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Old 10-21-2010, 08:33 PM   #1 (permalink)
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Exclamation Vacuum pump test 1994 ford E-350 / brake issues / abs brake bleed? / RABS

Hello, i had a questions regarding vacuum pump test for 1994 ford E-350 box truck with 7.3 lit diesel.

I am currently having brake issues. My brakes are very soft but they still stop. However, if im driving and i hit the peddle like 3 times real quick, my brake peddle gets support hard but i cant press them any more and if do, the brakes barley work. I wait for 5-10 seconds and i get a soft peddle again.

I spoke to 2 different ford dealer mechanics and they said the same thing, "bad vacuum pump" One said that if i test my pump, i should be getting around 23.. I have a harbor freight fuel and vacuum gauge tester item #: 93547 When i follow the steps that are listed in the link below, i get reads of 23hg in vac and 10hg cm vac. I also just unplugged the hose from the vacuum pump and stuck my finger into the hose line and i felt good suction. So this all sounds like i get good results from my vacuum pump doesn't it?

TheDieselStop.Com Photo Hosting - Vacuum test Part 1 of 2

TheDieselStop.Com Photo Hosting - Vacuum test Part 2

My other concern is the "RABS" or also known as Rear Anti-Lock Brake System. It is located right underneath the driver side mounted to the frame of the truck. Is it possible that this is bad? I dont know much about these things or how often they go bad or ways to test them if any? I think this could be my problem though. The reason is because when we tried bleeding brakes, here is what we did.

1. We had the truck off:

2. pumped the brakes. I started from the Rear Right Wheel. Bleed it 3 times. One thing to note, the more we bleed that wheel the less and less pressure of fluid came out.

3. We moved on to Rear Left wheel. Same thing. First two squirts where powerful, then we lost pressure as we went. So i only bled it like 3-5 times.

4. Then we to front wheels, Front Right and Front driver side bled it just fine with high pressure like 3 times. Fluid squirted out 100% with no air.

* We always check for fluid in the cylinder reservoir to make sure we where running it dry.

5. That's when i found that RABS. We bled that last like 3 times.

So that is why i think it might be faulty. Because the rear brakes lost pressure as we bled them. That could be because its faulty or because we are bleeding the brakes in-correctly or we needed to truck to be running? Anybody know the correct bleeding procedure to bleed these anti lock brakes?

I also pressure tested my brake booster and rest of my vaccumm lines for leaks using the harbor freight item # 39522 Manufacture. Everything seem to hold pressure nicely.

Anything else i should look for or do test on?

Thanks ahead of times fella's.
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Old 10-22-2010, 08:07 PM   #2 (permalink)
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Rear brakes, then RABs valve, then front brakes.........

Brake vacuum lasts about 3-4 pedal pumps and thats it until the vac pump catches up. Normally you don't pump the brakes rapidly to stop, however when backing a trailer down hill be carefull since vacuum is depleted at idle, so use assistance from the trailer brakes via the brake controller.
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Old 10-22-2010, 09:41 PM   #3 (permalink)
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What procedure do you use to bleed the brake?
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Old 10-25-2010, 04:35 PM   #4 (permalink)
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Originally Posted by Snotzalot View Post
What procedure do you use to bleed the brake?
1. We had the truck off:

2. pumped the brakes. I started from the Rear Right Wheel. Bleed it 3 times. One thing to note, the more we bleed that wheel the less and less pressure of fluid came out.

3. We moved on to Rear Left wheel. Same thing. First two squirts where powerful, then we lost pressure as we went. So i only bled it like 3-5 times.

4. Then we to front wheels, Front Right and Front driver side bled it just fine with high pressure like 3 times. Fluid squirted out 100% with no air.

* We always check for fluid in the cylinder reservoir to make sure we where running it dry.

5. That's when i found that RABS. We bled that last like 3 times.



I am gonna by pass the RABS system and see if it fixes my issue.

Thanks ahead of times fella's.
[/QUOTE]

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Old 10-27-2010, 10:25 PM   #5 (permalink)
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Ok so i by passed the RABS system today. Now the brakes brake better. However, i still get the hard peddle if i pump the brakes more then 4 times in a row. I noticed that if i shut down the engine and restart it, i get a normal peddel once again. What does this mean? Bad vacuum? But how could it be if the test turned out great and it seems to work even when finger testing.

what else could it be?
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Old 10-27-2010, 11:08 PM   #6 (permalink)
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Quote:
around 23.. I have a harbor freight fuel and vacuum gauge tester item #: 93547 When i follow the steps that are listed in the link below, i get reads of 23hg in vac and 10hg cm vac. I also just unplugged the hose from the vacuum pump and stuck my finger into the hose line and i felt good suction. So this all sounds like i get good results from my vacuum pump doesn't it?
You did do the vacum test at the "tree" right?
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Old 10-28-2010, 10:04 AM   #7 (permalink)
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For example on A2: TheDieselStop.Com Photo Hosting - Vacuum test Part 1 of 2

I unplug the brake booster hose from the splitter/tree/ where the brake booster hose normally plugs into a male point. Then using a female connection i connected my gauge to that sticking out male port where the brake booster hose would normally connect. At test resulted in 23 hg inches.

That's how i did a test of A2.

On test for A4:TheDieselStop.Com Photo Hosting - Vacuum test Part 2

I unplug the hose that comes from the vacuum pump into the plastic splitter/tree. I took that unplug vacuum pump hose and plugged it into my "T" connection of the gauge. From the other side of my "T" connection on the gauge, i ran a hose and used a female connection to connect to the male connector on the splitter/tree (where the vacuum pump hose normally would connect too). At first i got a reading of 23 hg inches. Then i pressed the brakes and it went way down and was steady around 10hg CM. If i pressed the brakes again, the pressure would go down by 75% but then come back up to 10hg CM in about 10-15 seconds. Keep in mind 10hg CM not in inches like the A2 test..

Did my testing method was incorrect? I also used a vacuum tester to test all the lines for leaks and every line held pressure.

Thanks for your help ahead of time.


EDIT: Come to think of it, the way i did my test, this wouldn't really test the plastic splitter / tree right? I noticed the splitter/tree had some extra closed port nipples that are made for testing maybe? What if my splitter/tree is plugged up? I doubt it, the test would have shown a failure somewhere right?

Last edited by knightOwl4786; 10-28-2010 at 10:11 AM.
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Old 10-28-2010, 10:31 AM   #8 (permalink)
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It sounds like your vacuum pump is weak. 10 CM is about 4", that's low. Funny thing is, mine may be weak, too. I just tested mine at the tree for comparison. I get about 16" initially. It drops to 10" the first time I apply the brake, then slowly recovers to 16". If I pump the brakes rapidly, I can drive it down to about 5", and it takes some to recover. The longer I pump, the harder my brake pedal gets, due to lack of vacuum. I've never noticed a problem while driving, though.
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Old 10-28-2010, 10:42 AM   #9 (permalink)
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Originally Posted by standbypowerguy View Post
It sounds like your vacuum pump is weak. 10 CM is about 4", that's low.
Why is that low if in the guide A4 says the maximum drop allowance should be 3 hg inches. If mine is steady 10cm and is about 4 hg when converting into inches, that passes the test doesn't it?

During the A4 test, are you suppose to hit the brakes and the testing is recorded while you are pressing the brakes instead of where the engine is idling at? I though you only press the brakes to reset the test and make sure the pressure builds to back to 10cm or 4"?

Last edited by knightOwl4786; 10-28-2010 at 10:47 AM.
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Old 10-28-2010, 10:50 AM   #10 (permalink)
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Originally Posted by knightOwl4786 View Post
Why is that low if in the guide A4 says the maximum drop allowance should be 3 hg inches. If mine is steady 10cm and is about 4 hg when converting into inches, that passes the test doesn't it?

During the A4 test, are you suppose to hit the brakes and the testing is recorded while you are pressing the brakes instead of where the engine is idling at? I though you only press the brakes to reset the test and make sure the pressure builds to back to 10cm or 4"?
That's part of it. IIRC it has to recover in the allowable time frame too to pass. I have a pressure/vacum meter. I will hook up to the tree and test mine. Results in a few.
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Old 10-28-2010, 11:11 AM   #11 (permalink)
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Vacum gauge hooked up at TREE

All readings are @ idle speed ( 650 RPM) First one is reading BEFORE brakes applied. Second is just after brakes applied. took 5 seconds to recover @ idle speed.


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Old 10-28-2010, 12:17 PM   #12 (permalink)
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So this means that the A4 testing guide is incorrect?: TheDieselStop.Com Photo Hosting - Vacuum test Part 2

It should of said "maximum drop should to be no less then 21hg inches" right? Or do they mean that a decrees from 23 should be no less then 3hg inch? example: 23-3 = 20

Thank you for the pictures. Very kind of you to post that. Is your results when you did the test A4?
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Old 10-28-2010, 12:28 PM   #13 (permalink)
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Quote:
Originally Posted by knightOwl4786 View Post
So this means that the A4 testing guide is incorrect?: TheDieselStop.Com Photo Hosting - Vacuum test Part 2

It should of said "maximum drop should to be no less then 21hg inches" right? Or do they mean that a decrees from 23 should be no less then 3hg inch? example: 23-3 = 20

Thank you for the pictures. Very kind of you to post that. Is your results when you did the test A4?
I didn't follow any "test" procedure. I warmed the truck up so that it idled at 650. Took a cap off the tree and hooked the gauge up. Stood by the drivers door and took a pic with the truck idleing in park. Then I pressed the brake once and took a picture as I let the brake off. Then counted seconds until it read the same in the first picture. I NEVER touched the go pedal.
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Old 10-28-2010, 12:32 PM   #14 (permalink)
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Rebuildable?

Can I rebuild my vacuum pump, or is it a replacement-only item?
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Mods: Gear Vendors overdrive, ATS 085/088
"Frankenturbo", boost and EGT gauges in pod,
K&N air filter, cold air intake, filter minder, rear
work lights, 'monback beeper, pintle+ball hitch,
brake controller, CB.

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Old 10-28-2010, 12:39 PM   #15 (permalink)
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Can I rebuild my vacuum pump, or is it a replacement-only item?
I don't know anywhere to get rebuild kits. I have replaced mine twice. First time it was failed. Second time it was okay, was having ABS light issues on a road trip. SO I have a good spare and the $100.00 pulley puller that I bought in Shasta City in August. My $19.95 puller was in the tool box at home.
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Pillar pod: Autometer C2 Series gauges: pyro,trans, boost, water, oil pressure
Hypermax Cowl induction, K&N air filter, flex-a-lite 26K trans cooler with fan,Tekonsha prodigy
Train Horns: Pictures here

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