Brake Booster Rebuild Help

[ToolBoy]

Just occurred to me when thinking of your initial question. The rubber reaction disk "E" that sits against the pushrod can fall inside the housing when the pushrod is removed if one isn't careful.  

[HappyZ]

I read the FSM, but couldn’t figure it out.  You pick really helped.
 

last question @ToolBoy ... will the booster hold vacuum without plate and seal installed with pushrod?

thank you...thank you

[ToolBoy]

Hey HappyZ,   Glad to help out a little as most of the time I'm confused and terrified.  After I had mine torn apart I went to the local Z mechanic to find out how the poppett assembly came apart. He said he didn't know as he had never done it and always "sent them out". The guys on this site saved me on that one. When you tear apart the entire unit and study it you see that the vacuum is held inside the front shell between that shell and the big rubber diaphram that is included of the rebuild kit. There are only a couple places vacuum can escape but one is to the front around the plate and seal and thru the pushrod. My suspicion is that if you don't have a perfect seal at the plate and seal, the installation of the master cylinder stops the vacuum after it has been fitted. I think I checked vacuum only after bolting that on.  ( I think ).

[Captain Obvious]

10 hours ago, HappyZ said:

will the booster hold vacuum without plate and seal installed with pushrod?

No, it will not hold vacuum without that front seal. If that seal is not in place, it's a direct link from the vacuum port to that hole.

[Captain Obvious]

9 hours ago, ToolBoy said:

My suspicion is that if you don't have a perfect seal at the plate and seal, the installation of the master cylinder stops the vacuum after it has been fitted. I think I checked vacuum only after bolting that on.

In reality, you don't ever want to draw a vacuum against the back of the master cylinder. In fact, on the original system, I there's a hole to prevent just that.

You shouldn't block that hole (like with a gasket or something). and because there IS a hole there, the bolting of the master cylinder to the booster will do nothing to retain vacuum.

 

[ToolBoy]

I wasn't sure and knew if it wasn't right I would hear about it. Thanks for that. I'll look for that hole too. 

[Patcon]

I believe there is a small dimple on the lower part of the hole the master cylinder bolts into on the booster. I believe it is designed to allow brake fluid to drain out instead of into the booster

[Captain Obvious]

ToolBoy, You can see the vent passage in one of the pics you previously posted:

I thought there was slot in the master cylinder or adapter as well. I looked for pics, but unfortunately don't have any that would help there.

[ToolBoy]

Perfect, I never noticed that passage before. I'm hoping I can get plate/seal/rod to seal well enough.

[zKars]

21 hours ago, ToolBoy said:

Just occurred to me when thinking of your initial question. The rubber reaction disk "E" that sits against the pushrod can fall inside the housing when the pushrod is removed if one isn't careful.  

I ALWAYS crazy glue the reaction disk to the piston when I take these things apart. No way I’m ever losing that thing again...

[Captain Obvious]

7 hours ago, ToolBoy said:

Perfect, I never noticed that passage before. I'm hoping I can get plate/seal/rod to seal well enough.

If the surface of the rod isn't all pitted with rust, it should seal pretty well. In the area where it matters, yours looks pretty good.

So about the vent passage... Are you sure the gasket you put on there isn't compressed into the vent and blocking it off? I'm beginning to think that there is NOT another passageway on the adapter plate or the back of the master cylinder. That slot may be the only vent?

[ToolBoy]

Thanks for the follow-up. The rod does look good although it might have a few tiny chips in it and I don't remember if I used the plate and seal from the kit or the one that came with the car. The first time I checked vacuum it held and the second time it dropped a little. I cut the gasket myself but given the new info I'll leave it off when I reassemble. You're in Philly?  My mom's brother lived in Philly for 30 years and my mom is from Beaver Falls. I'm originally from Lancaster.