The major contributing factors to the failure of the BTV is not its design but two factors that plague all classic cars whether they have a BTV or manual master cylinder. First is moisture and second is time. The moisture is absorbed into the brake fluid which plays havoc on any brake systems including the BTV. This causes the fluid to crystallizes blocking passages as well as corroding the aluminum of the master cylinder and the steel of the piston. This causes the seal to rip and leak fluid into the vacuum section. Time: many of these vehicles no longer see the daily use that they once saw back in the 50's and 60's.
A photo of the rust pitted piston:
<a href="http://s671.photobucket.com/user/JamesRFrom/media/BTV%20Unit%20Rebuilds/KIMG1503.jpg.html" target="_blank"><img src="http://i671.photobucket.com/albums/vv72/JamesRFrom/BTV%20Unit%20Rebuilds/KIMG1503.jpg" border="0" alt=" photo KIMG1503.jpg"/></a>
These vehicles sit idle for months at a time especially the farther north you go or in some cases years or decades. In time, seals dry out and become stiff which creates opportunities for leakage.
What can be done? Annual maintenance is key. Get familiar with your vehicle and its various systems. Following the factory service manual service intervals is not possible under today's conditions as you will not be racking up the miles as quickly as the factory engineers figured back in the 50's. Pertaining to the brake system the brake fluid should be checked at regular intervals. We recommend every three months for safety sake. Take a sample and check for cloudiness or discoloration. This is a sign of moisture which at that point would require flushing and refilling. At a minimum we recommend flushing and refilling every 2 years.
Prevention You should consider flushing your brake system and changing over to silicone based DOT 5 brake fluid. It carries better performance characteristics than the regular DOT 3 as it will not absorb water.
At the time of rebuilding, use a reputable builder of BTVs. One item to ask the rebuilder prior sending your unit is if they plug or block off the bypass port as we have found this done on units that have failed. By blocking off that port it negates an important safety design feature and can cause sudden failure. Make sure to upgrade to a stainless steel hydraulic piston. This will eliminate the possibility of rust building on the piston and ripping the seal. Most importantly make sure that the bypass port is clean and clear. If fluid were to get past the piston seal it would be re-routed back to the reservoir instead of into the hydraulic section.
The main thing that we all need to bear in mind is not the miles we put on between service but time.For most of us time moves faster than our odometers. When something sits that holds fluid whether it be an automobile, boat or plane, seals dry out and the environment has an effect. So inspection is imperative prior to operating.
The premise of this study is to debunk the myths that the BTV is and was dangerous. If that was the case, all the manufacturers would have halted use immediately instead of using it for an almost 10 year run. There were also no TSB's (Technical Service Bulletin) during the 50's as well. To that, the naysayers will say "Why did they stop using it?" Also, why did GM stop producing the 350? Simply put, technology improved, but that doesn't mean that there was anything wrong. It's just natural progression.
From our own research online through the various forums and pages of Google, we have not found any direct accounts of any BTVs that suddenly stopped working due to catastrophic failure where a lack of maintenance was not present at the time of disassembly. The same can be said for the single line manual master cylinders of the time. We have sold numerous manual master cylinders over our 50 years in business and many were purchased to replace ones that had failed. Failure of master cylinders is not just limited to the BTV as all are serviceable items.
Thanks
James From
Kanter Auto
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