1958 Cadillac Tredle-Vac Sensitivity

[Matt Innocenzi]

Good day all!  I had the original Tredle Vac power brake booster rebuilt on my 1958 Cadillac 6 years ago.  When the engine is first started from sitting, the brakes are so sensitive, a slight touch on them almost sends me through the windshield.  But, after the engine warms up, after about 5 minutes, the brakes swing to the more difficult side requiring significantly more force to stop the car.  I sent the power booster back to the rebuilder who re-inspected it, bench tested it and assured me it is fine.  I also replaced the hoses and one-way valve and rebuilt the carburetor with no change.  I've grown accustomed to the feel of the brakes and tried off an on for the past 5 years trying to diagnose it but it may just have me licked.  Any suggestions on what may be causing this?  Thanks in advance!

Matt
CLC #21633

[Warren Rauch]

 The problems you site can have exactly the opposite remedies. I checked THe 58 shop and a work book from the GM training center for 1958 Brakes. Things like brake lining , shoe adjustment  and loose backing plate seem out of the question. You don't mention if its Bendix or Moraine,but control valves can cause things like this (even if the unit is rebuilt).
My first step would be to check vacuum at the tredalvac,to see if it is different when the problem changes. I'd also check the air inlet(Filter) to the brake unit.The time you refer to is about how long the choke  may stay on. When it goes off the level of vacuum may change. The tredalvac needs to have both air pressuse and vacuum to work correctly.Warren