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Patcon

7" brake booster repair and restoration

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I thought I would post this up here instead of burying it in my build thread.

Does any one have ideas on how to bench test a brake booster? I have an assortment of 5 or so small boosters. I would like to bench test them to see if any of them are good. Then restore the best candidate

Thoughts?

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I just did this.  Put a mityvac tool with a gauge on the booster's port then draw 15" vacuum.  See how long it holds. Also with the vacuum at 15", you can slide the push rod in and out to see if the shaft to seal leaks under simulated operation.

 

39522_zzz_500.jpg

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18 minutes ago, 240260280 said:

I just did this.  Put a mityvac tool with a gauge on the booster's port then draw 15" vacuum.  See how long it holds. Also with the vacuum at 15", you can slide the push rod in and out to see if the shaft to seal leaks under simulated operation.

 

39522_zzz_500.jpg

I have that tool and that was my first thought. I assume you blanked off the master cylinder port? Did it take forever to draw the 15" of vacuum? You were moving the brake pedal clevis looking for leaks, correct?

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It is easy to do.  Just connect the mityvac to the port on the booster and draw vacuum.  It just takes ~ 30sec to pull 15".

There are adapters in the kit to connect larger diameter vinyl tubing to the smaller tubing on the gun.

Pressing the clevis will release the vacuum.  It does not really test much apart from checking normal functioning.

The two main tests are:

 

1. [Basic Leak Test] Will the booster hold vacuum for 10min with the rod in relaxed position.

2. [Rod to Rubber Seal check]  Will the booster hold vacuum as the rod is manually pulled out a couple of inches and returned. Pitting in the rod will leak air.

You may have to move a rod seal, lubricate a seal, or even sand down a rod to make one work nicely.

 

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I connected mine up to my vacuum pump. Used a little valve cracked a little as a regulator so I didn't suck the booster down to absolute zero.  LOL

3 hours ago, Patcon said:

I assume you blanked off the master cylinder port?

You don't have to blank off the master cylinder port. The rubber vacuum seal on the output shaft should keep the vacuum in the clamshell.

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Well evidently, I have 5 used boosters and none of them will hold a vacuum. I even blanked off the MC side of the most promising looking one and nothing,

I spent about an hour emailing companies all over the US to see if I can find someone that can rebuild the little booster without forfeiting a valuable body part...we'll see.

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If they won't hold vacuum (even with the M/C hole sealed off), then there is probably an internal leak. Hole in the diaphragm or the poppet valve seal is leaking. If that's the case, when you try to draw a vacuum on it (or in your case... pull air through it), you should be able to hear air entering in the assy at the pedal push rod. Through the little felt filter thingie.

Other possibility of not being able to hold a vacuum is that it's leaking at the seam between the two sections of the clamshell where the diaphragm is pinched, but you don't hear much about that happening. it's usually something internal.

Please make sure you let us know what you turn up for rebuild options and/or parts!

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I tried to listen for air leakage but the Mity Vac makes too much noise and pulls air too slowly.

I had planned on posting up a rebuild source if I can come up with something

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240260280 posted a detailed, DIY mastervac rebuild article on the old AtlanticZ website several years ago.  Have you seen this?  (I can send you a copy).  He used RTV sealant to repair the diaphragm -- apparently with good results.  My guess (valued at 2 cents) is that 95% of the vacuum failures are due to cracking of the diaphragm, rather than failure of the poppet valve.  The extent to diaphragm issues are accompanied by leakage from a corroded pushrod is probably related to whether the car lived in the salt-belt or near an ocean.  According to 240260280, the pushrod problem can be somewhat easily remedied.

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1 hour ago, Namerow said:

240260280 posted a detailed, DIY mastervac rebuild article on the old AtlanticZ website several years ago.  Have you seen this?  (I can send you a copy).  He used RTV sealant to repair the diaphragm -- apparently with good results.  My guess (valued at 2 cents) is that 95% of the vacuum failures are due to cracking of the diaphragm, rather than failure of the poppet valve.  The extent to diaphragm issues are accompanied by leakage from a corroded pushrod is probably related to whether the car lived in the salt-belt or near an ocean.  According to 240260280, the pushrod problem can be somewhat easily remedied.

I have seen some of that. I have also attempted that kind of repair with mixed results. We really just need to find a source for the diaphragms then we could repair our own

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IIRC, Steve Nix took a pass on replicating this piece because it's a safety-related item and would expose him to liability in that one failed in service.  Other low-volume parts casters will probably feel the same way.  The big parts rebuilding operations seem to have access to a source (although perhaps only because they purchased in volume from Nissan Service Parts years ago when the Z's were still 'current' and are now just working down through their inventory).  Seems questionable whether a rebuilder like Cardone would be willing to sell just the diaphragms -- even in a lot of a couple of hundred -- because it would be undercutting their primary business.  Still, maybe somebody like zcardepot.com might be willing to approach Cardone's business office with just such a proposition ("Sell us a hundred of the diaphragms and we'll carry your full rebuilt units in our catalog, too.')

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33 minutes ago, Namerow said:

IIRC, Steve Nix took a pass on replicating this piece because it's a safety-related item and would expose him to liability in that one failed in service.  Other low-volume parts casters will probably feel the same way.  The big parts rebuilding operations seem to have access to a source (although perhaps only because they purchased in volume from Nissan Service Parts years ago when the Z's were still 'current' and are now just working down through their inventory).  Seems questionable whether a rebuilder like Cardone would be willing to sell just the diaphragms -- even in a lot of a couple of hundred -- because it would be undercutting their primary business.  Still, maybe somebody like zcardepot.com might be willing to approach Cardone's business office with just such a proposition ("Sell us a hundred of the diaphragms and we'll carry your full rebuilt units in our catalog, too.')

Yes you are probably correct on all points.

I don't believe there is that much liability risk. If you make them under an LLC company your liability is very limited, and even if it fails you still have brakes. I suspect there are a number of z's out there with bad boosters that get driven and don't even realize it. I have considered making them myself but I really don't want to get another project added to the pile. I found some diaphragms a couple of years ago but I would have had to order like 1000 and that was a "non-starter". So we'll see what I can come up with. You would think a rebuilder would be fine with throwing some parts in a box and adding $50 on top and shipping it. That's probably better margins then they actually make on a rebuild in the shop, and easier too.

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28 minutes ago, Patcon said:

Yes you are probably correct on all points.

I don't believe there is that much liability risk. If you make them under an LLC company your liability is very limited, and even if it fails you still have brakes. I suspect there are a number of z's out there with bad boosters that get driven and don't even realize it. I have considered making them myself but I really don't want to get another project added to the pile. I found some diaphragms a couple of years ago but I would have had to order like 1000 and that was a "non-starter". So we'll see what I can come up with. You would think a rebuilder would be fine with throwing some parts in a box and adding $50 on top and shipping it. That's probably better margins then they actually make on a rebuild in the shop, and easier too.

 @zcardepot.com

Interested in pursuing the possibility of approaching Cardone, or similar, with a proposition like this?

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Weren't these Bendix boosters made in Japan under license from Bendix.

Like the SU's Datsun use look to be their version of the British SU.

The brake calipers Datsun used look just like Girling calipers used on Triumphs.

I had several British cars.

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34 minutes ago, Lumens said:

Weren't these Bendix boosters made in Japan under license from Bendix.

Like the SU's Datsun use look to be their version of the British SU.

The brake calipers Datsun used look just like Girling calipers used on Triumphs.

I had several British cars.

That wouldn't surprise me. What we really need to find is the guy that sells parts to these rebuilders. They probably can supply a diaphragm that would work.

2 hours ago, Namerow said:

Interested in pursuing the possibility of approaching Cardone, or similar, with a proposition like this?

I'm willing to pursue all options

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2 hours ago, 240260280 said:

LOL, I was looking for diaphragms a few months ago. This is what I came up with as potential donors. Not sure if they fit like the original Hitachi diaphragms like you posted above.

You will be taking a chance if you try.

 

7"

https://www.ebay.com/itm/Mustang-65-66-Bendix-Brake-Booster-Major-Repair-Kit/171755696030?hash=item27fd6fef9e%3Ag%3Aj~4AAOSw~AVYnPaD&_sacat=0&_nkw=+brake+booster+repair+kit&_from=R40&rt=nc&LH_TitleDesc=0|0

 

DUDE!!! That Mustang diaphragm looks really promising. The same dots around the perimeter and everything. That would be a home run if it fit! Mustang parts aren't going anywhere. I'll order one. I am ok with the risk... :beer:

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Ordered.

It's funny, I sent that vendor an email yesterday. He is in Canton, GA and was like 4 or 5 pages back in a Google search

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