Reply to "Pantera Brake Improvements"

quote:
Originally posted by Cowboy from Hell:

Growing population sounds like a nice way to give more weight to the opinion of a few people.

It appears this "growing population" advocates retention of the proportioning valve based on a theory. A "real" problem caused by its removal was not mentioned, the theory is leaving it in results in better balance. I'd like to rephrase that theory if I may. "The rear brakes are inadequate, so we should reduce the effectiveness of the front brakes so they are more balanced with the rears". But guys ... making the front brakes less powerful means less braking performance! Which is better, two inadequate brakes, or four inadequate brakes?

Removing the proportioning valve measurably shortens the braking distances. That's why owners have been doing it for 40 years. Control while braking is not compromised either. It does not create a two wheel braking situation, the pressure to the rear circuit doesn't change, and the weight on the rear wheels remains the same. The rears are braking just as hard either way. If balanced braking means longer braking distances, then I choose more powerful braking over better balanced braking.

Reducing the power of the front circuit to "balance" the braking front to rear is going about it the wrong way! Wouldn't it be better to increase the power of the rear circuit? I may well agree with Chris that a rear brake upgrade will improve the Pantera's braking performance, but I am not in agreement that removal of the proportioning valve without a rear brake upgrade is a bad idea. I can't go that far Chris.

-G


George,

It's not theory--it's fact.

The stock proportioning valve is actually a pressure-reduction valve. By having different-sized pistons inside, it takes X psi input and delivers Y psi (lower) output.

You advocate taking the thing out with the argument that people have been doing it for a long time. Well, if you look at the back issues of PI and the POCA newsletter from the 1970s and 1980s, you'll see a LOT of (shall we say highly questionable) things that people did a long time ago. Just because it was done a long time ago, doesn't mean it was smart.

With a given amount of pedal pressure, the front and rear brakes will deliver a given amount of stopping performance. If you sabotage the system by removing the proportioning valve (for effectively, that's what it is, unless you've done something else too, such as adding a second rear caliper to each side, which was commonly done at the same time back in the day, and apparently works, from the one example I've driven with that setup), then the front brakes will become more effective with a given amount of pedal pressure. To the (people who only drive their cars gently, and never have to make a panic stop or use the brakes at anywhere near max effectiveness), that sounds like an improvement. But anybody who actually drives his Pantera hard (meaning using the brakes at or close to their design limit) will soon discover that the front brakes are now overly sensitive. Simply put, they will lock prematurely, relative to the rears. Whereas before, it took a healthy amount of pedal pressure to generate wheel lock, now a much lower amount will generate front-wheel lock, with virtually no performance at all coming from the rear brakes. Once the front brakes lock, you've lost all steering control, and you really can't apply any further braking to try to get the rear brakes to stop you, because now you're skidding. Don't forget, a skidding tire increases stopping distances by about 25% over a max-performing braking tire.

Do you even know how the proportioning valve came into being? When the Pantera prototypes were first undergoing testing (which was performed in the USA by a lab in Orange County, by the way--I have a copy of the full report), they suffered from too much front braking, and stopping distances were abysmal. While the proper solution would have been to install better rear calipers, the band-aid fix was to go for a pressure-reduction system for the fronts. Once that was implemented, although pedal pressure was a bit higher, stopping distances were a lot shorter.

And ultimately, that should be the ONLY goal.

I would agree that IF the rear calipers are upgraded and the front ones are left alone, the new system would probably benefit from the removal of the proportioning valve. Only testing would determine the ultimate truth of that however.

I would also agree that anybody who wants to do any really serious driving in a Pantera would be wise to toss the entire braking system over the hedge, and start over with any of the various options provided by the Pantera vendors. As long as the braking SYSTEM is fully engineered, and balanced, and not just a hodge-podge of spiffy-looking components randomly thrown together, then a proportioning valve would be rendered moot and unnecessary altogether.

My Pantera has a complete Wilwood-based system from Dennis Quella, with no proportioning valve, and the braking performance is light-years better than stock. However, that performance isn't really measured on the first stop. On the first stop, a bone-stock Pantera in proper working order (well, one with the pads warmed up) will stop just as well as one equipped with a killer brake system. It's only after repeated stops, where heat starts to come into play, that the aftermarket setups really start to earn their money. They do so via greater rotor mass and venting, which allows the fluid to remain at a reasonable temperature and thus allows the system to continue functioning as it should.

Stock brakes, when exposed to the rigors of track use, will eventually overheat to the point where they become useless until they have cooled off again.

A point worth mentioning is that a stock Pantera in good working order should be able to lock the brakes--lock all four of them if you're determined enough. If yours can't do that, then something is wrong with it. When was the last time you checked the effectiveness of your power brake booster? People seem to completely forget that the Pantera's setup relies on the proper performance of this critical component, and if it is compromised somehow, then braking performance will be measurably reduced (or put another way, braking effort will be measurably increased for a given amount of stopping performance). I suspect that a lot of the people who removed their proportioning valves, did so out of desperation for this very reason.

It's possible to wreck your stock brakes, using your engine.

Huh?

Right--just put a wild camshaft in there that reduces the available vacuum for the power brake booster, and suddenly, your brakes don't work properly anymore. It's easy to then go off on a wild goose chase, trying to fix something that really isn't broken, and condemning the factory engineering when in fact the owner has created the problem himself.

The bottom line is that advocating removal of the stock proportioning valve on a stock brake system that functions as it was when new, is a dangerous thing to do. The brakes should work properly. If they don't, then find out what's wrong with them, and fix it. Don't sacrifice total stopping performance for the sake of expediency and a false sense of security.

(Edit follows)

George, you present a false choice--between having two calipers that work correctly, or four that don't work correctly. Again, I maintain that neither of these is acceptable, and advocating one of these choices is dangerous. I believe that the ONLY acceptable choice is the unstated one, which is four calipers that work properly, as they did when new.

Contrary to your assertion, I'm not attacking any people personally--you included. I'm attacking a dangerous belief that has been held by some, for many years, and has the potential to result in unnecessary damage and/or injury if followed.

To criticize a bad idea is not the same as criticizing the person who espouses it.
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