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A previous Pantera brakes thread got overly informative and so long that I can't remember what the most important points were.

I have a 1972 Pantera and a 1972 Corvette. I've owned the Pantera forever and the Vette for three years. The Pantera is like a new car, on the other hand the Corvette has been 'rode hard and put away wet' many times, but the Corvette brakes are still great and far, far better than the Pantera brakes.

There was much discussion concerning the proportioning valve being better out then in, and how newer larger tires will affect brake requirements.  I have 17/10 front wheels and 18/12 rear wheels, but the stock 11" rotors and calipers and stock proportioning valve. The pads are virtually new and the discs not worn or grooved.  The brake petal feels solid. Because I have Webers on the car, all my vacuum is supplied by an electric CVR vacuum pump that provides 20in of vacuum, I checked. 

Rather than installing a totally new, costly braking system, larger rotors and all, I'd like to start with new hydraulics, mainly the master cylinder and booster, and dispense with the proportioning valve.

Does this make sense? Any other cheaper ideas?



Thank you

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In what way are your Vette's brakes better than the Pantera's? You already have an aftermarket M/C. Why not just bypass the OEM pressure reducing valve and see if it feels better. You can always connect it back up if there's no improvement.

You have to wonder how many Pantera owners buy all new brakes when the only problem they really had was air bubbles trapped in the system!

@davidnunn posted:

In what way are your Vette's brakes better than the Pantera's? You already have an aftermarket M/C. Why not just bypass the OEM pressure reducing valve and see if it feels better. You can always connect it back up if there's no improvement.

You have to wonder how many Pantera owners buy all new brakes when the only problem they really had was air bubbles trapped in the system!

or a bad brakebooster (vacuum leak)

Simon

The brakes in my Corvette actually make me want to fall forward when stepping hard on the brake petal, you can feel them binding. I have to apply a GREAT DEAL more foot pressure when stepping on the Pantera brake petal to get similar results. If I stepped that hard on my corvette brake petal, I would lock up the brakes. When I manually switch off the vacuum pump, the results are typical of what you get when power brakes aren't functioning, so the booster is working, but maybe not well enough. I use a vacuum pump because of the Webers. Plumbing each runner creates some carb adjustment problems. However, there are times when I switch to a Holly carb and use engine vacuum, but the brakes are no better, and never were. When I bought the car forty-two years ago it had even more horsepower than it has now and I still remember my first panic stop.

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As I said before, try bypassing the pressure reducing valve in the front circuit.

A really thorough bleeding might help too. Years ago, one of our vendors told me, the secret to bleeding our front brakes was to dismount the calipers, then bleed them while turning them upside down and tapping on them with a hammer. If you try this, make sure you put a piece of wood between the pads that's approx. the same thickness as a rotor. He said our front calipers can trap air bubbles and no amount of bleeding, on the car, will ever get the air out.

Bob Byars used to sell a dual servo booster that (apparently) significantly reduced pedal effort. Unfortunately, I'm unaware of an alternate source. 

dont start engine , push brake pedal several times , push pedal and keep it pushed , start engine and the pedal must go deeper .

when it's not go deeper there is something wrong with the booster.

when engine running and  and when you push the brake pedal you must hear a light ,,slash"

you also can try to get vacuum with your mouth on the booster when there is no vacuum the booster is leak.

Simoin

ill03b

The part often called a proportioning valve is actually a Pressure Control Valve.  It is part #12 above.  It functions as a T and provides fluid to the left and right front brake calipers.  It is completely independent of the rear brakes.  It has a piston, a spring, and seals inside.  These valves are now fifty years old and most likely frozen.  Wilkinson explained to me that they tend to trap air and result in a spongy brake pedal.  He sells a brass T that eliminates it.

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P-valve, proportioning valve, pressure valve, call it what you will. Removing it with a tee will effectively disable the rear brakes. Yes, it is independent of the rear brakes. But what it does is Lower the front brake pressure thus causing increased REAR brake pressure at the same peddle pressure. This has been discussed 100’s of times and as a brake specialist, we have also tested all these configurations. The only time a tee should be used is if the rear brakes have been upgraded.

@zr1pantera posted:

P-valve, proportioning valve, pressure valve, call it what you will. Removing it with a tee will effectively disable the rear brakes. Yes, it is independent of the rear brakes. But what it does is Lower the front brake pressure thus causing increased REAR brake pressure at the same peddle pressure. This has been discussed 100’s of times and as a brake specialist, we have also tested all these configurations. The only time a tee should be used is if the rear brakes have been upgraded.

do you need always remove the P-valve when you have upgraded brakes ?

or can you use this P valve also on upgraded brakes  ?

there are rebuild kist for the Bonaldi pressure valve /proportion valves

www.musclecarresearch.com

Simon

Once the rears are upgraded, it is a must to remove the valve ( in most cases). Removing the valve gets you a free upgrade to the performance of the front brakes. With the combination of upgraded rear brakes, removing the valve is not an issue. The whole goal is to balance the system. The poor stock rear brakes do not balance well with the great front calipers that came stock. That’s why the valve was installed in the first place.

I have disassembled four of these valves.  Each one required a hammer and punch to drive the piston out.  And it took a lot pounding to get the piston out.  I cannot imagine any of these valves actuating after 50 years.  At best they are working as a tee.  Just about every original Pantera brake caliper piston is frozen at this point in time from what I have seen.  Why would this valve be exempt from freezing?

Simon, yes, if the rear brakes are upgraded, removing the valve is a must. I wouldn’t assume the valve is frozen. The key once the valve is removed is to test the brakes for balance in a safe place. You want to see where the front brakes lock compared to when the rear brakes lock. It is important to perform this check and obviously in a safe place. You want the fronts to lock first. If you have really good upgraded rear brakes and a functional p-valve still in the front system, it is possible that the rear’s could outperform the front’s. This would be bad and could lead to a spin during a panic stop.

I recall people doing this in the early '80's. The benefits were cost, ease of installation and it retained the OEM parking brake. The downside was weight. The bracket that mounts the OEM rear caliper is needlessly heavy. I remember people filling those brackets full of holes in order to reduce the weight. Things got complicated too, if you had larger than stock rotors. Nowadays, it seems like an impractical mod. when you can simply call Scott and buy a pair of 4 piston Wilwood calipers that are better in every way than doubling up on the OEM stuff.

although the brake pads are not the originals, that were fine until I changed them. I believe I bought the stock equivalent from PI, but don't recall an improvement in performance, as that's what I was hoping for.  All this talk would have been unnecessary if I hadn't driven that damn Ferrari, but now that I know what I'm missing, I hope to do better.

Reminds me of my first girlfriend. If I hadn't looked at other girls, I would have been very happy with her.

I think I have done all this…. Porterfield R4S pads (or is it RS-4), dual stock rear calipers (which I could inadvertently lock up before the fronts), replaced with SACC upgraded rear calipers, then a SACC Wilwood MC upgrade.

Finally got what I was looking for, but I haven’t really driven much else like my Pantera on the track, so hard for me to compare!

Rocky

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