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Discussion Starter #1
I was wondering if anyone knew the port orientation of a 1990 Caprice master cylinder. I installed the cardone 50-104 master/booster on my 1980 El Camino. It has a quick performance 9" rear and standard disk brake option. The rear calipers are spec'd off the front calipers. It also has a disk/disk proportioning valve. After all of this it seems that the rear brakes out power the front. They lock up really quick, yet the car doesn't seem to slow down as it should. All the lines on the car are stock. I was planning on doing the Blazer front brake upgrade. But I'm not sure that will fix my issue. Any suggestions would be very appreciated.

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Yes, the Blazer front brakes will help a lot. LS1 or C5 front brakes would be even better.
One thing for sure is the Metric D154 calipers you have on the front now absolutely suck.
 

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Discussion Starter #3
While working on the RF wheel converting to the Blazer brakes, I obviously lost some fluid in the master cylinder and it is draining from the rear reservoir. That seems backwards to me. The problem I see is the ports have different threads. So I can't just swap them.

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Rear reservoir is front brakes and the front reservoir is rear brakes.
What's the model number of that master cylinder?
 

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Discussion Starter #5
I bought it as a kit with booster p/n cardone 50-104. So what your saying is it all looks correct?

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That's a step-bore master cylinder. They are designed for low-drag front calipers. Blazer calipers are not that type.
 

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Discussion Starter #7
Well I can't catch a brake. Every since the rear disk swap I've had horrible brakes with the rest of the components oe replacement. (Everything new except hard lines, also bench bled) I went through 2 boosters and 3 master cylinders before trying the Caprice upgrade supposedly worked on the g body platform. It improved pedal firmness but I now only have rear brakes. And with putting on the Blazer front brakes today I must be feeling the drag because it sounds and feels like a swarm of bees in the front. Do you know if the stock master will work with this booster, or do I need to replace both again with oe replacement? BTW thanks for all of your help.

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Discussion Starter #8
I guess I answered my own question. The oe master bolts up and work. I just have a really mushy pedal again and I still have horrible front braking.

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The stock master is a step bore too. Both masters will work with the Blazer brakes but probably aren't ideal.
The stock D154 calipers inherently feel mushy. The Caprice booster will make that inherent mushiness more apparent. Blazer calipers will feel a lot better.
Are you using a disc/disc proportioning valve?
 

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Discussion Starter #10
The Caprice master had the best pedal feel. It was as firm as my 01 Silverado. The stock equipment ( oe master, booster and front brakes) seems like the pedal never stops. I do have a pv4 disk/disk proportioning valve... I have been dealing with this for months now. I feel so defeated, all I want to do is enjoyed all the other labor I've invested in this thing. But I can't because I can't get the car to stop. I even sent it to a mechanic shop to have the brakes looked over and re bleed to make sure I didn't miss anything. And I got it back with the same mushy pedal that I sent it in with. ( And I've had them work on my other cars with positive results). What master cylinder and booster do you recommend with the Blazer front brakes?

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Keep your Caprice booster.
A straight bore 1" master that is a bolt-in is an ACDELCO 18M974. You can get online but you won't find it at a local auto parts store. Application is a right hand drive S10.
Another 1" straight bore master that fits is an ACDELCO 18M95. Application is for a 1980 Riviera w/ rear disc brakes. This one is more expensive and has a cast body instead of aluminum. Some people also prefer the screw cap on the 18M974.
 

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Btw, I meant the Caprice booster will make the mushiness with stock D154 calipers more apparent. But yes, the larger step-bore Caprice master will give you a more firm pedal but less braking power.
Keep the Caprice booster and get a 1" straight bore master and get your Blazer spindles and calipers installed. I believe you will be happy then as long as your front to rear braking balance is OK. It it isn't, you may need to go with an adjustable proportioning valve. Can I assume you already replaced your stock disc/drum proportioning valve with a disc/disc one?
 

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Discussion Starter #13
Let's see if I understand the differences in calipers and master cylinders first. From what I have found out last night is that there were 2 different calipers available for the 78-87 El Camino. GM had a low drag set up and a non drag set up. And the straight bore master is supposed to be used for the low drag calipers and the step bore is for the non drag calipers. The step bore masters that I have seen online appear to have a taller section closest to the booster to accommodate a valve for the extra pressure needed for the non drag front calipers. And the only way to tell if the remanufactured calipers that I have are low drag or non drag is to apply pressure and release, then measure the tolerance of release. So would I be safe to say that I first need to find out what calipers I have before buying another master cylinder? Does this all sound correct or did I misunderstand what I have read?

BTW yes I did switch over to a disk/disk proportioning valve.


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Other way around. Step bore is for low drag calipers.
Regardless, you will want a straight bore 1" master for your new Blazer brakes.
 

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Discussion Starter #15
So I now have the Blazer brakes on the front with all new hardware, the 1" bore master, and I still have the soft pedal and no front braking power. I done a few 60-0 and 40-0 brake test and it takes forever to stop and wants to lock up the rear tires. Just for grins and giggles I went in reverse as fast as I felt comfortable (possibly 40mph) and hit the brakes and stopped in a 1/4 of the distance and hurt my neck in the process, with no break of traction.

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Discussion Starter #17
I've gone through about 5 gallons of dot3 over the past 2 mo. I'm going to need a sponsor to chase down this air pocket.

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Put needle nose vise grips on the rear hose at the axle. With care you can block-off the rear and not damage the hose. Try the pedal and see it it firms up. If it does, then you got trouble in the rear brakes.
 

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Discussion Starter #20
Put needle nose vise grips on the rear hose at the axle. With care you can block-off the rear and not damage the hose. Try the pedal and see it it firms up. If it does, then you got trouble in the rear brakes.
I am unable to do that with braided lines. I don't understand how it could be the rear when they are the brakes that are engaging. It feels like the rear have 75% and the fronts have 25% power.

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