Test an elec vacuum pump on my 85 300D - Page 3 - PeachParts Mercedes-Benz Forum

funola · #31 10-05-2015, 10:06 PM

Quote:

Originally Posted by mach4

Those are indeed the engine driven pump numbers.

Once I determined that the VCV continually bled vacuum (and not just bleeding vacuum down to the level required to send the simulated throttle position to the transmission) and the capacity of my electric vacuum pump was not capable of maintaining vacuum within a reasonable duty cycle (30% or so) I abandoned the project.

How did you determine how much your VCV bled? Is there a test spec for it? Same for the transmission modulator. Do you have specs for the elec vac pump you used? I did not buy the pump I used because I was looking for a high capacity pump. It just so happens I came across it a few years ago for no particular purpose and it was a good deal so I bought it. Without comparing specs or from testing, it is possible your pump may have higher capacity than mine.

mach4 · #32 10-05-2015, 11:09 PM

Quote:

Originally Posted by funola

How did you determine how much your VCV bled? Is there a test spec for it? Same for the transmission modulator. Do you have specs for the elec vac pump you used? I did not buy the pump I used because I was looking for a high capacity pump. It just so happens I came across it a few years ago for no particular purpose and it was a good deal so I bought it. Without comparing specs or from testing, it is possible your pump may have higher capacity than mine.

Here is a link to my test procedure - Electrical Vacuum Pump Conversion Project

funola · #33 10-06-2015, 10:26 AM

Quote:

Originally Posted by mach4

Here is a link to my test procedure - Electrical Vacuum Pump Conversion Project

With a setup consisting of just the vacuum pump, a check valve and a small reservoir (7 fl oz), the pump pulled 22" in about 5 seconds and with the pump off, held with no discernible leak-down.

I then hooked up the electrical vacuum pump in a test that isolated the VCV system as shown below. With the VCV in the circuit, the pressure went to 12" and held. There was enough leakage that it could not get above 12". Activating the throttle linkage showed the pressure dropping to 1" as it should, obviously dumping all vacuum above the 1" level.

i may want to run your test and see what results I get but I need some clarifications first:

In your first paragraph, did you use the engine driven pump or elec pump? What was the purpose, to show the reservoir and check valve has no leaks?

In the second paragraph with the diagram, you said you isolated the VCV, but the diagram shows a transmission modulator and a vent connected to it. I also do not see the check valve and reservoir from paragraph one.

mach4 · #34 10-06-2015, 11:07 AM

The first test was just to test the check valve and reservoir.

The second test isolated just the VCV circuit. I ran it through the check valve and reservoir. The modulator doesn't leak. It's just a diaphragm that pulls a pin that changes the shift characteristics. The vent is where the vacuum bleed air comes from. If it were blocked off, the VCV couldn't work.

My hope in doing this test was that the VCV would only bleed to the pressure required and hold - what I discovered was that it continually bled vacuum at the rate determined by the restrictor.

I actually thought briefly about creating a microcontroller system consisting of a couple of vacuum solenoids - one to build vacuum and one to release vacuum - that would be controlled by the TPS providing a synthetic vacuum signal to the modulator that would mimic the synthetic signal of the VCV that mimics the intake manifold vacuum of the gas engines....but quickly abandoned that interesting, but totally ridiculous idea. Implementing this system would have used only a tiny amount of vacuum as vacuum would be built or vented only when changing state and would make an electrical vacuum pump a solution.

I also considered trying to find a mechanical modulator that would work. Years ago when I installed a Perkins 4.236 diesel in a Ford Van coupled to a Chevvy transmission, I found a mechanical cable operated modulator that worked quite well. Again, just too much engineering for such a small advantage.

Hope this helps.

funola · #35 10-06-2015, 12:25 PM

Quote:

Originally Posted by mach4

The first test was just to test the check valve and reservoir.

The second test isolated just the VCV circuit. I ran it through the check valve and reservoir. The modulator doesn't leak. It's just a diaphragm that pulls a pin that changes the shift characteristics. The vent is where the vacuum bleed air comes from. If it were blocked off, the VCV couldn't work.

My hope in doing this test was that the VCV would only bleed to the pressure required and hold - what I discovered was that it continually bled vacuum at the rate determined by the restrictor.

I actually thought briefly about creating a microcontroller system consisting of a couple of vacuum solenoids - one to build vacuum and one to release vacuum - that would be controlled by the TPS providing a synthetic vacuum signal to the modulator that would mimic the synthetic signal of the VCV that mimics the intake manifold vacuum of the gas engines....but quickly abandoned that interesting, but totally ridiculous idea. Implementing this system would have used only a tiny amount of vacuum as vacuum would be built or vented only when changing state and would make an electrical vacuum pump a solution.

I also considered trying to find a mechanical modulator that would work. Years ago when I installed a Perkins 4.236 diesel in a Ford Van coupled to a Chevvy transmission, I found a mechanical cable operated modulator that worked quite well. Again, just too much engineering for such a small advantage.

Hope this helps.

I am getting very different results than you. Maybe you arrived at your conclusion that an elec vac pump is not viable for automatic transmission cars a bit prematurely? My tests indicate it is viable, at least on one example- my 85 300D. The only thing I'd worry about is the long term effect of removing the engine driven vac pump and installing a cover plate, leaving the driving mechanism unloaded. I have no immediate plans to install the elec vac pump. My test is for information purposes, for those who may want to try it.

I moved the vac gauge tee to the main vac line and the results look even better. I'll upload some pics and videos to show it shortly.

funola · #36 10-06-2015, 12:57 PM

Here's a pic of the new vac gauge location. Excuse the drawing, it's the best I can do with the photobucket editor

.

The blue circle is the check valve, to right of check valve is the elec vac pump, the red cable is power for the pump which runs inside to cig. lighter. Green circle is the vac gauge tee, which is right at the vac tank (black foot ball) nipple. Between the 2 circles is another tee with a hose which loops around 180 degrees which connects to and supplies vacuum to the Mercedes main vac hard line.

Here's a youtube video https://www.youtube.com/watch?v=pyxv9Kcj7zQ . Excuse the poor quality, the sun angle had something to do with it. Vacuum level at the main line is much more stable than when the gauge was at the VCV. At idle it is 3" higher at 18 " HG. Reving the engine at idle does not pull the vac down at all (it did before with vac gauge at the VCV), light acceleration or hard acceleration does not pull the vac level down either, it stays above 15 to 17" of HG.

Jarod · #37 10-06-2015, 01:32 PM

Quote:

Originally Posted by funola

Do you have a vac reservoir tank?

Nope. just a hose from the back to the front, connected to the brake booster the same way the mechanical pump was. I'll take a video of it this afternoon and post it.

mach4 · #38 10-06-2015, 01:34 PM

Interesting data....

I wouldn't want to drive around with less than 20-21". If you could get a pump that had an appropriate duty cycle and could pull say 23", you could then implement a switch or controller with set points of 19" and 22" - it would turn on at 19" and shut off at 22". I'd also implement a decent sized reservoir to offer ample cool down time between cycles. It might be possible to make the orifice smaller to reduce the vacuum load and still get decent shifts...just don't know.

Again, my design criteria were centered around using the VW pump. I wasn't interested in getting a large, expensive industrial vacuum pump.

funola · #39 10-06-2015, 02:05 PM

Quote:

Originally Posted by mach4

Interesting data....

I wouldn't want to drive around with less than 20-21". If you could get a pump that had an appropriate duty cycle and could pull say 23", you could then implement a switch or controller with set points of 19" and 22" - it would turn on at 19" and shut off at 22". I'd also implement a decent sized reservoir to offer ample cool down time between cycles. It might be possible to make the orifice smaller to reduce the vacuum load and still get decent shifts...just don't know.

Again, my design criteria were centered around using the VW pump. I wasn't interested in getting a large, expensive industrial vacuum pump.

What's the magic with 23" vs 20-21" vs 18" vs 15" of HG? The car stops and shifts normally at 15" HG when I was measuring at the VCV. Furthermore, with the engine driven vac pump connected, I was measuring the same reading (15" HG) at the VCV.

I don't know why your test with throttle input drops the vac down to 1" HG. Sounds like a leak somewhere and not an undersized pump as you think.

funola · #40 10-06-2015, 02:24 PM

Quote:

Originally Posted by mach4

........I'd also implement a decent sized reservoir to offer ample cool down time between cycles. .......

The football reservoir is a pretty good size already. I estimate it to be around 64 oz. Here's a video of it with the elec pump turned off, running off the vac in the reservoir. With 2 throttle input cycles, Vac dropped from 18" to 14" of HG. https://www.youtube.com/watch?v=AUMLJRtGV7k

dude99 · #41 10-06-2015, 02:52 PM

It would be interesting to know at what level of vacuum the brake booster becomes inoperable at...

mach4 · #42 10-06-2015, 03:12 PM

Quote:

Originally Posted by funola

What's the magic with 23" vs 20-21" vs 18" vs 15" of HG? The car stops and shifts normally at 15" HG when I was measuring at the VCV. Furthermore, with the engine driven vac pump connected, I was measuring the same reading (15" HG) at the VCV.

I don't know why your test with throttle input drops the vac down to 1" HG. Sounds like a leak somewhere and not an undersized pump as you think.

There's no magic involved....just risk tolerance. Seems like yours is lower than mine. The system was designed for 22" and I'd like to stick to that. You can still get one press of the brake with 8" so maybe that's enough???

There is no "right answer" just a range of acceptable answers based on risk tolerance.

funola · #43 10-06-2015, 07:35 PM

Quote:

Originally Posted by dude99

It would be interesting to know at what level of vacuum the brake booster becomes inoperable at...

Since my risk tolerance is high I'll risk my life and try that out for ya.

funola · #44 10-07-2015, 08:09 AM

Quote:

Originally Posted by Jarod

Nope. just a hose from the back to the front, connected to the brake booster the same way the mechanical pump was. I'll take a video of it this afternoon and post it.

Does your 95 with the 606 have a transmission that requires vacuum for shifting like on the 617's

Jarod · #45 10-07-2015, 02:25 PM

Quote:

Originally Posted by funola

Does your 95 with the 606 have a transmission that requires vacuum for shifting like on the 617's

yes. very similar if not the same. with no vacuum it slams into gears like you wouldn't believe. under light acceleration it feels like its going to tear itself apart.

I've got the video, I just need to stick it together, I had minor idiot issues when I took the initial video (left lights on, dead battery)... so I'll post that soon

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