brake issues

[NextENRG]

Good Morning,

first off this is a 1991 F350 7.3 dually with CTS turbo system

my problem just appeared while i was driving. when i put the brake pedal down everthing works.....if i let off the brake and try again it seems like i have no vaccuum and is very difficult to slow down. if i try for a 3rd application its next to no vaccuum assist.

vaccuum pump sucks and brake booster holds vaccuum and there are no leaks im aware of.

funny thing is if i sit at a light i can feel that the pedal returns to normal and even quicker if i put it in neutral and hold rpm higher, though if i pump the brake while doing this all assist disappears then comes back if i hold.

any thoughts or help much appriciated.

 

[NCheek]

Sounds like a tired vacuum pump... Someone will post the testing procedure.

 

[hesutton]

Like Nick said, it sounds like a vaccum pump to me too. I also have no idea about the vaccum pump test.

Find a post by Agnem (Mel) and check out his webshots galleries in his signature. There is a vaccum pump test in there somewhrere. It should not be hard to find one of his post.......they are everywhere.

Heath

 

[redneckaggie]

just went through this and just because it sucks doesnt mean it is good it HAS to get you to 23(i think) psi of vacum and when my brake booster went out the idiot light for the brakes would come on. the easiest way to test the pump is to remove the line coming off of it and hook a vacuum gauge to it crank the truck and let the pump reach its most highest vaccum. kill the truck and walk away. come back in about 5 to 10 min and see if it has bleed down my guess will be that it will. if it reaches 23 lbs and holds it then you have a leak in your lines or booster.

 

[NCheek]

Like Nick said, it sounds like a vaccum pump to me too. I also have no idea about the vaccum pump.

Find a post by Agnem (Mel) and check out his webshots galleries in his signature. There is a vaccum pump test in there somewhrere. It should not be hard to find one of his post.......they are everywhere.

Heath

Funny you say this Heath, because I scoured his photo galleries before I replied and couldn't find one, and I swore that Mel had it on there too...

 

[NextENRG]

23 psi or 23 inches of vacuum?

 

[fastass350]

That would have to be vacuum wouldn't it, if it was psi it would be pressure, and that wouldn't work out well. No? I don't know positive, but that's what my thinking tells me

 

[NCheek]

I think it's 21 inHg, iirc...

 

[LCAM-01XA]

Yes, that should be in inches of vacuum, inHg.

 

[david85]

Yes, that would be Hg. I think we are all hard wired to think in terms of PSI (tire, fuel and boost pressure). We won't talk about those other folks that fancy bar, or even kilo pascals.
They're not like you or me.

 

[LCAM-01XA]

Dave, you mean them strange creatures that are rumored to dwell in French Kanadia?

 

[Agnem]

This is a typical vacuum pump failure mode, and don't waste your time putting a gauge on it, unless your mounting it on your dash (which if you had done this previously, you would already be seeing what your problem is). Typically, it is not the presure that is the issue, but the volume of vacuum available. I've never seen a bad pump that couldn't pull down the 23 inches at sea level. What the problem almost always is, is HOW LONG it takes it to do that. The purpose of having a vacuum gauge as part of your instrumentation (just as important as a pyro in my opionion) is so that you learn the behavior in the swing of the needle. If you have a guage, you'll be seeing the fact that it is taking longer and longer to pump down. You need a new vacuum pump.

 

[icanfixall]

I think you have a vacuum leak. This could mean your vacuum pump is shot or there is a leak. Check out all the vacuum hoses and the vacuum resivour located on the drivers side fender well. That large tomato looking can usually has some rot near the bottom. Mine did and some rtv fixed it around 9 years ago. Still works fine...

 

[RedTruck]

rtv fixed it around 9 years ago. Still works fine...

I think this is the only fix I've seen Gary mention that doesn't involve a micrometer, dial indicator, precision straight edge, or knat's ****.

Paul

 

[david85]

Dave, you mean them strange creatures that are rumored to dwell in French Kanadia?

Careful, you'll get me in trouble