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

 I believe Dennis Q offers rebuilding. And I am sure Hemming‘s auto news has advertisers that do the same. I know that isn’t much and you probably already knew all that but just in case...... 😉

Larry 

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.

Larryw

You probably are in need of a new brake booster seal. Quella helped me a couple of years ago. Maybe he have some replacement fabricated.

Anders

Karp's Power Brake Supply,66 North Central Ave,Upland CA 91786, tele 909-985-0800 offers rebuilding services.

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.

arm chair mechanicing...

If you think they are junk, how about trying a few PSI air pressure to back flow and wiggling the pedal input and maybe clean the sealing surfaces

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.

A shop here in Orange County routinely rebuilds Pantera brake boosters.  They can refinish the housing to original as well for not much extra.  It is ABS Power Brake, Inc. in Orange, CA.  Here is one they did for me. 

Are there any safety concerns with those remote reservoirs connected with plastic tubing?

I have the same arrangement on my '71 with what I presume are stock-type black rubber hoses and hose clamps.

That looks like Tygon tubing; very tough and brake fluid or gasoline causes it to stiffen up after awhile to become virtually bullet-proof, like the OEM clutch line. No worries.

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.

Thanks Jack.  I will be swapping out the tubing with clear Tygon fuel line.

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...

I swapped the generic clear tubing pictured above with Tygon fuel line.  It looked promising and then it began it fail.  The tubing seemed to sweat brake fluid.  I like clear tubing in this application because it shows fluid along with air bubbles.  The air bubbles can be removed  by simply un-mounting the reservoirs and holding them up high until the air bubbles go away.

I am hoping that the version of Tygon tubing for brake systems noted below resolves the issue.  I will report back if this chemical resistant version of Tygon corrects the problem with brake fluid sweating.

https://www.amazon.com/gp/prod...00?ie=UTF8&psc=1

The Bonaldi diaphragms are available from Casa del Freno in Modena, Italy.

They just rebuilt my booster.

In two of the three misbehaving boosters I had the issue turned out to be the seal at the MC pushrod. Both had aftermarket MCs with adapters that coincidently used a special seal common to both. Karp had them on hand.

Booster number three will pull good vacuum, but doesn't provide any assist. It will just have to wait for now.

Are the GM boosters still available?

The vendor that offered the GM booster was Bobby Byars. He passed several years ago and the business is no longer active.

Larry

Steve:  my 71 (1744) has the same clear plastic tubing.  It has discolored due to age.  It also "sweats" brake fluid all the time (PITA).  OBTW, the little plastic reservoirs are actually a VW part.  I bought two new ones as I was going to replace mine but have not done yet.  The fittings on the new ones does not have the correct tubing on the connect and requires some modifications.

The Tygon brake line worked well.  It did not sweat or discolor.  I used something like this:

https://www.ebay.com/itm/16155...tkp%3ABk9SR5Tb-N7pYQ

good to know

To duplicate Bobby Byars GM conversion brake booster, the thing needs to be completely stripped and the stud pattern on the pedal side weld-converted from GM 3-stud SAE to a 4-stud metric to match DeTomaso's bolt pattern. Then reassembled and gold-alodined.

How Bobby did all this for the price he charged, I have no clue- and it had a warranty. The matched aluminum master cylinder was included.  Inside one MS port is a 'keep-alive' check valve about the size of a very thick nickel for the front calipers, I always remove those since I had such a valve stick, once upon a time.

Otherwise, the only thing to watch out for (in shipping) is the vulnerable plastic valve on the pedal side is not not damaged. I never asked what model of GM it came off of- sorry. Mostly just check the booster OD to be sure it fits under the Pantera hood; not much clearance and the GM is slightly larger. Good luck-.

Let me ask a somewhat stupid question - WHY do we even need the booster?  I know the GT40 and some other cars do not use one.  Is it because they had the dual cylinder system?

I test drove a Pantera for someone not long ago and there was little if any vacuum to the brake booster.  The car had good brakes.  The brake pedal was quite firm and the calipers seemed to be working correctly.  The hydraulics seemed healthy.  Without power assist it took ample effort to slow the car and it took me by surprise how much the booster helps.  I think I could drive a car without power brakes but I would need to be prepared for that type of braking.  It's easy to try out.  Just disconnect the brake booster hose and cap off the manifold or carb.

thanks Steve.  

@lf-tp2511 posted:

The vendor that offered the GM booster was Bobby Byars. He passed several years ago and the business is no longer active.

Larry

I'm sorry to hear that.

Are there different versions of Pantera brake boosters? Some seem to use a 3 bolt pattern, while others (My Deauville included) use a rectangular 4 bolt pattern.

All of them -at least the V-8s- use a 4-bolt pattern including the Mangusta, I believe. My '72 Pantera does. The 3-bolt pattern is typical of GMs.

Both of these are defined as "De Tomaso Pantera Brake booster" (Autoepoca)

This unit looks like it would fit on the Deauville,

This unit looks different, and the firewall bolt pattern looks like a 3-bolt.

PIM has boosters for sale on the eBay right now.

I've tried running without a booster but found the pedal was just too heavy to be comfortable. I'm not saying it's not possible but with my calipers and CNC dual master setup, the pedal was just too heavy. I believe the root cause was that there isn't enough leverage with the Pantera's "short" brake pedal. With a longer pedal, such as SACC's aftermarket "racing" pedal setup, the pedal effort, without a booster, is reasonable. 

Interesting info!

I decided to test my booster and hooked up a vacuum pump.  It took me about 99 pumps to get 15 inches of vacuum that slowly bled down.  Should it take a lot of pumps to get to 15 inches?  Should I be able to get more than 15 inches with this setup?

How well did it hold vacuum?

It held the vacuum and then leaked down very slowly.

You’re saying it took 99 pumps on that handheld vacuum pump?

I would say that makes sense – if you look at the difference in volume between the handheld pump cylinder, and the brake booster, it’s quite a big difference…

Rocky

I did not actually count the number of pumps that it took to get to 15 inches vacuum but it was a lot.  I continued to pump once it leveled out at 15 inches and did not get any more vacuum.  I am thinking there may be a leak.  My next step is to get the car warmed up and then check manifold vacuum with the booster connected and then with it disconnected and the manifold capped off.  The vacuum reading should not change.  If it increases with the booster disconnected then there's a leak.

I don't suppose any of you has a booster laying around on the work bench, and can confirm the bolt pattern on the firewall side of the brake booster?

On the Deauville, the pattern is rectangular, 107,5 x 85 mm.

Pantera measurements, close, but not precise show the short side at 100 mm and the two long sides at 128 mm

Larry

What year is this? Just above there is a post stating that they all have 4-bolt patterns?