Packard Forum Index » Post-War (1946-54)

I realise drawings are not always 100% accurate but the fitting in the cap in the instructions does not seem to protrude into the fluid in the res so this would be a "total fill" ie no airspace remote fill. Any thoughts? Brings the relief port and cover and gasket importance to new light.

I agree the caps are different so that must be an aftermarket cap. At any rate, Packard apparently didn't feel the airspace was important.

The relief port would still provide for the more common leaking hydraulic seal and hopefully prevent fluid being forced into the vacuum side but don't think with the remote kit there would be an indication of a problem. The fluid level would not change much so except for convenience, not much better than cars without.

A leaking vacuum side seal would draw fluid in so the kit would be a good indication of a bad vacuum seal because hopefully the owner or gas jockey would see the level falling and investigate. That would be an advantage but don't believe the vacuum side seals failed that often..

The hole and indicator tube could be an advantage in both cases -- as you said, fluid in the tube if hydraulic failed and air instead of fluid in the vacuum side if that seal failed..Problem is the covers. I don't think there is an easy way to use the bubble type and no idea how many of those are around or how the gaskets are being made now for the older flat covers.

One other consideration is how much fluid is designed to be in the port. Bendix mentions some leakage is expected and desired to keep the piston moist and lubricated so seals didn't dry out. Could that leakage also include some spillover from the reservoir.

well, just looking in this kit posted in another thread the cover gasket seems to be a full circle seal around the port and of an appropriate material. The failure of both the cup seal and the vacuum seal is less common but does occur though on the other threads when it does there is whith smoke from the tail pipe hopefully alerting of an issue so as not to drive until repaired. Does this give enough warning before the master is sucked dry? I remember the failures os trans vac modulators and as soon as they went the smoke out the tail pipe was unmistakeable. refhttps://packardinfo.com/xoops/html/modules/newbb/viewtopic.php?topic_id=12391&viewmode=compact&order=ASC&type=&mode=0&start=70&

Forget the idea of watching for a puff of white smoke, get into a routine of checking your brake fluid a couple of times a year. And although it's a bit of a chore to completely drain, flush and replace all the fluid, if you're using traditional brake fluid (DOt3 or DOT4) at least bleed off as much as practical and replace with new fluid every 3-5 years, especially important for cars that are subject to long periods of non-use.

One more question. the BTV is the name of the whole assembly or just the vacuum assist canister? I saw on a chev site a page from their service manual and the "master cyl" hydraulic unit was called Moraine hyd unit attached to the (same as packard) bendix tr vac canister. The picture and call outs showed a clearly different plunger and seal set up at its rear. So is the master (hyd unit) a packard engineered unit applied to the btv and other car companies used their own?

I don't think the BTV is an official name -- just an abbreviation used here standing for Bendix TreadleVac which is the official name of the unit Packard used. Many other mfgs of the era used the same unit but added their own name or twist to the operation or layout. Packard renamed the unit EasaMatic and BTV is easier to type in place of that name too. It is essentially a one piece off the shelf unit.

There were several versions of the TreadleVac over its 10 or 15 year lifespan. Packard started with the slide valve type and transitioned to the poppet valve type. There were several other versions all slightly different in how the sensitivity and feedback for pedal operation/vacuum control was accomplished. The common feature was all had the same displacement system for the hydraulics.

Moraine was a unit made by GM and was a functional clone of the BTV but having significant differences. Both of those units are one piece units unto themselves so just considered the power brake unit. Neither the hydraulic or the vacuum system will interchange with other items as power units today will. You can buy a vacuum side or a master side today and bolt many different sizes and combinations together -- not so on the BTV or Moraine units.

Yes I see and understand the variations of the vacuum side of the assem but I was wondering only about the hyd side. I have my answer from the pics posted and info on other threads that the hydraulic portion is cast with Bendix on it and the moraine units have a 7 digit number on them.

From the threads back in 2010+11 I was interested in acolds efforts on remote fill and Freds thoughts. I cringed when a vapor seal was suggested to the cap on the lid as I feared eventual contact or interference withthe compensator. sounds like a good idea on a remote though.
I still do not believe the relief port should be filled with fluid as some suggest and I would not want to see it plugged either. A "total fill" design with sealed lower cap would require the vent port to be extended through the cover and to atmosphere. I am wondering, were the people who had failures at about 1 year on a rebuild running a remote fill?

The rear seal has air on one side, and fluid on the other once some fluid sloshes over from the main reservoir or the hydraulic seal leaks a tad. So it is sealing a fluid at atmospheric pressure, or at worst a pressure differential of approx 6 psi when the vacuum canister sees full manifold vacuum during a panic stop. The fluid provides lubrication for what amounts to a piston rod packing for a vacuum cylinder. Adding the pressure of an 18 inch high column of fluid is inconsequential--the approx height of the remote reservoir above the Treadlevac.

I have customers who have run those reservoirs on their cars for years with no problems.

In the 40 or more BTV I have rebuilt over the years there is never anything esoteric or bizarre in the failures. There is improper assembly such as seals in backwards. There are rusty or pitted pistons that rip the seals up. Those things cause fluid loss to the vacuum side to varying degree. The instantaneous failures are almost always due to brake fluid that has broken down to the consistency of Gravy Train--the lumps hold the compensator open.

I agree with you on many points and appreciate your experience rebuilding the units and the service life you are reporting. It goes without saying improper service procedure, seals misinstalled and pitted plunger shafts will all cause failures and if individuals have no experience mechanically and cannot tell if a bore or shaft is in a serviceable condition to hold an air or hydraulic seal, they should not be attempting a rebuild. Those instances however do not explain failures of professionally rebuilt units. Some reporting multiple failures of such units at low service intervals.
Taking the 55-56 service manual information into account and the info I have referenced from other sources, as well as my experience in this area and my dealings with manufacturers justifications such as "some seepage,leakage,sweat etc etc etc is normal and desired... I do believe I have the backround to make an informed decision on the facts in question. Can you give me the source of the statement "some leakage is desired to lube...", and, " splash and flow into the relief port is as designed by the manufacturer" as I did not see those in print anywhere. The 55 service manual is very specific on the amount and type of products to be used on the rubber cup seal (primary), Wicking, Leather packing, and vacuum canister inner bore face. The fact that the leather cup seal(secondary) is installed with NO liquid or lube of any kind with just the residue left after the primary seal installation has swiped the hydraulic plunger shaft virtually dry is quite notable. If the leather vacuum packing seal is damaged when exposed to prolonged brake fluid contamination why would the leather secondary cup seal fair any better? As an additional note, Cadillac used the same BTV but installed it higher and horizontal on the fire wall. It is telling to observe their cover has a dipstick and a relief port tube which extends the port up via this external tube rising vertically up from the cover and bends into the air space high at the cap attaching area. We only need to verify that the original Cadillac lid is vented either at the cap or the dipstick handle, and that the "Full" line on their dipstick is at or below the lid mating surface. This can be done with a simple ruler measurement on the removed dipstick and compared to the tube-lid assembly. If anyone out there knows a friend with an original Cadillac could they reply with this info? If these 2 assumptions can be confirmed, there is no doubt bendix meant for that port to be exposed to atmosphere and not subjected to any splash or back flow of brake fluid. (Unless a 50s Cad can accelerate like a top fuel dragster or can stand on the bumper!)
It is also notable that during final reinstallation of the unit and the toe board into the vehicle that the service manual emphasizes careful alignment of the pedal and shaft. Upon close examination of the unit, the only thing keeping the the hydraulic plunger running straight at a perfect plane into the master and perpendicular with the seal lip is the steel washer and fiber washer and guide hole in the vac canister . If these are worn may this allow the plunger to ride crooked on the seal?
I want to stress that I am in no way suggesting any changes or modification to this or any brake system. Its functionality must remain exactly as the manufacturer intended it. It is also a fact that most drivers of these vehicles are ageing and if the design of a system makes it difficult to physically check a fluid level or condition as often as necessary for safety, then a modification to "see" the brake fluid is welcome but without a manufacturers specific instructions on a "relief port" we must determine its intended condition using all information available. It is unfortunate that the Cadillac cover protrudes and the dipstick is on the wrong side. The 54-55 Olds cover is flat with a dipstick on the driver side and could be a partial solution in that it allows a check of the level frequently but does not address the relief port however if the above items can be verified a proper remote fill can be utilized with the extended vent tube and LEVEL, CONDITION, and SEAL STATE OF HEALTH could be checked before every drive with a simple lift the hood,look and listen making driving these classics as safe as it can possibly be. Any thoughts?