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Discussion Starter · #1 ·
I am having a problem with my 48 chevy. I have 11" disk up front and drum in the rear. I have got all the air out of the lines but my problem is that my disk hit first way before the rears do. I have read about every thread on this, and still cant solve it. My power unit is on the firewall. Is there any type of valves that i need to install to solve this problem.. I really need some help.
 

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How did you adjust the rear brakes? Should snug them to take a slight drag on the drum.

You do want the fronts taking the majority of the brake force to minimize rearwheel lockup, have you actually driven the car to see?

Other thing I could think of is the MC may not be appropriate for you, i/e too small bore, or incorrect rod length.

You may very well need a 2lb resudual valve, what proportioning valve did you use?
 

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I don't think he needs an adjustablee proportioning valve for this particular problem, as they are used to decrease bias to the rear brakes, i've never hear of one being used to decraese bias to the front brakes.
 

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He needs residual valves 2 psi on the front and and 10 psi on the rear rear and a adjustable proportioning valve also. Speedway will have everything that you need.
 

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Discussion Starter · #7 · (Edited)
poncho62 said:
You need an adjustable proportioning valve.................Do you have a proportioning valve of any sort on it now?

No i do not. The diagrams i have seen show this located in the rear brake line, I dont see how this will help. I would think it would have to be going to the front disk so i can controll the flow to that area.It seems like im not getting fast enough pressure to the rear, and to fast at the front.Am i backwards on my thinking. And i have looked at many diagrams for disk and drum brakes. Maybe someone can make me understand this, or show me a correct diagram. I have thought of using a combination valve i saw on another website. Would this work for me.I have adjusted the rear brakes many times, i dont have any residual valves, as i thought these were used if my master was frame mounted.
 

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Mrwood said:
...my problem is that my disk hit first way before the rears do.

My power unit is on the firewall. Is there any type of valves that i need to install to solve this problem.. I really need some help.
To cure the front brake problem, you need a front metering valve and a 10lb. residual valve in the rear line.

The metering valve does not permit front brake application until the rear drums are about 30% energized. The rear residual valve keeps the shoes close to the drum for quicker application.

The proportioning valve prevents rear brake lockup on hard application. A pressure differential valve allows you to have a brake failure warning lamp and to limit pressure on a ruptured front or rear line.
 

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Discussion Starter · #9 ·
Does this mean i wont need the proportioning valve. Your idea sounds more like what i need, and just makes it sound more as to the problem im having. Do i need the 2lb residual valve to the front or just the 10lb to the rear. I think you may have the right setup for me.
 

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KULTULZ said:
To cure the front brake problem, you need a front metering valve and a 10lb. residual valve in the rear line.

The metering valve does not permit front brake application until the rear drums are about 30% energized. The rear residual valve keeps the shoes close to the drum for quicker application.

The proportioning valve prevents rear brake lockup on hard application. A pressure differential valve allows you to have a brake failure warning lamp and to limit pressure on a ruptured front or rear line.
A residual pressure valve only keeps the wheel cylinder from letting air leak by the rubber pucks on retraction of the shoes. The brake shoes rest on a stop so the residual valve doesn't keep the shoes close to the drum. Adjustment does. Also,the adjustable proportioning valve is only used to keep the rear brakes from locking up before the front. On all my cars I have the proportion valve adjusted all the way out so it does nothing to change the rear. Have you tried swapping the lines at the master cylinder? the line closest to pedal to rear. Or you still have some air in the rear. You can also change it to make rear come in faster with a smaller bore master cylnder. You'll have to draw that one out would take too long to explain. Think displacement of fluid. :D
 

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Mrwood said:
Does this mean i wont need the proportioning valve.
No. You need the PROP VALVE to prevent rear brake lockup due to vehicle weight/braking bias.

Your idea sounds more like what i need, and just makes it sound more as to the problem im having. Do i need the 2lb residual valve to the front or just the 10lb to the rear. I think you may have the right setup for me.
To correct the situation you are presently experiencing, you need the front metering valve on the front (disc) circuit and a 10lb residual valve on the rear (drum circuit).

2lb residual valves are only used in a vehicle if the master cylinder is below the level of the front/rear brake caliper/wheel cylinder.

snkbyt said:
KULTULZ said:
To cure the front brake problem, you need a front metering valve and a 10lb. residual valve in the rear line.

The metering valve does not permit front brake application until the rear drums are about 30% energized. The rear residual valve keeps the shoes close to the drum for quicker application.

The proportioning valve prevents rear brake lockup on hard application. A pressure differential valve allows you to have a brake failure warning lamp and to limit pressure on a ruptured front or rear line.
A residual pressure valve only keeps the wheel cylinder from letting air leak by the rubber pucks on retraction of the shoes. The brake shoes rest on a stop so the residual valve doesn't keep the shoes close to the drum. Adjustment does.
AGAIN. The 10lb residual is used on the rear circuit of a disc/drum setup to keep the brakes partially energized for quicker rear brake application. It also prevents cup collapse by not allowing the shoes to slam the wheel cylinder pistons upon application release. I do not know how many times I need to repeat this. Unless the system is plumbed correctly, it is just an invitation to getting someone hurt.

BEFORE giving out advice, please understand the theory you are trying to describe.
 

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Discussion Starter · #12 ·
What car can i get a used front metering valve that will work with the 1968 chevy power brake system im using, i got this off a pickup. New ones are out of my price range at this time.I almost had a Cadilac metering valve for $10.00 off of e-bay, but got outbid at the last minute.Any others that will work for me..
 

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From all that I have experienced in years of biulding streetrods. And never using a metering valve I can't tell you which to use. There are many Chev metering valves. Mitchell manuals will explain their purpose better than what is being done here. You do not need a residual pressure valve if the master cylinder is above the wheel cylinder and calipers height.(this is supported in streetrod mags and by Engineered Chassic Components ECC brakes, They also sell all these parts). You have something else going on and it has to do with either air in the rear or too big of a Master clinder bore or lines backwards. snkbyt OUT :rolleyes:
 

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Discussion Starter · #14 ·
I dont think the lines are wrong, as the two lines out of the master cyl are two different sizes so they can only hook up one way to the combination valve. The size of bore i cant answer, as i used the complete power brake unit out of a 1968 chevy pickup that was working fine, and just thought this would work on my project as i wanted to have the hanging brake and clutch pedals. I could have air in the rear lines yet, as the last time i bled the system i had good brakes for about two days, then started having problems again. I have checked for leaks and cant find any, everything to the rear is dry. I used the combination valve that came on the truck, and today i saw a rubber plug on the very forward end so i took it off. I dont know if this is some kind of adjustment for a metering valve or not, if so i dont know how it works or how to adjust.. These are about the only things i can tell you about my system.Maybe i just didnt get all the air out of the rear. Here is a photo of a valve that looks close to mine, but mine is just a bit different, as there is no rubber plug on this photo.
 

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WHOA!!!!!! Did I just see you were useing a "combination valve"???? Well that is just what it is !! The combination is it is a Metering valve and proportioning valve in ONE. So now sounds like an adjustment problem or AIR problem. THIS is the first time I see you were using a Combo Valve!!! Mr. Wood you agree???? Kultultz???
 

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OK now we're gett'n some where!!! When you bleed out the brakes have a partner or big vice grips or something (I have a tool that does this) push down on the button under the rubber to hold it down while being bled. That shuts off the fluid to tyhe back. Hold it down while bleeding til all air is out.
 

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Discussion Starter · #17 ·
snkbyt said:
WHOA!!!!!! Did I just see you were useing a "combination valve"???? Well that is just what it is !! The combination is it is a Metering valve and proportioning valve in ONE. So now sounds like an adjustment problem or AIR problem. THIS is the first time I see you were using a Combo Valve!!! Mr. Wood you agree???? Kultultz???


Ok, but how do i adjust the valve, and sorry i did not mention this valve sooner. Its just that around here where i live theres not to many that have any answers, or even know what im talking about. Its been people like you on this site that have gotten my dream car this far along, so if i dont explain things in the terms your use to you just have to forgive me.
 

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Discussion Starter · #19 ·
snkbyt, i tried to push down on the botton with vice grips, but it wont move. Im thinking i will need to replace this whole valve assembly as it may not be any good. So im kind of stuck on what to do. Thanks for all your help ok.
 

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I'm sorry. I lost track of this thread as I do not pay much attention to CHEV posts. Nothing personal.

If you have a combination valve from a disc/drum application, the metering valve will be included (a disc/disc comb. valave will not have a metering valve). The center section is the pressure differential valve and the rear section will be the proportioning valve (and this valve will be calibrated to brake/weight bias of the donor vehicle-not adjustable). The 10 lb residual valve will be included in either the master cylinder or combination valve outlet.

It sounds as if the metering valave portion is not working. If you have someone apply the brakes hard, you will see the pin move. If frozen, you will need to source a replacement from CHEV or source an overhaul kit.

I hope this simplifies it.
 

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