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> Proportioning Valve, replace with a "T"
rmital
post Feb 8 2006, 12:54 PM
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Brake system just about completely replace....master cylinder, all lines, etc. Just the proportioning valve still original.

Part A: Bleeding still producing a sloppy brake pedal...too much play. I'm hoping replacing the proportioning valve with a "T" will solve my problem. Has anyone had success with this?

Part B: Considering how the car is balanced, will the "T" replacement be safe...no fishtailing?

I hope I was clear with my description...be kind.

Thanks,
Ray
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Dr Evil
post Feb 8 2006, 01:00 PM
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Ray,
It is not usually a good idea to put a "T" in unless you have installed larger brakes in the front. The reson being is that with the stock equipment you are more likely to lock up your rears without the P-valve. I know that you didn't want to hear that as the P-valve can be a pain. Have you tried to vacuum bleed your rears? Sometimes sucking fluid throught he P-valve can be better than pushing fluid through.

Also things to consider:
Are you running stock lines? Are they in good repair?

Stock lines and a 17mm master cylinder will usually feel a bit spongy. 19mm will feel a little more firm and require less travel.

Kinda hard to tell from here as one mans spongy is anothers stock (IMG:http://www.914world.com/bbs2/html/emoticons/beer.gif)
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john rogers
post Feb 8 2006, 01:06 PM
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Replace it.
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SirAndy
post Feb 8 2006, 01:09 PM
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QUOTE (Dr Evil @ Feb 8 2006, 11:00 AM)
It is not usually a good idea to put a "T" in unless you have installed larger brakes in the front.

the stock P-Valve is there for a reason. a "T" can help to balance your brake bias if you changed your brake setup from stock ...

with stock brakes, a "T" does not sound like a gud idea ...
(IMG:http://www.914world.com/bbs2/html/emoticons/cool.gif) Andy
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rmital
post Feb 8 2006, 01:14 PM
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I'm convinced....replace. Any suggestions on finding a replacement?
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rmital
post Feb 8 2006, 01:23 PM
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I'm getting a couple inches of play now in the pedal....I'm assuming not unusual for a 17mm master cylinder?
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john rogers
post Feb 8 2006, 01:53 PM
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Have you checked to see how much free play there is in the pedal before the rod contacts the back of the m/c piston. If you have had the system apart that adjustment can easily change and result in a significant amount of pedal travel before anything happens. But there has to be some free play since the piston has be able to fully return. I forget what the book says, but it is pretty small like 0.1MM or something?
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Mueller
post Feb 8 2006, 02:05 PM
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QUOTE (rmital @ Feb 8 2006, 12:14 PM)
I'm convinced....replace. Any suggestions on finding a replacement?

(IMG:http://www.914world.com/bbs2/html/emoticons/screwy.gif) 2 no votes and 1 yes vote (IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif)

what kind of democracy do you follow?? hahaha

I'm in the NO camp, for bone stock calipers..."if" you do go that route, make sure you test (stomp on the pedal a few times) in a safe location (in wet if you can) to ensure that the rear brakes do not lock up 1st, if they do, you can spin and it might not be pretty (IMG:http://www.914world.com/bbs2/html/emoticons/headbang.gif)

other things to check is floorboard flexing, a member here sells a kit that supports the mastercylinder from underneath, it's a good idea and can eliminate some of the movement you feel......
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rmital
post Feb 8 2006, 02:15 PM
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QUOTE (Mueller @ Feb 8 2006, 12:05 PM)
(IMG:http://www.914world.com/bbs2/html/emoticons/screwy.gif)   2 no votes and 1 yes vote (IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif)

what kind of democracy do you follow?? hahaha

...rented a car in Aruba a long time ago...some kind of jeep. I locked up the brakes, not something I'd ever want to do again...at least not when I'm sober.

I got that answer (brakes locking up) from a few others, decided to post and get the 914club advice. So when Dr. Evil posted, I was pretty convinced that was what I had in store for me.
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Eric_Shea
post Feb 8 2006, 02:37 PM
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Do you have stock brakes?

Yes = Do not replace the P-Valve. Learn the proper procedure to bleed said P-Valve and enjoy safe braking.

No = What do you have?

As recommended in a previous post. Only if you've upgraded your front brakes should you eliminate this vital piece.
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jhadler
post Feb 8 2006, 02:38 PM
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Depending on what you want to do with the car, there are aftermarket (racing) proportioning valves that you can use as well. Far less likely to trap air than the stock vlave. But I agree, that if you're using stock brakes, a "T" is not a good idea.

You -could- run aggressive pads in front and weaker pads in back to compensate, but that might more of a PITA than it's worth...

-Josh2
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Eric_Shea
post Feb 8 2006, 02:38 PM
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I believe the good Doctors advice was:

QUOTE
The reson being is that with the stock equipment you are more likely to lock up your rears without the P-valve.
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rmital
post Feb 8 2006, 02:46 PM
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Yes, I have stock brakes....not planning on replacing Pvalve with a "T".

I'm just not sure what acceptable play in the brake pedal actually is.

...I don't want to spend $$, replace Pvalve and have same play in pedal. Once I get to test drive, I'll know for sure.
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914-8
post Feb 8 2006, 03:35 PM
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Stock 914-4 rear brakes,

with 911SC front brakes.

Replace with a T?
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jhadler
post Feb 8 2006, 03:41 PM
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If it's play in the pedal, then there are number of things to look at way before you replace the prop-valve. First off, you're talking about excessive pedal travel right? Not a floppy pedal... A floppy pedal probably says that something is wrong with your pedal cluster.

1) Bleed the brakes. This should be step one whenever diagnosing brake problems.

2) Inspect pads and rotors. If there is excessive wear, this will increase pedal travel.

3) Check rear brake adjusters. If they are way out of adjustment, you'll notice extra pedal travel.

4) Inspect the flex lines at the calipers. If they're really old rubber lines and are obvioulsy cracking and/or showing sinnes of wear, then they may be in need of replacement. Even new rubber lines will make a big difference over worn out cracking ones. The SS braided lines are nice, but you should inspect them regularly, as they won't give much warning in the unlikley even of failure. Rubber ones fail more gracefully most of the time...

5) Look at the master. Especially the mount. Check to see if there is a lot of flex in the mounting. Have someone press the brake pedal while you look at the master from the under the car. It shouldn't move. If it does, then maybe the bulkhead has weakened. This problem can be fixed quickly, cheaply, and easilly (if only they all could right?). There's a kit that one of our members has for sale. Here.

6) Make sure the master isn't leaking.

7) Replace, or upgrade the master to a 19mm. Upgrading to the 19mm master will result in a pedal with less travel, but will require more effort for the same braking force. Basic physics/hydraulics in effect there.

8) Replace the prop-valve...

After that, you're getting into "big brakes" and stuff like that...

How's that? (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

-Josh2
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914-8
post Feb 8 2006, 03:43 PM
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I think that is very well done!

But, after almost 25 years owning 914s, I can't say I've ever owned or driven one that had truly good feeling brakes with the stock p valve in place.
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Kerrys914
post Feb 8 2006, 03:45 PM
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Dear, the parts I just sold paid for that part ;)
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I have a recently rebuilt P-valve for sale (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

It came with some parts I bought last fall. It was rebuilt by someone on this board ( They maybe in the resource section)

All I know is it looks NEW and was told it was rebuilt.

If your interested shoot me an e-mail with what you want to pay for it....Treat yourself good when you give me a price (IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif)

Cheers
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Eric_Shea
post Feb 8 2006, 04:21 PM
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QUOTE
How's that?


Excellent...

He has basically all new stuff (phone call after my previous post).

They need to make sure the venting clearance is right and do a really good 914 bleed job. Leo's gonna help him (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

QUOTE
Stock 914-4 rear brakes,

with 911SC front brakes.

Replace with a T?


Yup.
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Trekkor
post Feb 8 2006, 04:32 PM
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With fresh fluid in the whole system and speed bleeders on the calipers, you can do like I did and recylcle the fluid back into the reservoir.

Only if it's fresh (IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif)

This way you can pump the pedal frantically to get all the air out of the p-valve.

Brake bleeding made simple...


KT
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cobra94563
post Feb 8 2006, 04:33 PM
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Helpful discussion. (IMG:http://www.914world.com/bbs2/html/emoticons/rolleyes.gif)

As to a source for the "T", where is the easiest place to pick one up - a local auto store or hardware store or mail order?

Chris
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