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I recently put my power brake booster on my ''53 and since all brake components are new or rebuilt I used silicone brake fluid! Well I seem to have a leak at the end of the master cylinder. The fluid has been in the system about 7 weeks! Well I called Ed Strain who has retired & now it is White Post Restorations and they informed me that Ed put a tag on every booster not to use silicone fluid but unfortunately mine didn't have the note! White Post informed me that I had ruined the booster & send it in & they will rebuild it again for $445 plus shipping!! I talked with another rebuilder & he told me to flush the system with Dot 4 fluid and it should be fine!! Have any of you other Packard owners ran into this issue and what are your opinions about flushing the system & how to do it??? Thanks

I've typically always rebuilt the power brake units myself as it's inexpensive and quite easy, and I use Dot 5 synthetic (not don't think it's silicone) without any problems when using modern rubber and seal components. I'm not an expert on brake fluids but as I understand it, DOT 5 has a higher rating than DOT 4 but seems to cost a whole lot less for some reason. Whichever you use, to switch to synthetic it's necessary to completely flush the brake system with methylated spirits or just alcohol, then blow out all the lines with dry compressed air, then flush them again with the new fluid that you are going to use. If you don't flush and the synthetic mixes with standard DOT 3 fluid (and it will eventually mix if not flushed!), you can have problems.

I think Ross would be the ultimate authority but would go with the second recommendation over the needing a complete rebuild bit & don't put much credence in recommendations by that particular company in light of all the problems another poster on the forum had with his rebuilt unit.

I used silicone fluid and then replaced with regular with no issues. I did two complete flushes and then the final fill. Some say a flush with denatured alcohol before doing a flush with regular fluid is a good idea and others say just a thorough and complete flush with the regular fluid is all that is needed. Important part is to get ALL of the silicone fluid out.

I am curious exactly where the leak was coming from. There is nothing down there to leak except the distribution fitting assy and a couple of O ring type seals. I would think seals could be replaced for a few $$ even if you had to buy a new rebuild kit to get them. As I recall there was a post and question some time back about the type of seals sent with rebuild kits so possibly that is where the problem lies.. I believe the poster with the problem with the one shipped in his kit was able to buy a butyl brake fluid compatible seal locally.

Thanks Don & Howard for the replies! The fluid seems to be leaking between the distribution fitting & the threaded fitting in the end of the master cylinder. But the "O" ring on the top where fluid is added is somewhat stretched I guess from the silicone. If that in an "O" ring above the distribution fitting I suppose it could be stretched also! I've been reading & some say to use denatured alcohol & some say don't! Booster Dewey is the one who told me to flush with Dot 4 but they don't rebuild Bendix Treadlevacs!

My, my, my. I think awhile ago the Kanter's posted a big show about how great a cure this was for them.
Don't mess around with brake systems. Do what it calls for.
Your life and guy in fronts is at stake when you press that pedal. Sez biased old guy... Frankly, I'd get rid of it and put a modern dual system in with the money to repair it. Like I say, if they were any good, they'd still be using them.

Preposterous panicking and finger pointing. Silicone fluid is astonishingly inert and will by no means cause rapid swelling of rubber parts.

If the unit is leaking where you say it needs to have a new copper washer inserted under the head of the retaining bolt and under the distribution block. There is no rubber there. Have you tried tightening the bolt?

It is also possible that the entire fitting at the end of the casting may have gotten rotated out a bit when the unit was installed. I believe White Post uses an o-ring there instead of the original style square cut ring. In any event, just make sure that large hex fitting is tight to the casting.

The reason silicone fluid does not see use in modern vehicles is lack of lubricity which wreaks havoc with rapidly cycling ABS components. Packard brakes don't generally cycle that rapidly unless the driver has the DTs.

The brake light switches also don't seem to like it much. The plus side of silicone is I and many customers have gotten very long service life out of their brake components --in excess of 20 years--with minimal maintenance.

Didn't think I was finger pointing or preposterous panicking as I have been restoring this car for years. Just stating what I was told to see what experts could tell me!!

Kanter Auto Products has been rebuilding Bendix Treadle Vacs for over 50 years and we have diagnosed failures in many units submitted to us by Packardinfo members.. We used to sell Silicone fluid until it became widely available. DOT 3, DOT 4 and DOT 5.1 are polyglycol based and absorb water, DOT 5 IS the only Silicone based brake fluid, DOT 5 and Silicone are just different names for the same thing. DOT 3,4,5 and 5.1 are compatible with each other, they mix without any problems. Mixing Silicone and other brake fluids does not cause a gooey mess/failure, if there were dangers the DOT would require warning labels on all fluids as it would be a safety danger.


The downside to mixing other fluids with Silicone/DOT 5 is the resultant mixture loses the non-water absorbing quality of Silicone/DOT5 thus performs like the newly introduced fluids.


The gasket at the filler opening is either a copper ring or a fiber washer, both are correct, a modern rubber o-ring will do fine as long as it is tested in brake fluid first. There is no pressure at this point, the gasket keeps splashing fluid in and dirt out of the threads.


Leaks at other joints are caused by incorrect installation, being too loose or missing copper washers. At the output distribution block there are two such washers: the larger one goes under the bolt head; smaller goes between the block and the "head nut" on the end of the power brake master cylinder section. Neither of these washers was supplied by Bendix in their kits, neither does the aftermarket. Obviously Bendix knew the the old ones could safely be reused.


A third PLACE IT COULD LEAK IS THE SQUARE CUT RUBBER O RING UNDER the "HEAD NUT" WHICH was supplied by Bendix with their rebuild kits as does the current aftermarket Any one of these missing or loose will cause a leak.


As shown in our long research reported here, failure is due to age, long periods of non-use or incorrect rebuilding.

Thanks J at Kanter! Bought many parts from you & Stewart! I was just reading an article from an engineer that used to work at one of the major brake manufacturers & he quotes that silicone will attack certain rubber components of the braking system! So I suppose that is the reason Ed recommended not use silicone fluid on his rebuilt BTV units!! So from everything I read I guess I will flush the system with Dot 4 & go from there!! Thanks

Follow Ross' advice in post 6 above.

I've been running silicone now for at least 12 years and 20K miles. NO PROBELMS!!! However i am using an 84 Ford power unit and and 66 Mustang master cylinder. The rest of the 56 Exec is stock brake system.