68 Brake Booster
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Mountain Pass
Joined: Oct 2001
Posts: 176
Likes: 2
From: Northwest
68 Brake Booster
I bought a used brake booster and master cylinder from a 68 F100 and installed it on mine. That was about 4 years ago. Shortly after the brake booster started leaking. I bought a rebuilt and installed it on the master cylinder. Just recently this rebuilt failed and began leaking so I will have to replace it again. When I press on the brake I hear the sucking air noise and the brakes work but I have to step down hard. I guess I'm wondering why the booster only lasted about 4 years. When I installed this rebuilt I remember seeing a 1 inch flat solid washer on the ground. It actually looked like it would fit directily into the hole that the master cylinder push rod went into. I didn't install it thinking it's just a coincidence. Now I'm wondering if this was a spacer or someting. During its operation everything seemed OK. I'm wondering if anyone can shed some light on this. Thanks,
Thread Starter
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Mountain Pass
Joined: Oct 2001
Posts: 176
Likes: 2
From: Northwest
Yes there is a line between the booster that leads to the intake manifold but it appears to be good. I cannot see or hear any vacumn leaks there. The leak sounds like it's coming from within the booster itself. What I'm trying to figure out is why it failed prematurely. Did I leave out a spacer that I mentioned and that caused the failure? I disassembled the old one from the master cylinder on my work bench. I noticed the nickel coin type solid washer on the ground during this. I hadn't seen it there before. I placed it in the hole where the plunger goes from the master cylinder into the booster and it fit perfectly. I still didn't believe it was part of the set up but now I'm wondering if it was and that leaving it out was wrong and could have cause early failure. I posted the question in preparation of taking things apart again. Or was it just a bad booster that wasn't rebuild correctly to begin with. I don't know, I just don't want it to happen again.
Fleet Mechanic
Joined: Aug 2007
Posts: 1,834
Likes: 260
From: Piney Woods of East Texas
There are only a few things that normally fail brake booster. One is a leaking master cylinder. The other if the fuel vapor is getting to the booster, there is a little check valve for keeping the vacuum in the booster. I would look closely at the plunger seal. This is a washer type seal about 1 1/2 - 2" in dia that seals the plunger to the booster. This is what the brake fluids eats if a leak.
When you assembly it back use some silcone vacuum grease on the seal, rod and booster flange, to insure a good seal. You should beable to check for leaks with out the MC.
When you assembly it back use some silcone vacuum grease on the seal, rod and booster flange, to insure a good seal. You should beable to check for leaks with out the MC.
Last edited by blue68f100; Sep 15, 2007 at 03:27 PM.
