Vacuum Leak

ctuinstra

Well-Known Member
#1
Kaleb took that car (via trailer) to get the wheels aligned and I noticed we have a terrible vacuum leak at the master cylinder as it mounts to the booster. I have the large, square O-ring in there. I noticed when I installed the MC that is never pulled in close to the booster and left a gap. I thought well I have the seal in place, maybe that's the way it supposed to be. I cannot tighten down the MC mounting bolts anymore, they are bottomed out. I can't imagine having to put two seals in place. Both the MC and the boost are new. There is no doubt that is were it's leaking from. Could it be a wrong model of booster/MC? Any ideas?

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Lethalcast

Well-Known Member
#2
I cant twll from the pic if your booster is flat or not. The lnf booster is flat at the mount point and the lsj has a raised lip. Maybe they sent you the wrong one. It also shows the ss and base are different boosters. Heres some pics for reference
s-l640.jpg
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ctuinstra

Well-Known Member
#3
The first picture is more like what I have. The second picture, I've never seen on either build. You say the base model and the SS use different booster? Rockauto list them as having the same? Could they be wrong?

I purchased:

ACDELCO 14PB4074 {#19286774} (Remanufactured) Professional; Reman. Info
w/o Master Cylinder

And the master cylinder:

ACDELCO 18M2449 {#19287358}

I don't have access to the parts manual, can anyone tell me if these are correct?

These are the parts when I received them.

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Lethalcast

Well-Known Member
#4
The second one is what was actually on mine. It has the different master cylinder than yours. I'll see if I can find it in the manual.
 

Lethalcast

Well-Known Member
#5
Pn for booster is 15261541
Pn for mc is 19209201. I just looked it up on gmpartsdirect.com and there is some variation in numbers.
 

ctuinstra

Well-Known Member
#6
Pn for booster is 15261541
Pn for mc is 19209201. I just looked it up on gmpartsdirect.com and there is some variation in numbers.

Thanks. Too many different part numbers for different manufactures. Even the ACDelco numbers aren't even of the same numbering format to be able to tell if I have the wrong one. They look like the correct unit.

If anyone has a 07 SS/SC and to that point that can take some really good pictures that I can use for reference, I would appreciate it. This one has me stumped.
 

ctuinstra

Well-Known Member
#7
Well I think I have it figured out. The gap, now that I look closer, is not even all the way around. This was newly rebuilt unit and may very well come from damaged core. Now I have to see if I can pull it without having to open the brake lines on the master cylinder. And then decide if I should try and fix it or return it to Rockauto.
 

ctuinstra

Well-Known Member
#8
I pulled off the master cylinder today. The large hole for the MC is not on the same plane at the two bolts. The entire surface should be flat. Mine had half of the opening for the MC pushed in about 3-4mm. The material is really soft and I was able to pull the hole out flush with the rest of the surface. Hopefully that will be the end of the vacuum leak!

Luckily I had a set of MC plugs to plug it off so as not to drip all over the place. I still have to re-bleed the brakes again to make sure to get rid of any air in the lines.