7" brake booster repair and restoration

[Patcon]

1 hour ago, Namerow said:

Thinking out loud here (always dangerous, I know).  Instead of the factory strategy of staking the part, is there enough wall thickness to take three short pins?  Dress the ends to make them round-ish.  Drill the holes for a close fit (Loc-tite) or a light interference fit.  The pins wouldn't be subjected to much in the way of long-axis loading.  Just 'wobble' loading.

I would think the rounded head would want to back the pins back out

[Captain Obvious]

2 hours ago, Patcon said:

That sounds above my paygrade. ?

You know I am going to end up at the Whack-a-Mole method?

Haha!! Yeah, I know. Whack-a-mole works great too! Doesn't have to be dead on balls accurate.

[Captain Obvious]

1 hour ago, Namerow said:

Instead of the factory strategy of staking the part, is there enough wall thickness to take three short pins?

I don't know, but I believe based on the the application that simplicity and reliability would be the top priorities over everything else. I'm not gonna mess with pins.

[Namerow]

12 hours ago, Patcon said:

I would think the rounded head would want to back the pins back out

If I understand the loads here, the staking on the collar is used simply to retain the head on the shaft as the shaft retracts.  Not much loading on the ends of the pins (or the staked dimples).  Interference fit, LocTite, or both. 

Anyway, my idea was offered as 'a possible alternative', rather than, 'a better solution'.  I look forward to seeing the DIY staking machine that you are trying to come up with.

[Captain Obvious]

Sorry, I wasn't trying to imply that it was a bad or stupid idea. I was just musing that the simpler the better here.

You're right that staking doesn't have to retain a lot of force. In fact the only thing it has to do is resist the spring force of the springs assembled onto the plunger itself. I think if you restaked it and then grabbed the tip in a bench vise and gave the other end a tug as hard as you could pull it (in addition to the spring force), that would be a four or five times normal operation safety margin test.

Maybe I'll work on that "fixture" today. Rumor has it that there's a valve seal on it's way to me. I should really have that tip re-plated first though before I put it back together. The rest of my valve pieces are in really good shape, but that tip got a little rusty.

[Zed Head]

Interesting thread on a generally similar topic.  Pretty sure we've discussed it over here before too.

http://forums.hybridz.org/topic/35455-brake-boostermaster-cylinder-options-on-a-73-240z/?page=2&tab=comments#comment-1206765

[Patcon]

I posted before, when I was looking for parts several years ago when I first broke this booster down. I just needed the "Hoover" to point me in the right direction

[240260280]

 

[Patcon]

So I did a little bit on the booster rebuild today. I was able to find a micro-manufacturer and the machinist there came up with an idea for staking the plunger end that he said should have been obvious to me. So I got it in the mail the other day. A very elegant solution...

The fixture is comprised of two haves that are machined to hold the plunger tip. The halves are held together with threaded screws. Then it has a hole that accepts a punch that reproduces the staking mark on the original plunger end

Now the staking punch has a lock nut that allows the depth of drive to be adjusted. So this can be set up in the press and then each stake can be reset to hold the plunger assembly together

This is a view of the original stake mark

[Patcon]

Well I worked on the booster some more today.

I started by stripping the last remnants of paint from the booster shell. Some of it didn't want to come off in the blasting cabinet. Under the paint it looks like yellow zinc.

You can see the yellow in a couple of the spots that were protected with paint. So did they plate the boosters first, then paint them. Otherwise, how did the studs get plated? I tried to remove a stud just to see if I could, but I think they are welded in some way even though I can't see where

Stacked up the plunger parts

Then clamped the plunger in to the cap. I actually had to tap the plunger into the cap with a hammer to get it to seat. Then clamped it in to the fixture.

You can see the staking mark through the fixture hole

Staked one side, then rotated 120 degrees and repeat. I staked it where it was originally staked. All done, ready for the booster

I didn't use the hydraulic press to stake it. Instead I clamped it in the vise. That way I had a tactile way to determine how hard I was staking it

[Captain Obvious]

Cool! The valve looks great. Don't forget to do a safety margin pull test on it.

And can I borrow that fixture when you're done with it?

[Patcon]

1 hour ago, Captain Obvious said:

Cool! The valve looks great. Don't forget to do a safety margin pull test on it.

And can I borrow that fixture when you're done with it?

Yeah, I need to do a pull on it, but since I actually had to tap it in to start, then staked it after that, I doubt it's coming back out

I guess you can borrow it... connect in Atlanta...