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914World.com _ 914World Garage _ Proportioning Valve

Posted by: rmital Feb 8 2006, 12:54 PM

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

Posted by: Dr Evil Feb 8 2006, 01:00 PM

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

Posted by: john rogers Feb 8 2006, 01:06 PM

Replace it.

Posted by: SirAndy Feb 8 2006, 01:09 PM

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 ...
Andy

Posted by: rmital Feb 8 2006, 01:14 PM

I'm convinced....replace. Any suggestions on finding a replacement?

Posted by: rmital Feb 8 2006, 01:23 PM

I'm getting a couple inches of play now in the pedal....I'm assuming not unusual for a 17mm master cylinder?

Posted by: john rogers Feb 8 2006, 01:53 PM

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?

Posted by: Mueller Feb 8 2006, 02:05 PM

QUOTE (rmital @ Feb 8 2006, 12:14 PM)
I'm convinced....replace. Any suggestions on finding a replacement?

2 no votes and 1 yes vote

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

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......

Posted by: rmital Feb 8 2006, 02:15 PM

QUOTE (Mueller @ Feb 8 2006, 12:05 PM)
2 no votes and 1 yes vote

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.

Posted by: Eric_Shea Feb 8 2006, 02:37 PM

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.

Posted by: jhadler Feb 8 2006, 02:38 PM

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

Posted by: Eric_Shea Feb 8 2006, 02:38 PM

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.

Posted by: rmital Feb 8 2006, 02:46 PM

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.

Posted by: 914-8 Feb 8 2006, 03:35 PM

Stock 914-4 rear brakes,

with 911SC front brakes.

Replace with a T?

Posted by: jhadler Feb 8 2006, 03:41 PM

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. http://www.914world.com/bbs2/index.php?act=ST&f=4&t=32748.

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?

-Josh2

Posted by: 914-8 Feb 8 2006, 03:43 PM

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.

Posted by: Kerrys914 Feb 8 2006, 03:45 PM

I have a recently rebuilt P-valve for sale

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

Cheers

Posted by: Eric_Shea Feb 8 2006, 04:21 PM

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

QUOTE
Stock 914-4 rear brakes,

with 911SC front brakes.

Replace with a T?

Yup.

Posted by: trekkor Feb 8 2006, 04:32 PM

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

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

http://www.914world.com/bbs2/index.php?act=ST&f=2&t=33778&hl=bleeding

KT

Posted by: cobra94563 Feb 8 2006, 04:33 PM

Helpful discussion.

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

Posted by: 914-8 Feb 8 2006, 05:14 PM

+1 on that - what's a good source for a T?

Posted by: Eric_Shea Feb 8 2006, 07:08 PM

http://www.cip1.com or James Adams here sells them (Resource section)

Posted by: Eric_Shea Feb 8 2006, 07:09 PM

Here's the http://www2.cip1.com/ProductDetails.asp?ProductCode=VWC%2D803%2D611%2D755 hard to beat $4.95

Posted by: cobra94563 Feb 8 2006, 09:41 PM

Thank you, Eric.

Posted by: Always Looking Feb 8 2006, 09:48 PM

1980 BMW 320i fronts, stock rears-

Replace with a T? (or adjust P-valve?)

Good discussion.

Posted by: J P Stein Feb 8 2006, 09:53 PM

QUOTE (Always Looking @ Feb 8 2006, 07:48 PM)
1980 BMW 320i fronts, stock rears-

Replace with a T? (or adjust P-valve?)

Good discussion.

Yeah, itteration # 73 if my memory serves ....which is questionable, I fear.

Posted by: rmital Feb 8 2006, 10:03 PM

QUOTE (jhadler @ Feb 8 2006, 01:41 PM)
3) Check rear brake adjusters. If they are way out of adjustment, you'll notice extra pedal travel.

Thanks for all the great responses....

I'm definitely concerned about the rear brake adjustments. What the heck is the check on that?

When depressing the brake pedal, it just kind of travels pretty much right to the floor board. Not really spongy, just consistent right to the floor.

Hopefully we could get a better bleed tomorrow. Maybe a sucking power bleeder would be better than a blowing bleeder.......to pull the air out of the pvalve....if that's the case.

...since pumping the crap out of the brake pedal didn't work!

This is really killing me...

Posted by: r_towle Feb 8 2006, 10:06 PM

The stock p-valve is designed to not let fluid through until pedal force, or fluid force reaches something like 750 lbs...
Here is how I do it...it works for me...

bleed the whole system twice, till you get decent pressure..

then push on the brake pedal really hard for about 3-5 minutes...you feel the air bubbles slowly work through the valve...the pedal kinda bumps on the way down each time a bubble goes through...

I had to do this twice...just the other night..

Your leg will get real tired...but you will get all the air past the valve..

Then bleed the system twice more...

now the pedal should be right up to the top...

this assumes venting clearance is correct, and push rod is set to the right length...

the air seems to be trapped just in front of the valve...so you have to push it through the valve...

Car has great brakes now.

Rich

Posted by: pek771 Feb 8 2006, 10:13 PM

Drive that buggy up the hill, and I'll take a look at them for you. I want to see what your car looks like anyway!
Pat

Posted by: Eric_Shea Feb 8 2006, 10:20 PM

320's have the same piston as the M-caliper. With stock rears, T.

Posted by: 914-8 Feb 8 2006, 11:09 PM

QUOTE (Eric_Shea @ Feb 8 2006, 05:09 PM)
Here's the http://www2.cip1.com/ProductDetails.asp?ProductCode=VWC%2D803%2D611%2D755 hard to beat $4.95

Does that just bolt right up in place of the P valve?

Posted by: Eric_Shea Feb 8 2006, 11:13 PM

Pretty much. Minor bending and tweaking. Minor.