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Old 06-26-2009, 11:28 PM   #1
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front c4 brake proportioning valve upgrade!

Hey everyone,
I have installed a c4 front brake install on my 88' iroc. Do I need to change the proportioning valve or is the stock ok? As i still don't get the braking power I should have. I do have a high lift cam and other goodies that pull a lot of vaccum which I know causes alot of my problem. I also have an aftermarket brake vaccum reservior, which does not seem to help at all.
Also the c4 brakes have been sitting a long time in storage when I purchased them a couple of years ago. Could it be they just need to to be broken in. They seem to be tight, no leaks.
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Old 06-27-2009, 06:32 AM   #2
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Re: front c4 brake proportioning valve upgrade!

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I have installed a c4 front brake install on my 88' iroc. Do I need to change the proportioning valve or is the stock ok?
Even the 1LE conversion requires a proportioning valve change.

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Old 06-27-2009, 08:05 AM   #3
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Re: front c4 brake proportioning valve upgrade!

Are you sure, as I've seen a couple of threads that as long as they have stock rears the 1le or c4 up grades would work fine with the stock prop valve.
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Old 06-27-2009, 08:21 AM   #4
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Re: front c4 brake proportioning valve upgrade!

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Are you sure, as I've seen a couple of threads that as long as they have stock rears the 1le or c4 up grades would work fine with the stock prop valve.
I've never read or seen that--though, of course, I haven't read or seen everything.

Anyway, I completed the 1LE swap some time ago (fronts first, then later rears) and instructions call for a different valve.

http://web.archive.org/web/200605221.../1LEbrake.html

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Old 06-27-2009, 09:08 AM   #5
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Re: front c4 brake proportioning valve upgrade!

Ok if I were to get this prop valve gm #14089496 for my 88' iroc. Which came oringinally factory disc all around, and now has c4's up front. Is that all I would need, do I need to do any mods, As I saw some kind of thread issue?
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Old 06-27-2009, 09:17 AM   #6
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Re: front c4 brake proportioning valve upgrade!

next question is where can I get one?
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Old 06-27-2009, 04:35 PM   #7
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Re: front c4 brake proportioning valve upgrade!

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Ok if I were to get this prop valve gm #14089496 for my 88' iroc. Which came oringinally factory disc all around, and now has c4's up front. Is that all I would need, do I need to do any mods, As I saw some kind of thread issue?
No mods that I'm aware of. Check the following link for the valve:

http://www.flynbye.com/

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Old 06-28-2009, 08:47 AM   #8
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Re: front c4 brake proportioning valve upgrade!

I don't believe that changing the proportioning valve is going to do much for the front brakes. They always get full pressure from the master cylinder. If you changed from rear drum to rear disc, then a different proportioning valve would be recommended.

Try putting a vacuum gauge on the line to the brake booster so it can be seen while driving. Then check that it stays above 14" of vacuum. Even better is 16 - 18" of vacuum.

If the vacuum is OK then a smaller diameter (the bore I.D.) master cylinder will boost pressure.

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Old 06-30-2009, 02:43 PM   #9
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Re: front c4 brake proportioning valve upgrade!

Thanks for the info.
I also found out I was suppose to bench bleed the fronts and since I rebuilt the rears that should have been done too. Hence alot of air in the lines that i'm still trying to get out.
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Old 07-01-2009, 10:41 AM   #10
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Re: front c4 brake proportioning valve upgrade!

Air just makes the pedal spongy. Unless of course there is so much air that the pedal hits the floor. So if the pedal has a good solid feel to it then I would doubt that there is air in the system.

If the bench bleed is for the calipers, I don't believe that to be true. The only bench bleeding that I am aware of is when a master cylinder is replaced. They need to be bench bled before install.

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Old 07-01-2009, 05:16 PM   #11
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Re: front c4 brake proportioning valve upgrade!

Quote:
Originally Posted by RBob View Post
The only bench bleeding that I am aware of is when a master cylinder is replaced. They need to be bench bled before install.
Or if air is allowed into the reservoir for some reason (bleeding calipers without checking fluid level, for example). Once it's there, bench bleeding or perhaps pressure bleeding is the only way to remove the air.

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Old 07-01-2009, 06:29 PM   #12
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Re: front c4 brake proportioning valve upgrade!

I've been bleeding the brakes now for the last few days and still problems. Brakes feel spongy and the pedel goes to the floor with only some resistance. I have the fronts bleed good as no air bubbles. The rears is the problem, I just can't seem to get rid of the air and its both sides. I called a brake shop up and told them my problem. They said I may have a big air pocket in the system, that is going to take time to bleed out. Or when I did the rebuild on the rears I may have not have seated the seals correctly and air is being sucked back in. BUt if thats the case I would think that the calipers would leak also. He suggested doing a gravity bleed on the rears again. Then rebleed the entire system again.
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Old 07-02-2009, 09:56 AM   #13
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Re: front c4 brake proportioning valve upgrade!

Quote:
Originally Posted by JamesC View Post
No mods that I'm aware of. Check the following link for the valve:

http://www.flynbye.com/

JamesC
I went to this website and they have two different proportioning valves for the 1LE 82-89 and 90-92. Should there really be a difference between the two?
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Old 07-02-2009, 11:05 AM   #14
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Re: front c4 brake proportioning valve upgrade!

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Originally Posted by Americanmouse View Post
I've been bleeding the brakes now for the last few days and still problems. Brakes feel spongy and the pedal goes to the floor with only some resistance....
If you have a MityVac or similar you can vacuum bleed. Need a small jar with a lid that seals (such as a pickle jar). Solder or epoxy two small tubes into the lid. Connect a bleeder hose between one tube and the bleeder. Connect other tube to vacuum pump.

Crack bleeder and apply vacuum. Some air will leak past the bleeder threads, but it doesn't matter. Can put some Teflon tape on the bleeder threads to cut back on the leakage.

It is obvious when air is pulled out of the system just by the sound.

If the master needs bleeding I would unbolt it from the booster. Then tip it so that the line ports are more to the top. Will need to flex the lines, so be careful not to excessively bend them.

Other notes on bleed methods. I tried a pressure bleeder but found it wasn't a good idea. Unless the lid seal to the master is perfect it pumps the fluid into the master cylinder and then out all over the master and whatever is below it. Only took one big mess to scrap that idea.

The best part about the vacuum bleeding it not needing someone to pump the pedal. Makes for a happier marriage too. The second best is that it works, quick and easy. Only thing to watch for is the fluid level in the master cylinder going down.

RBob.
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Old 07-02-2009, 11:27 AM   #15
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Re: front c4 brake proportioning valve upgrade!

Quote:
Originally Posted by MY87LT View Post
I went to this website and they have two different proportioning valves for the 1LE 82-89 and 90-92. Should there really be a difference between the two?
Never mind on my question, went to the 1LE site. Guess the earlier valve is 1.0 threaded fitting and the late 1989 to 1992 is 1.5.
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Old 07-02-2009, 06:46 PM   #16
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Re: front c4 brake proportioning valve upgrade!

Well "Live and Learn"
A friend of came over last night to help me. As he was watching he asked why I just put the rubber seal over the resivor instead of capping it with the plastic cap. I said its easy to refill as i'm bleeding them. So he suggested to put it together and try it. well it works I now have brakes.
What a waste of time and money!
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Old 07-03-2009, 03:47 PM   #17
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Re: front c4 brake proportioning valve upgrade!

I hate to say this, but if by putting the lid on and clamping it in place fixed the brake issue, there is still something wrong. All the lid is for is to keep the fluid in the reservoir.

RBob.
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Old 07-04-2009, 08:58 AM   #18
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Re: front c4 brake proportioning valve upgrade!

Thats what I thought too. But as we were topping of the reservoir several times during the bleeding process, I found that the rubber seal would create a suction and I would have to reform it before putting it back on. Also the pedel became firmer as we were bleeding the brakes. Were as before it didn't do that. I do have brake pedel now, but still a bit spongy unless I pump it once. So I''m going to bleed the brakes again.
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Old 07-04-2009, 08:58 AM
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