Packard Forum Index » V-8 (1955-56)

So i've seen a couple of posts that refer to the bendix brakes as death brakes. And i was curious what the safest and most cost effective replacement would be.

I would rather not have brakes one second and nothing the next. Id kind of like to keep this car around for a while.

I've been running my 400 with Bendix treadle-vac since 92 and I'm not dead yet The Achilles heel of the T/V system is the spring on a valve that seals off the reservoir chamber from the hydaulic chamber. If the spring fails the hydraulic chamber will not hold pressure and you have no brakes. On the other hand, if you rupture any of the three hydraulic hoses you will lose all your hydraulic fluid and will have no brakes. There is not yet a simple elegant replacement for the T/V unit that applies the same force for a miniamal input. Packard was not the only company to use this system. GM did and I don't recall reading any dire consequences happening to 5-6-7 Chebbies. There are a few very vocal critics of this system and predict all kinds of mass destruction. Then, of course, there is Al Gore and his Noebel prize claiming we are all doomed anyway. Read up on the subject and make up your own mind.

Don't believe all the hype.

Study the factory shop manual. The repro rebuild kits that I've gotten from Packard vendors usually come with a copy of of a Bendix "Restorograph" that doesn't describe the overhaul as well as the Packard shop manual, but has a better exploded view than the Packard parts book.

The most misunderstood thing about the Bendix TreadleVac is that the seals in the master cylnder remain in a fixed position, but the large diameter piston moves through them, displacing brake fluid into the lines and to the wheel cylinders.

Also, when the master cylinder piston begins to move, a spring-loaded compensator port valve closes off an equalizing passage to the fluid reservoir. If not assembled correctly, that vlave will not work properly.

So, be sure to read, understand, and follow the shop manual.

Beyond that (and all other things being equal), the afformentioned spring is critical to the proper operation of the hydraulic brake system. After so many years, that spring can break as a by-product of rusting. DOT3 and DOT4 fluids will abosrb water right out of the air, and it wasn't until the mid/late 1960s that master cylinder reservoirs were well-sealed to atmosphere.

Surprisingly, that compensator port valve spring was never included in any overhaul kit.

Once I get dug out from winter here, get my tax returns filed, and spring yardwork behind me, I hope to look into a suitable replacement spring, and I will post my ifndings here.

Properly serviced, the BTV is no less safe than any other single-chambered brake master cylinder.

BTW, you might be interested to know that I recently lost the brakes in my '98 Monte Carlo with front disc and rear drum and ABS. The pedal went to the floor, and I would not have been able to stop safely had it not been for applying the parking brake (something that might not be possible with some late-model rear disc brake systems). Knowing this car had a diagonally-split hydrualic system, I thought had blown BOTH rear lines (knew they were pretty badly rusted). The repair shop only found one leak, but replaced both rear lines (all 28 feet of them). I had a similar episode in a car 20 years ago, but had a more sure-footed stop with the "old-school" front/rear split plumbing.

No matter what type of master cylinder your car has, get to know the limits of your parking brakes, and keep them in good working order.

Brandon. If your TreadleVac (TV) is working ok then just go ahead and drive it. I drove mine for 4 years with a TV and no problems other than a little hissing from the power unit and brake fluid sucking into the power unit. Issue i could live with.
Go ahead and drive it if it works good. Consider a change at a later date.
HOWEVER, if a rebuild is needed right away i'd consider a retro fit of a more readily available replacement.

Keith -

A new port valve stem (with bonded seal) was included in each of the repro kits, that I purchased - as it was in the original Bendix minor overhaul kit.

It is not difficult to replace the stem in port assembly, especially while that assembly is removed for overhaul of the hydraulic section.

However, another member advised, in another thread past, that the compensator port valve spring is NOT included in even Bendix major overhaul kit. Though I have not yet been able to get to offsite storage to check my original, sealed, major kit, I suspect that is true.

Rest assured, I will find a proper replacement spring and post news here, but it's not gonna happen in the next day, week, or month.

Ok. That was my error and my MISunderstanding of previous threads. I was under the impression that the seal was not being reproduced. Apparently it is now.

SO, the ONLY thing not reproduced is the spring???? That should not be too difficult to find.

Yes, that spring is the now-critical part that is missing from the kits.

I suspect that any competent rebuilder would have these, as they repro'd the pistons and other parts, but they will only sell those "hard-to-find" items as part of their full rebuild service.

Any machinist can reporduce the piston, but spring-winding is a whole 'nuther matter.

I'll come up with a spring, but it will take time to do it right.