Recondition brake booster leaking brake fluid

[twosixtyzed]

I had my brake booster professionally (i.e. not me) removed, reconditioned, reinstalled in February 2026.  The car's sat in my garage since driving it 5mins back from the shop.  I noticed it's leaked about 1/2 the fluid since then and taken the paint with it. The master cylinder rear seal seems to be leaking at the master cylinder-to-booster mounting flange?  The nuts are all tight. It's not leaking from anywhere other than where the blue arrow and red arrow are.  I can't get a better read on it than that, it's an awkward spot.

My skill level is basic but willing to give things a try.  I could drain the fluid, undo the two master cylinder nuts from the facing plate. Then the two nuts on the booster then....what? Is it a gasket that wasn't seated right?  

I am inclined to go back to the mechanic and politely ask if he can take a look, but at the same time, it's my car, I gotta take responsibility and put some effort in but I don't want to c0ck it up and make it worse.  You know, a novice coming in thinking he knows more than he does.  I don't want to be that guy.  

 

[RichyRich]

Given you paid to have it restored (which I assume was the bore only because the outside looks unrestored), I’d take it back, tell them what’s happened, and see what they say.

Worst case, they don’t accept any responsibility, and you either have to pay them again / more, take it somewhere else, or do it yourself. But, at least it gives a chance they might fix it under some sort of warranty, or provide some explanation that might help decide the way forward.

It would cost nothing to take back to see what they say…so nothing to loose, really.

[joe71_240z]

Sounds like it wasnt put back together too well. Was it honed or sleeved? Was a new rubber seal kit installed? It will be the rear rubber seal inside the master around the pushrod that is leaking. Master needs to come back off to fix it.

Hope this helps. Please keep us updated as to your progress.

<Edit>

The seal/s in question are not around the pushrod; I wasnt thinking straight when I typed the reply. The seal around the pushrod at the rear is a dust boot, the seals that would be leaking are inside the bore of the master cylinder.

Edited Tuesday at 10:30 PM by joe71_240z

[Enzo]

You mention that the brake booster was reconditioned. The leak is from the master cylinder and from the looks of it, it wasn't reconditioned. (Correct me if I am wrong). Replace the master cylinder. 

David.

[twosixtyzed]

Thanks guys it has been really valuable having more eyes on this as I was thinking it was a bad recondition of the booster, you've steered me in a better direction.  

The MC was untouched that's correct (how did you guess, barely a blemish on it!).  My mechanic's text yesterday was "Need master rebuilt. Any chance you can pull it off?" - bit cheeky given he "Fixed" the brakes but anyway, I can't drive it to him in this state so it makes sense I have a crack.  So it looks like you're on the money. I will look at this positively, use it as an opportunity to learn.  I found a replacement Tokico MC for a 260z with bore size 22.22mm which I think is what I need, I'll keep the old one and restore it once I get better at all this.  I'll tackle this once the part arrives.

[joe71_240z]

Make sure you get the correct size flare nut spanner / line spanner so you dont do any damage to the flare nuts. Start soaking them in penetrating oil now to make loosening them easier, even though they would have been loosened to reco the booster.

[joe71_240z]

Sorry for my dribs and drabs posts on this one. If you dont have a flare nut spanner already get the best quality one that you are able to budget for as the cheaper ones tend to open up a little as you are using them. If you need to know the size please let me know I dont know it off the top of my head anymore as I havent "spannered" for a while but Im happy to check my toolbox over the weekend if you need the correct size.

[twosixtyzed]

Joe you're amazing, I am definitely reading your updates!  I am buying a flare nut spanner (10-12mm) at the weekend as I didn't even know about it until you said, my plan was to report back once I've either duffed it up or completed it successfully.  I've also bought a vacuum hand pump kit so I can bleed the brakes (never done it, always wanted to know how).  I am so...pumped...to start this work!

[joe71_240z]

No problems, Im happy to help out. Pull as much of the old fluid out of the master with a syringe before you take is off. Have plenty of old towels ready just in case. When you get it back you will more than likely have to "bench bleed" the master; search youtube as this is our modern day friend.

Keep us posted.