# not getting vacuum



## 300zxev (Dec 5, 2008)

Hi All

Finaly got around to connecting my KTA vacuum kit ...
I have set the vacuum switch to 20HG down to 10HG ...
Fired it up and it has trouble getting up to 20 ... then drops down to 10HG within about 10-20 secs ...
If I pump the brakes once it drops straight to 5HG ...

Have double checked all connections and they are tight.

Tried crimping the hose up near the brake booster and the pump then seems to be working ok.

Holds vacuum without dropping (well dropping much anyhow)

Let go of the hose and the vacuum starts dropping ...

Since the hose appears to be secure to the brake booster ... 
Where could the problem lie ?
It the brake boosted suposed to hold the vacuum ?


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## dtbaker (Jan 5, 2008)

the brake booster should hold vacuum without ANY loss for 'days'. If it isn't you've got a leak somewhere, or a bad diaphragm in the brake booster itself..... did you install the check valve? 

see picture at
http://www.envirokarma.org/ev/gallery/080723_03.vComplete.htm

depending on your altitude above sea level, the max vacuum will 'derate' about 1 inHg/1000' elevation, but it sounds like you have a leak.


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## electromet (Oct 20, 2009)

300,

Yes, the booster should hold vaccuum. Perhaps you have a pinhole in the booster diaphragm? Are you using a one-way valve between the pump and tank? Just a couple of random thoughts.


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## 300zxev (Dec 5, 2008)

Yes ... one way check valve was part of the kit ...
As I say ... when I crimp the hose just before the booster it holds vacuum fine ...
Don't know anything about the brake booster itself, so i'll dig out the workshop manual.
Any hints on what to look for ?


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## electromet (Oct 20, 2009)

300,

When you say it holds vaccuum, are you refering to the storage tank or booster? If the storage tank is holding, then the booster (or the plastic inlet fitting) is most certainly the culprit. To avoid any further aggravation, I'd be inclined to just buy a new booster.


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## 300zxev (Dec 5, 2008)

dtbaker

looks like you have the same kit as me ... do you know how many amps yours draws ...
Mine only draws 2.5A even though the pump is stamped 6.8A ?

Don't think that is the problem, but just another thing that is puzzleing me.


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## 300zxev (Dec 5, 2008)

electromet

i'm referring to the tank lines etc ... ... 
the vacuum doesn't drop with the booster out of the equation.

I think i'll have to be looking for that new booster ...

A quick search in google is worrying me though ... 
Checking for "brake booster not holding vacuum" ... brought up a whole bunch of results of people removing ABS from their vehicle then having that symptom.

We'll this car did / does have ABS ... what is the difference between an ABS booster and not ?


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## dtbaker (Jan 5, 2008)

I can't imagine ABS having an affect at rest.... The pulses during a skid condition would probably empty your tank and leave you with no power assist. Assuming your chip still talks to your abs.

regardless, I would bet on a pinhole in your booster, OR that very last fitting is leaking.


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## electromet (Oct 20, 2009)

300,

I'm not exactly a rocket scientist when it comes to electronics, but there may be sensors and/or pulse generators in the ecu that are looking for a very specific vaccuum value in order for the system to function properly. There are a couple guys on this forum that actually enjoy hacking into ecu's. They might have some answers before you run out for that booster.


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## electromet (Oct 20, 2009)

I think dtbaker and myself are in some kind of mind meld. I think I'll let him respond on his own next time.


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## 300zxev (Dec 5, 2008)

I have removed the main ECU and wiring harness long ago ...
I believe there may be a separate computer for the abs which I haven't touched ...


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## Tom W (Jun 9, 2008)

Do you have the heater/AC controls hooked to the vacuum hoses? If so, make sure they are in the off position and check vacuum.


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## PhantomPholly (Aug 20, 2008)

> not getting vacuum


Well, that sucks!


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## 300zxev (Dec 5, 2008)

Hi Tom

There aren't any additional vacuum lines connected in my circuit all the way to the brake booster ... ...

I haven't had a great look but didn't think there were any other lines going into the booster either ...

Checking the workshop manual there is a diagram of the brake booster removed and being tested with a handheld vacuum gauge ... So that would imply the booster should be holding the vacuum on its own ...

When the rain clears up I might attempt to remove the booster and take it somewhere to have it reconditioned ... ... hopefully they will have one of those handheld vacuum testers and be able to tell me it needs work ... ...

I don't want to start getting involved with telling mechanics exactly what I have done to the car incase they use that as a backdoor as to why the booster isn't working ...


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## Jimdear2 (Oct 12, 2008)

300zxev said:


> Hi Tom
> 
> There aren't any additional vacuum lines connected in my circuit all the way to the brake booster ... ...
> 
> ...


300zxev,

Check and make sure there is some free play in the brake pedal and push rod. You should have about a 1/4 to 1/2 inch of play before the push rod contacts the brake booster.

You can test the booster for leakage simply.
1.) Make sure your check valve is functioning properly.
2.) Build vacuum in the system
3.) To be sure the check valve is OK, do the test, pinching the the hose up stream of the check valve.
4.) The system should hold vacuum for at least a few minutes. A good systtem should hold vacuum for hours.
5.) If it is leaking, go under the dash and listen you will hear a hissing (again be sure there is some free play in the pedal push rod) If you hear a hissing the booster is bad. 

A piece of vinal hose with one end in your ear and the other end as a probe works well as a listening device.

The local autopart store should be able to supply you with a rebuilt booster. Be sure you follow instructions when replacing it.

Good luck


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## 300zxev (Dec 5, 2008)

Hi

I removed the booster and had it connected solely to the vacuum line ... but issue still persisted ... vacuum would get to about 15Hg and as the vac switch is set to 20, the pump stays on always ... hit the brake and drops to 5Hg immediately.

I sent the booster off to get reconditioned and the reco company said they had it on their test bench and it was working correctly ... they had it at 27Hg and it was holding vacuum ... 

They said it had a slight leak but not bad and they could do the reco anyhow ... but at $400 I passed on the offer. 

Put it back on the vac line ... this time with sealing tape and 2 clips ... still having trouble getting to 15Hg ... If I crimp the hose again just before the booster, it struggles to just over 20Hg. 

All this while, I contacted KTA to ask why the pump doesn't draw 6.8A as stated ... It only drew 2.2 ... response was it draws the 6.8A under load.

Just for interests sake, I monitored the amps as the pump reached 20Hg ... Instead of increasing in amps, it dropped slowly to 1.3A at 20Hg.


Anyone have any ideas about this setup ??? Don't know why the pump doesn't go anywhere near the amps it is suposed to.

At the moment I am suspecting this Gast Vac pump doesn't have adequate flowrate ... as in the writeup states 0.5 CFM (less than 0.1 CFM @ 20Hg) ...

Looking at alternates ... the Thomas apparently flows 1.4CFM to 23Hg and 8.5 Amps


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## dtbaker (Jan 5, 2008)

300zxev said:


> vacuum would get to about 15Hg and as the vac switch is set to 20, the pump stays on always ... hit the brake and drops to 5Hg immediately.


this sounds 'as expected'... without the reservoir in place, one pump of the brakes would use up all the vacuum. 15 Hg may be all you are going to get; what is your elevation above sea level? I had to set my switch to -13 (I am at 7000') so that the pump didn't run for long to try and get that last little bit of vacuum.



300zxev said:


> Put it back on the vac line ... this time with sealing tape and 2 clips ... still having trouble getting to 15Hg ...


you might wanna try a paste pipe dope instead of tape. Tape is intended to go in threaded connections.



300zxev said:


> All this while, I contacted KTA to ask why the pump doesn't draw 6.8A as stated ... It only drew 2.2 ... response was it draws the 6.8A under load.
> Just for interests sake, I monitored the amps as the pump reached 20Hg ... Instead of increasing in amps, it dropped slowly to 1.3A at 20Hg.


sounds 'as expected'... as the vacuum draws down the pump is no longer doing much work since it isn't drawing out any more air and the amps would drop. The amp rating is a MAX under full load... as it approaches its mechanical limit it is doing less work, and will draw less amps.



300zxev said:


> Looking at alternates ... the Thomas apparently flows 1.4CFM to 23Hg and 8.5 Amps


you might be kinda obsessing over this.  Even at -10 you get a fair amount of brake assist. I would set the switch low enough so it runs for maybe 15 sec after braking and see how it drives before you consider replacing the vac pump. What's the price on the Thomas pump? Is it LOUDER?

Only other thing I can think of is the orientation of the pump, but I don't think that is supposed to matter.


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## 300zxev (Dec 5, 2008)

> this sounds 'as expected'... without the reservoir in place, one pump of the brakes would use up all the vacuum. 15 Hg may be all you are going to get; what is your elevation above sea level? I had to set my switch to -13 (I am at 7000') so that the pump didn't run for long to try and get that last little bit of vacuum.


This was all happening with the reservoir (about 1L) in place. The elevation here is 80ft above sea level.



> you might wanna try a paste pipe dope instead of tape. Tape is intended to go in threaded connections.


I'll have a hunt around for this next time i'm down at the hardware store ... but i'm pretty sure that one connection isn't leaking 



> sounds 'as expected'... as the vacuum draws down the pump is no longer doing much work since it isn't drawing out any more air and the amps would drop. The amp rating is a MAX under full load... as it approaches its mechanical limit it is doing less work, and will draw less amps.


Perhaps the elevation effects the Amp draw then ... because I don't see any greater than 2.2A at startup.




> you might be kinda obsessing over this.  Even at -10 you get a fair amount of brake assist. I would set the switch low enough so it runs for maybe 15 sec after braking and see how it drives before you consider replacing the vac pump. What's the price on the Thomas pump? Is it LOUDER?


I might be obsessing over this but I had a brief inspection from the transportation engineers and he pointed out I have to have the Vac switch set to run between 25-20 Hg ... Getting the Thomas unit is throwing down another US$300 and it is probably louder ... Perhaps if I had a larger Vac storage tank it would be usable at 15Hg ... If no other suggestions arise I might look at making an additional 2L reserve and bolting it below the one i'm using.




> Only other thing I can think of is the orientation of the pump, but I don't think that is supposed to matter.


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## dtbaker (Jan 5, 2008)

your Inspection checks power brake vacuum? I'm AMAZED.... Anyway, I am pretty sure that most power brakes only require 10-20 inHg to work correctly. Mine with a peak of 13 makes for 'stiff' power brakes, but still a help compared to if I pump the brakes a couple times and empty the res on purpose.

One other thought is that the pump is perfect and the gauge is mis-calibrated. I'm not sure how you'd check it though.


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## azdeltawye (Dec 30, 2008)

300zxev said:


> ...Getting the Thomas unit is throwing down another US$300....


I would try to source a used OE electric vacuum pump. I found one off a 2002 VW new beetle. It pulls a vacuum down to 23" within 10 sec and it was only $50. It's also fairly quite as long as you use rubber isolation mounts. 

The application to look for is A4 (4th generation Jetta) or new beetle with the 1.8L turbo gas engine and auto tranny - apparently the turbo charged engine doesn't develop enough vacuum when used with the auto tranny so they threw in an electric pump. The TDI diesels use a mechanical pump so that wont work...


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