Fighting with the vacuum brakes

[bab029]

Been dealing with an intermittent hard brake pedal that turned into a brake pedal that'e hard all the time, as in no boost. I drove a 68 f100 with manual brakes in high school, so while disconcerting, the no boost situation is manageable. Anyway, I finally bought a vacuum gauge and got these numbers:

straight off the vacuum pump: 18 in/hg
at the inlet to the brake booster: 5 in/hg
off of another hose leading to a box I cant identify: 7 in/hg
at an hvac control on the passenger side: 3 in/hg

these numbers are all at an idle, and revving to 1000 or so did not have any effect. I know the vacuum right off the pump is pretty low, but it would seem like enough. Does it look like I have a leak to chase down, or is the pump going out? The thing that gets me is that sometimes I have a really nice firm pedal with lots of power. But most of the time it's just like the old 68. standing on the pedal and using the wheel for leverage. lol

let me know what you think!

 

[icanfixall]

You have mulitapal problems from what you describe. One is a bad vacuum pump and the other is a leak. Using the steering wheel for leverage to stop the truck is not a good thing. If someone or something jumped out in front of you theres no stopping that rig.. I've been there before and have the messy pants to prove it too...

 

[bab029]

Thanks, i'll start hunting a leak. And the cash for a vac pump. lol.

 

[bab029]

Any tips for locating a vacuum leak? There's basically no way i'm going to hear any hissing over the diesel clatter.

 

[lindstromjd]

I would start at the vacuum manifold on the firewall. Test the main line going to the pump first. If you're still getting really close readings to what is coming off the pump directly, then I'd say your manifold is probably the source of your leak. If it's not, then isolate each individual part one at a time. Or, just replace all the lines. Can't go wrong with new vacuum lines.

 

[riotwarrior]

Any tips for locating a vacuum leak? There's basically no way i'm going to hear any hissing over the diesel clatter.

Vacuum lines are not expensive, replace em all...

Try wiggling that plastic Vaccum Tee...that everything ties off, maybe it's cracked?

Eliminate one part at a time, hose, TEE etc until you find the culprit. If it was me...

HYDROBOOST 101

 

[bab029]

Yeah hydroboost would be awesome. But, since I'm in grad school and due to the election it's not all that likely i'll be able to get a job anywhere but mcdonalds after i graduate, economy of repair is the bottom line here.

 

[riotwarrior]

Yeah hydroboost would be awesome. But, since I'm in grad school and due to the election it's not all that likely i'll be able to get a job anywhere but mcdonalds after i graduate, economy of repair is the bottom line here.

Oh how I know and feel yer pains...

Thus as I suggested...eliminate on part at a time....and who knows....by checking local wreckers, you may find a hydro setup....for less or close to the price of a shiny new vacuum pump....just saying hint hint nudge nudge wink wink....

 

[dgr]

Smoke a cigar and apply some anti-vacuum to your hoses. You might get lucky and find a leak. At worst, you got to smoke a cigar.

 

[icanfixall]

Here is a vacuum pump like what you need. A new pump is around $160.00 or even higher..
http://www.ebay.com/itm/221150892448?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

 

[franklin2]

Just put a tee fitting on the line coming out of the pump, and put your gauge on it. Squeeze the line shut with some needle nose right after the tee, and you should get your 18 reading. Then work your way down the line, squeezing the lines together till the number jumps up. In other words, if you shut off the line going to the HVAC system and the gauge jumps way up, then you know the problem is over there. If you squeeze the line shut going to the booster and the vacuum jumps up, then you know there is a problem in the booster.

You definitely need power assist with disc brakes. They do not have the "help" feature like the drum brakes did(I forget what they called it)