How Much Vacuum?
Thread Starter
|
Tuned
Joined: Jul 2004
Posts: 476
Likes: 5
From: Delaware
How Much Vacuum?
I have a 1987 F250 with the 6.9 diesel engine. How many pounds of vacuum should the vacuum pump pull? The problem I have is sometimes the power brakes seem OK and other times I better have that second foot ready to help out on the brake pedal, right NOW. I'm not sure if it's a weak vacuum pump or weak brake booster. I don't want to blow $100 plus on a booster only to find out it's a weak pump, or buy the pump to find out it's the brake booster. With a gauge I get 8-12lbs at an idle, 13-14 at 1500rpm, and back down to about 12-13 at 2000 rpm. Does this seem weak to you? I've looked but I've not found the specs on just what pound of vacuum is within limits.
Thread Starter
|
Tuned
Joined: Jul 2004
Posts: 476
Likes: 5
From: Delaware
I checked for other leaks but I'm getting the same vacuum at the hose directly from the pump as I do at the brake booster. 14-15lbs max right from the hose to the pump before it goes anywhere else.
Junior User
Joined: Feb 2004
Posts: 63
Likes: 0
I had the same problem with the exception I only had 8 - 10 lbs... I changed Pump and 1 week later had to change the booster the new pump took out the booster!!!!!! $200.. for both a small price to pay so you don't wind up rear ending someone...
Posting Guru
Joined: Sep 2002
Posts: 1,897
Likes: 0
From: Northeastern Pa - USA
I had the same problem but only while pulling the trailer. I replaced the standard master cylinder with one from f 350 super duty. Had to ream the mounting holes a bit but it sure did the trick. It is possible that you are having a different problem.
Senior User
Joined: Jan 2004
Posts: 153
Likes: 0
From: Harrison County, Texas, C
Got the same problem here with my 86 250 with 6.9 IDI. This damned machine runs off of the vacume pump. I just got a new one this morning and will put it on. I am getting precious little vacume and the thing is supposed to suck like a two doller *****. Brakes and air controls don't hardly work without it.
Trending Topics
Senior User
Joined: Oct 2004
Posts: 228
Likes: 0
From: chino valley az
keep you eyes open at the junk yards. ford did use a hydroboost assembly. it was usually on the dually f350 and superdutys. i have found them, and have done the conversions quite a few times. replace the vacuum powered booster with the hydroboost, install the new power steering hoses, and junk old pump and booster. they use the same pump and fitting, so it is really a bolt in application. my 93 superduty had it (before a drunk nailed it) and it was the greatest! i have paid less for the used hydroboost and hoses than the new vacuum pump. hope that helps.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Top 10 Ford Trucks Coming to Mecum Indy 2026
Brett Foote
5 Best / 5 Worst Ford Truck Wheels of All Time
Joe Kucinski
Senior User
Joined: Jan 2004
Posts: 153
Likes: 0
From: Harrison County, Texas, C
OK, not trying to take over your thread but I thought I would let you all know that my brakes actually function like they are supposed to now that I installed my new vacume pump. The two vacume switches that work the blower speed and the control flapper in the plenum arn't working like they should though, maybe they need to be replaced too.