79 brake booster?
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Freshman User
Joined: Mar 2007
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79 brake booster?
After allowing my newly minted driving teenage son to use my 79 f150 302 2wd for the last three months, I finally pried him out of the drivers seat so that I could do some routine maintanence. The first thing I noticed was a drop in braking performance. He stated 'oh yeah I forgot to mention that'. I found the mc leaking fluid out the back where it bolts upto the booster. A quick trip to the parts store for a mc, bench bleeding the mc, installing it and bleeding the brakes all the way around and the pedal was normal again...except while the motor is running. This has me thinking the booster has gone bad in addition to the aforementioned leaking mc. The pedal is normal with engine off but with engine on the pedal goes to the floor. I'm thinking the vacuum pressure to the booster is normal as it works off the same vacuum tree as the auto trans and the trans shifts fine. I feel no leaks along the lenght of the booster hose back to the vacuum tree. Any troubleshooting suggestions would be welcome.
Postmaster
Joined: Aug 2000
Posts: 3,312
Likes: 1
From: Eldorado Ca. USA
I have the same problem, except my brakes are *still* not working all that great. I replaced the master cylinder, I have the exact same problem I did prior to the replacement. I bench bled the MC, then gravity and followed it up with a pressure bleed. I tried the brakes with the engine running, they were terrible. I parked the truck downhill so the MC sits level, I pressure bled the brakes again, then did it the old fashioned way with a helper. The brakes are very weak, it feels like only the rear is working. I read thru several service manuals(74 and 80 factory, Haynes and Chilton) some describe a procedure of pushing in, or pulling out a plunger on the brake proportioning valve, but none of them say which is which, and what exactly what needs to be done. I've bled thru 2 of the large bottles of fluid so far.
My guess on what your problem might be is that you need to re-bleed your brakes some more. In every case except for the one I am working on now, re-bleeding the brakes has always cleared up the problem. Have you tried driving the truck, and do the brakes work properly aside from the low pedal?
My guess on what your problem might be is that you need to re-bleed your brakes some more. In every case except for the one I am working on now, re-bleeding the brakes has always cleared up the problem. Have you tried driving the truck, and do the brakes work properly aside from the low pedal?
