Vaccum Mystery

[7.3IH_Eggrole]

So fellas lets see if yall can solve this riddle I've been having. Last year about this time (the time of the year when it starts getting a little cooler here in North Carolina) I began having problems with the brakes on my 1992. I drove it like that until about Feburary. I would push the pedal and it would be like stepping on a brick at idle (no problems otherwise). So I finally got tired of it and replaced the vaccum pump and drove it without problem until last night. I was coming down an off ramp off of I40 into Raleigh and went to mash the pedal and found another brick. So I bricked my way to the house and got up this morning and the issue had not fixed itself. It doesn't matter if I am idleing or wot, all brick.

So my issue is this, I had good brakes when the temperature was say 65 degress F or higher. Now that it has cooled off at night and during the day it doesn't get as warm I have no brakes. By the way I have put about 6k miles on that 8 month old vacuum pump.

Anyway give me some ideas, I dont understand why I only have problems in the cooler part of the year.

-Ed

 

[Dsl_Dog_Treat]

Have you run a test on the pump yet to see what type of vaccum it's pulling and recovery time?

 

[7.3IH_Eggrole]

Have you run a test on the pump yet to see what type of vaccum it's pulling and recovery time?

I haven't payed any attention to recovery time, but it pulls a little better than 18

 

[Dsl_Dog_Treat]

Doesn't sound too promising. It should be pulling 21 inches but the recovery rate is what needs to be looked at as well.

 

[7.3IH_Eggrole]

Doesn't sound too promising. It should be pulling 21 inches but the recovery rate is what needs to be looked at as well.

OK since it was asked I went and checked. I got 19" in about 8 seconds.

 

[Dsl_Dog_Treat]

OK since it was asked I went and checked. I got 19" in about 8 seconds.

That's an awful long time. You tested the pump directly and not the entire system I trust?

 

[icanfixall]

The low vacuum numbers tells me you have a vacuum leak somewhere or the pump is shot. Do the test right off the pump and not the entire system. The vacuum can that holds vacuum for the cruise control sitting on the drivers side fenfer well sometimes gets holes rotted in it on the bottom. Its a really hard find sometimes. Just follow all the vacuum hoses and see if they have rubbed holes or cracks in them. It wont take much of a hole to kill the vacuum. Or change the vacuum brakes over to the hydroboost brakes. Then you will have twice the brakeing pressure plus no more vacuum issues.

 

[Agnem]

If you had a vacuum gauge mounted in your instrument cluster all along, you would understand the normal behavior of your vacuum system and be able to tell right off the bat that you A) - have a problem brewing and B) - definitely have no brakes. I've said it hundreds of times. EVERYBODY who drives one of these trucks NEEDS to have a vacuum gauge in their instrument cluster, or switch to Hyrdoboost. It would be akin to operating a class 8 truck without an air presure gauge, and who in their right mind would do that?

 

[7.3IH_Eggrole]

If you had a vacuum gauge mounted in your instrument cluster all along, you would understand the normal behavior of your vacuum system and be able to tell right off the bat that you A) - have a problem brewing and B) - definitely have no brakes. I've said it hundreds of times. EVERYBODY who drives one of these trucks NEEDS to have a vacuum gauge in their instrument cluster, or switch to Hyrdoboost. It would be akin to operating a class 8 truck without an air presure gauge, and who in their right mind would do that?

Yes Mel I know you've said that before. And I feel that you are right, but my question here is why am I only haveing trouble in cooler temperatures. I have no problems from the months of March to September with the same system. It starts getting cold and for two years in a row now my brakes go away. Do yall think a line is causeing this, or the can, I think a line would leak at most any temperature.


Anyway thanks for the help.

 

[Dsl_Dog_Treat]

Well the lines can and do get hard and brittle over time.
It's possible that one of the lines has developed a crack and cooler temps have cause the material to contract, thus causing a leak.

Either that or it's just coincidence if the pump took a poop on ya.

 

[7.3IH_Eggrole]

That's an awful long time. You tested the pump directly and not the entire system I trust?

So right off the pump and the pump alone I am getting a little better than 19" and it is pretty instant. Also I left it connected and after an hour I lost no vacuum on the pump. Also put it back together and brought the system up (again with a stop watch I see 19" in about 8 or 9 seconds) and left it in and it hasn't lost anything as of now (30 minutes).

Again, the fact that is alluding me is why I dont have a problem any other time of the year but now. I mean I can put a gage in like Mel suggests, and watch the system year round, that would be the smart thing to do. But I haven't done that til now but I will have one from here on.

 

[7.3IH_Eggrole]

Well the lines can and do get hard and brittle over time.
It's possible that one of the lines has developed a crack and cooler temps have cause the material to contract, thus causing a leak.

Either that or it's just coincidence if the pump took a poop on ya.

Maybe so, I'll just buy a new pump, I just hate to waste the ~$250 if its a line, but I'm not losing anything when the system goes static. But I'll have a gauge this time.

 

[7.3IH_Eggrole]

Fellas,
Put a new pump on and new lines, problem fixed. Got a vacuum gage too. I know Mel will like that.

Ed

 

[Dsl_Dog_Treat]

Good to hear that Ed.

 

[Agnem]

Yay! *jumps up and down with glee

You won't regret it. Now I will have another person to help preach the Word!