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F750 chassis mount brake booster test


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Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

May 7, 2016, 12:00 PM

Post #26 of 28 (890 views)
  post locked   Re: F750 chassis mount brake booster test  

Refresh - NO - you have a rebuilt booster and it sat for a while. True it should lock vacuum in booster for days even if perfect such that engine off you still have power assist a time or two same as if stalled.
Don't keep pulling the check valve out or it isn't a maybe it will be a leak. It's barbed pretty hard into the grommet and if not why not? they really can tear up one time with new stuff but just wouldn't hold vacuum when not available as said.
If working now shut engine off and just wait 10 minutes. Without starting it should have power assist and if not that's proof of a leak. When running there's ample vacuum at all times except wide open throttle to cover a small leak but not a wide open one.
I somehow you or we are just not getting to the problem like about any issue this important seek out help in person. There's a limit to what you can do without being right there,


Tom



mbavers
User

May 12, 2016, 6:14 PM

Post #27 of 28 (865 views)
  post locked   Re: F750 chassis mount brake booster test  

End of the saga. I replaced all the hoses and fittings. There are a total of 12 separate connections on the vacuum line between the intake manifold and the booster (intake manifold connection, check valve in, check valve out, brass T fitting for vacuum gauge, reducer from T fitting to vacuum gauge, check valve to steel tube, steel tube to booster, etc.) Some of the old fittings were the wrong ones for the job. Instead of a hose barb T they had used a flare T with the vacuum line connected to the threaded ends of the flare fitting. No wonder it never held vacuum with the engine off! Drove it and brakes work perfectly and vacuum is a healthy 20-24 HG. The system holds vacuum overnight.
Reason this took so long is that I had to mail order a 1/2" X 1/2" X 3/8" hose bard reducer T.
Thanks to everyone for advice.


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

May 13, 2016, 1:32 AM

Post #28 of 28 (863 views)
  post locked   Re: F750 chassis mount brake booster test  

Thanks for the report of findings and the fix. I'll close out thread as solved to keep spammers away. YOU may request it to be re-opened upon YOUR request to any moderator,


T







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