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    Results 21 to 22 of 22
    1. #21
      Join Date
      Feb 2006
      Location
      Houston, TX
      Posts
      33
      Country Flag: United States
      Quote Originally Posted by ULTM8Z View Post
      Understood. But if I had a short pushrod, it seems to me that I would expect to see zero resistance on the pedal during that 3/4" of travel. And since without the pedal return spring installed, there would be no mechanism to force the pedal back to the neutral position when I let go. As it stands, there is some minimal amount of noticeable resistance and the pedal does return to neutral each time.

      I also did measure and double check the pushrod length when I put it in, so it seems unlikely to me that the I have excessive clearance in there at this point.

      Though, I can certainly check it again during the MC and prop valve swap. Won't know until after 1/9 since the MC was on back order at Summit.
      You can test your current master cylinder to see if it holds pressure and if it is still good. No use throwing good money after bad if your master cylinder is still good. I shouldn't matter how old it is, it is either holding pressure or its not.

      If you remove the lines from the ports of your current master cylinder and plug them with line plugs, your pedal should become rock hard with little movement. MAKE SURE THE BRAKE FLUID DOES NOT GET ON YOUR PAINT OR HEADERS. I would test the brake pedal movement and hardness when the car is running so the vacuum booster is working and applying pressure. If there is substantial movement, I would say your master cylinder is bad or there is air in it. If it holds pressure with little movement in the pedal, hold the pedal down for 45 seconds, while the car is running. If the pedal stays high and firm, then your master cylinder should be good. If it sinks to the floor over the 45 seconds, then your master is bad.

      Usually, a step bore master cylinder will not fit other vacuum booster because the housing diameter under the mounting flange is too large (a little under 2") to fit inside a normal vacuum booster. The step bore master cylinder bore usually starts with around 1-3/8" bore for the mid size 80s cars/S10 pickups and a little larger for the full size cars and 1/2 ton trucks (1.5+"). The primary pressure bore size of the mid size GM cars and s10 pickups are 24mm.

      The step bore master cylinder's "step" function is only used on the front brakes. The rear brakes use the smaller pressure bore 100% of the time.

      The step bore master cylinder's "step" function has a 100lb bypass valve build in. Once the pressure in the large bore reaches 100ftlb, then then the fluid bypasses to the smaller bore giving you higher line pressures and caliper clamping forces. Like said above, it was used for LOW drag calipers. LOW drag calipers needed the extra volume to get the pad back up against the rotor, once the pad was against the rotor, the master cylinder transitions to the smaller bore to apply the pressure.

      Also remember that the GM master cylinder bolt pattern is wider than a MOPAR or FORD master cylinder bolt pattern. If your current master cylinder is a GM based master cylinder, it should work with your booster. If not, it may not bolt to your current booster. The MOPAR and Ford master cylinders share the same bolt pattern, but the mounting holes in the MOPAR master cylinder are usually smaller as are the studs on a mopar vacuum boosters.

      Usually, most GM master cylinders have a shallow hole (more like dimple) on the end of the piston that the push rod will be centered on. A mopar and ford master cylinder usually will have a deeper hole on the end of the piston. The hole in a mopar master cylinder piston is usually shallower and narrower than a ford's master cylinder.

      I believe the S10 master cylinder listed above puts the outlets of the master cylinder on the left hand side and they are the normal GM outlet sizes of 1/2-20 inverted flare rear port and 9/16-18 inverted flare front port. This master cylinder comes from a 1998 and up right hand drive S10. All other S10 master cylinder from 1998 and up will have the outlets on the right hand side and the outlet sizes are both 1/2-20 inverted flare. All 1998 and up S10 should all have a 1.0" bore master cylinder. These are normal, NON step bore master cylinders.

      If you can fit a step bore master cylinder on your current booster and your booster mounts your master cylinder at an angle, go with the 1982-1988 and up GM mid size (g-body) master cylinder as the reservoir is made to mount on an angle. The outlets are 1/2-20 and 9/16-18. It has a 24mm pressure bore

      If you can fit a step bore master cylinder on your current booster and your booster mounts your master cylinder is level with the ground, go with the 1982-1997 and up s10 master cylinder as the reservoir is made to mount level to the ground. The outlets are 1/2-20 and 9/16-18. It has a 24mm pressure bore.
      David Schultz
      MalibuDave
      www.manualbrakes.com

    2. #22
      Join Date
      Jan 2006
      Posts
      385
      Country Flag: United States
      Just to update this thread...

      I had read that you need to engage the parking brake regularly to keep the rear calipers adjusted to the rotor.

      So ended up doing a deep dive inspection on the rear brakes...



      It's a little hard to describe in words and I didn't take pictures unfortunately, but the fix seemed to have improved the braking quite a bit, and now with the rear wheels off the ground, the rear brakes stop the rear wheels immediately.

      Any rate, what I found was the parking brake cable housing has a termination flange at the caliper where the retaining clip can be installed in two different locations as it attaches to the bracket on the caliper. One of the locations allows the flange to protrude too far past the bracket, such that when the parking brake is engaged, the eyelet on the cable bottoms out the flange (i.e., there isn't enough cable travel to fully engage the parking brake mechanism on the calipers no matter how far your push the parking brake pedal or adjust the cable tention hook under the chassis). I had the clip installed in the incorrect location.

      I moved the clip to the other location which moved the cable termination flange further away from the parking brake lever that the eyelet hooks to. This gave a lot more cable movement to pull on the caliper parking brake lever. I then cycled the parking brake on off about 25 times and then took the car for a drive and noticed the improvement.

      Basically it no longer feels like something is wrong with the system. It actually feels a little better than my friend's 1992 Corvette (I drove it several weeks ago for comparison purposes). I'm probably going to return the adjustable proportioning valve and new master to Summit as I don't anticipate getting benefits (if any) that are worth the money and hassle.

      But in any event, I would like some more initial bite though. So maybe I might look into some performance brake pads. Though I don't know if you can get higher performance brake pads without putting up with excessive noise?
      1971 Camaro
      GM HT383, MiniRam EFI, AFR heads
      "8-speed" trans (700R4 + Gear Vendors OD)


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