Pantera Brakes revisited

why do you have a electric vacuum pump ?

Simon

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.

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. 

I will try the reducing valve alternative but thought about replacing the booster as long as the system is open. The brakes feel petal feels hard, no softness from air bubbles.

check vacuum booster on leaks

Simon

How do typically do that?

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

Removing the p-valve with stock brakes will effectively disable the already poor rear brakes!!!

Is there a case where the p-valve with stock brakes may be doing too good a job and not letting the fronts share the work?

My rear wheels gather brake dust at a much faster rate than the fronts

I doubt it.

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.

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.

ZR1Pantera, thanks , on my project I have F+R Hurst airheart  brakes and was planned to use the Bonaldi valve , when the valve is a problem I can take out the pressure spring and keep my brakelines original.

what do you think of that ?

Simon

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.

Scott, thanks for the advice , the rear calipers are such as big as the front , when I will be make a test run/brake I will be warned.

It will take a few weeks before the first run , I build up a unfineshed project and was missing some parts.

And time flies.

Simon

When you upgrade the front and rear brakes, you would naturally put an adjustable proportioning valve in the rear line, so you can dial out excess rear braking. As Scott mentioned above, you NEVER want the rears to lock-up before the fronts.

VERY GOOD AND LOGICAL INFORMATION

Improving the Pantera's brakes, an inexhaustible subject.......

I understand that at the time it was fashionable to install two stock rear calipers per wheel; this solution is currently cheap because it is easy to find cheap original rear calipers. Has anyone here tried this and what do they think?

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.

This is off the hydraulic discussion, but are you using stock brake pads?

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.

You may do yourself a great sevice just by throwing the stock pads away and replacing them with aftermarket units , specifically from Porterfield. Hated my stock brakes until i did that upon recommendation of other members. Any one else here use the Porterfield R4-S and AP63 pads?

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

a little off topic, but I'll ask

could you see if the propertional valve is working by standing on the pedal and observe if the end of the valve moves.   If it is not moving (frozen), wouldn't it just be a "tee" anyway?

I cannot see this , because mine is dismantled.

Simon

You can point a camera at the end of the valve with the dust cap removed and record video to see if the piston moves when you stand on the pedal.

Can this proportional valve be opened without complete removal from the car?

maybe it should be removed for a rebuild?

You will need to take it out of the car for a rebuild.  I takes some effort to loosen the large nut and to drive out the piston if it is frozen.

Mike Drew posted this a few days ago on the email forum.

https://www.musclecarresearch....a-prop-valve-autopsy

I already post this here 11/7

Simon

you did. oops.