VACUUM PUMP FAILURE! Are you neglecting yours?? - Page 9 - PeachParts Mercedes-Benz Forum

whunter · #**121** 06-26-2012, 05:24 PM

Quote:

Originally Posted by funola

May I suggest:

1. Start with a brand new vac pump, ideally a piston type.

2. Drill a hole on the casing such that a borescope can be inserted, focusing on the cam and cam follower and shoot a video of the test.

Seeing is believing!

NO!!!

I have a new old stock, and grave bodily harm will happen to anyone cutting holes in it..

.

TheDon · #**122** 06-26-2012, 06:30 PM

I think I'll be ordering a new vp tomorrow. I see there is a vacuum check valve, can I just reuse the old?

funola · #**123** 06-26-2012, 10:04 PM

Hey Army, I'll get you those dimensions when I get the pump open. Not sure when that will be.

In the mean time, I got the needed parts and made this adapter tee.

funola · #**124** 06-26-2012, 10:19 PM

Quote:

Originally Posted by whunter

NO!!!

I have a new old stock, and grave bodily harm will happen to anyone cutting holes in it..

.

3/8" hole is all that's needed. Won't weaken it and can be easily plugged.

Wanna send me a rebuild kit for my spare pump? I'll drill a hole, shoot and post a video of the test.

Stretch · #**125** 06-27-2012, 03:16 AM

Quote:

Originally Posted by qwerty

It all depends on whether you are dealing in absolute terms or relative terms. Your vacuum pump might be able to easily pull a perfect vacuum in space. Unfortunately, your 100% vacuum will create a pressure differential of zero.

So, it's absolutely easier to create a vacuum as altitude increases, but the relative differential is diminished. You cannot pull a one bar differential at the 500 millibar level. And you cannot pull 29" Hg in Denver. (Note that it isn't "harder" to do; it is impossible.)

Not so clear as mud anymore =>

The gauge is a relative measurement not an absolute one.

Thanks from someone who has always lived (more or less) at sea level!

funola · #**126** 06-27-2012, 10:07 AM

Quote:

Originally Posted by funola

FSM 43-660 vacuum pump test:

engine at 750 rpm idle, vacuum at brake booster (custom Tee adapter needed) should reach 0.5 bar (14.7 in Hg) in around 15 secs (varies with the booster model). Engine shut off, if vacuum drops more than 0.2 bar in 30 seconds, check system for leaks. If no fault found, renew or recondition vacuum pump.

I just noticed the part: "If no fault found, renew or recondition vacuum pump", checked the FSM to be sure and sure enough, that's what it says!

Shouldn't it be: "If fault found, renew or recondition vacuum pump" ? Another typo!

qwerty · #**127** 06-27-2012, 10:16 AM

Quote:

Originally Posted by funola

I just noticed the part: "If no fault found, renew or recondition vacuum pump", checked the FSM to be sure and sure enough, that's what it says!

Shouldn't it be: "If fault found, renew or recondition vacuum pump" ? Another typo!

It's not a typo. The assumption being made is that if no leak (fault) is found, the pump must be responsible for the low vacuum condition. It would make no sense to renew the pump because of a leak in the system.

funola · #**128** 06-27-2012, 10:23 AM

Quote:

Originally Posted by qwerty

It's not a typo. The assumption being made is that if no leak (fault) is found, the pump must be responsible for the low vacuum condition. It would make no sense to renew the pump because of a leak in the system.

I think you're right. I need to update transcribing the exact wordings from the FSM.

The procedure should be something like this. To be sure, check FSM 43-660

engine at 750 rpm idle, vacuum at brake booster (custom Tee adapter needed) should reach 0.5 bar (14.7 in Hg) in around 15 secs (varies with the booster model). Engine shut off, if vacuum drops more than 0.2 bar (6 in Hg) in 30 seconds, check system for leaks.

If the specified data is not attained or if the vacuum drop is more than 0.2 bar in 30 s, check vacuum system for leaks. If no fault is found, recondition vacuum pump or renew.

funola · #**129** 06-28-2012, 11:01 AM

Did a quick test with a Pierburg piston pump. I pulled a vacuum on it with an adapter made from an old W123 plastic vacuum line with the check valve in the circuit and looked for movement in the Pierburg (there was none). Maybe that is because my vacuum source (a 12V RV vacuum pump) was only able to pull 22" Hg. I need a stronger vacuum source. Maybe I will use the vacuum pump from my 85 as the vac source and connect the two directly together. If that is not enough, I will look for a compressor from a 120 VAC air conditioner as a source of vacuum.

Stevo · #**130** 06-28-2012, 11:30 AM

Quote:

Originally Posted by funola

Did a quick test with a Pierburg piston pump. I pulled a vacuum on it with an adapter made from an old W123 plastic vacuum line with the check valve in the circuit and looked for movement in the Pierburg (there was none). Maybe that is because my vacuum source (a 12V RV vacuum pump) was only able to pull 22" Hg. I need a stronger vacuum source. Maybe I will use the vacuum pump from my 85 as the vac source and connect the two directly together. If that is not enough, I will look for a compressor from a 120 VAC air conditioner as a source of vacuum.

Nice job on the tester "T", shorter is better when it comes to fitting in the line. I must be missing something, I dont quite get how your testing your VP, what are you using your mity vac (type) for, just the gauge to see what your pumps putting out?

Orv · #**131** 06-28-2012, 02:53 PM

Quote:

Originally Posted by kerry

The most the gauge will read in Denver is about 18" due to the altitude since the measured is correlated to atmospheric pressure. Not sure what the pump 'would think' it is. Would it act as if it were measuring 25" at sea level or would it keep thinking it needed to pump more?
The whole issue is more dubious in my mind all the time.

Since the reference force is a spring, and springs are unaffected by altitude, it would try for a 25" pressure differential at all times.

kerry · #**132** 06-28-2012, 02:57 PM

Quote:

Originally Posted by Orv

Since the reference force is a spring, and springs are unaffected by altitude, it would try for a 25" pressure differential at all times.

Then this would imply that the vacuum pump would wear out much more rapidly at higher elevation.

funola · #**133** 06-28-2012, 03:05 PM

Quote:

Originally Posted by Stevo

Nice job on the tester "T", shorter is better when it comes to fitting in the line. I must be missing something, I dont quite get how your testing your VP, what are you using your mity vac (type) for, just the gauge to see what your pumps putting out?

Yeah I made it as short as possible. Don't know why the FSM suggests 3", that would bow the plastic line quite a bit. Mine is shorter than that.

My test was to try and see if I can "park" the cam follower of the vacuum pump.

vstech · #**134** 06-28-2012, 07:28 PM

whunter tested with a reclaimer, and the pump BRAND NEW would only park 2 out of 5 times... an old one would park about the same...

bottom line is this.

unrestricted flow through the pump is bad for it. the pump should only draw vacuum from the factory designed locations, and not through leaks under carpet/door jam/hood, other places with dirty air...
SEAL IT UP. it'll park when it can, but it'll stay CLEAN!~!!

Stevo · #**135** 06-28-2012, 07:56 PM

Quote:

Originally Posted by funola

Yeah I made it as short as possible. Don't know why the FSM suggests 3", that would bow the plastic line quite a bit. Mine is shorter than that.

My test was to try and see if I can "park" the cam follower of the vacuum pump.

Oh, I guess I wasn't paying close enough attention. Sounds like you could use one of those old reefer box compressor units for a tester/vacuum pump.