Panic Braking

Hi Bill,

I am glad everything turned out ok for your close call!

Removing the stock proportioning valve will allow more pressure to be delivered to the front brakes. If your front brake are in order, they should theoretical lock up together. If one is always locking before the other then that should be looked into.

With the stock proportioning valve removed and no other changes it is possible the problem could be worse. There is a lot of differing opinions on this topic. My suggestion would be to upgrade the rears AND remove the stock proportioning valve. You would not believe the improvement. There are quite a few forum members that have done this upgrade and are VERY happy with the results.

http://pantera.saccrestorations.net/sak41172.html

Take care, Scott

Glad you're OK my friend!

Yes ... x2 to what Scott wrote.

Remove the proportioning valve, replace the front disks with ventillated disks, and install rear brakes with more piston & pad area.

And find out why the right front is locking up before the left.

-G

lastpushbutton, if your front locked up, DO NOT remove the proportioning valve. If you do, more brake power will go to the front, less to the rear, making your brake balance problem even worse!

I'm puzzled people think that the factory put in the proportioning valve to make the car brake less efficiently, it has a purpose.

Here's what you should do.
-Either keep brakes pretty stock and keep proportioning valve
or
-Buy entire brake set from a knowledgeable vendor, they will see to that you get good brake balance from their system. Some systems will have proportioning valves, some not, not important as long as the whole system is balanced

All that said, if only one front wheel locked up, look at the other front wheel, is a caliper piston stuck? Brake pads gotten hard like glass? Fluid leak? Maybe a new set of pads all around?

Hope this helps, and drive carefully

Thanks All, After I cleaned out my underwear I went back to the street on a safe road and did a couple of panic stops. The first one both front locked and smoked the tires, but the car keeps going forward and straight. I did some more, and the key is not to lock them up. A controlled pressure on the pedal and it dives down in front and stops straight. It is just hard to remove some of your foot pressure once you committed to jumping on the panic action. It is about time for some new front tires too. I'm going to keep Scott's rear upgrade in mind. Bill 1362

One of the biggest problems with Pantera braking isn't even a brake issue; it's a suspension issue. As there isn't any anti-dive designed into the front suspension, hard braking causes the front end to "dive", which has the effect of transferring more weight (load) onto the front tires, making matters even worse. Therefore, if you put better (stiffer) shock absorbers and springs on the car, it reduces the "nose dive" and weight transfer that occurs during heavy braking. It will also give you better overall control during heavy braking.

As far as the pressure reducing valve in the front brake circuit is concerned, DeTomaso put it there to balance the front/rear braking pressure. Only remove it if you install larger calipers on the rear or install new calipers all around (in which case you should install an adjustable proportioning valve in the rear circuit).

Sure, some people remove the pressure reducing valve from the front circuit and say that it improved their braking but what they're talking about is braking during normal driving. Removing the valve has the effect of reducing the amount of brake pedal pressure required to slow down or stop the car and also gives the brake pedal a less "mushy" feel. Unfortunately, removing the valve upsets the front/rear brake balance which makes things worse in a panic stop situation, as the front brakes will lock-up sooner than if the valve was still there.

quote:

One of the biggest problems with Pantera braking isn't even a brake issue; it's a suspension issue

When the problem with the undersized rear brakes is corrected, the nose diving under braking is greatly reduced.

Bill when I first got my Pantera I had the same problem. Braking was scary. Fronts would lock and the car would skid a mile. I was afraid I would rear end some one.

I however have the dual MC. Several things on my car were put together but never adjusted. Timing, carb, etc.

I began moving the brake bias to the rear. I made adjustments then tore up the neighborhood; which I am sure was appreciated.

Once I found the spot the rears locked up first I slowly moved it back to it was barely front biased.

Once I completed the adjustment the braking would throw me into the windshield. The difference was scary. The rears actually help pull down on the fronts making them all work better when balance is correct.

On a side note, watching a show on performance cars on speed which attended Sema. They did several events to show they were not just show cars. One was the quickest 0-100-0. The car that won was a Cobra. What was funny was he was obviously slightly rear brake bias. Every time he stopped he ended up sideways.

quote:

hard braking causes the front end to "dive", which has the effect of transferring more weight (load) onto the front tires, making matters even worse

While I agree on the rest of David's post, I think this part is incorrect. When more weight moves to the front tires, it's actually harder for them to lock up, with all the weight on them pressing them into the asphalt. So if that weight transfer didn't happen, the fronts would lock up even earlier.

That's why a car with 4 equal brakes on 4 same size tires always ends up locking the rears, because the weight transfer gives more weight to the fronts and less to the rears, and the rears then easily lock up.

Interesting about the Cobra as well, the ideal braking car locks up all 4 wheels at the same time. But the balance changes during the braking, and maybe the Cobra owner figured out that just locking the rears just before stopping gives the best brake balance during the whole stopping effort. Not recommended for the street though...

For those interested I can tell you that I changed all my braking to a Pantera Performance/Quella kit this winter. 4 Willwood calipers, new discs in front, kept the rear discs, + new handbrake set up. It stops on a dime now, and doesn't lock up until maybe the last 2 feet (front). They work so fine I now have a problem with fuel from the secondary bowl sloshing into the engine when braking, will realign carb this winter.

I think the Cobra owner had a very close to an ideal balance but he was just slightly rear bias. I think if he tweaked the bias forward he still would of had the braking but would have been able to keep it straight.

THe basic problem with the factory non-adjustable brake proportioning valve is, it was designed to work with 185-70 x 15" belted bias front tires, and 205-70 x 15 rears. If you've changed ANYTHING- wheel size, tire width, brake pad compound etc, you are out of calibration of the stock system. Remove it. The part was apparently only added because Ford was panic-stricken at possible liability from selling high powered mid-engined cars to rookie drivers. Time has shown a proportioning valve of any kind is not needed short of pro racing or wholesale changes to the entire system.

A single locking caliper is often a stuck piston (or 2). There are rebuild kits for the calipers but they consist only of a square o-ring and a dust boot for each piston, and a stuck piston only need removal, scotch-brite polishing and careful reassembly. What happens is, owners simply will not change brake (or clutch) fluids yearly to get rid of absorbed water. Water plus heat from braking plus time generates varnish on everything, but the caliper pistons are moveable so they stick. Go to Mike Daily's giant website www.thepanteraplace.com for directions on doing this extremely messy but cheap cleanup. Incidently, the caliper pistons are chrome plated mild steel and eventually, the water will get under the plating and pit the piston. This then tears the seal, causing a leak. While a rebuild kit is cheap and has new seals, replacement pistons are completely unavailable. So the pitted piston tears the new seal too. CHANGE YOUR FLUIDS, PEOPLE!

Bill,

If only one side up front locked up, it doesn't matter what you do with proportioning valves and rear brakes, you still have a problem with one of your front calipers. Pull them apart and rebuild them! As Jack mentioned, there are inexpensive kits to do this.

Stock caliper rebuild article and videos linked here:
http://www.poca.com/index.php/...ront-caliper-rebuild

Some replacement stainless brake pistons are available. John Farrell had all my sizes in stock and provided the seal kit. They also have bleed nipples, pre-bent lines for the calipers etc.
John Farrell
Their website now looks horrible.

Thanks, Bdud- their website is useable and its good info. I no longer use stock calipers front or rear, but I did lose a chrome-plated piston in one aluminum 911-S caliper I have mounted on the rear of our Pantera. No replacements that I (or Pelican Parts) could find so I made a set of duplicates out of 304-ss in my shop. Not a bad job, but next time, I can recommend the e-store.