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Denatured alcohol is the only solvent to use to clean brake hydraulic parts except for detergent and water when cleaning them off the car.

Lacquer thinner is DANGEROUS to use as it is a petroleum product which will cause deterioration of the rubber and likely catastrophic failure. Do not use kerosene, gasoline, or any thinner ever. Even if you thoroughly dry it, residue can remain.

We disconnect the lines, blow through with air, then put denatured alcohol in the lines and blow through until it comes out perfectly dry. Any alcohol left in the system will greatly impair brake function.

Lacquer. Not for rubber. But point taken for fire reasons..

But. After cleaning. I would pump whatever brake fluid some one is using thru the lines to flush any remaining cleaner.

Edit. If one is doing this. Pull the off wheels. And remove wheel cyl cups. You will want to start fresh .

NEVER NEVER NEVER use lacquer thinner to flush a brake system.
If you flush it by pumping out the wheel cyl bleeders you will contaminate the master cyl and wheel cyl rubber parts and possibly leave thinner residue in the system.

Find me a credible source that recommends any petroleum product to flush a brake system.

The lacquer thinner is a fire hazard, but no more so than the gasoline in the fuel system.

We tested the unit this morning and it performed like new. The unit will be on its way back to its owner Monday.

But in the interim of this rebuild we had another unit come in as well. This unit was working but suffering from the pedal sticking when depressed. So since we were testing the freshly rebuilt one. I decided analyzed and test the one that just came in prior to rebuilding to see what was working and if we could recreate the customers complaint. Once hooked to the machine in held vacuum but when depressed it did exactly what the customer described in that the power piston did not return but it did create hydraulic pressure. I removed the reservoir cover the and inside was the cleanest of the units that we have gotten so far. But it to have rust color brake fluid. I than remove the power section cover and removed the power piston and just like in the 2 other units the fluid had leaked into the vacuum section creating a rusting sludge/goo that was causing the leather seal on the power piston to stick.

Disassembly of the unit will begin in Monday

Thanks
James

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Fred, I know the Packard owner of the newest test subject. When he told me of his brake problems I recognized the problem as belonging to the BTV. I recommended he contact you to take advantage of the offer to fix the BTV and add its ailments to your database. Glad it made it before the deadline. Thanks for contributing to our knowledge of these units. It seems like neglecting to change the fluid every 2-3 years is a major contributor to the failures.

(o[]o)

The unit has been disassembled the cause of the fluid leaking into the vacuum section creating a rusty sludge has caused the power piston to stick in the bore. Once the vacuum can was removed you can see that the brake fluid was leaking past the seal. The steel piston was removed and inspected and sure enough rust pits were found allowing fluid to leak past the seal. But on another note the bypass port that feeds fluid that gets past the cup and seals was was plugged with silicone. This port was put into place so brake fluid would feed back into the reservoir instead of into the booster.

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We have cleaned and inspected the hydraulic section so far. The piston was replaced with one of our new stainless steel piston as well as all the rubber components. The bypass port was also cleaned out as well.

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10-26-16
Thank you John for your input on my BTV. I took your advice and parked the car in the garage until this could be attended to. This morning I signed back into the forum to see what progress had been made on the diagnosis. Good job
Kanter! Thanks for helping us keep our Packards going.