This is what I have: 72 Chevelle, Front Disc, Rear Drum, Combination valve, 11" Power booster, Vette style Master Cylinder with equal size resorviors, Every part of this system is brand new.

Question: While bleeding (Front OR Rear) ONLY the front resorvior needs to be refilled. The rear resorvior fluid level doesn't change. Is this normal? :confused: I always assumed that each resorvior was for a specific section of the system (Front and Rear)

i'll assume your not getting any fluid out the back when you try to bleed the system?
sounds like its plummed wrong or you have a bad prop valve.
any pics of how its plummed?

i'll assume your not getting any fluid out the back when you try to bleed the system?
sounds like its plummed wrong or you have a bad prop valve.
any pics of how its plummed?

I'm getting plenty of fluid out all bleeding ports at each wheel. From the front resorvior the line goes to the front top of the proportion valve (1/4" line) From the rear resorvior the line goes to the top rear of the proportion valve. (Larger line 5/16")

http://inlinethumb32.webshots.com/44703/2418156360100380351S500x500Q85.jpg (http://good-times.webshots.com/photo/2418156360100380351ylPJZC)

http://inlinethumb59.webshots.com/9338/2822292170100380351S500x500Q85.jpg (http://good-times.webshots.com/photo/2822292170100380351RrMgCn)

Yeah, that's a weird one, alright. I haven't heard that complaint before.

Got a turkey baster, or rubber bulb for suctioning snot out of a baby's nose?

Suck some fluid out of the rear reservoir, see if the front reservoir level drops as the rear reservoir rises.

If it does, I'd expect the master cylinder to be defective--transferring fluid from front reservoir to rear so they equalize.

If it does not--I'm not sure where to go. How is the combination valve plumbed?

Yeah, that's a weird one, alright. I haven't heard that complaint before.

Got a turkey baster, or rubber bulb for suctioning snot out of a baby's nose?

Suck some fluid out of the rear reservoir, see if the front reservoir level drops as the rear reservoir rises.

If it does, I'd expect the master cylinder to be defective--transferring fluid from front reservoir to rear so they equalize.

If it does not--I'm not sure where to go. How is the combination valve plumbed?

I had this happen with my other (New) Master!! Fluid would transfer from one resorvior to the other. Got another Master (Warrenty was still good) Same type (Vette Style) That issue went away with new master.

Combination valve is plumbed factory. The only thing I can think of is that I might have the lines at the master crossed??

That shouldn't make a difference though should it?

Both resoviors are the same size, unlike original master where on was larger than the other. This was originally front disc rear drum as well. Maybe this Vette style master works differently?? I'm not sure?? But the master is the only thing that is different than factory!!

I checked all my plumbing and it seems to be right. With a factory Master with different size resorviors, the larger resorvior is used for the front brakes, the smaller one for the rear brakes. Since both my resorviors are the same size, (Vette Style Master) it's don't really matter which is for the front or the rear brakes. As for the lines going from my Master to my Combination valve (PV2: Combination valve mounted on the frame below master: Front Disc, Rear Drum) I'm using the smaller line (1/4") to feed the front section of my combination valve and the larger line (5/16") to feed the rear section of my combination valve. I couldn't mess up this connection at the combination valve because there are two different size fittings at the valve that match the line fittings. This is the Combination Valve i'm using.

http://inlinethumb50.webshots.com/17329/2516130720100380351S500x500Q85.jpg (http://good-times.webshots.com/photo/2516130720100380351numIWr)

The port to the right of the light switch is the feed from the front resorvior of the master (Smaller line, larger fitting). The port to the right of that goes to the drivers front disc. the port on the bottom (not visible) goes to the passenger front disc. The port to the left of the light switch is the feed from the rear resorvior of the master (Larger line, smaller fitting). The port to the left of that (Large front side) goes to the brake line going to the rear drums. Now the only things I don't have are some residual valves that this company calls for. http://www.mbmbrakeboosters.com/Tech-Support/Typical-Brake-System-Configurations.html

This is the Master I'm using

http://inlinethumb42.webshots.com/19177/2514490740100380351S500x500Q85.jpg (http://good-times.webshots.com/photo/2514490740100380351mZezzY)

Sorry to go on and on but I can't figure out why only the one resorvior needs refilled with fluid when I bleed both the front and rear brakes???? I'm baffled!!! WHY !@#$

I'm not an expert by any means but a couple of gremlins I have bumped into are in master cylinders. Drums frt@rear manual, drums frt@rear power, power disc frt with rear drums. Each one takes a different master. To me its so easy to end up with the wrong style master.

Also if you just tickle, slightly depress the brake pedal an 1/8 to 1/4 inch, whichever reservoir displaces fluid first, is the reservoir used for the front brakes. Irregardless if that reservoir is the front or rear on the master. Also the proportioning valve has to be correct for the type of master that is in use. Just some info, maybe it will help get down the right rabbit trail to resolve your problem

This is the other post. This is my second master cylinder, both new. Could this master be bad as well? I can't think of anything else it could be.

you may need to shorten the rod a turn or two. increase your pedal free play a 1/4". i was told w/ the corvette master you cant have any pressure on it. im not sure if thats your problem but i would crawl under the dash and check it out. do you have the pedal return spring in place still? when i did my first swap, i disconected that when i moved the clevis down. very tough to reattach. brake lights stay on sometimes with out that spring in place. pedal might be keeping pressure on mastr, cyl. not allowing fluid release.

you may need to shorten the rod a turn or two. increase your pedal free play a 1/4". i was told w/ the corvette master you cant have any pressure on it. im not sure if thats your problem but i would crawl under the dash and check it out. do you have the pedal return spring in place still? when i did my first swap, i disconected that when i moved the clevis down. very tough to reattach. brake lights stay on sometimes with out that spring in place. pedal might be keeping pressure on mastr, cyl. not allowing fluid release.

Jacked up the car, wheels are free, wheels lock after 1/2 to 3/4" of brake pedal stroke. Everything returns smoothly and wheels are free again. Rod adjusted properly, never had a return spring. Car originally came with front disc rear drum power brakes. Everything looks and works pretty good. I haven't had it on the road yet so I can't tell 100% how good the brakes work. It baffles me "why ONLY the fluid in the front resorvior depletes when bleeding the front AND/OR rear brakes. Rear resorvior fluid level never goes down. When I bench bled the master, fluid purged from both ports properly. So both resorviors are pumping. I'm thinking that the proportional valve has a problem.

There are two--and only two--places where the fluid could transfer from the "front" reservoir to the "rear" brakes.

You could have a seal problem at the master cylinder.

You could have some kind of VERY UNUSUAL fluid transfer at the combination valve--in which case it's the safety switch, NOT the proportioning valve that's in question.

There are no other places the fluid could cross from the front brake hydraulic circuit to the rear brake hydraulic circuit. And since the fluid level in the reservoir for the rear brakes doesn't go down even though you're getting fluid out of the rear brake bleeder screws--you MUST be transferring fluid from the front brake reservoir into the hydraulic circuit for the rear brakes.

And, like I said--this is really uncommon.

I'd be really interested to know HOW you are bleeding the brakes. Pressure? Manual by stepping on the pedal? Gravity? Vacuum?

When you have a helper "tickle" the brake pedal, do you see a small geyser in each reservoir? Or just in the front reservoir?

There are two--and only two--places where the fluid could transfer from the "front" reservoir to the "rear" brakes.

You could have a seal problem at the master cylinder.

You could have some kind of VERY UNUSUAL fluid transfer at the combination valve--in which case it's the safety switch, NOT the proportioning valve that's in question.

There are no other places the fluid could cross from the front brake hydraulic circuit to the rear brake hydraulic circuit. And since the fluid level in the reservoir for the rear brakes doesn't go down even though you're getting fluid out of the rear brake bleeder screws--you MUST be transferring fluid from the front brake reservoir into the hydraulic circuit for the rear brakes.

And, like I said--this is really uncommon.

I'd be really interested to know HOW you are bleeding the brakes. Pressure? Manual by stepping on the pedal? Gravity? Vacuum?

When you have a helper "tickle" the brake pedal, do you see a small geyser in each reservoir? Or just in the front reservoir?

I am bleeding the brakes using a helper to "Pump" the brake pedal for me, while I bleed the brakes at each wheel.

In the morning, I'll have my helper "tickle" the brake pedal and I'll watch for the movement in each resorvior. If I just see the "geyser" in the front resorvior, does that mean I got another bad master?

So your saying that it's "Very unlikely" the the proportional valve is bad? I'm hoping so. The master is a lot easier to change then getting to and changing the proportional valve. :)

Does it hurt anything if the helper pumps the brake pedal too hard or allows the pedal to go all the way to the floor when bleeding??

This is my second new master. The first one was obviously bad when fluid actually transfered from one resorvior to the other. I got another new one (Same Style) the other day. Installed it and got this other issue.

Thanks for your input on this!! Thank you everyone as well. :thumbsup: I'll keep you updated on the progress. :beers:

There are two--and only two--places where the fluid could transfer from the "front" reservoir to the "rear" brakes.

You could have a seal problem at the master cylinder.

You could have some kind of VERY UNUSUAL fluid transfer at the combination valve--in which case it's the safety switch, NOT the proportioning valve that's in question.

There are no other places the fluid could cross from the front brake hydraulic circuit to the rear brake hydraulic circuit. And since the fluid level in the reservoir for the rear brakes doesn't go down even though you're getting fluid out of the rear brake bleeder screws--you MUST be transferring fluid from the front brake reservoir into the hydraulic circuit for the rear brakes.

And, like I said--this is really uncommon.

I'd be really interested to know HOW you are bleeding the brakes. Pressure? Manual by stepping on the pedal? Gravity? Vacuum?

When you have a helper "tickle" the brake pedal, do you see a small geyser in each reservoir? Or just in the front reservoir?

Well I persuaded my helper (Wife) to "Tickle" my pedal :eek: Then we went out to the garage to do it there as well. :D The "geyser" is only coming from the front resorvior. Does this mean another bad Master? Thanks Bob

bob- no offense meant but, fluid from one brake resavoir cannot transfer to the other resavoir. try gravity bleeding rear brakes- open rear brake bleeders and take off master cylinder top. in about 5-10 min check resavoir and im shure it will be lower . rear drum brakes with wheel cylinders flow less volumn of fluid and dont bleed as fast ( or as much brake fluid ) as front discs. since your brake pedal is good, i doubt any air is in the system. good luck.

The "geyser" is only coming from the front resorvior.
Means that the primary piston in the master cylinder isn't coming back to it's at-rest position--it's stuck too far forward, so it never uncovers the compensating port.

There are several possibilities.
1. Brake pedal isn't coming back to it's at-rest position; keeps pressure on the master cylinder.

2. Linkage from pedal to booster is too long.

3. Pushrod from booster to master cylinder is wrong length. A few of them are adjustable; most aren't. There are at least two different lengths of non-adjustable booster-to-master pushrods; one for use with a master cylinder primary piston having a deep counterbore; and one for use with the shallow counterbore. (I'm thinking it's a Delco brake system vs. Bendix brake system; but I can never remember which one is deep and which one is shallow.)

One way or another, your primary master cylinder piston is staying slightly applied. Fix that FIRST, and see if the bleeding problem disappears on it's own.

I'd consider sliding the master cylinder off the studs of the booster, leaving the brake tubing connected and secure. Tickle the primary piston with a wood dowel or Phillips screwdriver. See if you get the geyser in both reservoirs.

Don't spill the fluid...

Means that the primary piston in the master cylinder isn't coming back to it's at-rest position--it's stuck too far forward, so it never uncovers the compensating port.

There are several possibilities.
1. Brake pedal isn't coming back to it's at-rest position; keeps pressure on the master cylinder.

2. Linkage from pedal to booster is too long.

3. Pushrod from booster to master cylinder is wrong length. A few of them are adjustable; most aren't. There are at least two different lengths of non-adjustable booster-to-master pushrods; one for use with a master cylinder primary piston having a deep counterbore; and one for use with the shallow counterbore. (I'm thinking it's a Delco brake system vs. Bendix brake system; but I can never remember which one is deep and which one is shallow.)

One way or another, your primary master cylinder piston is staying slightly applied. Fix that FIRST, and see if the bleeding problem disappears on it's own.

I'd consider sliding the master cylinder off the studs of the booster, leaving the brake tubing connected and secure. Tickle the primary piston with a wood dowel or Phillips screwdriver. See if you get the geyser in both reservoirs.

Don't spill the fluid...


I actually spaced the master away from the booster by using 4 washers (3/8") on each booster stud, tightened nuts to securly hold master to booster. Now 100% knowing the booster pushrod is definately clearing the master pin. I removed the cover and tickled the brake pedal. I still have no movement in the rear resorvior.

I actually spaced the master away from the booster by using 4 washers (3/8") on each booster stud, tightened nuts to securly hold master to booster. Now 100% knowing the booster pushrod is definately clearing the master pin. I removed the cover and tickled the brake pedal. I still have no movement in the rear resorvior.
But you get the geyser in the front reservoir???

I don't know how this can be anything other than a defective master cylinder.

If this were in my driveway, I'd have the master back on the bench; I'd verify that the primary piston can return properly and isn't getting hung-up in the bore somehow; and once the piston was out, I'd poke a teeny-tiny drill bit or paper-clip wire into the compensating port to assure it isn't plugged.

Or you just throw it on the counter of the parts store and get another...
Less scientific, but probably faster 'n' easier.

But you get the geyser in the front reservoir???

I don't know how this can be anything other than a defective master cylinder.

If this were in my driveway, I'd have the master back on the bench; I'd verify that the primary piston can return properly and isn't getting hung-up in the bore somehow; and once the piston was out, I'd poke a teeny-tiny drill bit or paper-clip wire into the compensating port to assure it isn't plugged.

Or you just throw it on the counter of the parts store and get another...
Less scientific, but probably faster 'n' easier.

Yes I get the geyser in the front resorvior. The plunger seems that it's returned in the bore. Where is the compensating port? Is it the tiny hole in the resorvior?

Is it the tiny hole in the resorvior?
At the bottom, drilled from the reservoir into the cylinder.

You might also have a small bolt at the bottom of the front reservoir--it's not in all master cylinders. No need to mess with that unless you pull the pistons out.

At the bottom, drilled from the reservoir into the cylinder.

You might also have a small bolt at the bottom of the front reservoir--it's not in all master cylinders. No need to mess with that unless you pull the pistons out.

I have the master on the bench with the bleeding tubes hooked to it. I ran a small staple through the hole. When I tickly it slightly I do in fact get a very small geyser from the rear resorvior but not anything like the geyser from the front resorvior.

Means that the primary piston in the master cylinder isn't coming back to it's at-rest position--it's stuck too far forward, so it never uncovers the compensating port.

There are several possibilities.
1. Brake pedal isn't coming back to it's at-rest position; keeps pressure on the master cylinder.

2. Linkage from pedal to booster is too long.

3. Pushrod from booster to master cylinder is wrong length. A few of them are adjustable; most aren't. There are at least two different lengths of non-adjustable booster-to-master pushrods; one for use with a master cylinder primary piston having a deep counterbore; and one for use with the shallow counterbore. (I'm thinking it's a Delco brake system vs. Bendix brake system; but I can never remember which one is deep and which one is shallow.)

One way or another, your primary master cylinder piston is staying slightly applied. Fix that FIRST, and see if the bleeding problem disappears on it's own.

I'd consider sliding the master cylinder off the studs of the booster, leaving the brake tubing connected and secure. Tickle the primary piston with a wood dowel or Phillips screwdriver. See if you get the geyser in both reservoirs.

Don't spill the fluid...

:hurray: Thanks to your information and suggestions the fluid/brake problem is solved. Like you said, the master was not coming fully to the return position. I took the master apart, exercised and lubricated the seals. More importantly the booster pushrod was slighty keeping the master from returning as well. I spaced the master away from the booster (3 washers on each stud) abot 1/16 of an inch. BINGO now when I bleed the rear brakes the rear resorvior depletes fluid. Thanks again!! Bob :beers:

:hurray: Thanks to your information and suggestions the fluid/brake problem is solved. Like you said, the master was not coming fully to the return position. I took the master apart, exercised and lubricated the seals. More importantly the booster pushrod was slighty keeping the master from returning as well. I spaced the master away from the booster (3 washers on each stud) abot 1/16 of an inch. BINGO now when I bleed the rear brakes the rear resorvior depletes fluid. Thanks again!! Bob :beers:
So you've adjusted the booster pushrod and removed the three washers from the studs?

So you've adjusted the booster pushrod and removed the three washers from the studs?

No I left the washer spacers there between the booster and the master. Will it hurt anything to leave them there?Can you adjust that rod? My master came with 2 rods, one long and one short. I can only use the short one.

No I left the washer spacers there between the booster and the master. Will it hurt anything to leave them there?Can you adjust that rod? My master came with 2 rods, one long and one short. I can only use the short one.
The master should fit tight to the booster. If it won't there's something wrong; we just haven't found it yet.

I'd take another look at the pedal-to-booster adjustment. Maybe the master doesn't fully return because the booster can't fully return.

The master should fit tight to the booster. If it won't there's something wrong; we just haven't found it yet.

I'd take another look at the pedal-to-booster adjustment. Maybe the master doesn't fully return because the booster can't fully return.

OK I'll ckeck into it this wekend. Thanks :thumbsup:

The master should fit tight to the booster. If it won't there's something wrong; we just haven't found it yet.

I'd take another look at the pedal-to-booster adjustment. Maybe the master doesn't fully return because the booster can't fully return.

I removed the spacers and the problem is back again. :mad: The washers spaced the master from the booster just a hair over 1/8". The pin in the booster on the master side is non adjustable right? It seems to retract all the way, even with the brake pedal unhooked from the booster clevis.What is the next thing I shoud look for? Pedal to booster adjustment? I don't see where that will make a difference. Trim 1/8 inch off the master pin? :confused: