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  #31 (permalink)  
Old 01-20-2013, 05:01 PM
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Hers's the deal...Typically a kit purchased for a disc/drum combo will come with a 1 1/8" master cylinder as you don't need as much line pressure with that combo.

If the kit came with a combination valve it will be incorrect with a disc/disc system because of the 10lb residual pressure valve going to the rear brakes and the metering portion will be wrong. It sounds like you had a stand-alone residual pressure valve, and in that case you should have switched the 10lb for a 2lb. The 2lb check valve keeps the pads from backing away from the rotor when you are not pressing the brake pedal. Also make sure they are installed in the proper direction.

With your booster, a 1" bore master cylinder with a 2lb check valve in the line to the front brakes and another in the line to the rear brakes along with an adjustable proportioning valve, (or the proper combination valve) will give you good brake action. I will assume that you haven' modified the brake pedal assembly as it came from the manufacturer.

Does the master cylinder you are using have a deep (about 1") depression in the rear of the piston, or a shallow one (about 1/4")? In most cases you need the shallow one with a power brake booster. Again, a photo showing the unit and the piston would be most helpful.

Lastly, what type of calipers are you using on the rear?

If we beat on this long enough it will eventually give in and work for you!

Andy

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  #32 (permalink)  
Old 01-20-2013, 05:06 PM
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That is a very common master cylinder. They came installed on 1982 Corvettes if I remember correctly. They are available in 1 1/8" and 1" bores, but I don't think they came in 1 1/16".

With the master cylinder bolted up to the booster, how far can you pust the rod on the pedal side of the booster before you feel it compressing the master cylinder piston?
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Old 01-20-2013, 05:11 PM
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Quote:
Originally Posted by chevyrestore View Post
this link is for the same master cylinder Classic Car and Truck Brake, Steering and Suspension Parts

It may or may not say disc disc or disc drum but when I bought it I told them disc drum and all they said was I would either use it as is for disc disc or add the inline valve for disc drum.

As for the booster, I have the adjuster nut on the booster turned all the way in and it feels like it is just barely touching the master when I bolt up the master to it. The pushrod between the master and booster is non adjustable.
When you say you have the adjuster nut on the booster turned all the way in, which nut are you talking about? Is it the pushrod that connects to the pedal?
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Old 01-20-2013, 05:16 PM
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The nut I am talking about is the small 8mm or so head on the booster that the master cylinder pushrod sits on. I cant push the pedal and feel the master cylinder at the same time so ill have to wait on that one until I get a helper. Honestly I feel like the booster is already touching the pushrod in the master when its bolted up.

As for the valves all I have is the hard brake lines going into the correct prop valve as per CPP's hookup diagram. I verified that the prop valve is for a disc disc setup, they did not say to use any additional valves. Not sure what you are talking about as far as the depression in the MC but I uploaded a few pics here.
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Old 01-20-2013, 05:17 PM
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dont know if the images worked but heres a link to the gallery

Postimage.org / gallery - IMG 0892, IMG 0893, IMG 0894, IMG 0895, IMG 0896
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  #36 (permalink)  
Old 01-20-2013, 05:50 PM
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Interesting...

What it looks like you have is a manual brake master cylinder with an insert installed to take up the space to the booster pushrod. Not a problem, but I haven't seen that before.

You also have a combination valve, and if I understand you correctly that is the same one that you used when it was disc/drum correct? If so, that is the wrong unit for disc/disc. Did you remove the drum brake check valve out of the combination valve, out of the master cylinder (some masters have them built in) or was it an inline valve?

What I would do is this. Disconnect your brake pedal from the booster so it isn't pushing against it at all. Put that spacer into the master cylinder, lengthen the pushrod coming out of the booster quite a bit. Then, slide the master onto the booster and you should feel the piston hit the pushrod. If so, shorten the booster pushrod and retest until you can just slide the master onto the booster without feeling resistance, then shorten it about 1/2 turn more. That way you can be sure the booster isn't preloading the master, and that there isn't too much clearace. Bolt on the master cylinder to the booster. Then, adjust the pedal pushrod until you get the pedal height you want and tighten the jam nut.

Now is where it gets interesting. If you like, bleed and test the system and see if it is any better. If not, remove the combination valve and set it aside. Install a 2lb check valve, one in the front lines near the master cylinder, and one in the rear line along with an adjustable proportioning valve in the rear line, bleed and retest. I think then things will be much better.

I still would like to know what kind of calipers you have on the rear axle.
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Old 01-20-2013, 07:58 PM
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the rear end is from a 93 camaro with the stock calipers, just verified the pistons move freely and put on brand new pads and rotors, no change in braking.

What insert are you talking about? If its the 3rd pic on the gallery thats what CPP calls the master cylinder pushrod (between the master and booster)

When it had rear drums it did NOT have the prop valve, just a residual valve inline going to the rears, when I switched to disc all I did was remove the inline residual valve and add the disc disc prop valve, used same master cylinder as per CPP's directions (although I cant guarantee the guy that gave me the advise on reusing the master was all that bright).
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  #38 (permalink)  
Old 01-20-2013, 09:21 PM
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That "master cylinder pushrod" is just a filler that company makes so you can use a manual master cylinder with a power brake booster. Since you can still adjust the pushrod in the booster, my technique for adjusting the clearance between the master and the booster is still valid.

Since the combination valve is for a disc/disc setup, you should be okay there. One other little quick check is to make sure there is no residual pressure check valve in the master cylinder itself. Take a small allen wrench or drill bit and put it into the fittings on the master where the brake lines attach. If there is a check valve, the tool will only go in about 1/8" past the seat that the brake line seals on. If there is no check valve, it will go in about 1/2" or a little more. You are probably okay there, it is just good to check.

Make sure that if there is a way to adjust the parking brake on those rear calipers that you adjust them up snug.
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Old 01-20-2013, 09:28 PM
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one side of the MC has 2 ports that are plugged with allen plugs, the other side has 2 ports that are occupied by the prop valve, do I need to check all 4 or only the 2 being used?

Ill adjust the booster tomorrow when its light out, if there is no internal valving like you said would this be the same as a disc disc MC or would it be beneficial to get a true disc disc MC?

The rear calipers do have an adjustment for the ebrake but its a weird setup, There is a small hydraulic piston that the brake pedal uses to push the pads into the rotor, then there is a bigger ebrake piston thats mechanical around the hydraulic piston (basically a piston inside of a piston), from what I can tell even if the ebrake was fully out of adjustment the hydraulic piston would still push out the pads and be in contact just as much as if it were adjusted.

I dont have ebrake cables connected because its a huge job to add that right now, is it possible this is a problem? I showed a GM tech that works with me and he said it looks like it wouldnt affect the hydraulic portion of the caliper and shouldnt be needed to operate the pedal properly.

I remember when putting in these brake lines that there were adapters in the MC, I tried to take those off and put the lines in by themselves and it went WAY into the cylinder so I put the adapters back, I guess that means there arent any internal valves?
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  #40 (permalink)  
Old 01-20-2013, 09:38 PM
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heres the alldata info I have on the rear caliper parking brake adjustments

Postimage.org / gallery - 42189419, 56531321
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  #41 (permalink)  
Old 01-20-2013, 09:43 PM
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You only need to check the ports that you are using. Having that check valve in the master when you don't need it won't make for hard braking, it will just make the pads drag on the rotors. It is good to check for it. If you find one, there is a way to take them out. Just let me know and I can talk you through that.

The lack of the check valve, and large reservoirs are the charactersitics of a disc/disc master cylinder, so if there are no check valves that master cylinder is fine to use.

It is possible that if the emergency brake is not adjusted properly it could reduce braking performance. I would do a GOOGLE search for those calipers and see what others have to say. The calipers on the 9" Ford rear axles out of the Lincoln Versailles are famous for that problem. Unless the parking brake is adjusted up tight, you will never have good rear brakes.

Keep us posted on your progress.

P.S. That combination valve looks pretty low to the ground. It isn't gonna drag on speed bumps or anything is it?
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Old 01-20-2013, 09:47 PM
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no on the Prop valve being close to the ground, its pretty high up but the only way I could get a good pic was in a weird angle, it looks much lower than it actually is and I have a crossmember directly under it to protect all the brake components from bumps and rocks or anything that may try to come into contact with it.
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  #43 (permalink)  
Old 01-20-2013, 10:13 PM
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Very good. Just thought I would ask.

Once you have the booster and master cyl set up properly, we can get into the bleeding process (that is brake bleeding, not human bleeding!).

Keep us posted...
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Old 01-20-2013, 10:15 PM
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Thanks will do. I already bled the brakes properly 2 times around to verify no air (yes the correct way farthest from the master to the closest)

I didnt need to crack the lines to pull the master back for the pics so ill do what I can to adjust the rears manually and the adjustment of the booster and give it a shot.
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Old 01-20-2013, 11:22 PM
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What I am really interested in once it is all put together is how much fluid volume you are getting at different points in the system. Do you get a real strong shot of fluid at all the calipers when you are bleeding them? Sometimes the front will have strong volume and the rears, not so much. There are different reasons for this that we can talk about if necessary.

Good luck!
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