Electrical Vacuum Pump Conversion Project - Page 7 - PeachParts Mercedes-Benz Forum

mach4 · #91 01-11-2014, 08:03 PM

Quote:

Originally Posted by Diesel911

????There must be something else going on as I drove around with the Vacuum Pump in the below thread and I have an Automatic Transmission and everthing operated norally with the exception that I worried that the Vacuum Pump was getting too hot (and I had no Resivoir or Check Valve Check Valve on the Vacuum Pump).
The Vacuum Pump ran all of the time as I had no Vacuum Shutoff in the circuit.

Electric Vacuum/Brake Booster Pump Tested

Everything would appear to operate "normally". The brake booster has a check valve to ensure that it maintains good vacuum even if there were to be leaks in the rest of the system. Orifices in the system keep the bleed rate within reason. The VCV would tend to make the system operate in the 1-12" range, give or take. Because of the check valve, the brakes would tend to have 12", maybe even a bit more, which is enough for decent operation. With a full charge you'd get 4-5 pumps of the brakes before hard pedal. You probably wouldn't see a braking issue, because, during braking, the VCV is at the "idle" position and would be allowing full available vacuum (12") to the brakes, probably enough for 2 or so pumps.

What I was hoping would happen is that the VCV would only "take 12 inches" and then "close off" - it doesn't, it bleeds it off excess vacuum continually, at the max rate allowed by the orifice (restrictor). That fact makes an electrical vacuum pump, or any pump that cannot run continually a non-solution.

funola · #92 01-11-2014, 10:53 PM

Quote:

Originally Posted by mach4

I read the entire thread and didn't see anything about removing the VCV. He did talk about removing the 3/2 and egr stuff but never the VCV... at least that I saw. Can you reference a specific post?

I thought the VCV is aka a 3/2 valve, which is on top of the valve cover. Maybe I'm mistaken and confused. Do you have a pic of what you call a VCV to alleviate my confusion?

Edit: Just looked at the pic you posted. So the VCV is on the IP. My mistake. Have you tried another VCV that is know to be good? Maybe your's is leaking more than it should?

Diesel911 · #93 01-11-2014, 11:39 PM

Quote:

Originally Posted by funola

I thought the VCV is aka a 3/2 valve, which is on top of the valve cover. Maybe I'm mistaken and confused. Do you have a pic of what you call a VCV to alleviate my confusion?

You could just trace the Vacuum Lines to a ususlly White Valve on the Fuel Injection Pump that is connected to the Fuel Injection Pump Throttle lever or Linkages; that is the Transmission Vacuum Valve.

On mine the 3/2 only conotrl the EGR. However, Vacuumleaks there can effect the Transmission Modulation if you have a Vacuum Transmission Modulator and the leak/s is/are big enough.

mach4 · #94 01-11-2014, 11:43 PM

Quote:

Originally Posted by funola

I thought the VCV is aka a 3/2 valve, which is on top of the valve cover. Maybe I'm mistaken and confused. Do you have a pic of what you call a VCV to alleviate my confusion?

Edit: Just looked at the pic you posted. So the VCV is on the IP. My mistake. Have you tried another VCV that is know to be good? Maybe your's is leaking more than it should?

Mine's good. It holds vacuum just fine... at least up to 12". It bleeds anything over that. As the throttle linkage is opened, the vacuum bleeds down to 1" which is again what it's supposed to do.

mach4 · #95 01-11-2014, 11:53 PM

The myth that it's possible to use an electrical vacuum pump on an automatic 617 vehicle is officially...

funola · #96 01-12-2014, 12:38 PM

[QUOTE=mach4;3269642.....................................

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.
.[/QUOTE]

7 oz is a very small reservoir. I have a feeling a larger reservoir (1 gal) will make a difference.

OM617YOTA · #97 01-12-2014, 05:44 PM

Could you put a regulator that DOESN'T vent excess vacuum ahead of the transmission VCV set to 12"? This would restore the function to exactly what you had intended and hoped.

mach4 · #98 01-12-2014, 10:42 PM

Quote:

Originally Posted by OM617YOTA

Could you put a regulator that DOESN'T vent excess vacuum ahead of the transmission VCV set to 12"? This would restore the function to exactly what you had intended and hoped.

Excellent idea! Unfortunately I don't think it will be a solution. For two reasons actually.

First, preliminary research puts vacuum regulators at somewhere around $100 and up. I spent a lot of time researching options and there isn't really any good "cheap" regulators or automotive applications/components that could be adapted.

Second, I think it might not help much. If the VCV does not maintain vacuum at the "set pressure" during normal cruise, it would still vent just like the stock system does. Let's assume for sake of argument that at 60mph level cruise the throttle position bleeds vacuum to 8". In that situation, the VCV would still be bleeding vacuum from the set point to 8" - not as bad as stock, but a constant bleed just the same. And then there would be the problem of doing a long climb up to the Continental Divide, for example, that would be long stretches at a "full bleed" situation that run the risk of ovestressing or overwhelming the pump.

Just for fun in the next few days, I'll hook up a vacuum gauge by teeing into the vacuum supply line between the dashpot and restrictor and just see what the actual pressures are at different throttle settings.

Years ago I put a Perkins 4.236 mated to a 350 automatic into an Econoline van. That transmission used a vacuum modulator that was worthless with the diesel, so we found a mechanical modulator that worked great. Had a cable that tied into the throttle and mechanically modulated the transmission. If there was a way to replace the MB vacuum modulator with a mechanical one, that might be a solution too. A quick search however turned up nothing practical.

The other thing I thought about was using a microprocessor, a throttle position sensor, a vacuum sensor and a vacuum solenoid to re-create the vacuum/throttle position curve of the VCV. Even if it could be done, I have doubts that it would be responsive enough to properly control the shifts. I think there would be way too much latency. And thinking about it just a little, it might actually take two vacuum solenoids - one to add vacuum and one to dump vacuum.

Alas, while still fun to think about, and it might be technically possible to do, it's getting further and further out in left field as something reasonable to do both from a cost and engineering standpoint.

dude99 · #99 01-12-2014, 10:57 PM

Quote:

Originally Posted by mach4

I have no idea what the vacuum amplifier does - it would be nice to know.

As far as I'm aware the vacuum amplifier (blue flying saucer) varies the vacuum being fed to the transmission modulator based on boost levels. This would allow the transmission to firm up the shifts under boost (more power being produced) and reduce slip\wear.

mach4 · #**100** 01-12-2014, 11:27 PM

Quote:

Originally Posted by dude99

As far as I'm aware the vacuum amplifier (blue flying saucer) varies the vacuum being fed to the transmission modulator based on boost levels. This would allow the transmission to firm up the shifts under boost (more power being produced) and reduce slip\wear.

Interesting...so the boost signal overrides all or part of the throttle position signal to vary the amount of modulation to the transmission.

I was running the blue-flying-saucer setup with my replacement 722.3x tranny for awhile and there was no discernible difference when I unhooked it and went with the "stock" 722.3x setup with just the VCV controlling modulation. I would take this to mean that the modulation curve on the 722.4x transmission is different allowing it to take advantage of the "vacuum amplifier" function.

Thanks

dude99 · #**101** 01-13-2014, 02:34 AM

Quote:

Originally Posted by mach4

I would take this to mean that the modulation curve on the 722.4x transmission is different

Possibly, but I'd wager that the difference is only in the modulator itself and not the transmission, that's just a guess though, not based on any fact whatsoever. I'd be curious to see what would happen if you took the modulator from your old one and installed it in your new transmission with the amplifier.

Stretch · #**102** 01-13-2014, 02:54 AM

There are indeed poo loads of different vacuum modulator variations out there...

mach4 · #**103** 01-13-2014, 03:51 PM

Quote:

Originally Posted by Stretch

There are indeed poo loads of different vacuum modulator variations out there...

...none of which are mechanical that would work on a 722.3x tranny, I would bet.

mach4 · #**104** 01-13-2014, 06:35 PM

I tapped into the vacuum line between the dashpot and the restrictor with a vacuum gauge and went for a short drive. At idle the vacuum to the modulator is 12". With the slightest press of the accelerator the vacuum drops instantly to 8". With the application of any appreciable throttle it drops to 2" or a little less. The response is immediate - it's almost as if the gauge is connected directly to the throttle pedal. So there is an almost constant bleeding of significant vacuum to adjust the modulator to throttle position.

Also just for fun, I plugged the vacuum to the VCV and went for a drive. It was virtually undrivable with horrible flaring. I'd be concerned with burning out clutches in no time driving that way.

So, barring any interesting solution to the VCV modulator issue, the myth of using an electrical vacuum pump to replace the engine driven pump on an automatic 617 remains busted.

Dan Stokes · #**105** 01-27-2014, 06:11 PM

Thanks for the heads-up on the VW pumps. I went to PnP today (we had really nice weather with snow coming tomorrow so I figured I better do it if I'm going to do it) and found a VW pump. Mine has an all aluminum body and should polish up really well.

I also took the bracket which is a royal pain to get out. It also holds the fuel pump (I guess) on the VW and I had to remove the whole fuel pump deal to get to the attaching bolts. I'll cut the bracket down to just hold the vacuum pump but that will require a lot of spot weld drilling. Pics to follow.

A couple of questions:
1) Is there a vacuum switch on a VW to turn it off and on? Mine won't need to run very often as it only needs enough slurp to shut the engine off but I'd like it to not run if not needed.

2) Which wire is ground? I got the pigtail and a little wire from the harness so I can make a plug-in connection but I don't know which wire is which.

Thanks

Dan