S10 front single calipers rear S10 blazer 2000 disc

[OldsStarfire]

I believe the recommended fix is a 4 wheel disc master cylinder out of a 79 Trans Am WS6 or corvette of the same age, that combined with an ajustable proportioning valve.

[67shovel]

I bumped up the master cylinder bore (1.25" I beleive) to the largest one that would still fit into my aftermarket small outside diameter power booster. The master cyl is from a 2002 F150 (e gads!). Also picked up and adjustable proportioning valve and replaced the factory saftey swith block. Pedal is firm now! Up on jack stands I can't hardly stop the rear wheels in gear! Pulled the rear center hose and have good flow to it. Now I'm pulling a caliper as I could hardy pump the piston out with it hanging in the air. Got to be swelled hoses or corroded calipers.

Update, just pulled one caliper, popped out piston. No corrosion, can blow thru brake hose, clean it with soap and water and reassembled using brake fuild. All back on car on jack stands, fire it up, put in gear and still can't stop the rear wheels from spinning while on stands It's got to be the master cylinder I guess. I didn't get a disc/disc MC as suggested and I guess that what I need to do next. I verified good fuild flow through the lines too

[hammerdown7]

Have you played with the adjustable proportioning valve?

Dick

[cosvega76]

I bumped up the master cylinder bore (1.25" I beleive) to the largest one that would still fit into my aftermarket small outside diameter power booster. The master cyl is from a 2002 F150 (e gads!). Also picked up and adjustable proportioning valve and replaced the factory saftey swith block. Pedal is firm now! Up on jack stands I can't hardly stop the rear wheels in gear! Pulled the rear center hose and have good flow to it. Now I'm pulling a caliper as I could hardy pump the piston out with it hanging in the air. Got to be swelled hoses or corroded calipers.

Update, just pulled one caliper, popped out piston. No corrosion, can blow thru brake hose, clean it with soap and water and reassembled using brake fuild. All back on car on jack stands, fire it up, put in gear and still can't stop the rear wheels from spinning while on stands It's got to be the master cylinder I guess. I didn't get a disc/disc MC as suggested and I guess that what I need to do next. I verified good fuild flow through the lines too

You went too large with the master cylinder bore, not you can't generate enough pressure with your foot without a booster. I'd recommend dropping down to a 15/16" or 1" master.

Chuck

[67shovel]

Got a booster. The pedal is real hard and to the top. Not the old two pump deal as before. Went to big a master clyinder ya think huh? I cranked the prop valve
all out for my best ..bad braking. It turned it in too. Turning it in I believe cuts the flow down. I apperciate you guys input cuz this is kicking my butt

[cosvega76]

Is that one of those 7" boosters? Single or dual diaphragm? I would have recommended a factory H-body booster, you may not get enough assist - especially if it is a single-diaphragm. How much idle vacuum do you have? You'll need at least 14-15 inches of vacuum for proper assist.

As far as the adjustable proportioning valve, all the adjustment changes is the "knee point" of the pressure. The way it works is the rear pressure tracks the same as the front until it reaches the knee point, then it doesn't increase as fast in proportion according to the rate engineered into the valve. Probably the lowest knee point you can adjust will be around 500-600 psi, which should still be enough to slow down the rear wheels in gear with them off the ground.


Chuck

[67shovel]

Chuck, I believe this is a dual diaphragm booster. I have another one that looks just like it that I had to disconnect on another project car since it was to powerful and manual brakes work fine on it (V8 Corvair). Maybe I should try swapping that one in? . I do have 15" of idle vacum. I believe the boosterr is working because the pedal moves down a little once the motor fires up.

[avewhtboy]

My experience with hard pedal has always been a bad booster.

I was having a conversation with a friend of mine last night about this, since I am in the middle of installing
a Blazer rear disc brake axle in my car, he mentioned that the difference between drum rear brake and
disc rear brake master cylinders is a check valve going to the rear wheels in a drum brake master. If you remove
that check valve you can turn your drum master into a disc master.

I suspect the F250 2002 had a disc rear axle? if not may want to check that out.

[67shovel]

My experience with hard pedal has always been a bad booster.

I was having a conversation with a friend of mine last night about this, since I am in the middle of installing
a Blazer rear disc brake axle in my car, he mentioned that the difference between drum rear brake and
disc rear brake master cylinders is a check valve going to the rear wheels in a drum brake master. If you remove
that check valve you can turn your drum master into a disc master.

I suspect the F250 2002 had a disc rear axle? if not may want to check that out.

My Ford Master has a device (1" hex x 1.25" roughly) screwed in to the rear port and after searching they said it was a proportioning valve. I took it off to "gut" it and found that it was just a straight hole through it, no valve. Does that make it a disc/disc M/C then? I hope as this is getting $$
The booster could be bad I pulled the vacume line off it last week and it was holding it's own vacume? Is that right? Might be that I used gas line and tubing for it vacum line and the gas line collasped. I have since replaced it with the correct type hose. I think my next more is swapping out to my other "Identical" power booster. I sorta stuck with these small boosters as I don't think a full size one would fit.

[avewhtboy]

My experience with hard pedal has always been a bad booster.

I was having a conversation with a friend of mine last night about this, since I am in the middle of installing
a Blazer rear disc brake axle in my car, he mentioned that the difference between drum rear brake and
disc rear brake master cylinders is a check valve going to the rear wheels in a drum brake master. If you remove
that check valve you can turn your drum master into a disc master.

I suspect the F250 2002 had a disc rear axle? if not may want to check that out.

My Ford Master has a device (1" hex x 1.25" roughly) screwed in to the rear port and after searching they said it was a proportioning valve. I took it off to "gut" it and found that it was just a straight hole through it, no valve. Does that make it a disc/disc M/C then? I hope as this is getting $$
The booster could be bad I pulled the vacume line off it last week and it was holding it's own vacume? Is that right? Might be that I used gas line and tubing for it vacum line and the gas line collasped. I have since replaced it with the correct type hose. I think my next more is swapping out to my other "Identical" power booster. I sorta stuck with these small boosters as I don't think a full size one would fit.

My "friend" was a service writer at a Ford dealership for about 25 years, So I suspect that may be a check valve? Basically it lets fluid run from master cylinder but
not back from the disc or drum. A disc brake needs to be able to return that fluid to the master cylinder where a drum brake does not. That's how it was explained
to me.

To check the booster you should be able to just pull a vacuum on it and if it hold it's good as far as I am aware. Unless there's some sort of mechanical
problem inside the booster. Might want to check the brake actuator rods to make sure all is well.

The power brake pedal and the manual brake pedal have the pin in a different spot on the pedal if you don't have the rod on the right pin it can cause interference
at the firewall as well.

Good Luck I have been chasing my poor braking situation as well hope to get four wheel lockup ability soon !!!

[67shovel]

I'll check the pedal pin location. Good idea. I do know that this device on the ford master cylinder rear output is not a propotioning valve cause I can pass an 1/8" drill bit right through it. It appears to be no more than a spacer.
I dunno, thinking the master cylinder is to big as suggested earlier.

[waybad]

more pictures of that corvair with the vett wheels?

[67shovel]

Here's a few more: This is a 65 Corvair Corsa w/ a "crown" conversion. These showed up a little before the time the Vega's were getting V8's stuffed in them. They have their own website called "V8registry" and it's the same format as this H body site. Just like here, they are good people willing to help you out and help you locate parts. The Corown kit was an early kit and they have all kinds of converted corvairs there too. Now they are sticking Corvette C5 or 6 rear ends in them now too and make good road racers in any form.
And just like my Vega I'm having hyd problems with it too. Hyd throw out bearing! Pretty much figured out that I could screw up my own hanging party!

[hammerdown7]

Corvair looks great. I had put a Cosworth in a Fiero and ended up giving up because of continual problems with the hydraulic clutch. I kept loosing the pedal, bled every which way, changed all the parts with no lasting luck.

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[waybad]

Thanks 67!! wicked cars for sure!!