vacuum minimum

[jimraelee]

On a typical gas engine, we can get upwards 30" of vac... but our trucks run a pump... I put a guage on it and its steady at 20". Is that normal???? I am having an issue with keeping the Speed control steady at a given speed.. seems to always slink, as if not enough vac to hold it steady

 

[Rot Box]

Hmmm not sure on your problem but my vacuum pump is fairly new and I draw 23-25 usually.

 

[jimraelee]

it started off about 15 then climbed to 20"... so not quite sure

 

[jwalterus]

I don't even want to know what mine is currently, either I developed a leak tonight at work or my vacuum pump is dying at idle my brake light is bright on, then after I get to 1000 rpm it starts to fade away and is gone at 2000 rpm, then it fades back in coming down towards idle again

guess I'll be replacing some vacuum lines and a pump this week

 

[Exekiel69]

25" is a healthy pump, now You can check if it holds whatever it is pulling and see if it a leak or just a weak pump.

 

[MIDNIGHT RIDER]

On a typical gas engine, we can get upwards 30" of vac... but our trucks run a pump... I put a guage on it and its steady at 20". Is that normal???? I am having an issue with keeping the Speed control steady at a given speed.. seems to always slink, as if not enough vac to hold it steady

It is not possible to have more than 29-inches HG of vacuum; if your gauge exhibits more, then it is faulty.

29-inches HG is considered a "perfect vacuum"; I sat up and paid attention during 5th grade science.

My two gauges show a steady 24- and 27- respectively, truck vacuum and trailer vacuum.

In a leak-free system, anything below a steady 20-inches is indicative of a weakening pump.

If a pump can barely hold 20-inches with no demand, it won't be able to keep up with multiple successive brake applications.

 

[GOOSE]

You are supposed to be above 20" of vaccuum and should not leak more than about 3" in one minute after shutting the engine down. I found a tin can vaccuum container to be the culprit in a truck that had brake issues. I simply disconnected everything from the vaccuum splitting manifold and plugged things back in one at a time untill I found the culprit.

 

[jimraelee]

thanks guys, I guess its working good...

 

[Agnem]

You DO have a vacuum gauge installed as a regular instrument on your dash don't you? If not, why are you guessing what is wrong? Get the gauge, and you will SEE if vacuum is your problem.

 

[jimraelee]

thank you moose man... No Im not guessing, no im not going to just start swapping out parts that can be properly tested.. yes I do have a vac gauge, no its not installed. I dont need a cluster of gagues all across the dash. I will however run the vac hose into the cab where I will monitor it with gague... Mearly sourcing vac readings from others is/was my intent

 

[FordGuy100]

I don't even want to know what mine is currently, either I developed a leak tonight at work or my vacuum pump is dying at idle my brake light is bright on, then after I get to 1000 rpm it starts to fade away and is gone at 2000 rpm, then it fades back in coming down towards idle again

guess I'll be replacing some vacuum lines and a pump this week

Thats exactly what happened to my truck when I was driving from Oregon to Texas, it happened in Oregon too. Basically had no vacuum for over 2000 miles . Went to the pick and pull and got a couple of thigns for $20 a vacuum pump included. Fixed it

 

[icanfixall]

Jimraelee... Usually the black tomato juice looking can under the master cylinder gets rust that eats thru it on the bottom. If thats whats happened to yours just some rtv and its all good again...

 

[jimraelee]

Jimraelee... Usually the black tomato juice looking can under the master cylinder

damm back in the day we called them Coffee cans and wondered if they had a deal with folgers or Maxwell house... I will take a better look. I really didnt dive to far into this on the last trip at dads... I tee'd the guage into the vac line going to the cruise actuator, and that was all I had time for... I will do more investigating when I get the truck back to Oregon.

 

[idi traveler]

Thats exactly what happened to my truck when I was driving from Oregon to Texas, it happened in Oregon too. Basically had no vacuum for over 2000 miles . Went to the pick and pull and got a couple of thigns for $20 a vacuum pump included. Fixed it

Sorry, I don't mean to hyjack this thread but are you in Tyler? and if so is there a pick and pull there? I live about 60 miles north west.

 

[OLDBULL8]

Tomato-Tomahto-Pineapple-Apple Juice-Chicken Broth-Beef Broth large 49.5 Oz. same size as the vacuum reservoir. Just have to use the contents first.

Seriously tho: if you get a Vac pump at a pick-n-pull the V-belt shaft is smaller then the Serpentine belt shaft, Serp. is larger, if you would have to change pulleys.