Brake booster won't hold vacuum, should I rebuild/replace it?

I cobbled together this arrangement to test a booster.

IMG_4441

I checked my adapter, using my fingertip as a plug I can quickly and easily pull and hold 25 inches on the gauge.

Now, using it on the booster, after 20 or 30 seconds of vigorous pumping, I can barely get a reading of 6 or 7 inches, which then leaks off over the course of a minute or so.

I have determined the external check valve at my adapter connection is good. And, if I push on the brake plunger rod I can hear the release of the little bit of vacuum I pulled.

I should be able to pull more than 6-7 inches on this thing, right?

Rebuild or replace? Any favorite rebuilders come to mind?

 

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You may have trouble home-rebuilding it. Bendix-Italia does not sell parts thanks to a lawsuit decades ago by someone who bought a then-available repair kit, exceeded his skill level and wrecked his car while testing, then sued the company. Some Pantera vendors do sell a complete replacement.

There is another alternative: an adapted GM booster assembly from Bob Byars at Precision Pro-formance in CA. This booster is a dual-diaphragm type with a slightly larger OD so it gives more boost, has a two-stage aluminum master cylinder with integral keep-alive circuit and is a true bolt-in (being made in the U.S, it does needs 2 short new hydraulic lines with flared ends rather than Euro-style bubble flares).  I bought one in 2002 for our '72 and have had zero problems to date. It was also cheaper than the available replacement (for a series-308 Ferrari).  Bob warranties his conversion.

I checked my other 'spare' booster yesterday. It's even worse that the first, can't pull/hold anything at all. And, I confirmed the one in the project car is also junk. That makes three.

After seeing that, I thought I should check the one in my driver. I can only pull about 16~17 inches on that one that bleeds off over the course of about a minute and half. Brakes on that car seemed fine. I guess they could be better.

We will make some calls today.

 

Many times, it's a ruptured diaphragm. And this can come from motor oil being sucked into the booster from the intake connection past the plastic check valve on the booster. Oil seems to rot the rubber Bendix used. Some desperate owners have TEMPORARILY fixed a torn/punctured diaphragm with silicone rubber (after alcohol cleaning), but you need to give the goo time to cure before firing up the engine. And it WILL come loose eventually- probably when you most need it- hence "temporary".

In my experience, by the time you get the booster vacuum leak fixed,  the master cylinder will begin leaking fluid- if it is not already. 'New' is more dependable- either a Byars conversion or the more expensive Ferrari 308 unit.

That's a good question.  This Pushbutton project came with clear tubing from the reservoirs that appeared to be original and I was trying to emulate.  The clear tubing in the photo is simply clear PVC tubing from Home Depot.  Any input about the correctness of the reservoir tubing is appreciated.

Doing some follow up I find:

1. ABS Power Brake (CA) - says rebuild is $150, plating an extra $25. 

2. Karp Power Brake supply (CA) says +/-$300 to rebuild, BUT, they say the Bonaldi booster diaphragms are presently unobtainium (unusually small diameter?). He is waiting on samples from a new vendor. Will advise in a week.

3. Harmon Classic Brakes (GA?) confirms diaphragm availability issue and advises that another part of these boosters very often breaks during the process and is unobtainium (Karps guy also warned about this, in case I wanted to try opening one up myself). Harmon won't even try them anymore.

4. John Stuart (Ontario, Canada) - wants me to send the master cylinder AND booster, he'd try and rebuild or he'll cobble together a substitute. Hmmm. $350-$400, better to use the Precision Proformance unit at that rate.

5. Power Brake Exchange (CA)- sent him a photo of the unit, he says he has parts and can rebuild. $180, and they'll plate it too.

Weird pricing on the plating. He says his guy will plate 10 to 100 lbs of parts, flat rate $150. I wonder if I could include some other things too?

6. Whitehorse Restorations/Ed Strain (OR)- one local guy with first hand experience, and one of the vendors above were less than lukewarm about these guys. Haven't called them yet.

I've got three boosters to rebuild, I think I'll send one off to ABS and see how they do and take it from there...

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