Test an elec vacuum pump on my 85 300D - Page 4 - PeachParts Mercedes-Benz Forum

BillGrissom · #46 10-07-2015, 03:02 PM

In another thread, I commented on mach4's test results (post #32). My comment was that it seems inconclusive that the "designed leak" thru the VCV was the culprit in the excess vacuum flow he noted (electric pump couldn't keep up). That is because he didn't cap off the VCV vent to stop that flow. Seems there could have been a leak from somewhere else, like a hose or the trans modulator's diaphragm.

I also don't understand the risk from using an electric vacuum pump. I am sure we have all lost vacuum before where the engine wouldn't shut off. Losing power brakes is the biggest threat, but you just go to "2 feet on the pedal" mode. In one case, I found a small split in a rubber vacuum hose. I have slowly been changing them to purty blue silicone hose in my two 300D's.

Jarod · #47 10-07-2015, 08:04 PM

https://youtu.be/J_nlZkMwyBo

That's the video of the electric vacuum pump on the 95 E300D.

hopefully its clear enough for you all to get the sense of what I've done to it.

funola · #48 10-07-2015, 08:53 PM

Thanks for the video Jarod. I am going to try it without the football reservoir and see how it behaves. In a way, you do have a small reservoir in the long run of hose between pump and booster.

Did you remove the engine driven pump? How did you cover it up?

Mxfrank · #49 10-07-2015, 09:20 PM

Does the 123 not have a reservac located inside the fender? My 190 does.

funola · #50 10-07-2015, 09:23 PM

Quote:

Originally Posted by Mxfrank

Does the 123 not have a reservac located inside the fender? My 190 does.

123 has a reservoir above the fuel tank that looks like an egg crate, but afaik, it serves the door locks only, nothing else.

funola · #51 10-07-2015, 09:43 PM

I rigged up an on off switch for the pump with a small light bulb to indicate when the pump is on. In this video https://www.youtube.com/watch?v=haTkAw7KB1A at 0:05 the bulb goes off= pump off and I drove 53 seconds (normal shifts and brakes) on reservoir vacuum for a few blocks stopping at a few stop signs till I lost power brakes at around 4" HG when I turned the pump back on at 1:07

funola · #52 10-07-2015, 09:55 PM

I thought I have an adjustable vacuum switch but I don't, it was a pressure switch. I wanted to see what kind of duty cycle the pump runs at. I don't want to buy a switch and have to wait so I will be the switch for the test. I picked 15" HG to turn the pump off and 11" HG to turn the pump on on the 2 minute 40 sec drive. https://www.youtube.com/watch?v=dhWgCyppx4k

If you look at the light bulb on/ off times, it looks like the duty cycle is around 40 % on time.

Jarod · #53 10-08-2015, 07:08 AM

Mxfrank brings up an interesting point, there is a good possibility my car has a reservoir, as it is a w124 body like his 190.

Also, the long hose run too helps for sure.

I removed the engine driven pump, basically gutted it, so there is no moving pieces or things that could come loose, and reinstalled it.

I'd say from your videos it looks fairly normal, it will vary during braking the most, but as long as the pump comes on before you're out of power brakes it has always caught up pretty quick for me.

Once cruising, not braking or using a bunch of vacuum on other things it looks like it stabilizes fairly well, which I'd expect to be normal, there shouldn't be a lot of leakage, some from the vcv is expected, but if it is that bad, perhaps the orifice is missing? I believe on my w123 as well as 124 there is a green oriface connector thingy between the vcv and the rest of the vacuum system.

funola · #54 10-08-2015, 01:53 PM

Jarod,

Is the digital vacuum readout thing in your video an adjustable elec vacuum switch? What is it made for originally with units of MPa? Is that megapascal or millipascal and how much does it cost?

I found this adjustable vac switch on Ebay

Adjustable Universal Vacuum Switch 6 24 Inhg Lockup 700R4 2004R 350C Superior | eBay Wondering if it is any good for the job.

Edit: I realize the ebay switch I found above will not do it alone. I need something that will turn the pump on and off at 2 separate pre-set vacuum levels. Will the SMC do that?

I found this unit on ebay with missing connector

http://www.ebay.com/itm/SMC-Pressure-Sensor-ZSE40A-01-R-M-/151825679924?hash=item2359840634 Will this one do?

Jarod · #55 10-09-2015, 05:41 AM

The smc switch measures either in mpa or kpa, the same style switch will measure vacuum, pressure ot both. If it says zsa it does either vacuum or both, if it says isa then it's only pressure.

They dont have 2 separate on and off points from what I can tell but they have a hysteresis function to keep the pump on past the turn on point for a specified amount or time which has worked well on my w124.

I got 2 of those switches for somewhere around 30 bucks used, I dont know where the other one went though, otherwise id send it to you

tjts1 · #56 10-09-2015, 06:52 AM

Quote:

Originally Posted by Jarod

https://youtu.be/J_nlZkMwyBo

That's the video of the electric vacuum pump on the 95 E300D.

hopefully its clear enough for you all to get the sense of what I've done to it.

Thank you for posting this, very informative. Turns out I have an identical SMC switch in my parts bag left over from a boost controller project. I'll use it for this instead.

Has anyone come up with a good blanking plate solution once the mechanical vac pump is removed?

Do you think it would be good idea to add a vac reservoir to keep the brake booster supplied through multiple hard brakings?

funola · #57 10-09-2015, 10:40 AM

Quote:

Originally Posted by Jarod

Mxfrank brings up an interesting point, there is a good possibility my car has a reservoir, as it is a w124 body like his 190.

Also, the long hose run too helps for sure.
.......................

Your car does have a vacuum reservoir, to the VCV for shifting, climate controls but not door locks.

http://www.peachparts.com/shopforum/diesel-discussion/300054-w124-vacuum-reservoir-purpose.html

dude99 · #58 10-09-2015, 10:47 AM

Quote:

Do you think it would be good idea to add a vac reservoir to keep the brake booster supplied through multiple hard brakings?

If you have the room for it I can't see it not being a good idea. At the very least it will allow your pump to remain off longer between cycles.

funola · #59 10-16-2015, 06:05 PM

Quote:

Originally Posted by Jarod

The smc switch measures either in mpa or kpa, the same style switch will measure vacuum, pressure ot both. If it says zsa it does either vacuum or both, if it says isa then it's only pressure.

They dont have 2 separate on and off points from what I can tell but they have a hysteresis function to keep the pump on past the turn on point for a specified amount or time which has worked well on my w124.

I got 2 of those switches for somewhere around 30 bucks used, I dont know where the other one went though, otherwise id send it to you

Bought this one from ebay

SMC Pneumatics ZSE40 T1 22L Precision Digital Pressure Switch 12 24VDC Sensor | eBay it's vacuum only. Got it tested on the bench with a DVM and mityvac and it appears to be working, I can trigger the output LED's. I can set the unit to display in inches of HG which I have a better feel for than Kpa or Mpa. I'll install it with a relay and see what kind of duty cycle the pump runs at under automatic control.

funola · #60 10-19-2015, 05:07 PM

Got it hooked up after some learning curve. These SMC switches are meant for programmable logic controllers and not automotive application. The open collector outputs @ 80 ma cannot drive most 12v relays which has 0.20 to 0.25 A coils. I ended up driving a low current reed relay to drive a Mercedes ice cube relay.

Here's a vid with engine off with set points: on at 12" Hg, off at 17" Hg. https://www.youtube.com/watch?v=754lEN9OeHA You can hear the pump in the background in sync with the light bulb.

This vid of a short highway drive showing the pump (light bulb) duty cycle to be approx 50% https://www.youtube.com/watch?v=DT6tuyewRdc Transmission and braking feels normal just like the engine driven pump.

I will try other vac set points that are closer together like 15" & 17" Hg.