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The NOS compensator valve was amongst a box full of NOS brake parts which I inherited wth the 56. The parts were NOS from one of the two Australian Packard Dealers in 1956. IRA BERKS in Sydney. It was not in it's original packaging but had no seating marks on the seal to indicate that it was used. The break was clean and I can only assume that it had been stressed during storage or was faulty from new. I doubt that it would be a common fault and I was amazed to see the part broken. The interesting thing about the pressurising of the brake system is that towards the end you could sit in the car after driving and watch the light come on after 5 minutes, without touching the brake, indicating the role that the compensating valve has in allowing the expanded system fluid to escape from the master cylinder to the reservoir. I am going to recondition one of my spare Treadle -vac units with some of the same NOS spares and be a bit more observant this time. Peter Toet

I still don't understand why people risk their lives using this completely unsafe brake setup. I guess when someone either wraps their car around a light pole or kills someone with 4800 lbs of Packard people will start listening to the fact that the Bendix Treadle-Vac is an unsafe brake component!!!

Hi Turbopackman, I feel that I may be inserting my head into a hole in the fence not knowing what is on the other side, and I may get it kicked but, what is so unsafe about the treadle-vac? Peter Toet

Eric -

With all due respect, there is NOTHING inherently wrong with the design of the Bendix Treadle-Vac system compared to any other single-chambered master cylinder. I'll agree that dual-chambered systems do offer an additional layer of safety, but they're not 100% immune from total failure. Even with a dual-chambered master cylinder, there's no guarantee that you'll have sufficient stopping distance once you realize the pressure is lost in either side of a split hydraulic system.

The big problem that I see with the T-V unit, beyond any lack of understanding on the part of the person performing an overhaul, is the failure to replace some critical components that aren't part of the minor kit. IMHO, the spring for the compensator port valve is the most overlooked such part. Anyone can hang a shingle out and offer rebuilding services for the T-V, but that doesn't guarantee a thorough and competent rebuild - as is the case with any rebuilt component. (Any one remember the wonderful Arrow line of rebuilt starters ove 30 years ago?)

Now, you would be amazed at the number of late model vehicles that we have to replumb brake and fuel lines at the dealership where I work - regardless of make/origin. It takes nearly 50 feet of tubing and a lot of labor hours to do that on vehicles equipped with ABS. Replacing brake lines, hoses and wheel cylinder seals (if not the entire cylinders themselves) on our beloved old cars is much less costly - cheap insurance, if you will. Yet, the brakes must also be periodically adjusted on our Packards as they predate self-adjuster mechanisms.

The important thing with ANY old car is to go through the brake system COMPLETELY - and for both the mechanical and hydraulic aspects.

The problem with the Bendix TV M/C is precisely in the compensator port. If the spring fails then NO BRAKES at all and no amount of pumping of the pedal will help and NO for-warning.

With conventional piston cup M/C's it is true that the cup can wear or become deficient over time and use. HOWEEVER, in ALL brake failures i have experienced (about 4 in 34+ years)as well as similar experience of others there is always a for-warning of either leaking fluid and its smell, spongy pedal, sudden pedal drop until braking effect takes place among other warnings. Usualy, the system can be safely brought to a repair location by prudent driving and pedal pumping. I've NEVER with ANY system ever experienced complete brake loss due to M/C failure.

I believe there is a good fix for the compensator port in the Bendix TV but just have not spent much time researching it. Or perhaps a modification of the M/C altogehter.

Quote:

EXACTLY!!! One-port master cylinders are extremely dangerous, Easamatic not withstanding, it's still a dangerous setup. Any and ever car I own or will own will be converted to a dual-port master cylinder, even if it's an $80,000 1956 Caribbean. I plan on driving my car/s on a regular basis. The Easamatic belongs in a museum car, NOT on a driver.

"Cutting to the chase", has anyone documented a case where the compensator port spring has actually failed in operation? I would doubt it as the spring is a very relaxed spiral, and does not compress in operation, simply holds a few pounds closing pressure tilting the seal underneath the port. My vocation takes me to a number of vehicle accident repairers, jam-packed with damaged current 2007 model BMW's, Mercedes, Saab and other vehicles with "fail-safe" braking systems. I would rate the "loose nut at the wheel" ahead of any perceived problem with the treadle-vac system on my 56. I am not sure but I understand that the spring is not included in the Bendix repair kit for the treadle vac. I would certainly check any springs such as these out for corrosion or damage during overhaul but where do you draw the line in overhauling and driving 50 to 100 year old vehicles? I recently had the steering head of my 1907 Triumph 500cc motor bike break off completely at 25 mph whilst negotiating a bridge crossing. I am sure that it never happened before and I have replaced the item and am confident of another 100 years on the bike ( I wish!) Risk Management is the key to survival in any vehicle, old or new. Peter Toet

Peter -

I've not personally experienced a broken compensator port valve spring in operation, but found one in a unit that someone sent me to inspect and supply them with good used parts (for those not supplied in the minor kit). Also, the spring from the T-V unit in a 1956 Patrician that had been left in a garage since 1967 (until I purchased it in 1990) was corroded and ready to break.

As far as actual use and reliability of the Easamatic/TreadleVac system, my father purchased a brand new Exec hardtop in 1956 and put 74,908 miles on that car through 1963, when he replaced it with a '63 BelAir. Imagine all those miles (including two 900-mile round trips to Chicago) with a single-chambered master cylinder, no HEI, no ABS, no airbags or seat belts. (GASP!) It's amazing that any of us ever lived to tell the tale - LOL!

In the examples that I've personally seen, the corrosion that occured and lead (or would lead) to failure of this fine-wire spring is something that took place over many years. The problem is that glycol-based fluids like DOT3 and DOT4 are hygroscopic; they will draw moisture right out of the air - even through rubber. Over time, moisture in the system will take its toll on the internal metal parts - from master cylinder to wheel cylinders. In fact, wheel cylinders with aluminum pistons set in a cast iron bore are particularly prone to bimetallic corrosion and can sieze. Pitted wheel cylinder bores and master cylinder plunger will work like a cheesegrater on the rubber seals.

Regardless of what master cylnder is used, it is important to go through the brake system, "from stem to stern", in these old vehicles and throughly inspect all components. Even when the cylinders are in good shape, I prefer to replace all the rubber parts in the hydraulic system, and upgrading to DOT5 follows naturally. (However, DOT5 appears to be a "no-no" in ABS systems.)

Last but no least, I've not found much problem in the vacuum section of the TreadleVac. With a bit of care and patience, the rubber gaskets can be freed from the metal components for inspection. However, unless there has been an obvious problem with power assist that is not external to the T-V unit, disassembly of the vacuum piston assembly is usually not necessary.

Peter packard wrote:
" Risk Management is the key to survival in any vehicle, old or ".

Precisely the point of my previous post. The spring is either broken or it is not. It either works or it does not work. It's called the law of "excluded middle". Kind of like On and Off. NOT kind of broken or sort of broken or somewhat broken. If it breaks there is NO, NONE , NOT ANY brakes whatsoever. There is NO forewarning!!! There is no recourse for pumping or slamming the pedal to achieve braking affect.

This is simply NOT true of the more convenventional piston and seal type cylinders wheather dual or single. If the seal becomes deficient then it tends to happen rather slowly by wearing at the sealing edge of the seal. USUALY the conventional type will (on FiRST WARNING) fail on a lite to moderate pedal pressure. When it goes to the floor the first reaction is to release and SLAM the pedal as hard as possible to the floor. This sudden and extreme act tends to expand the seal a little more allowing for adequate braking effect. OR a pumping action of the pedal.

Again, If the TV spring fails then there is NO brakes!!! NO RECOUrSE!!! NO WARNING!!!! NO NOTHING!!

I really do not know how to explain it any more plainly nor clearly than that.

"Cutting to the chase", has anyone documented a case where the compensator port spring has actually failed in operation? "

How much documentation exists (ever released to public or dealers) about ANYTHING failing prior to ca. 1965 ????
Witness the V8 oil pump. Relatively little documentation compared to the size of the problem as well as most of the documentation that is KNOWN to exist is questionable in relavence to the problem anyway.
It was FIFTY years ago. Not 10 years ago. It was a different world. A 30 day warranty. Not a 5 year warranty.

As for the steering head breaking on the 1907 Trump, i mean what do u want???? How much documentation exists for a 1907 ANYTHING ???? How much did they publish in 1907 anyway???? Probably very little.

One can not use 2007 expectations or analysis to explain something that is 50 to 100 years old.