. Who knows? If our cars had more mass and velocity and torque it may be a problem. I drive aggressively and auto-x the car and get no rear lock up.

My $.02



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Herb
'72 1.7 Tangerine 'Teen
'74 2.0 Red Rustmobile

[Jim T]

Yep, the mushy feel of 914 brakes is caused by the proportioning valve. Even if completely bled, it still causes mushiness.

The time honored attempt to cure mushiness goes like this: Bleed. Still mushy. SS lines. Still mushy (unless you are good at convincing yourself otherwise, i.e. easily fooled. May want to try a K&N and Slick 50, too). 19 mm MC. Still mushy, and you have to press harder to get the same braking.

Change out the proportioning valve, replace with T valve. Waa Laa! Night and day difference. Because THAT is where the mush is.

Now, there are possible disadvantages to the T valve, like the rear locking on a wet highway. Some are concerned about it, others seem to think its not a worry. I don't know the answer to that question, but it concerned me enough to live with the somewhat mushy brakes on my street 914, and leave the prop valve in place.

[TimW]

Well now I’m getting confused. Assuming the mushiness is from the prop value, is it because of a poorly designed prop value, or a poorly bled prop valve?

If the later is the case then how does one go about correctly bleeding it?

I have mushy brakes too, and I just haven’t gotten around to re-bleeding. If re-bleeding isn’t going to help I’ll just switch to a T; because I don’t want to drive with the way it is now.

Tim
’73 914 2.0L w/SS DOT-approved lines from PP.

[JmuRiz]

Is it true that if you get upgraded front brakes that the T will not lock up the rears? Say if you got a big brake kit from Rich Johnson...

Nathan

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'73 2.0 914

[John Rogers]

At the last auto-x in San Diego, one of the 914 drivers told me he had just replaced the prop valve with a tee ($12) and the pedal feel was fantastic and he had no problems locking the rear wheels before the fronts. This is the same as I have found as I have a tee on the race car and the street 914 and have no funny braking. I think the trouble with the prop valves is their age and corrosion inside that causes them to exhibit a soft pedal. You have to remember how old they are???? I'd recommend new replacement rubber lines if you are concerned about them since they are getting really old too. Good luck.

[Dave at Pelican Parts]

The potential for locking up the rears is the worst on dry pavement, with good tires, going downhill. That's when you get the most weight transfer away from the rear wheels, therefore when the rear grip is the lowest relative to the front grip.

I have heard and read (yes, including in a certain "tech tips" book) that a new stock-type proportioning valve will cure the mushy pedal that has eluded all bleeding attempts. One person I know reported that it firmed up his brake pedal a really amazing amount.

If the brakes feel dangerous, then something is wrong with the system. My pedal only feels so-so, but it can still lock up the tires at decent (~50 MPH) speeds if I really jump on it.

I suggest bleeding again. And again. If you have replaced your master cylinder recently, there might still be air in it. I hear those are a real pain to bleed thoroughly when they're totally empty.

Even if you use the ATE Gold and Super Blue fluids, that's only $25 or so. A lot cheaper than the M/C, the proportioning valve, new front brakes, etc. Plus, if you replace a part of the brake system you'll have to bleed the whole system again anyway. (You'd be amazed at how air bubbles can go from one end of the system to the other...)

If you do go with larger front brakes, you can probably get rid of the proportioning valve reasonably safely. The only real way to tell, though, is to try it out.

--DD

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http://www.pelicanparts.com/gallery/Dave_Darling

[pbanders]

FWIW, here's another comment. My car is a '70, I replaced the original rubber lines with new rubber OEM lines last year. I had a shop here do the work, my mechanic told me that the lines that came off the car were fine and showed no blockage. My brakes are nearly 100% stock, including the 17 mm MC and proportioning valve. I'm using Metal Master pads and ATE Blue fluid, and my mechanic uses his own method for bleeding. In both street and track use, I have more than enough brakes, no fade, and firm pedal.

Brad Anders

[Rob-O]

Hey Green,

There is a decent article on properly bleeding the proportioing valve in Excellence magazine, issue #58, December 1995. In the article Jim Pasha states that to properly bleed the proportioning valve, you must break the line going into the valve, and the line coming out of the valve. Bleed the line going into the valve, then re-attach it. Then bleed the proportioning valve, then attach the outgoing (to the rear calipers) line and bleed the rear brakes. He also reminds one to bleed both sides of the caliper, there are two bleeders on each caliper. Good Luck!

[green71]

Thanks, Rob. My likely course of action at this point is to replace the lines w/OEM & then try this meticulous & deliberate bleeding operation you've detailed above.

Mark