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> 914 brake question
honlude
post Jul 13 2008, 03:31 PM
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Hello

i am working on my 1975 914 1.8 , i rebuilt the master cyl , rebuilt right rear caliper , and replaced left rear caliper , replace the grommets on master cyl for resov. lines , i have set the rear brake venting to .008 and bleed the system multiple time , i have no air coming thru system at all , i have brakes now but they just dont seem to be correct , if i stand on the brakes hard they do not lock up while driving, are the brakes on these just that way or dose anyone have any other suggestions on what could be a problem , ... i have no leaks anywhere either and the park brake seems to hold the car under a light load

thanks craig
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3d914
post Jul 13 2008, 04:16 PM
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If its the stock master cylinder - that may just be the way it is. I've long since forgotten what the stock was like after I upgraded to the 19mm master. I have noticed though that pads will make a big difference. I've had performance pads that react great to firm pressure and others that would lock up the brakes every time with the same pressure. I had to relearn how to brake.

Did you also replace pads? That will have some affect also.
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wilchek
post Jul 13 2008, 04:23 PM
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Sounds like you did what you should have. The brakes on these cars are adequate but are not modern and will not work like modern brakes. I think the question that everyone will ask is what type of pads are you using. If you switch to more aggressive pads you will probably be happier. My stock brakes would barely lock up. I changed to BMW front calipers and more aggresssive pads. Some people say this is a bad idea as it adds heat, but I drive this as a street car and never had any issues and the brakes now lock if I want them to. Also this brake system has a proportioning valve on the firewall (under car driver side firewall near rear wheel). The valve is designed to make the front brakes lock first (safety feature). You really don't want the rears locking up as the back will come around (not fun). Also people have had issues bleeding the rears if new lines were put it. You may need to bleed with a power bleeder if you have not. Hope this helps.\\


Welcome to the club, good to see a local 914 owner. There are a couple of us in the area if you ever need help or parts.
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PeeGreen 914
post Jul 13 2008, 04:34 PM
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When I had my 4 I had stock pads in there that was terrible to stop the car with. The pedal was nice and firm but stopping sucked. Then I bought some Porterfield pads that I would lock up all four if I braked really hard. Try getting some Pagid Orange or Porterfields for your car.
http://www.paragon-products.com/product_p/u4304-rs44.htm


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ClayPerrine
post Jul 13 2008, 08:46 PM
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QUOTE(honlude @ Jul 13 2008, 04:31 PM) *

Hello

i am working on my 1975 914 1.8 , i rebuilt the master cyl , rebuilt right rear caliper , and replaced left rear caliper , replace the grommets on master cyl for resov. lines , i have set the rear brake venting to .008 and bleed the system multiple time , i have no air coming thru system at all , i have brakes now but they just dont seem to be correct , if i stand on the brakes hard they do not lock up while driving, are the brakes on these just that way or dose anyone have any other suggestions on what could be a problem , ... i have no leaks anywhere either and the park brake seems to hold the car under a light load

thanks craig



You used the wrong venting clearance. There is a typo in the Haynes manual. The actual venting clearance is supposed to be .004.

And you also have to bleed the proportioning valve. The brakes won't work correctly if you don't get all the air out of the prop valve. I personally dislike them, and replace them with a T fitting. The brakes feel better with less pedal travel if you do.


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honlude
post Jul 14 2008, 07:32 AM
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thanks for all the help i have replaced the rear pads and i feel confident that i got all the air out of the system , dose anyone know the tread size for the brake lines so i can replace the prop valve with a tee.

thanks craig
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wilchek
post Jul 14 2008, 07:56 AM
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should be 10mm but don't quote me on that. You can buy the part here. These guys are trustworthy and prices are fair. However, Be careful in taking out the proportioning valve it is there for a reason and if you don't upgrade the front brakes to be stronger than the rears it is not advisable to to put a T fitting in.


http://www.pelicanparts.com/catalog/shopca..._pg3.htm#item16

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davep
post Jul 14 2008, 07:58 AM
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These brake lines are 10mm by 1.0 pitch.
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Cap'n Krusty
post Jul 14 2008, 09:31 AM
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I dunno if you read the earlier post about the venting clearance, because you didn't acknowledge it, but the venting clearance is .004", NOT .008". Maybe it's an answer you didn't want to hear. Even the factory shop manual is wrong. They told us that in 914 brake class at the Porsche Training Center, 35 years ago. One of those things that never got fixed in print. If you don't set it correctly, you'll never get the brakes to feel right. Furthermore, you need to put at least a couple of hundred miles on the car, using the brakes frequently, before they're gonna begin to feel right. Removing the proportioning valve in an otherwise stock brake system is stupid.

The Cap'n
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VaccaRabite
post Jul 14 2008, 10:02 AM
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If you want it, I have a NIB spare ATE 19mm MC, and a pressure bleeder (borrow only).

If you want the MC, just let me know. I'd like to get back what I paid for it last week - so selling it to a local would be better then shipping back to Pelican.

From what Eric Shea has said (and I trust it) when your brakes are properly set and refurbished, you should be able to lock them up.

Make sure the rears are set to .004 like Crusty said.

Zach
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honlude
post Jul 14 2008, 11:13 AM
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thanks guys i will def go out today and double check the vent to .004 , i just wanna get them fixed so its safe to drive , for now im gonna stick with the stock mc but i appriciate the offer
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McMark
post Jul 14 2008, 10:41 PM
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I have no doubt that you still have air in your lines. A stock system should have a nice firm pedal. You should definitely be able to lock up the tires with any pads. I find on most 914s that I have to bleed, drive, bleed, drive, bleed some more. It's a MAJOR PITA! But something about getting the car out and using the brakes frees up more bubbles. BTW, I'm not talking about a long drive here. Just up and down the block. BE SAFE!

Did you bench bleed the M/C before you installed it? The M/C is a PITA to get all of the air out of. The Prop Valve is a PITA to get all of the air out of. You're not clear yet. Search for posts describing the long tube bleeding method. There is one by Trekkor and I think SirAndy has one in his 3.6 build thread.

Anyone who disses the stock system* has not had a completely correct system.

*motors larger than stock, or cars used on a large racetrack can complain about the stock system.
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honlude
post Jul 20 2008, 01:23 PM
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Hey i just wanted to thank everyone for there help as of today i seem to have good brakes !!! (IMG:style_emoticons/default/smilie_pokal.gif)
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Wanna9146
post Jul 20 2008, 01:29 PM
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QUOTE(honlude @ Jul 20 2008, 11:23 AM) *

Hey i just wanted to thank everyone for there help as of today i seem to have good brakes !!! (IMG:style_emoticons/default/smilie_pokal.gif)


So...whajda do? (IMG:style_emoticons/default/confused24.gif)
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jetboy
post Jul 20 2008, 01:52 PM
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QUOTE(Wanna9146 @ Jul 20 2008, 12:29 PM) *

QUOTE(honlude @ Jul 20 2008, 11:23 AM) *

Hey i just wanted to thank everyone for there help as of today i seem to have good brakes !!! (IMG:style_emoticons/default/smilie_pokal.gif)


So...whajda do? (IMG:style_emoticons/default/confused24.gif)


I'm wondering that as well. I can mash my brakes and they dont lock up either so I would like to hear what you did to resolve it (switched to M calipers?? (IMG:style_emoticons/default/biggrin.gif) ). Let us in on the secret (IMG:style_emoticons/default/beerchug.gif) .
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Eric_Shea
post Jul 20 2008, 02:20 PM
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http://www.914world.com/bbs2/index.php?showtopic=86026

Craig, I hope you read this before hacking away at the p-valve.
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Wanna9146
post Jul 20 2008, 02:27 PM
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QUOTE(Eric_Shea @ Jul 20 2008, 12:20 PM) *

http://www.914world.com/bbs2/index.php?showtopic=86026

Craig, I hope you read this before hacking away at the p-valve.


After all that, it turned out to be the pedal adjustment. Wasn't the proportioning valve after all... (IMG:style_emoticons/default/blink.gif)
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Eric_Shea
post Jul 20 2008, 04:13 PM
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Excellent! There's still a lot of good info in there on p-valves. Glad yours is working (IMG:style_emoticons/default/smilie_pokal.gif)
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